Polymer Degradation and Stability (v.96, #4)
Glycolysis of poly(ethylene terephthalate) (PET) using basic ionic liquids as catalysts by Q.F. Yue; C.X. Wang; L.N. Zhang; Y. Ni; Y.X. Jin (399-403).
The glycolysis of poly(ethylene terephthalate) (PET) was studied using several ionic liquids and basic ionic liquids as catalysts. The basic ionic liquid, 1-butyl-3-methylimidazolium hydroxyl ([Bmim]OH), exhibits higher catalytic activity for the glycolysis of PET, compared with 1-butyl-3-methylimidazolium bicarbonate ([Bmim]HCO3), 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and 1-butyl-3-methylimidazolium bromide ([Bmim]Br). FT-IR, 1H NMR and DSC were used to confirm the main product of glycolysis was bis(2-hydroxyethyl) terephthalate (BHET) monomer. The influences of experimental parameters, such as the amount of catalyst, glycolysis time, reaction temperature, and dosages of ethylene glycol on the conversion of PET, yield of BHET were investigated. The results showed a strong influence of the mixture evolution of temperature and reaction time on depolymerization of PET. Under the optimum conditions of m(PET):m(EG): 1:10, dosage of [Bmim]OH at 0.1 g (5 wt%), reaction temperature 190 °C and time 2 h, the conversion of PET and the yield of BHET were 100% and 71.2% respectively. Balance between the polymerization of BHET and depolymerization of PET could be changed when the reaction time was more than 2 h and contents of catalyst and EG were changed.
Keywords: Poly(ethylene terephthalate); Glycolysis; Basic ionic liquid; Catalysts;
Recycling of PVC wastes by Mehdi Sadat-Shojai; Gholam-Reza Bakhshandeh (404-415).
PVC is a universal polymer which can be processed into a wide variety of short-life or long-life products. As a result of increasing consumption of PVC-made products in recent years, the quantity of used PVC items entering the waste stream is gradually increased. Currently, there is a considerable public concern about the problem of plastic wastes, from which PVC has not escaped and the material or energy recycling may be a suitable way to overcome this problem. This review considers the various aspects of the PVC recycling such as recycling methods of PVC, special problems about some proposed processes, separation techniques, and recycling of mixed PVC wastes. In addition, an attempt is made to portray the current status of PVC recycling, the most recent technologies of recycling, and some recent scientific research in the field.
Keywords: Recycling; Polyvinyl chloride (PVC); Separation techniques; Mixed plastic wastes;
Mathematical modeling of the graft reaction between polystyrene and polyethylene by Ioana A. Gianoglio Pantano; Adriana Brandolin; Claudia Sarmoria (416-425).
Polystyrene (PS) and polyethylene (PE) are two major components of household plastic waste whose blends are immiscible. Recycling them together is an attractive option that requires a compatibilization process to improve the blend mechanical properties. If a PE/PS copolymer is added or formed in situ, it may act as compatibilizer. The structure and molecular properties of this copolymer are key factors to assure its effectivity as a compatibilizer. In this work, we study the graft copolymerization reaction between polystyrene and polyethylene using the catalytic system composed of AlCl3 and styrene. We develop a model of this process which considers that PE/PS grafting and PS degradation occur simultaneously. We propose a kinetic mechanism for the whole process and apply the method of moments to solve the mass balance equations. The model is able to calculate average molecular weights as well as the amount of grafted PS. It accurately describes the available experimental data, constituting a valuable tool for simulation and optimization purposes.
Keywords: Mathematical modeling; PS/PE graft copolymer; Lewis acid; Recycling;
Catalytic degradation of lignin model compounds in acidic imidazolium based ionic liquids: Hammett acidity and anion effects by Blair J. Cox; Songyan Jia; Z. Conrad Zhang; John G. Ekerdt (426-431).
Ionic liquids based on the 1-methylimidazolium cation with chloride, bromide, hydrogen sulfate, and tetrafluoroborate counterions along with 1-butyl-3-methylimidazolium hydrogen sulfate were employed to degrade two lignin model compounds, guaiacylglycerol-β-guaiacyl ether and veratrylglycerol-β-guaiacyl ether. The acidity of each ionic liquid was approximated using 3-nitroaniline as an indicator to measure the Hammett acidity (H0). While all of the tested ionic liquids were strongly acidic (H0 between 1.48 and 2.08), the relative acidity did not correlate with the ability of the ionic liquid to catalyze β-O-4 ether bond hydrolysis. The reactivity of the model compounds in the ionic liquids is dependent not only on the acidity, but also on the nature of the ions and their interaction with the model compounds.
Keywords: Biomass; Catalytic degradation; Ionic liquids; Lignin;
Sub-micron scale mechanical properties of polypropylene fibers exposed to ultraviolet and thermal degradation by Nandula Wanasekara; Vijaya Chalivendra; Paul Calvert (432-437).
Nanoindentation using atomic force microscopy (AFM) was conducted to investigate the affect of accelerated ultraviolet (UV) and thermal degradation on the mechanical properties of polypropylene fibers. The affect of degradation on Young’s modulus across fiber cross-sections was investigated with progressive nanoindentation from the surface to the center of the fiber. UV degradation initially increases the Young’s modulus both at the center and the surface of the fibers until 120 h of exposure with the increase being more rapid at the surface. Moduli started to decrease beyond 120 h of exposure. Wide angle x-ray scattering shows an increase of crystallinity up to 120 h of exposure and total destruction of crystallinity at 144 h. Infrared spectra showed the formation of carbonyl bonds with UV exposure. To investigate thermal degradation, the fibers were exposed to 125 °C for four weeks. Young’s modulus increased near the surface after four weeks exposure. These results support the idea that surface degradation may lead to embrittlement of textile fibers.
Keywords: Polypropylene; Nanoindentation; Atomic force microscopy; Ultraviolet; Thermal degradation;
Effect of contact surfaces on the thermal and photooxidation of dehydrated castor oil by K. Doudin; S. Al-Malaika; H. Dole; T. Stirling; M. Sharples (438-454).
The effect of stainless steel, glass, zirconium and titanium enamel surfaces on the thermal and photooxidative toughening mechanism of dehydrated castor oil films deposited on these surfaces was investigated using different analytical and spectroscopic methods. The conjugated and non-conjugated double bonds were identified and quantified using both Raman spectroscopy and 1D and 2D NMR spectroscopy. The disappearance of the double bonds in thermally oxidised oil-on-surface films was shown to be concomitant with the formation of hydroperoxides (determined by iodometric titration). The type of the surface had a major effect on the rate of thermal oxidation of the oil, but all of the surfaces examined had resulted in a significantly higher rate of oxidation compared to that of the neat oil. The highest effect was exhibited by the stainless steel surface followed by zirconium enamel, titanium enamel and glass. The rate of thermal oxidation of the oil-on-steel surface (at 100 °C, based on peroxide values) was more than five times faster than that of oil-on-glass and more than 21 times faster than the neat oil when compared under similar thermal oxidative conditions. The rate of photooxidation at 60 °C of oil-on-steel films was found to be about one and half times faster than their rate of thermal oxidation at the same temperature. Results from absorbance reflectance infrared microscopy with line scans taken across the depth of thermally oxidised oil-on-steel films suggest that the thermal oxidative toughening mechanism of the oil occurs by two different reaction pathways with the film outermost layers, i.e. furthest away from the steel surface, oxidising through a traditional free radical oxidation process involving the formation of various oxygenated products formed from the decomposition of allylic hydroperoxides, whereas, in the deeper layers closer to the steel surface, crosslinking reactions predominate.
Keywords: Oxidation of oil deposited on surfaces; Thermal oxidation; Photooxidation; NMR spectroscopy;
Investigation of polypropylene degradation during melt processing using a profluorescent nitroxide probe: A laboratory-scale study by Laleh Moghaddam; James P. Blinco; John M. Colwell; Peter J. Halley; Steven E. Bottle; Peter M. Fredericks; Graeme A. George (455-461).
Degradation of polypropylene (PP) during melt processing was studied using a novel profluorescence technique. The profluorescent nitroxide probe, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was added to PP during melt processing to act as a sensor for carbon-centred radicals. Trapping of carbon-centred radicals, formed during degradation of PP, led to an increase in fluorescence emission from TMDBIO adducts. Through analysis of viscosity changes during processing cumulative chain scission degradation was estimated. At processing temperatures of 210 °C or below, fluorescence emission from TMDBIO adducts could be correlated with cumulative chain scissions when the number of chain scissions was small. At higher temperatures, a correlation was not observed most probably due to radical-trap instability rather than decomposition of the TMDBIO. Thus, TMDBIO may be used as a profluorescent sensor for degradation of PP during melt processing when the processing temperature is 210 °C or below.
Keywords: Profluorescent nitroxide; Polypropylene; Extrusion; Degradation; Chain scission;
Assessing the progress of degradation in polyurethanes by chemiluminescence and thermal analysis. II. Flexible polyether- and polyester-type polyurethane foams by Jozef Rychlý; Agnes Lattuati-Derieux; Bertrand Lavédrine; Lyda Matisová-Rychlá; Marta Malíková; Katarína Csomorová; Ivica Janigová (462-469).
The thermooxidative and thermal stability of polyether- and polyester-type polyurethane foams were investigated by non-isothermal chemiluminescence (CL), differential scanning calorimetry (DSC) and thermogravimetry (TG). In the presence of air and humidity, the effect of various routes and conditions of polyurethane ageing (induced thermally or by light) on the chemiluminescence, DSC and thermogravimetry patterns was assessed. The rate constants determined from non-isothermal thermogravimetry and chemiluminescence measurements at 250 °C and their not very pronounced dependence on the atmosphere of degradation indicated that depolymerisation of the polyurethane containing the aliphatic polyester and aromatic polyisocyanate moieties preceded or occurred in parallel with thermal oxidation. Under conditions of 50% relative humidity, samples of the polyester-type polyurethane, aged either by light or thermally, as well as specimens of the polyether-type polyurethane, aged by light, gave increased amounts of carbonaceous residue when heated in nitrogen to 550 °C.
Keywords: Polyurethane foams; Chemiluminescence; Thermogravimetry; Differential scanning calorimetry; The effect of ageing; The rate constant of degradation;
Mechanical behaviour of a poydimethylsiloxane elastomer after outdoor weathering in two different weathering locations by Panagiota N. Eleni; Magdalini K. Krokida; Gregory L. Polyzois; Constantinos A. Charitidis; Elias P. Koumoulos; Vasiliki P. Tsikourkitoudi; Ioannis Ziomas (470-476).
The degradation of maxillofacial prosthetic elastomers that occur during physical weathering is usually responsible for the replacement of the prosthesis. In this study the mechanical behaviour of a polydimethylsiloxane (PDMS) elastomer was investigated, after 1 year outdoor weathering in two different weathering locations in Greece (Thessaloniki, Athens). The hypothesis investigated was that irradiation time did not affect the measured properties. Specimens (Elastomer 42) were prepared according to manufacturer’s instructions and exposed to solar radiation for 1 year. Compression, tensile and nanoindentation tests were performed before and after the exposure. Compression and tensile data were also subjected to analysis of variance (ANOVA) and Tukey Post hoc tests at a level of α = .05. These properties were selected due to their clinical significance for fabrication and maintenance of a facial prosthesis. According to statistical analysis all the measured properties changed significantly after outdoor weathering. More specifically, most of the properties presented significant changes after six months of weathering. The observed changes also depended on the weathering locations. The hypothesis investigated was rejected. Material A became harder and the observed differences in the mechanical behaviour resulted from photo-degradation and hydrolysis that might occur due to weathering. The study also provides new information about maxillofacial prosthetics serviceability obtained from nanoindentation tests.
Keywords: Compression; Nanoindentation analysis; Natural weathering; Polydimethylsiloxane; Tensile testing;
Flammability assessment of tannin-based cellular materials by A. Celzard; V. Fierro; G. Amaral-Labat; A. Pizzi; J. Torero (477-482).
Fire retardance of highly porous tannin-based rigid foams formerly suggested as new, ecological, insulation materials, has been investigated in detail. For that purpose, one standard composition was tested using samples having five different bulk densities. Besides, for one given median density, three foams whose formulation has been modified by incorporation of boric and/or phosphoric acid were investigated as well. The parameters measured were the time to ignition, the critical heat flux for ignition and the heat release rate. All led to the conclusion that such foams present outstanding fire retardance. The tests were done blindly to avoid any interpretation bias. No significant differences could be observed when materials of standard composition but having different bulk densities were tested, or when testing modified foams. While modified foams showed slight differences, it was not possible to correlate these differences to higher fire performance.
Keywords: Tannin; Rigid foam; Fire retardance; Ignition; Heat release rate;
Effect of hybrid phosphorus-doped silica thin films produced by sol-gel method on the thermal behavior of cotton fabrics by G. Brancatelli; C. Colleoni; M.R. Massafra; G. Rosace (483-490).
The aim of this work was to prepare hybrid organic–inorganic silica thin films to provide cotton fabrics with flame retardant properties and to investigate the films’ influence on the thermal and burning behavior of the treated samples. The fabrics were modified with three different sols in order to study the effect of pure silica sol-gel precursor, γ-aminopropyltriethoxysilane (APTES), and that of the hybrid sols consisting of the APTES and the phosphorus compound diethylphosphite. Furthermore, in order to improve the cross-linking degree and the phosphorus–nitrogen synergistic effect on flame retardancy of the P-doped silica thin film the melamine-based resin was added in the third sol. To evaluate the chemical structure of the coating material, pure xerogels of the treatment solutions were applied to glass slides and tested by ATR FT–IR spectroscopy. The cotton fabrics were impregnated with the sols by a padding–squeezing process and then dried. Thermal behavior of the treated cotton samples was investigated by thermogravimetric/differential scanning calorimetry analysis (TGA–DTG/DSC) and compared to the untreated one. The flame retardancy was tested according to the ASTM D 1230 standard method. The results showed a substantial enhancement of char-forming properties and flame retardancy for the fabrics modified with the thin films.
Keywords: Organic–inorganic hybrid; Sol-gel; Cotton; Flame retardancy; TGA;
Processing stability of polypropylene impact-copolymer during multiple extrusion – Effect of polymerization technology by Jiří Tocháček; Josef Jančář; Jan Kalfus; Soňa Hermanová (491-498).
Three commercially available polypropylene impact-copolymers (ICPP) produced by Innovene (INN), Spheripol (SPH) and Unipol (UNI) technologies were subjected to multiple extrusion using a twin-screw extruder W&P ZSK25 at 220 °C. Processing stability and changes in properties induced by extrusion were investigated. The materials were of similar MFR ∼6 dg/min, similar ethylene contents ∼7.5 wt. % and the same type and level 1200 ppm of phenol/phosphite stabilizer system was used. Ranking INN < UNI < SPH in processing and long-term (LTHA) stabilities observed was primarily related to the reactivity of catalyst residues rather than to other factors, such as contents of ethylene, quantity of extractables, EPR phase composition, levels of ash or individual elements in it. The mechanically demanding multiple extrusion conditions and consequently different extent of processing degradation, however, induced only minimum changes in morphology and impact strength of the solid ICPP matrix. Thus, regardless of changes in melt-flow properties induced by extrusions, all the three grades even after 5th extrusion at 220 °C exhibited Charpy notched impact strength at 23 °C only minimally changed.
Keywords: Processing; Stability; Multiple extrusion; Polypropylene; Impact; Copolymer; Polymerization;
Biosynthesis of a lactate (LA)-based polyester with a 96 mol% LA fraction and its application to stereocomplex formation by Fumi Shozui; Ken’ichiro Matsumoto; Ren Motohashi; Jian Sun; Toshifumi Satoh; Toyoji Kakuchi; Seiichi Taguchi (499-504).
A poly(lactic acid) (PLA)-like terpolyester consisting of 96 mol% lactate (LA), 1 mol% 3-hydroxybutyrate and 3 mol% 3-hydroxyvalerate was produced in recombinant Escherichia coli LS5218 expressing LA-polymerizing enzyme (LPE). The strain was grown on glucose with a feeding of valerate as the monomer precursor. The glass transition and melting temperatures of the terpolyester were close to those of chemically synthesized poly(L-LA)s (PLLAs) having similar molecular weights. Additionally, a blend of the terpolyester, which was composed entirely of (R)-LA (D-LA) due to the strict enantiospecificity of LPE, with PLLA formed a stereocomplex with higher melting temperature (201.9 °C). These results indicate that the biological PLA-like polyester produced via this one-step microbial process has comparable thermal properties to chemically synthesized PLAs.
Keywords: Polylactide; Biodegradable plastic; Microbial cell factory; PDLA; Biological PLA;
Flame retardancy and flame retarding mechanism of high performance hyperbranched polysiloxane modified bismaleimide/cyanate ester resin by Dongxian Zhuo; Aijuan Gu; Guozheng Liang; Jiang-tao Hu; Lei Cao; Li Yuan (505-514).
A novel kind of modified bismaleimide/cyanate ester (BCE) resins by copolymerizing with hyperbranched polysiloxane including high content of phenyl (HBPSi) was first reported. The effect of HBPSi on the curing mechanism, and that on the dielectric properties and flame retardancy of cured networks were systemically investigated. Results show that compared with BCE resin, HBPSi/BCE resin has obviously different cross-linked structure, and thus leading to simultaneously improved dielectric properties and flame retardancy. The reactions between HBPSi and the decomposition structure of BCE resin change the thermo-oxidative degradation mechanism of the first step in the thermo-oxidative degradation; in addition, the presence of HBPSi in BCE resin also significantly reduces the mass loss rate (MLR) and increases char yield at 800 °C under an air atmosphere. Therefore, the positive effect of HBPSi on improving the flame retardancy is attributed to the condensed phase mechanism. On the other hand, HBPSi/BCE resins exhibit improved dielectric properties (including decreased dielectric constant and loss) with increasing the content of HBPSi. More importantly, this investigation demonstrates that designing new polysiloxane with suitable chemical structure is important to develop high performance resins with attractive flame retardancy and dielectric properties.
Keywords: Flame retardancy; Hyperbranched polysiloxane; Dielectric property; Bismaleimide/cyanate ester resin; Decomposition kinetics;
Degradation as a result of UV radiation of bloodmeal-based thermoplastics by Casparus J.R. Verbeek; Talia Hicks; Alan Langdon (515-522).
Polymers are known for their susceptibility to degradation as a result of ultra-violet (UV) radiation. In this study, the UV stability of bloodmeal-based thermoplastics (BMT) was evaluated over a period of 12 weeks. Formulations with and without plasticiser were tested and moisture was excluded during accelerated weathering to isolate the effect of UV because of the material’s known sensitivity to moisture. It was found that embrittlement due to loss of water overshadowed the effect of UV degradation. Embrittlement caused the material’s toughness to be reduced by an order of magnitude after only two weeks of exposure, for either plasticised or unplasticised samples. An initial increase in tensile strength was observed after two weeks followed by a steady decline in strength. The elastic modulus reached a plateau after about two weeks of exposure. FTIR did not confirm any chemical changes after 12 weeks exposure and TGA suggested that low molecular mass species were quickly lost during the course of the test. The absence of chemical changes does not suggest resistance to environmental degradation, although the dark pigmentation of bloodmeal may have contributed to the lack of UV degradation. Embrittlement remains a greater concern and requires further attention.
Keywords: Bloodmeal; Ultra-violet; Thermoplastic; Degradation; Mechanical properties;
The influence of UV radiation on silk fibroin by A. Sionkowska; A. Planecka (523-528).
An investigation into the influence of UV-irradiation on regenerated silk fibroin dissolved in water was carried out using UV–Vis and fluorescence spectroscopy. It was found that the absorption of regenerated silk fibroin in solution increased during UV-irradiation of the sample, most notably between 250 and 400 nm. Moreover, after UV-irradiation a wide peak emerged between 290 and 340 nm with maximum at about 305 nm. The new peak suggests that new photoproducts are formed during UV-irradiation of regenerated silk fibroin.The fluorescence of regenerated silk fibroin was observed at 305 nm, at 480 nm and at 601 nm after excitation at 275 nm. UV-irradiation caused fluorescence fading at 305 nm and at 601 nm. The increase of fluorescence was observed at 480 nm, probably due to formation of new photoproducts. After excitation at 305 nm the fluorescence of regenerated silk fibroin was observed at 340 nm and at 400 nm. UV-irradiation caused fluorescence fading at 340 nm. FTIR spectroscopy showed that primary structure of regenerated silk fibroin was not significantly affected by UV radiation. SDS-PAGE chromatography showed alterations of molecular weight of silk after UV exposure.
Keywords: Silk fibroin; UV radiation; Fluorescence; FTIR;
The effect of nanoparticles on structural morphology, thermal and flammability properties of two epoxy resins with different functionalities by Charalampos Katsoulis; Everson Kandare; Baljinder K. Kandola (529-540).
The effect of layered silicate nanoclays, nano-silica and double-walled carbon nanotubes (DWNTs) on the thermal stability and fire reaction properties of two aerospace grade epoxy resins (a high temperature curing tetra-functional and a low temperature curing bi-functional resin) has been investigated using thermal analysis, cone calorimetry, LOI and UL-94 techniques. The morphology of the polymer–clay nanocomposites, determined by X-ray diffraction and transmission electron microscopy indicated intercalated structures. The addition of nanoclays (5-wt%) to both resins had a thermal destabilisation effect in the low temperature regime (<400 °C), but led to higher char yield at higher temperatures. The inclusion of nano-silica at 30-wt% significantly improved the thermal stability of the resins while DWNTs had an adverse effect due to their poor dispersion in the matrix. The nanoclays and carbon nanotubes significantly increased the fire resistance of the tetra-functional epoxy resin while a minimal effect was observed for the bi-functional resin.
Keywords: Polymer nanocomposite; Resin functionality; Morphology; Thermal stability; Flame retardancy;
Novel environmentally-benign methods for green-colour protection of bamboo culms and leaves by Min-Jay Chung; Sen-Sung Cheng; Chia-Ju Lee; Shang-Tzen Chang (541-546).
The objective of this study was to search for appropriate environmental-benign preservatives as green-colour protectors for the culms and leaves of ma bamboo (Dendrocalamus latiflorus), moso bamboo (Phyllostachys pubescens) and makino bamboo (Phyllostachys makinoi). Five water-borne copper-based preservatives, namely ammoniacal copper quaternary compound-type B (ACQ-B), copper azole-type A (CBA-A), copper azole-type B (CA-B), tanalith CY (TCY) and micronized copper quaternary (MCQ), were tested as green-colour protectors. Results revealed that excellent green-colour protection (a* values of −13.2, −7.6 and −6.3, respectively) was obtained when the culms and leaves of ma bamboo, moso bamboo and makino bamboo culms were treated with 0.25% aqueous TCY solution in a 100 °C water bath for 2 h. Furthermore, to evaluate the effects of 0.25% TCY treatment on the green-colour fastness of bamboo culms, two exposure tests including indoor exposure and outdoor weathering were employed in this study. Results from the 6-month exposure tests in both indoor and outdoor environment demonstrated that specimens treated with 0.25% TCY exhibited good colourfastness. To improve the treatment efficacy in bamboo culms, both atmospheric pressure impregnation and vacuum pressure impregnation were used. The results indicated that green-colour protection could be obtained by the two impregnation treatments in 0.25% TCY solution.
Keywords: Green-colour protection; Bamboo; Dendrocalamus latiflorus; Phyllostachys pubescens; Phyllostachys makinoi; Tanalith CY;
RNA analysis of anaerobic sludge during anaerobic biodegradation of cellulose and poly(lactic acid) by RT-PCR–DGGE by Hisaaki Yagi; Fumi Ninomiya; Masahiro Funabashi; Masao Kunioka (547-552).
Here, we apply a method to evaluate the anaerobic biodegradability of bioplastics, such as polycaprolactone and poly(lactic acid) (PLA), in aquatic (slurry) conditions at 55 °C. Previous reports have suggested that some of the microorganisms participating in the anaerobic biodegradation of cellulose and PLA differ. However, polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE) analysis was ineffective at detecting the microorganisms involved in the anaerobic biodegradation of cellulose and PLA. In this study, reverse transcription-PCR–DGGE analysis was employed instead. New DGGE bands appeared during the anaerobic biodegradation of cellulose and PLA, and some of these DGGE bands differed between the anaerobic biodegradation of cellulose and PLA, indicating that some of the microorganisms involved in these two processes differed. These results and those of our previous study therefore show that it is necessary to describe, not the anaerobic biodegradation rate of cellulose, as generally used at present, but the anaerobic biodegradation rate of plastic in the plastic anaerobic biodegradation test, to evaluate the sludge condition containing plastic anaerobic biodegradation activity in the sludge used in the anaerobic biodegradation test of plastics at 55 °C.
Keywords: Anaerobic biodegradation; Methane fermentation; Poly(lactic acid); 16S rRNA; 18S rRNA; RT-PCR–DGGE;
Compatibilizing effects for improving mechanical properties of biodegradable poly (lactic acid) and polycarbonate blends by Jae Bok Lee; Yun Kyun Lee; Gi Dae Choi; Sang Wook Na; Tae Sung Park; Woo Nyon Kim (553-560).
Mechanical, morphological and rheological properties of polycarbonate (PC) and poly (lactic acid) (PLA) blends with compatibilizers have been investigated. Three types of compatibilizers were used: poly(styrene-g-acrylonitrile)-maleic anhydride (SAN-g-MAH), poly(ethylene-co-octene) rubber-maleic anhydride (EOR-MAH) and poly(ethylene-co-glycidyl methacrylate) (EGMA). The maximum value of the mechanical properties such as impact and tensile strengths of the PC/PLA (70/30, wt%) blend before or after hydrolysis was observed when the SAN-g-MAH was used as a compatibilizer at the amount of 5 phr. From the interfacial tension between PC and PLA which was determined from the weighted relaxation spectra using Palierne emulsion model, minimum value of interfacial tension (0.08 mN/m) was observed when the SAN-g-MAH (5 phr) was used. From the morphological studies of the PC/PLA (70/30) blends, the PLA droplet size showed minimum (0.19 μm) at the 5.0 phr SAN-g-MAH. From the results of mechanical, morphological and rheological properties of the PC/PLA (70/30) blend, it is suggested that the SAN-g-MAH is the most effective compatibilizer to improve the mechanical strength of the PC/PLA (70/30) blends among the compatibilizers used in this study, especially at the amount of 5 phr.
Keywords: Polymer blends; Poly (lactic acid); Polycarbonate; Compatibility; Rheology;
Characteristics and durability of fluoropolymer thin films by David Cheneler; James Bowen; Stephen D. Evans; Marcin Górzny; Michael J. Adams; Michael C.L. Ward (561-565).
The use of plasma-polymerised fluoropolymer (CFxOy) thin films in the manufacture of microelectromechanical systems (MEMS) devices is well-established, being employed in the passivation step of the deep reactive ion etching (DRIE) process, for example. This paper presents an investigation of the effect of exposure to organic and aqueous liquid media on plasma-polymerised CFxOy thin films. Atomic force microscopy (AFM), scanning electron microscopy (SEM), ellipsometry, X-ray photoelectron spectroscopy (XPS) and dynamic wetting measurements were all employed as characterisation techniques. Highly basic aqueous solutions, including known silicon etchants, were found to cause delamination via degradation of the countersurface below the CFxOy thin film. Films were found to be stable in organic solvents, acidic aqueous solutions and slightly basic aqueous solutions.
Keywords: Fluoropolymer; Atomic force microscopy; X-ray photoelectron spectroscopy; Wetting; Etchant; pH;
Study of Glow Wire Ignition Temperature (GWIT) and Comparative Tracking Index (CTI) performances of engineering thermoplastics and correlation with material properties by Francesco Acquasanta; Corrado Berti; Martino Colonna; Maurizio Fiorini; Sreepadaraj Karanam (566-573).
Recent regulation IEC 60335-1 ed.4 (2008) was introduced for materials used in electric appliance, establishing new limits in Glow Wire Ignition Temperature (GWIT) performance for materials used for electric connectors. Development of new products with high GWIT is possible, but the main issue is to keep good mechanical properties and processability, as well as tracking resistance (Comparative Tracking Index-CTI). Only a few patents and scientific publications exist about glow wire test performance of polymers. In this work we report GWIT and CTI properties for three engineering thermoplastic polymers (PBT, PET and PC). We have also studied the phenomena involved in this test, treating the phenomena with the parameterisation approach already used in the studies of the fire behaviour of polymers. PC, PBT and PET filled with 30% w/w glass fibres have been tested, and material properties that can be related to GWIT and CTI performance have been measured by TGA, Laser Flash Thermal Diffusivity (LFTD), Pyrolysis-GC/MS. CTI seems to be correlated with the char formation tendency of the materials, so PBT show a higher tracking resistance than PET and PC. Polycarbonate was the only material that passed the glow wire test (GWIT higher than 775 °C) but generally GWIT performance is not directly related with degradation temperature, since PET is thermally more stable compared with PBT, but less stable in glow wire test. The ignition process, together with the unsteady heat and mass transfer process characteristic of glow wire testing, are affected by many parameters at the same time. That’s why it is not easy to relate results of TGA, Laser flash, Pyrolysis-GC/MS with the glow wire ignition temperature of the materials tested, but the whole of these properties can give useful indication.
Keywords: Glow Wire Ignition Temperature; Comparative Tracking Index; Thermal properties; Polycarbonate; Terephthalate polyesters;
FTIR spectroscopy of biodegraded historical textiles by Katja Kavkler; Nina Gunde-Cimerman; Polona Zalar; Andrej Demšar (574-580).
Fungal attack is a common and severe problem in the storage rooms of museums. Fungi can damage different materials; organic materials are especially sensitive. In this work two different FTIR spectroscopy methods (micro-spectroscopy with diamond anvil cell and ATR) were used to investigate structural changes on biodeteriorated and non-affected textile fibres obtained from different Slovene museums and sacred objects. Several structural changes were observed in spectra of biodeteriorated as well as of non-affected cellulosic fibres, whereas no changes were observed in proteinaceous fibres. In the scope of spectral analysis crystallinity index has also been calculated by comparing two different band ratios. The research showed that the crystallinity index, calculated from the band intensity ratio I 1372/I 2900 groups fibres into two groups; biodeteriorated fibres predominantly have lower crystallinity index.
Keywords: FTIR; Cellulose crystallinity index; Museum; Historical textile;
Thermo-oxidative stability of polypropylene/layered silicate nanocomposites by Zita Dominkovics; József Hári; Erika Fekete; Béla Pukánszky (581-587).
Several series of experiments were carried out to check the effect of components on the stability of PP/layered silicate nanocomposites. The amount of organophilic montmorillonite (OMMT) changed between 0 and 6, while that of maleated polypropylene (MAPP) between 0 and 50 vol%. The composites were prepared in an internal mixer at 190 °C. Mixing speed and time were changed to study the effect of processing conditions on stability. The structure of the samples was characterised by various methods, while stability by the induction time of oxidation (OIT), the onset temperature of degradation (OOT) and by colour. Contrary to numerous claims published in the literature, which indicate the positive effect of layered silicates on the stability of polymer nanocomposites, our results clearly proved that both OMMT and MAPP accelerate degradation during processing and deteriorate the properties of PP composites. Residual stability decreases drastically with increasing amounts of both components, chain scission leads to the decrease of viscosity and to inferior strength and deformability. In spite of expectations, the effect of the components is independent of each other. Discoloration is caused mainly by the inherent colour of the filler and it decreases with increasing exfoliation. The most probable reason for decreased stability is the reaction of the components with the stabilisers, but this explanation needs further verification. Processing conditions influence degradation considerably, increasing shear rate and longer residence times lead to more pronounced degradation. The basic stabilization of commercial grade polypropylenes is insufficient to protect the polymer against degradation and without additional stabilization processing under normal conditions results in products with inferior quality.
Keywords: Nanocomposites; Layered silicate; Polypropylene; Thermo-oxidative degradation; Antagonism;
Controversial influence of aqueous treatments on historic textiles by Ute Henniges; Lena Bjerregaard; Bigna Ludwig; Antje Potthast (588-594).
Different historic textiles were subject to aqueous treatments with and without sodium borohydride as a reducing agent. As the action of borohydride generates an alkaline environment that is potentially harmful for oxidized cellulose in historic textiles, two less alkaline treatment options using buffer systems were additionally tested.In order to track the impact of the treatments on the samples, the development of oxidized cellulose functionalities and of the molecular weight was analyzed by selective labelling of carbonyl and carboxyl groups combined with gel permeation chromatography and multi-detector set-up. The crystallinity index of the samples was analyzed by CP-MAS NMR to elucidate the impact of age and treatment on the historic material.Already pure aqueous treatment changed the molecular weight distribution of historic textiles in some cases. These changes are discussed in the context of oxidized cellulose functionalities and crystallinity index. Furthermore the chosen historic samples reacted best towards a reduction treatment with sodium borohydride that had not been buffered, whereas the two buffered systems caused more damage and failed to reduce carbonyl groups along the cellulose chain.
Keywords: Borohydride; Cellulose; CPMAS NMR; Degradation; Molecular mass distribution; Textile;
Accelerated ageing and degradation in poly-l-lactide/hydroxyapatite nanocomposites by Claire Delabarde; Christopher J.G. Plummer; Pierre-Etienne Bourban; Jan-Anders E. Månson (595-607).
Dry, compression molded films of medical grade poly-l-lactide (PLLA) showed a marked reduction in tensile strength and strain after accelerated ageing in aqueous NaOH at 50 °C, accompanied by mass loss, surface erosion, increased hydrophilicity and, in the case of the initially amorphous films, cold crystallization owing to the plasticizing effect of the ageing medium. Addition of well dispersed nanosized hydroxyapatite (nHA) particles resulted in increases in the rate of mass loss during ageing, identified with accelerated degradation at the matrix/particle interfaces. However, the associated decreases in tensile strength and strain to fail with ageing time were far less marked in the presence of the nHA than in the unmodified films. This implied that nHA acts as an effective toughener of the bulk material, consistent with TEM observations of the deformed films, which indicated failure of the particle–matrix interfaces to promote plastic deformation of the PLLA.
Keywords: Ageing; Degradation; PLLA; Hydroxyapatite; Nanocomposite; Mechanical properties;
The effect of volatile organic compounds and hypoxia on paper degradation by Matija Strlič; Irena Kralj Cigić; Alenka Možir; Gerrit de Bruin; Jana Kolar; May Cassar (608-615).
The possible effects of volatile organic compounds (VOCs) and of hypoxic conditions on the durability of library and archival collections have been investigated. There is growing evidence that particularly in micro-environments, there may be an important contribution of these indoor-generated pollutants to the degradation of paper. However, since the principal source of VOCs in repositories is the collections themselves, there are also significant possibilities for less stable papers, which are net VOC emitters, to promote the degradation of more stable papers, which may be net VOC absorbers.Using a range of model and real historic papers, the influence of acetic acid, formic acid, furfural, toluene, 1,4-diethylbenzene, iso-butylbenzol, 2-pentylfuran, paraformaldehyde, hexanal and vanillin was evaluated by adding them to samples degraded in closed vessels at elevated temperature. Possible protective effects of the use of activated charcoal cloth, oxygen removal, and of various chemisorbents were also investigated.The results strongly suggest that particularly VOCs with acidic or oxidisable functions can have a strong effect on degradation of cellulose. This is less pronounced in lignin-containing and acidic papers and more pronounced in papers with a small alkaline reserve. The removal of VOCs from the immediate environment can have a pronounced beneficial effect on papers emitting VOCs more intensively, in fact, the lifetime expectancy can be doubled.The results have immediate implications for storage of paper-based heritage in enclosures, but also for initiation of long-term VOC monitoring programmes in libraries and archives, where significant development is still needed.
Keywords: VOCs; Paper degradation; Oxidation; Hydrolysis; Conservation; Heritage science;
Photooxidation of polylactide/calcium sulphate composites by Mélanie Gardette; Sandrine Thérias; Jean-Luc Gardette; Marius Murariu; Philippe Dubois (616-623).
Stable CaSO4 β-anhydrite II (AII), a specific type of dehydrated gypsum and a by-product of the lactic acid (LA) production process, was melt–blended with bio-sourced polylactide (PLA) to produce highly filled composites. Samples containing different amounts of filler (10–40 wt.%) with various granulometries were used for preparation of films by compression moulding. The influence of adding filler (calcium sulphate) on the photochemical behaviour of PLA–AII composites was studied by irradiation under photo-oxidative conditions (λ > 300 nm, temperature of 60 °C and in the presence of oxygen). Several analytical methods were used to characterise the polymer degradation. Oxidation of the polymer matrix was evaluated by infrared and UV–visible spectroscopies, differential scanning calorimetry (DSC) and size exclusion chromatography (SEC). The main photoproducts formed upon UV-light irradiation of the PLA were identified along with the influence of filler content and its particle size on the rate of oxidation. It was shown that oxidation of PLA and PLA–AII composites occurred without any induction time and that the presence of the CaSO4 filler (AII) increased the oxidation rate of the polymer. Moreover, a faster degradation rate of PLA was observed in composites containing natural anhydrite of lower particle size (4 μm).
Keywords: Biodegradable polyesters; Polylactide; Calcium sulphate anhydrite; Composites; Degradation; UV irradiation;
Post-irradiation oxidation of different polyethylenes by Ilenia Carpentieri; Valentina Brunella; Pierangiola Bracco; Maria Cristina Paganini; Elena Maria Brach del Prever; Maria Paola Luda; Sara Bonomi; Luigi Costa (624-629).
The radiation-induced oxidative degradation of polyethylenes (PEs) with different degrees of crystallinity was characterized after electron-beam irradiation and during storage at room temperature.UHMWPE, HDPE, LDPE, LLDPE and an ethylene–octene copolymer (Engage) were e-beam irradiated to 30 or 60 kGy in vacuum or in air and stored at room temperature in air. EPR spectroscopy was used to investigate macro-radicals produced during irradiation and their post-irradiation changes. FTIR spectroscopy was used to monitor changes in the polymer structure, induced by irradiation, and to follow post-irradiation oxidation.We found that the crystallinity and the size of the crystalline lamellae, in particular, play a major role on the post-irradiation effects. The low-crystallinity polyethylenes showed no oxidation or oxidation only to a small extent, even when irradiated and stored in air. On the contrary, development of post-irradiation oxidation was observed in HDPE and UHMWPE. We attribute these results to a different reactivity of the macro-alkyl radicals formed upon irradiation in the amorphous or in the crystalline phase. While the radicals formed in the amorphous phase decay in short time, the migration time of the radicals trapped in the crystalline phase to the amorphous one is a key factor, governing the oxidation process.
Keywords: Oxidation; e-Beam irradiation; Polyethylene; Radicals;
Comparative analysis of commercial dermal fillers based on crosslinked hyaluronan: Physical characterization and in vitro enzymatic degradation by Annalisa La Gatta; Chiara Schiraldi; Agata Papa; Mario De Rosa (630-636).
The cosmetic market for hyaluronic acid (HA)-based dermal fillers is in continuous and rapid growth and, simultaneously, the development of more effective and safer products is strongly intensifying. In order to highlight the differences among the currently available fillers, in terms of their physical characteristics and on the relation of such properties with product effectiveness, an in vitro evaluation of eight marketed HA-based gels was performed.Filler swelling properties, soluble HA fraction and rheological behaviour were investigated. Furthermore the relative stability to enzymatic hydrolysis was tested. The presence of soluble HA in the formulations varied from 7 ± 1(%) to 33 ± 5(%) with respect to the total HA concentration. Chromatographic analyses showed that the soluble fractions consist of low molecular weight chains (M w: 260–480 kDa) presenting large distributions (M w/M n: 1.6–2.5). The investigated fillers were found to be non-equilibrium gels in their commercial formulation also showing different swelling capacities. Rheological measurements indicated a shear thinning behaviour for all the products and elastic modulus values varied over a wide range (100–1800 Pa). Fillers proved differently sensitive to enzymatic degradation. Swelling capacity and enzymatic stability were found consistently dependent on the total HA concentration, insoluble/soluble HA ratio and on the crosslinking extent.
Keywords: Hyaluronan; Dermal fillers; Crosslinking; Enzymatic hydrolysis; SEC-TDA;
Effect of thermal stabilizers composed of zinc barbiturate and calcium stearate for rigid poly(vinyl chloride) by Shumin Li; Youwei Yao (637-641).
Zinc barbiturate [Zn(H2L)2·2H2O, abbreviated as ZnL2] was synthesized by a precipitation method in aqueous solution, and investigated as a co-stabilizer with calcium stearate (CaSt2) for rigid poly(vinyl chloride) (PVC) by the discoloration test and the dehydrochlorination test at 180 °C. ZnL2 exhibits high stabilizing effect with excellent initial colour of PVC films. In comparison with the synergistic effect of CaSt2/ZnSt2 stabilizers, the CaSt2/ZnL2 stabilizers in mass ratios ranging from 0.3/1.2 to 0.6/0.9 exhibit better synergistic effect. Moreover, PVC films stabilized by CaSt2/ZnL2 show better initial colour with the addition of dibenzoyl methane as an auxiliary stabilizer. The mechanism of stabilizing action of ZnL2 is also proposed. ZnL2 may replace the labile chlorine atoms to interrupt the formation of conjugated double bonds in PVC chains, and act as the absorber of hydrogen chloride to restrain the self-catalytic dehydrochlorination.
Keywords: PVC; Thermal stabilizer; Zinc barbiturate; Calcium stearate; Zinc stearate; Dibenzoyl methane;
Accelerated ageing due to moisture absorption of thermally cured epoxy resin/polyethersulphone blends. Thermal, mechanical and morphological behaviour by S. Alessi; D. Conduruta; G. Pitarresi; C. Dispenza; G. Spadaro (642-648).
A model epoxy resin/anhydride system, modified with a polyethersulfone (PES) engineering thermoplastic toughening agent, has been studied under hydrothermal ageing in order to investigate the modification of the thermal, morphological and mechanical behaviour through dynamical mechanical thermal analysis, SEM microscopy and fracture toughness test respectively. Two different concentrations of the toughening agent were used in the blends and two ageing conditions have been considered, consisting of the immersion of the samples in distilled water at constant temperature of 70 °C for 1 week and for 1 month. Dynamical mechanical thermal analysis results on hydrothermally aged materials indicated the occurrence of progressive segregation effects with the formation of regions with different cross-linking degrees.Fracture toughness tests showed an increase of the K IC value with the increase of the toughening agent concentration, revealing both a dramatic decrease of the same parameter after 1 week ageing for all the materials and the tendency to reach an almost constant value after 1 month ageing for all the formulations, with a slight increase with respect to 1 week ageing. These results have been interpreted on the basis of the SEM analysis, showing the presence of a well defined micrometric PES particles distribution in the epoxy/anhydride matrix, and discussed in the light of different water absorption mechanisms at short and long ageing times.
Keywords: Epoxy resins; Hydrothermal ageing; Phase separation; Fracture toughness;
Outdoor and accelerated weathering studies of bisphenol A polycarbonate by Marjolein Diepens; Pieter Gijsman (649-652).
The influence of outdoor weathering on the degradation rate of unstabilized bisphenol A polycarbonate (BPA-PC) films is investigated and compared to the results found for indoor accelerated weathering conditions, using UV and IR spectroscopy. At the same dosage, changes in UV and IR were larger for the accelerated than for the outdoor weathered samples, this could be explained by the lower degradation temperature during outdoor exposures. The difference between outdoor and accelerated weathering is according to the IR measurement larger than according to the UV measurement. This difference is ascribed to difference in wavelength distribution between the spectra of the light emitted in the accelerated test and from the terrestrial sunlight. The larger difference for the IR results than for the UV results suggests a difference in ratio between photo-Fries rearrangements and photo-oxidation reaction between both exposures.
Keywords: Bisphenol A polycarbonate; Weathering; FT-IR; UV spectroscopy;
Controlling the evolution of polypropylene microstructure during melt free radical modification using zinc dithiocarbamate with different N-substituted groups by Zhenjiang Zhang; Dong Wan; Yanjie An; Feng Liu; Haiping Xing; Lu Wang; Zhiwei Jiang; Tao Tang (653-659).
The effects of zinc dithiocarbamates on degradation and branching of polypropylene (PP) were studied during melt radical modification using a tri-functional monomer (trimethylol propane triacrylate (TMPTA)). High-temperature size-exclusion chromatography (HT-SEC) coupled with differential refractive index detector (DRI), light scattering detector (LSD) and viscometer detector (VD) and rotational rheometry were used to analyse the microstructure of modified PP samples. The chemical structure of the N-substituted group showed an important influence in controlling the evolution of PP microstructure during melt radical reaction. The chain cleavage of PP was controlled in the presence of zinc N, N-dimethyldithiocarbamate (ZDMC), and a substantial long chain branched (LCB) fraction was formed. Without co-agent, the molecular weight of PP decreased measurably, and only a minor LCB fraction was formed. Importantly, considerable amounts of highly branched (microgel and hyperbranched) structures were formed in this case.
Keywords: Degradation; Long chain branched; Microstructure; Polypropylene;
A DFT study of H-isomerisation in alkoxy-, alkylperoxy- and alkyl radicals: Some implications for radical chain reactions in polymer systems by Ondrej Kyseľ; Šimon Budzák; Miroslav Medveď; Pavel Mach (660-669).
Intramolecular 1-n H-shift (n = 2, 3… 7) reactions in alkoxy, alkyl and peroxy radicals were studied by density functional theory (DFT) at the B3LYP/6-311+G∗∗ level and compared with respective intermolecular H-transfers. It was found that starting from 1 to 3 H-shift the barrier heights stepwise decrease with increasing n reaching minimum for 1–5 and 1–6 H-shifts. This dependence can be ascribed to the decrease of the strain with increasing transition state (TS) ring size, which is minimal in six- and seven-member rings. The barrier heights of H-shifts in alkyl radicals are systematically larger than those in alkoxy radicals: the respective activation energies (Ea) of 1–5 and 1–6 H-shifts are about 59–67 kJ/mol for alkyl radical and 21–34 kJ/mol for alkoxy radicals. Further increase of the TS ring size in 1–7 H-shifts leads to the increase of the barrier to 44 kJ/mol in the hexyloxy radical and 84 kJ/mol for n-heptyl radical. We have also found that intermolecular H-transfer reactions in all three types of free radicals have smaller barriers than respective intramolecular 1–5 or 1–6 H-shifts by 4–25 kJ/mol. The mentioned difference can be explained in terms of enhanced nonbonding repulsion interaction in the cyclic TS structures compared to respective intermolecular TS. B3LYP/6–311+G∗∗ geometric parameters and imaginary frequencies for 1-n H-shifts TS are consistent with respective calculated barrier heights. Reactivity of some other radicals compared to alkoxy, peroxy and alkyl radicals as well as other factors influencing their reactivity (π-conjugation, steric effect and ring strain in cyclic TS, etc.) are also briefly discussed in relation to free radical reactions in polymer systems.
Keywords: H-transfer; Radical isomerisation; DFT study; Reaction and activation energies;
Purification and characterization of an extracellular medium-chain length polyhydroxyalkanoate depolymerase from Thermus thermophilus HB8 by Christos P. Papaneophytou; Ekaterini E. Velali; Anastasia A. Pantazaki (670-678).
During growth on medium-chain length (mcl) polyhydroxyalkanoates (PHAs), or on sodium octanoate Thermus thermophilus HB8 produces an extracellular mcl-PHA depolymerase. This enzyme was purified from the culture medium of sodium octanoate-grown cells to electrophoretic homogeneity by hydrophobic interaction chromatography using Octyl-Sepharose CL-4B and gel permeation chromatography using Sephadex G-150. The molecular mass of the purified enzyme was approximately 28 kDa. A part of the gene TTHA1605 encoding a 24.17 kDa protein was demonstrated to encode the mcl-PHA depolymerase of T. thermophilus. The primary amino-acid sequence of purified enzyme reveals similarity to all reported so far extracellular mcl-PHA depolymerases. The purified enzyme could hydrolyze mcl – PHAs and p-nitrophenyl (pNP) esters but not short chain length (scl) – PHAs. The optimum pH range was 7.5–9 and the optimum temperature was 70 °C for pNP-octanoate (pNPO) hydrolysis. The Km value for pNPO was 53.2 μM. The enzyme was strongly inhibited by phenylmethylsulfonyl fluoride (PMSF) and non-ionic detergents (Tween 20, Tween 80 and Triton X-100). The results demonstrated in this study revealed that the mcl-PHA depolymerase from T. thermophilus is a distinct enzyme, which is different from those of other mcl-PHA-degrading bacteria.
Keywords: Medium-chain length polyhydroxyalkanoates (mcl-PHAs); Extracellular PHA depolymerase; Thermus thermophilus HB8; Biodegradation;
Crystalline properties and decomposition kinetics of cellulose fibers in wood pulp obtained by two pulping processes by Matheus Poletto; Vinícios Pistor; Mara Zeni; Ademir J. Zattera (679-685).
In this study two cellulose fibers, Eucalyptus grandis (CEG) and Pinus taeda (CPT), obtained through the kraft and sulfite pulping processes, respectively, were characterized. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were carried out. From the XRD analysis the interplanar distance, crystallite size and crystallinity index were calculated and the degradation kinetics parameters were determined by TGA at heating rates of 5, 10, 20 and 40 °C min−1 using the Avrami, Flynn-Wall-Ozawa (FWO) and Criado methods. The results obtained by FTIR showed that the composition of the fibers is similar, while from the XRD analysis slight differences in the crystallinity were observed. The thermogravimetric analysis showed higher thermal stability for CPT than CEG while the values for the activation energy (Ea ) were higher for CEG than CPT. The results obtained by Avrami and Criado methods showed that the degradation mechanism in the CEG samples involves a diffusion process while in the case of CPT the degradation process is a phase boundary controlled reaction. The degradation mechanisms demonstrated that the difference between thermal stability and Ea may be due to differences in the type of crystalline structure of the samples obtained through the two pulping processes.
Keywords: Eucalyptus grandis; Pinus taeda; Cellulose; Crystallinity; Kinetics; Degradation;
Decomposition of poly(propylene carbonate) with UV sensitive iodonium salts by Todd J. Spencer; Paul A. Kohl (686-702).
The decomposition characteristics of poly(propylene carbonate) containing a photoacid generator have been studied. The influence of casting solvent, photoacid concentration and type, UV exposure dose, substrate surface, and ambient gas were included in this study. Dynamic thermogravimetric analysis was used to analyze the decomposition characteristics. Kinetic parameters were extracted using the Kissinger method and the Coats–Redfern method. Fourier Transform Infrared Spectroscopy was used to analyze effects of casting solvent. The highest thermal stability was found to occur in high molecular weight, high-purity poly(propylene carbonate) samples. Cyclohexanone and trichloroethylene solvents were found to increase the thermal stability. Photoacid generators based on diphenyliodonium salts lowered the onset decomposition temperature and activation energy.
Keywords: Poly(propylene carbonate); Acid degradation; Thermal degradation; Diphenyliodonium; Microelectronics; Sacrificial polymer;
Degradability of linear polyolefins under natural weathering by Telmo Ojeda; Ana Freitas; Kátia Birck; Emilene Dalmolin; Rodrigo Jacques; Fátima Bento; Flávio Camargo (703-707).
High density polyethylene (HDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) containing antioxidant additives at low or zero levels were extruded and blown moulded as films. An HDPE/LLDPE commercial blend containing a pro-oxidant additive (i.e., an oxo-biodegradable blend) was taken from the market as supermarket bag. These four polyolefin samples were exposed to natural weathering for one year during which their structure and thermal and mechanical properties were monitored. This study shows that the real durability of olefin polymers may be much shorter than centuries, as in less than one year the mechanical properties of all samples decreased virtually to zero, as a consequence of severe oxidative degradation, that resulted in substantial reduction in molar mass accompanied by a significant increase in content of carbonyl groups. PP and the oxo-bio HDPE/LLDPE blend degraded very rapidly, whereas HDPE and LLDPE degraded more slowly, but significantly in a few months. The main factors influencing the degradability were the frequency of tertiary carbon atoms in the chain and the presence of a pro-oxidant additive. The primary (sterically hindered phenol) and secondary (phosphite) antioxidant additives added to PP slowed but did not prevent rapid photo-oxidative degradation, and in HDPE and LLDPE the secondary antioxidant additive had little influence on the rate of abiotic degradation at the concentrations used here.
Keywords: HDPE; LLDPE; PP; Polyolefin weathering and degradation; Antioxidant and pro-oxidant additives;
Significant enhancement of thermal stability in the non-oxidative thermal degradation of bisphenol-A/aniline based polybenzoxazine aerogel by Parkpoom Lorjai; Sujitra Wongkasemjit; Thanyalak Chaisuwan; Alexander M. Jamieson (708-718).
Previously we reported synthesis of a new type of organic aerogel from phenolic resins called polybenzoxazines and their transformation into carbon aerogels. Here, we further investigate the thermal degradation behaviors of both bulk polybenzoxazines and polybenzoxazine aerogels using Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA)/FTIR, and gas chromatography/time of flight-mass spectroscopy (GC/TOF-MS). The activation energy (E a) of the decomposition step was determined using the Kissinger method. It was found that the polybenzoxazine aerogels exhibit much higher degradation temperatures and char yields than the bulk. The decomposition temperatures at 10% weight loss and the char yields at 800 °C of the bisphenol-A/aniline based polybenzoxazine aerogel increased up to 24% and 97% higher, respectively, than the corresponding bulk values. Kinetic investigation indicated that the decomposition reaction of bulk polybenzoxazine exhibits three stages, whereas that of the polybenzoxazine aerogel features four stages with much higher overall activation energy. The enhanced thermal stability of the aerogel is ascribed to its highly porous structure, which increases the residence time of the primary decomposition products, and hence generates greater opportunity to form secondary reactions.
Keywords: Benzoxazine; Benzoxazine aerogel; Thermal degradation; Kinetics; Char yield;
Degradation of poly(lactide-co-glycolide) and its composites with carbon fibres and hydroxyapatite in rabbit femoral bone by A. Morawska-Chochol; J. Jaworska; J. Chlopek; J. Kasperczyk; P. Dobrzyński; C. Paluszkiewicz; G. Bajor (719-726).
The aim of the present work was to analyse the degradation rate of PGLA copolymer depending on a modifier (hydroxyapatite, carbon fibres) under in vivo conditions (rabbit femoral bone). Also, the influence of the implantation site on the degradation rate of a copolymer (rabbit mandible and femoral bone) was analyzed as a continuation of our previous research.The structural and phase changes of poly(lactide-co-glycolide) and its composite with hydroxyapatite and carbon fibres were determined on the basis of IR and NMR spectroscopy. Additionally, microscopic observations with elemental analyses were performed (SEM, EDS).The addition of a modifying phase accelerates implant degradation. However, modifying additives promote regeneration of the treated bone tissue simultaneously with faster polymer degradation. The compositions of a copolymer and composites are variable during degradation.The process of copolymer degradation in the femoral bone is much faster in comparison with previous studies on mandibles. This may be caused by higher activity of osteoblasts, differences in blood supply and oxygenation of tissue as well as different anatomical structure of these two kinds of bones.FTIR and NMR methods allow for following the changes occurring in the resorbable copolymer structure with time and they are very useful tools in analyzing the degradation mechanism and rate of aliphatic polyesters and their composites.
Keywords: Poly(lactide-co-glycolide); Hydroxyapatite; Carbon fibres; in vivo; FTIR; NMR;
In-bulk formation of a new tetrasubstituted furan from phenolic antioxidants and dibasic lead stearate by Stéphane Leconte; Aurélie Cena; Anne Balquet; Laurent Cauret; Thierry Falher; Denis Jouannet; Robert Dhal; Véronique Montembault; Pierre-Jean Madec; Christian Gondard (727-731).
The reaction between octadecyl 3-(3,5-di-tert-4-hydroxyphenyl)propanoate and dibasic lead stearate, two compounds added in most PVC formulations, has been investigated in bulk. The structure of the resulting product, obtained after a one-pot synthesis, was characterized by HRMS and 2D NMR analyses. The product of empirical formula C70H116O7 has been identified as an unknown highly substituted furan. The reaction mechanism between both products to produce this original furan has been established. The first step leads to a discoloured lead IV complex with bis-quinonemethide. The second step consist of a hydrolysis during the solvent extractions or under UV exposure leading to a tetrasubstituted furan.
Keywords: Phenolic antioxidant; Poly(vinyl chloride) (PVC); Dibasic lead stearate; Additive; Tetrasubstituted furan;
The degradation of DGEBA/DICY under 100 keV proton irradiation by Gang Liu; Hai Liu; Yong Liu; Shiyu He (732-738).
The degradation process of diglycidyl ether of bisphenol A (DGEBA)/ dicyandimide (DICY) solidified system under 100 keV proton irradiation was investigated. It was found that the proton irradiation results in mass loss, which the maximum is approximately 15.5 μg/cm2, and change in surface morphology of DGEBA/DICY. The analyses of FT-IR and XPS showed that, the proton irradiation induces the debonding of the weak groups such as –CH3, C–O, leading to formation of stable carbon-rich structure by recombination of the occurred free radicals, and chemical reaction between the free radicals with participation of proton. The degradation of DGEBA/DICY exhibits exponential variation with the proton fluence, which the degradation rate is high at the initial stage of irradiation, and becomes slow trending to constant after the proton fluence reaches 6 × 1015 /cm2.
Keywords: Epoxy resin; Proton radiation; Mass loss; Degradation;