Polymer Degradation and Stability (v.95, #9)

Calendar (IV).

Effect of molecular weight on the polymorphic transformation of isotactic poly(1-butene) by Aihua He; Chunsheng Xu; Huafeng Shao; Wei Yao; Baochen Huang (1443-1448).
The effect of molecular weight on the polymorphic transformation of isotactic poly(1-butene)(iPB) under room temperature had been investigated by fourier transform infrared spectroscopy(FT-IR). The phase transformation time, phase transformation rate and phase transformation time difference between phase I and phase II at a given transformation degree were used to analysis the phase transformation kinetics of iPB aging at room temperature. The results show that the reduction of phase II can occur quickly at room temperature and seem less dependent on the molecular weight. However, the molecular weight has great effect on the formation of phase I. When the phase transformation degree for phase I reach 90%, a distinct transformation time difference can be observed. In order to clearly explain the difference in the reduction of phase II and the growth of phase I, a phase transformation model from the chain conformation level for iPB with different molecular weight have been drawn. DSC analysis was used to support the proposed model.
Keywords: Poly(1-butene); Crystal phase transformation; Molecular weight; Polymorphism;

Polyimide (PI)-based composite films incorporated with carbon black (CB), carbon nanotube (CNT) and carbon nanofiber (CNF), respectively, were prepared using low-molecular-weight poly(amic acid) (PAA), a precursor of PI, as an impurity-free dispersant. High-energy ball mill was employed not only to downsize the nano-carbon agglomerates, but also to cut off the PAA chains for in-situ stabilizing the dispersion. Effect of the ball milling time, procedure, and filler species on the filler dispersion was investigated by means of electrical resistivity reproducibility, morphology observation, and mechanical testing. Comparing with direct dispersion of the nano-carbon in PAA, the composite films fabricated by a two-step approach, that is dispersion from the in-situ degradated low-molecular-weight PAA stabilized nano-carbon slurry, presented a uniform electrical conductivity with a lower percolation concentration and excellent reproducibility in the percolation region. A significant improvement in the Young’s modulus for the CNT loaded PI film was achieved, which was much more effective than those filled with CB or CNF.
Keywords: Polyimide; Conducitve polymer composites; Dispersion; Carbon nanotube;

Antimicrobial properties of Ag+ loaded zeolite polyester polyurethane and silicone rubber and long-term properties after exposure to in-vitro ageing by Peter Kaali; Emma Strömberg; Ragnhild E. Aune; György Czél; Dane Momcilovic; Sigbritt Karlsson (1456-1465).
In biomedical applications, tubes (e.g. catheters etc.) are commonly produced from polyurethane (PU) and silicone rubber which are known to be biocompatible materials. Several studies have shown that tubes, which are connected to the body (invasive) (especially urinary, tracheotomy and central venous catheters) are associated with infections. The present study reports the development of a new method aiming at obtaining antibacterial properties for PU and silicone rubber by mixing respective material with a natural antibacterial agent (Ag+ loaded zeolite) in different weight fractions. The influence of the zeolite content on the antimicrobial properties were analysed by exposure to bacteria (ISO 22196) and mixtures of fungi (ISO 846). The materials were also subject to artificial body fluids (Artificial Lysosomal Fluid (ALF) and Gamble’s solution) for periods up to three months and the subsequent changes in the chemical properties after in-vitro exposure were determined by Matrix Assisted Laser Deposition/Ionization Time Of Flight Mass Spectrometry (MALDI-TOF MS) and Attenuated Total Reflection Fourier Transform Infra Red spectroscopy (ATR-FTIR). It was established that the antimicrobial effect of the materials increased with the increase of the zeolite content. The wettability of the materials was found to decrease significantly during the in-vitro exposure, but this could not be correlated to the zeolite content. In the PU samples, the formation of free carbonyl and –OH groups was observed, which corresponds to oxidative degradation. In case of the silicone rubber the ratio of cyclic PDMS to linear PDMS (H, CH3 and dimethyl terminated) decreased, which indicates a change in the concentration of the compounds. The formation and increase of the O–H bond during the exposure was also confirmed by the infrared spectra of the material which corresponds to hydrolysis of the silicone rubber.
Keywords: Degradation; In-vitro; Silver zeolite; Antimicrobial; Polymer; MALDI-TOF MS;

Nano-Mg(OH)2 (nanometre magnesium hydroxide, nano-MH) was successfully introduced into the esterification and polycondensation system by in situ polymerization to obtain PET/magnesium salt composites (PETMS). The thermal properties and flame retardancy of PETMS were investigated by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), UL-94 vertical burning and limited oxygen index (LOI) test. The DSC and TGA results show that magnesium salts in the PET matrix have little effect on the thermal properties of PET, but a significant effect on the thermal stabilities of the composites. The results of LOI and UL-94 test show PETMS have higher LOI values (≥25%) and V-0 rating without melt dripping in the UL-94 test, indicating that PETMS have good flame retardancy and anti-dripping property. Moreover, the residues of magnesium salts and composites after TGA test were also studied by Fourier transform infrared spectroscopy (FTIR) to better understand the mechanism of flame retardancy, which reveals that magnesium salts accelerate the degradation of PET and catalyze the formation of char. The SEM results show the morphological structures of the char effectively protect the composites’ internal structures and inhibit the heat, smoke transmission and reduce the fuel gases when the fire contacts them.
Keywords: Anti-dripping property; Flame retardancy; Nano-MH; Polyester composites; Thermal stability;

Long-term (greater than 5 year exposures), low-temperature (as low as 37 °C) accelerated oven aging results were obtained for Nylon 6.6 fibers under thermo-oxidative conditions (air aging with an oxygen partial pressure of 13.2 cmHg in Albuquerque). To assess the importance of humidity on aging, experiments were also conducted under a combination of 100% RH plus 13.2 cmHg of oxygen partial pressure at temperatures ranging from 138 °C to 64 °C plus an additional experiment at 70% RH and 80 °C. The low-temperature tensile strength results showed that the Arrhenius activation energy under the pure oxidative degradation conditions dropped from ∼96 kJ/mol above ∼100 °C–∼30 kJ/mol below this temperature, indicative of a transition in the oxidative chemistry at low temperatures. Earlier work by our group on the same material concluded that hydrolytic degradation effects dominated oxidation effects at higher aging temperatures. However, the current long-term, low-temperature comparisons lead to the conclusion that humidity is not an important aging factor below ∼50 °C. By extrapolating time–temperature superposed oxidative degradation data using the low-temperature activation energy, we obtain predictions at 21 °C. At this temperature, we estimate that a tensile strength loss of 50% takes on the order of 70 years. The 21 °C predictions are shown to be reasonably consistent with long-term (up to 38 year) ambient results on similar Nylon materials removed from field-aged parachutes. Although the estimated average exposure temperature varies from parachute to parachute, the highest average temperature is estimated to be on the order of 21 °C.
Keywords: Nylon; Humidity; Thermal-oxidative; Arrhenius evaluation; Field aging; Tensile studies;

Dithiothreitol-based polyurethanes. Synthesis and degradation studies by Cristina Ferris; M. Violante de Paz; Francisca Zamora; Juan A. Galbis (1480-1487).
The synthesis, characterization, and some properties of new copolyurethanes are described. These copolyurethanes were obtained by reaction of 1,4-di-S-benzyl-d,l-dithiothreitol (DTTSBn) and triethylene glycol (TEG) with 1,6-hexamethylene diisocyanate (HMDI). The copolymer compositions were studied by 1H NMR, revealing that the content of the copolymer units is in good agreement with that of their corresponding feed. The PU(TEG–HMDI) homopolymer exhibited a high crystallinity, but the introduction of the DTTSBn diol led to a reduction in the crystallinity of the copolymers and an increase of the stiffness, with associated increases in the Tg values. In their TG curves, the copolymers exhibited a mixed trend of the related homopolymers; all of them were thermally stable, with degradation temperatures above 250 °C and with higher thermal resistance displayed by the polymers with higher TEG contents. The chemical and enzymatically catalyzed hydrolytic degradations of the macromolecules were tested. PU(TEG–HMDI) was the only polymer degraded under physiological conditions, but an increase of temperature markedly affected the degradation rates. Two proteolytic enzymes (papain and α-chymotrypsin) and two esterase enzymes (cholesterol esterase and lipase) were chosen to perform enzyme-mediated hydrolysis trials, the first reported use of pancreatic lipase for urethane-bond hydrolysis in polyurethanes.
Keywords: Polyurethane synthesis; DSC and TGA studies; Biodegradable polyurethanes; Lipase-catalyzed degradation; α-chymotrypsin-catalyzed degradation;

Knowledge of the mechanical properties of biocomposite components, especially cell walls, is of great interest for understanding reinforcement mechanisms. The aim of this work was to study nano-mechanical properties of flax fibres after a transformation cycle, such as injection moulding or film stacking. The mechanical and thermal behaviour of flax fibres were first studied by using TGA measurements and nanoindentation. Then, to better understand the influence of the process, a morphology study, nanoindentation and TGA experiments were carried out on flax fibres after a process cycle. The importance of water content and shear rate on the mechanical properties of the flax fibres has been shown.
Keywords: Flax fibres; Nanoindentation; Poly-(lactic-acid); Injection moulding; Film stacking mechanical properties;

Network characteristics of hydrogenated nitrile butadiene rubber networks obtained by radiation crosslinking by electron beam by Sophie Perraud; Marie-France Vallat; Marie-Odile David; Jerzy Kuczynski (1495-1501).
The effects of high-energy radiation on hydrogenated nitrile butadiene rubber (HNBR) copolymer structure and properties were studied. Characterization by FTIR spectroscopy, swelling and mechanical measurements of irradiated and un-irradiated sample permit us to correlate the change in structure with properties. The modifications obtained are dependent on the radiation dose of the incident electron beam. FTIR spectroscopy in absorption mode shows that irradiation of HNBR first induces trans-vinylene bond formation and secondly small amounts of carbonyl (C=O) groups. Moreover, more significant changes were observed with swelling method and mechanical behaviour showing the effect of crosslinking on the elastomer.
Keywords: Hydrogenated nitrile butadiene rubber (HNBR); Crosslinking; Electron beam; Radiation; Mechanical properties; Network;

Thermal stabilization of TEMPO-oxidized cellulose by Hayaka Fukuzumi; Tsuguyuki Saito; Yusuke Okita; Akira Isogai (1502-1508).
A partially C6-carboxylated cellulose with carboxylate content of 1.68 mmol/g was prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation of a softwood bleached kraft pulp. Thermogravimetric analyses of the TEMPO-oxidized cellulose (TOC) and its related materials were studied to improve thermal stability of the TOC. Thermal decomposition (Td) points of the TOC with sodium carboxylate groups, alkali-treated TOC with free carboxyl groups of 0.23 mmol/g and the original cellulose were 222 °C, 264 °C and 275 °C, respectively. Thus, the anhydroglucuronic acid units formed by TEMPO-mediated oxidation of the native wood cellulose and present in the TOC cause the decrease in Td point by decarbonation during heating process. When carboxyl groups in the TOC were methylated with trimethylsilyl diazomethane (TMSCHN2), the Td point increased from 222 °C to 249 °C, and the peak temperature in its derivative thermogravimetric (DTG) curve increased from 273 °C to 313 °C, which was almost equal to that of the original cellulose. Thus, the methyl esterification of carboxyl groups in the TOC is effective in improving thermal stability. When sodium ions present in the TOC as counter ions of carboxylate groups were exchanged to some other metal ions, thermal stability was improved to some extent. Especially, when CaCl2, Ca(OAc)2, Ca(NO3)2 and CaI2 solutions were used in the ion-exchange treatments, the peak temperatures in the DTG curves increased to approximately 300 °C. MgCl2, NiCl2, SrCl2 and Sr(OAc)2 solutions were also effective to some extent in increasing the peak temperatures of DTG curves. Thus, thermal stability of the fibrous TOC can be improved to some extent by methyl esterification of the sodium carboxylate groups present in the original TOC with TMSCHN2 or ion-exchange treatments with some metal salt solutions.
Keywords: TEMPO-oxidized cellulose; Thermal stability; Thermal decomposition; Methyl ester; Ion-exchange; Decarbonation;

Bio-based thermostable, biodegradable and biocompatible hyperbranched polyurethane/Ag nanocomposites with antimicrobial activity by Harekrishna Deka; Niranjan Karak; Ranjan D. Kalita; Alak K. Buragohain (1509-1517).
The enhanced thermal and antimicrobial activity of silver nanoparticles prompts their uses in many medical devices. Mesua ferrea L. seed oil based antimicrobial biocompatible hyperbranched and linear polyurethane/Ag nanocomposites have been prepared in dimethylformamide without using any extra reducing agent. Formation of the stable and well-dispersed Ag nanoparticles was confirmed by ultra violet, X-ray diffractometeric, transmission electron microscopic and Fourier transform infra-red spectroscopic analyses. The enhancement of properties like thermal stability by (46–53)°C and 42 °C, tensile strength to ∼170% and ∼180% for hyperbranched and linear polyurethanes respectively was observed by the formation of nanocomposites. The cytocompatibility test based on the inhibition of RBC hemolysis showed that the materials lack cytotoxicity. The nanocomposites showed biodegradability as conferred from the bacterial degradation. Dose dependent excellent antibacterial activity of the nanocomposites against Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli) bacteria and antifouling activity against Candida albicans was observed.
Keywords: Antimicrobial; Biodegradation; Thermostability; Biocompatibility; Polyurethane nanocomposites;

Stabilizing effect of extractives on the photo-oxidation of Acacia confusa wood by Tzu-Cheng Chang; Hui-Ting Chang; Chi-Lin Wu; Huan-You Lin; Shang-Tzen Chang (1518-1522).
This study shows the photo-stabilizing effect of extractives on wood. XPS and FTIR techniques were used to analyze the variations in chemical characteristics on the surfaces of non-extracted and extracted Acacia confusa heartwood after lightfastness test. XPS survey analyses reveal that non-extracted heartwood exhibits a higher O/C ratio than the extracted wood. Furthermore, results from the detailed analysis of C1s indicated that the photo-oxidative derivatives increased in both extracted and non-extracted specimens after lightfastness test. On extracted wood, the derivatives are mainly derived from lignin, whereas extractives are the major component responsible for the generation of derivatives on non-extracted wood surface. After leaching test of UV-irradiated specimens, it was noted that the degradation products were readily removed by water. More water-soluble derivatives were leached out from the extracted wood, although higher lignin content was observed on the non-extracted wood surface. In conclusion, it is shown that photodegradation of A. confusa wood can be retarded by extractives oxidation.
Keywords: Acacia confusa; Extractives; FTIR; Lignin; Photodegradation; XPS;

This study explores whether nanoparticles incorporated in polymers always act as synergists of conventional flame-retardant additives. For this purpose, two different filler nanoparticles, namely organically modified layered-silicate clay minerals or nanoclays and multi-walled carbon nanotubes, were incorporated in poly(methyl methacrylate) filled with an organophosphorus flame-retardant that acts through intumescence. Effective dispersion techniques specific to each nanoparticle were utilized and prepared samples were thoroughly characterized for their nanocomposite morphologies. Nanoclays were shown to outperform carbon nanotubes in respect of improving the fire properties of intumescent formulations assessed by cone calorimeter analysis. An intriguing explanation for the observed behaviour was the restriction of intumescence by strong carbon nanotube networks formed on the flaming surfaces during combustion contrary to enhanced intumescent chars by nanoclays. Carbon nanotubes surpassed nanoclays considering the thermal stability of intumescent formulations in thermogravimetry whereas mechanical properties were significantly superior with nanoclays to those with carbon nanotubes.
Keywords: Nanoclay; Carbon nanotube; Flame retardancy; Nanocomposite; Thermal stability; Mechanical properties;

Degradation products formed during UV exposure of polyethylene–ZnO nano-composites by Rui Yang; P.A. Christensen; T.A. Egerton; J.R. White (1533-1541).
Photodegradation of low density polyethylene (LDPE) containing nano-particulate ZnO has been studied using FTIR to follow the development of oxidation products in the polymer film and to monitor carbon dioxide evolved as a principal product of oxidation. The degradation behaviour of ZnO-free LDPE has been compared with that of compounds containing 0.25% and 0.75% ZnO and these results are compared with those obtained using similar films containing nano-particulate TiO2. Under UV exposure, the presence of ZnO accelerated the development of carbonyl groups and CO2 production. The carbonyl group development was more rapid when TiO2 was used whereas ZnO caused greater CO2 generation. Carbonyl group development seemed to correlate better with the reduction in mechanical properties whereas CO2 generation correlated better with weight change measurements. The influence of ZnO on the oxidation pathways in LDPE is discussed; it is proposed that photo-oxidation is relatively much more likely to occur at terminal sites (rather than at pendent sites) when ZnO is present.
Keywords: Zinc oxide; Polyethylene; LDPE; ZnO; Photodegradation; Photocatalysis;

Surface structure and properties of poly-(ethylene terephthalate) hydrolyzed by alkali and cutinase by Ilaria Donelli; Giuliano Freddi; Vincent A. Nierstrasz; Paola Taddei (1542-1550).
This study was aimed at comparatively investigating the hydrolysis of crystalline and amorphous poly-(ethylene terephthalate) films by alkali and cutinase. Changes of surface properties were investigated by FTIR spectroscopy (ATR mode). The A 1341/A 1410 and I 1120/I 1100 absorbance ratios, and the full width at half maximum of the carbonyl stretching band (FWHM1715) were used to evaluate the polymer crystallinity and its changes upon hydrolysis. The effect of different treatments on chain orientation was evaluated by calculating R ratios of appropriate bands. The spectroscopic indexes showed that both alkali and enzyme treatments induced structural and conformational rearrangements with a consequent increase in crystallinity in both amorphous and crystalline films. The crystalline PET film was modified more strongly by alkali than by cutinase, while the opposite occurred for the amorphous one. The trend of the water contact angle (WCA) clearly indicates that alkali is more effective than cutinase in enhancing hydrophilicity of PET films and that the effect is stronger on amorphous than on crystalline films. The values of WCA correlate well with the FTIR indexes calculated from the spectra of hydrolyzed crystalline PET films. The mechanism of the surface hydrolysis of PET by alkali and cutinase is discussed.
Keywords: Poly-(ethylene terephthalate) (PET); Cutinase; Alkali; FTIR spectroscopy; Water contact angle;

Photodegradation of polymeric materials leads to significant modifications in both chemical properties and mechanical–rheological behaviors over time. Thus, it is important to characterize both properties to gain a better understanding of the durability of the materials. In this contribution, the chemorheological tools based upon Fourier transform infrared (FTIR) spectroscopy and dynamic mechanical thermal analysis (DMTA) were used to study the effects of temperature and moisture on photodegradation of a model sealant/coating system based upon a styrene–butadiene–styrene triblock copolymer. Specimens were exposed coincidentally to ultraviolet–visible radiation between 295 nm and 600 nm, and one of four different combinations of temperature and relative humidity (RH), i.e., (a) 30 °C and <1% RH, (b) 30 °C and 80% RH, (c) 55 °C and <1% RH, and (d) 55 °C and 80% RH. The rate of photodegradation was examined in terms of formation of oxidation species and evolution of mechanical–rheological data, including glass transition temperatures, moduli, and the number of effective crosslinked butadiene chains per unit volume per exposure time. Environmental exposure resulted in similar degradation modes for all four environments but the rate of photodegradation was found to depend strongly on temperature. Conversely, the role of moisture on photodegradation was not significant. The study shows that chemical modification can be directly related to the corresponding rheological modifications. In addition, the relative stability of styrene and butadiene against photodegradation as a function of temperature and moisture was compared.
Keywords: Aging; Chemorheological tool; Coatings; Degradation; SBS; Sealants;

To prepare a novel photo-degradable polypropylene (PP) with a higher degradation rate, a PP composite containing a poly(ethylene oxide) (PEO)/modified TiO2 microcapsule was prepared. The modification of the TiO2 was performed by the synthesis of octacalcium phosphate intercalated with succinic acid ion (OCPC) under various Ca/P molar ratio conditions. It was found that the synthesis conditions of the Ca/P = 3.5 and 3.6 M ratios were suitable to prepare the OCPC. However, the microscopic composition on the TiO2 surface was different between these Ca/P conditions and affected the PP photo-degradation rate in the PP/PEO/modified TiO2 composite. It was found from the Fourier Transform Infrared (IR) and the tensile testing measurements that the existence of the OCPC covering material on the TiO2 surface brought about the higher PP photo-degradation rate. The facilitation behavior of the degradation was due to the release of the acid species (succinic acid ion) from the OCPC in the degradation process. In addition, the higher coverage of the OCPC on the TiO2 surface brought about an induction period for the degradation.
Keywords: Polypropylene; Poly(ethylene oxide); Titanium dioxide; Calcium phosphate; Degradation;

The influence of sulfonation degree on the thermal behaviour of sulfonated poly(arylene ethersulfone)s by L. Abate; V. Asarisi; I. Blanco; G. Cicala; G. Recca (1568-1574).
Initial decomposition temperature (T i), apparent activation energy of degradation (E a) and glass transition temperature (T g) of some low molar mass (M n ≈ 8000 g mol−1) sulfonated poly(arylene ethersulfone)s s-(PAES)s were determined to check their dependence on sulfonation degree ( SD ). The results obtained were compared with those for unsulfonated poly(arylene ethersulfone) PAES. In order to have an accurate control of the chemical structure, a pre-sulfonation route was followed for the preparation of sulfonated compounds. The thermal behaviour of the investigated s-(PAES)s as well as that of PAES appears not to be influenced by the environment (flowing nitrogen or static air atmosphere) of degradation. Both T i and T g values of s-(PAES)s were higher than those of PAES and increased quite linearly as a function of sulfonation degree. An analogous linear trend was observed for the apparent degradation energy of s-(PAES)s, but the values found were largely lower than those of unsulfonated homopolymer. The results are discussed and interpreted.
Keywords: poly(arylene ethersulfone)s; Sulfonation degree; Glass transition temperature; Thermal stability; Kinetics of degradation;

Crosslinking and ageing of 13C labelled polyisoprene part 1: Synthesis and polymerisation of 4-13C-isoprene by Jean-François Pilichowski; Myriam Morel; Farba Tamboura; Stefan Chmela; Mohamed Baba; Jacques Lacoste (1575-1580).
4-13C-isoprene was prepared by the Wittig reaction. All reaction steps were optimised using unlabelled compounds. By reaction with triphenyl phosphine, 13C labelled methyl iodide afforded labelled methyl-triphenyl phosphine iodide in 84% yield. This reacted with meth acrolein with production of 4-13C-isoprene in 64% yield. Labelled polyisoprene was prepared by anionic polymerisation initiated by t-butyl lithium. Based on 13CH3I the overall yield is ca 30%. The polymer was characterized by 1H and 13C NMR spectroscopy. The contribution of each microstructure was [cis 1-4, 72%]; [trans 1-4, 10%]; [3-4, 18%].
Keywords: 4-13C-Isoprene; 13C-polyisoprene; NMR; Elastomer degradation;

Wheat gluten (WG) and Attapulgite (ATP) was mixed in acidic solution and freeze-dried, thermally compression-molded to form nanocomposite sheet. The influences of reduction and sonication on structure of wheat gluten were examined by Raman spectrum. The variation of disulfide bonding in wheat gluten show that the sonication is more effective than reduction on the breakage of disulfide bonds, whereas the content of disulfide bonds in the WG sheet molded by sonicated WG powder is the highest in the molded sheets. FT-IR analysis displays that the bands in the range of 1700–1600 cm−1 shift to higher frequency after mixing WG and ATP powders and molding the nanocomposite. The tensile and bending properties of the WG sheet increase with addition of ATP powder, and the properties of the sheet molded by sonicated WG powder decrease for the reduction of the disulfide bonding, but the properties of the sheet can be improved by addition of ATP. The WG/ATP nanocomposite images observed by SEM and TEM show that rod-like ATP particles are evenly dispersed in WG matrix, but the crystal structure of ATP is impervious. The viscoelasticity of the WG sheet declines with addition of ATP particle, and that the α-relaxation of the WG sheet molded by sonicated WG powder shift to high temperature and become broad. Both mass and bending strength of 7 wt% WG/ATP nanocomposite sheet show a decline over a soil exposure time of 20 days.
Keywords: Wheat gluten; Attapulgite; Nanocomposite sheet; Structure and property;

Chemical recycling of networked polystyrene derivatives using subcritical water in the presence of an aminoalcohol by Kanji Suyama; Masafumi Kubota; Masamitsu Shirai; Hiroyuki Yoshida (1588-1592).
Subcritical water is a benign and effective media for polymer degradation. On subcritical water treatment in the presence of an aminoalcohol, unsaturated polyesters crosslinked with styrene were decrosslinked, and a linear polystyrene derivative bearing hydroxy-terminated side-chains was recovered. After modification of the hydroxy groups with maleic anhydride, the polystyrene derivative was re-crosslinked with styrene to form a networked structure again. The resulting solid was degradable by subcritical water treatment in the presence of the aminoalcohol to give another polystyrene derivative bearing hydroxy groups. These processes could be repeated successfully, demonstrating the applicability as a novel recycling system of thermosetting resins. The polystyrene derivative was also re-crosslinked again on heating with an alternative copolymer of styrene and maleic anhydride due to the formation of linkage between the hydroxy groups and carboxylic anhydride moieties.
Keywords: Subcritical water; Unsaturated polyester; Chemical recycle; Decrosslink; Re-crosslink;

A boron-containing layered hydroxy salt (LHS), ZHTMDBB, was prepared and compounded with a highly flammable synthetic polymer, poly (methyl methacrylate) {PMMA}, via melt blending: the composite structure was intercalated with poor dispersion. The effect of this LHS on the flammability, thermal stability and degradation kinetics of PMMA was investigated via cone calorimetry and thermogravimetric analysis. The addition of 3–10% by mass of ZHTMDBB to PMMA resulted in significant reduction of peak heat release rate (22–48%) of the polymer and improvements in thermal stability were observed in both air and nitrogen. Effective activation energies for the degradation process were evaluated using Flynn-Wall-Ozawa, Friedman, and Kissinger methods. All three methods indicated that the additive increased the activation energies of the first step of the degradation process in both air and nitrogen. Activation energies of the second step were lowered in nitrogen but were not significantly affected in air.
Keywords: Layered hydroxy salt; Nanocomposites; PMMA; Thermal stability; Degradation kinetics;

Degradation behavior of electrospun microfibers of blends of poly(lactide-co-glycolide) and Pluronic® F-108 by Rajesh Vasita; Kirubanandan Shanmugam; Dhirendra S. Katti (1605-1613).
Electrospun poly(dl-lactide-co-glycolide) (PLGA) microfibers have been explored as extra cellular matrix mimicking scaffolding systems for tissue engineering application. However, the hydrophobic nature of PLGA can be limiting in terms of protein adsorption. Hence, blending of PLGA with a hydrophilic polymer (Pluronic®) prior to electrospinning has been explored as a potential strategy to impart hydrophilicity to PLGA microfibers. In this study, PLGA (85/15) was blended with small quantities (0.5–2% w/v) of Pluronic® F-108 (PF-108) and electrospun into microfibers. Blending of PF-108 demonstrated a significant decrease in the surface hydrophilicity of microfibers as was evidenced by an increase in wetting tension. Surface analysis using XPS indicated the presence of PF-108 in the bulk of the fibers in addition to the surface of the fibers. The results of the water uptake studies indicated that the water uptake capacity and consequential fiber swelling was significantly increased in the presences of PF-108. The in vitro degradation studies demonstrated that the trend in molecular weight loss was not significantly influenced by the presence of small quantities of PF-108. Therefore, blending of PLGA with PF-108 could be an effective technique for surface modification of electrospun PLGA microfibers without compromising on the other advantages of PLGA.
Keywords: Degradation; Poly(lactide-co-glycolide) (PLGA); Pluronic®; Electrospinning; Blends; Microfibers;

Effect of carbon nanotubes on the photo-oxidative durability of syndiotactic polypropylene by Liberata Guadagno; Carlo Naddeo; Marialuigia Raimondo; Giuliana Gorrasi; Vittoria Vittoria (1614-1626).
Polymer nanocomposites with carbon nanotubes as fillers have attracted more attention than any other nanomaterials. A full development of these materials requires a deep understanding of the way they behave in the use conditions. In this work, the resistance to accelerated photooxidation of syndiotactic polypropylene/multi-walled carbon nanotube (sPP/MWCNTs) films was compared to the photooxidation behaviour of unfilled polypropylene films with the same structural organization. The chemical and structural modifications resulting from photooxidation have been followed using infrared spectroscopy and diffractometric analysis. It was found that a good dispersion degree of the nanofiller, evaluated by atomic force microscopy, contributes to reduction in the rate of photooxidation and an increase in the oxidative thermal stability of the polymeric matrix. Different concomitant effects are considered to explain these results, among which morphology and structure of the nanocomposites together with the MWCNT capacity to interact with oxygen molecules making them unavailable in the first stages of photooxidation.
Keywords: Polypropylene/carbon nanotubes; Nanocomposite; Nanocomposite photooxidation; sPP/MWCNTs;

High temperature reactions of an aryl–alkyl phosphine, an exceptionally efficient melt stabiliser for polyethylene by Gábor Pénzes; Attila Domján; Dóra Tátraaljai; Peter Staniek; Enikő Földes; Béla Pukánszky (1627-1635).
Bis(diphenylphosphino)-2,2-dimethylpropane (PMP) is a highly efficient melt stabiliser of polyethylene. This aryl–alkyl phosphine hinders the degradation of the polymer during processing even in small concentrations and in combination with a phenolic antioxidant its consumption rate is considerably slower than that of phosphites and phosphonites. In this study the reactions of PMP were studied at temperatures corresponding to those used for the processing of polyethylene in order to explore the processing stabilisation mechanism of this additive. Thermal and thermo-oxidative stability were determined by DSC and TGA, respectively by heating PMP in argon and oxygen at 200 and 240 °C. Reactions with peroxy, carbon-centred and oxy radicals, as well as with hydroperoxide were investigated at 200 °C. Reaction products were identified by FT-IR and solution-state NMR spectroscopy. The results revealed that the phosphine studied has sufficient thermal- and thermo-oxidative stability under the processing conditions of polyethylene. It oxidises easily with any oxidising agent including molecular oxygen of air. Consequently, PMP does not only decompose hydroperoxide groups and react with oxy macroradicals during the processing of polyethylene, as claimed by most references on phosphorous antioxidants, but it can also hinder the formation of peroxy macroradicals, i.e., the initiation reaction of thermo-oxidative degradation.
Keywords: Aryl–alkyl phosphine; High temperature reactions; Stabilising mechanism; Heat-stability; Oxidation; NMR;

The use of hydroxytyrosol (3,4-dihydroxy-phenylethanol) as a potential alternative to synthetic compounds in the melt stabilization of polyolefins is considered. Hydroxytyrosol was found to play a role in enhancing the oxidative stability of olive oil, and a similar reduction in polyolefins’ thermo-oxidative degradation during processing is expectable. Rheological tests (melt flow index and viscosity vs. shear rate) showed the good antioxidant performance of hydroxytyrosol during polypropylene processing as was also demonstrated by the increase in apparent activation energies and oxidation induction parameters after addition to polypropylene (0.1 wt%). Results were compared to those obtained for a commercial synthetic phenolic antioxidant and for a natural compound widely used in polymer stabilization (α-tocopherol). The main conclusion of this work is the good performance of hydroxytyrosol in polypropylene stabilization during processing and consequently the possibility of its use in formulations with improved resistance to oxidative degradation.
Keywords: Hydroxytyrosol; Polypropylene; Viscosity; Apparent activation energy; Oxidation induction parameters;

Accelerated weathering of polyaramid and polybenzimidazole firefighter protective clothing fabrics by Rick Davis; Joannie Chin; Chiao-Chi Lin; Sylvain Petit (1642-1654).
Exposure to simulated ultraviolet sunlight at 50 °C and 50% relative humidity caused a significant deterioration in the mechanical performance of polyaramid and polyaramid/polybenzimidazole based outer shell fabrics used in firefighter jacket and pants. After 13 days of exposure to these conditions the tear resistance and tensile strength of both fabrics decreased by more than 40%. The polybenzimidazole containing fabric was less impacted by these conditions as it maintained approximately 20% more of its mechanical properties. These conditions also significantly degraded a water repellant coating on the fabric, which is critical to the water absorption performance of the outer shell fabrics. However, these conditions had little impact on the ultraviolet light protection of the outer shell as both fabrics still blocked 94% of ultraviolet light after 13 days of exposure. Confocal microscopy showed these conditions caused significant surface decomposition of and the switch from ductile to brittle failure of the polyaramid fibers. Cleavage of the amide linkages and the formation of oxidation species (as observed by Infrared spectroscopy) suggested these conditions caused photo-oxidation of the polyaramid fibers. There was little evidence of polybenzimidazole fiber degradation.
Keywords: Polyaramid; Polybenzimidazole; Firefighter; Accelerated weathering;

This study focused on the fabrication of calcium phosphate (Ca–P)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposite scaffolds loaded with biomolecules using the selective laser sintering (SLS) technique and their evaluation. Ca–P/PHBV nanocomposite microspheres loaded with bovine serum albumin (BSA) as the model protein were fabricated using the double emulsion solvent evaporation method. The encapsulation efficiency of BSA in PHBV polymer microspheres and Ca–P/PHBV nanocomposite microspheres were 18.06 ± 0.86% and 24.51 ± 0.60%, respectively. The BSA loaded Ca–P/PHBV nanocomposite microspheres were successfully produced into three-dimensional porous scaffolds with good dimensional accuracy using the SLS technique. The nanocomposite microspheres served as protective carriers and maintained the bioactivity of BSA during SLS. The effects of SLS parameters such as laser power and scan spacing on the encapsulation efficiency of BSA in the scaffolds and in vitro BSA release were studied. An initial burst release was observed, which was followed by a slow release of BSA. After 28-day release, The PHBV matrix was slightly degraded after 28-day in vitro release study. It was shown that nanocomposite scaffolds with controlled architecture obtained via SLS could be incorporated with biomolecules, enhancing them with more functions for bone tissue engineering application or making them suitable for localized delivery of therapeutics.
Keywords: Selective laser sintering; Tissue engineering scaffold; Nanocomposite; Poly(hydroxybutyrate-co-hydroxyvalerate); Calcium phosphate; Bovine serum albumin (BSA);

Influence of electron beam pre-irradiation on the thermal behaviors of polyacrylonitrile by Peikai Miao; Dimeng Wu; Ke Zeng; Guoliang Xu; Chun’e Zhao; Gang Yang (1665-1671).
Thermal treatment of polyacrylonitrile pre-irradiated by electron beam was performed to investigate the radiation effects on thermally activated reactions. Thermal properties were characterized by differential scanning calorimetry and thermogravimetric analyses. Pre-irradiation lowers the onset temperature of reactions and alleviated the heat evolution process. Char yields (800 °C) of polyacrylonitrile increase significantly with increasing irradiation dose. FTIR was used to monitor the thermal reaction. The results reveal that the thermal reactions can be regulated by pre-irradiation dose. FTIR and UV–visible absorption spectra of pre-irradiation polyacrylonitrile illustrate the formation of –HC=N–N=CH– conjugation across the polymeric chains as a function of dose, which could improve the thermal behaviors of polyacrylonitrile.
Keywords: Polyacrylonitrile; Electron beam pre-irradiation; Crosslinked networks; Thermal behaviors; High char yields;

Effect of carbon nanotubes and their dispersion on thermal curing of polyimide precursors by Qing-Yuan Tang; Jie Chen; Y.C. Chan; C.Y. Chung (1672-1678).
The process of thermal imidization reaction is significant for temperature and time control in the polyimide industry. Here, we report the effect of carbon nanotubes and their states of dispersion on the thermal imidization of the precursor films of polyimide (poly(amic acid)) for the first time. The curing process was followed by measuring Fourier transform-infrared (FT-IR) spectra, fluorescence spectra, thermogravimetric-differential scanning calorimeter (TG-DSC) properties and the refractive indices of films. It was found that by evenly dispersing 1 wt% of carbon nanotubes assisted by a dispersant in the poly(amic acid),the full imidization temperature of the polyimide can be reduced from 300 °C to 250 °C. Different states of distribution of CNTs were observed by light microscopy and scanning electron microscopy, and proved that a better dispersion of carbon nanotubes dramatically enhanced the speed of imidization. Moreover, the DSC results showed that lower decomposition temperature of poly(amic acid) could be obtained with more uniform distribution of carbon nanotubes, which means the process of cyclodehydration of the poly(amic acid) was accelerated.
Keywords: Polyimide/carbon nanotube composite; Curing; Distribution; Thermal imidization; Fluorescence;

In vitro and in vivo degradation behavior of aqueous-derived electrospun silk fibroin scaffolds by Juan Zhou; Chuanbao Cao; Xilan Ma; Lan Hu; Liang Chen; Chunren Wang (1679-1685).
We investigated the in vitro degradation behavior of the electrospun silk fibroin (SF) scaffolds by protease XIV. Phosphate-buffered saline (PBS) without enzyme was used as a control. About 65% of the electrospun SF scaffolds were degraded within 24 d in protease XIV, while almost no scaffolds were degraded in PBS. A great deal of fragments was visible in protease XIV solution. SEM indicated surface erosion of the scaffolds increased during protease degradation with increasing exposure time. FTIR and XRD indicated the crystalline structure of the scaffolds decreased after protease degradation for 24 d, and a degradation mechanism was proposed. Furthermore, the results of the in vivo degradation by implantation in rats showed that the scaffolds were completely degraded in vivo after implantation for 8 weeks and well tolerated by the host animals. The insights gained in this study can serve as a guide to match desired degradation behavior with specific applications for the electrospun SF scaffolds, such as tissue engineering and drug delivery.
Keywords: Silk fibroin; Electrospun; Degradation; Enzyme; In vivo;

Sub- and supercritical glycolysis of polyethylene terephthalate (PET) into the monomer bis(2-hydroxyethyl) terephthalate (BHET) by Muhammad Imran; Bo-Kyung Kim; Myungwan Han; Bong Gyoo Cho; Do Hyun Kim (1686-1693).
Sub- and supercritical glycolysis of polyethylene terephthalate (PET) with ethylene glycol (EG) to bis(2-hydroxyethyl) terephthalate (BHET) was investigated for the purpose of developing a PET recycling process. Supercritical glycolysis was carried out at 450 °C and 15.3 MPa while subcritical glycolysis was carried out at 350 °C and 2.49 MPa or at 300 °C and 1.1 MPa. High yields (gt; 90%) of the monomer BHET were obtained in both super- and subcritical cases. For the same PET/EG weight ratio of about 0.06, the optimum reaction time was 30 min for supercritical glycolysis and 75 and 120 min for two cases of subcritical glycolysis. GPC, RP-HPLC, 1H NMR and 13C NMR, and DSC were used to characterize the polymer and reaction products. Supercritical glycolysis will be suitable to a process requiring a high throughput due to its short reaction time.
Keywords: PET; Supercritical; Subcritical; Glycolysis; Plastics recycling;

In this paper, green composites of the corn starch were developed by using resorcinol-formaldehyde (Rf) as the cross-linking agent and reinforced with graft copolymers Saccharaum spontaneum L(Ss) and methyl methacrylates (MMA) as principal monomer and its binary mixture with acrylamide (AAm), acrylonitrile(AN), acrylic acid (AA) prepared under micro-wave. The matrix and composites were found to be thermally more stable than the natural corn starch backbone. There was improvement in physico-chemical and mechanical properties of composite were found to exhibit better than matrix. Ss-g-poly(MMA)-MW reinforced composites were found to exhibit better tensile strength, on the other hand Ss-g-poly(MMA + AA)-MW reinforced composites showed maximum compressive strength and wear resistance than other graft copolymers reinforced composite and the basic matrix. Further the matrix and composites were subjected for biodegradation studies through soil composting method. Different stages of biodegradation were evaluated through FT-IR studies and scanning electron microscopic (SEM) techniques.
Keywords: Saccharaum spontaneum L; Graft copolymer; Corn starch; Resorcino-formaldehydes; Green composites;

Biodegradation and thermal decomposition of poly(lactic acid)-based materials reinforced by hydrophilic fillers by Eustathios Petinakis; Xingxun Liu; Long Yu; Cameron Way; Parveen Sangwan; Katherine Dean; Stuart Bateman; Graham Edward (1704-1707).
The effect of hydrophilic fillers (starch and wood-flour) on the degradation and decomposition of poly(lactic acid) (PLA) based materials was investigated. Biodegradation was evaluated by composting under controlled conditions in accordance with AS ISO 14855. Thermal decomposition was studied by thermogravimetry (TGA). Morphological variations during biodegradation were investigated by SEM examination. It was found that biodegradation rates of PLA/starch blends and PLA/wood-flour composites were lower than that of pure cellulose but higher than that of pure PLA. The biodegradation rate was increased from about 60% to 80% when the starch content was increased from 10% to 40% after 80 days. Both starch and wood-flour accelerated thermal decomposition of PLA, and starch exhibited a relatively stronger affect then wood-flour. The decomposition temperature of PLA was decreased about 40 °C when the filler content was increased to 40%. Small polar molecules released during thermal decomposition of starch and wood-flour were attributed to the thermal decomposition behaviours of the PLA based blends and composites and their role is further discussed in this paper.
Keywords: PLA; Degradation; Hydrophilic filler; Starch; Wood-flour;

Thermal oxidation of clay-nanoreinforced polypropylene by G. Gutiérrez; F. Fayolle; G. Régnier; J. Medina (1708-1715).
The thermo-oxidation process at low temperatures for a montmorillonite-nanoreinforced polypropylene (PP) was studied. Experimental aging kinetic data at 100, 80 and 60 °C have been obtained and compared with a computational simulation in which a kinetic model based on the closed loop approach was used. As a result, it has been found that the montmorillonite role is not limited to a role of inert filler in the polymer matrix but induces a slight catalytic effect leading to induction period reduction. This effect has been well simulated by increasing initial hydroperoxyde concentration. The consequences of kinetic control by oxygen diffusion have also been investigated by using micro ATR-FTIR mapping to assess concentration profiles of the oxidation products across the sample thickness. It has been found that the oxidized layer thickness is close to 17 μm for the pure polypropylene whereas it is around 10 μm for the nanocomposite at 100 °C. These profile variations have been attributed to differences in oxygen diffusion coefficient values. Simulations based on the kinetic model including diffusion-reaction coupling describe these profiles well.
Keywords: Polypropylene; Nanocomposite; Micro ATR-FTIR; Oxidation profiles; Modeling;

Three types of microcapsules of di-ammonium hydrogen phosphate (DAHP) with different polymeric shells were evaluated as flame retardants in commercial polyurea padding for textiles. Encapsulated FR agent has the advantage of being compatible with the polymer matrix. The thermal degradation for the three types of DAHP microcapsules shows that our microcapsules act as intumescent fire retardants. The reaction to fire of polypropylene fabrics padded with FR polyurea loaded with neat DAHP or microencapsulated DAHP was studied with the cone calorimeter as a fire model.
Keywords: Flame retardant; Phosphate; Microencapsulation; Thermal degradation; Textile; Padding;

Investigation of the chemical modifications of beech wood lignin during heat treatment by Nicolas Brosse; Roland El Hage; Mounir Chaouch; Mathieu Pétrissans; Stéphane Dumarçay; Philippe Gérardin (1721-1726).
Holocellulose, Klason lignin and milled wood lignin (MWL) of beech wood were extracted before and after heat treatment and analysed using CP MAS 13C NMR, 13C NMR, 31P NMR and size exclusion chromatography (SEC). Experimental results showed that the thermal treatment degrades hemicelluloses and affects lignin polymer through depolymerisation due mainly to cleavage of β-aryl-ether linkages and recondensation reactions. The spectroscopic analysis of MWL demonstrated that these recondensation reactions involved mainly guaiacyl units through formation of 5,5′-biphenolic and diarylmethane structures.Analysis of molecular weight distribution of MWL by SEC indicated that average molecular weights of heat treated milled wood lignin were lower than those of native milled wood lignin.
Keywords: CP/MAS 13C NMR; 13C NMR; 31P NMR; Heat treatment; Milled wood lignin; Thermal degradation;

Synthesis and characterization of aromatic polyazomethines bearing pendant pentadecyl chains by Arvind S. More; Prakash S. Sane; Anandrao S. Patil; Prakash P. Wadgaonkar (1727-1735).
Aromatic diamine monomer viz., 4-(4′-aminophenoxy)-2-pentadecylbenzenamine containing pendant pentadecyl chain was synthesized starting from cashew nut shell liquid – a renewable resource material and was characterized by FTIR, 1H and 13C NMR spectroscopy. A series of new (co) polyazomethines containing pendant pentadecyl chains and flexibilizing ether linkages was synthesized by polycondensation of 4-(4′-aminophenoxy)-2-pentadecyl benzenamine with commercially available aromatic dialdehydes viz., terephthaldehyde (TPA), isophthaldehyde (IPA) and varying mixture of TPA and IPA. Inherent viscosities and number average molecular weights of (co) polyazomethines were in the range 0.50–0.70 dL/g and 10,490-40-800 (GPC, polystyrene standard), respectively indicating formation of medium to reasonably high molecular weight polymers. (Co) polyazomethines containing pendant pentadecyl chains were found to be soluble in common organic solvents such as chloroform, dichloromethane, tetrahydrofuran, pyridine, m-cresol and could be cast into transparent and stretchable films from their solution in chloroform. (Co) polyazomethines were essentially amorphous in nature and the formation of loosely-developed layered structure was observed arising from the packing of pendant pentadecyl chains. Polyazomethines exhibited glass transition temperatures (T g) in the range 21–48 °C. The observed depression of glass transition temperature could be ascribed to the “internal plasticization” effect of pentadecyl chains. The temperature at 10% wt loss (T 10), determined from TGA in nitrogen atmosphere of polyazomethines were in the range 434–441 °C indicating their good thermal stability.
Keywords: Polyazomethines; Pentadecyl; Side-chain; Solubility; Cashew nut shell liquid; CNSL; Renewable;

In vitro and in vivo degradation of an injectable bone repair composite by Rongwei Tan; Qingling Feng; Zhengding She; Mingbo Wang; He Jin; Jinyu Li; Xing Yu (1736-1742).
In vitro and in vivo degradation behaviors of an injectable bone regeneration composite (IBRC) which comprised of nano-hydroxyapatite/collagen (nHAC) particles in alginate hydrogel carrier were investigated. In vitro degradation quantitative testing indicated that the alginate had a faster degradation rate in simulated body fluid (SBF) than in deionized water at 37 °C. Similarly, IBRC also had a higher degradation rate in SBF than in deionized water at 37 °C, which was evaluated by alginate molecular weight measurement, mechanical properties test and degradation kinetics evaluation. But molecular weight of alginate degraded slower in IBRC than that in aqueous solution. In vitro results showed that degradation medium SBF had influence on degradation of alginate molecules. In the in vivo degradation study, surprisingly, there was no obvious decreasing of molecular weight of alginate from 0 to 8 weeks. IBRC degraded mostly after 24 weeks implantation and was replaced by connective tissue. No fibrous capsule and acute inflammatory reaction were found during the observed 24 weeks after IBRC implantation. There is only a mild short-term inflammatory response in rat dorsum muscle. These results indicated that IBRC had a controllable degradability and biocompatibility. Therefore, IBRC may be a promising degradable material for bone repair and bone tissue engineering.
Keywords: In vitro; In vivo; Degradation; Injectable; Bone repair;

In order to study the relationship between structure and properties, multiblock copolymers composed of poly(butylene succinate) (PBS) and poly (1,2-propylene succinate) (PPSu) have been synthesized by chain-extension at various molar ratios of hexamethylene diisocyanate (HDI) to polyester-diols, which have been abbreviated as R-values in this paper. Molecular weights of soluble fractions, gel fractions and crosslink densities have been determined. Thermal properties, mechanical properties and biodegradability have been studied and correlated with R-values. Crystallization of copolymers becomes difficult with increasing R-value. Tensile strength, flexural strength and flexural modulus tend to increase with increasing R-value up to 1.2, and vary little when R-value increases from 1.2 to 1.3, then decrease with further increase in R-value. Impact strength achieves a maximum value at R-value of 1.3. Biodegradation rate reaches a minimum value when R-value is 1.1. Biodegradation has been studied systematically by attenuated total reflectance Fourier transform infrared (ATR-FTIR), 1H NMR and SEM.
Keywords: Crosslink density; Poly(butylene succinate); Mechanical properties; Biodegradation;

Effect of natural weather on the structure and properties of polylactide/Cloisite 30B nanocomposites by Lynda Zaidi; Mustapha Kaci; Stéphane Bruzaud; Alain Bourmaud; Yves Grohens (1751-1758).
The degradation of polylactide (PLA)/Cloisite 30B nanocomposites under natural weathering was investigated as a function of clay loadings (1, 3 and 5 wt.%) for up to 130 days using Fourier transform infrared (FT-IR) spectroscopy, size exclusion chromatography (SEC), nanoindentation measurements, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). For comparative purposes, the neat PLA was also considered. The FT-IR results showed that the photo-oxidation mechanism of PLA was not modified in the presence of Cloisite 30B, but only the degradation rates were accelerated. Moreover, the photo-oxidative degradation of PLA nanocomposite samples led to the formation of vinyl unsaturation, carbonyls, anhydrides and hydroperoxides groups as a result of the occurrence of several chemical mechanisms simultaneously. The decrease of the weight-average molecular weight, and the number-average molecular weight associated with an enhanced polydispersity of the nanocomposite samples indicated that chain scission was the most prominent phenomenon in natural weathering. The thermal degradation of the PLA was faster in the presence of clay. Modulus and hardness measured by nanoindentation increased slightly with exposure time for both neat PLA and PLA nanocomposite samples; the increase is also a function of the clay content. Finally, the weathering effect on the morphology of exposed samples observed by SEM revealed that the fractured surfaces exhibited many voids and cracks. These defects were much more pronounced for the PLA nanocomposites.
Keywords: Polylactide; Clay; Nanocomposites; Natural weather; Ageing; Photo-oxidation;

Two preparation techniques attempting to disperse nanoclays in high-impact polystyrene matrix yielded different clay dispersion states either as intercalated or phase-separated morphologies. By this means, the influence of micro- and nanocomposite formation on the synergistic flame retardancy between nanoclays and a conventional mineral-type flame-retardant additive, namely aluminium tri-hydroxide, was investigated in terms of limiting oxygen index, horizontal burning rates and cone calorimetric fire properties. Reductions in peak heat release rates in the cone calorimeter were doubled with nanocomposites relative to microcomposites, attributed to char enhancement and lower mass loss rates. This was accompanied by higher limiting oxygen index, lower burning rates and better mechanical properties. In particular, the formation of nanocomposites allowed for the recovery of tensile strength reductions caused by high loadings of aluminium tri-hydroxide in the polymer.
Keywords: Nanoclay; Intercalation; Nanocomposite; Microcomposite; Flame retardancy; Mechanical properties;

Effects of synthetic and natural zeolites on morphology and thermal degradation of poly(lactic acid) composites by Isinay E. Yuzay; Rafael Auras; Herlinda Soto-Valdez; Susan Selke (1769-1777).
Poly(lactic acid) (PLA) composites containing 5 wt% synthetic (type 4A) and natural (chabazite) zeolites were prepared using extrusion/injection molding. Morphological, structural, and thermal properties of composites were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). DSC results revealed that the glass transition and melting temperatures were not significantly changed; however, the incorporation of both type 4A and chabazite zeolites enhanced the nucleation of PLA crystallites as well as increased the percent crystallinity. Thermal degradation properties of PLA and PLA/zeolite composites were studied by non-isothermal thermogravimetric analysis (TGA) in nitrogen atmosphere. TGA results showed that at temperatures above 300 °C, PLA/type 4A synthetic zeolite composites were thermally decomposed more easily than the PLA and PLA/chabazite natural zeolite composites. The apparent activation energies of thermal degradation of PLA and PLA/zeolites composites estimated using both the Flynn–Wall–Ozawa and Kissinger methods followed the same order: PLA/type 4A < PLA/chabazite < PLA.
Keywords: Polylactic acid; Zeolites; Thermal degradation; Activation energy; Chabazite;

Storage stability study of salicylate-based Poly(anhydride-esters) by Brittany M. deRonde; Ashley L. Carbone; Kathryn Uhrich (1778-1782).
Storage stability was evaluated on a biodegradable salicylate-based poly(anhydride-ester) to elucidate the effects of storage conditions over time. The hydrolytically labile polymer samples were stored in powdered form at five relevant storage temperatures (−12 °C, 4 °C, 27 °C, 37 °C, 50 °C) and monitored over four weeks for changes in color, glass transition temperature, molecular weight, and extent of hydrolysis. Samples stored at lower temperatures remained relatively constant with respect to bond hydrolysis and molecular weight. Whereas, samples stored at higher temperatures displayed significant hydrolysis. For hydrolytically degradable polymers, such as these poly(anhydride-esters), samples are best stored at low temperatures under an inert atmosphere.
Keywords: Polyanhydride; Poly(anhydride-ester); Stability; Degradation; Biodegradable; Hydrolysis;

The effects of low (2.5, 0.2 keV) energy reactive oxygen ion bombardment and argon ion bombardment on poly(ethylene terephthalate) thin film (PET) surface chemical composition were studied. PET films have a high potential as a material for biomedical and electrical industries. The source of ions was an ECR Ion Gun with settable acceleration voltages. PET films were sputtered by ion bombardment for variable process time and the modified films were investigated by in-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Fourier transform infrared spectroscopy (FTIR). The significant changes in the chemical composition of surface layers were quantitatively studied by XPS. The ion bombardment scissions the chains in PET film surface layers. Selective sputtering of oxygen atoms from PET surface was observed when argon ion flux used. The 0.2 keV and 2.5 keV argon ion decreased O/C ratio from 0.37 to 0.25, 0.04 respectively. This phenomenon is responsible for the creation of carbon-rich up 96 at.% surface layer and the oxygen in ester bonds is detached first. The oxygen 2.5 keV ion bombardment had similar effect as argon ion bombardment; the ratio O/C was decreased. The ester bond was broken first. But oxygen 0.2 keV ion flux irradiation created an oxygen rich surface; the O/C ratio was in increased from 0.37 to 0.46. The changes in surface conductivity were investigated by shifts in C1s binding energy. Good agreement with atomic concentration of carbon in C–C bonds on the films surface was found. The FTIR analyses identified changes in chemical composition but with no obvious correlation to surface changes. Photons from the ion source irradiating the PET film during ion bombardment probably caused the observed changes in FTIR spectra.
Keywords: ESCA/XPS; Poly(ethylene terephthalate) (PET); Oxidation; Sputtering; Surface modification;

The migration of di(2-ethylhexyl)phthalate (DEHP) from poly(vinyl chloride) (PVC) to a surrounding gas phase at temperatures below 120 °C kinetically is controlled by evaporation. The effects on the DEHP loss rate of nitrogen flow rate, relative humidity and degradation of the plasticizer at 100 °C was assessed. The sample mass decreased linearly with time for both pristine DEHP and plasticized PVC at comparable rates, suggesting that a thin film of DEHP was present on the jacketing insulation during desorption. The latter hypothesis was supported by infrared spectroscopy and by the fact that DEHP is an amphiphilic molecule that will tend to aggregate at the surface with the hydrophobic 2-ethylhexyl units at the air interface. The effect on the migration rate of moisture present in the gas phase was negligible. The DEHP loss rate increased in a retarding non-linear fashion with increasing gas flow rate. In one of the experiments, DEHP was accidently degraded as revealed by discoloration, the presence of low molar mass degradation products (liquid chromatography) containing additional carbonyl groups (infrared spectroscopy) and an increase in the evaporation rate at temperatures between 100 and 130 °C.
Keywords: Di(2-ethylhexyl)phthalate; Poly(vinyl chloride); Evaporation; Gas flow rate; Relative humidity; Plasticizer degradation;

Aerobic biodegradation of calcium carbonate filled polyethylene film containing pro-oxidant additives by Lucie Husarova; Michal Machovsky; Pavel Gerych; Josef Houser; Marek Koutny (1794-1799).
Two low density polyethylene films, which contained pro-oxidant additives, where investigated, one of them containing micro-milled calcium carbonate filler. Both materials were subjected to controlled thermal oxidation, the oxidation was obviously retarded in the filler-containing sample. Following this, the biodegradability of samples pre-oxidized for 40 and 80 days was investigated. The levels of carbon mineralization reached 13% and 16% for the 40 and 80 days pre-oxidized polyethylene containing filler, respectively, after approximately 16 months in a soil environment at 25 °C, and both types of sample were mineralized to about 19% in compost environment at 58 °C during the same period. The sample not containing filler was mineralized to about 7% in soil after 13 months, and about 23%, after 8 months in compost. Scanning electron microscopy revealed dense colonization of the sample surfaces in both soil and compost. The data presented here provide clear quantitative evidence that part of the polyethylene material was biodegraded.
Keywords: Polyethylene; Pro-oxidants; Biodegradation; Gas chromatography; Scanning electron microscopy; Thermal oxidation;

Effects of melt processing conditions on photo-oxidation of PP/PPgMA/OMMT composites by S. Aslanzadeh; M. Haghighat Kish; A.A. Katbab (1800-1809).
This article reports the studies of photo-oxidative behaviour of polypropylene/maleic anhydride-grafted polypropylene/organic modified montmorillonite (PP/PPgMA/OMMT) composites prepared by two different melt processing methods. Samples of pristine polypropylene (PP) and PP/PPgMA/OMMT composites were prepared in an internal mixer and in a twin screw extruder. The samples were exposed to long wavelength radiations (λ > 300 nm) for the photo-oxidation. The samples were examined by FTIR, X-ray diffraction and microscopy. Similar to the pristine (PP), it is found that the photo-oxidation process in the composites depends on the melt processing conditions, which could cause the deterioration of organic modifier of the clay and the polymer matrix. The new radicals formed in addition to the iron impurities in the montmorillonite accelerate the photo-oxidation.
Keywords: Photo-oxidation; Polypropylene; Nanoclay; UV radiation; Montmorillonite;

How to reveal latent degradation of coatings provoked by UV-light by J.-F. Larché; P.-O. Bussière; J.-L. Gardette (1810-1817).
This paper deals with predictions of the service life of the two main technologies used for automotive clearcoats: acrylic-melamine and acrylic-urethane. This work demonstrates that the UV-light irradiation leads to chain scissions and crosslinking for the unstabilised and stabilised formulations. Mechanisms are proposed to explain the dramatic increase in the values of the mechanical properties for the two technologies as a function of the ageing time. For a determined critical value of the mechanical properties, water acts to reveal the latent damage by leading to the formation of cracks. Moreover, when the polymer reaches a certain level of network densification due to UV-light irradiation, the system cannot accept the stress induced by the water inflation/deflation and cracks will occur. Other solvents were also tested to understand the effects of polarity on the formation of the cracks.
Keywords: Photo-ageing; Water; Clearcoat; Cracking; Acrylic; Urethane; Melamine;

Structures and properties of the compression-molded istactic-polypropylene/talc composites: Effect of cooling and rolling by Md. Abdul Gafur; Rahima Nasrin; Md. Forhad Mina; Md. Abu Hashan Bhuiyan; Yukihiro Tamba; Tsutomu Asano (1818-1825).
Talc-loaded isotactic polypropylene (iPP) composites with various contents of talc were fabricated by compression molding, following slow- and fast-cooling processes, to obtain slow-cooled samples (SCS) and fast-cooled samples (FCS), respectively. Lamellar thickness of the α-crystal of iPP in the SCS is observed to be larger than that in the FCS by X-ray diffraction study. Rolled fast-cooled samples (RFCS) were also prepared at 25 °C in order to examine the crystal growth of iPP. An epitaxial growth mechanism of the α-crystal of iPP from the talc crystal is proposed. Surface of talc-loaded FCS appears with a smaller particle size than that of talc-loaded SCS and RFCS as observed by a scanning electron microscope. Young’s modulus and tangent modulus of FCS are found lower than those of SCS with the addition of talc up to 20 wt% and higher above this concentration, except microhardness which is higher in SCS at all contents of talc. From thermal studies, talc-loaded SCS and FCS are found to show higher melting temperature than the neat samples. Effect of cooling and rolling on the structures and properties of the fabricated composites are elaborately discussed.
Keywords: Composites; X-ray diffraction; Lamellar structure; Mechanical properties; Thermal properties;

Novel processable and heat resistant poly(phenylthiourea azomethine imide)s: Synthesis and characterization by Ayesha Kausar; Sonia Zulfiqar; Zahoor Ahmad; Muhammad Ilyas Sarwar (1826-1833).
N-(4-chloro-3-aminobenzal)N′(4-aminophenyl)thiourea having phenylthiourea and azomethine groups was synthesized and exploited as starting material for the fabrication of new polymers. Novel diamine was condensed with pyromellitic dianhydride, 3,3′,4,4′-benzophenone-tetrcarboxylic dianhydride and 4,4′-(hexafluoroisopropylidene) diphthalic dianhydride to obtain poly(phenylthiourea azomethine imide)s. The structural explication of monomers and poly(phenylthiourea azomethine imide)s were carried out by FTIR, 1H and 13C NMR techniques along with crystallinity, organosolubility, inherent viscosity and molecular weight measurements. Accordingly, polymers bearing C=S and –C=N– moieties in the backbone demonstrated an amorphous nature and were readily soluble in amide solvents such as DMAc, DMF, and DMSO. Poly(phenylthiourea azomethine imide)s encompassed η inh of 1.40–1.55 dL/g and were obtained in quantitative yields. In addition, GPC measurements of polymers revealed M w around 60,291–67,665. Thermal stability of these polymers was ascertained via 10% weight loss temperatures around 514–533 °C in an inert atmosphere. Besides, glass transition temperatures of polyimides were found to be 272–276 °C.
Keywords: Poly(phenylthiourea azomethine imide)s; Azomethine; Organosolubility; GPC; Thermal stability;

Ammonium polyphosphate (APP) with crystalline form V (APP-V) was synthesized by heating a mixture of 85% food-grade phosphoric acid and melamine under dry ammonia atmosphere. Effects such as raw material ratios, charging methods, dehydration temperature, condensation temperature and condensation time were investigated. Its water solubility was tested, its XRD and FTIR were characterized and compared with those of industrial APP-I and APP-II. Results showed that the prepared APP-V was insoluble in water, its XRD spectrum was the same as APP-V in literature. The molecular structures of the prepared APP-V and APP-I/APP-II were speculated and discussed in detail.
Keywords: Ammonium polyphosphate; Crystalline form V; Water solubility; Controllable synthesis;

Thermal behavior and fire performance of nylon-6,6 fabric modified with acrylamide by photografting by Wei Liu; Sheng Zhang; Xiaosui Chen; Lihua Yu; Xinjun Zhu; Qingli Feng (1842-1848).
Our previous study shows that surface photografting modification with maleic anhydride followed by reacting with triethanolamine can improve the flame retardancy of nylon-6,6 fabric. In this study, acrylamide was used as a grafting monomer to improve the flame retardancy of nylon-6,6 fabric. The effects of monomer concentration and irradiation time on photografting were investigated. The surface structure of the sample was analyzed by attenuated total reflection infrared spectroscopy (ATR-FTIR). Flame retardancy was characterized by limiting oxygen index test (LOI), the vertical burning test and cone calorimeter. The grafted sample has a higher LOI value than the untreated sample, and has no melting drip during the vertical burning test. The improvement of the flame retardancy and char formation of the nylon-6,6 fabric have also been verified by the thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) analysis.
Keywords: Photografting; Nylon-6,6 fabric; Flame retardancy; Acrylamide;

Degradation kinetics of functionalized novolac resins by Hsin Ho Wu; Peter P. Chu (1849-1855).
We report the relationships between the degradation behaviors (i.e. the degradation kinetics, degradation activation energy, weight loss conversion, and char formation) and the structure features in three modified novolac resins bearing different curable functional groups and aromatic units i.e. Carbonyl phenyl azo novolac resin (CPAN) , 4-(4-hydroxyphenyl azo) benzyl ester novolac resin (HPDEN) and Carbonyl phenyl 4-(4-hydroxyphenyl azo) benzyl ester novolac resin (CHABN) . These modifications enhanced the thermal stability of the cured novolac resins by delaying the decomposition temperature up to 30–100 °C and produced prominent residue char yield up to 68% (CPAN), 56% (HPDEN) and 64% (CHABN), respectively. The two heavily cross-linked samples, CPAN and CHABN displayed even higher Ea than HPDEN. All modified novolacs displayed much higher decomposition activation energy (over 237 KJ/mol*K) compared with the generic phenolic (PN).
Keywords: Thermal stability; Cross-linking density; Thermal degradation energies (Ea);

Degradation behavior of poly(lactide-co-glycolide)/β-TCP composites prepared using microwave energy by Hyeong-Ho Jin; Sang-Ho Min; Yong-Keun Song; Hong-Chae Park; Seog-Young Yoon (1856-1861).
Biodegradable poly(lactide-co-glycolide) (PLGA)/β-tricalcium phosphate (β-TCP) composites were synthesized through polymerization using microwave energy. The degradation behavior of the PLGA/β-TCP composites was carried out at 37 °C in a SBF without changing the solution in order to examine the effect of β-TCP on the degradation behavior. The changes in the molecular weight, mass, and morphology of the composites were examined with respect to the soaking time. An incubation time of 2 weeks was needed to degrade the β-TCP of the composites, indicating that degradation of β-TCP could be started when β-TCP was detached from the PLGA matrix or exposed from composites surface, caused by PLGA matrix was degraded into the SBF solution. The mass loss of the composites with respect to the soaking time revealed that PLGA transformed from a polymer to an oligomer as the degradation process proceeded. The whisker-like morphological changes, caused by the transformation and degradation of the polymer were observed in the composites after week 2. The degradation behavior of the PLGA/β-TCP composites was influenced by the β-TCP content in the composite, and the degradation rate of the composite could be controlled by the initial molecular weight of PLGA.
Keywords: In vitro; Biodegradable; PLGA; β-TCP; Microwave;

The thermal degradation of polyethylene includes two different kinds of pathways. These are random and chain-end scissions which include β-scission on the chain end and radical transfer scission. We conducted a quantitative analysis on these pathways by Pyrolysis-GC/MS and computer simulation. Two different distributions of scission products of polyethylene were observed at different temperatures. They are determined by the relationship between rate of reaction and that of volatilisation. Furthermore, a characteristic distribution was observed in lower molecular weight. It could be explained by direct scission and one to five-step radical transfer scissions. The pathway possibilities calculated with the accumulated schemes showed that the direct scission and one-step-radical transfer increased with the temperature. This indicates that β-scission occurs on the chain end before the radical transfer because the rate of the β-scission becomes faster as the temperature rises.
Keywords: Thermal degradation; Polyethylene; Random scission; Radical transfer; β-Scission;

Studies on thermal degradation of 1-4 and 1-2 polybutadienes in inert atmosphere by C. Sanglar; H. Nguyen Quoc; M.F. Grenier-Loustalot (1870-1876).
The degradation of 1,2 and 1,4 polybutadienes by heating in inert atmosphere was characterized by FTIR, NMR and TGA/TCT/GC/MS for the volatile organic compounds. Two distinct mass change stages in the thermogravimetric analysis indicated different temperature ranges of degradation. Below 300 °C, the predominant reactions depend on the chemical structure of PBs. Thus, M1 and M2 formation by heating 1,4-PB at 260 °C allows us to prove crosslinking reaction. On the other hand, heating 1,2-PB at 260 °C leads to decahydronaphthalene and methyl formation by cycloaddition and rearrangement. At about 300 °C, only radical scission occurs for 1,2-PB whereas Diels Alder and proton transfer mechanisms are described for 1,4-PB. The products of reaction are respectively conjugated diene, cyclic and linear unsaturated compounds sometimes with methyl groups. Above 400 °C, the main process is aromatisation for both PBs.
Keywords: Polybutadiene; Degradation mechanisms; FTIR; NMR; TGA/TCT/GC/MS;

In this study, emissions from a carpet adhesive and an acrylate dispersion in simulated humid and alkaline environments were investigated by the micro-scale head space vial (MHV) method. Relative humidity (RH) levels of 75%, 86% and 93% were tested in combination with pH values in the range 10–13. The polymeric materials were exposed at these conditions in sealed 20 mL headspace vials. Chemical analysis of the volatile emission products was performed by headspace solid-phase micro-extraction with subsequent gas chromatography mass spectrometry after three and 36 days. The effect of the RH and pH on the emissions was investigated. It was found that 2-ethyl-1-hexanol was one of the major volatile constituents, and that the emissions of this compound increased dramatically for pH > 12. This can be explained by alkali catalyzed hydrolysis of ester-linked 2-ethylhexyl groups. The other compounds that were detected after exposure of the adhesive were not as strongly dependant on pH and RH as 2-ethyl-1-hexanol.
Keywords: 2-ethyl-1-hexanol; Emission; Degradation; Adhesive; VOC; HS-SPME;

Study of the high temperature reactions of a hindered aryl phosphite (Hostanox PAR 24) used as a processing stabiliser in polyolefins by Ildikó Kriston; Gábor Pénzes; Gábor Szijjártó; Pál Szabó; Peter Staniek; Enikő Földes; Béla Pukánszky (1883-1893).
The processing stabilising performance of various phosphorous antioxidants in polyolefins is affected significantly by their chemical composition. In order to explore the mechanism of stabilisation, the reactions of a hindered aryl phosphite [tris(2,4-di-tert-butylphenyl)phosphite (DTBPP), Hostanox PAR 24] were investigated at temperatures corresponding to polyethylene processing. The thermal and thermo-oxidative stability of the additive was determined by differential scanning calorimetric (DSC) and thermogravimetric methods. DTBPP was heat treated under argon and oxygen at 200 and 240 °C. The stabiliser was reacted at 200 °C with azobisisobutyronitrile (AIBN) in oxygen-free environment (carbon centred radicals) and under oxygen (peroxy radicals), with dicumyl peroxide (DCP) in oxygen atmosphere (oxy radicals), and with cumene hydroperoxide (CHP) under argon. The reaction products were identified by FT-IR, HPLC and HPLC–MS. The results revealed that besides the known reactions of hindered aryl phosphites, thermal decomposition and recombination reactions also take place above the melting point of the antioxidant. DTBPP does not react with molecular oxygen, but its decomposition is accelerated by oxygen and especially by radicals. Accordingly, the heat-stability of phosphorous stabilisers also has to be taken into account in their application, as it is one of the factors which influence the processing stabilisation of polyolefins.
Keywords: Hindered aryl phosphite; Heat-stability; Reactions with radicals; Oxidation; Processing stabilisation of polyolefins;

Photocatalytic efficiency of TiO2/poly[acrylamide-co-(acrylic acid)] composite for textile dye degradation by Wiyong Kangwansupamonkon; Walasinee Jitbunpot; Suda Kiatkamjornwong (1894-1902).
A novel photocatalytically degradable TiO2/poly[acrylamide-co-(acrylic acid)] composite hydrogel (TiO2/poly[AAm-co-AAc]) was synthesized by polymerization in an aqueous solution with N,N’-methylenebisacrylamide as the crosslinker and ammonium persulphate and TEMED as the initiator pair. The combined and separate effects of photodegradation and adsorption processes for dye removal were evaluated using methylene blue (MB) as the model dye for a photodegradation target, and compared with those of the neat poly[AAm-co-AAc], and a commercially available TiO2 photocatalyst (Degussa P-25). Without photodegradation (i.e. in the dark), the TiO2/poly[AAm-co-AAc] composite adsorbed up to 85% of the MB from a 5 mg L−1 MB solution in 15 min compared to only 10% for the pristine TiO2. The reproducibility in photodegradation of the reused poly[AAm-co-AAc] composite was also investigated, where poly[AAm-co-AAc] was found to be photocatalytically degraded under UV irradiation. Therefore, the TiO2/poly[AAm-co-AAc] composite hydrogel is a good dye adsorber with self-photodegradability and it also can easily be separated from the reaction by simple filtration. With these properties, the TiO2/poly[AAm-co-AAc] hydrogel can be called a green polymer for use in the photodegradation–adsorption process for the abatement of various pollutants.
Keywords: TiO2; Hydrogel; Photocatalytic degradation; Dye removal;

Evaluation of various fire retardants for use in wood flour–polyethylene composites by Nicole M. Stark; Robert H. White; Scott A. Mueller; Tim A. Osswald (1903-1910).
Wood–plastic composites represent a growing class of materials used by the residential construction industry and the furniture industry. For some applications in these industries, the fire performance of the material must be known, and in some cases improved. However, the fire performance of wood–plastic composites is not well understood, and there is little information regarding the effectiveness of various fire retardants in the public domain. We used oxygen index and cone calorimeter tests to characterize the fire performance of wood flour–polyethylene composites, and compared the results with unfilled polyethylene and solid wood. We then evaluated the effect of five additive-type fire retardants on fire performance. Generally, magnesium hydroxide and ammonium polyphosphate improved the fire performance of WPCs the most while a bromine-based fire retardant and zinc borate improved fire performance the least.
Keywords: Wood–plastic composite; Fire retardants; Mechanical properties; Heat release rate; Oxygen index;

Calcium and aluminium-based fillers as flame-retardant additives in silicone matrices. I. Blend preparation and thermal properties by Siska Hamdani; Claire Longuet; José-Marie Lopez-Cuesta; François Ganachaud (1911-1919).
This series investigates silicone composites with enhanced thermal behaviour for cable applications. Calcium and aluminium-based fillers introduced into silicone formulations were classified according to three categories: non-hydrated fillers such as CaCO3 (precipitated calcium carbonate and natural calcite) and wollastonite, water-releasing fillers such as calcium hydroxide, ATH, boehmite, and hydroxyl-functionalized fillers including alumina and mica. The fillers were first characterized in detail, and the thermal stability of their blends with silicone was recorded by thermogravimetric analyses. A discussion on various aspects of the filler morphology (size, microstructure, release profile with temperature) on the silicone stability is finally given.
Keywords: Silicone; Fire retardants; Fillers; Thermal degradation; Thermogravimetry;

Novel poly(butylene succinate-co-lactic acid) copolyesters: Synthesis, crystallization, and enzymatic degradation by Licheng Tan; Yiwang Chen; Weihua Zhou; Huarong Nie; Fan Li; Xiaohui He (1920-1927).
A series of aliphatic biodegradable poly(butylene succinate-co-dl-lactide) (PBSLA) copolyesters were synthesized with the aim of improving the degradation rate of poly(butylene succinate) (PBS) by incorporation of dl-oligo(lactic acid) (OLA) into the PBS molecular chains. The composition and sequential structure of the aliphatic copolyesters were investigated by proton nuclear magnetic resonance (1H NMR) spectroscopy. The crystallization behaviors, the crystal structure and morphology of the copolyesters were investigated by using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarizing optical microscopy (POM), respectively. The results indicate that the crystallization of the copolyesters was restricted by the incorporation of lactide (LA) units, which further tuned the mechanical properties of the copolyesters. The copolyesters could form complete spherulites and exhibit the same crystal structure as that of PBS. Enzymatic study indicated that the copolyesters with higher content of LA units degraded faster, and the degradation began in the amorphous regions and then in the crystalline regions. The morphology and the resulting degradation products of the copolyesters were investigated by scanning electron microscopy (SEM) and 1H NMR analysis during the degradation process.
Keywords: Poly(butylene succinate); dl-oligo(lactic acid); Crystallization; Enzymatic degradation;

Flame retardancy properties of α-zirconium phosphate based composites by Jenny Alongi; Alberto Frache (1928-1933).
α-Zr phosphate (hereafter referred to as ZrP) based composites were prepared by melt blending in order to improve the flame retardancy properties of polyamide 6 (PA6), polyethylene terephthalate (PET), polypropylene (PP) and ethylene vinyl acetate copolymer (EVA). Different morphologies are distinguishable by electron microscopy: PA6-ZrP seems to be a nanocomposite by Transmission Electron Microscopy (TEM) whereas PET-, PP- and EVA-ZrP blends appear micro-composites by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses. ZrP acts as flame retardant in PA6 reducing the total heat evolved and consequently the heat release rate during the combustion measured by cone calorimetry. Moreover, ZrP reduces the flammability of PET and EVA acting in synergistic effect with phosphorous based flame retardants. Indeed, it is showed that it is possible to reduce the amount of phosphorous flame retardant adding ZrP to reach UL94 classification V0 for both polymers.
Keywords: α-Zr phosphate; PA6; PET; PP; EVA; Flame retardancy;

Improving the flame retardancy of PET fabric by photo-induced grafting by Lihua Yu; Sheng Zhang; Wei Liu; Xinjun Zhu; Xiaoping Chen; Xiaosui Chen (1934-1942).
Photo-induced surface grafting with glycidyl methacrylate (GMA) as monomer in association with a pad-curing treatment by using a flame retardant (FR) solution which contains 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP) and sulfamic acid (H2NSO3H) has been used to improve the fire performance of PET fabric in this study. The effects of initiator concentration, monomer concentration and the irradiation time on the grafting percentage were investigated. The chemical structure of grafted surface of the PET fabric was characterized by an attenuated total reflection-infrared (ATR-IR) spectroscopy. The fire performance was evaluated by the LOI and the vertical flammability tests, and the results indicate that the photo grafting treatment could improve the flame retardancy and dripping resistance of PET fabric. Thermal behaviour of treated PET fabric samples was investigated by thermogravimetric (TG) and differential scanning calorimetric (DSC). The morphology of the sample char residue was also investigated by scanning electron microscope (SEM).
Keywords: Photo-induced grafting; PET fabric; Flame retardancy; Dripping resistance;

In this work, we investigated the effects of an ethylene propylene diene monomer (EPDM) and poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) on the water tree resistance in cross-linked polyethylene (XLPE). The XLPE/EPDM and XLPE/SEBS blend samples were prepared by melting compounding and subsequent compression molding. It was found that SEBS could greatly increase the water tree resistance of XLPE and the resistance performance was improved with SEBS content within 15 phr, whereas EPDM did not show any improvement in the water tree resistance of XLPE. The frequency dependent behaviors of the water treeing phenomena and the effects of EVA on the water tree resistance of XLPE/EPDM and XLPE/SEBS blends were also investigated. The water treeing phenomena of the blends were interpreted from the viewpoints of electro-mechanical and electro-chemical mechanisms.
Keywords: XLPE; Cable insulation; Water tree; EPDM; SEBS;

Characterizations and thermal stability of soluble polyimide derived from novel unsymmetrical diamine monomers by Fengchun Yang; Yanfeng Li; Qianqian Bu; Shujiang Zhang; Tao Ma; Jiujiang Zhao (1950-1958).
Two kinds of novel aromatic, unsymmetrical diamines with ether–ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 3-amino-4′-(4-aminophenoxy)-benzophenone, was successfully synthesized by two different synthetical routes and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride, via a conventional two-step thermal or chemical imidization method to produce a series of fluorinated polyimides. The polyimides were characterized with solubility tests, viscosity measurements, mechanical properties tests, IR-FT, and thermogravimetric analysis. The polyimides had inherent viscosities of 0.54–0.77 dL/g and were easily dissolved in both polar, aprotic solvents and common, low-boiling-point solvents. The resulting strong and flexible polyimide films exhibited excellent thermal stability, with decomposition temperatures (at 10% weight loss) above 573 °C and glass-transition temperatures in the range of 222–251 °C. Moreover, the polymer films showed outstanding mechanical properties, with tensile strengths of 86.5–121.6 MPa, elongations at break of 9–16%, and initial moduli of 1.26–1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications.
Keywords: Polyimide; Solubality; Synthesis; Unsymmetrical diamine;