Polymer Degradation and Stability (v.94, #9)

Calendar (I-II).

A study of the properties of short glass fibre reinforced thermoplastic composites based on poly(ethylene terephthalate), poly(butylene terephthalate) and polyamide-6,6 in an aggressive environment is reported. The influence of the fibre/matrix interface on the composite behaviour in a moist environment is especially studied. Competitive phenomena may explain differences observed according to the nature of the fibre surface treatment. Among them these characteristics may be an intrinsic fragility of some chemical interfacial bonds, the hydrophilicity of some chemical groups, the presence of long macromolecular chains neighbouring the interface or of a transcrystalline interfacial area.
Keywords: Ageing; Interface; Thermoplastic composites; PA-6,6; PET; PBT;

Different compositions of poly(methyl methacrylate-co-methyl acrylate) (PMMAMA), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) and poly(methyl methacrylate-co-butyl acrylate) (PMMABA) copolymers were synthesized and characterized. The photocatalytic oxidative degradation of all these copolymers were studied in presence of two different catalysts namely Degussa P-25 and combustion synthesized titania using azobis-iso-butyronitrile and benzoyl peroxide as oxidizers. Gel permeation chromatography (GPC) was used to determine the molecular weight distribution of the samples as a function of time. The GPC chromatogram indicated that the photocatalytic oxidative degradation of all these copolymers proceeds by both random and chain end scission. Continuous distribution kinetics was used to develop a model for photocatalytic oxidative degradation considering both random and specific end scission. The degradation rate coefficients were determined by fitting the experimental data with the model. The degradation rate coefficients of the copolymers decreased with increase in the percentage of alkyl acrylate in the copolymer. This indicates that the photocatalytic oxidative stability of the copolymers increased with increasing percentage of alkyl acrylate. From the degradation rate coefficients, it was observed that the photocatalytic oxidative stability follows the order PMMABA > PMMAEA > PMMAMA. The thermal degradation of the copolymers was studied by using thermogravimetric analysis (TGA). The normalized weight loss and differential fractional weight loss profiles indicated that the thermal stability of the copolymer increases with an increase in the percentage of alkyl acrylate and the thermal stability of poly(methyl methacrylate-co-alkyl acrylate)s follows the order PMMAMA > PMMAEA > PMMABA. The observed contrast in the order of photostability and thermal stability of the copolymers was attributed to different mechanisms involved for the scission of polymer chain and formation of different products in both the processes.
Keywords: PMMA; Copolymers; Alkyl acrylates; Photooxidative degradation; Continuous distribution kinetics;

Thermal rearrangement study of low molecular weight polybutadiene by Farshid Ziaee; Hamid Salehi Mobarakeh; Mehdi Nekoomanesh (1336-1343).
Various polybutadienes (PBDs) of low molecular weight were heated below complete crosslinking at 250 °C under anaerobic nonpyrolytic conditions, and the structural changes were investigated. The predominant crosslinking reactions arise from the presence of 1,2-vinyl isomer and the most important one is intermolecular reaction accompanied with methyl group formation. The analysis showed that two crosslinking types as well as two types of methyl groups have been produced in which one was the result of 1,2-vinyl isomer of one chain crosslinked via methylene carbon of another chain of cis or trans isomer, and the second methyl group was the product of the reaction between 1,2-vinyl isomers of two PBD chains. Chain scission also occurred in two pathways due to the presence of 1,2-vinyl isomer, scission at two adjacent 1,2-vinyl isomer and scission at adjacent 1,2-vinyl with cis or trans isomer giving rise to methyl carbons.
Keywords: Polybutadiene; Thermal rearrangement; NMR; GPC; Chain scission; Crosslinking;

The kinetics of chitosan depolymerisation at different temperatures by Gordon A. Morris; Jonathan Castile; Alan Smith; Gary G. Adams; Stephen E. Harding (1344-1348).
The stability (in terms of molar mass) of chitosan potentially plays an important role in its behaviour and functional properties in a wide range of applications and therefore any changes over time must be understood.The weight-average molar masses and intrinsic viscosities of chitosan solutions at different temperatures (4, 25 and 40 °C) have been investigated using size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS) and a “rolling ball” viscometer respectively. The weight-average molar mass (M w) and the intrinsic viscosity ([η]) both decrease with increased storage time, although this phenomenon is more pronounced at elevated temperatures.Good correlation was found between the changes in molar mass and intrinsic viscosity with time and these parameters were used to determine the depolymerisation constant (k) and the activation energy (E a).Knowledge of the effect of storage conditions (e.g. temperature) is important in the understanding the stability of chitosan solutions, but whether or not chitosan depolymerisation will be detrimental to its intended application will depend on the functional significance of the changes that occur.
Keywords: Chitosan; Molar mass; Intrinsic viscosity; Stability; Kinetics; Activation energies;

Self-assemblies of enzymatically degradable amphiphilic oligopeptides as nonviral gene carrier by Tomoko Hashimoto; Reiko Iwase; Akira Murakami; Tetsuji Yamaoka (1349-1353).
Novel biodegradable oligopeptide-type gene carriers composed of cationic residues (KRRRKRKRRRKRKRRC) and oligo leucine segments were developed. The amphiphilic carrier was found to form micelle-like assemblies in aqueous solutions, when the oligo leucine is 12 amino acids length (Pep-L12). NMR, CMC, and GPC analysis revealed their hydrophobic/cationic core/shell morphology. Hydrophobic interaction between leucines is thought to be the major driving force behind formations of assemblies. The transient expression of luciferase introduced to COS-1 cells using Pep-L12 below the CMC is as low as that by the control cationic peptides without leucine residue (Pep-L0), while improved transgene expression was observed in the case of Pep-L12 above CMC. The self-assembly raised the apparent molecular weight and gene transfection ability without loosening their low cytotoxicity. These results indicate that the amphiphilic oligopeptides are very promising materials as highly efficient and less toxic gene carriers.
Keywords: Polymeric gene carrier; Self-assembly; Stability; Oligopeptide; Molecular weight;

Effects of zinc-based flame retardants on the degradation behaviour of an aerospace epoxy matrix by A. De Fenzo; C. Formicola; V. Antonucci; M. Zarrelli; M. Giordano (1354-1363).
Flame behaviour is a fundamental requirement for advanced aerospace composites. In this work, a commercial, low-viscosity epoxy system, typically used in liquid infusion composite processes, and its mixtures with three different zinc-based flame retardants (ZB, ZS, ZHS) at different weight percentages has been investigated by cone calorimetry and thermogravimetric analysis.Cone calorimetry has been performed to verify the flame retardancy effects induced by each filler composition. Nevertheless manufacturability issues require the evaluation of the rheological changes induced by filler on the unloaded matrix system. Rheological tests have been, therefore, performed to identify the maximum concentration of filler. Based on these results thermogravimetric tests have been performed to investigate thermal degradation kinetics of selected systems. The feasibility of Kissinger and Flynn-Wall-Ozawa method for the determination of characteristic degradation kinetics parameters has been evaluated and results were analysed. A simplified decomposition model was assumed to analyse epoxy degradation behaviour; it was found that this model gives appreciable matching with experimental TGA curve trend for neat epoxy whereas for the filled compounds additional stages were assume to occur.
Keywords: Epoxy; Thermogravimetric analysis; Flame retardants; Degradation kinetics; Cone calorimeter;

Structural changes during thermally induced crystallization and alkaline hydrolysis of Poly(l-lactic acid) (PLLA) films were investigated using differential scanning calorimetry (DSC), FTIR spectroscopy, weight loss, HPLC and optical microscopy. It was shown that crystallinity (χ c), glass transition temperature (T g) and melting temperature (T m) were found to be strongly annealing temperature (T a) dependent. The FTIR study of PLLA films suggested that the bands at 921 and 956 cm−1 could be used to monitor the structural changes of PLLA. An independent infrared spectroscopic method was developed for the first time to determine crystallinity of PLLA before degradation and it showed good qualitative correlation with DSC crystallinity. The higher crystallinity values determined by FTIR were attributed to the intermediate phase included in the IR crystallinity. Both the weight loss data and the percentage of lactic acid obtained by HPLC showed that the alkaline hydrolysis of PLLA films increased with increasing crystallinity. The DSC observation showed an increase in T g and no significant change in T m and heat of fusion, while IR showed an increase in IR crystallinity with increasing hydrolysis time. The increase in IR crystallinity and T g with hydrolysis time suggested that degradation progressed from the edges of the crystalline lamellas without decreasing lamellar thickness, but increased the intermediate phase and the short-range order.
Keywords: Hydrolytic degradation; FTIR spectroscopy; Crystallinity; Crystallization;

In this paper, a comparison of the role of boehmite (AlOOH) and alumina (Al2O3) in the thermal stability and flame retardant behaviour of poly(methyl methacrylate) (PMMA) is presented. PMMA–AlOOH and PMMA–Al2O3 nanocomposites were prepared by melt blending with different filler contents. These nanocomposites were studied by thermogravimetric analysis (TGA) and cone calorimetry. In the presence of the filler (alumina or boehmite), the thermal stability of the polymer appeared to be significantly improved. An increase of the decomposition temperature of between about 19 and 35 °C was demonstrated by TGA. Cone calorimeter measurements showed that the peak of heat release rate is lowered in the presence of AlOOH or Al2O3 in comparison to pure PMMA and that this decrease is higher when the filler content increases. When loading rate is higher (15 wt%), a significant improvement in fire resistance of PMMA was observed in both systems but with two different modes of action.
Keywords: Thermal degradation; Poly(methyl methacrylate); PMMA; Flame retardant; Nanocomposites; Al2O3;

A two-step process based on steam explosion pretreatment followed by alkaline ethanol solution post-treatment was used to fractionate Lespedeza stalks (Lespedeza cyrtobotrya). Steam explosion pretreatment, under at 15 kg/m2 to 25 kg/m2 for 4 min, followed by post-treatment with 60% aqueous ethanol containing 1% NaOH yielded 49.6–65.5% (% dry matter) cellulose rich fractions, compared to 68.6% from non-pretreated material. It was found that the content of glucose was gradually increased from 73.7 to 86.9% as the result of elevating steaming pressure, but the solubilisation of lignin maintained the same level (about 10–11%) regardless of the severity. The average degree of polymerization increased first and then decreased, revealing that autohydrolysis reactions were dominant in different regions during the steam explosion. Scanning electron microscopy images of the cellulosic residues show that steam explosion mainly resulted in breakage of the fibres, and extraction post-treatment led to solution of lignin (and hemicelluloses) and significant defibrillation. The increase of onset degradation temperature, together with the higher pyrolysis residues suggest that the thermal stability of cellulose rich fractions was increased by steam explosion and elevated steaming pressure. All the rich-in-cellulose fractions were further characterized by FT-IR, XRD, and CP/MAS 13C NMR spectroscopy.
Keywords: Cellulose; Steam explosion; Steaming pressure; Fractionation; Lespedeza cyrtobotrya;

Mechanical properties degradation of polyimide films irradiated by atomic oxygen by Hiroyuki Shimamura; Takashi Nakamura (1389-1396).
Mechanical properties of polyimide films are degraded by exposure to a low earth orbit environment. The main environmental factor for that degradation is atomic oxygen (AO). Using tensile tests, AO-irradiated surface topography observations, and fracture surface analyses, this study investigated the degradation behavior of polyimide films’ mechanical properties by increased AO fluence and its accompanying degradation mechanisms. Tensile strength and elongation of polyimide films were reduced concomitantly with increased AO fluence. Furthermore, AO-irradiated polyimide films fractured from the AO-irradiated surfaces, of which roughness became marked as AO fluence increased. These results reflect that reduction of mechanical properties is attributable to the roughness increase in AO-irradiated surfaces. Polyimide films coated with indium tin oxide (ITO) were also evaluated to confirm the degradation behavior of AO protective films. Surfaces of ITO-coated polyimide films remained smooth even after AO irradiation. However, undercut cavities were formed at ITO coating defect sites. Rupture of ITO-coated polyimide films initiates from the undercut cavities, engendering large reduction of tensile strength and elongation. The degradation of the mechanical properties of ITO-coated polyimide films increased substantially until the undercut cavities fully penetrated the film.
Keywords: Polyimide; Atomic oxygen; Mechanical properties; Fractography;

The anaerobic biodegradation tests of polycaprolactone (PCL) and poly(lactic acid) (PLA) powders were done at thermophilic temperature (55 °C) under aquatic conditions (total solid concentrations of the used sludge were 1.73% (undiluted sludge) and 0.86% (diluted sludge)) using a newly developed evaluation system. With this system, the evolved biogas is collected in a gas sampling bag at atmospheric pressure. This method is more convenient than using a pressure transducer or inverted graduated cylinder submerged in water. The biodegradation of PCL powder (10 g, 125–250 μm) in the diluted sludge stopped in about 47 days when the biodegradability reached 92%. The biodegradability of PLA powder (10 g, 125–250 μm) in undiluted sludge was 91% at about 75 days. The biodegradability of PLA powder (10 g, 125–250 μm) in diluted sludge was 79% at about 100 days. The biodegradability of PLA powder (5 g, 125–250 μm) in diluted sludge was 80% at about 85 days. It was found that the PCL and PLA powders were quite degraded using the new evaluation method. In addition, the smaller particle size PCL powder was biodegraded faster.
Keywords: Anaerobic biodegradation; Poly(lactic acid); Polycaprolactone; Methane fermentation;

Preparation and controlled degradation of oxidized sodium alginate hydrogel by Chunmei Gao; Mingzhu Liu; Jun Chen; Xu Zhang (1405-1410).
Degradation is often a critical property of materials utilized in tissue engineering. Although alginate, a naturally derived polysaccharide, is an attractive material due to its biocompatibility and ability to form hydrogels, its slow and uncontrollable degradation can be an undesirable feature. In this study, the degradation behavior of hydrogel based on oxidized sodium alginate (OSA) crosslinked with Ca2+ was studied in phosphate buffer solution (PBS, pH = 7.4) and Tris-(hydroxymethyl) aminomethane–HCl (Tris–HCl, pH = 7.4) at 37 °C. The degradation behavior of OSA hydrogels with different degrees of oxidation was evaluated as a function of degradation time by monitoring the changes of molecular weight and weight loss. It was found that the degradation behavior relied heavily on the degree of oxidation and the surrounding medium. This result indicates that the degradation rates of OSA hydrogels can be controlled by changing the degree of oxidation.
Keywords: Oxidized sodium alginate; Hydrogel; Degradation; Swelling kinetics;

Nanohybrid membranes based on the Keggin-type polyoxometalate (POM) H5PV2Mo10O40 and a poly(vinyl alcohol)/polyethyleneimine (PVA/PEI) blend were prepared as a chemical and biological protective material. The objective of the study was to develop and evaluate permeable membranes (PVA/PEI) impregnated with reactive nanoparticulates (POM) that can protect against simulants of chemical and biological warfare agents. The physical properties of the PVA/PEI–POM hybrids were examined using SEM, TEM, TGA, and UV–Vis spectroscopy, the results of which indicated that the POM was incorporated in the PVA/PEI matrix after impregnation. The redox properties against 2-chloroethyl-ethyl sulfide (CEES) were investigated based on significant color changes and UV absorption in the POM upon reduction by CEES. The antibacterial effects of the PVA/PEI–POM hybrids were assessed by the zone of inhibition, minimum inhibitory concentration (MIC), and plate-counting methods. The results of this study showed that PVA/PEI–POM hybrids that act against simulants of chemical and biological weapons while retaining their ability to transmit moisture vapor could be obtained.
Keywords: Poly(vinyl alcohol); Polyethyleneimine; Polyoxometalate; Permeable membrane; Antibacterial effect;

Although poly(lactic acid) is known as a biodegradable polymer, its hydrolytic degradation is extremely slow, taking years in water and in the human body. In this study the effects of blending oligomeric poly(aspartic acid-co-lactide) (PALs) on the hydrolytic degradation of poly(l-lactic acid) (PLLA) were studied in detail. It was found that the addition of PAL did not accelerate the hydrolysis of the PLLA in air (25 °C, 60% relative humidity), but significantly accelerated it in a phosphate buffer solution. The degradation rate becomes higher for the blends containing PAL with higher molar ratios of lactide to aspartic acid units, [LA]/[Asp], when PLLA/PAL blends prepared with different PALs are compared at the same PAL concentration. TEM results, in which the distribution of PALs with higher [LA]/[Asp] occurs at a smaller scale in blends, imply that higher miscibility of the PAL with PLLA results in higher contact area between the components, thereby accelerating the degradation efficiently.
Keywords: Poly(l-lactic acid); Hydrolysis; Aspartic acid; Miscibility;

Preparation, properties and cytotoxicity evaluation of a biodegradable polyester elastomer composite by Quanyong Liu; Junyue Wu; Tianwei Tan; Liqun Zhang; Dafu Chen; Wei Tian (1427-1435).
Multi-walled carbon nanotube (MWCNT)/poly(glycerol–sebacate–citrate) (PGSC) elastomer composite were prepared and their morphologies, compositions, glass transition temperatures, mechanical properties, water absorption, biodegradation and cytotoxicity were investigated. Results showed that the chemical structures of PGSC elastomers were hardly influenced by the MWCNT loadings, and physical adsorption was thought as the main interaction between the MWCNTs and PGSC matrixes. When the MWCNT loading was 3 wt%, MWCNTs displayed a homogenous dispersion in the matrixes, and the composite's strength and modulus respectively reached 4.4 MPa and 9.2 MPa, increasing by 62.96% and 33.33% than that of pure PGSC matrixes. The degradation rates of the composites tended to decrease with the increase of MWCNT loadings in simulated body fluid (SBF) solution. The composites presented no cytotoxicity especially when the MWCNT loadings were above 1 wt%. We expect the composites can be used as degradable bio-coatings and tissue engineering scaffolds in future.
Keywords: Polyester elastomer; Composite; Biodegradable; Multi-walled carbon nanotubes; Preparation; Cytotoxicity evaluation;

The effect of humidity on the degradation of Nafion® membrane by Cheng Chen; Thomas F. Fuller (1436-1447).
Controlling the activity of water in the reactant streams is critical both to the design of fuel–cell systems and to the useable life of membrane separators. In this study, fuel–cell durability tests were conducted under different levels of relative humidity. The emission rates of various degradation products such as HF, SO4 2− and TFA (trifluoroacetic acid) were determined as a function of water activity. The degradation of the membrane was accelerated as the level of water activity is reduced. The membranes become less conductive, more brittle and rigid after fuel–cell testing. ATR-FTIR investigations showed that the decomposition of the ether group in the middle of side chain corresponds well with the detection of a TFA product. Thermogravimetric analysis also showed a decrease in thermal stability after testing at lower humidity. Formation of cracks was observed in membranes degraded under conditions of low humidity. A model of membrane degradation based on the main chain unzipping process indicates that the mechanism changes with water activity. Finally, the representative reaction pathways in each degradation scheme were postulated.
Keywords: Nafion® membrane; Relative humidity; ATR–FTIR; TGA; Degradation mechanism;

Melt stabilisation of Phillips type polyethylene, Part II: Correlation between additive consumption and polymer properties by Ildikó Kriston; Ágnes Orbán-Mester; Gábor Nagy; Peter Staniek; Enikő Földes; Béla Pukánszky (1448-1456).
Phillips type polyethylene stabilised with combinations of 700 ppm phenolic antioxidant and different amounts of various phosphorous stabilisers (sterically hindered aryl phosphite [Hostanox PAR 24], phosphonite [Sandostab P-EPQ], and aryl–alkyl phosphine [PEPFINE]) was processed by six consecutive extrusions. The polymer was characterised by FT-IR spectroscopy, rheological (melt flow index, creep compliance), colour and oxidation induction time measurements. Films were prepared by blowing and their mechanical strength was determined by Elmendorf and dart drop tests. The consumption of the antioxidants was compared to the characteristics of the polymer and to the strength of the films. The consumption rate of both the phenolic and the phosphorous antioxidants is reduced in their combinations compared to single antioxidants. The chemical structure of the polymer is modified considerably in the first extrusion even at high antioxidant levels. The mechanism of stabilisation is determined by the type of the antioxidant(s) in further processing steps. The phenolic antioxidant does not prevent the formation of long chain branches. The phosphonite and the phosphine hinder efficiently hydrogen abstraction from the polymer chain and long chain branching. Their efficiency is similar, but the phosphonite is consumed fast, while the phosphine oxidises slowly. The investigated phosphite is less reactive; the contribution of the phenolic antioxidant to the inhibition reactions is significant in phenol/phosphite combinations, therefore long chain branching increases continuously with increasing number of processing steps.
Keywords: Polyethylene; Phenolic antioxidant; Phosphorous antioxidant; Stabilisation;

A variety of oxidation products of antioxidants based on N,N′-substituted p-phenylenediamines by Peter Rapta; Andrea Vargová; Júlia Polovková; Anton Gatial; Ladislav Omelka; Petr Majzlík; Martin Breza (1457-1466).
Electrochemical and spectroscopic (EPR, UV–Vis, IR) studies of the aromatic secondary amines N,N′-diphenyl-1,4-phenylenediamine (DPPD), N-phenyl-N′-isopropyl-p-phenylene diamine (IPPD), N-phenyl-N′-(α-methylbenzyl)-p-phenylenediamine (SPPD) and N-phenyl-N′-(1,3-dimethyl-butyl)-p-phenylenediamine (6PPD), which represent the most important group of antioxidants used in the rubber industry, are presented. During oxidation, all the compounds show reversible redox couples in acetonitrile/0.1 M TBABF4. The first oxidation potential depends substantially on the R substituent at the –N′H– moiety. Very similar UV–VIS spectra of monocation radicals and dications for all the compounds were observed by applying anodic oxidation as well as oxidation by tert-butyl hydroperoxide both in air and in inert atmosphere. The samples with N′-bonded aliphatic carbon in the molecule (e.g. IPPD) heated in air undergo consecutive chemical reactions leading to the formation of –N′=C– group. By the use of RO2 • radicals only very low concentration of nitroxide radicals was obtained. Very high concentration of nitroxide radicals was achieved using 3-chloroperbenzoic acid. In the oxidation of investigated aromatic secondary amines with powder PbO2 no EPR spectra were observed and UV–Vis and IR studies indicate the rapid formation of the final dehydrogenated oxidation product.
Keywords: Phenylenediamines; Antioxidants; Cyclic voltammetry; Spectroelectrochemistry; Radical intermediates;

A new pyrolysis–GC/MS system incorporating with on-line micro-ultraviolet (UV) irradiation was developed to make rapid evaluation of the synergistic material deterioration during UV irradiation under thermal and oxidative atmospheres. The basic effectiveness of the system was demonstrated by polystyrene, polypropylene and polycarbonate as the test samples. The volatile products evolved during deterioration of the polymers were analyzed on-line by thermal desorption GC/MS, and then the residual degraded polymers were analyzed by evolved gas analysis (EGA) and/or Py–GC/MS to obtain specific thermograms and pyrograms. Based on these results, the deterioration mechanism of the polymeric materials during irradiation under thermal and oxidative atmosphere can be evaluated using a sub-milligram polymer sample within a relatively short period of time.
Keywords: On-line micro-UV irradiator; Pyrolysis–GC/MS; Evolved gas analysis; Material degradation; Polymer deterioration;

Plasticized PVC formulations have traditionally been used in the production of medical devices, such as tubes and bags for plasma or blood because of their good performance in mechanical and thermal properties as well as their low cost. Clinical practice, in particular re-use after sterilization, can damage and promote degradation of these materials with the risk of release of polymer additives into physiological fluids and consequently risks to patient's health. Formulations with commercial plasticizers, alternative to traditional phthalates (citrate and carboxylate compounds) have been proposed in this work and their behaviour after repeated sterilization has been evaluated. Structural, mechanical, thermal and surface properties have been tested and no significant degradation was observed. No apparent risk of massive damage to plasticized PVC could be considered after repeated sterilization.
Keywords: Plasticized PVC; Medical devices; Sterilization; Mechanical properties; Surface morphology;

FTIR and NMR study of poly(lactide-co-glycolide) and hydroxyapatite implant degradation under in vivo conditions by J. Chlopek; A. Morawska-Chochol; C. Paluszkiewicz; J. Jaworska; J. Kasperczyk; P. Dobrzyński (1479-1485).
The influence of hydroxyapatite (HAP) addition on the rate and mechanism of lactide-co-glycolide copolymer (PGLA) degradation after implantation (in vivo study) was analyzed and compared with the process taking place during in vitro studies. Structural and phase changes of poly(lactide-co-glycolide) and its composite with hydroxyapatite were determined using IR and NMR spectroscopy.Degradation of PGLA and PGLA + HAP composite in biological environment proceeds faster than under in vitro condition. Concentration of glycolidyl units in the copolymer chain decreases and that of lactidyl units increases during in vivo degradation both, in PGLA and in PGLA + HAP composite. However, in the case of the composite the decrease of glycolidyl units concentration is slower and after 6 weeks of degradation the contents of lactidyl and glycolidyl units remain stable. On the other hand, PGLA + HAP composite degrades faster than pure PGLA. The addition of HAP nanoparticles distinctly accelerates degradation of PGLA copolymer which is probably connected with the increase of hydrophilicity of the composite and inhibition of semi-crystalline lactidyl domains formation during the degradation process. Observation of the bone tissue after implantation of PGLA + HAP allows to conclude that the degradation of the composite occurs simultaneously with the implant replacement by the bone cells.
Keywords: poly(l-lactide-co-glycolide); Hydroxyapatite; In vivo; NMR; Biodegradation; FTIR;

Restabilization of the aging resistance of compatibilized blends of pre-aged low density polyethylene and high-impact polystyrene (LDPE/HIPS) by D. Michálková; J. Pospíšil; I. Fortelný; J. Hromádková; F. Lednický; P. Schmidt; Z. Kruliš (1486-1493).
Blends of pre-aged low density polyethylene (LDPE) with high-impact polystyrene (HIPS) compatibilized with a 1:1 mixture of styrene–butadiene block copolymer (SBS) and ethylene-propylene-diene statistical terpolymer (EPDM) were upgraded for thermooxidative resistance with N,N’-disubstituted 1,4-phenylenediamine. The impact strength after the oven test was improved. A model experiment confirmed that the efficiency of the phenylenediamine was not lost in the system after a partial sacrificial transformation of PD into the corresponding quinone diimine. The beneficial thermal effect of the upgrading used is a consequence of cooperation between the components of the blend. The system does not protect however against photooxidative stress without a suitable fortification with photostabilizers. The material properties of the upgraded blend upon oxidative stresses were assessed by monitoring of changes in the impact strength, carbonyl index and fracture surfaces on samples aged for various time intervals. It is shown that blends fortified by proper photostabilizers (carbon black or a combination of the UV absorber with photoantioxidant HAS) have sufficient stability for outdoor application.
Keywords: Blends with pre-aged LDPE; Upgrading of impact strength; Thermal restabilization; Outdoor restabilization;

Novel nano-hydroxyapatite (n-HAp)/poly((1,2-propanediol-sebacate)-citrate) (PPSC) composites, with varying the amount of n-HAp (5–20 wt%), for potential use in the soft tissue engineering were developed in the present work. The structure of composites was characterized by FT-IR and 13C NMR, the micromorphology of n-HAp and the dispersion property of n-HAp in n-HAp/PPSC composites were characterized by SEM and TEM. The experimental results showed that no obvious chemical bonds generated between n-HAp and PPSC matrix. Homogeneous distribution of nanoparticles in the polymer matrix was validated. DSC and DMA indicated that the Tg of the composites decreased with increasing the n-HAp content, as the chemical cross-linking density of the composites decreased. The mechanical properties of the composites were prominently improved, when the amount of n-HAp increased up to 20 wt%, the modulus of the composites increased 11.4 times, and the tensile strength of the composites increased 8.2 times. The hydrophilicity, water absorption, and degradation rate of composites can be tuned through varying the concentration of n-HAp. In vitro cytotoxicity was evaluated by the MTT assay with the L929 cell. The cell relative growth rates of the composites with the amount of n-HAp more than 10 wt% exceeded 75% after 7 days of incubation.
Keywords: Nano-hydroxyapatite (n-HAp); 1,2-PPSC bioelastomer; Reinforcement; Biodegradation;

A silicon-based acrylate (SHEA) was synthesized via the reaction between 2-hydroxylethyl acrylate and dimethyldichlorosilane, and characterized by Fourier transform infrared (FTIR), 1H NMR spectroscopy and 29Si NMR spectroscopy. The SHEA was blended with phosphorus-containing tri(acryloyloxyethyl) phosphate (TAEP) at different ratios to obtain a series of UV-curable flame retarded resins. The final unsaturation conversion of the SHEA films was determined by FTIR. Their combustion behaviors were examined by microscale combustion calorimetry (MCC). The thermal degradations of TAEP/SHEA composites were characterized using thermogravimetric analysis/infrared spectrometry (TG–IR). The MCC results present that the addition of TAEP into SHEA was able to decrease the HRR, HRC, T max and THC. Among the TAEP/SHEA resins, Si1 (TAEP:SHEA is 1:1) owns the highest initial decomposition temperature and leaves the most char residue at 800 °C. The change of chemical structure during the thermal degradation process was monitored by real-time FTIR analysis to study the condensed-phase flame retarded mechanism.
Keywords: Thermal properties; Combustion behaviors; UV-curable; TG–IR;

Cellulose degradation in newsprint paper ageing by František Kačík; Danica Kačíková; Michal Jablonský; Svetozár Katuščák (1509-1514).
The degradation of cellulose is an important factor influencing its physical, mechanical, optical and chemical properties and the longevity of paper in the electrical industry and in stored paper and books. A study of the accelerated ageing of newsprint paper has been performed at 98 °C during 0, 1, 2, 3, 5, 7, 10, 15, 20, 30 and 60 days. Degradation has been studied by viscometry, gel permeation chromatography (GPC) and saccharides determination. In the first stages of the accelerated ageing the cellulose depolymerisation takes place homogeneously (mainly due to the hydrolysis), later other reactions (oxidation, crosslinking) take place. The saccharides content in the paper decreases and the hemicelluloses are degraded faster.
Keywords: Paper ageing; Cellulose; Viscometry; Gel permeation chromatography; Tricarbanilates;

Boron trifluoride-catalyzed degradation of poly-ɛ-caprolactone at ambient temperature by Song-Dong Ding; Yu-Zhong Wang; Christopher D. Rudd (1515-1519).
Poly-ɛ-caprolactone (PCL) can be accelerated to degrade in the presence of boron trifluoride at ambient temperature. The degradation behaviors were studied by using the inherent viscosity measurement, gel permeation chromatography (GPC), infrared analysis (FTIR), nuclear magnetic resonance analysis (NMR), and thermal analysis (DSC). With increasing the addition amount of boron trifluoride, the molecular weight of PCL decreases; the molecular weight distribution is broadened; and the degree of crystallinity of PCL increases at first at low BF3 level, then decreases when BF3 content exceeds to 2.64 wt%. The results of IR, 1HNMR and GPC reveal that ɛ-caprolactone monomer does not occur and the main degradation products are the oligomers of PCL with low molecular weight. The mechanism for boron trifluoride-catalyzed degradation of PCL is discussed.
Keywords: Poly-ɛ-caprolactone; Boron trifluoride; Degradation; Transesterification;

Synergistic effect of decabromodiphenyl ethane and montmorillonite on flame retardancy of polypropylene by Xiao-Sui Chen; Zhong-Zhen Yu; Wei Liu; Sheng Zhang (1520-1525).
Polypropylene (PP) is melt-compounded in a twin-screw extruder with surface-modified decabromodiphenyl ethane/antimony trioxide (DBDPE/Sb2O3) and organically modified montmorillonite (OMMT). The intercalation and dispersion microstructure of OMMT in the nanocomposites are investigated by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thermal stability and char residue are characterized by thermogravimetric and differential thermal analysis (TGA–DTA). Flame retardant properties are evaluated by limited oxygen index (LOI) and UL-94 vertical burning test.The results indicate that better flame retardancy can be achieved for the composite containing a modified mixture DBDPE/Sb2O3. The presence of DBDPE/Sb2O3 could improve the dispersion of OMMT in polypropylene, leading to higher thermal stability and more char residue. A synergistic effect between OMMT and DBDPE/Sb2O3 has been observed and discussed.
Keywords: Montmorillonite; Decabromodiphenyl ethane; Antimony trioxide; Flame retardancy; Polypropylene;

A series of novel polyimides (3ad) were prepared from 3,3′,5,5′-tetramethyl-4,4′-diaminodiphenyl-4”-tert-butyltoluene (1) with four aromatic dianhydrides via a one-step high-temperature polycondensation procedure. The obtained polyimides showed excellent solubility, with the dissolvability at a concentration of 10 wt% in most amide polar solvents and chlorinated solvents. Their films were nearly colorless and exhibited high optical transparency, with the UV cutoff wavelength in the range of 322–350 nm and the wavelength of 80% transparency in the range of 395–414 nm. They also showed low dielectric constant (2.72–2.91 at 1 MHz) and low water absorptions (0.37–0.62%). Moreover, these polyimides possessed high glass transition temperatures (T g) (above 321 °C) and good thermal stability with 10% weight loss temperatures in the range of 526–547 °C in nitrogen atmosphere. In comparison with the analogous polyimides non-containing 3,3′,5,5′ -tetramethyl pendant groups, the resultant polyimides 3ad showed better solubility, higher optical transparency and lower dielectric constant.
Keywords: Polyimides; Solubility; Optical transparency; Dielectric constant;

Cross-linking of polytetrafluoroethylene during room-temperature irradiation by David L. Pugmire; Christopher J. Wetteland; Wanda S. Duncan; Rollin E. Lakis; Daniel S. Schwartz (1533-1541).
Exposure of polytetrafluoroethylene (PTFE) to α-radiation was investigated to determine the physical and chemical effects, as well as to compare and contrast the damage mechanisms with other radiation types (β, γ, or thermal neutron). A number of techniques were used to investigate the chemical and physical changes in PTFE after exposure to α-radiation. These techniques include: Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and fluorescence spectroscopy. Similar to other radiation types at low doses, the primary damage mechanism for the exposure of PTFE to α-radiation appears to be chain scission. Increased doses result in a change-over of the damage mechanism to cross-linking. This result is not observed for any radiation type other than α when irradiation is performed at room temperature. Finally, at high doses, PTFE undergoes mass-loss (via small-fluorocarbon species evolution) and defluorination. The amount and type of damage versus sample depth was also investigated. Other types of radiation yield damage at depths on the order of mm to cm into PTFE due to low linear energy transfer (LET) and the correspondingly large penetration depths. By contrast, the α-radiation employed in this study was shown to only induce damage to a depth of approximately 26 μm, except at very high doses.
Keywords: Cross-linking; Differential scanning calorimetry (DSC); FTIR; Polytetrafluoroethylene PTFE); Radiation;

Ultra-High Molecular Weight Polyethylene (UHMWPE) has been the material of choice for load-bearing articular components used in total joint arthroplasty in the past 30 years. However, the durability of the whole implant has often been compromised by oxidation of UHMWPE components. Since the use of a suitable, biocompatible stabilizer would minimize this inconvenience, the possibility to use vitamin E has been introduced.In the present work, medical grade UHMWPE was blended with 1.1, 2.3 and 11 mmol/l of vitamin E and consolidated by compression moulding. Small blocks of reference and of vitamin E-blended UHMWPE were then electron-beam irradiated at 30, 60 and 90 kGy, both in vacuum and in air. FTIR spectroscopy was used to monitor changes in both the polymer and the additive. Thin sections of irradiated virgin and vitamin E-blended UHMWPE were aged in air, at room temperature and in the dark and the kinetics of oxidation followed by FTIR. The reaction between vitamin E and macro-alkyl radicals or unlikely with peroxy radicals has been demonstrated and a correlation between the decrease of macroradicals and the stabilization effect of vitamin E has been shown.
Keywords: UHMWPE; Oxidation; Vitamin E; Antioxidant;

The thermal degradation behaviour of polydimethylsiloxane/montmorillonite nanocomposites by James P. Lewicki; John J. Liggat; Mogon Patel (1548-1557).
A series of novel polydimethylsiloxane/montmorillonite (PDMS/MMT) nanocomposites was prepared. The thermal degradation behaviour of these nanocomposites was studied by means of Thermal Volatilization Analysis (TVA) and Thermogravimetric Analysis (TGA). The major degradation products were identified as cyclic oligomeric siloxanes from D3 to D7, and higher oligomeric siloxane residues. Other minor degradation products include methane, bis-pentamethylcyclotrisiloxane, propene, propanal, benzene and dimethylsilanone. The results demonstrate that the nanoclay significantly alters the degradation behaviour of the PDMS network, modifying the profile of the thermal degradation and reducing the overall rate of volatiles evolution. The results also indicate that the nanoclay promotes the formation of dimethylsilanone and benzene by inducing low levels of radical chain scission.
Keywords: Poly(dimethylsiloxane); Nanocomposite; Thermal degradation; Montmorillonite;

The ESCR of three propylene impact copolymers in the presence of isopropanol was investigated and the variation in stress crack resistance was evaluated in terms of polymer characteristics. The effect of removing both soluble and crystalline material from the copolymers on the ESCR was evaluated. The stress crack resistance appears to be dependent on the crystallinity of the materials, but not solely so. The amount and distribution of the rubbery copolymer in these materials appears to play a role as well.
Keywords: Stress crack resistance; Propylene copolymers; Temperature rising elution fractionation; Fraction removal;

Effect of montmorillonite treatment on the thermal stability of poly(vinyl chloride) nanocomposites by Karin Sterky; Thomas Hjertberg; Harald Jacobsen (1564-1570).
The aim of this research was to study the effect of different intercalants on the thermal degradation/dehydrochlorination of poly(vinyl chloride) (PVC). PVC nanocomposites were prepared containing 2 phr of montmorillonite clay. The montmorillonite was treated with different organic intercalants and analysed by thermogravimetric analysis and X-ray diffraction. All intercalants were found to intercalate the clay. The nanocomposites were prepared on a two-roll mill and pressed into 0.7 mm thick plates. The degradation was analysed by yellowness index, Congo red test and UV–visible spectroscopy. All cationic intercalants were found to accelerate the dehydrochlorination of PVC whereas the non-ionic did not affect thermal degradation. On the other hand, some non-ionic intercalants showed poor dispersion.
Keywords: Nanocomposites; PVC; Montmorillonite; Dehydrochlorination; Thermal degradation; Intercalation;

Effect of extrusion and photo-oxidation on polyethylene/clay nanocomposites by N.Tz. Dintcheva; S. Al-Malaika; F.P. La Mantia (1571-1588).
Polyethylene (a 1:1 blend of m-LLDPE and z-LLDPE) double layer silicate clay nanocomposites were prepared by melt extrusion using a twin screw extruder. Maleic anhydride grafted polyethylene (PEgMA) was used as a compatibiliser to enhance the dispersion of two organically modified monmorilonite clays (OMMT): Closite 15A (CL15) and nanofill SE 3000 (NF), and natural montmorillonite (NaMMT). The clay dispersion and morphology obtained in the extruded nanocomposite samples were fully characterised both after processing and during photo-oxidation by a number of complementary analytical techniques. The effects of the compatibiliser, the organoclay modifier (quartenary alkyl ammonium surfactant) and the clays on the behaviour of the nanocomposites during processing and under accelerated weathering conditions were investigated. X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), rheometry and attenuated reflectance spectroscopy (ATR-FTIR) showed that the nanocomposite structure obtained is dependent on the type of clay used, the presence or absence of a compatibiliser and the environment the samples are exposed to. The results revealed that during processing PE/clay nanocomposites are formed in the presence of the compatibiliser PEgMA giving a hybrid exfoliated and intercalated structures, while microcomposites were obtained in the absence of PEgMA; the unmodified NaMMT-containing samples showed encapsulated clay structures with limited extent of dispersion in the polymer matrix. The effect of processing on the thermal stability of the OMMT-containing polymer samples was determined by measuring the additional amount of vinyl-type unsaturation formed due to a Hoffman elimination reaction that takes place in the alkyl ammonium surfactant of the modified clay at elevated temperatures. The results indicate that OMMT is responsible for the higher levels of unsaturation found in OMMT-PE samples when compared to both the polymer control and the NaMMT-PE samples and confirms the instability of the alkyl ammonium surfactant during melt processing and its deleterious effects on the durability aspects of nanocomposite products. The photostability of the PE/clay nanocomposites under accelerated weathering conditions was monitored by following changes in their infrared signatures and mechanical properties. The rate of photo-oxidation of the compatibilised PE/PEgMA/OMMT nanocomposites was much higher than that of the PE/OMMT (in absence of PEgMA) counterparts, the polymer controls and the PE–NaMMT sample. Several factors have been observed that can explain the difference in the photo-oxidative stability of the PE/clay nanocomposites including the adverse role played by the thermal decomposition products of the alkyl ammonium surfactant, the photo-instability of PEgMA, unfavourable interactions between PEgMA and products formed in the polymer as a consequence of the degradation of the surfactant on the clay, as well as a contribution from a much higher extent of exfoliated structures, determined by TEM, formed with increasing UV-exposure times.
Keywords: Clay–PE nanocomposites; Processing; Photo-oxidation; Polyethylene-graft-maleic anhydride;

A detailed study of early colour change in Scots pine (Pinus sylvestris) due to accelerated simulated sunlight exposure was undertaken focusing on the first 24 h of change. Colour changes were monitored with a Datacolor check spectrophotometer and compared with a set of controls. Measurements on both samples and controls were performed hourly for the first 24 h and there after daily until 168 h’ exposure with extra measurements at 200, 350 and 500 h. A subset of samples was extracted prior to exposure to check the effects of any colour change due to the presence of extractives. Data was analysed using the reflectance spectra (400–700 nm) as well as the CIE-L a b system and ΔE. The majority of colour changes were found to occur within the first 24 h. This was unaffected by the removal of extractives from the wood and was independent of temperature. Mechanical properties and weight changes were also monitored to allow a comparison of sensitivity between the differing methods.
Keywords: Photodegradation; Colour changes; Wood surfaces; Pinus sylvestris; Reflectance spectra; CIE-L a b parameters;

Kinetics of the dehydrochlorination of poly(vinyl chloride) in the presence of NaOH and various diols as solvents by Tomohito Kameda; Katsuaki Imai; Guido Grause; Tadaaki Mizoguchi; Toshiaki Yoshioka (1595-1597).
The dehydrochlorination of PVC in the presence of NaOH was investigated in different diols. Diethylene glycol (DEG), triethylene glycol (TEG), and propylene glycol (PG) were found to be effective in accelerating the dechlorination of PVC. The dehydrochlorination was promoted in the order TEG > DEG > PG, which was in agreement with the compatibility between PET and the diol. Compatibility resulted in an improved penetration of the PVC particle by the solvent, leading to the acceleration of the dehydrochlorination. The dehydrochlorination of PVC in NaOH/diol followed first-order kinetics, confirming the progress of the reaction under chemical reaction control. The apparent activation energies were 82 kJ mol−1, 109 kJ mol−1, and 151 kJ mol−1 for TEG, DEG, and PG, respectively. The lower the activation energy became the faster the dehydrochlorination of PVC proceeded.
Keywords: Poly(vinyl chloride); Dechlorination; Diol; Apparent activation energy;

Corrigendum to “A kinetic study of the decross-linking of cross-linked polyethylene in supercritical methanol” [Polym Degrad Stab 93 (2008) 2084–2088] by Hong-shik Lee; Ju Hyeong Jeong; Hang-Kyu Cho; Chong Min Koo; Soon Man Hong; Hwayong Kim; Youn-Woo Lee (1598).