Polymer Degradation and Stability (v.97, #11)
Editorial Board (IFC).
Structural analysis of biodegradable low-molecular mass copolyesters based on glycolic acid, adipic acid and 1,4 butanediol and correlation with their hydrolytic degradation by Spyridon Soulis; Despina Triantou; Steffen Weidner; Jana Falkenhagen; Johannis Simitzis (2091-2103).
Copolyesters of glycolic acid combined with adipic acid and 1,4 butanediol were synthesized, their in vitro hydrolytic degradation was studied and correlated with their structure. The hydrolytic degradation of the copolyesters was directly related with the degree of crystallinity and the diameter of the crystallites. It was found that glycolate units disturb the ordering of the butylene adipate units, which results in a decrease of the crystallinity. By comparing the hydrolysis parameters of synthesized copolyesters with those of similar aliphatic copolyesters a hydrolysis mechanism was proposed. According to this mechanism, the degradation takes place not only by the loss of end units, but also through the removal of larger segments. MALDI-TOF MS data showed that the possibility of a copolyester macromolecule forming cyclic structures correlates with the arrangement of ester groups in the macromolecules and the structure of the linear segments.
Keywords: Biodegradable; Biopolymers; Hydrolytic degradation; Ft-IR; Matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF MS);
Co-pyrolysis of LignoBoost® lignin with synthetic polymers by Mihai Brebu; Iuliana Spiridon (2104-2109).
Co-pyrolysis of LignoBoost® lignin with synthetic polymers (polyethylene, polypropylene, polystyrene and polycarbonate) was performed in a semi-batch reactor at 500 °C and self-generated pressure. The mass yields and composition of degradation products were determined in order to identify the interactions between components. Generally the degradation of lignin is slightly diminished while that of synthetic polymers is enhanced. Particular behaviour was observed for co-pyrolysis of lignin and polycarbonate, both materials having phenol-type structure. The stronger interactions between components in this case led to higher amounts of pyrolysis oil, which had simpler composition.
Keywords: LignoBoost® lignin; PE; PP; PS; PC; Co-pyrolysis;
Thermal decomposition of polymeric resin [(C29H24N205)n]: Kinetic parameters and mechanisms by D. Perondi; C.C. Broetto; A. Dettmer; B.M. Wenzel; M. Godinho (2110-2117).
The casting sand generated in the foundry industry is classified as hazardous waste. Two types of sand are generated by the foundry industry: core sand (CS) and green sand (GS). The surface of CS is coated with a polymeric resin. The polymeric resin used in this work is formed by the reaction of formaldehyde with phenol-methylene diphenyl isocyanate catalyzed by dimethyl propylamine. Pyrolysis is an alternative method for the removal of the polymeric resin that is attached to the surface of CS. The kinetic parameters were determined for the removal of polymeric resin incorporated into the sand. The kinetics were monitored by thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) under isothermal and non-isothermal conditions. The triplet kinetics were evaluated by model-fitting methods (Coats–Redfern/MacCallum–Tanner/van Krevelen). The thermogravimetric analysis indicates that the degradation of the polymeric resin occurs in three distinct steps. In the main weight loss step (553–773 K), the activation energy ranged from 73.09 to 115.35 kJ/mol, and the pre-exponential factor ranged from 9.27 × 105 to 1.70 × 109 min−1 under non-isothermal conditions. Under isothermal conditions, the activation energy was 61.98 kJ/mol, and the pre-exponential factor was 3.13.102 s−1. Experiments performed under isothermal conditions indicate that the pyrolysis kinetics of the polymeric resin are controlled by a chemical reaction (Fn) at conversions lower than approximately 0.8, whereas at conversions above 0.8, a change in the rate-limiting step (chemical reaction to diffusion) was observed.
Keywords: Pyrolysis; Kinetics; Foundry sand; Polymeric resin;
Thermal behaviour and thermodegradation kinetics of poly(vinyl chloride) plasticized with polymeric and oligomeric medium-chain-length poly(3-hydroxyalkanoates) by Mei Chan Sin; Irene Kit Ping Tan; Mohd Suffian Mohd Annuar; Seng Neon Gan (2118-2127).
Poly(vinyl chloride) (PVC) is a well-known polymer with low thermal stability. With the aim to improve the physical properties of PVC, biopolyesters were investigated for the plasticizing and thermal effects in PVC. In this study, polymeric medium-chain-length poly(3-hydroxyalkanoates) (mcl-PHA) were produced by Pseudomonas putida PGA1 using renewable carbon substrates and oligomeric mcl-PHA were generated by partial thermal degradation of the polymers. The effects of blending these biopolyesters with PVC were investigated in terms of thermal behaviour and thermodegradation kinetics. The PVC/PHA blends showed a single T g with lower values than PVC, indicating that mcl-PHA was compatible with PVC. T g from DSC analysis agreed well with theoretical T g predicted from Gordon–Taylor equation. The apparent activation energy (E d ) and pre-exponential factor (A) for the thermodegradation of PVC and its blends were determined using Kissinger method. Change in entropy of activation (ΔS) for the thermodegradation was also determined. All PVC/PHA blends had lower E d , A and ΔS than PVC. Higher reduction of E d , A and ΔS was observed when the proportion of PHA was increased in the blend; and when oligomeric PHA was used as the plasticizer instead of polymeric PHA. The dependence of E d on the extent of conversion (α) for the thermodegradation process of PVC and PVC/PHA was determined by Flynn–Wall–Ozawa method and results showed that E d is an increasing function of α. This indicated that the thermal decomposition of PVC and its blends display complex reaction mechanism(s).
Keywords: PVC; Mcl-PHA; Plasticizers; Gordon–Taylor; Kissinger; Flynn–Wall–Ozawa;
Synergistic effect of zinc hydroxystannate with intumescent flame-retardants on fire retardancy and thermal behavior of polypropylene by Xinqing Su; Yuwen Yi; Jie Tao; Hongqiang Qi (2128-2135).
The flammability and thermal degradation properties of polypropylene (PP) composites containing zinc hydroxystannate (ZHS) and intumescent flame retardant additives (IFR), i.e. ammonium polyphosphate (APP) and pentaerythritol (PER) were characterized respectively by limiting oxygen index (LOI), UL-94 measurements, Cone calorimeter test (CCT) and Thermogravimetry analysis (TGA) in this work. A synergistic effect in flame retardancy was observed when ZHS was used in combination with APP and PER. The experimental data indicated that ZHS enhanced the LOI value, UL-94 ratings and restricted the dripping of the composites. The PP/IFR composites passed the UL-94 V-0 rating test in the presence of 1 wt% ZHS. The CCT tests indicated that the heat release rate (HRR), peak rate of heat release (PHRR) and mass loss rate (MLR) values of the PP/IFR/ZHS samples were much lower than those of the PP/IFR and pure PP samples. The TGA results showed that ZHS could accelerate the char formation of IFR, therefore, greatly increase the thermal stability of PP composites. The Fourier transformed infrared spectra (FTIR) revealed that the flame retardant mechanism of ZHS could be ascribed to its catalysis degradation of the PP resin, which promoted the formation of charred layers with the P–O–P and P–O–C complexes in the condensed phase. SEM observation further indicated that ZHS could promote forming stable and compact intumescent char layer and effectively protect the underlying polymer from burning.
Keywords: Zinc hydroxystannate; Polypropylene; Synergistic; Intumescent flame retardant; Cone calorimeter;
Acrylic protective coatings modified with titanium dioxide nanoparticles: Comparative study of stability under irradiation by Dominique Scalarone; Massimo Lazzari; Oscar Chiantore (2136-2142).
Acrylic coatings based on Paraloid B72 were modified with different types of titanium dioxide nanoparticles to obtain transparent, non-yellowing and chemically stable coatings, having also self-cleaning properties. To finely disperse the inorganic nanoparticles in the polymer matrix two strategies were followed: i) ex-situ functionalization of nanoparticles and ii) use of organic–inorganic coupling agents. Characterization focussed especially on the photooxidative stability of TiO2 modified coatings. This is actually one of the most critical aspects of organic materials containing photoactive nanoparticles. The highly oxidant environment produced on the catalyst surface by photogenerated species is capable to mineralize many organic compounds, but in a poorly selective way, and this often undermines the stability of the polymer that binds the photocatalyst. Improved dispersability of TiO2 nanoparticles generally resulted in a diminished chemical stability of the acrylic medium, but by using tetraethoxysilane (TEOS) as a coupling agent, oxidation and cross-linking reactions were considerably reduced, ensuring better stability and reversibility in comparison to Paraloid coatings containing photoactive TiO2 nanoparticles without TEOS.
Keywords: Acrylic coatings; Titanium dioxide; Nanoparticles; Photodegradation; Self-cleaning;
Thermal degradation characteristics of flame retardant polylactide using TG-IR by Xilei Chen; Jinlong Zhuo; Chuanmei Jiao (2143-2147).
Flame retardant polylactide (PLA) composites were prepared using PLA and a hyperbranched polyphosphate ester (HPE). The flammability and thermal stability of flame retardant PLA composites were investigated by limiting oxygen index (LOI), UL-94 vertical burning, microscale combustion calorimetry (MCC), and thermogravimetric analysis/infrared spectrometry (TG-IR). The results showed that HPE had excellent flame retardant abilities for PLA. The TGA curves suggested that HPE has good ability of char formation, hence improved the flame retardant property. The volatilized products formed on thermal degradation of flame retardant PLA indicated that the volatilized products are mainly aldehyde containing compounds, CO, aliphatic esters, and CO2.
Keywords: Polylactide; Flame retardant; Thermal degradation; TG-IR;
Thermal properties of epoxy resin/filler hybrid composites by Fan-Long Jin; Soo-Jin Park (2148-2153).
Epoxy resin/filler hybrid composites were prepared by the melt blending of diglycidylether of bisphenol-A (DGEBA), as the epoxy resin, with nano-Al2O3 or nano-SiC particles, as the nanoscaled fillers. The thermal properties, such as the curing behavior, thermal stability, dynamic mechanical properties, and thermal mechanical properties of the DGEBA/nano-Al2O3 and DGEBA/nano-SiC composites were examined using a range of techniques. As a result, the DSC curve peak temperature of both composites decreased with increasing filler content. The integral procedure decomposition temperature increased from 630 °C to 853 °C for DGEBA/nano-Al2O3 composite and 858 °C for DGEBA/nano-SiC composite. The char yield at 800 °C increased from 14.3% to 26.2–26.6% for both composites. Both composites had a 10 °C higher glass transition temperature than the neat epoxy resin. The coefficient of thermal expansion of both composites at the glassy and rubbery regions decreased with increasing filler content.
Keywords: Epoxy resin; Filler; Thermal stability; Glass transition temperature; Coefficient of thermal expansion;
Investigation of fire-resistance mechanisms of the ternary system (APP/MPP/TiO2) in PMMA by Blandine Friederich; Abdelghani Laachachi; Michel Ferriol; Marianne Cochez; Rodolphe Sonnier; Valérie Toniazzo; David Ruch (2154-2161).
The thermal and fire-resistance properties of the ternary system ammonium polyphosphate/melamine polyphosphate/titanium dioxide (APP/MPP/TiO2) was studied in poly(methyl methacrylate) (PMMA). PMMA-7.5%APP/7.5%TiO2 showed an interesting thermal stability and synergy effects on the peak of heat released rate (pHRR). Mechanisms were investigated following the analysis of residues and gas phase. Residues were analyzed by Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscope (SEM). Gases emitted during degradation were analyzed by Pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Comparison between cone calorimetry and pyrolysis–combustion flow calorimetry (PCFC) tests was a helpful tool for determining whether fire-retardancy mainly occurred by a physical or chemical pathway and for explaining the obtained results.
Keywords: Thermal properties; Poly(methyl methacrylate) (PMMA); Flame retardant; Nanocomposites; Polyphosphates;
Photo-oxidative degradation of poly(p-dioxanone) under ultraviolet light source by Bingqing Liang; Daolin Pang; Chao Jin; Fang Li; Yuzhong Wang (2162-2169).
The variations of structure and property of poly(p-dioxanone) (PPDO) in the process of photo-oxidative degradation and the mechanism of degradation were investigated in this work. The photo-oxidative degradation of PPDO was performed in air under ultraviolet light with two kinds of wavelength 365.0 nm and 253.7 nm. The extent of photo-oxidative degradation of the polymer was determined by morphological analysis, weight loss ratio, changes of viscosity and scanning electron microscope method (SEM). Infrared spectrometry (IR) and nuclear magnetic resonance (NMR) method were used to infer the mechanism of the photo-oxidative degradation. The changes of glass-transition temperature (T g ) and melting temperature (T m ) were characterized by differential scanning calorimetric (DSC) test. The morphological examination, IR and NMR testing revealed that the extent and mechanism of photo-oxidative degradation for PPDO are not closely correlated with its initial molecular weight. The main influence of initial molecular weight on the degradation is to change the ultimate distribution of the molecular weight. The conclusion is supported by the results of DSC test. All results from the research show the excellent photodegradable property of PPDO.
Keywords: Poly(p-dioxanone); Photo-oxidative degradation; Ultraviolet wavelength; Extent and mechanism of degradation;
Effects of poly(l-lactic acid) hydrolysis on attachment of barnacle cypris larvae by Nobuyuki Ishimaru; Takayuki Tsukegi; Minato Wakisaka; Yoshihito Shirai; Haruo Nishida (2170-2176).
Poly(l-lactic acid) (PLLA) applied to immersed solid surfaces in seawater inhibited colonization by barnacles due to the slow-release property of lactic acid. The effect of molecular weight of PLLA on anti-macrofouling activity was confirmed for the first time, with the lowest molecular weight PLLA producing the lowest attaching ratio of cypris larvae of Balanus amphitrite. From the direct addition of lactic acid into a culture of cypris larvae, it was found that the anti-barnacle settlement effect was due to the action of slow-released lactic acid to cypris larvae. The anti-macrofouling function of low molecular weight PLLA was also confirmed in a natural sea environment.
Keywords: Poly(l-lactic acid); Lactic acid; Slow-release; Anti-macrofouling; Barnacle; Cypris larvae;
Study on biodegradation mechanism of novel oxo-biodegradable polypropylenes in an aqueous medium by Kensuke Miyazaki; Takayuki Arai; Kazuto Shibata; Minoru Terano; Hisayuki Nakatani (2177-2184).
In this work, the biodegradation behavior of the polypropylene (PP)/poly(ethylene oxide) (PEO)/TiO2 and the PP/PEO/TiO2/octacalcium phosphate intercalated with succinic acid ion (OCPC) composites was studied. The photodegraded PP/PEO/TiO2 sample was mineralized up to ca. 10% after the respirometric biodegradation test for 80 days, and the specimen (20 × 5 mm) was biodegraded to a small piece (ca. 3 × 3 mm). The molecular weight was decreased by the biodegradation as well as the photodegradation, suggesting that not only the low molecular weight oxidation products but also the oxidized PP matrix were biodegraded. The result of the 1H NMR measurement indicated that the biodegradation occurred anaerobically. The photodegraded PP/PEO/TiO2/OCPC sample was mineralized up to ca. 20% after the test for 80 days. The specimen (20 × 5 mm) was biodegraded to a very small piece (ca. 40 × 20 μm). The acceleration of the mineralization rate was observed at between the 30 and 50 days in the test. As the PP matrix was biodegraded, the contained OCPC was released to the solvent surroundings. The dissolved succinic acid contaminated them and initiated the aerobic biodegradation leading to the increase of the mineralization.
Keywords: Polypropylene; Biodegradation; Mineralization; Respirometric test; Reaction mechanism;
The effect of styrene-methyl methacrylate monomeric arrangement on the ultrasonic degradation of copolymers by Mallory J. Morris; André M. Striegel (2185-2194).
Ultrasonic degradation is a convenient means of studying the degradation of macromolecules in transient elongational flows. Cavitation results in non-random, near-midchain scission of linear polymers, which reach a limiting molar mass M lim beyond which degradation is no longer possible. Also, the flow fields produced as a result of ultrasonic bubble collapse are kinetically and fluid-mechanically equivalent to those produced during more experimentally intractable manifestations of transient elongational flow. Here, we describe results from the ultrasonic degradation of dilute solutions of block, random, and alternating copolymers of styrene and methyl methacrylate, along with the degradation of their respective homopolymers. Results from the degradation experiments were monitored using size-exclusion chromatography with on-line triple detection including multi-angle static light scattering, differential viscometry, and differential refractometry. The influence of monomeric arrangement on solution structure was found to have concomitant influence on copolymer degradation, both mechanistically and kinetically. Noteworthy was the correspondence between persistence length and both M lim and degradation rate k when comparing the alternating to both the block and random copolymers, in qualitative agreement with the previously-postulated modified path theory of polymer degradation in transient elongational flows. Most differences in M lim and k could be explained by a combination of effects due to molar mass, monomer ratio, monomer arrangement, and resultant chain stiffness in solution, except for differences in M lim between the random and block copolymers studied, which proved too subtle to measure.
Keywords: Copolymers; Degradation; Transient elongational flow; Sonication;
Correlation between (nano)-mechanical and chemical changes occurring during photo-oxidation of filled vulcanised styrene butadiene rubber (SBR) by Grégory Mertz; Fatima Hassouna; Philippe Leclère; Abdesselam Dahoun; Valérie Toniazzo; David Ruch (2195-2201).
Photo-oxidation at λ > 290 nm was performed on vulcanised styrene butadiene rubber (SBR) designed for flooring applications. The effect of the presence of coated titanium dioxide (TiO2), used as a pigment, was evaluated. The chemical and nano-mechanical changes occurring at the surface during irradiation were studied by micro-FTIR spectroscopy and atomic force microscopy (AFM). Both techniques were used to obtain the oxidation profiles in the depth of the composites (in the absence and presence of TiO2) to characterise the oxidative layer formation. The nano-mechanical and chemical profiles were superimposed for both composites (SBR and SBR/TiO2) suggesting a correlation between both properties. Indeed, the increase of the DMT modulus determined by AFM reflects the crosslinking reactions which occur simultaneously with the formation of oxidised photo-products.Moreover, during irradiation, the mechanical properties were followed at low and high degree of deformation by means of dynamic mechanical analysis (DMA) and tensile test until break, respectively. We demonstrate that the physico-chemical properties of the oxidised layer which represents 20 μm of the 600 μm of the material can explain the loss of mechanical properties for both composites based on vulcanised SBR and SBR/TiO2 during irradiation at λ > 290 nm. We also demonstrate a different mechanical behaviour in presence of TiO2 compared to neat SBR that could be due to a competition between formation of photo-products and the filler-rubber debonding during photo-oxidation.
Keywords: Styrene butadiene rubber; Vulcanisation; TiO2; Photo-oxidation; Depth profiling; Mechanical properties;
Study of the thermal stability of Nitrile rubber-coconut flour compounds by C. Albano; M.N. Ichazo; I. Boyer; M. Hernández; J. González; A. Karam; M. Covis (2202-2211).
The aim of the present work was to study the kinetics of the thermal degradation and the degradation mechanisms of neat nitrile rubber (NBR)-coconut flour (treated and non-treated) compounds. Thermogravimetric analysis was followed under N2 atmosphere from 25 °C to 700 °C, with the purpose of evaluating the thermal stability of the blends, and determining the kinetic parameters according to the E 2 Function and Invariant Kinetic Parameters (IKP) methods. The thermal stability of NBR was increased significantly when coconut flour was added, increasing the E inv from 89 kJ/mol to 277 kJ/mol. When coconut flour was treated with zirconate, the positive effect on the thermal stability was even higher (E inv 298 kJ/mol). In addition, no significant changes were obtained in the maximum temperature of decomposition when the filler was present. With regard to the degradation of NBR, it can be concluded that it takes place according to the following degradation mechanisms: nucleation and nuclei growth, interphase reaction, reaction order and power law. The NBR-coconut flour compounds do present these degradation mechanisms plus the diffusion mechanism.
Keywords: NBR – Coconut flour; Thermal stability; Degradation mechanism; Chemical treatment; IKP; Coats- redfern and E 2 function;
Characterisation of paper containing iron gall ink using size exclusion chromatography by J. Kolar; J. Malešič; D. Kočar; M. Strlič; G. De Bruin; D. Koleša (2212-2216).
Iron gall inks were the most often used inks from the Middle Ages until the 20th century; examples include the drawings by Leonardo and scores by Bach. These masterpieces are threatened by the corrosive properties of the ink. In order to increase the longevity of the materials, stabilisation treatments have been developed during the last two decades. Their effectiveness has often been determined by comparing rates of degradation during accelerated tests. However, such evaluation using historical materials is limited by the amount of material required by various analytical methodologies.The paper describes the use of size exclusion chromatography (SEC) of cellulose containing iron gall ink, derivatised using phenyl isocyanate. A linear correlation is observed between the weight average degree of polymerisation obtained with SEC and the one obtained using viscometry, with a slope of 1.4. The method was used to evaluate the extent of stabilisation of historic documents containing iron gall inks during accelerated degradation. Despite considerable uncertainty, also caused by the heterogeneity of historic materials, it is demonstrated that efficient stabilisation by factors of 10 and 20 times is achievable using a calcium phytate treatment.
Keywords: Cellulose; Size exclusion chromatography; Iron gall ink; Viscometry;
Thermal decomposition of flame retarded formulations PA6/aluminum phosphinate/melamine polyphosphate/organomodified clay: Interactions between the constituents? by Fabienne Samyn; Serge Bourbigot (2217-2230).
The aim of this article is to investigate the thermal decomposition in pyrolytic and oxidative conditions of a phosphorous flame retardant (combination of melamine polyphosphate and aluminum phosphinate: AlPi-MPP) alone as well as in combination with an organo-modified clay (o-MMT) and of polyamide 6 formulations containing these additives. The gases evolved during the decomposition have been analyzed using TGA-FTIR. A detailed condensed phase study has been carried out combining X-ray diffraction (XRD) analyses and 27Al, 31P and 13C solid-state nuclear magnetic resonance (NMR) measurements on samples heat treated at different characteristic temperatures. It is demonstrated that no reaction leading to the formation of new species between the additives or the additives and the matrix occurs. However, Lewis acid/base interactions are highlighted resulting in the catalytic decomposition of the components particularly under nitrogen. Under air, the combined action of oxygen and Lewis interactions leads to an even more catalyzed decomposition process. Mechanisms of thermal decomposition are proposed.
Keywords: Polyamide 6; Flame retardancy; Aluminum phosphinate; Melamine polyphosphate; Nanocomposite; Solid state NMR;
The influence of metal hydroxide fire retardants and nanoclay on the thermal decomposition of EVA by Artur Witkowski; Anna A. Stec; T. Richard Hull (2231-2240).
Ethylene-vinyl acetate (EVA) copolymers compounded with mineral filler fire retardants, such as aluminium hydroxide (ATH) and magnesium hydroxide (MH) represent an important class of fire-safe materials, especially as PVC replacements in the cable industry. The thermal decomposition of these materials has been investigated in the presence or absence of montmorillonite nanoclay using simultaneous thermal analysis (STA) interfaced to a Fourier transform infrared spectrometer (FTIR) for analysis of volatiles.STA-FTIR spectra were deconvoluted to give profiles of individual species' evolution as a function of temperature, in order to identify the individual processes involved. The first step of the degradation, the loss of acetic acid by chain stripping, has been shown to be accelerated by the presence of clay but changed to a loss of acetone by mineral filler fire retardants. This is ascribed to the catalytic properties of the freshly formed alumina and magnesia surfaces. The products of the second step of decomposition are also changed by the various additives.
Keywords: TGA-FTIR; Ethylene-vinyl acetate; Magnesium hydroxide; Aluminium hydroxide; Nanoclay; Acetone;
Study on mechanism of phosphorus–silicon synergistic flame retardancy on epoxy resins by Wenchao Zhang; Xiangmei Li; Haibo Fan; Rongjie Yang (2241-2248).
A series of flame-retarded epoxy resins (EPs) loaded with two kinds of silsesquioxanes and DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), respectively, have been prepared. The thermal stability and quantity of the char of these EPs have been investigated by TGA, and the results have indicated that the combined use of silsesquioxane and DOPO enhanced the quantity of the char more efficiently than when using silsesquioxane or DOPO alone. Details of fire behavior, such as TTI, HRR, p-HRR, TSR, SEA, and THR, have been tested by means of a cone calorimeter. In the EP under combustion, the interactions between DOPO and silsesquioxane in the condensed phase induce a better flame retardancy capability than that with either silsesquioxane or DOPO alone. The char residues of the EP composites have been investigated in detail by FTIR and XPS. The interactions between DOPO and silsesquioxane in the condensed phase involve the formation of –P(＝O)–O–Si– structures. The formation of a –P(＝O)–O–Si– structure increases both the quantity and the thermal stability of the char. The flame retardancies of these EPs have been tested according to the LOI and UL-94 standards, and the results have indicated that the interactions of DOPO with the silsesquioxane have important effects on the flame retardancy of EP composites.
Keywords: Epoxy resin; Phosphorus–silicon synergy; Flame-retardancy mechanism; Condensed phase; Blowing-out effect;
Activation of poly(ethylene terephthalate) surfaces by atmospheric pressure plasma by Tomáš Homola; Jindřich Matoušek; Beáta Hergelová; Martin Kormunda; Linda Y.L. Wu; Mirko Černák (2249-2254).
We report a study on effects of atmospheric pressure plasma treatment of poly(ethylene terephthalate) PET surfaces. The atmospheric pressure plasma was generated using Diffuse Coplanar Surface Barrier Discharge (DCSBD) in ambient air. The changes in wettability of PET surfaces were studied by water contact angle measurement. The surface energy was calculated using van Oss–Chaudhury–Good model from contact angles of water, ethylene and diiodomethane. The changes in surface chemistry after the plasma treatment were studied by X-ray photoelectron spectroscopy (XPS). We also observed changes in surface roughness investigated by Atomic force microscopy (AFM). We found that DCSBD plasma treatment for 1 s led to decrease of water contact angle from 78.4° to 40.1°. The surface energy analysis showed that water contact angle decrease is related to increase of polar part of surface energy. XPS measurement confirmed that the plasma treatment led to increase of polar groups on PET surface which explained the changes in surface energy. AFM investigation showed that plasma treatment led to an increase of surface roughness, which could be a benefit for further processing of PET, because higher roughness increases surface area, which can result into higher adhesion between PET and coatings.
Keywords: Poly(ethylene terephthalate) PET; Atmospheric plasma treatment; Diffuse plasma; Polymer surface; Water contact angle; XPS;
Grafting of α-tocopherol upon γ-irradiation in UHMWPE probed by model hydrocarbons by Remo P. Badertscher; Reto Lerf; Daniel Delfosse; Christian Adlhart (2255-2261).
Today, UHMWPE implants are stabilized with α-tocopherol and cross-linked by irradiation in order to reduce wear. Little is known about the structural transformation of the antioxidant α-tocopherol upon irradiation. In the present investigation, the major irradiation reaction products of α-tocopherol dissolved at 0.1 wt.% in liquid model hydrocarbons were characterized spectroscopically and by independent synthesis. We observed only a single product group, namely phenolic alkyl ethers formed by radical recombination of a phenoxyl radical with a secondary alkyl radical. The irradiation dose is the parameter which controls the amount of consumption of α-tocopherol. At a dose of 27.5 kGy, 31–34% of α-tocopherol was transformed into the corresponding ether, while at 97.9 kGy, the degree of transformation was 68–76%. The observed ether formation in the liquid model hydrocarbons explains two significant observations for the α-tocopherol stabilized polymers, namely depletion of the α-tocopherol's phenol group upon irradiation and “grafting”, i.e. formation of a chemical bond between the polymer and its antioxidant.
Keywords: Vitamin E; Mechanism; Gamma irradiation; Grafting; Degradation; Antioxidant;
The effect of extensive mechanical recycling on the properties of low density polyethylene by Huiying Jin; Joamin Gonzalez-Gutierrez; Pavel Oblak; Barbara Zupančič; Igor Emri (2262-2272).
Low density polyethylene (LDPE) was exposed to one hundred (100) consecutive extensive extrusion cycles to simulate mechanical recycling. Collected samples were characterized by means of small amplitude oscillatory measurements to investigate rheological properties, by gel permeation chromatography (GPC) to measure molecular weight, and with differential scanning calorimetry (DSC) to study thermal properties. Finally, solid time-dependent mechanical properties were characterized by measuring creep compliance. The results show that simulated recycling did not significantly change the melting and crystallization temperatures of LDPE. However, results from rheological measurement, crystallinity, creep measurements and GPC suggest that thermal degradation and gelation of LDPE occur after extensive extrusion which leads to simultaneous chain scission and crosslinking of the polymer chains. It can be concluded that processability, measured by rheological parameters at high frequency and durability of LDPE measured by creep compliance, are only affected after the 40th extrusion cycle. These observations correspond to the molecular changes of LDPE measured through GPC, MFI and crystallinity calculations obtained from DSC measurements.
Keywords: Low density polyethylene; Mechanical recycling; Extrusion; Differential scanning calorimetry; Rheology; Gel permeation chromatography;
Effect of organic montmorillonite on cold crystallization and hydrolytic degradation of poly(l-lactide) by Haiming Chen; Jingwei Chen; Jie Chen; Jinghui Yang; Ting Huang; Nan Zhang; Yong Wang (2273-2283).
The effect of organic montmorillonite (OMMT) on cold crystallization of poly(l-lactide) (PLLA) in different conditions including during the DSC heating process and during the annealing treatment was evaluated. The variations of crystalline structure of PLLA in different samples were comparatively investigated by using wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The results show that OMMT exhibits an apparent nucleation effect for the cold crystallization of PLLA matrix. During the annealing treatment, the degree of crystallinity (X c ) increases with the increase of OMMT content. Specifically, the presence of OMMT leads to the formation of α΄-form crystallites. Study on the hydrolytic degradation behaviours of different samples shows that the hydrolytic degradation rate decreases with the increase of X c , but it increases with the increase of OMMT content. The enhanced hydrophilicity and the formation of α΄-form crystallites are suggested to be the main reasons for the greatly improved hydrolytic degradation ability of samples which contain high content of OMMT. Furthermore, hydrolytic degradation also induces the change of microstructure of the samples. For pure PLLA, hydrolytic degradation promotes the increase of X c . However, for PLLA/OMMT nanocomposites, hydrolytic degradation leads to the decrease of X c and the degree of the decrease is dependent on the content of OMMT.
Keywords: PLLA/OMMT nanocomposites; Cold crystallization; Annealing; Hydrolytic degradation;
Physicochemical and mechanical impacts of photo-ageing on bisphenol a polycarbonate by S. Collin; P.-O. Bussière; S. Thérias; J.-M. Lambert; J. Perdereau; J.-L. Gardette (2284-2293).
This article focuses on the photo-ageing of polycarbonate and aims to evaluate the impact of light irradiation on the mechanical properties of the material. The properties were investigated using micro-hardness testing and AFM nano-indentation experiments. The variations in the polycarbonate macromolecular architecture were then determined using AFM nanoscale thermal analyses. Finally, infrared spectroscopy allowed the identification of some chemical changes involved in the changes in the macromolecular structure. The absorption and degradation profiles were studied with UV–Visible and infrared microspectroscopy analyses, respectively. A new reaction pathway, which corresponds to a cross-linking reaction route, was added to the current photo-oxidation mechanism.
Keywords: Polycarbonate; Ageing; Photo-oxidation; Cross-linking; AFM; Nano-indentation;
Glutathione-responsive biodegradable polyurethanes based on dithiodiundecanol by Jing Wang; Peiyu Sun; Zhen Zheng; Fangjie Wang; Xinling Wang (2294-2300).
Biodegradable polyurethanes were prepared from 11,11′-dithiodiundecanol employed as soft segment incorporating hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO) serving as hard segment. The disulfide bonds in dithiodiundecanol could be cleaved into thiols in the presence of glutathione (GSH) through disulfide-thiol exchange reaction, which fulfilled the polyurethanes with responsive biodegradability. In vitro degradation test in PBS buffer at 37 °C, the molecular weight of polyurethanes substantially decreased and the surface morphology was significantly eroded after 8 days. The degradation reaction constants were calculated and kinetic equations were established.
Keywords: Biodegradable; Polyurethane; Dithiodiundecanol; Glutathione; Responsive;
Biodegradation in a soil environment of activated sludge derived polyhydroxyalkanoate (PHBV) by Monica V. Arcos-Hernandez; Bronwyn Laycock; Steven Pratt; Bogdan C. Donose; Melissa A.L. Nikolić; Paul Luckman; Alan Werker; Paul A. Lant (2301-2312).
Mixed culture (activated sludge) polyhydroxyalkanoates (PHAs) produced in conjunction with wastewater treatment and compounded into bioplastics have applications in agriculture. Rates of biodegradation and any influence of degradation products need to be characterised in-situ in soil environments for applications involving PHA-based product degradation (either as a controlled intent in product service or a criterion for product end-of-life management). We performed such characterisation as part of the initial stages of product development of native copolymers of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV). This PHBV was accumulated in and recovered from activated sludge produced in pilot and full-scale wastewater treatment processes. The rates of PHBV biodegradation in soil were quantified using a broad range of HV content material (12 mol %–72 mol %) and referenced to a cellulose control. For mixed culture PHBVs, 90% biodegradation was expected to occur between 10.7 and 22.2 months. Germination studies using a standard cress seed assay indicated that PHA biodegradation products had no influence on germination activity in soil. Soil extracts examined during polymer degradation were non-toxic (Microtox).Mechanisms of biodegradation were examined by means of physico-chemical characterisation and Atomic Force Microscopy (AFM). Biodegradation occurred at the polymer surface and the rate was governed by both biodeterioration and depolymerisation, which were shown to be controlled by a combination of copolymer composition, crystallinity, microstructure and surface morphology.
Keywords: Polyhydroxyalkanoates; Mixed cultures; Activated sludge; Biodegradation; Microstructure; Surface morphology;
UV-stabilisation of polystyrene-based nanocomposites provided by polyhedral oligomeric silsesquioxanes (POSS) by N.Tz. Dintcheva; E. Morici; R. Arrigo; F.P. La Mantia; V. Malatesta; J.J. Schwab (2313-2322).
The photo-ageing behaviour of Polyhedral Oligomeric SilSequioxane (POSS)-polystyrene (PS) nanocomposites has been investigated for the first time. POSS having different inorganic framework and pendant organic groups have been used in the PS nanocomposite preparation and the formulated films were subjected to accelerated weathering. Compared to pristine PS, the POSS-containing PS developed a lower level of carbonyl and hydroxyl groups as a function of the exposure time, indicating a significantly improved resistance of the nanocomposites to photo-degradation. The results suggest that all of the investigated POSS molecules play a protective role and may extend the in-use lifetime of the polymeric matrix. The protection efficiency seems to depend on the structure of the POSS used, i.e. the type of their inorganic framework and organic pendant groups. The efficacy of the protection provided by POSS is more pronounced for the open-cage POSS-triols than for the closed-cage POSS, suggesting an active role of the POSS-triol free OH group in the PS stabilisation process. The pendant organic groups significantly influence the nanocomposite's local morphology by controlling the formation of POSS re-aggregates and/or the POSS dispersion into the matrix, and its response to photo-oxidation.
Keywords: Photo-oxidation; POSS nanofiller; Polystyrene; Molecular silica; UV-stabilizers;
Structural and thermal characterization of lauroylated hemicelluloses synthesized in an ionic liquid by Hai-Tao Wang; Tong-Qi Yuan; Ling-Jun Meng; Diao She; Zeng-Chao Geng; Run-Cang Sun (2323-2330).
Chemical modification provides an efficient way to obtain novel biomaterials from abundant biomacromolecules. In this case, lauroylated hemicelluloses (LH) with degree of substitutions (DS) between 0.43 and 1.82 were synthesized in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) ionic liquid. The influence of reaction parameters including the molar ratio of lauroyl chloride (LC) to anhydroxylose units in hemicelluloses (0.5:1–3:1), reaction temperature (80–90 °C), and reaction time (15–90 min) was studied. The results indicated that homogeneous modification was successfully conducted and highly substituted hemicelluloses esters were obtained. In comparison, the hemicellulose and LH were characterized by both degradative methods such as thermal analysis (TGA/DTG), and non-degradative techniques such as Fourier transform infrared (FT-IR), 13C nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy (SEM). It was found that a significant degradation of the hemicellulose polymers occurred during lauroylation with the increase of the molar ratio, time, and temperature. The thermal stability of LH was lower that of the native hemicelluloses, and the morphological properties of hemicellulose were significantly changed after the chemical modification.
Keywords: Biomaterial; Lauroylated hemicellulose; Ionic liquid; Degradation; Thermal stability;
Development of an atomistic-based chemophysical environment for modelling asphalt oxidation by Pan Tongyan; Lu Yang; Wang Zhaoyang (2331-2339).
Asphalt is the primary binding and waterproofing component in road pavements and roof shingles, and is expected to meet certain minimum performance requirements based on its rheological properties. With an optimum mixture design, desirable performance of asphalt can be ensured in its early service stage. However, being an organic end product of petroleum serving under the general open-to-air conditions, asphalt can lose the desired rheological properties with time due to oxidative hardening or aging that frequently leads to increase in viscosity, separation of components, and loss of cohesion and adhesion, and thereby becomes hardened. Oxidative hardening of asphalt can cause reduce mixture performance and eventually lead to failure of pavements and roof tiles. The study of asphalt oxidative hardening has thus far focused on the changes in the physical properties, mainly the viscosity and ductility of bulk asphalt. Such phenomenological approaches meet the direct engineering needs; however they do not contribute to understanding the fundamental physicochemical mechanisms of asphalt hardening. From this standpoint, this research study aims at exploring the chemical basis of asphalt oxidative hardening by establishing an ab initio quantum chemistry (QC)-based chemophysical environment in which the possible chemical reactions between asphalt ingredients and oxygen, as well as the changes in their physical behaviour can be readily studied. X-ray photoelectron spectroscopy (XPS) was used to validate the bulk asphalt model, of which the results showed high agreement to the model predictions.
Keywords: Asphalt; Oxidative aging; Quantum chemistry; XPS;
Reinforcement properties of 3-aminopropylmethyldiethoxysilane and N-(2-Aminoethyl)-3-aminopropylmethyldimethoxysilane on polyurethane ester foam by Eleonora Pellizzi; Agnès Lattuati-Derieux; Jean-Baptiste d'Espinose de Lacaillerie; Bertrand Lavédrine; Hervé Cheradame (2340-2346).
Museum artifacts made of polyurethane foam are frequently affected by conservation issues mainly related to the loss of their mechanical properties. While effective polyurethane ether foam treatments already exist, no convenient consolidation treatment exists for polyurethane ester foams. The possibility of a reinforcement effect expected to prevent the mechanical properties loss has been evaluated. Two aminoalkylalcoxysilanes (AAAS), the 3-Aminopropylmethyldiethoxysilane and the N-(2-Aminoethyl)-3-aminopropylmethyldimethoxysilane, which gave promising results for consolidation of paper, have been tested on modern industrial flexible polyurethane ester foam samples. AAAS solutions at different concentrations have been applied, by immersion, on polyurethane ester foam samples. Mechanical properties have been studied by Compression Force Deflection Test, which shows that after AAAS treatment the resistance of the foam to compression improves. The color of the samples before and after consolidation has been monitored to assess the impact of the treatment on the visual aspect of the foam. The AAAS distribution in the thickness of the samples has been investigated by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Magic angle spinning nuclear magnetic resonance (MAS NMR) has been used to confirm AAAS polymerization and to evaluate its average polymer chain length. The promising results obtained suggest that AAAS could be an efficient solution for the consolidation of polyurethane ester foams.
Keywords: Aminoalkylalkoxysilanes; PUR ester; Foam; Reinforcement; Interpenetrating polymer networks;
Abiotic degradation of poly(dl-lactide), poly(ɛ-caprolactone) and their blends by Kikku Fukushima; Jose Luis Feijoo; Ming-Chien Yang (2347-2355).
An effective hydrolytic degradation of PDLLA, PCL and their blends in a phosphate-buffered solution of pH 4.0 at 37 °C for 18 weeks was achieved, observing a considerably faster degradation of PDLLA as compared to PCL due to the hydrophobic and semicrystalline nature of PCL matrix, able to partially prevent water diffusion into the bulk specimen.DSC and FTIR results indicated that PCL phase, in compositions rich in PCL, was very stable against hydrolysis, but the presence of PDLLA in the PDLLA/PCL blends seemed to catalyze the hydrolytic degradation of the PCL phase, probably associated to easier diffusion of water into the PCL domains by the presence of PDLLA amorphous regions. This last trend was proportional to the content of PDLLA in the blends, excepting for the composition 64%PDLLA/36%PCL. It was confirmed that PCL molecules partially delayed hydrolysis of PDLLA molecules, according to FTIR analysis, and the water diffusion prevention level was proportional to the content of PCL in the blends, except for the system 64%PDLLA/36%PCL, which presented a lower extent of degradation than neat PDLLA but higher than the blend 80%PDLLA/20%PCL. This indicated that PCL molecules did not significantly impede hydrolysis of PDLLA molecules in this blend, possibly due to the achievement of a particular structure of the PDLLA/PCL interphase in this blend. In general, hydrolysis of PDLLA/PCL blends was found to be a complex phenomenon depending not only on the content of both polymer phases, but also on the polymer phase crystallinity and morphology.
Keywords: PDLLA; PCL; Blends; Abiotic degradation; Hydrolysis;
Conductivity, polarization and electrorheological activity of polyaniline nanotubes during thermo-oxidative treatment by Jianbo Yin; Xiang Xia; Xiaopeng Zhao (2356-2363).
A facile thermal oxidation method in air is suggested to treat chemically synthesized conducting polyaniline (PANI) nanotubes in order controllably to decrease the conductivity. The structure, morphology and conductivity were characterized, and the polarization and electrorheological (ER) properties of nanotubes when dispersed in insulating oil were measured as a function of the thermal-oxidative time. Results showed that the appropriate thermal oxidation treatment did not destroy the nanotube morphology but induced the deprotonation and oxidation of PANI backbone. As a result, the conductivity was decreased and the polarization properties were changed. The nanotubes obtained after thermal oxidation at 200 °C for 4 h demonstrated the optimal ER performances. The ER activity decreased as the thermal oxidation time increased, and this could be explained by the change of polarization properties.
Keywords: Polyaniline nanotubes; Thermal oxidation; Conductivity; Polarization; Electrorheology;
Synthesis of phosphinated polyurethane foams with improved fire behaviour by A. Lorenzetti; M. Modesti; E. Gallo; B. Schartel; S. Besco; M. Roso (2364-2369).
Both alkylphosphinates and inorganic phosphinates (based on sodium, calcium, magnesium or zinc) have been recently proposed as flame retardants for polyesters, polyamides and polyurethane foams as well. The main aim of this work was to compare the flame retardant effectiveness of inorganic (already proofed in PU foams) and organic phosphinates in PU foams which have never been used in polyurethane (PU) foams. The thermal stability in nitrogen and air as well as limiting oxygen index and cone calorimeter behaviour have been studied to assess the effectiveness of such flame retardants in PU foams.The results obtained showed that both inorganic and organic phosphinates are effective in enhancing fire behaviour of PU foams since they improve thermal stability, LOI and fire performance. Cone calorimetry highlighted the flame inhibition action in the gas phase due to the release of phosphorus-containing molecules. The better results obtained for inorganic phosphinate are probably related to the better quality of the char layer developed during burning, but may also be related to the higher phosphorus content of such flame retardant with respect the other ones. It was also verified that both inorganic and organic phosphinate containing N-synergic compound showed a fuel dilution effect, deriving from water and/or ammonia release in the gas phase.
Keywords: Phosphinate; Polyurethane foam; Flame retardancy; Fire behaviour;
Antioxidant consumption in squalane and polyethylene exposed to chlorinated aqueous media by W. Yu; T. Reitberger; T. Hjertberg; J. Oderkerk; F.R. Costa; U.W. Gedde (2370-2377).
Squalane stabilized with 0.2 wt.% of Irganox 1010 and a medium-density polyethylene containing 0.1 wt.% of the same antioxidant were exposed to two different aqueous media (water solutions containing either 10 ppm Cl2 or 10 ppm ClO2, both buffered to pH = 6.8) at different temperatures between 30 and 70 °C. The squalane phase was characterized by differential scanning calorimetry (oxidation induction time, OIT) and infrared spectroscopy, and the aqueous media were analysed after concentrating the analytes using liquid–liquid extraction by liquid chromatography, mass spectrometry and infrared spectroscopy. OIT measurements were carried out on the polyethylene samples after exposure to the chlorinated aqueous media. Exposure of the squalane systems to water containing ClO2 resulted in discolouration by the formation of quinoid structures and a faster depletion of the antioxidant than exposure to water containing Cl2. The activation energy for the loss of antioxidant activity on exposure to ClO2-water was very low (<10 kJ mol−1) in the squalane test (no diffusion control) and 21 ± 2 kJ mol−1 at a depth of 1–2 mm from the surface of polyethylene plaques (diffusion control). Calculation from earlier published OIT data from a HDPE exposed to Cl2-water yielded an activation energy for the loss antioxidant activity of 68 kJ mol−1. The antioxidant degradation products obtained from the exposure to the ClO2 aqueous medium were found at a higher concentration, were more polar and exhibited a higher proportion of low molar mass species than those obtained after exposure to the Cl2 aqueous medium. The important chemical difference between ClO2 and Cl2 is that the former is a one-electron oxidant whereas the latter preferentially reacts by hydrogen substitution. Possible further reactions, in agreement with the observations made, are proposed.
Keywords: Polyethylene; Squalane; Irganox 1010; Chlorinated aqueous media; Degradation;
X-ray diffraction and biodegradation analysis of green composites of natural rubber/nanocellulose by Eldho Abraham; P.A. Elbi; B. Deepa; P. Jyotishkumar; L.A. Pothen; S.S. Narine; S. Thomas (2378-2387).
The biodegradation of the composites of natural rubber (NR) reinforced with nanocellulose was studied by vermicomposting method with reference to the crosslinking of the matrix. An epigeic vermicompost worm Eudrilus eugeniae was used for this purpose. Nanocellulose isolated from raw jute fibre by steam explosion is the reinforcing element for the composite. Morphological, X-ray diffraction (XRD) and tensile strength results indicate that a strong cellulose/NR interaction exist in the cross linked samples. The rate of biodegradation of the NR composites indicates that the cellulose has to be hydrolysed before microorganisms can utilise it as a nutrient source. The weight percentage of reinforced nanocellulose highly influences the rate of biodegradation of the composite. The rate of biodegradation by vermicomposting was found to be comparatively higher in non-cross linked composites than its cross linked counterparts. The effectiveness of Eudrilus eugeniae for the biodegradation of NR/cellulose composites either it is cross linked or non-cross linked is clearly depicted.
Keywords: Biodegradation; Biocomposite; Natural rubber; Nanocellulose; Zn–cellulose complex;
Utilization of peanut husks as a filler in aliphatic–aromatic polyesters: Preparation, characterization, and biodegradability by Chin-San Wu (2388-2395).
The biodegradability, morphology, and mechanical properties of composite materials made of poly(butylene adipate-co-terephthalate) (PBAT) and peanut husks (PH) were evaluated. Composites containing maleic anhydride-grafted PBAT (PBAT-g-MA/PH) exhibited noticeably superior mechanical properties because of greater compatibility between the two components. The dispersion of PH in the PBAT-g-MA matrix was highly homogeneous as a result of ester formation between the anhydride carboxyl groups of PBAT-g-MA and hydroxyl groups in PH and the consequent creation of branched and cross-linked macromolecules. Each composite was subjected to biodegradation tests in Aminobacter aminovorans compost. Morphological observations indicated severe disruption of film structure after 60 days of incubation, and both the PBAT and the PBAT-g-MA/PH composite films were eventually completely degraded. Water resistance of PBAT-g-MA/PH was higher than that of PBAT/PH, although the weight loss of composites buried in A. aminovorans compost indicated that both were biodegradable, even at high levels of PH substitution. The PBAT-g-MA/PH films were more biodegradable than those made of PBAT, implying a strong connection between these characteristics and biodegradability.
Keywords: Biodegradable; Polyesters; Peanut husks; Composites;
Influence of swift heavy ion beams and protons on the dielectric strength of polyimide by T. Seidl; A. Plotnikov; E. Mustafin; R. Lopez; D. Severin; E. Floch; C. Trautmann; A. Golubev; A. Smolyakov; D. Tommasini; W. Ensinger (2396-2402).
The breakdown voltage of radiation damaged polyimide is investigated. Motivated by the application of polyimide as insulator used in ion accelerator magnets of the future Facility for Antiproton and Ion Research (FAIR), two different kinds of polyimides were irradiated with different high energetic ion beams (p, C, Ni, Ru and Au) and with gamma radiation from a Co-60 source. Breakdown voltage measurements showed that the dielectric strength of irradiated polyimide was found to decrease as a function of the irradiation dose. The rate of decrease was found to be dependent on i) the type of radiation and ii) the angle of incident beam. Gamma and proton radiation leads only to minor changes in the observed dose regime while heavy ion irradiation drastically decreases the dielectric strength at even low doses. For heavy ion irradiation the rate of decrease is found to be dependent on the energy loss of the used particle beams. Furthermore an increase in incident beam angle, i.e. closer to the surface normal gives a lower decrease in the dielectric strength suggesting that the breakdown follows the path length of the produced ion tracks. Weibull analysis was used on a selected data set to discuss failure expectations for the later FAIR magnets.
Keywords: Ion irradiation; Dielectric strength; Radiation damage; Polyimide;
Probing the molecular dynamics in XLPE aged at different temperatures by 1H NMR relaxation time measurements by Jobby Paul; Eddy Walther Hansen; Jaan Roots (2403-2411).
Ageing of cross-linked polyethylene (XLPE) insulation used in high voltage cable was monitored using low-field solid-state 1H NMR. The effect of thermal ageing at different temperatures on the phase composition and molecular mobility was studied by 1H NMR relaxation time experiments. The onset and progress of oxidation is observed to be very different for XLPE aged at different temperatures. Crystalline fraction dropped monotonically after the onset of oxidation for sample aged above melting point while it remained constant after a small initial drop for the sample aged near the melting point. Thermal oxidation caused a drastic change in molecular dynamics of the amorphous region as indicated by the change in correlation time. Thermal oxidation is confined to the amorphous region in the case of sample aged close to the melting point. The change in phase composition and relaxation time suggest that chain scission was predominant during the early stages of oxidation and later dominated by crosslinking. The presence of antioxidant prolonged the onset of oxidation depending on the ageing temperature.
Keywords: Ageing; Cross-linked polyethylene (XLPE); 1H NMR; Relaxation; DSC;
Influence of processing and intrinsic polymer parameters on photochemical stability of polythiophene thin films by Morten V. Madsen; Thomas Tromholt; Arvid Böttiger; Jens W. Andreasen; Kion Norrman; Frederik C. Krebs (2412-2417).
Intrinsic polymer parameters such as regio-regularity, molecular weight, and crystallinity play an important role when studying polymer stability. 18 different batches of poly-3-hexyl-thiophene (P3HT) were degraded in a solar simulator (AM1.5G, 1000 W/m2) and the degradation kinetics were monitored. The results suggest that the radical reaction responsible for the photodegradation takes place at terminal thiophene rings exposed at points were the conjugation is broken. This proposed mechanism is supported by the fact that stability scales with regio-regularity following the ratio of head-to-tail connected thiophene units. Annealing was found to relax the P3HT films and increase conjugation length and, in turn, increase stability observed as a delayed spectral blueshift caused by photochemical degradation. Crystallinity was found to play a minor role in terms of stability. Oxygen diffusion and light shielding effects were shown to have a negligible effect on the photochemical degradation rate. The results obtained in this work advance the understanding of polymer stability and will help improve the design of materials used for polymer solar cells resulting in longer lifetimes, which will push the technology closer to large-scale applications.
Keywords: P3HT; Photooxidation; Organic photovoltaics; Photo-chemical stability; Degradation;
A comparative study on the efficacy of varied surface coatings in fireproofing glass/epoxy composites by Baljinder K. Kandola; Waqas Bhatti; Everson Kandare (2418-2427).
This paper investigates the efficacy of varied (non-intumescent and intumescent) polymer-based surface coatings in providing fire protection to glass fibre-reinforced (GFR) epoxy composites exposed to one-sided radiant heating. In addition to an intumescent surface coating, two other non-intumescent surface coatings are considered – one that is active in the condensed phase and promotes surface char formation and another that is active in the gaseous phase and inhibits flaming combustion. The fire resistance of surface-coated GFR epoxy composite laminates is evaluated using the cone calorimeter at incident heat fluxes of 25, 50 and 65 kW/m2. For all tests conditions considered, there is a significant improvement in the fire performance of surface-protected GFR epoxy laminates relative to their unprotected counterparts. The intumescent surface-coated laminate showed the most significant variations in fire reaction properties with changes in irradiance.
Keywords: Glass/epoxy composites; Fire retardation; Char formation; Flame inhibition; Intumescence;
Flame retardancy and thermal decomposition of flexible polyurethane foams: Structural influence of organophosphorus compounds by Shuyu Liang; Matthias Neisius; Henri Mispreuve; Reinold Naescher; Sabyasachi Gaan (2428-2440).
In this study the structural effect of different phosphorus compounds on the flame retardant (FR) properties of flexible polyurethane foams (FPUF) was investigated. A series of organophosphorus compounds (phosphonates, phosphates and phosphoramidates) with systematical structure variations were synthesized and incorporated into the flexible foam during its polymerization process. The flame-retarding efficiency of these phosphorus compounds was subsequently evaluated by subjecting their corresponding flame-retarded foams to standard fire tests such as limiting oxygen index (LOI), BKZ-vertical burning test and UL 94-horizontal burning test for foamed materials. It was observed that the synthesized phosphonates and analogous phosphoramidates were more effective than the corresponding phosphates. The presence of an allyl moiety within the molecular structure further improved the FR efficacy of the phosphonate and phosphoramidate compounds, whereas a benzyl group reduced the flame retardant efficiency significantly. The thermogravimetric (TGA) analysis and pyrolysis combustion flow calorimetry (PCFC) results for the FPUF indicated that the most effective FRs might act predominantly in gas phase and exhibit lower condensed phase action (i.e. catalyze the decomposition of FPUF to happen at lower temperatures). Mass spectrometric analysis of FRs indicates that phosphonate and phosphoramidate derivatives appear to support the phosphoryl radical formation more than the investigated phosphate compounds.
Keywords: Foam; Flame retardant; Phosphate; Phosphonate; Phosphoramidate; PO;
The degradation of poly(vinyl acetate) as a material for design objects: A multi-analytical study of the effect of dibutyl phthalate plasticizer. Part 1 by Francesca Toja; Daniela Saviello; Austin Nevin; Daniela Comelli; Massimo Lazzari; Marinella Levi; Lucia Toniolo (2441-2448).
The influence of dibutyl phthalate (DBP) plasticizer on poly(vinyl acetate) (PVAc) degradation was investigated. A multi-analytical approach (combining FTIR and Fluorescence spectroscopy, NMR and DSC analyses) was used to study how thermal- and photo-oxidative ageing treatments act on the polymer and assess the role of the additive in the degradation pattern. Standard and plasticized PVAc films were artificially aged at 60 °C in a thermal regime and irradiated at wavelengths above 290 nm in a photo-oxidative ageing regime, with exposure between 100 and 2000 h. The two types of ageing differ mainly in the formation of C＝C double bonds along the polymer backbone, enhanced by thermal ageing, and the formation of aldehydic structures, following photo-oxidative treatment and in the degree to which plasticizer is lost. The integration of results from different analytical methods highlights the utility in combining complementary analyses for the study of PVAc degradation.
Keywords: Poly(vinyl acetate); Fluorescence spectroscopy; FTIR spectroscopy; Thermal ageing; Photo-oxidative ageing; Design objects;
Synthesis, characterization, and thermal properties of new polysiloxanes containing 1,3-bis(silyl)-2,4-dimethyl-2,4-diphenylcyclodisilazane by Yan Zheng; Yongxia Tan; Lina Dai; Zhen Lv; Xuezhong Zhang; Zemin Xie; Zhijie Zhang (2449-2459).
New polysiloxane derivatives (P1 and P2) having mixed phenyl-substituted cyclodisilazane in the main-chain were synthesized. Their thermal properties have been characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperature (T g) of P1 and P2 would be dependent on the polymer structure and were in the range of −27∼−80 °C. The T gs decreased considerably with an increase in the content of the siloxane main-chain groups and increased with higher content of phenyl groups. All of the copolymers showed good thermal stability, with their temperatures at 5% weight loss (T d5) being higher than 490 °C and char yields over 50% under nitrogen. The chemistry of pyrolytic conversion was investigated by FT-IR, solid NMR and mass spectrometry. The results demonstrate that the cyclodisilazane group significantly alters the degradation behavior of the PDMS, modifying the profile of the thermal degradation and reducing the overall rate of volatiles evolution. The thermal stability and degradation behavior also indicate that the inter-molecular rearrangement occurs prior to the intra-molecular backbiting reactions by these OH-terminated copolymers. The thermolysis of the Si4N2 groups in the backbone could bring the greater thermal stability to form the silicon-nitrogen networks via the consumption of Si–OH bonds. Retardation of the degradation rate is resulted from this cross-linking that prevents rearrangement of the siloxane to allow further depolymerization.
Keywords: Cyclodisilazane; Polysiloxane; Polycondensation; Thermal stability;
Kinetics of the hydrolytic degradation of poly(lactic acid) by F. Codari; S. Lazzari; M. Soos; G. Storti; M. Morbidelli; D. Moscatelli (2460-2466).
The hydrolysis of water soluble PLA oligomers of different chain lengths and chirality was investigated at acidic pH and temperatures in the range from 40 to 120 °C. The time evolution of the concentrations of all oligomers was measured by HPLC and the corresponding degradation rates were evaluated for each specific chain length. In agreement with the preferential chain end scission mechanism suggested in the literature, the ester groups were classified as α (chain end esters) and β (backbone esters). A kinetic model was developed from the resulting kinetic scheme and it was found to well reproduce the concentration values of all different oligomers during degradation as a function of time. The corresponding rate constants k d α and k d β were estimated over the whole temperature range, with activation energies of 73 and 58 kJ/mol and pre-exponential factors of 8.21·107 and 1.77·105 l/mol/h, respectively. It is seen that the faster hydrolysis of the ester groups close to the carboxylic and hydroxyl chain end groups (α) with respect to those inside the polymer chain (β) is mainly due to the largely different pre-exponential factors. This steric effect can be explained considering that the water approach is favoured by the hydrophilic nature of the chain end groups compared to the hydrophobic character of the polymer backbone. No dependence of k d α and k d β on chiral composition was found, suggesting that the differences reported earlier in the literature are due to the effect of crystallinity on diffusion phenomena rather than to different reactivity of the two stereoisomers.
Keywords: Biopolymers; Degradation kinetics; Hydrolysis; Chirality; Poly(lactic acid);
A durable flame retardant for cellulosic fabrics by Zongyue Yang; Xiaowen Wang; Dapeng Lei; Bin Fei; John H. Xin (2467-2472).
A novel halogen- and formaldehyde-free flame retardant named Neo-FR was synthesized and applied to cellulosic fabrics. The chemical structure of the flame retardant was characterized by Fourier-transform infrared spectroscopy (FTIR). The flame retardant performance was evaluated by Limiting oxygen index (LOI) and vertical flammability tests. The results indicated that the flame retardant had excellent flame retardancy and durability for cellulosic fabrics. The surface morphology of treated fibre and fibre char residue were observed through scanning electron microscope (SEM). The SEM graphs demonstrated that the Neo-FR system played intumescent flame retarding mechanism on cotton fibre. The thermal property of the flame retardant treated cotton fabric was investigated through thermal gravimetric analysis (TGA). The results indicated that char residue of the treated fabrics was about 36.5%, which was much higher than that of untreated fabric. The mechanical properties such as tensile strength and elongation of the cotton samples treated with Neo-FR system were much less affected than those treated by a commercial durable flame retardant agent (Pyrovatex CP New). The laundering test results show that the Neo-FR system is a durable flame retardant for cellulosic fabrics.
Keywords: Flame retardant; Cellulosic fabric; Thermal property; Durability;
Enzymatic degradation of poly(3-hydroxybutyrate) by a commercial lipase by Rodríguez-Contreras Alejandra; Calafell-Monfort Margarita; Marqués-Calvo María Soledad (2473-2476).
Polyesters such as poly(3-hydroxybutyrate) (PHB) have attracted commercial and academic interest as new biotechnological materials. In previous studies it was confirmed that two commercial lipases hydrolyzed the ester bonds from the 3HB fractions of P(3HB-co-4HB) copolymer. In this study, one of the previously used commercial lipases has been used for the enzymatic degradation of PHB homopolymer obtained via fermentation with Cupriavidus necator in order to obtain low molecular mass polymer. The results confirmed the enzymatic reaction of the used lipase with this PHB and show a controlled decrease of the molecular mass from 300,000 Da–4000 Da.
Keywords: Polyhydroxyalkanoates; Lipase; Poly(3-hydroxybutyrate); Enzymatic degradation;
Corrigendum to “The effect of silica nanoparticles on the morphology, mechanical properties and thermal degradation kinetics of PMMA” [Polym Degrad Stab 97 (2012) 452–459] by M.L. Saladino; T.E. Motaung; A.S. Luyt; A. Spinella; G. Nasillo; E. Caponetti (2477).