Polymer Degradation and Stability

Published by Elsevier
Online ISSN: 0141-3910
Publications
Article
An amphiphilic macromolecule (AM) was exposed to ionizing radiation (both electron beam and gamma) at doses of 25 kGy and 50 kGy to study the impact of these sterilization methods on the physicochemical properties and bioactivity of the AM. Proton nuclear magnetic resonance and gel permeation chromatography were used to determine the chemical structure and molecular weight, respectively. Size and zeta potential of the micelles formed from AMs in aqueous media were evaluated by dynamic light scattering. Bioactivity of irradiated AMs was evaluated by measuring inhibition of oxidized low-density lipoprotein uptake in macrophages. From these studies, no significant changes in the physicochemical properties or bioactivity were observed after the irradiation, demonstrating that the AMs can withstand typical radiation doses used to sterilize materials.
 
Infrared spectra of representative samples including stretch bands that indicate polymer degradation. From top to bottom: (red) unexposed sample (0 kGy); (blue) sample exposed to 50 kGy e-beam; (green) sample exposed to 50 kGy gamma; and (black) hydrolytic degradation product (diacid 4).  
Cell viability at 48, 72 and 96 h in culture media with polymers at concentration of (A) 0.10 mg/mL media and (B) 0.01 mg/mL media. Data represent mean and standard deviation of 3 samples. No significant differences against the media control were observed.  
Light microscope images (10X magnification) of L929 mouse fibroblasts after 96 h of culture in polymer 1 (0.10 mg/mL) exposed under various conditions: (1) 50 kGy e-beam, (2) 50 kGy gamma, (3) unexposed polymer control, (4) media control. Scale bar is 200 µm in all images.  
Article
The effect of electron beam and gamma radiation on the physicochemical properties of a salicylate-based poly(anhydride-ester) was studied by exposing polymers to 0 (control), 25 and 50 kGy. After radiation exposure, salicylic acid release in vitro was monitored to assess any changes in drug release profiles. Molecular weight, glass transition temperature and decomposition temperature were evaluated for polymer chain scission and/or crosslinking as well as changes in thermal properties. Proton nuclear magnetic resonance and infrared spectroscopies were also used to determine polymer degradation and/or chain scission. In vitro cell studies were performed to identify cytocompatibility following radiation exposure. These studies demonstrate that the physicochemical properties of the polymer are not substantially affected by exposure to electron beam and gamma radiation.
 
Chemical structure of polymer 1, poly[1,6-bis(o-carboxyphenoxy)hexanoate].  
Change in sample glass transition temperature over four weeks as a function of storage condition.
Comparison of IR spectrum of fresh polymer and representative stored samples after four weeks.  
Change in molecular weight of polymer 1 as an effect of storage temperature over four weeks.  
Article
Storage stability was evaluated on a biodegradable salicylate-based poly(anhydride-ester) to elucidate the effects of storage conditions over time. The hydrolytically labile polymer samples were stored in powdered form at five relevant storage temperatures (-12 °C, 4 °C, 27 °C, 37 °C, 50 °C) and monitored over four weeks for changes in color, glass transition temperature, molecular weight, and extent of hydrolysis. Samples stored at lower temperatures remained relatively constant with respect to bond hydrolysis and molecular weight. Whereas, samples stored at higher temperatures displayed significant hydrolysis. For hydrolytically degradable polymers, such as these poly(anhydride-esters), samples are best stored at low temperatures under an inert atmosphere.
 
Article
The role of hydration in degradation and erosion of materials, especially biomaterials used in scaffolds and implants, was investigated by studying the distribution of water at length scales from 0.1 nm to 0.1 mm using Raman spectroscopy, small-angle neutron scattering (SANS), Raman confocal imaging, and scanning electron microscopy (SEM). The measurements were demonstrated using L-tyrosine derived polyarylates. Bound- and free- water were characterized using their respective signatures in the Raman spectra. In the presence of deuterium oxide (D(2)O), H-D exchange occurred at the amide carbonyl but was not detected at the ester carbonyl. Water appeared to be present in the polymer even in regions where there was little evidence for N-H to N-D exchange. SANS showed that water is not uniformly dispersed in the polymer matrix. The distribution of water can be described as mass fractals in polymers with low water content (~5 wt%), and surface fractals in polymers with larger water content (15 to 60 wt%). These fluctuations in the density of water distribution are presumed to be the precursors of the ~ 20 μm water pockets seen by Raman confocal imaging, and also give rise to 10-50 μm porous network seen in SEM. The surfaces of these polymers appeared to resist erosion while the core of the films continued to erode to form a porous structure. This could be due to differences in either the density of the polymer or the solvent environment in the bulk vs. the surface, or a combination of these two factors. There was no correlation between the rate of degradation and the amount of water uptake in these polymers, and this suggests that it is the bound-water and not the total amount of water that contributes to hydrolytic degradation.
 
Article
Fourteen explanted Dynesys® spinal devices were analyzed for biostability and compared with a reference, never implanted, control. Both poly(carbonate-urethane) (PCU) spacers and polyethylene-terephthalate (PET) cords were analyzed. The effect of implantation was evaluated through the observation of physical alterations of the device surfaces, evaluation of the chemical degradation and fluids absorption on the devices and examination of the morphological and mechanical features. PCU spacers exhibited a variety of surface damage mechanisms, the most significant being abrasion and localized, microscopic surface cracks. Evidence of oxidation and chain scission were detected on PCU spacers ATR-FTIR. ATR-FTIR, DSC and hardness measurements also showed a slight heterogeneity in the composition of PCU. The extraction carried out on the PCU spacers revealed the presence of extractable polycarbonate segments. One spacer and all PET cords visually exhibited the presence of adherent biological material (proteins), confirmed by the ATR-FTIR results. GC/MS analyses of the extracts from PET cords revealed the presence of biological fluids residues, mainly cholesterol derivatives and fatty acids, probably trapped into the fiber network. No further chemical alterations were observed on the PET cords. Although the observed physical and chemical damage can be considered superficial, greater attention must be paid to the chemical degradation mechanisms of PCU and to the effect of byproducts on the body.
 
Article
Photochromic indolylfulgimides covalently attached to polymers have beneficial properties for optical switching. A 3-indolylfulgide and two 3-indolylfulgimides with one or two polymerizable styrene groups attached on the nitrogen atom(s) were synthesized. Copolymerization with methyl methacrylate (MMA) provided linear copolymers (one styrene group) or a cross-linked copolymer (two styrene groups). The properties of the monomers and copolymers in toluene or as thin films were characterized. The new copolymers were photochromic (reversible Z-to-C isomerization), absorbed visible light, and revealed good thermal and photochemical stability. At room temperature, all copolymer films showed no loss of absorbance after 5 weeks. At 80 °C in either toluene or as films, the Z-forms copolymers were less stable than the C-form copolymers, which showed little or no degradation after 400 h. The degradation rate due to repeated ring-closing - ring opening cycles was less than 3% per 100 cycles. The cross-linked copolymer showed photochemical stability comparable to monomeric fulgides in toluene, <1% per 100 cycles. In general, the properties of the linear and cross-linked copolymers were similar to the corresponding monomers in toluene. In films, the conformations of the Z-form were restricted due to the matrix indicating that the preparation of films from the C-form is advantageous.
 
Conference Paper
In many cases of accelerated thermal aging of polymeric materials of electrical interest, for various Arrhenius lifelines corresponding to various properties of a given material, to various materials with the same endlife criterion, and to various endlife criteria for a given material, a linear correlation exists between the logarithm of the preexponential factor and the activation energy. An attempt is made to demonstrate that, in many important cases, the existence of such a correlation, called the compensation effect, results from the non-Arrhenian character of the kinetics. An experimental and a numerical example show that, for an aging process resulting from two successive steps, the non-Arrhenian kinetics leads to an apparent compensation effect. Another experimental and numerical example shows that, for a sequential process, an apparent compensation effect can also be observed in a comparative study of various materials of close composition
 
Article
Degradable bioelastomers represent a useful class of biomaterials. In this paper, a novel biodegradable network of elastomeric polyesters, poly((1,2-propanediol-sebacate)-citrate) (PPSC), was synthesized by condensation of 1,2-propanediol, sebacic acid and citric acid without any catalyst. An oligomeric diol of 1,2-propanediol-sebacate was first synthesized by carrying out a controlled condensation reaction between 1,2-propanediol and sebacic acid, and then a pre-polymer was synthesized by condensation of the diol and citric acid, whereat the pre-polymer was post-polymerized and simultaneously crosslinked in mold at 120 °C. A series of PPSC polymers were prepared at different post-polymerization times and different monomers' ratio. Tg confirms that PPSC is totally amorphous at 37 °C. The mechanical properties of PPSC testified that the new polymers are typical elastomers with low hardness and large elongation. The different post-polymerization times and monomers' ratio had strong influence on the degradation rates and mechanical performances. The material was expected to be useful for drug controlled delivery, tissue engineering scaffold and other biomedical applications.
 
Article
The important polymer stabilizer, 1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine, which serves a dual role as a metal deactivator and antioxidant, is shown to have crystal polymorphism. Although the published melting range is 225–232 °C, which is well above the processing temperature of many polymers in which it is used, existence of a second polymorph that transforms below 205 °C is demonstrated. This α polymorph, which is thermodynamically stable at room temperature, is thermodynamically un-favored at temperatures above about 176 °C. It is shown that under some conditions the α polymorph can endothermically pass directly into the melt state at temperatures below 205 °C, while under other conditions it undergoes a direct endothermic solid–solid transition to the higher melting β polymorph.The results highlight the potential importance of polymorphs for controlling polymer additive behavior and elucidate important phenomena relevant to dispersion of this additive in polymer compounds.
 
Article
In order to study the relationship between structure and properties, multiblock copolymers composed of poly(butylene succinate) (PBS) and poly (1,2-propylene succinate) (PPSu) have been synthesized by chain-extension at various molar ratios of hexamethylene diisocyanate (HDI) to polyester-diols, which have been abbreviated as R-values in this paper. Molecular weights of soluble fractions, gel fractions and crosslink densities have been determined. Thermal properties, mechanical properties and biodegradability have been studied and correlated with R-values. Crystallization of copolymers becomes difficult with increasing R-value. Tensile strength, flexural strength and flexural modulus tend to increase with increasing R-value up to 1.2, and vary little when R-value increases from 1.2 to 1.3, then decrease with further increase in R-value. Impact strength achieves a maximum value at R-value of 1.3. Biodegradation rate reaches a minimum value when R-value is 1.1. Biodegradation has been studied systematically by attenuated total reflectance Fourier transform infrared (ATR-FTIR), 1H NMR and SEM.
 
Article
The products of pyrolysis, in the temperature range up to 440°C both in vacuum and in nitrogen, from an unsaturated polyester based on HET-acid (1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid), maleic anhydride and 1,2-propanediol have been analysed. The major products are HET-anhydride, hexachlorocyclopentadiene, pentachlorocyclopentadiene, tetrachlorocyclopentadiene, maleic anhydride and isomers of dimethyldioxane. An especially remarkable product is 1,2,3,4,7,7-hexachlorobicyclo[2.2.1]hepta-2,5-diene, the Diels-Alder adduct of hexachlorocyclopentadiene with acetylene. Further chlorinated maleic esters, esters containing the HET-acid unit, 5-hydroxy-α-pyrone, and an alkyl-substituted 5-hydroxy-α-pyrone are identified among the minor products of pyrolysis. Detailed mechanisms are proposed to explain the formation of the various products. For example, the formation of two dimethyldioxane isomers is explained via intermediate polyether formation.
 
FT-IR spectra of weathered veneers after different exposure times; untreated controls (A), treated with 10% DMDHEU (B), 30% DMDHEU (C) and 50% DMDHEU (D). FT-IR assignments: (a) carbonyl stretching in wood and DMDHEU; (b, c) aromatic skeletal vibration in lignin; (d) CeO stretching in lignin and hemicellulose; (e) CeO stretching in lignin, acetyl and carbonylic vibration in hemicellulose as well as CeO vibration at the N-methylol group of DMDHEU.
Tensile strength of unmodified and DMDHEU treated veneers before and after 144 h weathering (A). Tensile strength loss of the veneers due to 144 h weathering (B).
Visual appearance of untreated and DMDHEU treated veneers after accelerated weathering in a QUV (144 h exposure). 
Changes in the morphology of unmodified and DMDHEU treated earlywood tracheids as a result of artificial weathering (SEM, cross sections). A, untreated, unweathered; B, untreated, after 48 h weathering; C, untreated, after 144 h weathering; D, 10% DMDHEU, unweathered; E, 10% DMDHEU, after 48 h weathering; F, 10% DMDHEU, after 144 h weathering; G, 50% DMDHEU, unweathered; H, 50% DMDHEU, after 48 h weathering; I, 50% DMDHEU, after 144 h weathering. 
Radial sections of unmodified and DMDHEU treated veneers (SEM). A, untreated earlywood tracheids, unweathered; B, untreated earlywood tracheids, after 144 h weathering; C, untreated parenchyma cells, after 144 h weathering; D, 10% DMDHEU treated earlywood tracheids, unweathered; E, 30% DMDHEU treated earlywood tracheids, after 144 h weathering; F, 30% DMDHEU treated parenchyma cells, after 144 h weathering. 
Article
N-methylol compounds are used as a wrinkle-resistant finish in the textile industry. They are expected to enhance the resistance of wood to weathering because they can cross-link the cell wall and dimensionally stabilise wood. Scots pine veneers were modified with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) to weight percent gains (WPG) of 10%, 27% or 48% and exposed to artificial weathering. Initially, weight losses of unmodified veneers were significantly greater than those of DMDHEU treated specimens even though DMDHEU was leached from wood at a higher rate than loss of wood substance. The weight losses of all treated veneers after 144 h of weathering, however, were similar to those of the unmodified controls. Therefore we conclude that in the short term DMDHEU treatment can restrict weight losses of wood during weathering, which occur due to degradation of lignin and hemicellulose and loss of degraded wood fragments from wood.Infrared spectroscopy suggested that treatment of wood veneers with DMDHEU to high WPG (48%) stabilised lignin to some extent. Tensile strength losses of DMDHEU treated veneers during weathering were lower than those of untreated veneers. DMDHEU treatment, however, had a deleterious effect on the tensile strength of the veneers, possibly associated with the presence of magnesium chloride catalyst in the treatment solution. Scanning electron microscopy revealed that DMDHEU treatment was highly effective at preventing the degradation of the wood cell wall during weathering. Tracheids in unmodified veneers became distorted within 48 h of weathering exposure, whereas cells in modified veneers, especially those reacted to higher weight percent gains, retained their shape even after 144 h weathering.
 
Article
The radiation chemistry of the copolymer of tetrafluoroethylene and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (Teflon AF®) was investigated using γ-irradiation under vacuum. Two types of resin were studied which differed in dioxole content; AF1600 65 mol% dioxole and AF2400 87 mol% dioxole. The cyclic fluoroplastic was found to undergo predominant main chain scission upon radiolysis, both above and below the glass transition temperature, which was characterised by a decrease in the glass transition temperature. FTIR analysis showed the formation of new carboxylate end groups as well as terminal unsaturation. Both CF· and CF2·, radicals were identified using Electron Spin Resonance upon γ-radiolysis and subsequent thermal annealing. The G-value for radical production at 77 K, G(R), was 1.6 for both resins.
 
Article
This study synthesizes a series of cyclohexanedimethanol (CHDM)-based alicyclic/aliphatic copolyesters (PBSCs) using succinic acid, 1,4-butanediol and 1,3/1,4-CHDM at various molar ratios to investigate the effects of these compositions on crystallinity, biodegradability and the mechanical properties of PBSCs. The PBSCs were characterized using proton nuclear magnetic resonance, gel permeation chromatography, wide-angle X-ray diffraction, differential scanning calorimeter and thermogravimetric analysis. Biodegradability was evaluated by enzymatic hydrolysis with a lipase from Pseudomonas cepacia. The mechanical properties of PBSCs were determined using a tensile testing machine.Experimental results reveal that the PBSCs containing 1,3/1,4-CHDM in total diol with less than 50 mol% are crystallizable, while those containing 1,3/1,4-CHDM with more than 50 mol% are amorphous. The biodegradability test results suggest that PBSCs can be classified as surface-eroding polymers with a random endo-type scission. Surface hydrophilicity of PBSCs was the predominant effect on enzymatic hydrolysis, not crystallinity.
 
Article
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.
 
Article
Poly(2,6-dimethyl-1,4-phenylene oxide) (PPE) films were exposed to monochromatic radiation (254 nm, 365 nm) and to polychromatic radiation (λ300 nm, outdoor exposure) in the presence of atmospheric oxygen. Thermooxidation of PPE samples was carried out in the temperature range 100 °C–170 °C. Products formed in irradiated and thermooxidized films were identified by coupling FTIR spectroscopy to chemical derivatization reactions, physical treatments and gas phase analysis. The nature and the distribution of oxidation products are shown to be different in the two conditions of degradation.
 
Article
In order to improve our understanding of the reactions occurring during the photodegradation of poly(2,6-dimethyl-1,4-phenylene oxide) we analyzed the formed products which were eluted from the irradiated solid polymer material by three different chromatographic techniques, namely GC/MS, HPLC/MS and HPLC in combination with a diode array detector. We found that there are only a few types of chromophores, like xanthones, lactones and benzoquinones which are responsible for the yellowing. These coloured species and several types of colourless species each appear in a series of homologous compounds differing by one monomeric unit. In most cases it is only one monomeric unit which is modified, e.g. by oxidation of the methyl groups. In combination with the results obtained by time-resolved experiments (Schneider S, Richter F, Brem B, 1998, Polym Degrad and Stab 1998;61:453) several new conclusions can be drawn with respect to the mechanism of photodegradation in this polymer. The by far, most important primary photochemical process is the cleavage of the hydroxyl end group of the polymer. Secondary reactions lead to the scission of a nearby ether bond thus giving rise to the formation of homologous series of photoproducts. Since a variation of the spectral composition of the photolysis light did not result in a different product distribution, we conclude that the most important primary photochemical reaction steps are independent of excitation wavelength.
 
Article
A series of biodegradable aliphatic/aromatic copolyesters, poly(butylene terephthalate)-co-poly(butylene cyclohexanedicarboxylate)-b-poly(ethylene glycol) (PTCG), were prepared by a two-step melt polycondensation method and characterized by means of GPC, FTIR, NMR, DSC, TGA, etc. The effects of aliphatic ester content on the physical, mechanical and thermal properties, as well as in vitro and in vivo degradation behaviors were investigated. The decrease in mechanical strength was observed with an increase in poly(butylene cyclohexanedicarboxylate) (PBC) molar fraction. DSC results showed one melting point and two glass transition temperatures in all samples, and the melting temperature was found to go down gradually as more cyclohexanedicarboxylic acid (CHDA) was added. During the in vitro and in vivo degradation processes, erosion of the surface was dominant as evidenced by scanning electron microscopic observations. The copolyesters containing many CHDA units were featured by the higher water uptake and faster degradation due to much richer amorphous phase within them.
 
Article
Nowadays, poly(vinyl alcohol) (PVA) has caused serious pollution in the natural environment. To eliminate PVA pollution, PVA-degrading enzymes (PVADE) were studied. Previously our group has detected PVADE in a mixed microbial culture. In this study, it was found that 1,4-butanediol could enhance PVADE production. High PVADE activity (3.43 U ml−1), which was 4.6 folds of the control (0.75 U ml−1), was achieved with 1,4-butanediol as carbon source. Concomitantly, the average PVA-degrading rate improved 2.0 folds compared to the control. Specifically, diauxic growth coupled with increased PVA-degrading rate was observed. Based on this phenomenon, two-stage fermentation by adding another carbon source at a proper time was designed. By applying this strategy, high PVADE productivity (60.8 U l−1 h−1) was achieved. Further, the two-stage fermentation was extended to three-stage fermentation by adding PVA to improve PVADE production. The PVADE activity per unit biomass (YPVADE/x) was significantly enhanced over two-stage fermentation and the maximum increment was 418 U g−1.
 
Article
To evaluate the feasibility of poly(1,4-dioxan-2-one) (PPDO) as a feed stock recycling material, the pyrolysis kinetics of PPDO were investigated. The pyrolysis of PPDO exclusively resulted in the distillation of 1,4-dioxan-2-one (PDO). From thermogravimetric measurements conducted at different heating rates, the kinetic parameters of the pyrolysis: activation energy, Ea=127 kJ mol−1; order of reaction, n=0; and pre-exponential factor, A=2.3×109 s−1, were estimated by plural analytical methods. The estimates show that the decomposition of PPDO proceeds by unzipping depolymerization as main reaction and random degradation process with lower Ea and A values. Equivalent isothermal degradation curves calculated from the thermogravimetric curves were supported by experimental isothermal degradation data. The calculation that PPDO is converted smoothly into PDO at 270°C agrees with the reported ceiling temperature of PPDO.
 
Article
The miscibility, morphology and biodegradability of binary blends of poly(3-hydroxy butyrate) (PHB) with poly(ε-caprolactone) (PCL), poly(1,4-butylene adipate) (PBA) and poly(vinyl acetate) (PVAc) have been studied by analysis of differential scanning calorimetry, mechanical properties, scanning electron micrography (SEM) and enzymatic degradation. The glass-transition temperature (Tg) data indicated that the PHB/PCL and PHB/PBA blends were immiscible in the amorphous state, while the PHV/PVAc blend was miscible. On the basis of the mechanical properties and SEM of the immiscible blends, it was suggested that the PHB/PCL blend has a macro-phase separated structure and the PHB/PBA blend has a modulated structure with a micro-phase separation. The enzymatic degradation of the PHB-based blend films was carried out at 37°C and pH 7·4 in an aqueous solution of an extracellular PHB depolymerase from Alcaligenes faecalis T1. The profiles of enzymatic degradation of PHB-based blends were strongly dependent upon the polymer component blended with PHB. In the case of PHB/PCL blend film, a complicated dependence of PCL weight fraction on the rate of enzymatic degradation was observed. In contrast, the weight loss of PHB/PBA or PHB/PVAc blend film by the PHB depolymerase decreased monotonously with increase in the weight fraction of PBA or PVAc. The enzymatic degradation data have been discussed in connection with the morphologies of PHB-based blend films.
 
Article
The ratio of kinetic constants has been determined for the reaction of peroxy radicals with inhibitors of the 3-aniline-1,5-diphenylpyrazole series in the oxidation of cumene and ethylbenzene at 60 and 65°C. The chemiluminescence method and the solution calorimetry method yielded comparable results. The dependence of the ratio on the initial concentration of inhibitor is discussed.
 
Article
Cellulose, the basic material of all plant substance, is also produced by green algae (Valonia) and some bacteria, principally of the generaAcetobacter, Sarcina andAgrobacterium. Special attention has been given to strains fromAcetobacter, speciallyAcetobacter xylinum.Acetobacter strains are well known for oxidizing alcohols to acids and ketones, especially for the production of vinegars using ethanol, wine or cider as carbon sources. The formation of the cellulose pellicle occurs on the upper surface of the supernatant film. Cellulose production was reported to be stimulated by addition of lactic acid, methionine, tea infusion and corn steep liquor. Although for the production process new non-conventional bioreactors have been developed, static cultures are still preferred. A large surface area is important for a good productivity. Relatively low glucose concentrations also gave better productivity and yields than higher ones. Bacterial cellulose can be applied in areas where plant cellulose can hardly be used. New applications were described as thickener to maintain viscosity in food, cosmetics, etc., as nonwoven fabric or paper for old document repair, as food additives and others. We could make use of cellulose films as a temporary substitute for human skin in the case of burns, ulcers, decubitus and others. Biofill®, Bioprocess® and Gengiflex® are products of microbial cellulose that now have wide applications in surgery and dental implants.
 
Article
Chemiluminescence under isothermal and non-isothermal conditions has been used for a more detailed study of the oxidation of isotactic polypropylene stabilised with Irganox 1010 and Irganox 1076. Annealing of the stabilised films of polypropylene at lower temperatures prolongs the induction time of oxidation measured at higher temperatures. Arrhenius plots of induction time over a wide temperature interval have been derived from non-isothermal chemiluminescence runs.
 
Article
The 3-dimensional structure of the Paucimonas lemoignei poly(3-hydroxybutyrate) (PHB) depolymerase PhaZ7 has significant similarity to Bacillus subtilis lipase LipA but differs from the latter by the presence of an additional domain. Analysis of this lid-like domain revealed the presence of many hydrophobic amino acid residues including Tyr105. In this study we constructed His-tag fusions of PhaZ7 for simplified purification and investigated the effect of amino acid exchange of eight tyrosine codons of the lid-like domain. Exchanges of Tyr103, Tyr172, Tyr173, Tyr203 or Tyr204 to alanine or serine had no phenotype but muteins with substitution of Tyr189, Tyr190 and Tyr105 to alanine showed a lag phase of the in vitro PHB depolymerase reaction. Replacement of Tyr105 by glutamate further increased the lag phase. Binding assays of the purified PHB depolymerase proteins with the natural substrate, native PHB granules, revealed a significantly reduced binding ability of the Tyr105Glu mutant compared to the wild type protein and confirmed that Tyr105 is involved in interaction with the polymeric substrate.
 
Article
Polymers which are biodegradable currently achieve high interest in materials science since they offer reductions of landfill space during waste management as well as new end-user benefits in various fields of applications. Among these materials, those from renewable resources such as polysaccharides additionally offer CO2-neutrality, partial independence from petrochemistry-based products and the exploitation of natures synthesis capabilities via photosynthesis. Cellulose, being a constituent of wood, is regenerated in much larger quantities than starch by natural photosynthesis from CO2 and water. The very substantial, but so far little exploited category of cellulose-based materials, which has lead to some of the very first industrial polymer-products such as celluloid and cellophane still offers numerous new possibilities for polymeric materials. Basically two main groups of cellulose-materials can be distinguished: regenerated celluloses are suitable only for fibre and film production from conventional and new processes. Secondly, thermoplastically processable cellulose derivatives such as esters can be used for extrusion and moulding. Based on general considerations on the correlation between biodegradability and molecular structure, cellulose derivatives allow both thermoplastic processing and post-consumer waste management via biological decomposition. Ways to realise this demanding new mix of properties considering biodegradability, thermoplastic behaviour and material-properties as well as possible synthetic strategies and their realisation are presented.
 
Article
Electrospun poly(dl-lactide-co-glycolide) (PLGA) microfibers have been explored as extra cellular matrix mimicking scaffolding systems for tissue engineering application. However, the hydrophobic nature of PLGA can be limiting in terms of protein adsorption. Hence, blending of PLGA with a hydrophilic polymer (Pluronic®) prior to electrospinning has been explored as a potential strategy to impart hydrophilicity to PLGA microfibers. In this study, PLGA (85/15) was blended with small quantities (0.5–2% w/v) of Pluronic® F-108 (PF-108) and electrospun into microfibers. Blending of PF-108 demonstrated a significant decrease in the surface hydrophilicity of microfibers as was evidenced by an increase in wetting tension. Surface analysis using XPS indicated the presence of PF-108 in the bulk of the fibers in addition to the surface of the fibers. The results of the water uptake studies indicated that the water uptake capacity and consequential fiber swelling was significantly increased in the presences of PF-108. The in vitro degradation studies demonstrated that the trend in molecular weight loss was not significantly influenced by the presence of small quantities of PF-108. Therefore, blending of PLGA with PF-108 could be an effective technique for surface modification of electrospun PLGA microfibers without compromising on the other advantages of PLGA.
 
Article
BAK-type polyesteramides are new polymers. The combination of high technical performance and full biodegradability is significant for this new generation of thermoplastic materials. All thermoplastic processes such as extrusion, film blowing, film casting, injection molding, blow molding, fiber spinning and others open a wide field of applications.
 
Article
Diffusion coefficients (D) and solubilities (S) of a phenolic antioxidant (Irganox® 1098) in polyamide 6 were determined in the temperature range of 139–180 °C. D and S show Arrhenius and van’t Hoff dependences on temperature respectively, with discontinuities at the melting temperature of the antioxidant. The activation energies for diffusion and enthalpies of solution are lower above than below the melting temperature. Based on the determined parameters for diffusion and solubility, the blooming of Irganox® 1098 as a function of temperature and time was calculated.
 
Article
Crosslinked hyaluronan gels are used in various applications where their stability is a prerequisite. The sensitivity of such gels to hyaluronidase can be determined as an index of stability by several approaches: chromatography, electrophoresis, and viscometry. We describe here a test based on the colorimetric determination of the N-acetyl-d-glucosamine released by hyaluronidase in standardized conditions. The sensitivities to bovine testicular hyaluronidase of 11 different gels used to fill skin wrinkles (Restylane; Perlane; Juvéderm 18, 24, 24HV, 30, and 30HV; Surgiderm 18, 24XP, 30, and 30XP) were compared.The method was reproducible, easy to perform, not time-consuming and allowed us to demonstrate that the sensitivity to testicular hyaluronidase was dependent on the degree of crosslinking of the gels and also on their monophasic/biphasic nature. Under our conditions, Surgiderm 30, 24XP and 30XP were the most resistant gels.We propose to retain the hyaluronidase test to predict the in situ stability of a crosslinked gel used to fill skin wrinkles.
 
Article
The results of a mechanistic and kinetic study show that ammonium polyphosphate (APP) strongly modifies the thermal degradation process in aliphatic polyamides 11 (PA-11) and 12 (PA-12) by lowering their temperatures of decomposition and changing the composition of the resulting volatile products. From both PA-11 and PA-12, α- and β-unsaturated nitriles are the major volatile products of degradation in the presence of APP. On the other hand, α-unsaturated nitriles are evolved from both pure PA-11 and pure PA-12, together with dodecalactam from PA-12. Minor amounts of hydrocarbons, CO, CO2, are also evolved from the pure polyamides, their formation being suppressed in mixtures with APP. A charring process occurs in parallel with the volatilization of PA-11 and PA-12 on which APP seems not to have a significant effect.A mechanism is proposed for the interaction of APP with PA-11 and PA-12, involving the formation of intermediate phosphate ester bonds whose further decomposition accounts for the thermal behaviour of the mixtures. The intumescent behaviour acquired by the char formed in the presence of APP can explain its fire-retardant action in PA-11 and PA-12.
 
Article
Tin(IV) oxide, either alone or in combination with melaminium betaoctamolybdate or molybdenum(VI) oxide, has been found to be an effective flame retardant/smoke suppressant for rigid PVC. 119mSn Mössbauer spectroscopy has been used to study the chemical changes undergone by the tin species during: (a) thermal degradation and (b) combustion. Under these conditions, the SnO2 is partially reduced to tin(II) species (SnCl2 and SnO) and metallic β-Sn. Elemental analysis of the char residues indicates that a proportion of the tin and molybdenum is lost from the polymer (possibly as volatile metallic chlorides or oxychlorides) and it is suggested that these metals can operate as fire retardants in both the condensed and vapour phases.
 
Article
Thermal degradation of polybutadiene (PBD) in anaerobic atmosphere at 250 °C had been studied by carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) before complete crosslinking. In this investigation four types of low molecular weight PBD with different 1,2-vinyl isomer content had been chosen, then pure and mixed samples of PBD were heated in different time periods. 13C NMR spectra showed that two kinds of crosslinking mechanisms occur that both of them produce methyl groups. The first mechanism is a reaction between 1,2-vinyl isomers of two PBD chains, and the second one occurs between 1,2-vinyl isomer of one chain via methylene carbon of cis or trans isomer in another chain. Also 13C NMR results showed that the presence of 1,2-vinyl isomer in the PBD structure is necessary and without it none of the mentioned reactions will occur. Furthermore isomers sequence is another important parameter which affects crosslinking. Results show that cis or trans isomer which is not adjacent to 1,2-vinyl isomer does not take part in crosslinking reaction. Moreover such cis or trans isomer can take part in second mechanism of crosslinking that 1,2-vinyl isomer was attached from head to cis or trans isomer, thus in this arrangement of isomers second mechanism of crosslinking will become dominant rather than first mechanism of crosslinking.
 
Article
Polychloroprene, also known as neoprene, is an elastomer commonly utilised in the electrical and automobile industries. Its degradation is known to occur predominantly in a two stage process: HCl is lost in the initial step, whilst the second step involves the production of volatile hydrocarbons through chain scission. In this paper we describe the use of solid state 13C NMR as a probe for structural changes in the condensed phase during these degradative steps. Cross polarisation-magic angle spinning (CP-MAS) analysis of virgin polychloroprene and a series of samples degraded at temperatures between 275 and 550 °C reveals that as degradation becomes more advanced there is a steady loss of sp3 carbon with a commensurate growth in sp2 carbon. The bulk of the chlorine loss occurs by 350 °C with the aliphatic carbon lost by 550 °C, by which temperature the residue is essentially aromatic carbon. Dipolar dephasing experiments show that this residue is essentially a network of, on average, tri-substituted phenyl rings.
 
Article
Ketone end groups formed during acrylate copolymerization are a main source of free radical formation during the initial stages of weathering in crosslinked coatings formulated with these copolymers. During weathering, the rate of formation of radicals changes. Other chromophores such as hydroperoxides are also observed. To better understand the photooxidation process, magic angle spinning C-13 NMR spectroscopy has been used to measure the change in concentration of ketone end groups in crosslinked acrylic copolymer coatings as a function of weathering time. A clear correlation has been established between ketone concentration, hydroperoxide concentration, and free radical formation rates in weathered coatings.
 
Article
The essential chemical modifications involving the polymeric constituents of wood in friction welding occur in the first 5–6 s slowing down or even stopping afterwards. FT-IR and CP-MAS 13C NMR of the welded area of wood have shown dehydration and an apparent increase in the crystallinity of cellulose. A certain level of hemicelluloses degradation occurs, accompanied by the generation of some furfural. Cellulose degradation is instead very slight. Both analytical techniques show an increase in the proportion of lignin in the welding interphase. A proportion of methoxy groups of lignin is de-etherified to phenolic hydroxy groups. Self-condensation of lignin occurs by internal rearrangement with the formation of Ar–Ar and Ar–CH2–Ar bridges. This progresses throughout the whole process of welding. The formation of C–O–C bridges, although stopping after 6 s welding, at the start of wood carbonisation, also appears to contribute to the increase in cross-linking of the lignin network.
 
Article
We have investigated oxidative degradation of low density polyethylene (LDPE) by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Replacing 16O2 in the exposure atmosphere by 18O2 makes it possible to identify species originating from the artificial ageing, since oxygen present in the material prior to ageing can then be distinguished from oxygen introduced in the ageing process. The yield of O-ions in TOF-SIMS is very high, making oxygen-18 an excellent tool for following early stages of oxidative degradation. Furthermore, we have identified two 18O-containing ions, CH318O+ and C2H318O+, which can also be used to follow the oxidation processes.
 
Article
In the past decade, Biodegradable materials that are capable of in situ formation have attracted increased attention for use in restorative orthopedic devices. In this communication, the surface erosion biodegradable polymers derived from 1.0G-polyamidoamine-double bond (PAMAM-DB) and methacrylated sebacic anhydrides (MSA) were evaluated over 2 months period under physiological conditions. Rectangular shaped samples were prepared by crosslinking the components using both chemical and photo initiators and exposure to UV light. The effects of PAMAM-DB: MSA ratio on local pH, water uptake, mass loss, and mechanical properties were explored. Polymers were characterized by 1H NMR, 13C NMR, FT-IR, compressive strength testing and SEM. It is found that copolymer with 50–60% PAMAM-DB (mass fraction) show more excellent mechanical properties compared with other formulations. Copolymers degraded mainly by surface erosion but the bulk erosion pattern also appeared at the initial time of degradation for formulation 30% and 40%. The material was expected to be useful for drug controlled delivery, tissue engineering scaffold and other biomedical applications.
 
Article
Radiation induced degradation in a commercial, filled silicone composite has been studied by SPME/GC–MS, DMA, DSC, swelling, and multiple quantum NMR. Analysis of volatile and semi-volatile species indicates degradation via decomposition of the peroxide curing catalyst and radiation induced backbiting reactions. DMA, swelling, and spin–echo NMR analysis indicate an increase in crosslink density of near 100% upon exposure to a cumulative dose of 250 kGray. Analysis of the sol fraction via Charlesby–Pinner analysis indicates a ratio of chain scission to crosslinking yields of 0.38, consistent with the dominance of the crosslinking observed by DMA, swelling and spin–echo NMR and the chain scissioning reactions observed by MS analysis. Multiple quantum NMR has revealed a bimodal distribution of residual dipolar couplings near 1 krad/s and 5 krad/s in an approximately 90:10 ratio, consistent with bulk network chains and chains associated with the filler surface. Upon exposure to radiation, the mean 〈Ωd〉 for both domains and the width of both domains increased. The MQ-NMR analysis provided increased insight into the effects of ionizing radiation on the network structure of silicone polymers.
 
Article
The photochemical stability and photodegradation pathways of poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) and copolymers of 1H,1H,2H,2H-perfluorodecyl methacrylate with 2-ethylhexyl methacrylate (XFDMA–EHMA) have been investigated under artificial solar light irradiation. The extent of degradation was assessed by weight loss and gel content determination, size exclusion chromatography and FTIR spectroscopy. PTFEMA exposed up to 2000 h showed only molecular changes due to a low extent of chain scission. The two XFDMA–EHMA copolymers underwent much more degradation, with extensive cross-linking, formation of low-molecular weight products, and oxidation reactions on the chains. The behaviour of the copolymers is controlled by the reactivity of the EHMA units, as was shown by comparison with results obtained on degradation of PEHMA homopolymer.
 
Article
Nineteen sulphonated 2-hydroxybenzophenones and three sulphonated 2,2′-dihydroxybenzophenones have been prepared and compared with a commercially available member of each class of uv absorber as photo-protective agents for wool. Treated fabrics were exposed to Philips ML G/74 lamps and the extent of photo-tendering was assessed by measuring breaking loads and tear strengths. In general, 2-hydroxybenzophenones with 3-alkyl substituents provide better protection against photo-tendering than absorbers lacking 3-alkyl substituents. 2,2′-Dihydroxybenzophenones are more effective than 2-hydroxybenzophenones.On the basis of effectiveness and ease of synthesis, 2,2′-dihydroxy-4,4′-bis-w-sulphobutyloxybenzophenone (VIIb) shows most promise as a photo-protective agent. At the 5% level of application it trebles the lifetime of wool fabric during exposure to sunlight through window glass. It also retards the photo-tendering and fading of wool fabrics containing either a red or a blue milling acid dye.
 
Article
Degradable tri-component copolymers were synthesized by the bulk copolymerisation of 2,2-dimethyl trimethylene carbonate (DTC), ϵ-caprolactone (CL) and glycolide (GA) using stannous octanoate as catalyst at 140 °C for 36 h. The mole fraction ratio in the feed of DTC and CL was fixed at 20/80 and the mole percent of GA was varied to obtain copolymers with different properties. The polymerisation products were characterized by 1H NMR, 13C NMR, FT-IR, GPC and DSC. It was found that the hydrophilicity of these materials increased with increasing GA content, according to measurements of static contact angles of distilled water on the surface of polymer films. Mechanical tests and hydrolytic degradation assays showed that copolymers of different degradability and mechanical properties could be tailored by adjusting the compositions. For the polymer P-3 (GA content about 10 mol%), the tensile strength and the elastic modulus could reach 4.3 MPa and 22 MPa, respectively. It took 4 weeks for the copolymer P-3 to degrade to about 82% (Mn,t/Mn,0) and 10 weeks to 40%. These low crystallinity copolymers could be processed into porous films with stable structures by means of combination of solvent volatilisation with salt leaching. These materials are expected to be useful for nerve reconstruction and other biomedical applications.
 
Article
The effect of an antioxidant, 2,2′-thiobis(4,6-di-tert-butylphenol) (I) and of the derived sulphoxide (II) and sulphone (III), on the decomposition of tert-butyl hydroperoxide (IV) at 65, 75, 85 and 100°C was investigated. The results indicate a change in the rate of decomposition of IV with sulphide, I, after consumption of about 2 moles of IV per mole of I and the active rôle played by II and III in the process. The formation of new compounds in the reaction mixture, which may be connected with an acceleration of the decomposition of IV, was identified by means of TLC. 7
 
Article
The thermal decomposition under non-oxidative conditions of a copolymer of vinylidene cyanide (VCN) and 2,2,2-trifluoroethyl methacrylate (MATRIF) was investigated by thermogravimetry (TG) and Pyrolysis-GC–MS. The type and composition of the pyrolytic products and the shape of the TG curve indicate that both the main thermal degradation process, with onset at 368 °C, and a minor weight loss at around 222 °C are mainly associated with random main-chain scission. The kinetic parameters were determined by means of dynamic and, in the case of the main degradation stage, also isothermal methods. The results obtained from the dynamic methods (Friedman, Flynn–Wall–Ozawa, and Kissinger, respectively) are in good agreement with those obtained from isothermal TG data. The activation energy was in the 177–213 kJ/mol range for the first stage, and 224–295 kJ/mol for the second stage, the highest respective values being determined from the kinetic analysis according to the Kissinger method.
 
Article
The photochemical stability of copolymers of 2,2,2-trifluoroethyl methacrylate with butyl vinyl ether (TFEMA/BVE) and of methyl α-trifluoromethyl acrylate with 2-ethylhexyl vinyl ether, has been investigated under artificial solar light irradiation. In both copolymers, as well as in a reference ethyl methacrylate/BVE copolymer, the photoageing behaviour is controlled by the reactivity of the corresponding ether component. The degradation occurs mainly in the tertiary positions of the ether units, followed either by formation of γ-lactones or by chain scissions. Only in the case of TFEMA/BVE does the fluorinated methyl of the side chain have an influence on the degradation pathways, i.e. a clear inhibition of cyclization.
 
Article
Alkanox P24 is a commercial phosphite antioxidant, well known in the literature for its excellent processing stability. As in the case of many processing phosphites, however, Alkanox P24 might undergo hydrolysis when exposed to small amounts of water. A number of products proposed recently in the hydrolytic pathway of the phosphite [Ortuoste N, Allen NS, Papanastasiou M, McMahon A, Edge M, Johnson B, et al. Polym Degrad Stab; 2006;91:195–211] are investigated in this study by atmospheric pressure ionisation-mass spectrometry (API-MS). The applicability of atmospheric pressure photoionisation (APPI) and atmospheric pressure chemical ionisation (APCI) ion sources is tested and the ion formation characteristics of Alkanox P24 are compared in both sources. In positive ion mode, ionisation of the parent phosphite occurred by protonation. In negative ion mode no pseudo-molecular ion peak was detected and the deprotonated species were more dominant in APPI. This source was employed further for the investigation of the hydrolysis products, since it exhibited lower limits of detection. High performance liquid chromatography (HPLC) with single ion monitoring (SIM) detection was used for the separation of the species formed. Hydrolysis of the phosphite proceeded via the scission of the two P–Ophenol bonds exclusively to give 2,4-di-tert-butyl phenol quantitatively as a final product.
 
Article
In the autoxidation of squalene (rubber model) the title compound (I) first behaves as an effective antioxidant which, however, gradually loses its efficiency in the course of autoxidation without being destroyed. This behaviour is caused by a reaction in which radical (III), derived from antioxidant (I), reacts with the hydrogen atom in the oxidation products of squalene. The hydrogen atom is not that of the hydroperoxide group. In the reaction, (I) is regenerated and an active radical is formed from the substrate which continues the oxidation. Oxidation of (I) with lead dioxide gave rise to the dimer of the radical (III).
 
Article
Convenient one-pot–two-step processes for chemical recycling of commercially available polyesters were conducted to produce the corresponding hydroxamic acids and hydrazides in high yields. Glycolysis of poly(ethylene 2,6-naphthalenedicarboxylate) in diethylene glycol into the corresponding oligomers, followed by aminolysis with hydroxylamine and hydrazine yielded 2,6-naphthalenedicarbohydroxamic acid in 96% and 2,6-naphthalenedicarbohydrazide in 85% overall yields. In a similar manner, terephthalohydroxamic acid and terephthalohydrazide were produced in 92 and 91%, respectively, from degradation of poly(tetramethylene terephthalate).
 
Article
The reaction of guaiacol and 2,6-dimethoxyphenol with metal oxidants has been used as a model in order to better understand the chromium mediated reaction and photostabilization of lignin on wood surfaces. Even with a simple lignin model such as guaiacol the reaction is complex and some of the reaction products are not easily characterized. The reaction of aqueous ferric chloride with guaiacol in a 1:2 molar ratio yields an organic product with the isomeric diphenoquinones 5-(4-hydroxy-3-methoxy-phenyl)-3,3′-dimethoxy-bicyclohexylidene-2,5,2′,5′,-tetraene-4,4′-dione (A) and 3-(4-hydroxy-3-methoxy-phenyl)-5,3′-dimethoxy-bicyclohexylidene-2,5,2′,5′,-tetraene-4,4′-dione (B) as major components. By comparison the reaction of chromic acid with guaiacol at 1:2 and 1:5 molar ratios affords amorphous chromium (III) complexes in good yield. Reductive degradation of these complexes with sodium borohydride in tetrahydrofuran yields the coupled guaiacol trimer 3,5′,3″-trimethoxy-[1,1′;3′,1″]terphenyl-4,4′,4″-triol as the major component. The formation of this trimer is consistent with the presence of bound diphenoquinones (A) and (B) in the original chromium (III) complex. Oxidation of 2,6-dimethoxyphenol is less complicated and clarifies the nature of chromium (III) complexes formed during these reactions. Oxidation of 2,6-dimethoxyphenol with aqueous ferric chloride yields the symmetrical diphenoquinone coerulignone. Oxidation of 2,6-dimethoxyphenol with chromic acid unambiguously yields an amorphous chromium (III) coerulignone complex which was characterized by solid state 13C MAS NMR and IR spectroscopy as well as by reductive degradation. It is postulated that chromic acid oxidizes lignin phenols in wood affording related chromium (III) quinone complexes that confer weather stability to the treated wood surface.
 
Article
In recent years, poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers have become prominent in high strength applications such as body armor, ropes and cables, and recreational equipment. The objectives of this study were to expose woven PBO body armor panels to elevated temperature and moisture, and to analyze the chemical, morphological and mechanical changes in PBO yarns extracted from the panels. A 30% decrease in yarn tensile strength, which was correlated to changes in the infrared peak absorbance of key functional groups in the PBO structure, was observed during the 26 week elevated temperature/elevated moisture aging period. Substantial changes in chemical structure were observed via infrared spectroscopy, as well as changes in polymer morphology using microscopy and neutron scattering. When the panels were removed to an ultra-dry environment for storage for 47 weeks, no further decreases in tensile strength degradation were observed. In a follow-on study, fibers were sealed in argon-filled glass tubes and exposed to elevated temperature; less than a 4% decrease in tensile strength was observed after 30 weeks, demonstrating that moisture is a key factor in the degradation of these fibers.
 
Top-cited authors
Giovanni Camino
  • Politecnico di Torino
Charles Wilkie
  • Marquette University
Serge Bourbigot
  • Université de Lille
Norman Allen
  • Manchester Metropolitan University
Costa Luigi
  • Università degli Studi di Torino