Polymer Degradation and Stability (v.95, #12)

Calendar (I-II).

Naturally occurring mixtures of hydromagnesite and huntite have found important industrial use. Their endothermic decomposition over a temperature range similar to that of commonly used polymers and their release of water and carbon dioxide, has led to such mixtures being successfully used as fire retardants. They have replaced aluminium hydroxide and magnesium hydroxide in many applications. The current understanding of the thermal decomposition mechanism of both minerals and their combination in natural mixtures has been reviewed and related to their fire retardant action. Both minerals contribute to the reduction in flammability of polymers although the extent of these interactions has not been fully investigated. However, the fire retardant mechanism of these minerals appears more complicated than either aluminium hydroxide or magnesium hydroxide.
Keywords: Hydromagnesite; Huntite; UltraCarb; Fire; Flame; Retardant;

We attempted to synthesize novel polyhydroxyalkanoate (PHA) containing new 3-hydroxy-4-methylvalerate (3H4MV) monomer from the transformed strain of Cupriavidus necator PHB4 harboring the PHA synthase gene of Chromobacterium sp. USM2 (phaC Cs). Novel PHA containing SCL and MCL monomers were successfully synthesized from crude palm kernel oil (CPKO) and isocaproic acid. Results showed that P(3HB-co-1 mol% 3HV-co-3 mol% 3H4MV-co-18 mol% 3HHx) possessed higher thermal stability, higher elastomeric behavior at room temperature and higher ductility than the P(3HB-co-5 mol% 3HHx). The novel PHA film was found to possess an interesting rubber-like elasticity and flexibility property which has not been reported. The soil surface degradation study showed that the novel PHA film was degraded faster than the 3HB homopolymer and copolymer with 5 mol% of 3HHx.
Keywords: Polyhydroxyalkanoate (PHA); 3-Hydroxy-4-methylvalerate; 3-Hydroxyhexanoate; Isocaproic acid; Crude palm kernel oil; Chromobacterium sp;

To further understand the kinetics of the thermal denaturation of type I collagen, the 16 and 8 mg/mL bovine hide collagen solutions were studied by differential scanning calorimetry at different heating rates. The activation energy of the denaturation process was examined utilizing the differential (Friedman) and the integral (Ozawa-Flynn-Wall) isoconversional methods, and several kinetic models were evaluated using the method of multivariate non-linear regression. Besides, the denaturation behavior was simulated under different temperature conditions. Results showed that the activation energy decreased in a different way at lower and higher degrees of conversion, respectively. A three-state model, in which a reversible step was followed by an irreversible one, was the best of the estimated models to describe the denaturation process, which could be approximated by single-step or two-consecutive-step in terms of temperature conditions.
Keywords: Type I collagen; Solution; Thermal denaturation; Kinetics; Model;

The effect of extrusion processing on Zein by Gordon W. Selling (2241-2249).
Extrusion processing was carried out on zein where extrusion temperatures were varied between 100 and 300 °C. Differential scanning calorimetry and thermogravimetric analysis showed that thermal degradation begins around 220 °C. The color of the extrudate changed the most above temperatures of 160 °C. Sodium dodecyl sulfate polyacrylamide gel electrophoresis shows that the protein begins cross-linking at 120 °C and chain cleavage begins above 180 °C. Examination of the protein structure of the extrudate using near and far-UV circular dichroism shows a gradual reduction in α-helix and β-sheet content between 100 and 240 °C; above 240 °C the rate of secondary structure loss is increased. Infrared spectroscopy displayed differences in the carbonyl absorption with the carbonyl peak becoming narrower and shifting towards higher wavenumber with increased extrusion temperature. The peak at 1533 cm−1 becomes slowly smaller with higher extrusion temperature until 220 °C after which its loss accelerates. Nuclear magnetic resonance spectroscopy demonstrated the formation of new carbonyl peaks and the loss of alkoxyl carbons suggesting that in addition to protein backbone cleavage the alcohol moieties of serine and threonine are oxidizing to carboxylic acids. Tensile properties begin to deteriorate when extruding above 140 °C; extruding above 220 °C yields a material that cannot be molded.
Keywords: Zein; Thermal degradation; Extrusion; Protein degradation;

Unusual change in molecular weight of polyhydroxyalkanoate (PHA) during cultivation of PHA-accumulating Escherichia coli by Jumiarti Agus; Prihardi Kahar; Manami Hyakutake; Satoshi Tomizawa; Hideki Abe; Takeharu Tsuge; Yasuharu Satoh; Kenji Tajima (2250-2254).
This study aimed to investigate the factors affecting molecular weight of poly[(R)-3-hydroxybutyrate] [P(3HB)] when polyhydroxyalkanoate (PHA) synthase (PhaRCBsp) from Bacillus sp. INT005 was used for P(3HB) synthesis in Escherichia coli JM109. It was found that the molecular weight of P(3HB) decreased with time in mid- and late-phase of culture and was strongly affected by culture temperature. At 37 °C culture temperature, the molecular weight of P(3HB) rapidly decreased from 4.4 × 105 to 4.8 × 104 with culture time, whereas it was almost unchanged at 25 °C. Kinetic analysis suggested that the decrease in molecular weight of P(3HB) was due to random scission of the polymer chain. The decrease in molecular weight of P(3HB) was not observed when PHA synthases other than PhaRCBsp were expressed. This study sheds light on the unique behaviour in molecular weight change of P(3HB) that is synthesized by E. coli expressing PhaRCBsp.
Keywords: Polyhydroxyalkanoate; PHA synthase; Bacillus; Molecular weight; Random scission;

Use of wood elemental composition to predict heat treatment intensity and decay resistance of different softwood and hardwood species by Mounir Chaouch; Mathieu Pétrissans; Anélie Pétrissans; Philippe Gérardin (2255-2259).
Heat treatment is an attractive alternative to improve decay resistance of low natural durability wood species. Decay resistance is strongly correlated to thermal degradations of wood cell wall components. Some recent studies proposed the use of wood elemental composition as a valuable marker to predict final properties of the material. These results, initially obtained with pine, have been extended to different softwood and hardwood species to check validity of the method using equipment specially designed to measure mass losses during thermal treatment. Heat treatment was performed on two softwood species (pine and silver fir) and three hardwood species (poplar, beech and ash) at 230 °C under nitrogen for different times to reach mass losses of 5, 10 and 15%. Heat-treated specimens were exposed to fungal decay using the brown rot fungus Poria placenta and the weight losses due to fungal degradation determined as well as initial wood elemental composition. Correlations between weight losses recorded after fungal exposure and elemental composition indicated that carbon content and O/C ratio can be used to predict wood durability conferred by heat treatment. Moreover, it was observed that for given curing conditions thermo-degradation patterns differed considerably according to the wood species. The sole analysis of wood physical properties like its density, thermal conductivity and diffusivity cannot allow explaining the observed differences, which should also depend on thermally activated chemical processes depending on wood chemical composition.
Keywords: Elemental composition; Decay; Durability; Heat treatment; Thermo-degradation; Wood;

A series of homo- and copolymers of acrylonitrile was prepared under radical initiation in DMF solutions. The thermal and flammability characteristics of these polymers were evaluated through thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and by limiting oxygen index (LOI) measurements. The thermal degradation behaviours of the polymers were assessed primarily with a view to designing comonomers, for acrylonitrile-based polymers, bearing flame retardant moieties. Broadly speaking, in LOI tests acrylic-based comonomers were found to improve fire performance. For instance, the incorporation of methacrylic acid gave a limiting oxygen index value of 26.4 at 30.9 mol% loading, and an intumescent char was produced upon burning.
Keywords: Polyacrylonitrile; Styrenic and acrylic copolymers; Thermal analyses; LOI measurements;

Physicochemical characterisation of degrading polycaprolactone scaffolds by Lucy A. Bosworth; Sandra Downes (2269-2276).
A degradation study investigating the hydrolysis of different scaffolds of polycaprolactone suspended in phosphate buffer solution at 37 °C was performed over a three month period. Structures included electrospun fibres, held as 2D mats and 3D bundles, and solvent cast films. These structures and their surrounding solutions were physiochemically characterised using a range of techniques. Changes in scaffold physicochemical properties were observed over the course of the study, including significant loss in molecular mass, increases in thermal properties and crystallinity, and increases in tensile properties. The presence of degradation products, such as capronic acid containing compounds was also identified in the surrounding solution. 3D electrospun bundles - as a consequence of being the least crystalline scaffold and hence most susceptible to hydrolysis – demonstrated greatest reduction in molecular mass over the three months, followed by 2D electrospun mats, and the lowest mass loss was observed for solvent cast films.
Keywords: Hydrolytic degradation; Polycaprolactone; Electrospinning; Surface area; Crystallinity;

Enzymatic degradation of oxidized cellulose hydrogels by Ung-Jin Kim; Noriyuki Isobe; Satoshi Kimura; Shigenori Kuga; Masahisa Wada; Jae-Heung Ko; Hyun-O Jin (2277-2280).
The cellulose-based hydrogel with abundant aldehyde groups was prepared by periodate oxidation of cellulose hydrogel prepared by dissolution-regeneration of cellulose by aqueous LiOH/urea solvent. Aldehyde groups could be introduced retaining the nanoporosity of the cellulose gel. The enzymatic degradation of three grades of oxidized cellulose hydrogel, with aldehyde contents of 3.3, 8.1 and 18.6 per 100 glucose unit, was carried out using solutions containing cellulase and β-glucosidase at 37 °C up to 48 h. The degradation of oxidized gels was remarkably slower than that of original cellulose gel, depending strongly on the degree of oxidation. The portion except for the amount of glucose released was greater than the degree of oxidation, but became closer to the latter with increase in the degree of oxidation. This behavior can be interpreted in terms of the enzymatic recognition of the chemically modified cellulose chains.
Keywords: Cellulose hydrogel; Periodate oxidation; Dialdehyde cellulose; Enzymatic degradation; Biomaterials;

Studies on novel thermally stable segmented polyurethanes based on thiourea-derivative diols by Ayesha Kausar; Sonia Zulfiqar; Zahoor Ahmad; Muhammad Ilyas Sarwar (2281-2288).
Novel thermoplastic segmented poly(urethane-thiourea)s (PURs) were synthesized via one-step polymerization from aromatic diols containing sulfur (thiourea linkage) in the main-chain, including terephthaloyl bis (3-(2-hydroxopyridyl) thiourea) (TBHPT) and terephthaloyl bis (3-(5-naphtholyl) thiourea) (TBNT), along with 1,4-phenylene diisocyanate (PDI) as hard segment and 20, 50 and 80 mol% polyethylene glycol (PEG) as a soft segment. The prepared chain extenders and polymers were characterized by conventional methods, and physical properties such as ηinh, solubility, thermal stability and thermal behavior were studied. Easily processable PURs with excellent thermal stability were obtained by incorporating 20 mol% PEG in the soft segment. Thermogravimetric analysis indicated that poly(urethane-thiourea)s were fairly stable above 500 °C and own high glass transition temperatures about 263–266 °C. These polymers also showed partially crystalline structures. Ultimately, weight average molecular weights (Mw) of PURs were up to 109 × 103. Compared to typical polyurethanes, PURs exhibited better thermal stability and T g’s owing to rigid hard segment structure.
Keywords: Thiourea; PEG; Chain extender; Phenylene diisocyanate; Solubility; Thermal stability;

Catalyst creates new grades of polyethylenes while their degradation phenomena determine the resulting application profiles. The resins and the end-products eventually contain residual catalysts. Therefore, the effects of the following two residual catalysts—one Ziegler–Natta [PQ Silica/Bu2Mg/tBuCl/TiCl4], and the other metallocene [PQ Silica/MAO/(nBuCp)2ZrCl2]—on the UV-induced degradation of the resulting unstabilized ethylene homopolymer films were studied. The MetCat HomoPE film was found to be more susceptible to UV-induced degradation degradation than the Z–N HomoPE one despite the residual Zr level was 1/15th of the Ti content. Therefore, the zirconocene residual catalyst better (i) facilitated the UV-initiated reaction, and (ii) decreased the activation energy required for the decomposition of the resulting hydroperoxide. These findings were explained from the differences in (i) electronic configuration and atomic radius, and (ii) surface chemistry and solid-state electronic environment of these catalyst systems. In both films, Tpm and Tpc did not significantly vary with the exposure time. The change of % crystallinity showed to be irregular and disturbed. As a function of carbonyl index, Tpm and Tpc,varied in a similar fashion in the MetCat HomoPE film. However, they significantly differed for the Z–N HomoPE film. Here, Tpm did not appreciably change whereas Tpc initially increased very mildly; then it did not essentially differ.
Keywords: Residual catalyst; Surface chemistry and solid-state electronic environment; Thermo- and photooxidative degradation; Ethylene homopolymers; Thermal properties;

In libraries and archives some of the items which, upon ageing, have acidified considerably since their production are so brittle that they cannot be handled without risking loss of material. In contrast to current deacidification processes, aminoalkylakoxysilanes (AAAS) improve the mechanical properties of paper. A simple AAAS, aminopropylmethyldiethoxysilane (AMDES) was used as a model to better understand previous observations made on these systems (hydrolysis, condensation and possible reactions with the organic substrate). The evaluation of the mechanical properties of papers that were treated with AMDES showed that there was no formation of a polymer network on the fibres’ surface. However, treated papers not only exhibited a high alkaline reserve, but also a significant increase in both their tensile breaking length and their folding endurance. Treatment of hygrothermally aged papers with AMDES provided improved folding endurance as well as a good resistance to ageing. Various oxidation treatments of the model papers using sodium hypochlorite led to the conclusion that the nature of the oxidised groups formed on cellulose did not seem to play a significant role in the strengthening mechanism but rather that this effect of AMDES mainly arose from hydrogen bonding between the two molecules.
Keywords: Paper; Deacidification; Reinforcement; Oxidation; Aminoalkylalkoxysilanes; Artificial ageing;

Biodegradation of chemically modified wheat gluten-based natural polymer materials by Xiaoqing Zhang; Yesim Gozukara; Parveen Sangwan; Dachao Gao; Stuart Bateman (2309-2317).
Biodegradation of a series of chemically modified thermally processed wheat gluten (WG)-based natural polymers were examined according to Australian Standard (AS ISO 14855). Most of these materials reached 93–100% biodegradation within 22 days of composting, and the growth of fungi and significant phase deformation were observed during the process. Chemical crosslinking did slow down the rate or reduce the degree of the biodegradation with different behaviours for different modified systems. The segments containing structures derived from the reactions with additives such as tannin or epoxidised soybean oil remained in the degradation residues while the glycidoxypropyl trimethoxysilane agent produced ∼20% un-degraded residues containing silicon-crosslinking structures. The biodegradation rate of each component of the materials was also different with the protein and starch components degraded fast but lipid degraded relatively slowly.
Keywords: Wheat gluten; Biodegradation; Chemical modification; Natural polymer materials;

Photodegradation of poly(3-hydroxybutyrate) by Roberta K. Sadi; Guilhermino J.M. Fechine; Nicole R. Demarquette (2318-2327).
The effect of ultraviolet radiation on the properties of poly(3-hydroxybutyrate) (PHB) was studied. The PHB investigated is produced from microbial fermentation using saccharose from sugarcane as the carbon source to the bacteria. The material was exposed to artificial UV-A radiation for 3, 6, 9 and 12 weeks. The photodegradation effect was followed by changes of molecular weight, of chemical and crystalline structures, of thermal, morphological, optical and mechanical properties, as well as of biodegradability. The experimental results showed that PHB undergoes both chain scission and crosslinking reactions, but the continuous decrease in its mechanical properties and the low amount of gel content upon UV exposure indicated that the scission reactions were predominant. Molar mass, melting temperature and crystallinity measurements for two layers of PHB samples with different depth suggested that the material has a strong degradation profile, which was attributed to its dark colour that restricted the transmission of light. Previous photodegradation initially delayed PHB biodegradability, due to the superficial increase in crystallinity seen with UV exposure. The possible reactions taking place during PHB photodegradation were presented and discussed in terms of the infrared and nuclear magnetic resonance spectra. A reference peak (internal standard) in the infrared spectra was proposed for PHB photodegradation.
Keywords: Polyhydroxybutyrate; PHB; Photodegradation; Photo-oxidation; UV;

Nanocomposites based on silver (Ag) and organically-modified silicate (Ormosil) were prepared by an in situ reduction method, in which silver nitrate, tetraethoxysilane (TEOS) and aminosilanes with different amine groups acted as precursor, linker and colloidal suspension stabilizers, respectively. The objective of the study was to develop and evaluate aminosilanes-modified silicate impregnated with Ag nanoparticles, in which Ag dispersion is stabilized, to create a composite that protects against biological warfare agents. The physical properties of the Ormosil/Ag nanocomposites were examined using NMR, ESR and SEM spectroscopy, the results of which indicated that the extent of the reduction reaction increases with aminosilanes with a higher number of amine groups. The number of amine groups in the aminosilane has also a strong effect on the size of the resulting Ag particles. The antibacterial effects of the Ormosil/Ag nanocomposites were assessed by the zone of inhibition and plate-counting methods, and an excellent antibacterial performance was discovered.
Keywords: Polymer–matrix composites; Silver (Ag); Organically-modified silicate; Antibacterial performance;

Thermodegradation of medium-chain-length poly(3-hydroxyalkanoates) produced by Pseudomonas putida from oleic acid by Mei Chan Sin; Seng Neon Gan; Mohd Suffian Mohd Annuar; Irene Kit Ping Tan (2334-2342).
Medium-chain-length poly(3-hydoxyalkanoates) (mcl-PHA), comprising six to fourteen carbon-chain-length monomers, are natural thermoplastic polyesters synthesized by fluorescent pseudomonades. In this study, mcl-PHA was produced by Pseudomonas putida from oleic acid in aerobic shake flask fermentation. Thermal degradation of mcl-PHA was performed at temperatures in the range of 160–180 °C. Thermodynamic parameters of mcl-PHA thermal degradation were determined where degradation activation energy, Ed and pre-exponential factor, A equal to 85.3 kJ mol−1 and 6.07 × 105 s−1, respectively; and exhibited a negative activation entropy (∆S) of −139.4 J K−1 mol−1. Titration was carried out to determine the carboxylic terminal concentration and used to correlate number-average molecular weight (Mn ) of the polymers. Thermally-degraded PHA contained higher amount of carboxylic terminals and lower Mn compared to the initial PHA and these results coincide with the decreased Mn in GPC analysis. Thermal properties of initial and degraded mcl-PHA were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal decomposition mechanism was investigated following the analyses of the degradation products using 400-MHz 1H NMR, FTIR spectroscopy and GC analysis. The overall decomposition reaction is the hydrolysis of ester linkages to produce hydroxyl and carboxylic terminals. A small proportion of unsaturated side chain fragments would undergo oxidative cleavage at C=C linkages, producing minor amount of low-molecular weight esters and acids. At higher temperatures, the hydroxyl terminal can undergo dehydration to form an alkenyl terminal.
Keywords: Thermal degradation; Medium-chain-length poly(3-hydroxyalkanoates); Thermo-kinetic parameters; TGA; Thermal decomposition mechanism;

A chemiluminescence study of madder lakes on paper by Jacob Thomas; Joyce H. Townsend; Stephen Hackney; Matija Strlič (2343-2349).
The photo degradation of watercolour drawings prepared with madder lake pigments on gelatine-sized paper was studied by chemiluminometry, viscometry, and colorimetry. A method of recto irradiation and verso measurement was developed to overcome absorption of the emitted photons by the paint layer. A complex relationship between paper substrate, applied chromophores and associated transition metals was observed with strong correlations between the presence of transition metals associated with the madder lakes and the degradation of the paper substrate and the applied paint layer as well as evidence of pro-oxidative activity by the chromophores in the applied paint layers. The pro-oxidant behaviour appears to be dependent on the type of transition metal present. This is the first in-depth research into the photodegradation of madder lake-based watercolours which attempts to understand the chemistry of the processes.
Keywords: Photo degradation; Chemiluminometry; Photo-Fenton reaction; Anthraquinones; Cellulose; Heritage science;

Biodegradation of polyhydroxyalkanoates (PHAs) in tropical coastal waters and identification of PHA-degrading bacteria by T.G. Volova; A.N. Boyandin; A.D. Vasiliev; V.A. Karpov; S.V. Prudnikova; O.V. Mishukova; U.A. Boyarskikh; M.L. Filipenko; V.P. Rudnev; Bùi Bá Xuân; Vũ Việt Dũng; I.I. Gitelson (2350-2359).
Biodegradability patterns of two PHAs: a polymer of 3-hydroxybutyric acid (3-PHB) and a copolymer of 3-hydroxybutyric and 3-hydroxyvaleric acids (3-PHB/3-PHV) containing 11 mol% of hydroxyvalerate, were studied in the tropical marine environment, in the South China Sea (Nha Trang, Vietnam). No significant differences have been observed between degradation rates of 3-PHB and 3-PHB/3-PHV specimens; it has been found that under study conditions, biodegradation is rather influenced by the shape of the polymer item and the preparation technique than by the chemical composition of the polymer. Biodegradation rates of polymer films in seawater have been found to be higher than those of compacted pellets. As 3-PHB and 3-PHB/3-PHV are degraded and the specimens lose their mass, molecular weight of both polymers is decreased, i.e. polymer chains get destroyed. The polydispersity index of the PHAs grows significantly. However, the degree of crystallinity of both PHAs remains unchanged, i.e. the amorphous phase and the crystalline one are equally disintegrated. PHA-degrading microorganisms were isolated using the clear-zone technique, by inoculating the isolates onto mineral agar that contained PHA as sole carbon source. Based on the 16S rRNA analysis, the PHA-degrading strains were identified as Enterobacter sp. (four strains), Bacillus sp. and Gracilibacillus sp.
Keywords: Polyhydroxyalkanoates, PHA; PHA properties; Degradation of polymers; Biopolymers in marine environment; PHA-degrading microorganisms;

Mechanistic study of hydrolytic erosion and drug release behaviour of PLGA nanoparticles: Influence of chitosan by Gaurav K. Jain; Shadab A. Pathan; Sohail Akhter; Niyaz Ahmad; Nilu Jain; Sushma Talegaonkar; Roop K. Khar; Farhan J. Ahmad (2360-2366).
The hydrolytic erosion of poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles (PLGA-NPs) was investigated in vitro. The changes in physical properties of the nanoparticles with time were evaluated by ultra high-pressure liquid chromatographic (UHPLC) analysis, particle size analysis and scanning electron microscopy (SEM). Mass reduction data demonstrated a triphasic erosion pattern for PLGA-NPs with nearly no mass loss (3.0%) up to a week, followed by a rapid mass loss (weeks 1–3, 61.4%), and further followed by slow mass loss (weeks 3–5, 19.8%). SEM revealed microcavitation on the surface of nanoparticles, which tended to increase with the erosion time and eventually particle fragmentation was evident at 5 weeks. A significant increase in particle size was observed at 4 weeks which can be attributed to particle aggregation, however, at about 5 weeks, the particle size decreased significantly owing to particle fragmentation. The hydrolytic erosion of PLGA-NPs was found to be specifically proton catalyzed. The release profile of the model drug, moxifloxacin, from PLGA-NPs was closely related to nanoparticle erosion except for the initial burst release which was based on diffusion. The presence of chitosan in the PLGA-NPs accelerated the rate of erosion of the nanoparticles and reduced the burst release of the drug. An understanding of the erosion mechanism and alteration in erosion by chitosan could give desirable and more uniform drug release kinetics from PLGA-NPs.
Keywords: Erosion; Chitosan; Nanoparticles; Drug release; Poly(d,l-lactide-co-glycolide);

Assessing the progress of degradation in polyurethanes by chemiluminescence. I. Unstabilised polyurethane films by Marta Malíková; Jozef Rychlý; Lyda Matisová-Rychlá; Katarína Csomorová; Ivica Janigová; Heinz-Wilhelm Wilde (2367-2375).
The thermooxidative and thermal stabilities of polyurethanes synthesized from polyisocyanate and polyester polyol were assessed by chemiluminescence and thermogravimetry. The effect of varying heating rates, synthesis procedures (i.e., with or without a crosslinking catalyst), sample preparations for the measurements, atmospheres (oxygen, nitrogen and their mixtures) and long-term ageing under laboratory conditions were examined and a mechanism of oxidative degradation was proposed based on comparisons of the — separately determined — oxidisability of polyisocyanate and polyester polyol to that of polyurethane.
Keywords: Polyurethanes; Chemiluminescence; Thermogravimetry; Polyol; Polyisocyanate;

The influence of degradation on non-isothermal crystallization from the melt of a segmented copolymer constituted of glycolide and trimethylene carbonate units and used as a bioabsorbable surgical suture was studied by optical microscopy, differential scanning calorimetry and time-resolved X-ray diffraction. Fibrillar positive spherulites were obtained with slightly degraded samples but new axialitic morphologies were detected when samples had a molecular weight, Mw , lower than 29,000 g/mol and the crystallization started at a high temperature.Crystal growth kinetics of samples degraded under different conditions was evaluated over a wide temperature range by a non-isothermal method. Two crystallization regimes (I and II) were determined for the more degraded samples (i.e., those able to crystallize according to axialitic and spherulitic morphologies), whereas only regime II was found for samples of higher molecular weights. Primary nucleation density decreased with the extent of degradation provided no morphological changes occurred, and so did the regularity of lamellar stacking, as shown by synchrotron measurements, although the morphological parameters remained practically constant.
Keywords: Polyglycolide; Surgical sutures; Hydrolytic degradation; Crystal morphology; Non-isothermal crystallization;

The flame retardancy and thermal stability of ammonium polyphosphate/tripentaerythritol (APP/TPE) intumescent flame retarded polystyrene composites (PS/IFR) combined with organically-modified layered inorganic materials (montmorillonite clay and zirconium phosphate), nanofiber (multiwall carbon nanotubs), nanoparticle (Fe2O3) and nickel catalyst were evaluated by cone calorimetry, microscale combustion calorimetry (MCC) and thermogravimetric analysis (TGA). Cone calorimetry revealed that a small substitution of IFR by most of these fillers (≤2%) imparted substantial improvement in flammability performance. The montmorillonite clay exhibited the highest efficiency in reducing the peak heat release rate of PS/IFR composite, while zirconium phosphate modified with C21H26NClO3S exhibited a negative effect. The yield and thermal stability of the char obtained from TGA correlated well with the reduction in the peak heat release rate in the cone calorimeter. Since intumesence is a condensed-phase flame process, the MCC results showed features different from those obtained from the cone calorimeter.
Keywords: Polystyrene; Intumescent flame retardant; Cone calorimetry; Microscale combustion calorimetry;

In the context of protecting of the environment, this work studies the biodegradation of PEG-based polyurethane elastomer films in the presence of the soft rot fungus Chaetomium globosum, determined via the Petri-dish test. Using PEG with high-molecular weight (MW = 1500) as a chain extender led to polyurethane elastomers with lower physical crosslink density and higher swelling rates. The structural modifications in the hard-segment area (C=O and N–H peaks) are considerable and were analyzed by FTIR spectroscopy. Biodegradation lowers the final mechanical properties, but increases yield points, especially in the case of polyurethane elastomers crosslinked with castor oil. Polyurethane elastomer samples showed visible degradation proved by the mechanical weakening of the films. Thus, breaking strains decrease from 670–1180% to 500–680% and tensile strengths decreased from 11.5–27.5 MPa to 4–11.5 MPa after 130 days of fungal biodegradation. The changes in the morphology of the polyurethane films surface were analyzed by SEM and have been found to exhibit increasing porous structure and fungal hyphae. The effects of the hard-segment composition of the polyurethane elastomers on the fungal biodegradation behaviour were investigated.
Keywords: Polyurethane; Elastomers; Fungi; Biodegradation; Mechanical properties;

Thermal-oxidative degradation of polyamide 6,6 containing metal salts by Pierfrancesco Cerruti; Cosimo Carfagna (2405-2412).
The thermal-oxidative stability of oven aged polyamide 6,6 (PA6,6) doped with Co, Cu, Ni and Zn chlorides combined with KI was examined. Aging caused a depression in melting temperature and an increase in enthalpy of fusion of PA6,6 films due to the formation of a strongly degraded crystalline fraction with a lower molecular weight. A build-up of carbonyl absorption in the range 1700–1780 cm−1 due to primary and secondary photo-oxidation products was detected. The kinetics of carbonyl accumulation was affected by the morphology of the samples, and it was observed that at a later stage of aging the crystalline phase was also involved in the oxidation process. The above mentioned changes were greatest in the case of neat, Co and Ni doped polymer, suggesting that these metal salts acted as pro-oxidants. On the other hand, the use of Cu and Zn chlorides brought about a substantial increase in long-term polymer stabilization.Tensile tests revealed a large reduction in ductility as a result of aging for neat, Co and Ni doped polymer, whereas long-term retention of tensile properties was found for the polymer stabilized with Cu and Zn. The presence of the metal salts combined with KI led to increased stabilization for chlorides of Ni, and Co, owing to the participation of KI in non-radical decomposition of peroxides. No effect due to KI was observed for ZnCl2.
Keywords: Polyamide 6,6; Thermal oxidation; Stabilization; Tensile properties; Metal chlorides; Potassium iodide;

Studies of the hydrolytic stability of poly(urethane–urea) elastomers synthesized from oligocarbonate diols by Janusz Kozakiewicz; Gabriel Rokicki; Jarosław Przybylski; Krystyna Sylwestrzak; Paweł G. Parzuchowski; Karolina M. Tomczyk (2413-2420).
Polyurethane and poly(urethane–urea) elastomers synthesized from oligocarbonate diols are characterized by very good mechanical properties, biocompatibility and excellent resistance to both oxidation and hydrolysis and therefore are widely used in medical applications. In this paper the results of studies on hydrolytic stability of poly(urethane–urea) elastomers (PURC) obtained by moisture-curing of corresponding urethane prepolymers synthesized from isophorone diisocyanate (IPDI) and four different oligocarbonate diols (OCD) are presented. OCD were synthesized from dimethyl carbonate and 1,6-hexanediol, from cyclic ethylene carbonate and 1,6-hexanediol as well as from trimethylene carbonate. The changes of the sample weight, mechanical properties and surface properties after immersion in a standard phosphate buffer solution (pH = 7.4) for up to 3 months at 70 °C were monitored. It was shown that neither sample weight nor mechanical properties changed significantly for PURC obtained from OCDs synthesized from 1,6-hexanediol and dimethyl carbonate or ethylene carbonate what confirms good resistance to hydrolysis of those PURC. Also SEM studies of those samples before and after immersion did not reveal any surface degradation effects. However, PURC sample obtained from OCD synthesized from trimethylene carbonate showed significant changes in mechanical properties and distinct change of appearance and surface erosion after 3 months immersion. The initial decrease and later increase of stress at break observed for PURC samples during immersion, was explained by the reaction of residual NCO groups present in PURC with water leading to molecular weight increase which proceeded during immersion period in parallel to hydrolysis of carbonate bond.
Keywords: Poly(carbonate–urethane–urea)s; Poly(carbonate–urethane)s; Oligocarbonate diols; 1,6-Hexanediol; Dimethyl carbonate; Ethylene carbonate;

Weathering resistance of halogen-free flame retardance in thermoplastics by U. Braun; V. Wachtendorf; A. Geburtig; H. Bahr; B. Schartel (2421-2429).
The influence of weathering on the fire retardancy of polymers is investigated by means of a cone calorimeter test, before and after artificial weathering. The surface degradation was monitored using different techniques (ATR–FTIR, microscopy, colour measurement). Different kinds of polymeric materials were chosen, all as they are used in practice: polycarbonate (PC) blends, polyamide (PA) and polypropylene (PP) flame-retarded with arylphosphate, melamine cyanurate (MC) and intumescent formulation based on ammonium polyphosphate (APP), respectively.All samples show material degradation at the surface due to weathering. No significant weathering influence occurs on the flame retardancy when it is a bulk property, as was observed for aryl phosphates in PC blends and MC in PA. When the fire retardancy is dominated by a surface mechanism, dependence on the duration of weathering is detected: for intumescent formulations based on ammonium APP in PP, a worsening in the formation of the intumescent network was observed.
Keywords: Fire retardancy; Weathering resistance; Degradation; Intumescence; Cone calorimeter;

Sensitivity analysis of a predictive model for the fire behaviour of a sandwich panel by Antonio Galgano; Colomba Di Blasi; Eva Milella (2430-2444).
A sensitivity analysis to assumptions and input variables is carried out for a predictive model previously developed [1] for the fire response of a glass-fibre/polyester panel and a glass-fibre/polyester–Vermiculux sandwich. It is an unsteady, one-dimensional model using the porous medium approximation and a constant gas pressure with two-step, finite rate kinetics for the thermal decomposition and combustion of the polymeric resin, moisture evaporation described by an Arrhenius rate law, heat and mass transfer by convection, heat conduction and radiation described by effective thermal conductivities, variation of the volumetric fractions of the polymeric resin and the moisture with the conversion degree, effective specific heats, external heat transfer resistances and surface ablation. The strongest impact on the model predictions is exerted by the imposed external heat flux with variations on the characteristic process times between 49 and 774%. An important role in sample heating/conversion is also played by surface ablation and/or external heat transfer resistance with variations up to 30–72% or, when ablation is disregarded, with temperatures along the core layer well below those of the degrading skin. These are also significantly affected by surface heat losses, with the assumption of adiabatic bottom surface leading to heterogeneous ignition of the lower skin, and evaporation of moisture with variations in the characteristic times up to 35%. The model for the effective thermal conductivity of the fibre-reinforced skin (the Parallel, the Maxwell–Eucken and the Effective Medium Theory models versus the Series model) is also important resulting in characteristic time variations up to 35%. The absence of local thermal equilibrium between the condensed and the gas/vapour phase and the kinetic details of the polymer reactions are comparatively less important (maximum diminution in the characteristic times of 16%). Moreover, although over-pressures, modelled by the Darcy law, become quite high especially during the moisture evaporation stage (up to ten times the atmospheric value), their effects on the thermal response of the structure are completely negligible when structural changes are not modelled. Finally, a sensitivity analysis is also carried out to input parameters.
Keywords: Glass-reinforced plastics; Sandwich panels; Mathematical modelling; Fire response; Sensitivity analysis;

A novel series of aromatic s-triazine-containing ring-chain polymers, which typically require high pressures to produce, were prepared by the bulk polymerization of low-melting bis(ether nitrile)s (BENs) with or without the presence of terephthalonitrile (TPH) in the catalysis of ZnCl2 under normal pressure. Four kinds of BENs were readily synthesized by the nucleophilic displacement reaction of 4-chlorobenzonitrile with commercially available aromatic bisphenols or bisphenol-like monomers. Chemical structure of the obtained BENs and their polymers was characterized by FT-IR, WAXD and elemental analysis. Conversion studies indicate that cyano concentration, mobility and reactivity are all important factors for the polymerization, while among of them the cyano reactivity plays a dominant role. The addition of a small mount of TPH is found to be effective in promoting s-triazine forming reaction of the BENs. The synthesized polymers are insoluble, and exhibit good chemical-resistant property towards strong acids and bases together with good hydrolysis-resistant property. No detectable endothermic inflection for glass transitions is observed in the DSC traces of all polymers up to 450 °C, and the polymers exhibit excellent thermal stability with decomposition temperatures for 5% mass-loss ranging from 493–540 °C. All these attracting properties make the s-triazine-containing ring-chain polymers good candidates as matrixes for high performance polymeric materials.
Keywords: Bis(ether nitrile)s; Cyano; Trimerization; s-triazine; Heat-resistant;

Preparation and thermal degradation kinetics of terpolymer poly(ɛ-caprolactone-co-1,2-butylene carbonate) by Yanfei Liu; Dongming Peng; Kelong Huang; Suqin Liu; Zhenbao Liu (2453-2460).
Poly(ɛ-caprolactone-co-1,2-butylene carbonate) (PBCCL) was successfully synthesized via terpolymerization of carbon dioxide, 1,2-butylene oxide(BO) and ɛ-caprolactone (CL). A polymer-supported bimetallic complex (PBM) was used as catalyst. The influences of various reaction conditions such as reaction content, reaction time and reaction temperature on properties of terpolymers were investigated. When CL content increased, the viscosity-average molecular weights (M v), glass transition temperature (T g) and decomposition temperature (T d) of PBCCL improved relative to those of poly(1,2-butylene carbonate) (PBC). Prolonging the reaction time resulted in increase in M v and T g. As reaction temperature increased, the molar fractions of CL ( f CL ) increased obviously. When the reaction temperature went beyond 80 °C, the resulting copolymers tended to be crystalline. The thermal properties and degradation behaviors of PBCCL were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The apparent activation energy and thermal degradation model of PBCCL was estimated by means of Ozawa–Flynn–Wall method and Phadnis-Deshpande method, respectively. The results showed that T g and T d of the terpolymer PBCCL were much higher than those of PBC. The thermal degradation behavior of PBCCL was evidenced by one-step thermal degradation profile. The average apparent activation energy is 77.06 kJ/mol, the thermal degradation kinetics follows the power law thermal decomposition model.
Keywords: Aliphatic polycarbonate; Terpolymer; Thermal properties; Thermal degradation kinetics;

Dielectric properties of thermally degraded chloroprene rubber by H. Kuwahara; S. Sudo; M. Iijima; S. Ohya (2461-2466).
We performed dielectric measurements on thermally aged carbon-black-filled chloroprene rubber (CR). Primary and secondary processes were observed in unaged and thermally aged CR. The primary process is due to the cooperative motion of chloroprene chains in CR, and the secondary process is due to the local motion of chloroprene chains. For the primary process, the relaxation time slightly increases and symmetric shape parameter of the loss spectrum decreases with increasing aging time. For the secondary process, the relaxation strength decreases with increasing aging time, and reaches zero after 50 h. These changes in the dielectric relaxation parameters are due to the progress of the dehydrochlorination reaction at the chloroprene chains.
Keywords: Chloroprene rubber; Thermal aging; Dielectric spectroscopy; Dielectric relaxation;

Effect of UV irradiation on mechanical properties and structure of poly(1,3,4-oxadiazole) fibers by Xiao Yang; Meiwu Shi; Linan Dong; Yingying Ma; Guangdou Ye; Jianjun Xu (2467-2473).
The accelerated ultraviolet aging behavior of poly(1,3,4-oxadiazole) fibers (POD fibers) exposed to artificial environment for different durations were studied. The influence of ultraviolet light on the intrinsic viscosity, structure, appearance and morphology, mechanical properties of POD fibers were investigated during aging by ATR-FTIR and UV-spectra, XPS, WXRD, SEM and tensile strength tester. The results revealed that the structure and properties of POD fibers were affected by UV light. Tensile strength and breaking elongation of POD fibers were severely decreased after 48 h UV light irradiation, and the change of intrinsic viscosity indicated that only degradation but not crosslink occurred. Disruption of oxadiazole rings and formation of carbonyl and amide were observed. UV aging process in nitrogen atmosphere suggested that the oxygen was indispensable and the essence of POD UV aging was photo-oxidation process. POD was amorphous and the recrystallization on surface was present after UV aging due to degradation. Morphology of POD fiber surface was damaged after UV aging.
Keywords: Poly(1,3,4-oxadiazole)s; Photodegradation; UV irradiation; Properties and structure;

A flame retarding biodegradable polylactic acid (PLA) nanocomposite based on flame retardant composites (containing ammonium polyphosphate (APP), pentaerythritol (PER) and melamine cyanurate (MC) by controlling the weight ratio was 2:2:1) and organomodified zinc aluminum layered double hydroxide (Zn-Al-LDH) has been prepared by melt-compounding directly. The morphology and burning behaviour of nanocomposite with 2 wt% Zn-Al-LDH loadings were investigated. The extent of dispersion of LDH was quantified by wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM), illuminating the good dispersion state for ZnAl-LDH in the PLA matrix. Significant improvements in fire retardant performance were observed for the nanocomposite from microscale combustion calorimeter (MCC) and cone calorimetry (reducing both the heat release rate and the total heat released). It revealed that incorporation of FR and ZnAl-LDH was very efficient in improving the flame retardance of PLA composite.
Keywords: Poly(lactic acid); Nanocomposite; LDH; Flame retardancey;

Stability of chromogenic colour prints in polluted indoor environments by Ann Fenech; Matija Strlič; Ilaria Degano; May Cassar (2481-2485).
Chromogenic colour prints are known to be sensitive to storage environments. However, limited research is available on the effect of atmospheric pollutants on these materials, especially pollutants generated indoors. The stability of photographic dyes is of particular interest and the rate of their change can be best described using the standard RGB colour model. Therefore, the colourimetric method was compared to dye extraction and liquid chromatographic analysis to justify its use as a rapid, non-destructive method for quantitative assessment of the rate of change in dye content of colour photographs during degradation. The effects of typical indoor (acetic acid, formaldehyde) and outdoor (nitrogen dioxide) generated pollutants on chromogenic colour prints were then investigated at 80 °C, 60% RH. It was identified that acetic acid leads to the most pronounced changes in photographic dye concentrations, which is significant considering that acetic acid is often the most prominent pollutant in archival environments. On the other hand, formaldehyde exhibited a slight protective effect in comparison to the blank experiment.
Keywords: Colour photographs; Dye stability; Colourimetry; Chromatography; Indoor environment; Pollution; Accelerated degradation;

The influence of UV irradiation on the properties of chitosan films containing keratin by A. Sionkowska; J. Skopinska-Wisniewska; A. Planecka; J. Kozlowska (2486-2491).
The mechanical, thermal and surface properties of chitosan and chitosan containing keratin hydrolysates have been studied and the influence of UV irradiation on these properties has been compared. The surface properties of chitosan films containing 5%, 15% and 30% of keratin hydrolysate before and after UV irradiation (λ  = 254 nm) were investigated by means of contact angle measurements allowing the calculation of surface free energy. The chemical and structural changes during UV irradiation were studied by UV–vis and FTIR-ATR spectroscopy.The changes in mechanical properties such as breaking strength, percentage elongation and Young’s modulus have been investigated. The results have shown that the mechanical properties of the chitosan/keratin films were greatly affected by UV irradiation, but the level of the changes of these properties was smaller in the blend than in pure chitosan and strongly dependent on the time of irradiation and composition of the samples. The contact angle and the surface free energy were altered by UV irradiation, which indicates photooxidation and an increase of polarity of specimens. The range of these changes point to greater susceptibility of chitosan to photooxidation in the presence of keratin.
Keywords: Chitosan; Keratin; UV radiation; Surface properties; Mechanical properties;

Novel soluble thermally stable silane-containing aromatic polyimides with reduced dielectric constant by Samal Babanzadeh; Ali Reza Mahjoub; Shahram Mehdipour-Ataei (2492-2498).
Bis(p-aminophenoxy)diphenylsilane (BPS), bis(m-aminophenoxy)diphenylsilane (BMS) and bis(5-amino-1-naphthoxy)diphenylsilane (BAS) as three silane-diamines were prepared by the reactions of 4-aminophenol, 3-aminophenol, and 5-amino-1-naphthol respectively, with dichlorodiphenylsilane in the presence of triethylamine. The related silane-containing polyimides were prepared by two-step polycondensation reactions of these diamines with three different aromatic dianhydrides. All the polymers were characterized and their physical and thermal properties were studied. The polymers showed high thermal stability while their solubility was greatly increased in polar aprotic solvents. Wide angle X-ray diffraction showed that all the polyimides were almost amorphous. Also their dielectric constants were decreased due to the incorporation of softening and low-polarizing siloxane units into the polymer backbone.
Keywords: Polyimide; Thermal properties; Silane; Dielectric constant;

Compression set in gas-blown condensation-cured polysiloxane elastomers by Mogon Patel; Sarah Chinn; Robert S. Maxwell; Thomas S. Wilson; Stephen A. Birdsell (2499-2507).
Accelerated thermal ageing studies on foamed condensation cured polysiloxane materials have been performed in support of life assessment and material replacement programmes. Two different types of filled hydrogen-blown and condensation cured polysiloxane foams were tested; commercial (RTV S5370), and an in-house formulated polysiloxane elastomer (Silfoam). Compression set properties were investigated using Thermomechanical (TMA) studies and compared against two separate longer term ageing trials carried out in air and in dry inert gas atmospheres using compression jigs. Isotherms measured from these studies were assessed using time-temperature (T/t) superposition. Acceleration factors were determined and fitted to Arrhenius kinetics. For both materials, the thermo-mechanical results were found to closely follow the longer term accelerated ageing trials. Comparison of the accelerated ageing data in dry nitrogen atmospheres against field trial results showed the accelerated ageing trends over predict, however the comparison is difficult as the field data suffer from significant component to component variability. Of the long term ageing trials reported here, those carried out in air deviate more significantly from field trials data compared to those carried out in dry nitrogen atmospheres. For field return samples, there is evidence for residual post-curing reactions influencing mechanical performance, which would accelerate compression set. Multiple quantum-NMR studies suggest that compression set is not associated with significant changes in net crosslink density, but that some degree of network rearrangement has occurred due to viscoelastic relaxation as well as bond breaking and forming processes, with possible post-curing reactions at early times.
Keywords: Foamed polysiloxanes; Compression set; Stability; Ageing; NMR;

Kinetics of the thermal decomposition of processed poly(lactic acid) by F. Carrasco; P. Pagès; J. Gámez-Pérez; O.O. Santana; M.L. Maspoch (2508-2514).
The kinetics of the thermal decomposition of processed poly(lactic acid) has been studied and compared to that of raw material. Processing consisted of two different industrial processes: 1) Injection (with or without further annealing); 2) Extrusion followed by injection (with or without further annealing). For this study, an integral method (based on the general analytical solution), differential methods (based on the first conversion derivative and on the 2nd derivative) and special methods have been used. On the other hand, a method based on the maximum decomposition rate has been considered. By doing that, the kinetic parameters (reaction order, frequency factor and activation energy) have been determined. It has been demonstrated that there was only one first-order reaction for the entire conversion range. A new equation (based on the second conversion derivative plot as a function of temperature) was developed allowing the calculation of the reaction order. This method quantifies peak areas (and not peak heights, as reported by Kissinger). It is very useful because it considers both peak shape and width. Activation energy, as determined by using the general analytical solution, was 318 kJ/mol for unprocessed poly(lactic acid) whereas it was 280 ± 5 kJ/mol for processed materials. All the processed materials had approximately the same thermal stability (T 5 = 333.0–335.8 °C, at 95% confidence level), which was slightly lower than that of unprocessed materials (T 5 = 337.5 °C). PLA melting (during extrusion and injection) was responsible for depolymerization reactions (the small molecules formed during melting processes can volatilize readily).
Keywords: Poly(lactic acid); Injection; Extrusion; Kinetic models; Thermogravimetric analysis (TGA); Thermal stability;

Durability of a polymer with triple-shape properties by Thorsten Pretsch (2515-2524).
A series of cyclic thermo-mechanical measurements was conducted on segregated poly(ester urethane) to study substantial changes in triple-shape properties as a result of hydrolytic aging (80 °C). Prior to the analysis of aging effects, a concept of triple-shape testing was elaborated, starting with the implementation of two distinct programming units. The first one included a deformation at 60 °C to ɛ m1 = 100% (temporary shape B) and its fixing through soft segment crystallization by cooling to −20 °C under constant strain. The second one consisted of a deformation at −20 °C to ɛ m2 = 200% (temporary shape A) and its stabilization through soft segment vitrification as achieved by cooling to −60 °C under fixed strain constraint. Then, gradual heating of the polymer from below to above its thermal transition temperatures gave two independent shape recovery responses in the reverse order of shape fixing: A → B through passing the glass transition by heating from −60 to 23 °C and B → C (back to the permanent shape), when heating the material from 23 to 60 °C and thus above its soft segment melting temperature. In a progressive approach, the storage of loading history through the sequential fixing of two temporary shapes was proven by the development of shape recovery stresses under constrained environment. With the implementation of the two testing methods several aging-related effects could be detected. Good shape fixing abilities ≥90% for both shapes were found and contrasted by significant changes in shape recoverabilities and stress storage capacities. Further insights derived from differential scanning calorimetry (DSC) measurements, indicating an aging-related growth in soft segment crystallinity, and dynamic mechanical analysis (DMA), suggesting a plasticizer effect of water onto the polymer matrix and that aging favoured an increase in cross-linking density.
Keywords: Triple-shape polymer; Shape memory polymer; Tandem shape memory polymer; Active polymer; Poly(ester urethane); Durability;

Structural changes in the condensed phase of bisphenol A polycarbonate (containing 0.45 wt% poly(tetrafluoroethylene))/silicone acrylate rubber/bisphenol A bis(diphenyl-phosphate) (PC/SiR/BDP) and PC/SiR/BDP/zinc borate (PC/SiR/BDP/ZnB) during thermal treatment in nitrogen atmosphere and in fire residues were investigated by solid-state NMR. 1H, 11B, 13C and 31P NMR experiments using direct excitation with a single pulse and 1H–31P cross-polarization (CP) were carried out including 31P{1H} and 13C{31P}double-resonance techniques (REDOR: Rotational Echo Double Resonance) on a series of heat-treated samples (580 K–850 K). Because many amorphous phases occur in the solid residues, and solid-state NMR spectroscopy addresses the most important sites carbon, phosphorus and boron, this paper is the key analytical approach for understanding the pyrolysis and flame retarding phenomenon in the condensed phase of PC/SiR/BDP and PC/SiR/BDP/ZnB.For the system PC/SiR/BDP it is shown that (i) at temperatures around 750–770 K (main decomposition step) carbonaceous charring of PC occurs and arylphosphate structures are still present, reacted in part with the decomposing PC; (ii) for higher temperatures from 770 K the phosphorus remaining in the solid phase increasingly converts to amorphous phosphonates and inorganic orthophosphates with a minor amount of crystalline orthophosphates; and (iii) 1H–31P{1H} CP REDOR and 1H–13C{31P} CP REDOR NMR experiments suggest that the phosphates and phosphonates are bound via oxygen to aromatic carbons, indicating the interaction with the carbonaceous char.When ZnB is added to the system PC/SiR/BDP, (i) ZnB leads to a slightly enhanced PC decomposition for temperatures below 750 K; (ii) α-Zn3(PO4)2 and borophosphate (BPO4) are formed in small amounts at high temperatures suggesting a reaction between BDP and ZnB during thermal decomposition; and (iii) most of the borate remains in the solid residues, forming an amorphous pure borate network, with the BO3/BO4 ratio increasing with higher temperatures.The NMR data of thermal and fire residues are highly correlated, underlining the importance of this work for understanding the pyrolysis and flame retardancy mechanisms in the condensed phase during the burning of the PC/SiR blends.
Keywords: Flame retardance; NMR; Polycarbonate (PC) blends; Bisphenol-A bis(diphenyl)phosphate (BDP); Zinc borate;

Solid residues of bisphenol A polycarbonate (containing 0.45 wt% poly(tetrafluoroethylene))/silicone acrylate rubber/bisphenol A bis(diphenyl-phosphate) (PC/SiR/BDP) and PC/SiR/BDP/zinc borate (PC/SiR/BDP/ZnB) after thermal treatment were investigated by solid-state and liquid-state NMR, focusing on the role and interaction of SiR with the other components of the polymer blend.In PC/SiR/BDP, part of the SiR reacts to an amorphous silicate network rather than being completely released in the gas phase. The silicate network consists of Q4 and Q3 groups formed via intermediate D and T groups. The D groups are formed by a reaction of SiR with bisphenol-A units as well as phenyl groups of PC and BDP. In addition a small amount of silicon diphosphate was observed after thermal treatment at temperatures higher than 810 K. The same decomposition products (without SiP2O7) occur in the solid residues of PC/SiR/BDP/ZnB samples. The formation of intermediate D and T groups occurs earlier, at slightly lower temperatures. Any formation of a borosilicate network was excluded.The results also apply for the fire residues of PC/SiR/BDP and PC/SiR/BDP/ZnB and are thus valuable for understanding the impact of SiR on pyrolysis and flame retardancy mechanisms in the condensed phase during the burning of PC/SiR/BDP blends. SiR was found to influence the pyrolysis and the char formed. Beyond the replacement of highly combustible mechanical modifiers, SiR harbours the potential to enhance flame retardancy.
Keywords: Flame retardance; 29Si NMR; Polycarbonate (PC) blends; Bisphenol A bis(diphenyl)phosphate (BDP); Silicone rubber;

A novel polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-POSS) has been incorporated into polycarbonate (PC) composites in order to study its effect on mechanical and thermal properties and flame retardancy. The mechanical and thermal properties of the DOPO-POSS/PC composites have been investigated by tensile and flexural testing, DSC, and DMA. Slight enhancements of yield stress, and flexural strength and modulus, and obvious decreases of fracture strength and strain of the DOPO-POSS/PC composites were observed with an increase in DOPO-POSS loading. The glass transition temperatures (T g) of the composites were reduced with increasing DOPO-POSS loading. The morphology of the PC composites was evaluated by SEM, which indicated that the DOPO-POSS was dispersed with a particle size of 100–250 nm in the PC matrix. The thermal degradation behaviour and flame retardancies of PC composites with different DOPO-POSS loadings were investigated by TGA, LOI, UL-94 standard, and cone calorimetry. The composite had an LOI value of 30.5 and a UL-94 rating V-0 when the content of DOPO-POSS was 4%.
Keywords: Polycarbonate; Polyhedral oligomeric silsesquioxane; Organic phosphorus compound; DOPO; POSS; Flame retardancy;

Several compatibilising systems were added to high-density polyethylene (HDPE) and polyamide 6 (PA6) blends in the presence of an organically modified montmorillonite (OMM). All the blends were prepared by using a co-rotating twin-screw extruder and characterized by SEM, TEM and XRD analyses. In addition, the rheological behaviour and the mechanical properties – tensile and impact – were evaluated.The presence of OMM affects the dimensions of the polymeric phases in the blend but not their mutual adhesion, granted only by the compatibilisers.TEM, SEM and XRD analyses indicated that there is a strict correlation between the compatibilisation level and the final interlayer distance achieved by OMM.Even if some filled compatibilised blends showed a fairly good morphology – in terms of phase adhesion, dispersion and dimension – the mechanical performance was not so satisfactory. These results were interpreted considering the possible thermo-oxidative degradation of the organic modifier of OMM and the subsequent interaction between and the degradation products and the compatibilising systems. In order to prevent these phenomena, a stabilizing system was added to the nanocomposite blends. In this case, an improvement of mechanical properties was achieved.
Keywords: Nanocomposites; Organoclay; Compatibilisation; Degradation; Stabilization;

Organically modified clay – reinforced hydrogenated nitrile rubber vulcanizate was subjected to accelerated heat aging to estimate its long-term thermo-oxidative stability and its useful lifetime was compared with that of the virgin polymer for the first time. Changes in technical properties such as tensile strength, modulus and elongation at break were studied as a function of time and temperature of aging. The infrared spectroscopic analysis of the degraded products revealed that under aerobic hot aging conditions, hydrogenated nitrile rubber (HNBR) compounds undergo cross-linking reactions that lead to embrittlement and ultimately failure. Incorporation of clay filler, however, resulted in significant improvement of the degradation profile of the nanocomposite at elevated temperatures. Loss of ductility during aging of the nanocomposite was also milder, relative to the unfilled polymer, indicating a restricted degradation by the clay filled rubber, thus prolonging the durability. From the scanning electron microscopy and atomic force microscopy studies, it was found that nanofillers protected the elastomer from surface rupture that took place on oxidation. Life prediction of both virgin elastomer and the nanocomposite indicated a three-fold increase in the effective service temperature range of the HNBR using 8 parts organically modified nanoclay.
Keywords: Hydrogenated nitrile rubber; Organically modified nanoclay; Accelerated heat aging; Life time prediction;

Poly l-lactide-layered double hydroxide nanocomposites via in situ polymerization of l-lactide by Vimal Katiyar; Nathalie Gerds; Christian Bender Koch; Jens Risbo; Hans Christian B. Hansen; David Plackett (2563-2573).
The use of clay nanofillers offers a potential route to improved barrier properties in polylactide films. Magnesium–aluminium layered double hydroxides (LDHs) are interesting in this respect and we therefore explored synthesis of PLA-LDH nanocomposites by ring-opening polymerization. This method is attractive because it should ensure good dispersion of LDH in the polymer. The effect of adding either LDH carbonate (LDH-CO3) or laurate-modified LDH (LDH-C12) was investigated. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy revealed that exfoliated nanocomposites were obtained when using LDH-C12 but that LDH-CO3 gave a partly phase-separated morphology. Thermogravimetric analysis showed that PLA-LDH combinations exhibited higher degradation onset temperatures and differential scanning calorimetry confirmed that LDHs can act as nucleating agents. However, PLA molecular weight was significantly reduced when in-situ polymerization was conducted in the presence of the LDHs and we suggest that chain termination via LDH surface hydroxyl groups and/or metal-catalyzed degradation could be responsible.
Keywords: Polylactide; Layered double hydroxides; Nanocomposite; in-situ Polymerization;

Stability of conducting polyester/polypyrrole fabrics in different pH solutions. Chemical and electrochemical characterization by J. Molina; J. Fernández; A.I. del Río; R. Lapuente; J. Bonastre; F. Cases (2574-2583).
The stability of conducting fabrics of polyester (PES) covered with polypyrrole/anthraquinone sulfonic acid (AQSA) has been tested in different pH solutions (1, 7, 13) and after washing tests. It is important to determine the stability of the counter-ion in the polymer matrix, since its loss causes the decrease of the conducting properties of the fabrics. X-ray photoelectron spectroscopy (XPS) studies were done to quantify the amount of counter-ion in the polymer and to obtain the doping level (Nδ+/N). Surface resistivity changes after the different tests were measured by electrochemical impedance spectroscopy (EIS). An increase in the solution pH caused a decrease of the doping level (Nδ+/N), the release of part of the counter-ions and an increase in the surface resistivity. Cyclic voltammetry (CV) measurements showed a gradual loss of electroactivity as pH increased. The influence of the scan rate on the characterization of conducting fabrics has been also demonstrated by CV. Lower scan rates produce a more characteristic response than higher ones. Scanning electrochemical microscopy (SECM) measurements showed a loss of electroactivity when the sample was tested in the pH 13 solution, although the material continued being electroactive.
Keywords: Conducting fabrics; Polypyrrole; Anthraquinone sulfonic acid; X-ray photoelectron spectroscopy; Scanning electrochemical microscopy;

The synergistic effect of four different boron containing substances, zinc borate (ZnB), borophosphate (BPO4), boron silicon containing preceramic oligomer (BSi) and lanthanum borate (LaB), were studied to improve the flame retardancy of a polypropylene (PP) intumescent system composed of ammonium polyphosphate (APP) and pentaerythritol (PER). The flame retardancy of PP composites was investigated by limiting oxygen index (LOI), UL-94 standard, thermogravimetric analysis (TGA) and cone calorimeter tests. The addition of 20 wt% intumescent flame retardant (IFR) improves the flame retardancy by increasing the char formation. According to LOI and UL-94 test, boron compounds show their highest synergistic effect at 1 wt% loading. BPO4 containing composite shows the highest LOI (30), lowest maximum heat release rate (HRR) and lowest total heat release rate (THR) value. Although the char yield increases as the amount of boron compounds increases, the flame retarding effect decreases. Cone calorimeter and TGA data indicate that the boron compounds are likely to show their synergistic effect by reinforcing the integrity of char which improves its barrier effect rather than increasing the char yield.
Keywords: Intumescent flame retardants; Boron compounds; Polypropylene; Cone calorimeter;

Variable amounts of zinc and nickel salts, such as ZnSO4·7H2O and NiSO4·6H2O, have been incorporated into blends of polypropylene (PP)/ammonium polyphosphate (APP)/dipentaerythritol (DPER) with the aim of studying their effect on intumescent flame retardance (IFR). The PP/IFR/salt composites have been prepared using a twin-screw extruder, and their IFR behaviours have been evaluated through limiting oxygen index (LOI), vertical burning tests (UL-94), and cone calorimeter tests (CONE). The results show that, at an appropriate level, zinc and nickel salts can increase the LOI and decrease the heat release rate (HRR). The composites have been studied with the aid of thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The flame-retardant mechanism of the PP/IFR/salts system is also discussed in terms of catalytic charring. ZnSO4·7H2O has been shown to be the most effective among the aforementioned metal salts, which has proved to be strongly associated with its low melting point and the interaction between DPER and SO4 2−.
Keywords: Zinc and nickel salts; Intumescent flame retardant; Catalysis; Polypropylene;

Effects of transesterification and degradation on properties and structure of polycaprolactone–polylactide copolymers by Vitali T. Lipik; Leonardus K. Widjaja; Sing S. Liow; Marc J.M. Abadie; Subramanian S. Venkatraman (2596-2602).
Ester bonds of biodegradable polymers, such as poly (α-hydroxy esters), synthesized by the coordinated anionic ring opening polymerization (CAROP), are subject to transesterification during synthesis. In this work, a series of poly(ɛ-caprolactone)-poly(l-lactide) (PCL-PLA) block and random copolymers with targeted molar mass of 10,000 Da was synthesized to study the mechanism of transesterification reactions via NMR and MALDI-TOF.Polylactide segments are more vulnerable to transesterification compared to polycaprolactone. As a result, the actual quantity of l-lactide in the polymers was less than the target for all studied copolymers because of the decarboxylation and consequent CO elimination from fragments of macromolecules after transesterification. The presence of decarboxylation during transesterification was confirmed analytically and was reflected in the MALDI-TOF and 13C NMR spectra. An analysis of the polymer structure pointed to dehydration reactions that led to the formation of cyclic structures and double bonds with possible crosslinking.
Keywords: Transesterification; Polycaprolactone; Polylactide; Dehydration; Decarboxylation;

Facile synthesis and properties of a new generation of soluble and thermally stable polyimides by Ayesha Kausar; Sonia Zulfiqar; Zahoor Ahmad; Muhammad Ilyas Sarwar (2603-2610).
A new diamine, 1,4-phenylene bis((E)-1-(4-chloro-3-aminobenzylidene) thiourea) (PCABT), containing phenylthiourea and azomethine groups was prepared from the reduction of dinitro compound, 1,4-phenylene bis((E)-1-(4-chloro-3-nitrobenzylidene)thiourea), PCNBT. The structures of resulting monomers were characterized by elemental analysis, FTIR, 1H and 13C NMR techniques. Afterwards, this diamine was reacted with various aromatic dianhydrides (ODPA, BTDA and 6FDA) in glacial acetic acid to afford poly(phenylthiourea azomethine imide)s (PPTAIs) with η inh of 1.59–1.66 dL/g, depending on the dianhydride used. The ensuing PPTAIs exhibited ample solubility in organic solvents (DMAc, DMF, DMSO and NMP) and were obtained in quantitative yields. Also, all polyimides were amorphous according to wide-angle X-ray determination. GPC measurements of polymers revealed M w around 69,000–72,000. Moreover, thermogravimetric analyses indicated that PPTAIs were fairly stable up to 550 °C, and 10% weight loss temperatures were recorded in the range of 563–578 °C (N2 atmosphere). Ultimately, these polyimides own high glass transition temperatures about 281–285 °C.
Keywords: Phenylthiourea; Azomethine; Solubility; Thermal stability; Wide-angle X-ray diffraction;

Novel thermally stable and organosoluble poly(thiourea–amide–imide)s (PTAIs) were synthesized through the condensation of various diamines with a new kind of aromatic diacid chloride monomer containing pyridine units, 2-(3-(2-(3-(chlorocarbonyl)pyridin-2-yl)-1,3-dioxoisoindoline-5-carbonyl) thioureido) nicotinoyl chloride, CPDITNC. Spectroscopic and elemental analyses were carried out for the structure elucidation of synthesized monomers. Accordingly, the ensuing PTAIs were characterized by FTIR, 1H and 13C NMR techniques along with crystallinity, organosolubility, inherent viscosity and GPC measurements. Consequently, polymers bearing phenyl thiourea and pyridine moieties in the backbone exhibited good organosolubility in a variety of highly polar solvents such as DMAc, DMF, DMSO and NMP. PTAIs encompassed η inh of 1.24–1.46 dL/g and two of the polymers showed crystalline behavior. Moreover, GPC measurements of polymers revealed M w around 33,000–50,000. Thermal stability of these polymers was ascertained via 10% weight loss temperatures in the range of 548–562 °C (inert atmosphere). Ultimately, these polymers own high glass-transition temperatures about 264–270 °C.
Keywords: Poly(thiourea–amide–imide)s; Condensation; Phenyl thiourea; Pyridine moieties; Organosolubility;

A simple method was adopted to prepare poly(l-lactide)-grafted graphite oxide (PLLA-g-GO) by ring opening polymerization of l-lactide in the presence of graphite oxide (GO) with hydroxyl groups. GO was firstly treated with tolylene-2,4-diisocyanate (TDI) to create an anchor site on GO, and then reacted with 1,4-butanediol (BD) to afford functional hydroxyl groups grafted onto the surface of GO. So that, the dispersity of GO in the organic solution was enhanced. According to the thermogravimetric analysis (TGA), the organic composition of GO treated with TDI and BD (GO-TDI-OH) was estimated to be about 13 wt%. Also, using TGA, the composition of GO in the PLLA-g-GOs could be estimated. The hydroxyl groups on the GO surface acted as initiators for the ROP of l-lactide. Further, they also played as a vital role in controlling the molecular weight of the PLLA. The synthesized PLLA-g-GOs were characterized by the FTIR, 1HNMR and UV/Vis spectroscopies. The dispersion states of GO in the PLLA-g-GOs were investigated by wide angle x-ray diffraction patterns. According to differential scanning calorimeter study, it was found that GO platelets have nucleating effect on the crystallization of PLLA in the PLLA-g-GO. Additionally, the incorporation of GO improved the electrical conductivity of PLLA, indicating that GOs is a good conducting-modifiers for polymers.
Keywords: Biodegradable polyester; Poly(l-lactide); Graphite oxide; Electrical conductivity; Thermal degradation; Crystallization behaviors;

Flexural creep behavior of nylon 6/6 (NY66)– and polypropylene (PP)– based long fiber (l/d = 2000−10 000) thermoplastic (LFT) composites was investigated as a function of ultraviolet irradiation and moisture absorption. Extrusion/compression-molded panels were prepared according to ASTM D-2990 and conditioned according to ASTM D-618. NY66 and PP LFTs were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Fourier-transform infrared (FTIR) spectroscopy in the unexposed condition, and as-exposed to 253.7 nm UV radiation. The creep compliance of PP LFT increased with increasing UV exposure, whereas the creep compliance of NY66 LFT showed a moderate decrease with increasing UV exposure. Moisture absorption experiments were performed in boiling water until saturation on NY66 and its LFT composites. Characterization of desorbed moisture absorption specimens suggested slight variation in the structure, and an analysis of creep compliances showed minimal changes as compared to the dry/unexposed specimens.
Keywords: Polymer matrix composites; Long fiber thermoplastics; Flexural creep; Ultraviolet radiation; Moisture absorption; Infrared spectroscopy;

Biodegradation and hydrolysis rate of aliphatic aromatic polyester by Thitisilp Kijchavengkul; Rafael Auras; Maria Rubino; Susan Selke; Mathieu Ngouajio; R. Thomas Fernandez (2641-2647).
The biodegradation and hydrolysis rates of an aliphatic aromatic copolyester were measured in manure, food, and yard compost environments and in phosphate buffer solution (pH = 8.0) and vermiculite at 58 °C. Mineralization, molecular weight reduction, and structural changes determined by DSC, FTIR, and 1H NMR were used as indicators of the biodegradation and hydrolysis rates. Poly(butylene adipate-co-terephthalate), PBAT, film biodegraded at distinctive rates in manure, food, and yard compost environments having different microbial activities. The highest biodegradation rate was found in manure compost, which had the highest CO2 emissions and lowest C/N ratio. The possible presence of extracellular enzymes in manure and food composts may facilitate the hydrolytic reaction since greater molecular weight reduction rates were observed in these composts. 1H NMR and thermal analysis revealed that, while PBAT is a semi-crystalline copolyester with cocrystallization of BT and BA dimers, the soft aliphatic domain (BA) and the amorphous region are more susceptible to hydrolysis and biodegradation than the rigid aromatic domain (BT) and the crystalline region.
Keywords: Mineralization; Poly(butylene adipate-co-terephthalate); PBAT; Composting;

Effects of adjacent groups of benzimidazole on antioxidation of polybenzimidazoles by Zhihong Chang; Hongting Pu; Decheng Wan; Ming Jin; Haiyan Pan (2648-2653).
The chemical oxidative stabilities of poly(2,2-(m-phenylene)-5,5-bibenzimidazole) (PBI-ph), poly(2,5-benzimidazole) (ABPBI), poly(2,2′-hexyl-5,5′-bibenzimidazole) (PBI-hex), and poly(2,2′-imidazole-5,5′-bibenzimidazole) (PBI-imi) are studied. By means of FTIR and 1HNMR analysis, more information about the degradation process of PBI-ph is found as: CH2 groups are left in the residual polymers; after the N–H bond and the trisubstituted benzene ring are oxidized by oxidative free radicals, the meta-phenylene is relatively stable. Through Fenton tests, the chemical oxidative stabilities of these PBIs are compared and results show that PBI-ph is the stablest material while PBI-imi is the unstablest one. Through FTIR analysis, the structure changes to those degraded PBIs are compared. The conjugated structure formed between meta-phenyl and benzimidazole can protect the main chain of PBI-ph from the attack of oxidative free radicals. Additionally, effects of acid on PBI-ph degradation rate are evaluated and the results show that phosphoric acid can slow down the chemical oxidative degradation.
Keywords: Polybenzimidazole; Degradation; Proton exchange membrane; Oxidation; Polymer electrolyte membrane fuel cells;

Photodegradation of some ethylene–norbornene random copolymers by Kenshiro Nakade; Yasutaka Nagai; Fujio Ohishi (2654-2658).
We investigated the photodegradation of specific ethylene-norbornene random copolymers (ENRC) – a group of substances which has been attracting much attention in recent years. ENRCs having various contents of norbornene were studied. After irradiation, each sample was separated into chloroform-insoluble and soluble portions. The chloroform-insoluble portion was weighed and analyzed by FTIR. The chloroform-soluble portion was analyzed by size elimination chromatography (SEC), FTIR and 1H NMR. The yield of the chloroform-insoluble portion increased with increased irradiation time. Formyl, formate, acyl, hydroxy groups and a carbon–carbon double bond were formed by photo-irradiation. Apparently, hydrogen atoms bound to the tertiary and secondary carbon atom in the parent ENRCs are abstracted. From these results, it is suggested that auto-oxidation results from photo-irradiation of the ENRCs. In ENRCs with similar stereoregularity, the degree of photodegradation increases with increasing norbornene content.
Keywords: Ethylene–norbornene random copolymers; Cyclic olefin copolymers; Photodegradation; Norbornene content;

Photodegradation and weathering effects on timber surface moisture profiles as studied using dynamic vapour sorption by Victoria Sharratt; Callum A.S. Hill; Jalaludin Zaihan; Darwin P.R. Kint (2659-2662).
The moisture sorption kinetic profiles of Scots pine (Pinus sylvestris) earlywood and latewood were studied using a Dynamic Vapour Sorption apparatus and the equilibrium isotherms determined. The samples were chosen to give an insight to the effects that photodegradation and weathering have on the moisture behaviour of the surface layers of timber. Samples were subjected to indoor and outdoor exposure regimes. Significant differences were found between the sorption isotherms of exposed and unexposed wood, as well as with the sorption kinetics profiles. The reasons for these differences are discussed.
Keywords: Photodegradation; Weathering; Wood surfaces; Pinus sylvestris; Dynamic vapour sorption; Sorption isotherms;

Sodium hydroxide-assisted dechlorination of a poly(vinylidene chloride)-containing wrapping film in ethylene glycol solution by Tomohito Kameda; Masashi Ieshige; Guido Grause; Toshiaki Yoshioka (2663-2665).
Poly(vinylidene chloride) (PVDC) wrapping film was dechlorinated using solutions of NaOH in ethylene glycol (EG) at temperatures between 150 and 190 °C. The reaction was comparable to that for PVDC powder; however, it occurred at a lower NaOH concentration, which can be explained by the dissolution of additives present in the wrapping film. Therefore, the best results for the dechlorination of the wrapping film were obtained at a temperature of 190 °C and NaOH concentrations of 0.1 M and 0.5 M, resulting in dechlorination yields of almost 90% after 135 min. For the dechlorination reaction, the activation energy of the PVDC wrapping film (185 kJ mol−1) was determined to be higher than that of PVDC powder; this finding could be attributed to the presence of a stabilizer and the smaller surface area of the PVDC wrapping film.
Keywords: Poly(vinylidene chloride); Wrapping film; NaOH(EG) solution; Dechlorination; Apparent rate constant; Apparent activation energy;

Thermo-cleavable polymers: Materials with enhanced photochemical stability by Matthieu Manceau; Martin Helgesen; Frederik C. Krebs (2666-2669).
Photochemical stability of three thermo-cleavable polymers was investigated as thin films under atmospheric conditions. A significant increase in lifetime was observed once the side-chain was cleaved emphasizing the detrimental effect of solubilizing groups on the photochemical stability of conjugated polymers. In addition to their ease of processing, thermo-cleavable polymers thus also offer a greater intrinsic stability under illumination.
Keywords: Thermo-cleavable conjugated polymers; Side-chain cleavage; Photochemical stability; Organic photovoltaics; UV–visible absorbance;

The effect of different storage temperatures on the physical properties of pectin solutions and gels by Gordon A. Morris; Jonathan Castile; Alan Smith; Gary G. Adams; Stephen E. Harding (2670-2673).
The stability (in terms of viscosity and gel strength) of pectin solutions and gels potentially plays an important role in their behaviour and functional properties in a wide range of applications and therefore any changes over time must be understood. The gel strength of pectin gels and intrinsic viscosity of pectin solutions at different temperatures (4 °C, 25 °C and 40 °C) have been investigated using a “rolling ball” viscometer and a texture analyser respectively. Both the intrinsic viscosity ([η]) and gel strength decrease with increased storage time, although this more pronounced at elevated temperatures. The changes in intrinsic viscosity with storage time and temperature were used to determine the depolymerisation constant (k). Pectin storage conditions and particularly temperature have an influence on depolymerisation, particularly elevated storage temperatures, but whether or not this will be detrimental to its intended application will depend on the functional significance of the changes that occur. In this case based on the previous diffusion studies on a model drug (paracetamol) we conclude that the decreases in viscosity and gel strength within the range observed have no detrimental effect on the drug release properties.
Keywords: Pectin; Molar mass; Intrinsic viscosity; Gel strength; Stability; Drug release;