Polymer Degradation and Stability (v.97, #9)

In order to clarify the role of dispersion on the fire retardant properties of polystyrene/LDH nanocomposites, two types of composites were prepared. The largely exfoliated polystyrene/Ca−Al−LDH−B nanocomposites (PS/Ca−Al−LDH−B) were prepared by in situ bulk polymerization while PS/Ca−Al−LDH−B composites were prepared by melt blending. X-ray diffraction and transmission electron microscopy were used to characterize the morphology of the samples while the thermal stability and fire properties were studied by thermogravimetric analysis and cone calorimetry. Good dispersion of LDH in the PS matrix was obtained by in situ bulk polymerization and those nanocomposites showed better thermal and fire properties compared to the composites with poorly-dispersed LDH obtained by melt blending.
Keywords: Layered double hydroxides; Nanocomposites; Fire retardancy; Dispersion;

Photostabilisation of poly(p-phenylenebenzobisoxazole) fibre by Bo Song; Qixin Zhuang; Linghui Ying; Xiaoyun Liu; Zhewen Han (1569-1576).
Poly(p-phenylene benzobisoxazole) (PBO) fibre has excellent mechanical properties and good thermal stability. However, the use of PBO fibre is limited because of its low photostability. Thus, this work aimed to study the improvement of PBO fibre photostability. Two methods of adhering UV absorbers to PBO fibre surface, namely, coordination bond method and physical adsorption method, were compared. The photo aging results show that the PBO fibres covered by UV absorbers via the coordination bond method were smooth and had no evident particle agglomeration. These fibres showed more improved photostability compared with those covered by UV absorbers via physical adsorption. After 125 h of photo aging, the tensile strength retention rate of PBO fibres covered with UV absorbers via the coordination bond method was still over 90%, which is far higher than that of untreated PBO fibres (approximately 75%).
Keywords: High performance fibre; PBO fibre; Photodegradation; Photostability;

Effects of pigment, disinfection, and accelerated aging on the hardness and deterioration of a facial silicone elastomer by Marcelo Coelho Goiato; Aldiéris Alves Pesqueira; Amália Moreno; Daniela Micheline dos Santos; Marcela Filié Haddad; Lisiane Cristina Bannwart (1577-1580).
The failure of facial prostheses is caused by limitations in their flexibility and durability. Therefore, we evaluated the effects of disinfection and aging on Shore A hardness and deterioration of a facial silicone with different pigmentations. Twenty samples with addition of each pigment (ceramic (C), make-up (M)) and without pigment (L) were made. For each pigment type and no pigment, 10 samples were subjected to two types of disinfectant solution (soap (S) and Efferdent (E)), totaling sixty samples. The specimens were disinfected three times per week for 60 days, and subjected to accelerated aging for 1008 h. The hardness of the facial silicone was measured with a durometer, and its deterioration was evaluated by obtaining the weight difference over time. Both the hardness and weight of the samples were measured at baseline, after chemical disinfection, and periodically during accelerated aging (252, 504, and 1008 h). Deterioration was calculated during the periods between baseline and chemical disinfection, and between baseline and each aging period. The results were analyzed using three-way repeated measures ANOVA and the Tukey's HSD Post-hoc test (α = 0.05). Specifically, samples containing pigment exhibited significantly higher hardness and deterioration values than those lacking pigment (P < 0.05). In addition, period of time (disinfection and accelerated aging) statistically increased the hardness and deterioration values of the silicone (P < 0.05). It can be concluded that both pigment and time statistically affected the hardness and deterioration of the silicone elastomer.
Keywords: Deterioration; Polymer; Disinfection; Hardness; Accelerated aging;

Thermally and hydrolytically stable polyimides containing naphthalimide units by Shafiq urRehman; Peng Li; HongWei Zhou; XiaoGang Zhao; GuoDong Dang; ChunHai Chen (1581-1588).
This work reports the synthesis and characterization of six-membered naphthalene dianhydrides based polyimide films and their significantly enhanced thermal and hydrolytic stabilities. 4,4′-Binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BNTDA) and 4, 4′-Ketone binaphthyl-1, 1′, 8, 8′-tetracarboxylic dianhydride (KBNTDA) were prepared by the dehalogenation-coupling of 4-bromo-1, 8-naphthalic anhydride and insertion reactions respectively. The structures of BNTDA and KBNTDA were characterized by FTIR, 1H NMR and 13C NMR. A series of polyimides were successfully synthesized from BNTDA, KBNTDA, and various diamines such as 4,4′-diaminodiphenyl ether (ODA), 4,4′-diaminodiphenylmethane (MDA), and 2,5-bis (4-aminophenoxy)-biphenyl (p-TPEQ). The higher molecular weight polyimides exhibited better solubility in common aprotic solvents. The thermal characterization of polyimides by DMA, DSC and TGA techniques, demonstrated super thermal stability of polyimides containing naphthalimide. Glass transition temperature (T g) of the all polyimides were above 326 °C and the 5% weight loss temperature was above 525 °C in air and 545 °C in N2. Hydrolytic stability of the polyimide films was evaluated by immersing the films into deionized water, 10% NaOH and 10% H2SO4 aqueous solutions. Mechanical properties remained stable before and after treatment. Six-membered polyimides derived from KBNTDA and BNTDA, exhibited better hydrolytic stability than those with five-membered phthalic anhydrides.
Keywords: Polyimides; Hydrolytic stability; Thermal stability; Six-membered naphthalene dianhydrides; Pd/C catalyzed reaction; Carbon monoxide;

Thermal degradation mechanism of poly(butylene carbonate) by Wenxiang Zhu; Chuncheng Li; Dong Zhang; Guohu Guan; Yaonan Xiao; Liuchun Zheng (1589-1595).
Thermal degradation mechanism of poly(butylene carbonate) (PBC) was elucidated by means of thermogravimetric analysis (TGA), 1H nuclear magnetic resonance (1H NMR) and pyrolysis-gas chromatography mass spectrometry (Py-GC/MS). The results indicated that there are three main pathways for the thermal degradation of PBC, including unzipping, β-H transfer and decarboxylation reactions. The unzipping reaction can be facilely induced at low temperature of 200 °C, and all of the three reactions occur at high temperature above 300 °C. TGA results suggested the thermal stability order: hydroxyl-terminated PBC < acetyl-terminated PBC < methyl carbonate terminated PBC. The hydroxyl end group can induce the unzipping reaction, while methyl carbonate chain-end depresses the occurrence of it.
Keywords: Poly(butylene carbonate); Thermal degradation mechanism; Chain-end group; Pyrolysis-gas chromatography mass spectrometry;

In this work, a reactive polymeric intumescent flame retardant (PDSPB) was synthesized and applied to ABS resin. The flame retarded materials were prepared by direct melt blending of ABS and PDSPB (ABS/PDSPB), as well as melt cross-linking of PDSPB to ABS (ABS-c-PDSPB). The cross-linking reaction was characterized by fourier transform infrared spectrometry (FTIR) and gel content measurement. The thermal stability, flame retardancy, carbonization chemistry and dynamic mechanical properties were investigated by TGA, dynamic FTIR, SEM, CONE calorimetry and dynamic mechanical analysis (DMA). The results showed that the addition of PDSPB can effectively reduce the flammability properties including peak heat release rate (PHRR), total heat release (THR) and average mass loss rate (AMLR). An improvement of the limited oxygen index value was also observed. Especially, the cross-linking of PDSPB can improve the ignition time and reduce THR during combustion. Moreover, ABS-c-PDSPB displayed a more obvious intumescent char layer and char weight than that of ABS/PDSPB blends. Furthermore, cross-linking of PDSPB enhanced the thermal stability and considerably delayed the thermal oxidation degradation of ABS. The dynamic mechanical properties were improved and the plasticization effect was reduced by cross-linking of PDSPB.
Keywords: Acrylonitrile-butadiene-styrene copolymer; Cross-linking; Carbonization chemistry; Flammability; Thermal stability;

A modulated-TGA approach to the kinetics of lignocellulosic biomass pyrolysis/combustion by Kun Cheng; William T. Winter; Arthur J. Stipanovic (1606-1615).
Microcrystalline cellulose, Birchwood xylan, and Organosolv lignin were selected as the representatives of the three major components in lignocellulosic biomass: cellulose, hemicelluloses and lignin, respectively. The thermal decompositions, both pyrolysis and combustion, of these biomass components as well as a natural woody biomass (Acer saccharum) were investigated using High-Resolution Modulated TGA. The activation energies of each decomposition process were determined by Modulated TGA without any assumptions and mathematical model fitting. For the combustion of microcrystalline cellulose, the char residues underwent glowing ignition due to the presence of oxygen, and its first derivative of weight loss curve showed two thermal decomposition peaks, while only a single peak was observed for pyrolysis of microcrystalline cellulose in a nitrogen atmosphere. However, the effect of air was less evident in the thermal degradation of the Birchwood xylan. With air as the sample environment in the TGA experiment, the thermal decomposition of Organosolv lignin was simplified, and the onset of the primary decomposition shifted to temperatures greater than 300 °C, the decomposition zone became narrower, and the mass of residual solids at 600 °C was negligible. Since the sum of the TGA profiles (in air) of the three major biomass components closely matched the TGA profile (in air) of an actual wood sample (A. saccharum), the potential of using TGA to predict biomass compositions was indicated.
Keywords: Modulated-TGA; Biomass; Lignin; Pyrolysis; Combustion; Activation energy;

A simplified theory for the crystallisation of biodegradable polyesters induced by polymer chain scissions during biodegradation is presented following a theory developed by Han and Pan. The original theory is greatly simplified so that it becomes very straightforward to use and the number of material parameters is significantly reduced. Furthermore it is demonstrated that the spherulite structure widely observed in polymers can be taken into account using the theory. The simplified theory is fitted to the experimental data of poly-l-lactic acids (PLLAs) obtained from literature. It is shown that the simplified theory is equally able to fit the data as the original one. It is also shown that the theory can fit degradation data for PLLAs of different initial degrees of crystallinity with spherulite structures.
Keywords: Biodegradable polymers; Biodegradation; Crystallization; Modelling; Poly-l-lactic acid;

Hydrolytic degradation of PLLA/PCL microporous membranes prepared by freeze extraction by Luis A. Gaona; J.L. Gómez Ribelles; Jairo E. Perilla; M. Lebourg (1621-1632).
Poly(l-lactic acid) – Poly(ε-caprolactone) blends (PLLA/PCL) porous membranes were prepared by freeze extraction (a modification of freeze drying) with ratios 100/0, 80/20, 60/40, 40/60, 20/80, 0/100 in weight. Degradation of the membranes in phosphate buffer solution (PBS) up to 65 weeks was studied using weight loss measurements, high performance liquid chromatography (HPLC), differential scanning calorimetry (DSC), mechanical indentation, gel permeation chromatography (GPC), and scanning electron microscopy (SEM). Degradation rate as observed by weight loss and reduction of molecular weight and mechanical properties depended on the composition of the blends. In most blends the degradation was more prominent in the PLLA phase and was accompanied by consequent recrystallization that formed a crystalline phase with increased resistance to hydrolysis. Occurrence of such crystalline phases and degradation of intercrystalline domain led to formation of nearly monodisperse molecular weight populations.Membranes with only 20% PCL presented favorable behavior compared to pure PLLA membranes as reflected in a lower degradation rate and a limited loss of the mechanical properties. At the same time, degradation rate of 80/20 membranes was enhanced with respect to pure PCL, and membranes were stiffer than PCL membranes at all degradation times. This composition could thus be useful for use in tissue engineering for bone or cartilage applications.
Keywords: Poly(l-lactic acid); Poly(ε-caprolactone); Polyester blends; Hydrolytic degradation;

Structurally similar silicone ceramers were synthesized by sol–gel processing of organic silanes. The chemical structures of the hardened ceramer materials were investigated by studying the gaseous products produced during elevated temperature heating. Fourier transformation infra-red (FTIR) spectroscopy and thermogravimetric analysis (TGA) were utilized to study the degradation phenomenon in the ceramers. The pyrolyzed residues were analyzed by Raman and 29Si solid-state nuclear magnetic resonance (SSNMR) and X-ray diffraction (XRD) techniques. The surfaces of the residues were analyzed with a scanning electron microscope (SEM). The results from the characterization techniques were utilized to investigate the degradation mechanisms of the ceramer materials.
Keywords: Silicone; Ceramer; FTIR spectroscopy; Raman spectroscopy; Thermogravimetry; Mechanism;

Ammonium polyphosphate and poly(acrylic acid) have been chosen to build a complex, four-layered (or quadlayered) hybrid organic-inorganic architecture exploiting the Layer by Layer assembly, in order to promote the formation of an aromatic and stable carbonaceous structure (char), able to thermally protect cotton, polyester and their blends. To this aim, a different number of quadlayers (namely, 1, 5 and 10) consisting of poly(diallydimethylammonium chloride)/poly(acrylic acid)/poly(diallydimethylammonium chloride)/ammonium polyphosphate have been deposited on the chosen fabrics and investigated. Thermogravimetric analysis coupled to isothermal tests performed in a gravity convection oven at fixed temperatures has shown that the presence of such architectures is able to enhance the char formation in a remarkable way. Furthermore, infrared spectroscopy has pointed out the aromatic nature of the residues left by the treated fabrics upon heating at high temperatures, regardless of the quadlayer number and the fabric type.
Keywords: Thermal degradation; Char; Layer by layer assembly; Ammonium polyphosphate; Poly(acrylic acid);

Experimental tests and technical characteristics of regenerated films from agricultural plastics by Pietro Picuno; Carmela Sica; Rocco Laviano; Aleksandra Dimitrijević; Giacomo Scarascia-Mugnozza (1654-1661).
Current agricultural practices require the use of large quantities of plastics, which contribute to a significant increase of the quantity and quality of agricultural production, but also require high quantities of plastic waste to be disposed in such way that will not have a negative effect on the landscape and the agro-ecosystem. In this paper the results of an experimental investigation of the possibilities of producing new regenerated plastic films through mechanical recycling, from post-consume agricultural plastic films are analysed. Six recycled films, made from agricultural low tunnel and greenhouse covering films as well as from HDPE bags for agrochemical packaging, have been extruded producing films of different thickness. These regenerated films were characterized by means of mechanical and spectrometric tests and SEM + EDS analysis. The obtained results show that without adding any additives into the blends good mechanical and spectral properties can be achieved by mixing the greenhouse and low tunnel recycled plastic film coverings.
Keywords: Agricultural plastic waste; Mechanical recycling; Plastic films; Plastic film mechanical properties; Plastic film radiometric properties;

Degradable “click” polyesters from erythritol having free hydroxyl groups by Manuel Bueno; Inmaculada Molina; Juan A. Galbis (1662-1670).
Click Cu(I)-catalysed polymerization and thermal polyaddition of diynes having ester linkages and 1,4-diazido-1,4-dideoxyerythritol were performed to obtain polyesters containing 1,2,3-triazole rings along the polymer chain. The resulting polyesters had weight-average molecular weights in the 13,000–37,000 range. Thermal studies revealed them to be mainly amorphous and stable up to 250 °C under nitrogen. The polymers are hydrophilic, several of them being water-soluble. Degradation studies of a water-soluble prototype polymer showed they are hydrolytically degradable. These studies were carried out at 37 °C in doubly distilled water and buffered salt solution at pH 7.4, and were monitored by GPC, and IR and NMR spectroscopies.AA-BB type polyesters were obtained by click Cu(I)-catalysed polymerization and thermal polyaddition of the sugar-based monomer 1,4-diazido-1,4-dideoxyerythritol to diynes having ester linkages. The polymers were mainly amorphous and stable up to 250 °C. Polyesters were hygroscopic and those derived from PEG were water-soluble. The hydrolytic degradation occurs by breaking of the ester linkages, and it takes place more quickly at pH 7.4 than at pH 5.0.Display Omitted
Keywords: Click polymerization; Hydrophilic polymers; Water-soluble polymers; Polyesters; Hydrolytic degradation;

Application of TGA/FTIR to the study of the thermal degradation mechanism of silanized poly(ether-urethanes) by R.H. Aguirresarobe; L. Irusta; M.J. Fernandez-Berridi (1671-1679).
TGA/FTIR was employed to investigate the thermal degradation mechanism of two types of self-curable Polyurethanes obtained from isophorone diisocyanate (IPDI), Poly(propyleneglycol) (PPG), and (trimethoxysilyl) propyl isocyanate and N-butyl 3-trimethoxysilyl propyl amine respectively. The TGA/FTIR results for isocyanatesilane based systems showed that the degradation behavior differed between the cured and non-cured samples in relation to the evolution of isocyanate moieties in the first case and CO2 in the second one.Aminosilane based systems, both non-cured and cured samples released isocyanate containing volatile compounds.
Keywords: Silanized Poly(ether-urethanes); Thermogravimetric analysis; Infrared Spectroscopy; TGA/FTIR; Thermal degradation mechanism;

Natural weathering properties of acetylated bamboo plastic composites by Ke-Chang Hung; Yong-Long Chen; Jyh-Horng Wu (1680-1685).
The hydrophilic properties of lignocellulosic materials pose problems when they are used as reinforcement in plastics. The hydrophilicity of lignocelluloses influences its durability and also the interfacial adhesion between lignocellulose and polymers. Chemical modification, especially acetylation, has been used successfully to decrease the hydrophilicity and increase the weathering resistance of lignocellulose. Therefore, the purpose of this study is to investigate the natural weathering properties of bamboo plastic composites (BPCs) reinforced with bamboo fibers acetylated to different weight gains (WGs). The results showed that the retention ratios of mechanical properties of acetylated BPCs, especially those containing fibers with a high WG, were significantly improved as compared to the unmodified composite during natural weathering. In addition, the crystallinity of the high-density polyethylene (HDPE) in all BPCs increased after natural weathering for 120–240 days and then leveled off. This result indicates that the chain scission of HDPE mainly occurred during this period, producing shorter and more mobile chains and enabling them to undergo secondary crystallization. Furthermore, the mildew resistance of the acetylated BPCs was higher than that of unmodified composite. These results indicate that the durability and decay resistance of BPCs can be enhanced through acetylation of the bamboo reinforcement.
Keywords: Natural weathering; Bamboo plastic composite; Acetylation; Crystallinity; Mildew resistance;

Impact of ionizing radiation on physicochemical and biological properties of an amphiphilic macromolecule by Li Gu; Kyle Zablocki; Linda Lavelle; Stanko Bodnar; Frederick Halperin; Ike Harper; Prabhas V. Moghe; Kathryn E. Uhrich (1686-1689).
An amphiphilic macromolecule (AM) was exposed to ionizing radiation (both electron beam and gamma) at doses of 25 kGy and 50 kGy to study the impact of these sterilization methods on the physicochemical properties and bioactivity of the AM. Proton nuclear magnetic resonance and gel permeation chromatography were used to determine the chemical structure and molecular weight, respectively. Size and zeta potential of the micelles formed from AMs in aqueous media were evaluated by dynamic light scattering. Bioactivity of irradiated AMs was evaluated by measuring inhibition of oxidized low-density lipoprotein uptake in macrophages. From these studies, no significant changes in the physicochemical properties or bioactivity were observed after the irradiation, demonstrating that the AMs can withstand typical radiation doses used to sterilize materials.
Keywords: Amphiphilic macromolecule; Electron beam radiation; Gamma radiation; oxLDL inhibition; Stability;

New diamines bearing substituted 1,2,4-triazole and quinoxaline moieties with OCH3 or Br units were successfully synthesized and used for preparation of novel polyamides (PAs) by direct polycondensation with aromatic and aliphatic dicarboxylic acids. Chemical structure of the diamines as well as the resulting polymers was confirmed by elemental analysis, FT-IR and 1H NMR spectroscopic methods. Inherent viscosities of these PAs were in the range of 0.52–0.56 dL/g, they were readily soluble in a variety of organic solvents and formed low-coloured and tough thin films via solution casting. The aromatic PAs exhibited T g between 284 °C and 300 °C, and their 10% weight loss temperatures were in excess of 420 °C with up to 70% char yield at 600 °C in N2. These PAs emitted green or blue fluorescence in dilute NMP solution and in the solid state. Silicon carbide (SiC) nanoparticles modified by silane coupling agent were used to prepare SiC/PA particle-reinforced composites by solution blending. Thermal properties of nanocomposites by using DMTA, DSC and TGA and also solubility and optical properties were investigated. The results show that both the uniform particle dispersion and the strong chemical bonding between the nanoparticles and the polymer–matrix contributed to the enhanced T g, storage modulus and thermal stability.
Keywords: Particle-reinforced nanocomposites; Polyamides; Thermal and optical properties; Fluorescent; Triazole;

Thermal ageing behavior of styrene–butadiene random copolymer: A study on the ageing mechanism and relaxation properties by Kewei Xiang; Xiaoan Wang; Guangsu Huang; Jing Zheng; Jingyun Huang; Guangxian Li (1704-1715).
Thermal oxidative ageing process of commercial available styrene–butadiene random copolymer (SBR) has been studied by the combination use of in-situ collected dynamic FTIR spectrum and two dimensional correlation analysis. The modification on the viscoelastic properties were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). It was found that the degradation took place predominantly in the aliphatic segment at the allylic position, giving rise to a maximum absorption at 1725 cm−1 in the carbonyl stretching region. The initiation process occurring in the aromatic parts produced acetophenone end groups as evidenced by the shoulder peak at 1679 cm−1. A series of oxygenated species were identified in the dynamic spectrum including anhydrides, lactones, peracids, aliphatic ketones and unsaturated carbonyl species. However, the band of unsaturated carbonyl species at 1695 cm−1 varied nonmonotonously, first increase sharply and then decreased. Concerning the concentration of double bonds, a detailed analysis revealed the different evolving trend between benzylic and aliphatic vinyls. The former showed an increment whereas the later were found to decrease, resulting in the broadening at 1638 cm−1. Furthermore, the relative generation rates of different carbonyls were ranked by two dimensional correlation analysis together with two shoulder peaks at 1713 and 1679 cm−1 identified subtly in the asynchronous spectrum. On the basis of the above spectroscopic results, the mechanisms of thermal degradation were proposed.The relaxation behavior of thermally degraded SBR was studied by DMA and DSC. Both of the two techniques evidenced an increasing and broadening T g , suggesting the crosslinking reaction dominated thermal degradation. After checking the normalized spectra, it is found that all of the relaxation curves (irrespective of storage modulus, loss modulus or loss tangent) get widen over ageing. Two parameters, steepness (S) and wideness index (W) were defined in normalized storage modulus plot to make a quantitative discussion. The S reduced whereas the W rose up after degradation. The broader glass transition zone after ageing was attributed to the more heterogeneous relaxation environment and the wider size distribution of motion units participating in the transition.
Keywords: Styrene–butadiene copolymer; Thermal oxidative ageing; Two-dimensional FTIR spectrum; Relaxation behavior;

Multi-walled carbon nanotubes (MWNTs) were grafted with poly (acrylic acid), and subsequently coated with a close-packed layer of silica nanospheres, namely SiO2-g-MWNTs. Such blob-like MWNTs/silica nanospheres hybrids were introduced into poly (methyl methacrylate) (PMMA) as a kind of flame retardant. From determinations of thermogravimetric analysis and cone calorimeter tests, it was indicated that the SiO2-g-MWNTs not only increased the initial degradation temperature and the maximum weight loss rate temperature of PMMA, but also decreased the peak of heat release rate. Observation using scanning electron microscopy revealed that the silica nanospheres on the surface of MWNTs strengthened the protective network layer during combustion.
Keywords: Silica nanosphere; Multi-walled carbon nanotube; Hybrid; Thermal stability; Flame retardancy;

DSC study of selected antioxidants and their binary mixtures in styrene–butadiene rubber by Andrea Černá; Zuzana Cibulková; Peter Šimon; Ján Uhlár; Peter Lehocký (1724-1729).
The antioxidant effects of iminostilbene, phenothiazine, diphenylamine, three substituted diphenylamines and their mixtures with commercial product N-(1,3-dimethyl-butyl)-N′-phenyl-benzene-1,4-diamine (6PPD) in thermal oxidation of styrene–butadiene rubber (SBR) were examined by non-isothermal DSC measurements. For the treatment of experimental data, isoconversional methods based on two non-Arrhenian temperature functions have been applied. Protection factors were calculated to compare the stabilizing effect of individual compounds and their mixtures. Among the individual compounds, the highest antioxidant performance in the stability of SBR is observed for iminostilbene. In the case of mixtures the best stabilizing properties can be assigned to the mixture of 6PPD with 4-phenylamino phenol. The cooperation between antioxidants in the binary mixtures was characterized by the values of S-factor. The results indicate that only the mixture of 6PPD with 4-phenylamino phenol exhibits a synergistic effect at 130 °C.
Keywords: Styrene–butadiene rubber; Antioxidants; Induction period; Thermal oxidation; DSC;

Investigation of mechanical properties and cure behavior of DGEBA/nano-Fe2O3 with polyamine dendrimer by Omid Zabihi; Aminreza Khodabandeh; Somayyeh Ghasemlou (1730-1736).
The preparation of epoxy/iron (III) oxide nanoparticles (nano-Fe2O3) and studying the effect of nano-Fe2O3 on improving mechanical and thermal characteristics of the epoxy matrix, is highlighted in this work. Epoxy nanocomposites are prepared by dispersing nano-Fe2O3 in diglycidyl ether of bisphenol A (DGEBA) and, subsequently, cross-linking by using polypropylenimine octaamine dendrimer (PPOD) as curing agent with low volatility. Preparation of epoxy/nano-Fe2O3 nanocomposites are carried out for different concentrations (0, 1, 5, 10 and 15%) of nano-Fe2O3. The mechanical experiments showed that the nano-Fe2O3 increasing from 0% to 10% led to an increase and 15% of nano-Fe2O3 led to a decrease in the tensile properties. Curing reaction kinetics of DGEBA/10% nano-Fe2O3 with PPOD was investigated by DSC at dynamic mode. A two-parameter (m, n) autocatalytic model (Sestak–Berggren equation) was found to be the most adequate selected kinetic model. The dynamic curing behavior of DGEBA/PPOD/10% nano-Fe2O3 could be described by ⅆ α / ⅆ t = 7.1 × 10 9 exp ( − 57 , 230 / R T ) ( 1 − α ) 0.82 α 0.41 .
Keywords: Epoxy nanocomposite; Polyamine dendrimer; Mechanical properties; Cure behavior;

Influence of antimony oxide on flammability of polypropylene/intumescent flame retardant system by Na Li; Yin Xia; Zongwen Mao; Liang Wang; Yong Guan; Anna Zheng (1737-1744).
An intumescent system consisting of ammonium polyphosphate (APP) as an acid source and blowing agent, pentaerythritol (PER) as a carbonific agent and antimony oxide (Sb2O3) as a synergistic agent was used in this work to enhance flame retardancy of polypropylene (FR-PP). Sb2O3 was incorporated into flame retardant formulation at different concentrations to investigate the synergistic mechanism of Sb2O3 with the flame retardant materials. The content of APP and PER was fixed at 25 wt% of total amounts of flame retardant-PP composite. The synergistic effects of Sb2O3 on novel intumescent flame retardant-PP composites were evaluated by limited oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results show that LOI is increased from 27.8 to 36.6% in the presence of Sb2O3 and meets the UL-94 V-0 standard at the loading of 2 wt% Sb2O3. The SEM, and FT-IR results indicated that Sb2O3 could react with APP and form the stable charred layer which can inhabit the oxygen and heat transfer.
Keywords: Antimony oxide; PP; Intumescent flame retardant; Flame retardancy;

Kinetics of the thermal and thermo-oxidative degradation of polypropylene/halloysite nanocomposites by B. Lecouvet; S. Bourbigot; M. Sclavons; C. Bailly (1745-1754).
In this work, halloysite nanotubes (HNTs) are used to prepare a polypropylene (PP)/HNTs nanocomposite via a melt blending process. The thermal stability of PP/clay nanocomposite compared to virgin PP is investigated in both inert nitrogen and air atmospheres using thermogravimetric analysis. The model-free isoconversional method according to Friedman is used to estimate activation energies as a function of the conversion degree. The thermal behavior of PP and PP/HNTs 8 wt% nanocomposite is then modeled and simulated. A very good agreement, especially under nitrogen, is obtained between simulated curves and experimental ones, both in dynamic and isothermal conditions. Activation energies of the PP/HNTs nanocomposite increase compared to pure PP, whatever the degradation conditions. These results correlate well with the higher thermal stability of PP observed in presence of halloysite nanotubes, as well as the reduced flammability of PP/HNTs nanocomposites reported in a previous study.
Keywords: Kinetic analysis; Thermal stability; Polymer nanocomposites; Halloysite; Polypropylene;

The effects of external environments on the mechanical behaviour and surface micro-structure of single Kevlar fibre have been investigated. Wave diffraction theory and digital image correlation (DIC) were applied to measure the longitudinal and transverse strain of a single Kevlar fibre. The stability and credibility of transverse and longitudinal strain measurement results is guaranteed by averaging the intensity of some images and adopting an optical array extensometer respectively. The results show that the elastic modulus of a single fibre treated under UV irradiation and in water increased 30% and decreased 15% compared to that of untreated ones respectively, the surface roughness increases drastically to a maximum value and then gradually reduces to a stable value with increasing treatment time, which can provide guidance for further study of the interface performance of composite material.
Keywords: Single Kevlar fibre; Fraunhofer diffraction pattern; Digital image correlation; Mechanical properties; Micro-structure analysis;

The hydrolytic and enzymatic degradation of PBT copolyesters obtained by replacing partially the diol or the diacidic monomers by bicyclic acetalized carbohydrate-based monomers from galactaric acid was studied. Changes taking place in sample weight, molecular weight, chemical constitution, crystallinity and morphology of the polyesters were evaluated. The partial replacement of 1,4-butanediol by 2,3:4,5-di-O-methylene-galactitol resulted in copolyesters with enhanced hydrodegradability compared to PBT. On the other hand, copolyesters obtained by partial replacement of dimethyl terephthalate by dimethyl 2,3:4,5-di-O-methylene-galactarate were biodegradable in the presence of lipases, and were hydrodegraded at a rate that increased with the content in galactarate units.
Keywords: Sugar-based polyester; Biodegradable PBT; PBT; Sugar-based PBT; Acetalized cyclic sugar monomers; Polycondensation sugar-based monomers;

A novel polymeric intumescent flame retardant: Synthesis, thermal degradation mechanism and application in ABS copolymer by Xiaoping Hu; Yuyang Guo; Li Chen; Xiuli Wang; Liangjun Li; Yuzhong Wang (1772-1778).
A novel polymeric intumescent flame retardant containing phosphorous–nitrogen (PSPTR) was synthesized and characterized by FTIR, 1H NMR and 31P NMR. Moreover, a new intumescent flame retardant (IFR) system, which was composed of PSPTR and Phenol Formaldehyde Resin (PF), was used to impart flame retardancy for ABS. Flammability properties of ABS/IFR composites were investigated by Limiting Oxygen Index (LOI) and vertical burning test (UL-94), respectively. The results showed that when the total addition content was 30 wt%, the weight ratio of PSPTR to PF is 1:1, the LOI value of ABS/IFR reached 28.2, and UL-94 reached V-1 rating. A distinct synergistic flame retardant effect exists between PSPTR and PF. The TGA data showed that the IFR (PSPTR/PF = 1:1, wt%) had three weight-loss stages and had a high residue of 50.21 wt% at 700 °C. The thermal degradation process of PSPTR and char-forming mechanism of IFR was studied by thermogravimetric analysis/infrared spectrometry (TG-IR) detailedly.
Keywords: Synthesis; Characterization; Synergistic flame retardancy; Charring flame retardant mechanism; TG-IR;

This study investigates the photostabilizing effect of the reactive UV-absorber 2-hydroxy-4(2,3-epoxypropoxy)-benzophenone (HEPBP) when used as a primer for wood. The present work further includes a study on the effect of HEPBP used in combination with an epoxy functionalized vegetable oil as a primer system. The study is based on reactions performed on pine veneers using 3-pentanone as a solvent and 4-(dimethylamino)pyridine (DMAP) as a catalyst, varying the reaction time and temperature. Results from FTIR and SEC measurements indicate that a desired reaction between HEPBP and wood does occur and that there are synergetic effects when HEPBP and oil are combined. Color measurements also indicate that the use of HEPBP and epoxidized soybean oil as pretreatment for wood results in a lower color change after 400 h of artificial weathering. We conclude that using HEPBP in combination with epoxy functionalized soybean oil does improve photostability of wood exposed to artificial weathering.
Keywords: UV-protection; 2-Hydroxy-4(2,3-epoxypropoxy)-benzophenone (HEPBP); Wood; Epoxy functionalized soybean oil; Grafting;

Oil from poly(vinyl chloride): Unprecedented degradative chain scission under mild thermooxidative conditions by Györgyi Szarka; Attila Domján; Tibor Szakács; Béla Iván (1787-1793).
Surprising new results were obtained during our investigations on the thermooxidative degradation of poly(vinyl chloride) (PVC) in dioctyl phthalate, DOP (bis(2-ethylhexyl) phthalate, DEHP), at 200 °C, i.e., in the range of the processing temperature of PVC. Enhanced dehydrochlorination of the polymer was found in DOP on the one hand. It is a striking observation that oily products are formed after 3 h of reaction time, on the other hand. GPC measurements proved that severe chain scission with nearly constant rate occurs under the applied mild conditions. FTIR and NMR analyses revealed the oxidation of the main PVC chain and simultaneous attachment of DOP to the polymer backbone in the course of the radical chain reaction of this oxidative process. Both the partially oxidized PVCs at lower and the oily products formed at longer degradation times may open new routes for PVC recycling, such as broadening its blending possibility with other polymers and polymeric waste materials.
Keywords: PVC; Thermooxidative degradation; Dioctyl phthalate; Chain scission; Recycling; Oil;

Thermoplastic polyurethanes with polycarbonate soft phase: Effect of thermal treatment on phase morphology by Elisa Cipriani; Marco Zanetti; Valentina Brunella; Luigi Costa; Pierangiola Bracco (1794-1800).
The thermal sensitivity of thermoplastic polyurethanes with polycarbonate soft phase (PCU) is considered. Thermal treatments were coupled with differential scanning calorimetry and infrared spectroscopy to investigate the effect of temperature on the phase morphology. PCU is characterized by a biphasic morphology: ordered hard polyurethane micro-domains are dispersed in a soft phase matrix, containing both hard and soft segments. Heating may completely destroy the short and long range order or simply change it. The infrared behaviour of the CO and NH stretching regions gives information on the organization of the segments. Thermal treatments above the processing temperature lead to an unstable monophasic morphology, that at room temperature is subjected to segregation of the hard segments, in order to recreate the biphasic morphology. Annealing treatments below the processing temperature cause reorganization in the hard micro-domains, inducing changes in their amount and dimensions. The result of the annealing depends on the temperature and on the exposure time. The thermal sensitivity also involves the chemical properties, given the thermal lability of the urethane bonds in the range of the processing temperature.
Keywords: Polycarbonate urethane; Processing; Morphology; DSC; FT-IR;

Ammonium polyphosphate (APP) and triphenyl phosphate (TPP) were added in a dicyclopentadiene (DCPD) modified unsaturated polyester resin (UPR) as intumescent flame retardant (IFR) and the combustion resistance effects were investigated. Flammability and thermal stability were investigated through limiting oxygen index (LOI) test and UL-94 vertical burning test and by using thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). When 57.6 wt.% of the flame retardant was added, the LOI value increased from 20.9 to 27.2 and a V-0 rating in UL-94 test was obtained. The fire-resistant time reached to 26∼34 min. The TGA and DSC analyses showed that the char yield was increased by the introduction of APP and TPP system and decomposition of the phosphorous additives yielded strongly phosphoric acids which effectively promoted the cross-linking reaction during the burning process. So, a profound flame retardant effect was obtained as APP and TPP were added to the unsaturated polyester resin.
Keywords: Unsaturated polyester resin; Phosphorous-containing flame retardant; Thermal stability; Char formation;

Novel thermally stable and organosoluble aromatic polyamides with main chain phenyl-1,3,5-triazine moieties by Guipeng Yu; Bin Li; Junling Liu; Shaofei Wu; Haijun Tan; Chunyue Pan; Xigao Jian (1807-1814).
The syntheses and properties of phenyl-1,3,5-triazine functional aromatic polyamides are described. From 2,4,6-trichloro-1,3,5-triazine (1), an aromatic diacid, namely 4-(4,6-diphenyl-1,3,5-triazin-2-yl)benzoic acid (6), was prepared by a three-step reaction in satisfactory yields. A model reaction of 6 with aniline (7) was carried out to determine feasibility of amidization. Aromatic poly(phenyl-1,3,5-triazine amide)s (10a–10e) with inherent viscosities ranging from 0.28 to 1.26 dL/g were synthesized from Yamazaki phosphorylation polycondensation of 6 with aromatic diamines (9a–9e). The reactions were conducted in N-methyl-2-pyrrolidone (NMP) to yield high-molecular-weight amorphous polymers in essentially high yields. All polymers are readily soluble in NMP and N,N-dimethylacetamide (DMAc) at room temperature, and formed transparent films from their solution. The films exhibit good mechanical properties with tensile strengths of 71.5–94.7 MPa, elongations at break of 6.1–10.0%, and initial moduli of 2.3–2.8 GPa except that of 10a is slightly brittle. These polymers have high glass transitions from 311 to 330 °C, depending on the aromatic diamines used in the polycondensation, and they demonstrate excellent thermal stabilities in excess of 440 °C (5% weight loss in air). Isothermal TGA measurements reveal that the obtained benzene-1,3-diamine-based poly(phenyl-1,3,5-triazine amide) (10b) belongs to the most superior class of heat resistant polymers such as polyamide Kevlar®.
Keywords: Polyamides; 1,3,5-Triazine; Synthesis; High performance polymers;

New mechanistic studies of structural defect formation in ordinary poly(vinyl chloride) (PVC) are summarized and critiqued. Evidence relating to the creation of some of the internal double bonds is tentatively suggested to imply the occurrence of hydrogen transfer via one or more cyclic transition states having ≥9 ring atoms. The absence of free chlorine atoms from polymerizations of vinyl chloride (VC) is reaffirmed, and a new mechanism, not yet verified, is identified as a possible explanation for a reported enhancement of the chloromethyl branch concentration at high conversions of monomer. This mechanism involves an intramolecular 1,5 hydrogen shift in a 1,3,5,6-tetrachlorohexyl radical. Copolymerization of VC with the chloroallylic chain ends of PVC is argued to be insignificant, and the new information in the literature is shown not to invalidate the currently accepted chemistry for the polymerization of vinyl chloride by standard free-radical methods.
Keywords: Poly(vinyl chloride); PVC synthesis; PVC microstructure; PVC stability; Vinyl chloride polymerization; Free-radical reactions;

Thermal, mechanical and morphological characterization of plasticized PLA–PHB blends by Mohamed A. Abdelwahab; Allison Flynn; Bor-Sen Chiou; Syed Imam; William Orts; Emo Chiellini (1822-1828).
A blend of poly(lactic acid) (PLA) (75% by weight) and poly(3-hydroxybutyrate) (PHB) (25% by weight) with a polyester plasticizer (Lapol 108) at two different concentrations (5 and 7% by weight per 100 parts of the blends) were investigated by TGA, DSC, XRD, SEM, mechanical testing and biodegradation studies. PLA/PHB blends showed a good distribution of the major components and absence of phase separation. XRD showed that the original crystal structure of PHB in the PLA75/PHB25 blend had been disturbed. DSC curves of PLA or PHB with plasticizer exhibited one T g value, indicating that both major blend components are miscible. The T g values also decreased with increased amount of plasticizer and showed good correlation to the Fox Equation, The melting temperature of PLA and PHB blends mostly did not change with an increase in plasticizer content, and the thermal stability of PLA and PHB was not affected. Also, the elongation at break of the PLA/PHB blend was greatly improved with the addition of plasticizer. In addition, in preliminary biodegradation studies carried in natural compost neat PHB showed some biodegradation, whereas the samples containing PLA did not experience a substantial biodegradation. This last aspect is worthy of further investigation in a more comprehensive and detailed approach.
Keywords: Poly(lactic acid); Poly(3-hydroxybutyrate); Blend; Plasticizer; Thermal stability; Mechanical properties;

The thermal and photolytic decomposition of poly(propylene carbonate) (PPC) in the presence of a photoacid generator (PAG) was studied. The mechanism of previously observed shifts in the decomposition temperature of PPC was investigated. The decomposition temperature of PPC can be altered when PPC/PAG films contact copper metal. X-ray photoelectron spectroscopy (XPS) analysis showed that a small amount Cu(I) was incorporated into the PPC/PAG film causing the increased stability and the Cu(I) concentration was similar to that of the PAG. PPC/PAG temperature stability was studied for a number of iodonium and sulfonium-based PAGs. Every iodonium-based PAG showed a PPC decomposition temperature shift and no sulfonium-based PAG showed the thermal stability effect. It appears that Cu(I) interacts with iodonium in the cation of the PAG causing a change in the acid creation mechanism of the PAG.
Keywords: Sacrificial polymer; Poly(propylene carbonate); Thermal stability; Iodonium; Metal ion coordination; Microelectronics;

Poly(trimethylene terephthalate) (PTT) was depolymerized in hot compressed water (HCW) using a fused-silica capillary reactor (FSCR) and a batch-type autoclave reactor. The phase behavior of PTT in water during the heating, reaction, and cooling processes was observed in an FSCR with a microscope and recorded by a digital camera. It was found that PTT can dissolve in water in a temperature range of 240–320 °C and form a homogeneous aqueous solution. The effects of the reaction temperature (240–320 °C) and reaction time (5–60 min) were evaluated in a batch-type autoclave reactor. The main depolymerization products of PTT were terephthalic acid (TPA) and 1,3-propanediol (1,3-PDO), which were identified by liquid chromatography mass spectrometry, Fourier-transform infrared spectroscopy, gas chromatography mass spectrometry, Raman spectroscopy, and quantified by high-performance liquid chromatography as well as gas chromatography. Additionally, it was found that 1,3-PDO was converted to 1,5-dioxocane partly in the presence of TPA. Under optimal reaction conditions, i.e. 300 °C, 15 min, with a water/PTT ratio of 8:1 (w/w), complete depolymerization was achieved, and the yields of TPA and 1,3-PDO reached 90.5% and 69.03%, respectively. Based on the results, a reaction mechanism for PTT depolymerization in HCW was proposed.
Keywords: Depolymerization; Poly(trimethylene terephthalate); Hot compressed water; Sub-critical water; Phase behavior;

Degradation of polydopamine coatings by sodium hypochlorite: A process depending on the substrate and the film synthesis method by Doriane Del Frari; Jérôme Bour; Vincent Ball; Valérie Toniazzo; David Ruch (1844-1849).
Polydopamine coatings are promising new versatile coatings able to be deposited on almost all kinds of materials. Such films synthesized either by oxygenation or by electrochemistry on indium tin oxide (ITO) and glassy carbon substrates, were degraded by an oxidizing sodium hypochlorite solution. Films were successively immersed in a sodium hypochlorite solution (1 g/L) during different times. The characterizations of film degradation were made by XPS spectroscopy and AFM. They confirmed a homogeneous degradation of polydopamine, due to an oxidation reaction. The influence of the synthesis method and the nature of the substrate on the polydopamine degradation were also studied in this paper: coatings deposited on ITO by oxygenation degrade much faster than those deposited on glassy carbon or by electrochemistry. This suggests that the adhesion of the polydopamine films and their stability is markedly dependant on the used substrate (ITO vs. glassy carbon) as well as on the deposition method (oxygenation vs. electrochemistry), whereas the film thickness reached during deposition is almost substrate independent.
Keywords: Degradation; Polydopamine; Oxygenation; Electropolymerization; Sodium hypochlorite;