Polymer Degradation and Stability (v.95, #6)
Synthesis and characterization of hydrolysable poly(ether–urethane–urea)s derived from l-leucine anhydride cyclopeptide; a green synthetic method for monomer by Fatemeh Rafiemanzelat; Elahe Abdollahi (901-911).
l-leucine anhydride cyclodipeptide (LAC) was prepared through a green method under microwave irradiation with good yield. Then a new class of hydrolysable poly(ether–urethane–urea)s (PEUUs) was synthesized via two-step polymerization method. In the first step, 4,4′-methylene-bis-(4-phenylisocyanate) (MDI) was reacted with LAC to produce isocyanate-terminated poly(imide-urea) oligomers (hard segment). Reaction of the resulting pre-polymer with different molecular weights (MW) of polyethyleneglycols (PEG)s such as PEG-400, PEG-600, PEG-1000 and PEG-2000 was the second step to furnish a series of new PEUUs. The resulting multiblock copolymers have inherent viscosities in the range of 0.4–1.8 dL/g. These multiblock copolymers are hydrolysable, thermally stable and soluble in amide-type solvents. Polymers containing different molecular weights of PEGs soft segments show different thermal stability, phase separation, hard segment cohesiveness and hydrolysis rate. Some structural characterization and physical properties of these PEUUs are reported.
Keywords: Amino acid anhydride; PEG Poly(ether–urethane–urea)s; Copolymerization; Hydrolysis;
Isolation and characterization of microorganisms degrading nylon 4 in the composted soil by Koichiro Tachibana; Kazuhiko Hashimoto; Masato Yoshikawa; Haruki Okawa (912-917).
Two kinds of microorganisms, a bacterium (KT-1 strain) and a fungus (KT-2 strain), degrading nylon 4 (polyamide 4), which was easily prepared by the anionic ring-opening polymerization of 2-pyrrolidone, were isolated from the composted soil with the utilization of enrichment cultures and the culture using nylon 4 as a carbon source. KT-1 and KT-2 strains were identified as neighboring species to Stenotrophomonas sp. and Fusarium sp., respectively, by their morphological properties and the nucleotide sequences. These strains were confirmed to grow in the culture medium containing nylon 4 powders as a carbon source. In addition, nylon 4 film was decomposed in both mineral media containing KT-1 and KT-2 strains, respectively, and disappeared within two months. The MALDI TOF-MS analysis of nylon 4 recovered during the biodegradation test suggest that the isolated KT-2 strain recognize the acyllactam or carboxy chain end and degrade them or their neighboring amide bond.
Keywords: Nylon 4; Biodegradation; Bacteria; Fungi; Soil; Compost;
Curing kinetics of Benzoxazine–epoxy copolymer investigated by non-isothermal differential scanning calorimetry by Chanchira Jubsilp; Kanokwan Punson; Tsutomu Takeichi; Sarawut Rimdusit (918-924).
The reaction of epoxy novolac resin cured with benzoxazine resin (BA-a) was investigated under non-isothermal DSC at different heating rates. The kinetic parameters and the kinetic models of the curing processes of the benzoxazine-epoxy novolac mixtures were examined utilizing isoconversional methods, Flynn-Wall-Ozawa and Friedman methods. The benzoxazine-epoxy novolac mixture exhibits two dominant curing processes. The reaction 1 at lower temperature is attributed to the reaction among the benzoxazine monomers, while the reaction 2 corresponds to the formation of an etherification between hydroxyl group of polybenzoxazine and epoxide group or homopolymerization reaction of epoxide group at high temperature. The average activation energies of the reaction 1 and reaction 2 were determined to be 81 kJ mol−1 and 118 kJ mol−1, respectively. The autocatalytic kinetic model was found to be the best description of the investigated curing reactions. In addition, the predicted curves from our kinetic models fit well with the non-isothermal DSC thermogram.
Keywords: Benzoxazine resin; Epoxy; Cure kinetics; Isoconversional method; Autocatalytic curing;
Alcoholysis of Poly(l-lactic acid) under microwave irradiation by Koichi Hirao; Yuta Nakatsuchi; Hitomi Ohara (925-928).
Chemical recycling of poly(l-lactic acid) (PLLA) by alcoholysis under microwave irradiation was investigated. Reaction rates in ethanol (140–180 °C) and butanol (130–210 °C) were greater under microwave irradiation than under conventional heating. However, because activation energies were almost the same under both conditions, the reaction mechanisms would be the same, but the reaction rates differed due to the reaction frequency factor.
Keywords: Activation energy; Alcoholysis; Microwave; Poly(lactic acid); Recycling;
Structures and gas-sorption properties of carbonaceous film prepared by radio-frequency sputtering of polysaccharides pectin by Iwao Sugimoto; Masumi Okamoto; Kazuyuki Sone; Kazuhiko Takahashi (929-934).
Carbonaceous films with microcolumnar layer have been prepared by radio-frequency sputtering of polysaccharides pectin. The repeated sputtering has developed the densely packed seamless microcolumns, which are separated by the narrow grooves. The residual film stress has formed the honeycomb-patterned ridges. X-ray photoelectron spectroscopy and energy dispersion spectroscopy revealed the inclusion of nitrogen in the film constituents. The film surface is hydrophilic mainly due to the polar functional groups, such as the carboxyl and amino groups. Nitrogen adsorption measurement revealed that the specific surface area of the film was no less than 109 m2/g. Impedance analysis of the film-coated quartz crystal resonator clarified that the film had the higher adsorption capacities to the polar and cohesive vapors, such as ethyl alcohol. The adsorption of organic vapors has not induced the viscoelastic changes in the film.
Keywords: Carbonaceous film; Biopolymer; Radio-frequency sputtering; Plasma degradation; Gas sorption;
In vitro and in vivo degradation behaviors of thermosensitive poly(organophosphazene) hydrogels by Mi-Ran Park; Chong-Su Cho; Soo-Chang Song (935-944).
Biodegradable and thermosensitive poly(organophosphazenes) with various substituents were synthesized and their hydrolytic degradation properties were investigated in vitro and in vivo. The aqueous solutions of all polymers showed a sol–gel phase transition behavior depending on temperature changes. The side groups of polymers significantly affected the polymer degradation and accelerated hydrolysis of polymers in the order of carboxylic acid > depsipeptide > without carboxylic acid and depsipeptide. The increased gel strength led to the decreased hydrolysis rate. The polymer hydrogels with 750 Da of α-amino-ω-methoxy poly(ethylene glycol) were rapidly decreased by dissolution. The polymer degradation was also influenced by pH and temperature. The in vivo behaviors of mass decrease of the polymer hydrogels were similar with the in vitro results. These results suggest that the biodegradable and thermosensitive poly(organophosphazenes) hold great potentials as an injectable and biodegradable hydrogel for biomedical applications with controllable degradation rate.
Keywords: Thermosensitive hydrogel; Poly(organophosphazene); Depsipeptide; Hydrolytic degradation; Dissolution;
Flame retardant polyoxymethylene with aluminium hydroxide/melamine/novolac resin synergistic system by Zhang-Yu Wang; Yuan Liu; Qi Wang (945-954).
Polyoxymethylene (POM), having the lowest limiting oxygen index (LOI) (only ∼ 15%), is well known as the most difficult to be flame retarded plastic among all the polymers. In this paper, a novel synergistic flame retardant system composed of aluminium hydroxide (ATH), melamine (ME) and novolac resin was designed and successfully applied to flame retard POM. ATH took effects through heat absorption and water release. Both ME and novolac could react with the decomposition product of POM, formaldehyde, thus improving the flame retardancy. Particularly, novolac resin and ME played the roles of macromolecular charring agent and gas source, enhancing the flame retarding actions in the condensed and gaseous phases, respectively. This ternary synergistic system exhibited fine flame retardancy for POM (UL94 V-1 rating for 1.6 mm bar), and the obtained flame retardant POM also showed good processability and mechanical properties due to the lubrication, compatibilization and aid-dispersion effects of novolac resin.
Keywords: Halogen-free flame retardant; Polyoxymethylene; Aluminium hydroxide; Synergistic effect;
The diffusion and solubility of Irganox® 1098 in polyamide 6 by Weifu Dong; Pieter Gijsman (955-959).
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.
Keywords: Diffusion; Solubility; Blooming; van’t Hoff plot; Arrhenius plot;
Identification and localization of organic coating degradation onset by impedance imaging by M. Szociński; K. Darowicki; K. Schaefer (960-964).
The aim of this work was to demonstrate the potential of a localized impedance measurement technique to identify and spatially localize the onset spots of polymeric coating degradation. The technique, which has not yet been applied in the field of organic coatings, utilizes atomic force microscopy (AFM) in contact mode. During the scan a single-frequency voltage perturbation signal is applied between the AFM tip and the coated metal substrate. A current response signal is registered. As a result an impedance map of the scanned region is created. The method was applied to investigation of acrylic coating degradation during exposure to UV radiation. Localized topography and impedance images revealed formation of micro-cracks in the coating layer, which gradually converted into through-the-coating defects with an increase in the irradiation time. Thus the method allowed early identification and localization of the sites of degradation onset, which was not possible using classical impedance measurement.
Keywords: Localized impedance measurements; Atomic force microscopy; Organic coating; Local defects; UV degradation;
Thermo-oxidation behaviour of composite materials at high temperatures: A review of research activities carried out within the COMEDI program by M.C. Lafarie-Frenot; J.C. Grandidier; M. Gigliotti; L. Olivier; X. Colin; J. Verdu; J. Cinquin (965-974).
The present paper presents a review of the main activities carried out within the context of the COMEDI research program, a joint collaboration involving three research teams focusing on the thermo-oxidation behaviour of composite materials at high temperatures.The scientific aim of the COMEDI research program was to better identify the link between the physical mechanisms involved in thermo-oxidation phenomena: oxygen reaction–diffusion, chemical shrinkage strain/stress, degradation at different scales and to provide tools for predicting the thermo-oxidation behaviour of composite materials under thermo-oxidative environments including damage onset.This aim was accomplished by investigating experimentally the thermo-oxidation behaviour of pure resin samples – both industrial and “model” materials – and by interpreting the results by a coupled reaction–diffusion–mechanics multiphysics model.A dedicated numerical model tool has been developed and implemented into the ABAQUS® finite element commercial software. This tool was employed to simulate the thermo-oxidative behaviour of a fibre-matrix microscopic representative composite cell.Finally, the model predictions for the composite have been validated by comparing the experimental and the simulated local matrix shrinkage displacements and the mass loss of composite specimens.
Keywords: Polymer-matrix composites (PMCs); Durability; Thermo-oxidation; Multi-scale modelling; Optical microscopy;
Effects of ozone in surface modification and thermal stability of SEBS block copolymers by Carmen Peinado; Teresa Corrales; Fernando Catalina; Sara Pedrón; Valentín Ruiz Santa Quiteria; María Dolores Parellada; Juan Antonio Barrio; Dania Olmos; Javier González-Benito (975-986).
SEBS block copolymers were treated under mild conditions in an ozone atmosphere, producing very slightly chemically-modified surfaces. The thermal stability was analysed by chemiluminescence and related to morphological changes observed by AFM. The intrinsic thermal stability was diminished by ozone exposure, but the oxidation induction times were delayed which indicates an enhancement of thermal stability under oxidative conditions. Also, chemiluminescence analysis showed the presence of a typical order–disorder transition at temperatures around 120 °C. Two different sets of samples which showed different morphological patterns were imaged by AFM. The effects of micro-domain separation and inter-domain structure on thermal properties are discussed and explained by a coarsening of the internal interface induced by ozone. A detailed 2D Fourier transformed analysis of AFM images allowed us to identify a regular wrinkled nano-pattern induced by uniaxial strain combined with ozone treatment, offering new opportunities in applications ranging from organic electronics to bio-patterning.
Keywords: Thermoplastic elastomers; Block copolymers; Order–disorder transition; Ozone; Degradation; Chemiluminescence;
Surface molecular degradation of 3D glass polymer composite under low earth orbit simulated space environment by Firas Awaja; Jin Bum Moon; Shengnan Zhang; Michael Gilbert; Chun Gon Kim; Paul J. Pigram (987-996).
Epoxy resin reinforced with 3D parabeam glass fibre was subjected to low earth orbit (LEO) simulation conditions comprising ultra high vacuum, temperature cycling (TC), and ultraviolet (UV) radiation and atomic oxygen (AO) bombardment. Inspection of the same composite using only a selection of these hazardous conditions provided comparison measures to identify the effect of each condition on the surface degradation of the resin composite. Each of the individually selected conditions showed a different degradation mechanism that is accelerated by the presence of other conditions. X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM) were used to provide surface information. The resin composite samples suffered surface oxidation that increased the oxygen content to 17.24% in comparison with the untreated sample (only 14.2%). The samples that were treated with AO showed higher C–O and C＝O functional groups on the surface in comparison with the rest of the samples (as indicated by XPS). Molecular information (from ToF-SIMS) showed that surface oxidation differs with different conditions and in comparison with the use of all conditions. All treated samples were shown to suffer significant chain scission and loss of volatiles as a result of the LEO conditions. The extent of the chain scission reaction for each condition can be indicated by the extent of the reduction of the relative concentration of the aliphatic hydrocarbon ions. The relative intensity of the C4H11N4O2 + ion showed that AO bombardment accelerated the oxidation of the surface. The AO effect is doubled when UV and TC are also present. SEM results indicated that sample surfaces were eroded and roughened upon exposure to LEO conditions. Presence of AO and UV in the LEO conditions introduced white deposits onto the surface, believed to be crosslinked formations.
Keywords: LEO; XPS; Polymer composites; 3D glass; AO;
Effects of process severity on the chemical structure of Miscanthus ethanol organosolv lignin by Roland El Hage; Nicolas Brosse; Poulomi Sannigrahi; Arthur Ragauskas (997-1003).
Ethanol organosolv lignin extracted from Miscanthus ×giganteus with differing levels of severity (1.75 < CS<2.8) were subjected to comprehensive structural characterization by 13C, 31P NMR, FTIR spectroscopy and gel permeation chromatography. The results were compared to those from milled wood lignin from the same feedstock. The results showed that an increase in the severity of the treatment enhanced the dehydration reactions on the side chain and the condensation of lignin, increased the concentration of phenol groups and decreased the molecular mass of lignin fragments. It appeared that for the experimental conditions generally employed the cleavage of α-aryl ether bonds is primarily reaction responsible for lignin depolymerization under the organosolv conditions examined.
Keywords: Miscanthus ×giganteus; Lignin; Organosolv pre-treatment; NMR spectroscopy; FTIR spectroscopy; SEC;
Enhanced interlayer interaction in cellulose single nanofibre and poly(l-lactic acid) layered films by plasma-initiated surface grafting of poly(acrylic acid) onto poly(l-lactic acid) films by Weihua Kai; Shinichro Iwamoto; Kazuki Akamatsu; Shinichi Nakao; Akira Isogai; Tadahisa Iwata (1004-1010).
The surface of a poly(l-lactic acid) (PLLA) film was modified with poly(acrylic acid) (PAA) by plasma-initiated polymerization to increase the interaction between PLLA and cellulose single nanofibres (CSNF). The surface wettability of the PAA grafted PLLA film (PLLA–PAA film) was investigated by contact angle measurements. Modification of the PLLA film with PAA decreased the contact angle from 61° to 50°. The surface morphologies of the PLLA film, PLLA–PAA film and CSNF-coated PLLA–PAA film were studied by atomic force microscopy. The interaction between the CSNF and PLLA layers was strengthened by incorporation of a PAA layer onto the PLLA films and it is higher than 2N as proved by a peeling test. This is probably because the carboxyl groups of PAA form hydrogen bonds with the hydroxyl groups of CSNF.
Keywords: Poly(l-lactic acid); Cellulose single nanofiber; Surface modification; Plasma-initiated polymerization; Interlayer interaction;
Comparison of the biodegradability of various polyethylene films containing pro-oxidant additives by Stéphane Fontanella; Sylvie Bonhomme; Marek Koutny; Lucie Husarova; Jean-Michel Brusson; Jean-Paul Courdavault; Silvio Pitteri; Guy Samuel; Gérard Pichon; Jacques Lemaire; Anne-Marie Delort (1011-1021).
The biodegradability of high density polyethylene films (HDPE), low density polyethylene films (LDPE) and linear low density polyethylene films (LLDPE) with a balanced content of antioxidants and pro-oxidants (manganese + iron or manganese + iron + cobalt) was studied. Abiotic pre-treatment consisting of photooxidation and thermal oxidation corresponding to about three years of outdoor weathering (including 3–4 months of exposure to daylight) was monitored by FTIR and SEC measurements. The oxidized samples were then inoculated with the strain Rhodococcus rhodochrous in mineral medium, and incubated up to 180 days. The metabolic activity of the bacteria was assessed by measuring adenosine triphosphate content (ATP) and the viability of the cells. Complementary experiments were performed by 1H NMR spectroscopy to monitor the biodegradation of soluble molecules excreted from the polymer in the incubation medium. Finally SEM was used to visualize the formation of a biofilm at the surface of the polymer. Three samples among the 12 tested were investigated in compost and soil environments. The results show that the main factor controlling the biodegradability of the polyethylene films is the nature of the pro-oxidant additive and to a lesser extent that of the matrix. Except for the samples containing very high content of cobalt additive, the various polymer films were used as substrates by the bacteria.
Keywords: Polyethylene; Biodegradation; Pro-oxidant; Photooxidation; Thermal oxidation;
Chemical recycling of post-consumer PET wastes by glycolysis in the presence of metal salts by R. López-Fonseca; I. Duque-Ingunza; B. de Rivas; S. Arnaiz; J.I. Gutiérrez-Ortiz (1022-1028).
Chemical recycling of poly(ethylene terephthalate) (PET) has been the subject of increased interest as a valuable feedstock for different chemical processes. In this work, glycolysis of PET waste granules was carried out using excess ethylene glycol in the presence of different simple chemicals acting as catalysts, namely zinc acetate, sodium carbonate, sodium bicarbonate, sodium sulphate and potassium sulphate. Comparable high yields (≈70%) of the monomer bis(2-hydroxyethyl terephthalate) were obtained with zinc acetate and sodium carbonate as depolymerisation catalysts at 196 °C with a PET:catalyst molar ratio of 100:1 in the presence of a large excess of glycol. The purified monomer was characterised by elemental analysis, differential scanning calorimetry, infrared spectroscopy, and nuclear magnetic resonance. These results revealed that, although the intrinsic activity of zinc acetate was significantly higher than that of sodium carbonate, this latter salt could indeed act as an effective, eco-friendly catalyst for glycolysis. Also an exploratory study on the application of this catalytic recycling technology for complex PET wastes, namely highly coloured and multi-layered PET, was performed.
Keywords: Post-consumer PET waste; Chemical recycling; Glycolysis; Zinc acetate; Sodium carbonate;
Influence of fillers on mechanical properties of ATH filled EPDM during ageing by gamma irradiation by Emilie Planes; Laurent Chazeau; Gérard Vigier; Jérôme Fournier; Isabelle Stevenson-Royaud (1029-1038).
The presence of a significant content of fillers accelerates the degradation of ATH filled EPDM subjected to gamma irradiation at room temperature. Above the melting temperature of the EPDM, this induces a decrease in the apparent mechanical reinforcement of the fillers. This also promotes de-cohesion mechanisms which leads to an increase in the strain at break with irradiation dose. It is not clear whether the use of a filler treatment attenuates this accelerating effect or not; however, part of this treatment remains efficient at a high dose and seems also to delay but not suppress the occurrence of de-cohesion mechanisms at large strain. Moreover, at room temperature, i.e. below the melting temperature, all the consequences of ageing by gamma irradiation are strongly attenuated by the presence of a semi-crystalline microstructure, the morphology of which is not too strongly modified by irradiation.
Keywords: Filled rubber; Irradiation; Mechanical properties;
Thermal and weathering degradation of poly(propylene carbonate) by Jobi Kodiyan Varghese; Sung Jae Na; Ji Hae Park; Dongjin Woo; Inmo Yang; Bun Yeoul Lee (1039-1044).
High molecular-weight poly(propylene carbonate) (PPC) can remain intact upon storage in ambient air or in water for 8 months once the catalyst is completely removed. Catalyst-free pure PPC is also thermally stable below 180 °C. At 200 °C, degradation occurs, mainly due to attack of the chain-ended hydroxyl group onto a carbonate linkage, through which the molecular weight distribution is broadened by simultaneous formation of low and high molecular weight fractions. Incomplete removal of hydrogen peroxide generated during the catalyst preparation results in a prepared polymer that contains a substantial amount of polymer chains grown biaxially from hydrogen peroxide, which gives rise to more severe thermal degradation. Experiments conducted in a weathering chamber at high temperature (63 °C) and high humidity (50%) revealed another degradation process involving chain scission through an attack of water molecules onto the carbonate linkage, which progressively and temporally lowers molecular weight.
Keywords: Poly(propylene carbonate); Carbon dioxide; Thermal degradation; GPC; Weathering;
Influence of nucleating agent on the formation and enzymatic degradation of poly(butylene adipate) polymorphic crystals by Ni Jiang; Lifen Zhao; Zhihua Gan (1045-1053).
The effects of nucleating agent multimethyl-benzilidene sorbitol (TM6) on crystallization and morphology of poly(butylene adipate) (PBA) with polymorphic crystal structures were studied by means of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical micrographs (POM). In addition to the heterogeneous nucleation, TM6 changes the formation conditions of PBA polymorphic crystals. The addition of TM6 is favorable for the formation of PBA α-form crystals, resulting in the morphological changes from spherulites to interpenetrated fibrils. The influences of TM6 on enzymatic degradation of PBA were studied in terms of the morphological change and weight loss. The results indicate that the α-form crystals induced by TM6 show much slower degradation rate. This work provides an efficient method to control the polymorphic crystal structure and further to regulate the biodegradation rate of polymer materials through modulating the homogeneous and heterogeneous nucleation modes by adding nucleating agents.
Keywords: Biodegradation; Heterogeneous nucleation; Isothermal crystallization; Polymorphism; Morphology;
Influence of temperature on the thermo-oxidative degradation of polyamide 6 films by Weifu Dong; Pieter Gijsman (1054-1062).
The thermo-oxidative degradation of polyamide 6 (PA6) was studied at relative high temperatures (between 120 and 170 °C) using oxygen uptake and hydroperoxide determination methods, chemiluminescence, FT-IR and UV–VIS spectroscopy as well as solution viscosity and tensile property measurements.The relation between the results of the different analytical techniques and influence of temperature on these relations was determined. Arrhenius plots of the degradation determined with the different methods are linear; however the activation energies determined from these plots depend on the analytical method used. For oxygen uptake measurements and changes in UV absorbance (at 280 nm) and solution viscosity an activation energy of about 120 kJ/mol was calculated, for the increase in carbonyl index of about 80 kJ/mol and for the decrease in elongation at break of about 150 kJ/mol.The changes in oxygen uptake UV absorbance and solution viscosity are probably due to the same chemical process. The lower activation energy from changes in the carbonyl index is attributed to the formation of gaseous products, which play a larger role at higher temperatures. The higher activation energy from the elongation at break measurements was ascribed to the contribution of physical changes that play the largest role at the highest temperatures.
Keywords: Polyamide 6; Thermo-oxidative degradation; Temperature; Oxygen uptake; UV absorbance; Carbonyl index;
Effect of expanded graphite/layered-silicate clay on thermal, mechanical and fire retardant properties of poly(lactic acid) by Kikku Fukushima; Marius Murariu; Giovanni Camino; Philippe Dubois (1063-1076).
Preparation of PLA based nanocomposites was carried out by using two different nanofillers: expanded graphite and organically modified montmorillonite. The addition and co-addition of these nanofillers to PLA using the melt-blending technique provides nanocomposites that showed significant enhancements in rigidity, thermal stability and fire retardancy of the polymer matrix. The presence of dispersed graphite nanolayers in PLA significantly accelerated the polyester crystallization, whereas the essential increase of thermal resistance is mainly connected to the addition of organoclay. The structure of the nanocomposites was examined by Wide Angle X-ray Scattering Analysis and Transmission Electron Microscopy. The improvement of thermal and mechanical properties obtained by the presence of both nanoparticles in PLA were associated to the good (co)dispersion and to the co-reinforcement effect, whilst the fire retardant properties were found to be related to the combined additive action of both nanofillers.
Keywords: Poly(lactic acid); Expanded graphite; Clay; Nanocomposites; Biodegradable polymer;
Oxidation of natural rubber using a sodium tungstate/acetic acid/hydrogen peroxide catalytic system by Jing Zhang; Qian Zhou; Xian-Hong Jiang; An-Ke Du; Tao Zhao; Johannes van Kasteren; Yu-Zhong Wang (1077-1082).
A catalytic system based on Na2WO4/CH3COOH/H2O2 effectively oxidizes natural rubber (NR) to prepare telechelic epoxidised liquid natural rubber (TELNR). The Na2WO4/CH3COOH/H2O2 catalytic system possesses a much higher epoxidation efficiency than the traditional CH3COOH/H2O2 system: the epoxidation degree (X epoxy) of products increases from merely 5.6% (CH3COOH/H2O2) to values as high as 52.1% (Na2WO4/CH3COOH/H2O2) by reacting for 24 h at 60 °C. Moreover, this catalytic system also induces hydrolytic degradation so that the weight average molecular weight ( M w ¯ ) of NR decreases, e.g., from 14.10 × 105 Da (NR) to 0.57 × 105 Da (TELNR) after reacting for 30 h.The catalytic process probably proceeds via a mononuclear tungsten peroxo-species with coordinated peracetyl/acetyl group, as suggested by ESI-MS measurements. During oxidation, the tungstic anion [W(CH3COOO)(O)(O2)2]− not only catalyzes NR epoxidation, but also induces a further oxidation of epoxy groups to form ketones and aldehydes.
Keywords: Natural rubber; Sodium tungstate; Epoxidation; Degradation; Waste tyre;
Optical and microstructural studies on electron irradiated PMMA: A positron annihilation study by Ismayil; V. Ravindrachary; R.F. Bhajantri; S.D. Praveena; Boja Poojary; Dhanadeep Dutta; P.K. Pujari (1083-1091).
The effect of electron irradiation on the free volume related microstructural and optical properties of Poly(methyl methacrylate) have been studied using Positron Annihilation and other techniques. The FTIR spectral study on the irradiated films suggests the existence of C＝C group and is understood by invoking the carbonaceous clusters as a consequence of chain scission in PMMA. Using UV–Visible absorption spectra the optical parameters like optical energy bandgap and activation energy were determined and the variation of these parameters suggests the existence of defects within the irradiated sample. Following Robertson’s theory, the carbonaceous cluster size is estimated and it increases with increase in electron dose. The XRD study indicates the enhancement of amorphous nature of the film due to chain scission by irradiation. The Positron annihilation result shows that electron irradiation affects the free volume related microstructure and the carbonaceous clusters may act as positron scattering centers.
Keywords: Poly(methyl methacrylate) (PMMA); Electron beam irradiation; Microstructure; Chain scission; Carbonaceous cluster; Positron annihilation lifetime spectroscopy;
Thermal stability and flame retardancy of novel phloroglucinol based organo phosphorus compound by Hai Vothi; Congtranh Nguyen; Kyunghoon Lee; Jinhwan Kim (1092-1098).
A series of organo phosphorus flame retardants (FR) based on cyclic phosphates were synthesized in an attempt to find an efficient FR for polycarbonate (PC) and acrylonitrile-butadiene-styrene copolymer (ABS). The success of synthesis was confirmed by FT-IR and 1H and 31P NMR. Their thermal stability and flame-retarding efficiency as a single component additive were investigated and compared with those of aromatic based phosphate, resorcinol bis(diphenyl phosphate) (RDP). Thermogravimetric analysis (TGA) results reveal that cyclic phosphates synthesized in this study show more than one-step degradation and act in the condensed phase mechanism rather than in the vapor phase mechanism. Flame-retarding efficiency was evaluated by UL-94 test method. V-0 rating was achieved at 3–5 wt% of FR loading for PC, which is better than the FR performance of RDP. The high P–OH generation tendency is responsible for the better FR performances of these compounds. The degradation path is also discussed.
Keywords: Flame-retardant; Cyclic phosphate; Aromatic phosphate; PC; ABS;
Thermal degradation studies of polyurethane/POSS nanohybrid elastomers by James P. Lewicki; Krzysztof Pielichowski; Pauline Tremblot De La Croix; Bartlomiej Janowski; Deborah Todd; John J. Liggat (1099-1105).
Reported here is the synthesis of a series of polyurethane/POSS nanohybrid elastomers, the characterisation of their thermal stability and degradation behaviour at elevated temperatures using a combination of thermogravimetric Analysis (TGA) and thermal volatilisation analysis (TVA). A series of PU elastomer systems have been formulated incorporating varying levels of 1,2-propanediol-heptaisobutyl-POSS (PHIPOSS) as a chain extender unit, replacing butane diol. The bulk thermal stability of the nanohybrid systems has been characterised using TGA. Results indicate that covalent incorporation of POSS into the PU elastomer network increases the non-oxidative thermal stability of the systems. TVA analysis of the thermal degradation of the POSS/PU hybrid elastomers have demonstrated that the hybrid systems are indeed more thermally stable when compared to the unmodified PU matrix; evolving significantly reduced levels of volatile degradation products and exhibiting a ∼30 °C increase in onset degradation temperature. Furthermore, characterisation of the distribution of degradation products from both unmodified and hybrid systems indicate that the inclusion of POSS in the PU network is directly influencing the degradation pathways of both the soft and hard-block components of the elastomers: The POSS/PU hybrid systems show reduced levels of CO, CO2, water and increased levels of THF as products of thermal degradation.
Keywords: Polyurethane; POSS; Thermal degradation; Elastomer;
Oxidation and biodegradation of polyethylene films containing pro-oxidant additives: Synergistic effects of sunlight exposure, thermal aging and fungal biodegradation by Andrea Corti; Sudhakar Muniyasamy; Manuele Vitali; Syed H. Imam; Emo Chiellini (1106-1114).
Synergistic effects of sunlight exposure, thermal aging and fungal biodegradation on the oxidation and biodegradation of linear low density poly(ethylene) PE-LLD films containing pro-oxidant were examined. To achieve oxidation and degradation, films were first exposed to the sunlight for 93 days during the summer months followed by their incubation with fungal strains previously isolated from the soil based on the ability to grow on the oxidized PE-LLD as a sole carbon source. Some films were also thermally aged at temperatures ranging between 45°C and 65 °C, either before or after fungal degradation. Films with pro-oxidant additives exhibited a higher level of oxidation as revealed by increase in their carbonyl index (COi). In addition to increase in the COi, films showed a slight increase in crystallinity and melting temperature (T m), considerably lower onset degradation temperatures, and a concomitant increase in the % weight of the residues. The level of oxidation observed in thermally aged films was directly proportional to the aging temperature. The PE-LLD films with pro-oxidant exposed to sunlight followed by thermal aging showed even higher rate and extent of oxidation when subsequently subjected to fungal biodegradation. The higher oxidation rate also correlated well with the CO2 production in the fungal biodegradation tests. Similar films oxidized and aged but not exposed to fungal biodegradation showed much less degradation. Microscopic examination showed a profuse growth and colonization of fungal mycelia on the oxidized films by one strain, while another spore-producing strain grew around the film edges. Data presented here suggest that abiotic oxidation of polymer's carbon backbone produced metabolites which supported metabolic activities in fungal cells leading to further biotically-mediated polymer degradation. Thus, a combined impact of abiotic and biotic factors promoted the oxidation/biodegradation of PE-LLD films containing pro-oxidants.
Keywords: PE-LLD; PE; Oxo-biodegradable; Films; Fungal biodegradation; Pro-oxidants;
Heat release and structural collapse of flexible polyurethane foam by R.H. Krämer; M. Zammarano; G.T. Linteris; U.W. Gedde; J.W. Gilman (1115-1122).
Flexible polyurethane foam used in upholstered furniture remains one of the major fire hazards to date. The heat release rate of burning items made of foam depends strongly on the foam's physical behavior, notably its collapse to a burning liquid that can result in a pool fire. In this contribution, the cone calorimeter was used to study the physical processes and to determine their influence on foam combustion over a range of external heat fluxes. The initial stage of foam collapse can be described as the propagation of a liquid pyrolysis layer through the foam sample. The rate of propagation of the liquid layer was found to depend strongly on the convective heat transfer from the flame, which simultaneously defined and depended on the sample shape. The effective heat of combustion during foam collapse and pool fire was matched to the heat release potential of the components of the foam formulation to deduce which are consumed. The proposed analysis can serve to clarify the mechanism of flame retardant action, as demonstrated for a commercial brominated-phosphorous compound.
Keywords: Polyurethane; Flexible; Foam; Heat release; Melt dripping; Combustion;
Post-deposition ageing reactions of plasma derived polyterpenol thin films by Kateryna Bazaka; Mohan V. Jacob (1123-1128).
Owing to the structural flexibility, uncomplicated processing and manufacturing capabilities, plasma polymers are the subject of active academic as well as industrial research. Polymer thin films prepared from non-synthetic monomers combine desirable optical and physical properties with biocompatibility and environmental sustainability. However, the ultimate expediency and implementation of such materials will dependent on the stability of these properties under varied environmental conditions. Polyterpenol thin films were manufactured at different deposition powers. Under ambient conditions, the bulk of ageing occurred within first 150 h after deposition and was attributed to oxidation and volumetric relaxation. Films observed for further 12 months showed no significant changes in thickness or refractive index. Thermal degradation behaviour indicated thermal stability increased for the films manufactured at higher RF powers. Annealing the films to 405 °C resulted in full degradation, with retention between 0.29 and 0.99%, indicating films' potential as sacrificial material.
Keywords: Ageing; Ellipsometry; Encapsulating layer; Thermal degradation;
Kinetic studies of the decomposition of flame retardant containing high-impact polystyrene by Guido Grause; Jun Ishibashi; Tomohito Kameda; Thallada Bhaskar; Toshiaki Yoshioka (1129-1137).
The thermal decomposition of flame retardant free high-impact polystyrene (HIPS) and four HIPS samples containing brominated flame retardants has been studied using TGA at different heating rates between 2.5 and 10 K min−1. Decabromodiphenyl ether (DPE) and decabromodibenzyl (DDB) were used as flame retardants, and two of the samples contained antimony trioxide (Sb2O3) synergist besides the brominated additives. The activation energies (EA ) and frequency factors (k 0) were calculated by the methods of Kissinger and Ozawa. A compensation effect was observed and used for the identification of changes in the degradation kinetics. In a third step, the kinetic model of the reaction was determined. Both Kissinger and Ozawa showed that the HIPS degraded with an EA of 200 kJ mol−1. The choice of the flame retardant had, however, little impact on the TGA plot. The addition of a flame retardant as well as the addition of Sb2O3 reduced the EA . Fire retardant free HIPS degraded mainly by power-law kinetics, while the addition of a flame retardant caused the mechanism to change to a phase-boundary controlled mechanism after a weight loss of 80 wt%.
Keywords: Decabromodibenzyl; Decabromodiphenyl ether; Antimony oxide; TGA; Kinetic triplet; Nucleation;
Halogen-free flame retardant PUF: Effect of melamine compounds on mechanical, thermal and flame retardant properties by M. Thirumal; Dipak Khastgir; G.B. Nando; Y.P. Naik; Nikhil K. Singha (1138-1145).
Water blown rigid polyurethane foam (PUF) was prepared with melamine polyphosphate (MPP) and melamine cyanurate (MC) as fire retardant (FR) additives. The effect of these additives on the properties of rigid PUF such as physico-mechanical, morphological, thermo-oxidative stability, flame retardancy and smoke density properties were studied. The mechanical and thermo-oxidative stability of PUF filled with MC was found to be better than those of MPP filled PUF. The insulation property of both MPP and MC filled PUF was improved with respect to the neat PUF. The FR properties of these filled PUF were evaluated by cone calorimeter, limiting oxygen index (LOI), smoke density, rate of burning and char residue estimation. The FR property of MPP filled PUF was better than that of the MC filled PUF.
Keywords: Rigid polyurethane foam; Melamine compounds; Mechanical; Thermal properties; Flame retardancy;