Polymer Degradation and Stability (v.96, #12)

Dose–response functions for historic paper by Eva Menart; Gerrit De Bruin; Matija Strlič (2029-2039).
Paper degradation has been studied extensively over the past few decades from both the conservation and the material science perspectives. This review focuses on the quantifiable impacts of the environment and material composition, from the viewpoint of long-term storage of historic paper-based collections. Therefore, temperature, relative humidity and their variation, and pollution are of major interest while photoinitiated processes are covered only briefly.New experiments comparing the effects of the most abundant indoor pollutants (NO2, acetic acid and formaldehyde) and the effects of fluctuating temperature and relative humidity are also presented as part of the discussion. This work highlights the need for revision of the existing dose–response (damage) functions for paper and their further development.
Keywords: Historic paper; Hydrolysis; Oxidation; Viscometry; Colorimetry; Heritage science;

Development of new approach based on Raman spectroscopy to study the dispersion of expanded graphite in poly(lactide) by Fatima Hassouna; Abdelghani Laachachi; David Chapron; Yamna El Mouedden; Valérie Toniazzo; David Ruch (2040-2047).
A new approach has been developed to study the dispersion/delamination of expanded graphite (EG) in poly(lactide) (PLA) by using Raman spectroscopy. This technique is more sensitive and therefore fully complementary to more standard dispersion characterization techniques like SEM, TEM and X-ray diffraction. The incorporation of EG into PLA was carried out by a twin-screw micro-extruder. The effects of the dispersion and delamination of EG on the thermal and thermo-mechanical properties of polylactide-EG nanocomposites were investigated. In contrast to the standard techniques, Raman spectroscopy was able to show a partial exfoliation, which could therefore explain the slight improvement of the PLA–EG thermal and thermo-mechanical properties.
Keywords: Poly(lactide) (PLA); Nanocomposite; Expanded graphite; Dispersion; Thermal properties; Raman;

A number of multifunctional ABx-type monomers exist in plant metabolites, and studies on the formation of hyperbranching polymers from ABx-type monomers are very significant in the development of bio-related polymeric materials. We established a method for the preparation of well-defined structures in bio-based, hyperbranched (HB) polyarylates by the copolycondensation of caffeic acid (DHCA) as an AB2-monomer and p-coumaric acid (4HCA) as an AB-monomer, using the highly efficient catalyst Na2HPO4 to regulate the polymerization speed. 1H NMR analysis revealed the time course of the formation of the hyperbranching structures. which strongly affected the glass transition and degradation temperatures, as well as the molecular weight and composition.
Keywords: Hyperbranched polymers; Bio-based polymers; Biomimetics; Polyarylates; NMR analyses;

Rate of polymer degradation is very important for implantable biomaterials since controlling the degradation rate may complement the biological response and affected mechanical property requirements. In spite of numerous publications on the potential use of combinations of poly lactic acid/bioactive glass fillers for degradable bone plate, little information exists on the controlling degradation rate and its effects on the other aspects such as biomechanical compatibility, bioactivity, etc. Our previous study revealed that a composite bone plate consist of poly l-lactic acid/braided bioactive glass fibers has the initial mechanical properties near to cortical bone. In this study, degradation rate and mechanical behavior of the composite bone plate were assessed, and also degradation rate was controlled by using proper manufacturing process and improving bonding between matrix and reinforcement. Moreover, bioactivity of the composite was considered before and after controlling degradation rate, because of the important role of bioactivity and ion release in healing acceleration. Results showed that degradation process of the composite could be controlled properly. Strength of the treated composite decreased only about 5% through 2 weeks and about 35% after 8 weeks while, the strength loss for the untreated composites was about 50 and 70 percent after 2 weeks and 8 weeks of degradation respectively. Although calcium-phosphate formation on the surface of the composite was postponed in the treated samples, the bioactivity of the composite remained unchanged and bone-like apatite was formed on the composite surface which is important for the application of the composite in bone tissue environment.
Keywords: Degradation rate control; Bioactivity; Mechanical properties; Composite bone plate;

Cross-link network of polydimethylsiloxane via addition and condensation (RTV) mechanisms. Part I: Synthesis and thermal properties by Mohamad Riduwan Ramli; Muhammad Bisyrul Hafi Othman; Azlan Arifin; Zulkifli Ahmad (2064-2070).
A series of highly cross-linked polysiloxane was synthesised via hydrosilylation and condensation reaction. Structural identification using Fourier Transform Infrared (FTIR) and 1H-NMR confirmed their chemical structures. Their thermal and, mechanical properties, and crystallinity, were analysed and related to the level of cross-link density. These systems displayed elevated thermal and hardness properties at an increased cross-link density. Furthermore, the level of crystallinity was reduced as displayed by XRD analysis. Along with this observation, the calculated fractional free volume (FFV) showed a decreasing trend leading to the ‘densification’ effect. It was envisaged that the linear polysiloxane chain segments aligned parallel to each other in a triclinic crystal system to generate a crystalline domain. The spacing between these stacking chains was found to be about 7.2 Å as measured from simulated XRD pattern.
Keywords: Polysiloxane; Cross-link network; Thermal; Crystallinity; Fractional free volume; X-ray diffraction;

Novel biodegradable and biobased thermoplastic elastomers, poly[dodecanolide-12-hydroxystearate (12HS)], poly(pentadecanolide-12HS) and poly(hexadecanolide-12HS) with M ws of 140,000–290,000 g mol−1 were prepared by the enzymatic copolymerization of a macrolide as the hard segment and methyl 12HS as the soft segment. Their thermal properties, such as T m and T c, were measured by DSC. Physicochemical and mechanical properties, such as crystallinity, were also measured. The polymer structures were analyzed with respect to the sequence of the two monomers by 1H NMR spectroscopy using an europium shift reagent. The randomness of the two monomer units in the polymer chain increased with the polymerization time. Both Young’s modulus and tensile strength decreased with increasing 12HS content in the copolymer. In contrast, elongation at break increased with increasing 12HS content, thus demonstrating the copolymers’ elastomeric properties. These copolymers showed biodegradabilities by activated sludge, which also increased with increasing 12HS content.
Keywords: Biodegradable polymers; Biobased polymer; Lipase; Aliphatic polyesters; Thermoplastic elastomers; Enzymatic polymerization;

Effects of organic–inorganic hybrid coatings on durability of cross-linked polyethylene by Andrea Saccani; Maurizio Toselli; Francesco Pilati; Davide Fabiani; Fabrizio Palmieri (2080-2087).
Cross-linked polyethylene (XLPE) films have been coated with nanostructured hybrid organic–inorganic coatings in order to improve their durability. For this purpose, bi- and mono-layer coatings containing different amount of silica and different organic polymers have been prepared through sol-gel reactions and applied to XLPE commercial films. The thermo-oxidative stability, electrical strength and conductivity of XLPE coated films have been investigated after ageing in air at temperatures above the on-service conditions, i.e. at 105 and 120 °C for 1900 and 600 h, respectively. The performed investigations (FT-IR, DSC, TGA and electrical properties) showed that all the coatings tested were able to strongly protect XLPE against oxidation, and that the coating with a PVOH/SiO2 layer gave the best protection. The increase of thermal resistance induced by the coatings reflects on the electrical strength after ageing, which is higher for coated samples than for uncoated ones. Moreover, while ageing has only a slight effect on electrical conductivity in different coated samples, a strong increase of conductivity was observed after ageing for highly oxidated uncoated samples.
Keywords: Thermo-oxidation; XLPE; Organic–inorganic hybrid coatings; Nanocomposite; Electrical properties;

How the biodegradability of wheat gluten-based agromaterial can be modulated by adding nanoclays by Anne Chevillard; Hélène Angellier-Coussy; Bernard Cuq; Valérie Guillard; Guy César; Nathalie Gontard; Emmanuelle Gastaldi (2088-2097).
The objective of this work was to investigate the influence of clay nanoparticles on the biodegradability of wheat gluten-based materials through a better understanding of multi-scale relationships between biodegradability, water transfer properties and structure of wheat gluten/clay materials. Wheat gluten/clay (nano)composites materials were prepared via bi-vis extrusion by using an unmodified sodium montmorillonite (MMT) and an organically modified MMT. Respirometric experiments showed that the rate of biodegradation of wheat gluten-based materials could be slowed down by adding unmodified MMT (HPS) without affecting the final biodegradation level whereas the presence of an organically modified MMT (C30B) did not significantly influence the biodegradation pattern. Based on the evaluation of the water sensitivity and a multi-scale characterization of material structure, three hypotheses have been proposed to account for the underlying mechanisms. The molecular/macromolecular affinity between the clay layers and the wheat gluten matrix, i.e. the ability of both components to establish interactions appeared as the key parameter governing the nanostructure, the water sensitivity and, as a result, the overall biodegradation process.
Keywords: Biodegradation; Wheat gluten; Montmorillonite; Nanocomposite; Water sensitivity;

Glow wire ignition temperature (GWIT) and comparative tracking index (CTI) of glass fibre filled engineering polymers, blends and flame retarded formulations by Francesco Acquasanta; Corrado Berti; Martino Colonna; Maurizio Fiorini; Sreepadaraj Karanam (2098-2103).
Engineering thermoplastic polymers such as polyamides, polycarbonates, semi-crystalline aromatic polyesters and their blends are widely used as insulating materials in electrical and electronic appliances. Flame retardants are often employed in the formulation of these materials, since good performance in terms of ignition and tracking resistance, evaluated by Glow Wire Tests (GWIT) and Comparative Tracking Index (CTI) are required in these applications. In this paper, a comparative evaluation of GWIT and CTI performances has been simultaneously performed for a wide set of glass fibre filled materials chosen among engineering thermoplastics and their blends. Some flame retarded formulations have been also tested, in order to screen the effects of various additives. Useful indications have been obtained on the effect of each polymer and additives on GWIT and CTI properties. In addition, interesting synergies have been observed, especially by blending polyesters and polyamides. Thermogravimetric measurements of char yields have been successfully related with CTI behaviour. The presence of additives changes the structure of the carbonaceous residue, hence the conductivity of the tracks. Neat polycarbonate passed the GWIT test but not CTI, while poly(butylene terephthalate) showed the best balance of GWIT and CTI performance among the pure resins tested. Blending polycarbonate with polyester did not improve significantly GWIT performance, but had a negative effect on tracking resistance. Polyesters/polyamide blends were dominated by polyester in GWIT, but they showed synergistic effects in CTI.
Keywords: Glow wire ignition temperature; Comparative tracking index; Thermal properties; Flame retardants; Blends;

Study of flammability and thermal properties of high-impact polystyrene nanocomposites by Zvonimir Katančić; Jadranka Travaš-Sejdić; Zlata Hrnjak-Murgić (2104-2111).
To increase thermal stability and flammability of high-impact polystyrene (HIPS) nanocomposites with silica nanoparticles and two types of polyphosphate flame retardants were prepared by extrusion. Nanocomposites were characterized by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, limiting oxygen index (LOI) analysis and the evaluation of mechanical properties. It was found that organic polyphosphate in combination with silica increased thermal stability and fire retardancy by 50% in LOI test. Morphology characterization revealed existence of crystalline order which affected mechanical properties; tensile strength was approximately the same as virgin HIPS while elasticity was sharply decreased. Ammonium polyphosphate did not affect mechanical properties as much as the organic material but was not equally efficient in flame retardancy which was just marginally increased.
Keywords: Flammability; Thermal degradation; High-impact polystyrene; Silica; Nanocomposites;

A UV–Visible/Raman spectroelectrochemical study of the stability of poly(3,4-ethylendioxythiophene) films by B. Zanfrognini; A. Colina; A. Heras; C. Zanardi; R. Seeber; J. López-Palacios (2112-2119).
Poly(3,4-ethylendioxythiophene) films were electropolymerized in aqueous medium without using any surfactant, on glassy carbon electrodes. UV/Vis and Raman spectroelectrochemical techniques were used to analyze the degradation of the polymer film occurring at different pH values. Spectroelectrochemistry has proven to be a very useful analytical tool for this purpose, thanks to its ability to provide information not only about the extent of degradation, but also about mechanistic aspects of the process. From our results we extracted important information about the main factors that play a role in the degradation, in particular about the influence of repetitive doping and de-doping cycles and of photo-induced processes, as a function of the characteristics of the solution, i.e. of pH.
Keywords: Conducting polymers; PEDOT; Electrochemistry; Spectroelectrochemistry; Raman spectroscopy;

Effect of temperature and nanoparticle type on hydrolytic degradation of poly(lactic acid) nanocomposites by K. Fukushima; D. Tabuani; M. Dottori; I. Armentano; J.M. Kenny; G. Camino (2120-2129).
PLA and its nanocomposite films based on modified montmorillonite (CLO30B) or fluorohectorite (SOM MEE) and unmodified sepiolite (SEPS9) were processed at a clay loading of 5 wt% and hydrolytically degraded at 37 and 58 °C in a pH 7.0 phosphate-buffered solution. An effective hydrolytic degradation for neat PLA and nanocomposites was obtained at both temperatures of degradation, with higher extent at 58 °C due to more extensive micro-structural changes and molecular rearrangements, allowing a higher water absorption into the polymer matrix.The addition of CLO30B and SEPS9 delayed the degradation of PLA at 37 °C due to their inducing PLA crystallization effect and/or to their high water uptake reducing the amount of water available for polymer matrix hydrolysis. The presence of SOM MEE also induced polymer crystallization, but it was also found to catalyze hydrolysis of PLA. Concerning hydrolysis at 58 °C, the presence of any nanoparticle did not significantly affect the degradation trend of PLA, achieving similar molecular weight decreases for all the studied materials. This was related to the easy access of water molecules to the bulk material at this temperature, minimizing the effect of polymer crystallinity clay nature and aspect ratio on the polymer degradation.
Keywords: Poly(lactic acid); Nanocomposites; Sepiolite; Montmorillonite; Hydrolytic degradation;

Mechanical properties, structure analysis and enzymatic degradation of uniaxially cold-drawn films of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] by Jiaqi Zhang; Kenichi Kasuya; Takaaki Hikima; Masaki Takata; Akio Takemura; Tadahisa Iwata (2130-2138).
Poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate] (P(3HB-co-4HB)) films were prepared by uniaxial cold-drawing from an amorphous preform at a temperature below, but close to the glass transition temperature. Molecular and highly-ordered structures and physical properties of cold-drawn films were investigated by tensile testing, wide-angle X-ray diffraction and small-angle X-ray scattering. Enzymatic degradation of P(3HB-co-4HB) films was performed using an extracellular polyhydroxybutyrate depolymerase purified from Ralstonia pickettii T1. Tensile strength, elongation to break and Young’s modulus of P(3HB-co-4HB) with cold-drawn ratio 1200% reached 290 MPa, 58% and 2.8 GPa, respectively. X-ray fibre diagrams of cold-drawn P(3HB-co-4HB) films showed a strong reflection on the equatorial line, indicating a planar zigzag conformation (β-form) together with 21 helix conformation (α-form). The β-form seems to contribute to the high tensile strength, and a new mechanism of generation of the β-form is proposed. The enzymatic degradation rate increased with increasing draw ratio, and increased greatly with increasing 4HB content.
Keywords: Structure analysis; Physical property; Enzymatic degradation; Uniaxial cold-drawing; Poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate];

Elastomeric materials are used in the manufacture of structural dampeners due to their high damping coefficient and ease of production. However, elastomers, and in particular thermoplastic polyurethanes (TPU), are susceptible to degradation from environmental conditions. Samples of TPU were investigated, in terms of their mechanical properties, under the influence of four factors; time (up to 10 weeks thermal exposure), temperature (20–80 °C), strain (10% and 25%) and moisture (pre-soak/testing in water). Compression, hardness and compression set tests were used to determine the major contributors to the degradation process. It was found that pure thermal loading at 70 °C for 10 weeks did not result in any changes in material properties, other than an initial drying phase causing an increase in hardness of 2–3 Shore D. The compression set values were found to be heavily dependent on the test temperature, with a significant increase in compression set being seen between 70 and 80 °C. The presence of water (introduced by testing in water) acted as a plasticiser and resulted in a larger amount of compression set, than testing in the absence of water. The level of compression set was shown to be insensitive to the strain level. Overall, it was found, for the conditions tested, that temperature was the major driving force behind the compression set of the TPU material.
Keywords: Thermoplastic polyurethane; Compression set; Environmental degradation; Structural dampeners;

Effects of silphenylene units on the thermal stability of silicone resins by Zhizhou Yang; Shuang Han; Rong Zhang; Shengyu Feng; Changqiao Zhang; Shengyou Zhang (2145-2151).
A series of silicone resins containing silphenylene units were synthesized by a hydrolysis–polycondensation method, with methyltriethoxysilane, dimethyldiethoxysilane and 1,4-bis(ethoxydimethylsilyl)benzene. Their thermal degradation behaviours were studied by thermogravimetric analysis (TGA), differential thermogravimetry (DTG) and Fourier-transform infrared (FTIR) spectroscopy, and the effect of silphenylene units on the thermal stability of silicone resins was also investigated. Results showed that the thermal stability of silicone resins was improved by the introduction of silphenylene units into the backbone. Under nitrogen atmosphere, the temperature for maximum degradation rate of silicone resins with silphenylene units was lower compared to the pure methylsilicone resin. With the increase of silphenylene units, the amount of degradation residues increased under nitrogen atmosphere while it decreased under air atmosphere. Additionally, the short-term and long-term stability of silicone resins were also improved by the introduction of silphenylene units.
Keywords: Silicone resin; Silphenylene units; Thermal degradation; Thermal stability;

Natural antioxidants for polypropylene stabilization by V. Ambrogi; P. Cerruti; C. Carfagna; M. Malinconico; V. Marturano; M. Perrotti; P. Persico (2152-2158).
A study on the efficiency of bio-based compounds as stabilizers for polypropylene (PP) is reported. A water extract from French maritime pine bark (Pycnogenol®), a by-product containing polyphenols obtained from wine production, and a carotenoid-containing oleoresin from processing of tomatoes were used. Their stabilizing activity was compared with that of a commercial phenolic antioxidant. Thermogravimetric analysis and Oxidative Induction Time measurements performed on unaged samples, as well as infrared spectroscopy on samples aged at 70 °C, provided evidence for the effectiveness of the natural stabilizers. Mechanical characterization was carried out on aged films and injection moulded samples. Experimental results indicated that particularly grape extract could provide long-term stabilization to PP under conditions of oxidative degradation. Therefore, it could be used as efficient and high value-added additive for polypropylene. Pycnogenol® also showed antioxidant activity, however the achievement of a more homogeneous dispersion in the polymer matrix could improve the mechanical performance of aged samples.
Keywords: Polypropylene; Thermal oxidation; Natural additives; Carotenoids; Phenols; Long-term stability;

The effects of thermal treatment on the antioxidant activity of polyaniline by Ashveen V. Nand; Sudip Ray; Marija Gizdavic-Nikolaidis; Jadranka Travas-Sejdic; Paul A. Kilmartin (2159-2166).
The thermal stability of chemically synthesized polyaniline (PANI) was examined, including granular (G) polyaniline powders formed conventionally in an HCl medium, and nanorod (NR) samples prepared using a falling-pH synthesis. The samples were examined before and after dedoping (dd) using thermogravimetric analysis (TGA), which showed small mass losses in the 200–300 °C temperature range, and greater mass losses due to oxidative degradation at higher temperatures. Furthermore, samples were treated thermally at 100, 125, 150, 175, 200, 250 and 300 °C for 30 min in air. SEM images did not show any pronounced effect on the morphologies of the samples from thermal treatment up to 300 °C. The ratios of the intensities (Q/B) of the predominantly quinonoid (Q) and benzenoid peaks (B) from FTIR spectroscopic analysis revealed that NR-PANI and NR-PANIdd underwent cross-linking upon thermal treatment up to 175 °C and were oxidized after treatment above 175 °C. G-PANI and G-PANIdd also underwent the same chemical changes with oxidation occurring above 200 °C. The free radical scavenging capacity of the samples was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, and was found to be independent of the spin concentrations of the samples. All samples exhibited a rapid decline in free radical scavenging capacity when exposed to temperatures above 200 °C, indicating that any polymer processing should be undertaken at temperatures less than this value to achieve high antioxidant activity.
Keywords: Polyaniline; Thermal treatment; Nanorods; Oxidation; Radical scavenging;

Novel flame retardancy effects of DOPO-POSS on epoxy resins by Wenchao Zhang; Xiangmei Li; Rongjie Yang (2167-2173).
A series of flame retarded epoxy resins (EP) was prepared with a novel polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-POSS). The flame retardancy of these EPs was tested by the LOI, UL-94, which indicates that DOPO-POSS has meaningful effects on the flame retardancy of EP composites. 2.5 wt.% DOPO-POSS incorporation into epoxy resin (EP-2.5), results in a LOI value 30.2 and UL-94 V-1 (t 1  = 8 s and t 2  = 3 s) rating. Moreover, self-extinguishing effect through the pyrolytic gases spurt is observed in UL-94 test for the EP-2.5. The pyrolytic gases and thermal stability of epoxy resins with and without DOPO-POSS were detected by TGA-FTIR under air atmosphere. Releases of gaseous species are found to be similar for the pure EP and EP-2.5. The details of fire behaviour, such as TTI, HRR, p-HRR, TSR, SEA, COPR, CO2PR, and TML, were tested by cone calorimeter. It is notable that 2.5 wt.% DOPO-POSS could make COPR and CO2PR reach a maximum, which could explain the blowing-out extinguishing effect.
Keywords: Epoxy resin; DOPO-POSS; Flame retardancy; TGA; Cone calorimeter;

Synthesis, characterization and hydrolytic stability of poly (amic acid) ammonium salt by Dongdan Cai; Jianfeng Su; Mei Huang; Yanhua Liu; Jianjun Wang; Lixing Dai (2174-2180).
A series of new poly (amic acid) ammonium salt (PAAS) precursors were prepared by incorporating different amounts of triethylamine (TEA) into terpolymer polyamic acid (PAA), which was synthesized by pyromellitic dianhydride (PMDA), 4,4’-oxydianiline (ODA) and p-phenylenediamine (PDA) in dimethylacetamide (DMAc). Then, the PAAS films were made by casting their solutions onto glass plates followed by the evaporation of the solvent. The chemical structure of PAAS films was confirmed by 1H NMR and FTIR spectroscopy. Mechanical properties, intrinsic viscosities and solubility of PAAS precursors were examined, respectively. It was found that the intrinsic viscosity of PAA solution obviously decreased with storage time during 30 days, while no distinct changes were observed in the intrinsic viscosity of the PAAS (the mole ratio of TEA/repeating unit of PAA = 2/1) solution after 90 days. The results suggested that hydrolytic stability of the PAAS films was significantly improved as compared with that of PAA film due to the polyelectrolyte structure of PAAS. Moreover, the thermal and mechanical properties of polyimide (PI) films prepared from PAAS precursors were also investigated, respectively.
Keywords: Poly (amic acid) ammonium salt; Polyimide; Hydrolytic stability; Synthesis; Characterization;

Preparation and characterization of oxidized sesbania gum and evaluation of its warp sizing performance for fine cotton yarns by Ding Shen; Man Xue; Lei Zhang; Huijuan Liu; Lin Gao; Yuanchen Cui (2181-2188).
Sesbania gum (SG) was oxidized by sodium hypochlorite. Resultant oxidized sesbania gum (OSG) was characterized by means of Fourier transformation infrared spectrometry, scanning electron microscopy, and high resolution transmission electron microscopy. The thermal stability of OSG was analyzed by means of thermal analysis and the apparent viscosity of its slurry was also measured by rotary viscometer. Moreover, the effect of OSG slurry as a warp sizing agent on the physico-mechanical properties of fine cotton yarns was investigated. It was found that fine cotton yarns sized with OSG had increased tensile strength and decreased elongation at break than the untreated ones. Besides, the fine cotton yarns treated with the OSG slurry had obviously decreased hairiness index and slightly increased abrasion resistance, and OSG slurry had good adhesion. In one word, as-synthesized OSG slurry may find promising application as a novel high-performance warp sizing agent for fine cotton yarns.
Keywords: Oxidized sesbania gum; Preparation; Characterization; Warp sizing performance;

Bioencapsulation allows the protection of biologically active substances or cells from the biological environment. As such, bioencapsulation is often used for the delivery of drugs, growth factors and therapeutically useful cells. Depending on the site of implantation, the biocapsules are subjected to different pH environments, which will affect the degradation properties, mechanical properties and swelling behaviour of the biocapsules. As such, the encapsulation material plays an important role in the long term stability and performance of the biocapsules in vivo. In this study, five types of encapsulation materials were investigated: (i) alginate (A), (ii) alginate–chitosan (AC), (iii) alginate–chitosan–alginate (ACA), (iv) alginate–chitosan–polyethylene glycol (PEG) (ACP) and (v) alginate–chitosan–polyethylene glycol (PEG)–alginate (ACPA). Degradation studies were carried out by immersing the microcapsules in solutions of different pH values to investigate the role of the material as well as the number of encapsulation layers in maintaining the stability of the microcapsules in the different pH environments. Compression testing indicated that even with the presence of PEG on the surface membrane, there was not much difference in mechanical strength between ACA and ACPA microcapsules. However, the use of PEG did affect the weight change of the ACPA microcapsules when immersed in water and three different pH solutions. For the swelling test, the ACPA microcapsules showed a lower water uptake than ACA microcapsules. For degradation, the presence of PEG led to a lower increase in weight change compared to non-PEG chitosan microcapsules. Hence, the study revealed that PEG influenced the integrity of the surface membrane and not the mechanical strength of the microcapsules. With the inclusion of PEG, the interpenetrating network on the surface membrane would be further reinforced. As such, the addition of PEG to the alginate–chitosan microcapsules led to protection against an acidic environment, whilst the number of coating layers only influences the swelling properties and not the degradation and Young’s modulus of the microcapsules.
Keywords: Alginate; Chitosan; Polyethylene glycol; Degradation; Microcapsules;

Synthesis and properties of phosphorus polyesters with systematically altered phosphorus environment by Oliver Fischer; Doris Pospiech; Andreas Korwitz; Karin Sahre; Liane Häußler; Peter Friedel; Dieter Fischer; Christina Harnisch; Yana Bykov; Manfred Döring (2198-2208).
Monomers with phosphorus-containing substituents were incorporated into aromatic–aliphatic polyesters to develop polymeric halogen-free flame retardants as additives for poly(butylene terephthalate) (PBT). They were built into the polyester backbone of PBT substituting 1,4-butane diol as monomer by phosphorus-containing aromatic–aliphatic diols. Starting from 10-(2,5-bis(2-hydroxyethoxy)phenyl)-9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO-HQ-GE), the chemical structure of the phosphorus monomers was systematically varied resulting in new polymers with diphenyl phosphine oxide substituents and bridged phosphine oxide units. The polymers were prepared by transesterification polycondensation in the melt in lab-scale as well as in a 2.4 l-autoclave. The properties of the polyesters were determined and compared to the DOPO-based polyester with respect to the achieved molar mass and polydispersity, solid state structure, glass transition temperature, thermal stability and combustion behavior.It was found that the different phosphorus substituents lead to different glass transition temperatures. The polymers containing bridged phosphorus structural units showed higher glass transition temperatures T g and resulted in higher char yields after thermal decomposition. Both phosphine oxide structures showed only one-step decomposition with a shoulder at the end of the step. In contrast, two separate steps were observed in the polyesters with DOPO-substituents. The results indicated that the phosphorus polyesters under discussion are suitable to adjust the flame retarding mechanism.
Keywords: Thermal decomposition; Flame retardant; Phosphorus-containing polyesters; Polycondensation; Transesterification;

A novel method is proposed to produce PMMA with excellent thermal stability by a continuous process composed of polymerization and devolatilization steps. It is based on the fact that free radical polymerized PMMA is a mixture of polymer chains with different structure, a small fraction of which, containing head-to-head linkages or unsaturated ends, is less thermally stable and the major portion without those defect structures which is much more stable. Our idea is selectively remove the unstable chains from this mixture by pre-decomposing them at suitable temperatures in a continuous process, leaving the stable portion as the final PMMA product. The results showed that during the continuous process, the chains with head-to-head linkages were eliminated by conducting the polymerization at 155 °C, and then the chains with unsaturated ends were removed by devolatilization at 300 °C. The final PMMA was thermally stable up to 313 °C.
Keywords: Poly(methyl methacrylate); Thermal stability; Free radical bulk polymerization; Head-to-head linkages; Unsaturated chain ends;

Halogen-free flame retardant linear low density polyethylene (LLDPE)/ethylene-acrylic acid copolymer (EAA) blends were prepared in a melt process using magnesium hydroxide (MH) as flame retardant. The effect of EAA on flame retardancy and properties of LLDPE/EAA/MH composites was studied. The flammability of composites was investigated using Limiting Oxygen Index (LOI) and Cone calorimeter test. The results showed that the introduction of EAA into composites apparently increased LOI from 28% to 39%, meanwhile, reduced heat release rate (HRR) and smoke production rate (SPR) according to Cone calorimeter results, which was mainly due to the uniform dispersion of MH as a result of hydrogen bonding and acid-base reaction between MH and EAA. This improved interfacial adhesion was confirmed by Scanning Electronic Microscopy (SEM). Thermogravimetric analysis (TGA) showed that EAA could enhance the thermal oxidative stability of composites. It was attributed to the formation of a stable barrier to prevent the heat and mass transfer in fire, which was confirmed by the observation of fire performance with Cone calorimeter. The crystallization and rheological behaviour of composites were studied using Differential scanning calorimeter (DSC) and oscillatory rheological measurements. Mechanical test results indicated that the addition of EAA could increase the elongation at break and impact strength of composites.
Keywords: Linear low density polyethylene; Magnesium hydroxide; Ethylene-acrylic acid copolymer; Flame retardant;

Crack initiation and evolution in vulcanized natural rubber under high temperature fatigue by Gengsheng Weng; Guangsu Huang; Hangxin Lei; Liangliang Qu; Yijing Nie; Jingrong Wu (2221-2228).
The nanoscaled crack initiation and evolution of natural rubber under high temperature (85 °C) and small strain amplitude (strain maximum α = 1) fatigue condition were investigated. It was shown by scanning electron microscopy (SEM) images that cracks and cavities with dimensions in nanoscale in the NR matrix appear during the high temperature fatigue. FTIR study indicated that thermal oxidation effect leads to the crosslinking structure destruction. According to the combined analysis of SEM, energy-dispersive X-ray (EDX) spectrometer and small angle X-ray scattering investigations, it was deduced that the destruction of crosslinking structure mainly locates in the vicinity of the ZnS particles with a diameter of 20.2 nm. The ZnS particles are generated as a byproduct in the vulcanization process. Further, the real-time SAXS analysis revealed that the cracks are primarily initiated at relative higher strains (0.7<α < 1) in the region of ZnS aggregations and larger cavities are derived from the enlargement of the cracks.
Keywords: Natural rubber; Crack initiation and evolution; High temperature fatigue; SEM; SAXS;

“Linear” 1-arm and 2-arm poly(dl-lactide) [i.e., poly(dl-lactic acid), or PDLLA] polymers with relatively low number-average molecular weights (M n in the range 0.2–6 × 104  g mol−1) were synthesized using ring-opening polymerization of dl-lactide initiated with tin(II) 2-ethylhexanoate (i.e., stannous octoate) and coinitiators of dl-lactic acid and ethylene glycol (these PDLLA polymers are hereafter abbreviated as 1-DL and 2-DL, respectively). Their glass-transition properties were monitored by differential scanning calorimetry, and their hydrolytic degradation was investigated using gravimetry and gel permeation chromatography. The results of the present study indicate that the coinitiator-induced molecular structural difference of the terminal groups, the chain directional change, the incorporated coinitiator moiety as an impurity in the middle of the molecule, and the molecular weight each affect both the hydrolytic degradation behavior and rate, and the glass-transition properties of the “linear” 1-DLs and 2-DLs. The glass-transition temperature (T g) values were higher for the 2-DLs than for the 1-DLs, indicating low chain mobility and a strong inter-chain interaction of 2-arm PDLLA. However, the coinitiator-induced molecular structural difference did not produce a difference in the excess free volume of the end groups between the 1-DLs and 2-DLs, despite the difference produced in the terminal groups. On the other hand, although the hydrolytic degradation of the 1-DLs and 2-DLs proceeds via bulk erosion, significant surface erosion also occurs in the 2-DLs. This should have caused a larger weight loss and lower decrease rate of M n of the 2-DLs compared to those of the 1-DLs. Moreover, the results of the present study indicate that in 2-arm PDLLA selective chain cleavage at the terminal ester groups or second ester groups from the chain terminals, which are induced by two terminal hydroxyl groups, is the significant hydrolytic degradation route. However, the random cleavage of ester groups, irrespective of their position, is the main hydrolytic degradation route.
Keywords: Poly(dl-lactide); Hydrolysis; Glass transition; Linear polymers;

Analysis of photo-chemical degradation behaviour of polyethylene mulching film with pro-oxidants by Ioanna Kyrikou; Demetres Briassoulis; Miltiadis Hiskakis; Epifaneia Babou (2237-2252).
It is generally accepted that polyolefins are bioinert. The last years, a new class of photodegradable polyethylene films with pro-oxidants has been developed, exhibiting optimised operational properties in terms of controlled UV and/or thermal ageing leading to an abrupt, predefined to some extent, rapid fragmentation into very small fragments. These photodegradable or fragmentable polyethylene films are promoted in the market for various commercial applications. In some cases, these materials are presented as, or are claimed to be, biodegradable materials. Such materials are already used in agriculture in the form of photodegradable mulching films which become fragmented into small remains after the end of their useful lifetime and are incorporated into the soil. However, it has not been verified yet beyond any doubt, that these remains do in fact biodegrade in natural soil, under what conditions, at which rate and what are their effects in agricultural production, the soil and the environment. An experimental investigation has been carried out focusing on the combined effects of critical factors on the controlled (predefined) photo-chemical degradation of photodegradable mulching LLDPE films with pro-oxidants and the behaviour of their remains in the soil. The analysis of the photo-chemical degradation behaviour presented in this paper was carried out through parallel experiments performed under real field and controlled laboratory conditions. The main factors investigated include materials, exposure time, temperature and UV radiation.
Keywords: Photodegradable mulching films; Polyethylene with pro-oxidants; UV artificial ageing; Mechanical performance; Degradation performance; Photo-chemical degradation mechanisms;

The photodegradation of BPA polycarbonate (PC) can be described as an autoaccelerating process initiated by the formation of biphenol products arising from a formal photo-Fries reaction pathway. Evidence comes from spiking PC films with model compounds of photo-Fries reaction products, pre-exposure of films to generate photo-Fries products, and kinetic analysis. Published data on products formed during natural PC weathering are consistent with this pathway.
Keywords: Bisphenol-A polycarbonate; Weathering; Photodegradation; Photo-Fries; Mechanism; Kinetics;

Degradation of electrospun SF/P(LLA-CL) blended nanofibrous scaffolds in vitro by Kuihua Zhang; Anlin Yin; Chen Huang; Chunyang Wang; Xiumei Mo; Salem S. Al-Deyab; Mohamed El-Newehy (2266-2275).
Nanofibrous scaffolds of silk fibroin (SF) and poly(l-lactic acid-co-ɛ-caprolactone) (P(LLA-CL)) blends fabricated via electrospinning possessed good mechanical property and biocompatibility, as demonstrated by a previous study in vitro. However, the degradation behavior of the scaffolds, which may significantly influence tissue repair and regeneration, needs further exploration. In this study, in vitro degradation of pure SF, P(LLA-CL) and SF/P(LLA-CL) blended nanofibrous scaffolds were performed in phosphate-buffered saline (PBS, pH 7.4 ± 0.1) at 37 °C for 6 months. A series of analyses and characterizations (including morphologic changes, loss weight, pH changes of PBS solutions, DSC, XRD and FTIR-ATR) were conducted to the nanofibrous scaffolds after degradation and the results showed that the pure SF nanofibrous scaffolds were not completely degradable in PBS while pure P(LLA-CL) nanofibrous scaffolds had the fastest degradation rate. Moreover, the addition of SF reduced the degradation rate of P(LLA-CL) in SF/P(LLA-CL) blended nanofibrous scaffolds. This was probably caused by the intermolecular interactions between SF and P(LLA-CL), which hindered the movement of P(LLA-CL) molecular chains.
Keywords: Degradation in vitro; SF/P(LLA-CL) nanofibrous scaffolds; Mechanism; Tissue repair;

Thermal stability of the copolymers of silicon-containing arylacetylene resin and acetylene-functional benzoxazine by Jian Zhang; Jianxiang Huang; Wei Du; Farong Huang; Lei Du (2276-2283).
Acetylene-functional benzoxazine resin (AFBEN) was used to modify silicon-containing aryacetylene resin (SCAAR). The thermal stability, degradation and ablation mechanisms were investigated. Based on the results of Py/GC/MS methods, we concluded that the cross-linking reactions of poly(dimethylsilyleneethynylene–phenyleneethynylene)(DMSEPE, a class of SCAAR) were due to (1) the Diels–Alder reaction between Ph–CC and CC, (2) the ring trimerization of CC and (3) radical polymerization of CC to form polyene structure. During the curing of AFBEN, polyene was the main product of the polymerization of ethynyl in AFBEN and the activation of the para positions of the aniline ring increased due to the introduction of ethynyl. XRD and XPS results showed that SiO2 and SiC formed on the surface of the composites in the process of ablation.
Keywords: Silicon-containing arylacetylene resins; Acetylene-functional benzoxazine; Thermal property; Degradation; Ablation;

This study describes the mechanism of flammability reduction in flame-retarded polymer matrix organo-montmorillonite reinforced nanocomposites. Morphologies of untested polymer nanocomposites and char residues formed by combustion in the mass loss calorimeter are characterized by XRD and TEM techniques. It is postulated that a combination of well-dispersed montmorillonite platelets and flame retardants in the polymer matrix provides nano-structured char formation. Initial montmorillonite dispersion in flame-retarded nanocomposites is found to be a major controlling factor on formed char nanostructures. An initially intercalated structure is invariantly converted to complete montmorillonite collapse whereas an initially exfoliated structure transforms to nano-structured chars demonstrating retained exfoliation or a new state of intercalation via incomplete collapse of montmorillonite layers. It is proposed that nano-structured char formation is the effective mechanism of flammability reduction, i.e. reduction in rate of heat release during combustion, in flame-retarded polymer nanocomposites.
Keywords: Nanocomposite; Flammability; Montmorillonite; Flame retardant; Mechanism;