Polymer Degradation and Stability (v.97, #5)

Synthesis and properties of an epoxy resin containing trifluoromethyl side chains and its cross-linking networks with different curing agents by Zhongguo Liu; Gang Zhang; Zhuang Liu; Hongcheng Sun; Chengji Zhao; Shuang Wang; Guibin Li; Hui Na (691-697).
The epoxy resin with a trifluoromethyl side chain, (3-trifluoromethyl) phenylhydroquinone epoxy resin (3F-PQE), was synthesized via a three-step procedure. The chemical structures were confirmed by FT-IR, 1H NMR, 13C NMR and elemental analysis. A series of trifluoromethyl epoxy networks has been prepared with four curing agents: poly (propylene glycol) bis (2-aminopropy) ether (D230), 2-methylimidazole (2MI), 4, 4-methylene-dianiline (DDM) and phthalicacidanhydride (PA). All samples exhibited excellent thermal stabilities (the decomposition temperature of 5% weight loss (Td)) ranged from 335 to 362 °C in N2 and 291–355 °C in air). The 3F-PQE-DDM sample showed the highest T g of all the samples. Moisture absorption of 3F-PQE-DDM and 3F-PQE-PA at 80 °C for 24 h was no more than 1 wt %. The cured fluorinated epoxy resins exhibited that the contact angles were more than 90°, which is the hydrophobic properties.
Keywords: Epoxy resin; Trifluoromethyl; Thermal stability; Glass-transition temperature; Contact angle;

Novel low phosphorus-content bismaleimide resin system with outstanding flame retardancy and low dielectric loss by Xiangxiu Chen; Aijuan Gu; Guozheng Liang; Li Yuan; Dongxian Zhuo; Jiang-tao Hu (698-706).
A novel modified bismaleimide resin system (BDP) with significantly improved flame retardancy and decreased dielectric loss was successfully prepared by copolymerizing 4,4′-bismaleimidodiphenyl methane (BDM) with 2,2′-diallyl bisphenol A (DBA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Compared with BDM/DBA resin, BDP resin has obviously different crosslinked structure, and thus simultaneously improved dielectric properties and flame retardancy. Most attractively, with a very low content of phosphorus element, the BDP resins show significantly improved flame retardancy. For example, when the content of phosphorus is as low as 0.5 wt%, the flame retardancy of BDP resin is evaluated to be UL94 V-0 level, while that of BD resin is classified as UL94 V-1 level; in addition, the total heat release (THR) of BDP resin reduces to about 61% of that of BD resin, and similar phenomenon is also observed on the weight ratio of CO/CO2. This outstanding flame retardancy of BDP resins is attributed to the attractive phosphorus-nitrogen synergistic effect. The main flame retardancy mechanism of BDP resins is evaluated to be condensed phase mechanisms. On the other hand, BDP resins exhibit improved dielectric properties; specifically, the dielectric constant and loss at 1 GHz of BDP resin with 19.7 wt% of phosphorus are 2.90 and 0.0058, only about 92% and 51% of that of neat BD resin, respectively. These interesting results demonstrate that the co-reaction of DOPO with BD resin is important, and the method proposed herein is a new approach to develop high performance resins with attractive flame retardancy and dielectric properties.
Keywords: Flame retardancy; Synergistic effect; Phosphorus; Bismaleimide; Dielectric property;

The synergistic effects of lanthanum oxide (La2O3) on the thermal degradation and flame retardancy of a novel intumescent flame retardant polypropylene composites (PP/IFR) were investigated by the means of limited oxygen index (LOI), catalytic effectivity analysis (CAT-EFF), vertical burning test (UL-94), thermogravimetric analysis (TGA), cone calorimeter test (CCT), scanning electron microscopy (SEM), Laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). It was found that a small amount of La2O3 could enhance the LOI value of the PP/IFR composite dramatically and the materials can pass the UL-94 V-0 rating test. The catalytic effectivity (CAT-EFF) results showed that when 1wt.% La2O3 was added, it had the highest CAT-EFF, and could promote the LOI value of the composites from 27.1 to 32.5. The TGA data revealed that La2O3 could change the degradation behavior of the IFR and PP/IFR, enhance the thermal stability of the PP/IFR systems at high temperature and increase the char residue, especially in the air environment. The presence of La2O3 could change the decomposition behavior of the PP/IFR, and enhance the fire retardant performance, resulting consequently in a great reduction in peak heat release rate (p-HRR), total heat release (THR), smoke production rate (SPR) and total smoke production (TSP) of the PP/IFR system. The morphological structures observed by digital photos and SEM demonstrated that La2O3 could promote to form the more continuous and more compact intumescent char layer. The LRS measurements illustrated that the strength of the outer surface of the char residue with La2O3 is enhanced. The XPS analysis indicated that La2O3 can remain more O, N and P to enhance the strength of outer and inner char. Thus, a suitable amount of La2O3 plays an excellent synergistic effect with IFR on the flame retardancy, thermal degradation at high temperature, smoke suppression of IFR composites, and promotes the formation of compact char structures in the PP/IFR composites.
Keywords: Synergistic effect; Lanthanum oxide; Flame retardancy; Thermal degradation; Intumescent flame retardant; Polypropylene;

This study evaluated the influence of γ irradiation and ethylene oxide sterilization on the release characteristics of vancomycin from biodegradable poly[(d,l)-lactide-co-glycolide] (PLGA) composite beads. Biodegradable composites incorporating vancomycin were prepared using a compression-sintering method. They were then subjected to various doses of γ irradiation and ethylene oxide treatment. After sterilization, the composites were placed in 3 ml of phosphate buffered saline and incubated at 37 °C. An in-vitro elution method and a high-performance liquid chromatography (HPLC) were used to characterize the release rates of the antibiotics over a 30-day period. A bacterial inhibitory test was also employed to examine the bioactivity of released antibiotics. All sterilizations were found to result in a decrease of the crystallinity of the polymeric materials, as well as the total release period of antibiotics. The ethylene oxide treatment led to a significant change of the morphology of the composites. Furthermore, the results suggest that the biodegradable composites can release high concentrations of antibiotics (well above the minimum inhibitory concentration) in-vitro for up to 28 days after γ irradiation of less than 25 kGy.
Keywords: Biodegradable composites; Sterilization; γ irradiation; Ethylene oxide; Release characteristics; Vancomycin;

Effect of TiO2 nanoparticles on the long-term hydrolytic degradation behavior of PLA by Yan-Bing Luo; Xiu-Li Wang; Yu-Zhong Wang (721-728).
The longer-than-one-year hydrolytic degradation of poly (lactic acid) (PLA)/TiO2 nanocomposites was investigated in phosphate buffer solution of pH 7.4 at 37 °C so as to elucidate the effect of nanofillers on the degradation characteristics of PLA. The temporal changes in appearance, water absorption, number-average molecular weight (Mn), glass transition temperature, melting temperature, and crystallinity of the samples were traced. The results showed that the heterogeneous degradation and bulk-erosion were general mechanisms for PLA and its TiO2 nanocomposites. The change in surface morphology and molecular weight after hydrolysis revealed that the hydrolysis of nanocomposites occurred at the interface of PLA matrix and nanofillers, and the degradation rate was accelerated by the addition of the TiO2 nanofillers. The dispersion of nanofillers in polymer matrix affected the water absorption and degradation rate. The rapid increase of crystallinity also affected the degradation rate of nanocomposites. The present study suggested that the hydrolyzability of PLA could be controlled by adding TiO2 nanoparticles.
Keywords: PLA; TiO2; Nanocomposites; Hydrolysis; Degradation;

Thermal degradation kinetics of PP/OMMT nanocomposites with mPE and EVA by Jordana Palacios; Rosestela Perera; Carmen Rosales; Carmen Albano; José María Pastor (729-737).
The thermal properties and the kinetics of thermal degradation of nanocomposites of polypropylene (PP) and montmorillonite (OMMT) and an ethylene-co-vinyl acetate copolymer (EVA) as a minority phase, including a third elastomeric component represented by poly(ethylene-co-octene) (mPE) were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Two maleic anhydride modified PP (PP-g-AM), one of them commercial and the other one prepared in our laboratory, were used as compatibilizers. The expected nucleating effect of the organoclay in the nanocomposites and the increase on crystallization temperature was observed. The degradation kinetic parameters were obtained using the Coats – Redfern integral method to obtain the reaction order and the E2 function methodology to calculate the activation energy. The PP/OMMT nanocomposites with mPE or EVA exhibited higher degradation temperatures and activation energies than the neat PP and also a higher decomposition temperature than the PP nanocomposites without the elastomeric minority phase. The employment of the commercial compatibilizer generated more exfoliated structures on the ternary nanocomposites that contributed to a better thermal stability. The degradation mechanisms involve crosslinking, chain branching and chain scission reactions for the ternary PP/OMMT/mPE nanocomposites and an additional accelerated deacetylation process for the ternary PP/OMMT/EVA nanocomposites.
Keywords: PP ternary nanocomposites; Blends; Thermal stability; Thermal degradation kinetics;

Effect of urea additive on the thermal decomposition kinetics of flame retardant greige cotton nonwoven fabric by Sunghyun Nam; Brian D. Condon; Robert H. White; Qi Zhao; Fei Yao; Michael Santiago Cintrón (738-746).
Urea is well known to have a synergistic action with phosphorus-based flame retardants (FRs) in enhancing the FR performance of cellulosic materials, but the effect of urea on the thermal decomposition kinetics has not been thoroughly studied. In this study, the activation energy (E a ) for the thermal decomposition of greige cotton nonwoven fabrics treated with various amounts of urea at fixed contents of diammonium phosphate (DAP), was measured using the Kissinger, Friedman, and Flynn-Wall-Ozawa methods. The three methods produced consistent results revealing a dual function of urea additive in the kinetics depending on the concentration. Those functions were correlated with the synergistic FR action of urea. Up to a certain concentration, the addition of urea raised the overall E a . The steeply increasing trend of E a observed in the low conversions indicates that urea enhanced the multiple reactions of DAP, which were confirmed by 31P MAS NMR and ATR-FTIR. Higher concentrations of urea additive, however, significantly lowered the E a values for both the DAP reactions and the decomposition of cellulose. As evidenced by a slight reduction in char yield, the decrease in E a suggests that the excess of urea acted to facilitate the diffusion of volatiles and heat transfer in the cotton structure, resulting in catalyzing the decomposition of cellulose at low temperatures. The latter function was predominant when the greater synergistic FR action of urea was achieved.
Keywords: Cotton; Flame; Nitrogen phosphorus synergy; Kinetics; Thermogravimetry; NMR;

Protein-based, biodegradable hybrid nanofibers were fabricated by electrospinning an aqueous solution of soy protein isolate (SPI)/Poly vinyl alcohol (PVA) mixtures. The ratio of SPI to PVA and pH level in the solution was experimentally designed for the preparation of spinning dopes. The effects of SPI content and pH level on the mechanical and biodegradable properties of electrospun SPI/PVA hybrid nanofiber mats were studied. The mechanical strength of the electrospun nanofiber mats decreased gradually as the SPI content increased. At the same SPI content, a higher pH level of the solution increased the denaturation of the protein and produced thinner fibers, leading to substantial reduction in the mechanical strength. The composting process was monitored for about one month to evaluate the biodegradability of the electrospun SPI/PVA hybrid nanofiber mats. The degradation rate of the electrospun SPI/PVA hybrid nanofiber mats was largely influenced by the amount of SPI exposed to the microorganism environment. This study suggests that the biodegradation rate and thus the lifetime of SPI-based nanofibers can be controlled by changing the ratio of SPI to PVA and also the distribution of SPI in electrospun SPI/PVA hybrid nanofibers.
Keywords: Soy protein isolate; Poly vinyl alcohol; Electrospinning; Green nanofiber; Biodegradation; Composting;

In the present study the highly flammable nature of isotactic polypropylene (iPP) is suppressed by incorporating the inorganic flame retardant filler, magnesium hydroxide (MH), and the flame-retardant polymer, poly(2,6-dimethyl-1,4-phenylene ether) (PPE). In the iPP/PPE/MH composite, the MH is selectively dispersed in the PPE domain with the average domain size about 1.5 μm. However, upon addition of polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SEBS), the MH moves to the SEBS phase located at the interface between iPP and PPE, whereas the domain size of PPE was drastically reduced to less than 0.3 μm and the domains tended to form aggregates. It was demonstrated that interface modification by dodecanoic acid as a surface treatment reagent for MH and by SEBS as a compatibilizer between iPP and PPE significantly improves the macroscopic mechanical and thermal properties of the composites in a synergetic manner. Cone calorimetry tests revealed that incorporation of PPE and SEBS drastically reduces the peak heat release rate and that PPE facilitates char formation, which serves as a physical barrier for heat flux from the flame to the polymer surface, as well as a diffusion barrier for gas transport to the flame. The idealized mechanism of flame retardancy is also proposed for the iPP/PPE/MH composites.
Keywords: Polypropylene; Poly(phenylene ether); Composite; Interface;

The thermo-mechanical degradation of acrylonitrile-chlorinated polyethylene-styrene (ACS) terpolymer was investigated by means of high temperature shearing in a Haake Rheomixer. The results showed that the chain scission takes place in the poly(styrene–acrylonitrile) (SAN) component while the residual rate of the ACS resin after extraction of SAN increases gradually with increasing the shearing time. FTIR and DSC analysis confirmed that the increase in the residual rate is due to the thermo-mechanical degradation-induced grafting of SAN to the CPE chain. SEM and TEM observation revealed a remarkable reduction in the CPE domain size and formation of a salami-like structure in which many CPE-g-SAN micelles are embedded in the fine CPE domain. These changes result in a significant improvement in the impact strength of the ACS resin. The mechanism of the thermo-mechanical degradation-induced grafting and the morphology change were discussed.
Keywords: Acrylonitrile-chlorinated polyethylene-styrene (ACS) terpolymer; Thermal degradation; Grafting; Reactive blending;

Crystal structure of cutinase Est119 from Thermobifida alba AHK119 that can degrade modified polyethylene terephthalate at 1.76 Å resolution by Kengo Kitadokoro; Uschara Thumarat; Ryota Nakamura; Kousuke Nishimura; Hajime Karatani; Hideyuki Suzuki; Fusako Kawai (771-775).
We determined the crystal structure of a cutinase from Thermobifida alba AHK119 (Est119) at a resolution of 1.76 Å. The overall structure of Est119 displays a typical α/β-hydrolase fold consisting of a central twisted β-sheet of nine β-strands that are flanked by nine α-helices on both sides. The refined model contains two monomers in the asymmetric unit that form a dimer interface; a polyethylene glycol fragment is bound in the interface. Polyethylene glycol-binding site on the protein may suggest a glycol-binding site. A putative polymer-recognizing groove is observed to continue through the catalytic pocket. Water molecules are bound to hydrophilic amino acids along the groove, indicating the alternating pattern of polar and hydrophobic residues.
Keywords: Est119; Cutinase; Polyester-degrading enzyme; Thermobifida alba; Structural biology; Crystal structure;

Enhanced thermal stability of polychloroprene rubber composites with ionic liquid modified MWCNTs by Kalaivani Subramaniam; Amit Das; Liane Häußler; Christina Harnisch; Klaus Werner Stöckelhuber; Gert Heinrich (776-785).
Thermal degradation of polychloroprene rubber (CR) composites based on unmodified and ionic liquid modified multi-walled carbon nanotubes (MWCNTs) is studied using thermogravimetric analysis (TGA) in aerobic and anaerobic (nitrogen) conditions. The CR and its composites exhibit three stage and four stage degradation in nitrogen and air respectively. The presence of unmodified CNTs alone does not improve the thermal stability of composites to a great extent whereas a reasonable enhancement is observed in case of modified CNTs/CR composites which can be attributed to the interfacial interactions of ionic liquid/modified tubes with CR and to the fine dispersion of modified tubes in CR. The degradation products of CR and its composites were analysed using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and the mechanism of degradation is discussed. Non-isothermal degradation kinetics were studied using Kissinger and Flynn-Wall-Ozawa methods and the activation energy of thermal decomposition is found to be high for modified CNTs/CR composites. Isothermal degradation of modified CNTs/CR composites at 290 °C for 30 min in nitrogen reveals decreased weight loss (14%) as opposed to CR (31%) and unmodified CNTs/CR composites (30%). The combustion behaviour of the composites was dealt using microscale combustion calorimeter (MCC) and the flame retardancy of the composites is discussed.
Keywords: Polychloroprene rubber; Thermal degradation; Carbon nanotubes; Ionic liquids; Elastomeric composites; Thermal stability;

Impact of fungi on contemporary and accelerated aged wool fibres by Katja Kavkler; Andrej Demšar (786-792).
In the present study we observed structure and mechanical properties of fungal deteriorated wool textiles. Contemporary non-aged and accelerated aged wool textiles were inoculated with six different fungal strains, which were selected among several strains isolated from museum textile objects. Inoculated wool samples were incubated 8 and 20 weeks and then analyzed. Some structural changes occurred, which influenced mechanical properties of the fibers in a negative way. Several mechanical damages were observed after inoculation and tensile properties of the threads decreased. Accelerated aged fibers were more affected by fungi than non-aged fibers.
Keywords: Wool; Biodeterioration; Fungi; Mechanical changes; Structure;

Thermal and flammability properties of polypropylene/carbon black nanocomposites by Xin Wen; Yujie Wang; Jiang Gong; Jie Liu; Nana Tian; Yanhui Wang; Zhiwei Jiang; Jian Qiu; Tao Tang (793-801).
Polypropylene/carbon black (PP/CB) nanocomposites were prepared by melt compounding to investigate the effect of nanofiller loadings on the thermal and flammability properties of PP. The obtained nanocomposites displayed not only dramatically enhanced thermal stability both under nitrogen and in air, but also improved flame retardancy to some extent. Moreover, the higher the loading level of CB, the better was the improved effect. This enhanced mechanism was attributed mainly to trapping of peroxy radicals by CB nanoparticles at elevated temperature to form a gelled-ball crosslinked network, which act as a barrier to both heat and mass transfer. The thermal-oxidation cross-linking reaction was supported by the results of rheological properties, gel measurements and FTIR analysis.
Keywords: Carbon black; Flame retardancy; Nanocomposite; Polypropylene;

Modelling degradation of PTFE under electron irradiation by A. Palov; H. Fujii; Yu. Mankelevich; T. Rakhimova; M. Baklanov (802-809).
The electron slowing-down in polytetrafluoroethylene (PTFE) was investigated on the basis of a proposed physical model considering the elastic and inelastic electron scattering on bound fluorine and carbon atoms, electron–phonon scattering and electron trapping. The resonance dissociative and non-dissociative electron attachment cross sections for с–C4F8 molecule were suggested as a basis set to describe the electron trapping in PTFE. Modification of the basis set was carried out by comparison of the calculated total secondary electron yield (TSEY) from PTFE with its experimental values for electron beam energies of 100 eV–5 keV. The electron trajectories were simulated on the base of Monte Carlo technique up to the electron dissociative or non-dissociative attachment. It was shown the calculated positions of electron traps because of dissociative attachment to give the distribution of the broken C–F bonds which cause the (–CF2–) chain scission and appearance of vinyl groups, and, consequently, the PTFE degradation. The calculated TSEY as a function of the large (>80°) incident electron angles demonstrated a sharp drop for high energy electron beams that has never been published anywhere.
Keywords: Secondary electron emission; Trapping; Charge distribution; Charge-up;

The present work is to investigate thermally reworkable cycloaliphatic epoxy resins containing two or three phosphate groups per molecule for electronic and LED encapsulations. Different form the conventional reworkable epoxy resins, the epoxides here were cured via thermo-initiated cationic polymerization at a moderately low temperature. The experimental results showed that the incorporation of thermally-labile phosphate groups made the cured products start to degrade at around 220 °C, and lose over 50% weight after thermal treatment at 250 °C for only 3 min. The residue could be conveniently removed, exhibiting excellent reworkable properties of thermosetting epoxy resins. More importantly, through the copolymerization of phosphate-containing epoxide with commercial ERL-4221, the degradation temperatures could be readily tuned within the desirable reworking temperature range from 200 °C to 300 °C by adjusting the ratio of two monomers. The comparison of degradation behaviors and mechanism as well as the physical properties between the cationic and anhydride curing methods were studied by means of thermogravimetry, infrared spectroscopy and dynamic mechanical analysis in detail.
Keywords: Cycloaliphatic epoxide; Cationic polymerization; Thermal degradation; Electronic packaging;

Controlled chemical degradation of natural rubber using periodic acid: Application for recycling waste tyre rubber by Faten Sadaka; Irène Campistron; Albert Laguerre; Jean-François Pilard (816-828).
Presently, the disposal of thousands of tons of waste tyres produced every year in the whole world is a major environmental problem. Since tyre rubbers do not decompose easily on account of crosslinking and stabilizers, the processing of the waste tyre rubber constitutes a significant technical challenge. This work describes the use of periodic acid for the controlled one-pot oxidative cleavage of carbonyl telechelic cis-1,4-oligoisoprenes (CTNR) and natural rubber (NR) as model compounds and the application of this method to the degradation of ground waste tyre rubber. Average molecular weight analysis of the degraded material indicates that the reaction time and the periodic acid quantity can be used to control the degree of breakdown; we obtained materials in the average molecular weight range of 700–5000 g mol−1. The processed material shows ketone and aldehyde groups at the chain ends. Degradation studies of waste tyre rubbers were also carried out using this oxidative cleavage by periodic acid, to achieve carbonyl telechelic oligomers. Well-defined structures were obtained with an average molecular weight from 3000 to 7000 g mol−1 according to the periodic acid/waste tyres rubber ratio used.
Keywords: Rubber; Recycling; Chemical degradation; Oxidation; Periodic acid;

Influence of nano-graphite platelet concentration on onset of crystalline degradation in polylactide composites by Esmaeil Narimissa; Rahul Gupta; Madhu Bhaskaran; Sharath Sriram (829-832).
Nano-carbon fillers offer enhanced thermal and mechanical properties to biodegradable polymer matrices. In this work, we study extruded nano-graphite platelet (NGP) loaded polylactide (PLA) using thermal, mechanical, and microstructural analysis techniques. The influence of NGP loading on polymer crystallization, the Young’s modulus, tensile strength, and crystallography of the polymer composite are determined. We establish the optimal NGP loading concentration beyond which agglomeration effects degrade crystalline and structural properties of PLA-NGP composites.
Keywords: Polylactide; PLA; Nano-graphite platelet; Mechanical properties; Loading concentration; Crystallisation;