Polymer Degradation and Stability (v.111, #C)

Chlorine dioxide resistance of different phenolic antioxidants in polyethylene by W. Yu; T. Reitberger; T. Hjertberg; J. Oderkerk; F.R. Costa; V. Englund; U.W. Gedde (1-6).
A series of polyethylene tape samples containing 8 different phenolic antioxidants (concentration = 0.1 ± 0.01 wt.%) were exposed to water containing 10 ppm chlorine dioxide buffered to pH = 6.8 at 70 °C for different periods of time. The degradation rate and depletion time of the antioxidants in the polyethylene were obtained by oxidation induction time measurements using DSC. The majority of the tape samples (6 out of 8) showed a simple behaviour: the rate of antioxidant loss decreased and the antioxidant depletion time increased in linear fashion with increasing initial molar concentration of phenolic groups in the polymer. The tape that contained Hostanox O3 had a high initial phenolic concentration but it exhibited a short antioxidant depletion time due to the limited solubility of this antioxidant in polyethylene. Tapes containing Irganox 1330 and Cyanox 1790 showed antioxidant depletion times that were almost twice that of the other antioxidants with the same initial molar concentration of phenolic groups.
Keywords: Polyethylene; Phenolic antioxidants; Chlorine dioxide; Antioxidant degradation;

Monitoring the effect of chlorine on the ageing of polypropylene pipes by infrared microscopy by Subin Damodaran; Tobias Schuster; Karsten Rode; Abhishek Sanoria; Robert Brüll; Mirko Wenzel; Martin Bastian (7-19).
The effect of hot water and chlorinated water at 95 °C on differently nucleated random polypropylene pipes was analysed with respect to the chemical changes occurring to the polymer and antioxidants (AOs). Infrared microscopy (μFT-IR) was used to monitor the loss of the AOs as well as to identify their degradation products during ageing. For the quantification of the primary AO, 1, 3, 5-Tris (3, 5-di-tert-butyl-4-hydroxybenzyl)-2, 4, 6-methylbenzene (AO-13) in a mixture with Pentaerythritol tetrakis (3-3, 5-di-tert-butyl-4-hydroxyphenyl) propionate (AO-18) and the processing stabiliser tris(2,4-di-tert-butylphenyl) phosphate (PS-2) in PP-R, a new μFT-IR method has been developed and the results were supported by extraction → HPLC. Degradation products of phenolic AOs were profiled for the first time across the pipe wall using μFT-IR. Time and space resolved content of AO-18 and AO-13 left in the pipes with time was quantified. For both ageing conditions, AO-18 and AO-13 exhibited a bilateral loss from the wall of PP-R1 whereas in PP-R2, the loss was mainly unidirectional. Oxidative induction time (OIT) measurements of mechanically prepared samples across the pipe wall also validate the bilateral and unidirectional loss profiles of AOs. The loss in average molar mass of the polymer as a result of chain scission was analysed by gel permeation chromatography. The linear relations drawn for molar mass against the relative content of AOs explain that the deterioration of the pipes was accelerated with chlorinated water. From the substantial differences in the AO loss coefficients which were calculated using μFT-IR, it can be speculated that nucleation of the PP-R exerts an influence on the depletion of AOs.
Keywords: Chlorination; Polypropylene; Degradation; Ageing; Antioxidant; IR microscopy;

Synthesis, characterization and water retention study of biodegradable Gum ghatti-poly(acrylic acid–aniline) hydrogels by Kashma Sharma; Vijay Kumar; B.S. Kaith; Vinod Kumar; Sudipta Som; Susheel Kalia; H.C. Swart (20-31).
A natural polysaccharide, Gum ghatti (Gg), was modified to prepare cross-linked hydrogels using the grafting method initiated by gamma-radiation. Acrylic acid (AA) and aniline monomers were used as the grafted monomers. Grafted copolymer based on Gg and AA was synthesized using N, N′-methylene-bis-acrylamide as a cross linker. The effects of monomer and cross linker concentration, gamma dose and the amount of solvent on the grafting percentage and percentage swelling were investigated. The degree of grafting and percentage swelling were found to be greatly dependent on the reaction parameters. Whereas, aniline monomer was absorbed into the network of Gg-cl-poly(AA), followed by a polymerization reaction between aniline monomer initiated by gamma-radiation. Biodegradation of synthesized hydrogels was also investigated using a composting soil method and Gg-cl-poly(AA-ipn-aniline) showed better degradation efficiency in comparison to Gg-cl-poly(AA). Furthermore, the degraded sample was characterized by FT-IR and surface morphology by SEM. Our results showed that Gg-cl-poly(AA) degraded at a rate of ∼6.1% after 6 days, whereas the degradation rate for Gg-cl-poly(AA-IPN-aniline) was ∼10%. Application of hydrogels to improve the water retention properties of different soils was studied for agricultural purposes and found that the IPN hydrogel can improve the moisture retention capacity of soil for cultivation.
Keywords: Graft copolymer; Biodegradability; Moisture retention; Methyl orange;

Processing degradation of polypropylene-ethylene copolymer-kaolin composites by a twin-screw extruder by Lip Teng Saw; Du Ngoc Uy Lan; Nor Azura Abdul Rahim; Ab Wahab Mohd Kahar; Cao Xuan Viet (32-37).
Degradation resulting from the extrusion processing of polypropylene-ethylene kaolin composites (PPE/kaolin) was investigated. Degradation of the polymer matrix was evidenced by the formation of hydroxyl, carbonyl and alkene groups, as detected by Fourier transform infrared spectroscopy measurements. These measurements also confirmed that the filler loading accelerated the degradation process and resulted in scission of high-molecular weight chains. These degradations resulted in significant reductions in the thermal stabilities of the composites, whereas the rheological behaviours and mechanical properties of the composites were strongly influenced by the filler contents rather than by degradation.
Keywords: Polypropylene copolymer-kaolin composites; Thermo-mechanical degradation; Processing degradation; Twin-screw extruder;

Study on the thermal degradation behavior of sulfone-containing polybenzoxazines via Py-GC-MS by Huachuan Zhang; Wu Gu; Rongqi Zhu; Qichao Ran; Yi Gu (38-45).
A stepwise-temperature testing method by Py-GC-MS was applied to study the thermal degradation processes of two polybenzoxazines containing sulfone group. This new method can give lots of information about degradation gas products and the variation of chemical structures in bulk. The results showed that (1) for 4,4′-sulfonylbiphenol/aniline based polybenzoxazine (PBS), the thermal degradation fragments tend to form heterocyclic compounds in bulk phase; (2) for 4,4′-sulfonyldianiline/phenol based polybenzoxazine (PBAS), crosslinked phenol and aniline structures were preferentially produced from the thermal decomposition fragments in bulk phase. Therefore, it means that PBS is more likely to generate thermally stable fused rings like chars in bulk during pyrolysis process. As the result, a deep insight into the pyrolysis process of polybenzoxazines was achieved by this method, which probably provides a new way to study the degradation behavior of other polymers.
Keywords: Polybenzoxazine; Thermal degradation; Py-GC-MS; Pyrolysis product; Carbonization reaction;

Sheets of low-density polyethylene (LDPE) were subjected to photo-oxidation in the presence of air using a xenon lamp to irradiate the samples for times between 1 day and 6 weeks. The formation of long-chain branching (LCB) up to one week of degradation and the competition between chain scission and crosslinking at longer periods of radiation were investigated by rheological characterization, Fourier transform infrared spectroscopy, and the solvent extraction method (Rolón-Garrido and Wagner. Polym Degrad Stabil 2014, 99:136, Rolón-Garrido and Wagner. J Rheol 2014, 58:199). In the present contribution the same samples are studied by size exclusion chromatographic characterization using triple detection (concentration, light scattering and viscosity). The gel content is determined by filtration followed by the analysis of the soluble polymer fraction. The influence of photo-oxidation time on the molecular weight distribution (molar masses and polydispersity), the mean square radius of gyration and the intrinsic viscosity contraction factors is discussed. The results are correlated with the model parameters (β and f max 2 ) of the molecular stress function (MSF) theory, used to describe quantitatively the rheological data in uniaxial elongation. It is verified that LCB occurs as an aside process, which up to one week of degradation dominates over chain scission, before gelation plays a critical role. It is confirmed that the model parameter β correlates with the gel content, which reflects the competition between chain scission and crosslinking, while f max 2 is found to correlate with the experimentally determined contraction factors. By comparing the data of this study with those obtained earlier for polystyrene comb melts with well defined structure, the influence of the branching frequency (i.e. the number of branch points per 1000 carbon atoms) on f max 2 becomes evident.
Keywords: Contraction factor; Triple detection; Chromatography; Rheology; MSF model; Photo-oxidative degradation;

Absorption kinetics and swelling stresses in hydrothermally aged epoxies investigated by photoelastic image analysis by Giuseppe Pitarresi; Michele Scafidi; Sabina Alessi; Maria Di Filippo; Claude Billaud; Giuseppe Spadaro (55-63).
The present work proposes an experimental optical methodology able to measure the transient swelling stresses induced by the water uptake ageing of polymers. In particular, the work describes the implementation of a Photoelastic technique to quantify internal stresses arising during the hydrothermal ageing of cast epoxy samples. The material investigated is a model DGEBA/DDS epoxy system. Curing and post-curing cycles have been optimised in order to obtain a fully cured, high T g, and completely stress free initial condition. Rectangular beam samples were then left in a hydrothermal bath at 90 °C, and regularly monitored by gravimetric and photoelastic analyses. The quantitative evolution of stresses induced by water ingress was obtained by a Photoelastic Stress Analysis technique applied during water absorption, and successive desorption in controlled conditions. The evolution of stresses is correlated with gravimetric data, allowing to gain a new insight to investigate the complex swelling and diffusion kinetics of water ingress into thermoset polymer networks.
Keywords: Hydrothermal ageing; Swelling stresses; Photoelastic stress analysis; Thermosetting resin;

Enhanced thermal stabilization and reduced color formation of plasticized Poly(vinyl chloride) using zinc and calcium salts of 11-maleimideoundecanoic acid by Fiaz S. Mohammed; Mark Conley; Amber C. Rumple; Steven R. Saunders; Jackson Switzer; Esteban Urena-Benavides; Rani Jha; Jeffrey M. Cogen; Bharat I. Chaudhary; Pamela Pollet; Charles A. Eckert; Charles L. Liotta (64-70).
Above certain temperatures, untreated PVC undergoes dehydrochlorination to produce conjugated polyenes in the polymer backbone. This is accompanied by formation of color in the polymer. In order to address both the thermally induced dehydrochlorination process and the accompanying color formation the dienophilic zinc and calcium salts of 11-maleimidoundecanoic acid (Zn11M and Ca11M, respectively) were synthesized and employed as stabilizing additives. The stabilizing effect of the Zn11M and Ca11M on PVC was studied at 170 °C in air. Evidence is presented which shows that this combination of salts performs a dual role of reducing both the rates of dehydrochlorination and formation of color in plasticized PVC.
Keywords: Plasticized PVC; Thermal stabilization; Color stability; Epoxidised soybean oil; Maleimide;

Enzymatic degradation of graphene/polycaprolactone materials for tissue engineering by Eoin Murray; Brianna C. Thompson; Sepidar Sayyar; Gordon G. Wallace (71-77).
Graphene/polycaprolactone composites have proven to be promising substrates for biodegradable tissue engineering scaffolds for electro-responsive tissue types. The degradation behaviour of these materials will be critical to any future application. To that end, the effect of chemically converted reduced graphene oxide (CCG) on the enzymatic degradation of graphene/polycaprolactone composites in phosphate buffered saline was examined. Two types of graphene/polycaprolactone composites were tested; a simple blend and our previously developed covalently-linked composites. A number of graphene concentrations of each type were tested. Covalently linked graphene/polycaprolactone (cPCl-CCG) showed a consistent degradation profile maintaining the graphene:PCL ratio throughout the degradation process. However, the mixed blended sample (mixPCl-CCG) showed inconsistent graphene loss indicative of non-homogeneous dispersion throughout the polymer matrix. Increasing the graphene concentration up to 1 wt% did not change the rate of degradation but at higher concentrations degradation was slowed. The degradation products were also shown to be non-toxic to the proliferating cells.
Keywords: Polycaprolactone; Graphene; Enzymatic degradation; Lipase; Composite; Tissue engineering;

Thermo and photo-oxidation of functionalized metallocene high density polyethylene: Effect of hydrophilic groups by M.U. de la Orden; J.M. Montes; J. Martínez Urreaga; A. Bento; M.R. Ribeiro; E. Pérez; M.L. Cerrada (78-88).
Incorporation of a small content of undecenoic acid is proposed as an approach to introduce polar groups within the macromolecular architecture of high density polyethylene-based materials in order to promote an easier degradation after their useful service life. The influence of these hydrophilic groups during thermo and photo-oxidation processes has been then evaluated by several complementary techniques. In addition to different degradation rates, distinct ratios of oxidized species (lactones, ketones, carboxylic acids, esters and aldehydes) are found depending on: a) the initial material (neat high density polyethylene or ethylene-co-undecenoic acid copolymer); b) the type of oxidation (thermo or photoinduced); and c) the absence or presence of a specific prodegradant additive. An important increase of crystallinity has been observed in the final oxidized samples, indicating that the extent of degradation is rather significant.
Keywords: Undecenoic acid; Polyethylene; Oxidation processes; Prodegradant; FTIR; Crystallinity;

Effect of swift heavy ions on an EPDM elastomer in the presence of oxygen: LET effect on the radiation-induced chemical ageing by Y. Ngono-Ravache; Z. Damaj; A. Dannoux-Papin; M. Ferry; S. Esnouf; F. Cochin; G. De Combarieu; E. Balanzat (89-101).
With the aim of understanding the radiation effects of alpha particles on polymers, this paper analyses the role of the heterogeneity of energy deposition, at the nanometric scale, on the radiation-induced oxidation of an ethylene-propylene-diene elastomer based on 1,4 hexadiene (EPDMh). This polymer was irradiated with 20Ne, at various Linear Energy Transfer (LET), in the presence of oxygen. Macromolecular defects such as carbonyls, alkenes and alkynes were monitored on-line, using Fourier Transform Infrared Spectroscopy (FTIR), and their evolution as a function of both LET and irradiation dose were studied.Carbonyl group consists of various chemical functions which absorption bands overlap one another in a limited spectral area. The different components were extracted by curve fitting, allowing monitoring the specific evolution of each of these chemical functions as a function of the irradiation conditions. Among carbonyl containing functions, the creation of ketone groups is the most important.LET influences the alkene radiation chemical yield at initial dose and, apart from trans-vinylene, it also influences the dose evolution of their concentration. Conversely, LET has no significant influence on the total carbonyl concentration.
Keywords: Ethylene-propylene-diene monomer; Irradiation; Ion beam; Oxidation; Linear energy transfer; Carbonyl;

Thermal stability of polypropylene–montmorillonite clay nanocomposites: Limitation of the thermogravimetric analysis by Lays B. Fitaroni; Juliana A. de Lima; Sandra A. Cruz; Walter R. Waldman (102-108).
The development of nanocomposite materials with polymeric matrices, especially those using layered silicates, provides an alternative to composites with conventional fillers. One of the controversial aspects in the scientific literature about polypropylene-montmorillonite nanocomposites (PP/OMMT) regards its thermal stability compared to the PP matrix. The aim of this work is to evaluate the influence of the presence of montmorillonite clay in the degradation of composites, showing the limitations of thermogravimetric analysis (TGA) and emphasizing the importance of complementary analyzes such as differential scanning calorimetry (DSC) and oxidation induction time (OIT). The TGA results showed that the higher the organoclay content, the higher the temperature at which the release of volatiles takes place. However, the OIT results indicated a lower temperature for the onset of exothermic reactions for these materials and consequently the stability of the material is reduced. The use of DSC method simulating conditions of TGA, called oxidation induction temperature or dynamic OIT, was used to evaluate the stability of the composites explaining the divergence between the TGA and OIT results. The thermal analysis results were correlated to organoclay morphology, as evaluated by WAXS. It was concluded that the clay contributed to the beginning of exothermic oxidation reactions and to the kinetics decrease of volatile release and its formation.
Keywords: Thermal analysis; Degradation; Polypropylene; Montmorillonite clay;

Chemical recycling of poly(p-phenylene sulfide) in high temperature fluids by Kenji Okubo; Taichi Sugeno; Hideyuki Tagaya (109-113).
Poly(p-phenylene sulfide) (PPS) is the engineering plastic with high thermal stability. In this study, the effective decomposition reactions of PPS were confirmed in the high temperature fluids. In high temperature water, 50% conversion was attained at 430 °C by adding the basic compound although perfect solubilization could not be attained. However, in high temperature methanol, perfect solubilization was attained by the reaction at 430 °C. It was also confirmed that even by the reaction at 370 °C, conversion reached to 75% by the reaction in methanol for 5 h. Main reaction products of PPS in high temperature fluids were oligomers and monomeric compounds such as thiophenol, diphenyl sulfide, thioanisole and dibenzothiophene.
Keywords: Poly(p-phenylene sulfide); PPS; Chemical recycling; High temperature fluid; Thiophenol;

A novel industrial technique for recycling ethylene-propylene-diene waste rubber by Saeed Ostad Mohaved; Ali Ansarifar; Sakineh Karbalaee Nezhad; Sepideh Atharyfar (114-123).
Recycling waste rubber has gained importance in recent years. Ethylene-propylene-diene rubber (EPDM) is used to manufacture various automotive parts. Reclaiming EPDM rubber waste is a major problem. Waste powder from discarded EPDM automotive parts was devulcanized using an industrial autoclave which provided both heating and high pressure steam. To aid the devulcanization process, 2-mercaptobenzothiazoledisulfide (MBTS) and tetramethylthiuram disulfide (TMTD) devulcanizing agents, and aromatic and aliphatic oils were also used. A portion of the virgin EPDM rubber in a common formulation for the automotive rubber strips was replaced with the devulcanized product to produce blends, which were revulcanized using a semi-efficient (SEV) vulcanization system. The viscosity, cure and mechanical properties of the blends were subsequently determined.This study showed that the oils had different effects on the devulcanization of the waste powder and MBTS was more efficient than TMTD. Replacing 60 wt% of the virgin rubber in the automotive rubber strips with the devulcanized powder had no adverse effect on the scorch and optimum cure times, crosslink density, rate of cure, and viscosity. Also, when 20 wt% of the virgin rubber was replaced, the hardness, compression set, and modulus at 20% elongation were unaffected. It was concluded that the reclaimed rubber could be used in low percentage in order not to extremely deteriorate the mechanical properties of the virgin rubber. This provided a new effective recycling route for the waste EPDM powder in the automotive rubber strips.
Keywords: EPDM waste powder; Devulcanization; Autoclave; Chemicals; Oils;

Preparation and properties of novel polydimethylsiloxane composites using polyvinylsilsesquioxanes as reinforcing agent by Dongzhi Chen; Xiaoyun Hu; Hongwei Zhang; Xianze Yin; Yingshan Zhou (124-130).
A series of novel polydimethylsiloxane (PDMS) composites were prepared using polyvinylsilsesquioxanes (PVS) as reinforcing agent by hydrolytic condensation in the presence of organotin catalyst for the first time. The cross-linked network, morphology, thermal behavior and mechanical properties of these novel PDMS composites were examined by attenuated total reflection infrared spectroscopy (ATR-IR), scanning electron microscope (SEM), thermogravimetric analysis (TGA) and universal tensile testing machine, respectively. Experimental results showed that both thermal and mechanical properties of the PDMS composites were improved greatly by adding PVS. The prominent improvements in thermal and mechanical properties were likely attributed to the reinforcing interaction of PDMS chains and formed particles resulted from PVS self-crosslink. Meanwhile, we also found that with the increment in loading PVS, the resistance to thermal degradation of the PDMS composites in nitrogen atmosphere was enhanced obviously, but their resistance to thermal oxidation in air was not improved apparently. The unobvious improvement in resistance to thermal oxidation of the novel composites was likely due to the catalysis of oxygen.
Keywords: Particle; PDMS composites; Reinforcing agent; Thermal properties; Mechanical properties;

Carbamate end-capped poly(oxymethylene) (POM) copolymer was prepared by reactive extrusion and its stability has been studied by means of thermogravimetric analysis (TGA) both in air and in nitrogen, content of formaldehyde generated (C.F.G) and isothermal weight loss. 4, 4′-diphenylmethane diisocyanate (MDI) was used as an end-cap agent to react with POM molecules during extrusion. MFI results and FTIR spectra indicate that MDI did react with POM, which replaced the labile hydroxyl chain ends with thermally more stable carbamate structures and at the same time increased the molecular weight due to chain extension or possible branching. At low MDI contents (≤1 wt%), end-capping dominated the procedure while chain extension or possible branching occurred more frequently with the increase of MDI, resulting in the continuous reduction of MFI. The presence of branched or crosslinked structure has been verified by the huge difference between weight-average molecular weights deduced from two different methods and melt flow ratio. Side reactions also occurred during extrusion, including the self-polymerization of MDI and reactions between MDI and active-hydrogen containing compounds. According to TGA and C.F.G results, crude M90 extruded with MDI showed superior thermal stability to either original crude M90 or commercial POMs. Similar stabilization effect can be found in commercial M90 and commercial M270 but was less prominent because of their inherently better stability. Such stabilization effect depends largely on end-capping, although some of it should attribute to the roles of formaldehyde absorbent the carbamate structures and side products played. Thermal stability of crude M90 with 1 wt% MDI was further improved through the addition of stabilizer package. After end-capping, the mechanical properties of the POM still remained at an acceptable level.
Keywords: Poly(oxymethylene) (POM); Stabilization; Thermal stability; Degradation; End-cap; Carbamate; Reactive extrusion;

Flame retardant rigid PU foams (RPUF) were prepared by using nanostructured zinc oxide (ZnO), Zeolite and montmorillonite (MMT) combined with traditional phosphorus flame retardants as flame retardant systems. Phosphorus flame retardants were ammonium phosphate (APP) and dimethyl methyl phosphonate (DMMP). The former mainly took effect in condensed phase and the latter mainly played role in gas phase. Nanostructured additives (Nanos) were used to reduce flammable gas release rate and to form highly protective char layer. Research results showed that RPUFs showed different combustion performances, when different Nanos added together with APP and DMMP. ZnO and MMT narrowed the heat release peak of RPUFs, but the intensity of the peak did not reduce. Heat release rate (HRR) of RPUF with Zeolite/DMMP/APP flame retardant system was only 91 kW/m2, which was 56% lower than that of pure RUPF and 26% lower than RPUF only with DMMP/APP flame retardant system, while the limiting oxygen index (LOI) of RPUF reached 29.5%. Further study indicated that structure of Nanos and the interaction between Nanos and phosphorus flame retardants was essential to the effect of flame retardant system.
Keywords: Rigid polyurethane foam; Flame retardant; Nanostructured additives; Mesoporous Zeolite;

The effect of electron beam on sheep wool by Mária Porubská; Zuzana Hanzlíková; Jana Braniša; Angela Kleinová; Peter Hybler; Marko Fülöp; Ján Ondruška; Klaudia Jomová (151-158).
The effect of accelerated electron beam with absorbed doses of 0–400 kGy on wool fibres was investigated. The S-oxidized species, CH groups, secondary structure, temperature and enthalpy of crystal cleavage, strength and elongation of the fibres were monitored. All the properties showed fluctuation with the absorbed dose and are related with change of the secondary structure. Increasing absorbed dose led to progressive predominance of β-sheet over α-helix conformation. The helical conformation favoured generation of S-sulphonate while the β-sheet suppressed it. Changes in the abundance of –CH– groups indicated a slight networking. High absorbed doses resulted in the polypeptide chain breaking and the formation of shorter fragments with helical conformation. The fibre strength was not changed significantly and the elongation, after an initial increase, monotonously decreased due to further denaturation and chain breaking.
Keywords: Sheep wool; Electron beam; Chemical change; Secondary structure; Material testing;

Degradation of styrene butadiene rubber (SBR) in anaerobic conditions by Oscar Vernáez; Sylvie Dagreou; Bruno Grassl; Alejandro J. Müller (159-168).
In this work, the degradation kinetics of styrene butadiene rubber (SBR) in solution was studied in anaerobic conditions. Degradation reactions in the presence of cumene hydroperoxide at different concentrations (0.20, 0.28, 0.32, 0.50, 0.60% in weight), temperatures (60, 75, 85, 100 and 120 °C) and aromatic solvent (10 and 20%) were performed. The fragmentation rates of polymer chains, which define the degradation kinetics, were calculated from the change in molecular weight distribution with time. The degradation was performed in a reactor with anaerobic conditions and the characterization was performed by multiangle light scattering coupled to size exclusion chromatography (SEC-MALS). Using population balance equations, it was possible to calculate the kinetic constants for thermal and thermooxidative degradation. Analysis of the results led to the conclusion that random scission of polymer chains produced by macroradicals formed by hydrogen abstraction constituted the predominant SBR degradation mechanism. Adding alkylbenzene as a transfer agent significantly reduced the degradation.
Keywords: Styrene butadiene rubber; Population balance equations; Polymer in solution; MALS-SEC; Anaerobic degradation;

The influence of processing solvents (water, diethyl ether and ethyl alcohol) on thermal stability of nitrocellulose in smokeless powders was investigated by heat flow calorimetry. Powders subjected to different methods of volatiles removing were used for measurements. The dependence of accumulated heat on temperature was applied for analysis. The results indicate that residual water destabilizes studied powders most of all. Experiments proved that thermal effects during the first step were controlled by reactions of diphenylamine with nitrocellulose decomposition products. The relation between the heat generation constant and the diphenylamine concentration was determined. The analysis of experimental data shows that the stabilizing effect of diphenylamine can be observed only at low extent of nitrocellulose conversion.
Keywords: Nitrocellulose; Smokeless powders; Diphenylamine; Processing solvents; Heat flow calorimetry; Thermal stability;

Biodegradation of waste PET based copolyesters in thermophilic anaerobic sludge by Soňa Hermanová; Pavla Šmejkalová; Jan Merna; Marie Zarevúcka (176-184).
A series of poly(ethylene terephthalate-co-lactate) copolyesters with random microstructure was prepared from PET waste beverage bottles and l-lactic acid. Square specimens, sectioned from melt-pressed film, were incubated in thermophilic sludge (55 °C, alkaline environment) for 394 days. The biodegradability of the samples, determined from biogas yield, reached 34–69 % depending on the starting aromatic to aliphatic units' ratio.Water uptake study in sludge and abiotic buffers at 55 °C showed sharp border around 57% of aromatic units in copolyester composition between polymers susceptible and resistant to both hydrolytic attack by hydrolases and the abiotic hydrolysis. Samples biodegraded in sludge and those abiotically aged in buffers were characterized by 1H NMR, ATR-FTIR, SEC, DSC, and TGA analysis to gain an insight into the chain scission mechanism.Aromatic oligomers as model of copolyester degradation intermediates were prepared and proved to biodegrade in sludge as well.
Keywords: Poly(ethylene terephthalate); Copolymers; Sludge; Biodegradation; Hydrolysis; Waste;

Characterization of the influence of specimen thickness on the aging behavior of a polypropylene based model compound by Klemens Grabmayer; Susanne Beißmann; Gernot M. Wallner; David Nitsche; Karl Schnetzinger; Wolfgang Buchberger; Harald Schobermayr; Reinhold W. Lang (185-193).
Specimens with varying thickness of different polypropylene random copolymer formulations were oven aged in hot air at 135 °C. Besides macro-sized specimens die-punched from 2 mm thick extruded sheets, 50 μm, 200 μm and 500 μm thick micro-sized specimens, cut edgewise from the sheets by an automated planing procedure, were investigated. The formulations included a base stabilized reference compound and four formulations prepared with systematically varied additional contents of the primary antioxidants Naugard 445 and Irganox 1010 and the secondary antioxidants Irganox PS-800 and Irganox PS-802. Aging characterization was performed by tensile testing, differential scanning calorimetry and high performance liquid chromatography employing strain-at-break, oxidation onset temperature (OOT) and the content in phenolic antioxidants as aging indicators, respectively.Aging characterization revealed a systematic thickness dependence of the embrittlement time and the rate of the reduction in OOT as well as the reduction of phenolic antioxidants. The 50 μm thick specimens exhibited embrittlement times between 50% and 65% of the 2 mm thick macro-sized specimens. For low thicknesses, a high surface to volume ratio is presumably responsible for the fast physical loss of antioxidants, while for thick specimens, physical stabilizer loss is limited by the rate of stabilizer diffusion from the bulk to the surface. Hence, thicker specimens showed longer embrittlement times. Regarding stabilizer loss, Naugard 445 and Irganox PS-800 exhibited significantly higher loss rates than Irganox 1010 and Irganox PS-802.
Keywords: Polymer degradation; Aging characterization; Polypropylene; Thickness dependence; Antioxidants; Thiosynergists;

A high-molecular-weight ABA tri-block copolymer ([RS]-PHB/PEG), consisting of poly(3-[RS]-hydroxybutyrate) ([RS]-PHB: A) and poly(oxyethylene) (polyethylene glycol; PEG: B), was synthesized by ring-opening polymerization of [RS]-β-butyrolactone ([RS]-βBL) in the presence of PEG and 1,3-dichlorotetrabutyldistannoxane (DTD) as the catalyst. By using a series of PHB derivatives including the new block copolymer, cell adhesion was evaluated with 3T3 fibroblast cells. It was found out that the attached cells didn't extend on [RS]-PHB, but extended on [R]-PHB although the numbers of the attached cells were very small on both [RS]-PHB and [R]-PHB. [RS]-PHB/PEG exhibited even poorer cell adhesion than [RS]-PHB because of the increased hydrophilic nature due to the PEG segments. Although the amount of fibronectin adsorbed on the surface of [RS]-PHB was higher than that on the surface of [R]-PHB, the cell adhesion became poorer on the fibronectin-pre-adsorbed [RS]-PHB. These differences in cell adhesion among these PHB derivatives were reasonably attributed to their surface properties related with the accumulation of methyl groups.
Keywords: Poly(3-hydroxybutyrate); Block copolymer; Cell adhesion; Fibroblast cell; Protein adsorption;

A series of high molar mass terpolymers are synthesized by ring-opening polymerization of l-lactide (LLA), 1,3-trimethylene carbonate (TMC) and glycolide (GA). In vitro degradation of the obtained terpolymers was realized in phosphate buffered saline (PBS) at 37 °C for one year, in comparison with PLLA-TMC copolymer and a composite made up of a PLLA-TMC-GA terpolymer matrix reinforced by poly(l-lactide-co-glycolide) (PLGA) fibers. Degradation was characterized as a function of incubation time by using GPC, DSC and 1H NMR.PLLA-TMC-GA terpolymers degrade faster than PLLA and PLLA-TMC because of lower chain regularity and lower crystallinity. In the case of the composite, the fast degradation of PLGA fibers speeds up the degradation of the PLLA-TMC-GA matrix due to internal autocatalysis. Morphological changes with increase of melting enthalpy were observed in all cases with crystallization of degradation by-products and selective degradation of amorphous domains. On the other hand, compositional changes appeared more complex since different phenomena are involved, including crystallization of LLA component, selective degradation in amorphous domains, and release of soluble oligomers. Among the various polymers, PLTG90/10/5 and PLTG95/5/5 present appropriate degradation rates, and are promising for the fabrication of totally bioresorbable stents.
Keywords: In vitro degradation; (l-lactide-trimethylene carbonate-glycolide) terpolymers; Biomaterial; Cardiovascular stent;

Deterioration of acrylonitrile butadiene rubber in rapeseed biodiesel by S. Akhlaghi; M.S. Hedenqvist; M.T. Conde Braña; M. Bellander; U.W. Gedde (211-222).
The deterioration of acrylonitrile butadiene rubber (NBR) exposed to rapeseed biodiesel at 90 °C was studied. The oxidation of biodiesel and NBR during ageing was monitored by 1H NMR and infrared spectroscopy, HPLC and titration methods. The oxidation of biodiesel was impeded in the presence of NBR, but promoted in biodiesel-exposed rubber. This was explained as being due to the migration of stabilizer from the rubber to biodiesel, the diffusion of dissolved oxygen from biodiesel into NBR and the absorption of oxidation precursors of biodiesel by the rubber. The resemblance between the anomalous sorption kinetics of biodiesel in NBR and the equilibrium benzene uptake by the aged rubbers revealed that biodiesel caused a network defect in NBR, resulting in a gradual increase in the equilibrium swelling. The cleavage of crosslinks was implausible since the Young's modulus of the rubber at low strains, disregarding an initial decrease, increased with increasing exposure time. The appearance of ‘naked’ carbon black particles in the scanning electron micrographs of the aged rubbers and a drastic decrease in the strain-at-break of NBR after exposure to biodiesel suggests that internal cavitation was caused by the attack of biodiesel on the acrylonitrile units of NBR.
Keywords: Biodiesel; Acrylonitrile butadiene rubber; Oxidation; Degradation mechanism;

The early stages of the reaction mechanism of ozone with N,N′-substituted p-phenylenediamines 6PPD and 77PD as well as the alkyl-p-phenylenediamine substituted sym-triazine (PPDTZ) commercially known as “DURAZONE” were investigated at room temperature in ethanol and acidic ethanol solutions with electron spin resonance (ESR) and electronic absorption spectroscopy (UV–VIS). It was found that both 6PPD and 77PD react with ozone through the electron transfer mechanism giving the respective radical cations 6PPD+• and 77PD+• which were detected with ESR and with UV–VIS. It was also found that 6PPD+• and 77PD+• are stabilized and clearly detected in acidic ethanol. In the case of 6PPD ozonation also gave the relative nitroxyl radical which was detected with ESR. PPDTZ was reacted with ozone in ethanol to give a nitroxyl radical detected with ESR and with UV–VIS spectroscopy. No radical cation was detected on ozonated PPDTZ solutions.
Keywords: Antiozonants; ESR; UV–VIS; Radical cation; Nitroxyl radical; Rubber protection;

Two novel macromolecular hindered phenol antioxidants containing thioether and urethane groups were synthesized by the combination of thiol-acrylate Michael addition and nucleophilic addition. First, a hindered phenol with hydroxyl (GM-ME) was synthesized by Michael addition between 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylphenyl) methyl-4-methylp-henyl acrylate (GM) and 2-mercaptoethanol (ME). Then macromolecular antioxidants GM-ME-IPDI and GM-ME-TDI were obtained after GM-ME reacted with isophorone diisocyanate (IPDI) and toluene diisocynate (TDI), respectively. The structures of the macromolecular antioxidants were confirmed by FT-IR, 1H NMR and MALDI-TOF-MS. TG analysis showed that the thermal stability of the GM-ME-IPDI and GM-ME-TDI were higher than that of the GM. The oxidation induction time (OIT) and accelerated thermal aging tests of natural rubber vulcanizates showed that the thioether and urethane groups of GM-ME-IPDI and GM-ME-TDI played an important role in improving antioxidative efficiency. In addition, it was found that the urethane group connected with benzene ring had better antioxidative ability than that connected with alicyclic ring.
Keywords: Macromolecular antioxidant; Antioxidative efficiency; Hindered phenol; Urethane;

Effect of chemical structure and cross-link density on the heat resistance of phenolic resin by Yong Wang; Shujuan Wang; Cheng Bian; Yuhu Zhong; Xinli Jing (239-246).
Limited by the knowledge of the structure and pyrolysis mechanism of cured phenolic resin (PR), the influence of cross-link density (CLD) on the heat resistance of PR remains unclear. The objective of this work is to characterize the structure of PR and understand the relationship between structure and heat resistance. The CLD of cured PR is characterized by theoretical and experimental approaches based on the full understanding of the chemical structure. The influence of CLD on the heat resistance is studied by analyzing the pyrolysis behavior of cured PR, and the results reveal that cross-link can improve the thermal stability and char yield of cured PR simultaneously. A novel pyrolysis mechanism and a quantitative relationship between the CLD and residual weight of PR are proposed. The results of our paper provide a theoretical basis to develop resins with good heat resistance.
Keywords: Phenolic resin; Cross-link density; Heat resistance; Pyrolysis;

Decomposition of waste carbon fiber reinforced epoxy resin composites in molten potassium hydroxide by Weidong Nie; Jie Liu; Wenbin Liu; Jun Wang; Tao Tang (247-256).
Recycling of carbon fiber reinforced epoxy resin composites has been investigated using molten potassium hydroxide as reaction media. The epoxy resin in composites was decomposed at temperatures ranged from 285 to 330 °C. The recovered carbon fibers were characterized by SEM, XPS and single fiber tensile test. More than 95% of the tensile strength of the virgin carbon fibers was retained. The surface C–OH decreased and COOH increased with increasing temperature. The decomposition products of epoxy resin in KOH was separated and analyzed by FTIR and MALDI-TOF. A possible mechanism for the decomposition of epoxy resin is proposed. The real-world CFRP wastes containing various contaminants such as thermoplastics, paints, sealants and glass fibers were also decomposed in the molten KOH.
Keywords: Carbon fiber reinforced epoxy resin composites; Recycling; Molten salt; Potassium hydroxide;

Kinetics of long-term degradation of different molar mass hyaluronan solutions studied by SEC-MALLS by Vasile Simulescu; Jakub Mondek; Michal Kalina; Miloslav Pekař (257-262).
The degradation of hyaluronan of four molecular weights in aqueous solutions containing sodium azide as a protectant was studied by SEC-MALLS determination of molecular mass and polydispersity and conformation parameters. The solutions were stored either at laboratory or refrigerator temperatures for up to seven months. After this time the molar mass decreased in 9–15% (room temperature) or 5–10% (fridge) depending also on the storage conditions of solid samples from which the solutions were prepared. Two degradation phases were observed at room temperature conditions. Two kinetic models were employed to fit the data – zero order and exponential with no statistical preferences of any of them. The polydispersity of all samples was low and remained unaltered during the whole degradation at both temperatures which indicates non-random mechanism of degradation.
Keywords: Hyaluronic acid; Degradation; SEC-MALLS; Polymer conformation;

Equilibrium and dynamic vapour water sorption properties of biochar derived from apple wood by Carmen-Mihaela Popescu; Callum A.S. Hill; Rosie Anthony; Graham Ormondroyd; Simon Curling (263-268).
The water vapour sorption properties of biochar derived from apple wood (Malus sp.) have been studied. The biochar used in the study were formed from wood samples taken from different parts of the trunk and they exhibited different cell wall densities and surface area values when charred under identical conditions. The water vapour adsorption and desorption characteristics of the biochar were investigated over the relative pressure range P/P o = 0–0.95 in a dynamic vapour sorption apparatus and the kinetics was analysed in terms of the parallel exponential kinetics (PEK) model. The PEK model comprises two exponential sorption kinetic terms which are termed fast and slow sorption processes. The fast process is attributed to a linear driving force mass transfer diffusion model, while the slow process is attributed to a relaxation-limited kinetic process. Markedly different sorption behaviour was found between the biochar samples, which had been produced under identical conditions.
Keywords: Biochar; Malus sp; Dynamic vapour water sorption; Parallel exponential kinetics;