Polymer Degradation and Stability (v.94, #10)
Reactive processing of polymers: Structural characterisation of products by 1H and 13C NMR spectroscopy for glycidyl methacrylate grafting onto EPR in the absence and presence of a reactive comonomer by K. Doudin; A. Ahmad; S. Al-Malaika (1599-1614).
Grafted GMA on EPR samples were prepared in a Thermo-Haake internal mixer by free radical melt grafting reactions in the absence (conventional system; EPR–g–GMACONV) and presence of the reactive comonomer divinyl benzene, DVB (EPR–g–GMADVB). The GMA-homopolymer (poly-GMA), a major side reaction product in the conventional system, was almost completely absent in the DVB-containing system, the latter also resulted in a much higher level of GMA grafting. A comprehensive microstructure analysis of the formed poly-GMA was performed based on one-dimensional 1H and 13C NMR spectroscopy and the complete spectral assignments were supported by two-dimensional NMR techniques based on long range two and three bond order carbon–proton couplings from HMBC (Heteronuclear Multiple Bond Coherence) and that of one bond carbon–proton couplings from HSQC (Heteronuclear Single Quantum Coherence), as well as the use of Distortionless Enhancement by Polarization Transfer (DEPT) NMR spectroscopy. The unambiguous analysis of the stereochemical configuration of poly-GMA was further used to help understand the microstructures of the GMA-grafts obtained in the two different free radical melt grafting reactions, the conventional and comonomer-containing systems. In the grafted GMA, in the conventional system (EPR–g–GMACONV), the methylene protons of the GMA were found to be sensitive to tetrad configurational sequences and the results showed that 56% of the GMA sequence in the graft is in atactic configuration and 42% is in syndiotactic configuration whereas the poly-GMA was predominantly syndiotactic. The differences in the microstructures of the graft in the conventional EPR–g–GMACONV and the DVB-containing (EPR–g–GMADVB) systems is also reported
Keywords: 1H and 13C NMR; Structural characterisation; Grafted GMA; EPR;
Degradation of Technora aramid fibres in alkaline and neutral environments by Guillaume Derombise; Laëtitia Vouyovitch Van Schoors; Peter Davies (1615-1620).
Technora fibres are high performance aramid fibres which have been used in ropes and protective clothing for many years. They are also now being proposed as geotextiles for soil reinforcement. However, there is a lack of experience on the long-term behaviour of Technora fibres in an alkaline environment (lime-treated ground…). Consequently, aging studies have been performed under different conditions (deionised water, pH9 and pH11). Hydrolytic degradation has been evaluated by FTIR, viscometry, TGA, density measurements, SEM, and by tensile measurements. Some chain degradation and finish rearrangements have been highlighted, but Technora fibres retain their mechanical properties for all the conditions considered here.
Keywords: Aramids; Fibres; Technora; Hydrolysis; Long-term behaviour;
On the morphology of some irradiated ultra high molecular weight polyethylenes by Declan Barron; Colin Birkinshaw (1621-1631).
The morphology of various grades of ultra high molecular weight polyethylene (UHMWPE), prepared for use in orthopaedic implants, has been examined using differential scanning calorimetry (DSC), wide and small angle X-ray diffraction (WAX and SAX) and Raman spectroscopy. Preparation included gamma irradiation at various dose rates and mechanical annealing, and post-irradiation changes were of particular interest. The experimental results are interpreted in terms of previous proposals that UHMWPE is best considered as a three phase material, fully amorphous, all-trans amorphous and fully crystalline. The all-trans amorphous material is thought to be interfacial. The phase analysis shows that the age related increase in crystallinity occurs through conversion of all-trans material to fully crystalline, and there is little change in the total amorphous content of the polymers. SAX patterns show a change in the sharpness of the main diffraction peak and the emergence of a second diffraction peak at a higher q value, and this is considered to arise from crystallisation of all-trans amorphous material. Increasing the irradiation dose rate has a similar effect on the crystallography as does ageing the material. Mechanically annealed polymer also shows a similar trend towards a bimodal crystal population, accompanied by a reduction in interfacial material.
Keywords: Polyethylene; Crystalinity; Irradiation; Morphology;
Characterization of milled wood lignin and ethanol organosolv lignin from miscanthus by Roland El Hage; Nicolas Brosse; Laurent Chrusciel; Christian Sanchez; Poulomi Sannigrahi; Arthur Ragauskas (1632-1638).
Ethanol organosolv lignin extracted from Miscanthus × giganteus (using the following conditions: T = 190 °C, t = 60 min, sulfuric acid = 1.2% w/w, EtOH/H2O = 0.65) and milled wood lignin from Miscanthus × giganteus were subjected to a comprehensive structural characterization by 13C, 31P NMR, FTIR, UV spectroscopies and size exclusion chromatography. The results showed that Miscanthus lignin is an H/G/S type (4%, 52%, 44% respectively) with ∼0.41 β-O-4 linkage per aromatic ring and contains coumarylate linkages (0.1/Ar). It was shown that during organosolv treatment, cleavage of β-O-4 linkages and of ester bond (acetyl and coumaryl residues) was the major mechanisms of lignin breakdown but the process did not significantly change the core of the lignin structure.
Keywords: Miscanthus × giganteus; Lignin; Organosolv pre-treatment; 13C NMR; 31P NMR; UV spectroscopy;
The use of SSA fractionation to detect changes in the molecular structure of model ethylene–butene copolymers modified by peroxide crosslinking by Claudio J. Pérez; N. Villarreal; J.M. Pastor; M.D. Failla; E.M. Vallés; J.M. Carella (1639-1645).
Four model ethylene–butene copolymers of different molecular weights modified with various concentrations of peroxide were analyzed by a DSC based successive self annealing method. The original copolymers had the same intra and intermolecular homogeneous branching distribution along the linear chains with approximately 2.4% mol of ethyl branches. The copolymers with average molecular weights of 29,000, 45,000, 81,000 and 125,000 g/mol were modified with different amounts of 2,5-dimethyl-2,5-di(tert-butyl peroxy)-hexane (DBPH) as a crosslinking initiator. The molecular changes induced by the reaction with the peroxide affect the semicrystalline structure of the material. Variations in the crystal thickness distributions of the material as a consequence of the modification are related to the peroxide induced free radical reactions.
Keywords: Ethylene–butene copolymers; Organic peroxide; Crosslinking; Successive self-nucleation and annealing;
Biodegradation of poly(lactic acid) and its nanocomposites by K. Fukushima; C. Abbate; D. Tabuani; M. Gennari; G. Camino (1646-1655).
PLA nanocomposites based on organically modified montmorillonites at 5% w/w loading were prepared by melt blending using an internal mixer and then degraded in a commercial compost. The addition of nanoclays was found to increase the PLA degradation rate, especially for the highest dispersed clay in the polymer matrix. Biodegradation by microorganisms isolated from the compost showed the bacterium Bacillus licheniformis as one of the responsible for PLA biodegradation in compost. It was also found that clays can influence the polymer bacterial degradation depending on their chemical structure and affinity of the bacterium towards the clay.
Keywords: Poly(lactic acid); Nanocomposites; Biodegradation; Microbial degradation;
Thermal degradation behaviour of novel wholly para-oriented aromatic polyamide–hydrazides containing sulfone–ether linkages by Noura Yahya Al-mehbad; Nadia Ahmed Mohamed (1656-1665).
Thermal stability and degradation behaviour of a series of novel wholly para-oriented aromatic polyamide–hydrazides containing flexibilising sulfone–ether linkages in their main chains have been investigated in nitrogen and in air using differential scanning calorimetry (DSC), thermogravimetry (TG), infrared spectroscopy (IR) and elemental analysis. All of these polymers have similar structural formula except for the presence of sulfone, ether, or sulfone–ether linking groups between appropriate aromatic nuclei in their main chains. The influence of incorporation of these linkages on the thermal stability and degradation behaviour of these polymers has also been studied. The polymers were prepared by a low temperature solution polycondensation reaction of 4-amino-3-hydroxybenzhydrazide (4A3HBH) and an equimolar amount of either 4,4′-sulfonyl dibenzoyl chloride (SDBC), 4,4′-[sulfonyl bis (1,4-phenylene)dioxy] dibenzoyl chloride (SODBC), 4,4′-[sulfonyl bis (2,6-dimethyl- 1,4-phenylene)dioxy] dibenzoyl chloride (4MeSODBC), or 4,4′-(1,4-phenylenedioxy)dibenzoyl chloride (ODBC) in anhydrous N,N-dimethyl acetamide (DMAc) as a solvent at −10 °C. A related polyamide–hydrazide without the flexibilising linkages is also investigated for comparison. It was synthesized from 4A3HBH and terephthaloyl chloride (TCl) by the same synthetic route. The results clearly reveal that these polymers are characterized by high thermal stability. Their weight loss occurred in three distinctive steps. The first was small and was assigned to the evaporation of absorbed moisture. The second was appreciable and was attributed to the cyclodehydration reaction of the o-hydroxy polyamide–hydrazides into the corresponding poly (1,3,4-oxadiazolyl-benzoxazoles) by losing water. This is not a true degradation, but rather a thermo-chemical transformation reaction. The third was relatively severe and sharp, particularly in air, and corresponded to the decomposition of the resulting poly(1,3,4-oxadiazolyl-benzoxazoles). There is a slight shift of the decomposition temperature of these polymers to a lower temperature as the sulfone–ether linkages were introduced into the polymer chains. The decomposition seems to start by breaking the sulfonyl groups as confirmed from DSC measurements. The results also indicate that the incorporation of the flexibilising linkages into the polymer main chains did not seem to significantly influence the thermal stability of these polymers in comparison with that of the polymer free from these linkages.
Keywords: Polyamide–hydrazides; Sulfone–ether linkages; Differential scanning calorimetry; Thermogravimetric analysis; Poly (1,3,4-oxadiazolyl-benzoxazoles);
TGA/FTIR studies of segmented aliphatic polyurethanes and their nanocomposites prepared with commercial montmorillonites by J.M. Cervantes-Uc; J.I. Moo Espinosa; J.V. Cauich-Rodríguez; A. Ávila-Ortega; H. Vázquez-Torres; A. Marcos-Fernández; J. San Román (1666-1677).
Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (Cloisite™ Na+, Cloisite™ 15A, Cloisite™ 30B) were studied using thermogravimetric analysis coupled with Fourier Transform Infrared Spectroscopy (TGA/FTIR). The results showed that the thermal degradation of unfilled SPU and the 4, 6 and 10 wt% hand mixed nanocomposites occurred in two stages being the first due to degradation of hard segments and the second due to the degradation of soft segments. It was also found that the thermal stability of these nanocomposites was not improved by increasing nanoclay concentration except for SPU/Cloisite™ 15A nanocomposites were a 40 °C increase was observed. In a similar manner, FTIR spectra of the evolved gases obtained after the thermal degradation of these nanocomposites were qualitatively similar to the unfilled polymer except in those containing Cloisite™ 30B where isocyanate absorptions were detected. In contrast, SPU/Cloisite™ 30B nanocomposites prepared by in-situ polymerization, exhibited higher thermal stability than the corresponding hand mixed nanocomposites. In addition, these nanocomposites exhibited the presence of carbon dioxide in the evolved gases during its second degradation stage which was not observed in the hand mixed nanocomposites. In this case, it can be said that the presence of clays in the nanocomposites has a significant effect on the thermal degradation pathways.
Keywords: Thermal degradation; TGA/FTIR; Polyurethane/montmorillonite nanocomposites; Thermal decomposition; Segmented polyurethanes/Closites composites;
Catalytic cracking of polyethylene waste in horizontal tube reactor by A. Angyal; N. Miskolczi; L. Bartha; I. Valkai (1678-1683).
In this study catalytic and thermal cracking of polyethylene waste were investigated in continued tube reactor system. HZSM-5 and equilibrium FCC type catalysts were tested. Both the resistance to deactivation and the regeneration process of the catalyst were studied. Reaction temperature of 545 °C and residence time of 20 min were used during the cracking treatment. The reaction products were analyzed and the textural properties of catalysts were also determined. It was found that after the first reaction run the FCC catalyst lost 75% of its cracking activity, in case of HZSM-5 the rate of deactivation was higher. The cracking activity of catalyst could be improved by regeneration process with only 2–3% compared to the coked catalyst. The isomerisation effect of the catalysts was also observed. The effect of coked FCC catalyst could be improved by the regeneration process with 50% in case of HZSM-5 it was only 25%.
Keywords: Plastic waste; Catalytic cracking; Deactivation; Regeneration;
Collagen stabilization and modification using a polyepoxide, triglycidyl isocyanurate by Y. Di; R.J. Heath (1684-1692).
This paper reports a study on the crosslinking behaviour of dermal collagen with the polyepoxide triglycidyl isocyanurate (TEPIC), which is thought to introduce a specific stabilization effect into a collagen matrix. TEPIC shows a higher reactivity towards collagen compared to glycerol triglycidyl ether, a water-soluble epoxide with the same tri-functionality but having an aliphatic backbone in its molecular structure, and one of the most commonly used epoxide monomers reported in the literature. Significant stabilization of the collagen matrix treated with TEPIC has been shown in our work, based on the examination of hydrothermal properties, thermal degradation and enzyme degradation properties, amino acid analysis and measurement of mechanical properties. Collagen's dimensional stability was also found to be improved, from tensile testing and fibre morphology observations (here by scanning electron microscopy). The overall stabilization effect of TEPIC is comparable or better than the conventionally used crosslinker, glutaraldehyde, and so implies that a stable three-dimensional, covalent network is formed by the TEPIC within the collagen supermolecule, instead of the two-dimensional crosslinked bridging systems in the case of glutaraldehyde. These results also suggest that the additional stabilization by TEPIC may relate to its triazine nucleus, which introduces a more rigid conformation into the collagen polypeptide chains. In addition, the treated collagen matrix has been found to have increased adsorption ability for anionic dyes. This study has shown that TEPIC can be considered as one of the more effective aldehyde alternatives, which could have a potential significance in leather and textile industrial applications.
Keywords: Collagen stabilisation; Epoxy crosslinking; Aldehyde alternatives; Protein fibre modification;
Development of a DOPO-containing benzoxazine and its high-performance flame retardant copolybenzoxazines by M. Spontón; G. Lligadas; J.C. Ronda; M. Galià; V. Cádiz (1693-1699).
A DOPO-containing benzoxazine, which could not be prepared by the traditional approaches, was successfully prepared from phenol, aniline and DOPO by a three-step procedure. The first step is the condensation of 2-hydroxybenzaldehyde with aniline, forming an intermediate imine. The second step is the addition of DOPO to the imine resulting a secondary amine. The third step is the ring closure condensation leading to DOPO-containing benzoxazine. All these structures were confirmed by 1D and 2D NMR spectra. The curing of mixtures of DOPO-containing benzoxazine and benzoxazine of bisphenol A has been studied. In the samples the molar ratio of benzoxazine monomers was varied to achieve different phosphorus content. The phosphorus-containing polybenzoxazines have been characterized by dynamic mechanical thermal analysis and thermogravimetric analysis. Limiting oxygen index values indicates good flame retardant properties.
Keywords: Benzoxazine; Phosphorus-containing polymer; Flame retardant; Thermal stability; DOPO;
Synthesis and biodegradability of l-lactide/glycidol copolymers by A. Petchsuk; A. Nakayama; S. Aiba (1700-1706).
Random copolymers of l-lactide (LA) and glycidol (G) were systematically synthesized via ring-opening polymerization (ROP). It was found that thermal properties of copolymers were strongly dependent on polymer composition which was successively controllable by changing comonomer feed ratio. The effects of polymerization conditions as well as polymer compositions on polymer properties were thoroughly studied. The biodegradation and enzymatic hydrolysis of copolymers were also examined. It was found that the biodegradability by an activated sludge of L/G copolymers was strongly affected by both polymer composition and crystallinity whereas their hydrolyzability by proteinase K was merely influenced by polymer composition.
Keywords: Lactide; Glycidol; Copolymer; Biodegradable polymers; Enzymatic degradation;
Degradation of perfluorinated sulfonic acid films: An in-situ infrared spectro-electrochemical study by Xiang Fang; Pei Kang Shen; Shuqin Song; Vaios Stergiopoulos; Panagiotis Tsiakaras (1707-1713).
The in-situ Fourier transform infrared (FTIR) spectro-electrochemical method was used to evaluate the degradation mechanism of perfluorinated sulfonic acid (PFSA) polymer for the first time. The effect of H2O2 concentration in Fenton's reagent on the PFSA film degradation was studied. It was found that the effect of the H2O2 concentration on the chemical degradation of the PFSA film was limited, whereas, the electrochemical degradation was obviously enhanced at higher H2O2 concentrations. The chemical degradation of PFSA film in Fenton's reagent was similar to that in pure H2O2 solution. However, the results indicated that the electrode potential is the dominating factor affecting the degradation of the PFSA film. It is clear that the electrochemical degradation of PFSA film in Fenton's reagent is more serious than that in pure H2O2 solution. Moreover, it is indicated that the main cause of the membrane degradation is the instability of the backbone of the polymer chain under electrochemical conditions and secondarily the loss of sulfuric groups in the side-chains. It is concluded that the in-situ FTIR spectro-electrochemical method could be used to evaluate more objectively the degradation of the polymer film.
Keywords: Polymer electrolyte membrane fuel cells; Perfluorinated sulfonic acid; In-situ Fourier transform infrared spectro-electrochemistry; Membrane degradation;
XPS and XAES of polyethylenes aided by line shape analysis: The effect of electron irradiation by B. Lesiak; J. Zemek; J. Houdkova; P. Jiricek; A. Jóźwik (1714-1721).
X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) have been used to investigate different polyethylene surfaces, i.e. low density polyethylene (PELD), high density polyethylene (PEHD) and polyethylene of ultra high molecular weight (PEUHMW). The ratio of Csp2/sp3 was evaluated from (i) fitting of XPS C 1s spectra, (ii) the width of XAES C KLL spectra (parameter D) and (iii) line shape analysis by the pattern recognition (PR) method using the fuzzy k-nearest neighbors (fkNN) rule. The proposed approaches investigate: (i) the differences between various polyethylene surfaces, (ii) their surface changes and degradation due to electron irradiation under various doses and (iii) their stability under electron beam irradiation.The results of proposed approaches, i.e. C 1s fitting, C KLL width evaluation and PR line shape analysis applied to C 1s and C KLL transitions, are qualitatively consistent. The unirradiated polyethylenes indicate nearly Csp3 hybridizations. Under an electron dose a rapid decrease of Csp3 is observed, starting at a dose of 100 Cm−2. The quantitative differences observed between results obtained from analyses using the C KLL and C 1s spectra, can be explained with a smaller average information depth of C KLL transition. However, quantitative discrepancies between results of various approaches using the same electron transition, i.e. C KLL or C 1s, are smaller. The surface degradation due to X-ray irradiation was negligible in comparison to electron beam irradiation. The PR method was efficient in identifying the polyethylene surfaces under various electron doses. The largest stability under an electron beam is exhibited by the PEUHMW.
Keywords: Polyethylene; XPS; XAES; Line shape analysis; C sp2/sp3 hybridization; Electron beam degradation;
Effect of multiple extrusion on molecular structure of polypropylene impact copolymer by Soňa Hermanová; Jiří Tocháček; Josef Jančář; Jan Kalfus (1722-1727).
Neat and multiple processed polypropylene impact-copolymer (ICPP) were fractionated using series of hydrocarbon solvents with increasing solvent power. The analyses of the fractions obtained in successive extractions showed significant decrease in weight-average molecular weight (Mw) and narrowing the molecular weight distribution (MWD) of investigated samples after extrusions. Although the changes due to thermooxidation were observed in all phases of the system, the most intensive degradation was found in the prevailing PP homopolymer phase.
Keywords: Polypropylene impact-copolymer; Thermooxidation degradation; Fractionation; Extrusion;
Influence of POSS structure on the fire retardant properties of epoxy hybrid networks by Elsa Franchini; Jocelyne Galy; Jean-François Gérard; Daniela Tabuani; Andrea Medici (1728-1736).
Monofunctional Polyhedral Oligomeric Silsesquioxanes (POSS), differing in chemical structure, were introduced into an epoxy-amine formulation in order to obtain hybrid organic/inorganic epoxy networks. The process developed allows the POSS to be either covalently bonded to the network and organized in small amorphous domains, or completely dispersed in larger crystalline domains. Morphology, thermal and fire retardant properties were studied through electron microscopy, DSC, TGA, cone calorimeter experiments and UL94 tests. It was demonstrated that POSS nanoclusters induced an effective fire retardant effect, which was controlled by several factors. It was shown that POSS bearing phenyl ligands were far more effective than POSS with isobutyl ligands, and that the presence of a chemical linkage between the phenyl-based POSS clusters and the matrix favoured the dispersion of the nanoclusters, resulting in enhanced fire retardancy. The fire retardant effect was only slightly enhanced by increasing the amount of POSS nanoclusters.
Keywords: Polyhedral oligomeric silsesquioxane; Epoxy networks; Degradation; Cone calorimeter; TGA;
Influence of mechanical activation on the graft copolymerization of sugarcane bagasse and acrylic acid by Zuqiang Huang; Xingtang Liang; Huayu Hu; Li Gao; Yongjun Chen; Zhangfa Tong (1737-1745).
Sugarcane bagasse (SCB) was mechanically activated by home-made high efficiency stirring mill. Graft copolymers (SCB–g–PAA) of SCB with different mechanical activation times (t M) and acrylic acid (AA) have been synthesized by using ammonium persulfate/sodium sulfite redox pair as an initiator in aqueous solution. The effect of t M on the graft co-polymerization was evaluated by grafting ratio (GR) and grafting efficiency (GE). In addition, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to characterize the granular morphology, functional groups, crystal structure and thermal properties of the product. It was found that the mechanical activation could split fiber bundles and decrease significantly the crystallinity. SCB degraded after the mechanical activation (MA) and its thermal stability declined. Moreover, the graft copolymerization was enhanced obviously by MA processing. And GR and GE increased with the increase of activation time.
Keywords: Sugarcane bagasse; Mechanical activation; Graft copolymerization; Influence; Acrylic acid;
Novel fluorinated polyimides derived from 9,9-bis(4-amino-3,5-difluorophenyl)fluorene and aromatic dianhydrides by Chenyi Wang; Xiaoyan Zhao; Guang Li; Jianming Jiang (1746-1753).
Novel fluorinated polyimides (PIs) were prepared from 9,9-bis(4-amino-3,5-difluorophenyl)fluorene with three aromatic dianhydrides via a one-step high-temperature polycondensation procedure. These obtained PIs showed excellent solubility and could be readily soluble in a variety of organic solvents such as NMP, DMAc, DMF, CHCl3, CH2Cl2 and THF. All the PIs could afford flexible and strong films with low dielectric constants (2.62–2.79 at 1 MHz) and low moisture absorptions (0.18–0.41%). Thin films of these PIs exhibited high optical transparency and light color, with the cutoff wavelength at 341–355 nm and transmittance higher than 80% at 450 nm. Meanwhile, these PIs possessed eminent thermal stability, with decomposition temperatures (T d) above 570 °C in both air and nitrogen atmospheres and glass transition temperatures (T g) beyond 376 °C. Moreover, these fluorinated PI films showed low surface free energy and hydro-oleophobic character. The contact angles on the films for water and glycerol were in the range of 102.3–107.9° and 94.0–100.3°, respectively. In comparison with the analogous PI non-containing fluorine group, these fluorinated PIs showed better solubility, higher optical transparency, lower dielectric constants and lower surface free energy.
Keywords: Fluorinated polyimides; Solubility; Dielectric constant; Optical transparency;
Thermal stability and thermokinetics studies on silicone ceramer coatings: Part 1-inert atmosphere parameters by Atul Tiwari; L.H. Hihara (1754-1771).
Two silicone ceramer coatings were synthesized and studied according to their thermal stability, using Fourier Transformation Infra-red (FTIR) spectroscopy. Differential thermal analysis was conducted on a liquid precursor to the coatings to study the phase transformations occurring in the material as the temperature was altered. The kinetics of the thermal degradation of coatings was analyzed; and the corresponding thermokinetics parameters were determined using Friedman's method, the Flynn-Wall-Ozawa method and the American standard test method E698. A thermogravimetric analysis was conducted on the liquid precursors as well as on the solidified coatings at various heating rates. The gaseous products that were obtained as a result of pyrolysis were analyzed employing an attached FTIR spectrometer.
Keywords: Silicone coatings; FTIR spectroscopy; Thermokinetics; Thermogravimetry; Differential thermal analysis;
Effects of stress ratio on fatigue crack growth of thermoset epoxy resin by C. Kanchanomai; A. Thammaruechuc (1772-1778).
The influences of stress ratio (R) on fatigue crack growth (FCG) of thermoset epoxy resin with polyamine hardener were investigated. The FCG growth rates (da/dN) have been correlated by the linear-elastic fracture mechanics parameters (ΔK and K max), and nonlinear-elastic fracture mechanics parameter (ΔJ). The effects of R on FCG were observed when the ΔK and ΔJ were used as fracture mechanics parameters for FCG. However, the K max successfully characterized FCG under cyclic-dependent condition (FCGs at R = 0.1 and 0.4); but it failed to characterize the FCG under time-dependent condition (FCG at R = 0.7). As a time-dependent fracture mechanics parameter, C* was applied to correlate the time-dependent FCG rate (da/dt). A reasonable agreement was obtained between time-dependent FCG (R = 0.7) and creep crack growth (CCG) results.
Keywords: Epoxy resin; Fatigue crack growth; Cyclic dependence; Time dependence; Creep effect;
Direct ESR detection and spin trapping of radicals generated by reaction of oxygen radicals with sulfonated poly(ether ether ketone) (SPEEK) membranes by Mariana Pinteala; Shulamith Schlick (1779-1787).
The stability of membranes under the strong oxidizing conditions in fuel cells is one of the major challenges in the development of fuel cells based on proton exchange membranes (PEMs). This study is centered on the determination of the susceptibility to degradation of SPEEK membranes exposed to •OH radicals, using both direct ESR and spin trapping with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). In order to achieve a complete picture on SPEEK degradation, two types of experiments were performed: 1. UV irradiation at 77 K of SPEEK membranes swollen by aqueous solutions of H2O2; 2. UV irradiation of SPEEK membranes swollen by aqueous solutions of H2O2 in the presence of DMPO as a spin trap. UV irradiation without oxygen of SPEEK at 77 K in acid or basic form in the presence of H2O2/H2O produced phenoxyl radicals as the predominant radicals detected by direct ESR or spin trapping methods. At pH 4, the oxygen radicals produced phenyl radicals as the predominant species detected by spin trapping methods. The hydroperoxyl radical, as DMPO/OOH adduct, was detected only when the DMPO/OH adduct was absent. The appearance of phenyl and phenoxyl radicals provides the evidence that •OH radicals react with the aromatic ring of SPEEK or leading to the scission of its ether bridge.
Keywords: Sulfonated poly(ether ether ketone) (SPEEK); Electron spin resonance (ESR); 5,5-Dimethyl-1-pyrroline-1-oxide (DMPO); Spin trapping; Free radicals;
Thermal degradation mechanism of dodecylbenzene sulfonic acid- hydrochloric acid co-doped polyaniline by Ting Chen; Chaofang Dong; Xiaogang Li; Jin Gao (1788-1794).
Co-doped polyaniline (PANI) was synthesized in microemulsion by hydrochloric acid (HCl) and dodecylbenzene sulfonate (SDBS) then thermal treated in air at 160 and 200 °C for 0.5 h, respectively. The changes of structure, thermal stability, micromorphology and electrical conductivity after thermal treatment were studied by Fourier transformed infrared (FT-IR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM) and four-probe technique. It was found that the conductivity of PANI decreased about 50% after thermal treated at 160 °C, and droped by 2 orders of magnitude at 200 °C. This may be explained by that only a fraction of total mass of HCl losses during thermal treatment at 160 °C, but after heating at 200 °C, the dedoping of dodecylbenzene sulfonic acid (DBSA) along with cross-linking, chain scission and oxygen incorporation in a form of carbonyl groups take place, resulting in destruction of crystal structure, decrease of the emeraldine sequence, lower thermal stability and heterogeneous micromorphology.
Keywords: Polyaniline; Conductivity; Degradation mechanism; Thermal treatment;
Depolymerization of polysilicic acid by tiron by Shuqin Bai; Yoshihiro Okaue; Takushi Yokoyama (1795-1799).
As a preliminary experiment for the development of an effective silica scale inhibitor at geothermal power plants, the effect of tiron, a ligand to monosilicic acid, on the polymerization of silicic acid was investigated by gel chromatographic method. The experiments were carried out at Si concentration of 400 ppm (14 mM) and at pH 8 where are a similar condition to geothermal water. The tiron concentration was varied (0–50 mM). At 30 mM of tiron, the polymerization of silicic acid occurred rapidly within first 1 h in spite of the presence of tiron, however, polysilicic acids were depolymerized by tiron. The depolymerization mechanism of polysilicic acids was discussed based on zeta potentials for silica gel particles in the absence and presence of tiron.
Keywords: Polymerization of silicic acid; Polysilicic acid; Depolymerization; Tiron; Complexation; Gel chromatography;
Preparation and biodegradation of electrospun PLLA/keratin nonwoven fibrous membrane by Jiashen Li; Yi Li; Lin Li; Arthur F.T. Mak; Frank Ko; Ling Qin (1800-1807).
As a kind of natural protein, wool keratin was used to improve the cell affinity of poly(l-lactic acid) (PLLA). After small keratin particles were prepared from keratin solution by spray-drying process, they were blended with PLLA solution. PLLA/keratin nonwoven fibrous membrane was produced by electrospinning the blend solutions. The release rate of keratin from the composite membrane was detected by Fourier transform infrared (FTIR) after PLLA/keratin membranes were degraded in PBS up to 4 weeks. The chemical compositions of the PLLA/keratin surface were examined by X-ray photoelectron spectroscope. Although more than half of the keratin was removed from PLLA/keratin membrane during the first few hours of degradation, some keratin particles were still embedded in the PLLA fibers. Osteoblast cells were used to evaluate the cellular behaviors of the composite membrane. After 7 days culturing, more cells were observed on PLLA/keratin membranes than on pure PLLA membranes. MTT assay and alkaline phosphatase (ALP) activity results suggested that keratin could improve the interactions between osteoblast cells and the polymeric membranes.
Keywords: Keratin particles; Poly(lactic acid); Electrospinning; Fibrous membrane;
Photostabilizing of bisphenol A polycarbonate by using UV-absorbers and self protective block copolymers based on resorcinol polyarylate blocks by Marjolein Diepens; Pieter Gijsman (1808-1813).
Bisphenol A polycarbonate degrades due to sunlight, humidity and oxygen. In this study two possible techniques to stabilize the polymer were compared, i.e. blending of UV-absorbers (UVAs) into the polymer or using block copolymers based on resorcinol polyarylates. Combination of different analysis techniques shows that the protection by UVAs is not as good as by the resorcinol polyarylate block copolymers. The block copolymer rearranges itself through a photo-Fries rearrangement within hours into a UV-absorbing top layer. Two different block compositions were studied, and the copolymer with the highest concentration of resorcinol polyarylate groups shows the best protection.
Keywords: Bisphenol A polycarbonate; Resorcinol polyarylate; Hydroxybenzophenone; Stabilisation; Self protection;
An investigation of the accelerated thermal degradation of different epoxy resin composites using X-ray microcomputed tomography and optical coherence tomography by Firas Awaja; Benedicta Arhatari; Karin Wiesauer; Elisabeth Leiss; David Stifter (1814-1824).
Epoxy resin composites reinforced with hollow glass microspheres, microlight microspheres, 3D parabeam glass, and E-Glass individually were subjected to accelerated thermal degradation conditions. X-ray microcomputed tomography (XμCT) was used to evaluate density changes, reinforcement filler damage, homogeneity, cracks and microcracks in the bulk of the different epoxy resin composites. XμCT 3D images, 2D reconstructed images and voids calculations revealed microspheres damage, filler distributions and showed cracks in all composites with different shapes and volume in response to the thermal degradation conditions. In addition, expansion of air bubbles/voids was observed and recorded in the microsphere and microlight epoxy composite samples. In a complementary way, optical coherence tomography (OCT) was used as a novel optical characterisation technique to study structural changes of the surface and near-surface regions of the composites, uncovering signs of surface shrinkage caused by the thermal treatment. Thus, combining XμCT and OCT proved useful in examining epoxy resin composites' structure, filler–resin interface and surface characteristics.
Keywords: Syntactic foam; X-ray computed tomography; Epoxy resin; Optical coherence tomography; Thermal damage;
Thermo-oxidative processes in biodegradable poly(butylene succinate) by Paola Rizzarelli; Sabrina Carroccio (1825-1838).
Aliphatic polyesters have acquired significant interest as environmentally friendly thermoplastics for a wide range of applications, and understanding their degradation behaviour has relevance both for processing and end uses. We have investigated the thermal and thermo-oxidative degradation processes occurring in synthetic and commercial poly(butylene succinate) (PBSu). Thermal oxidation was performed in atmospheric air using extremely thin polymer films at 170 °C for up to 6 h. The oxidized compounds were analyzed by size exclusion chromatography (SEC), NMR spectroscopy, and Mass Spectrometry (MALDI-TOF MS). A measurable reduction of the molar mass of the polyesters was soon apparent, promoting the formation of PBSu oligomers with different end groups. MALDI mass spectrometry combined with the use of extremely thin polyester films provided a virtual magnifying glass to obtain exhaustive information on the structure of the oxidation products. An α-H abstraction mechanism has been unambiguously ascertained to be the primary step in PBSu oxidation. The oxidized polymer chains originating from the decomposition of the hydroperoxide intermediate by radical rearrangement reactions had not been revealed before. The latter products subsequently undergo chain scission processes, which can be accurately traced from the chemical species identified in our work. Thermal degradation experiments were also performed under nitrogen at 240–260 °C. The new species identified in the MALDI spectra support a decomposition pathway taking place through a β-hydrogen-transfer mechanism, followed by the production of succinic anhydride from succinic acid end molecules via a back-biting process.
Keywords: Biodegradable polymers; Thermal oxidation; Thermal degradation; MALDI mass spectrometry;
Mechanistic investigation, kinetic modeling and analysis parameters of poly(3-hexylthiophene) degradation to fullerenes by P. Karthik Reddy; Prasanta J. Goutam; Dilip K. Singh; Aloke K. Ghoshal; Parameswar K. Iyer (1839-1848).
Thermal degradation of Poly (3-hexylthiopene) (P3HT) was studied under nitrogen environment. Kinetic parameters of thermal degradation were determined using Vyazovkin model free method and model fitting method. Vyazovkin model free kinetic analysis is carried out to understand the variation of activation energy (E α) required for degradation of polymer with conversion (α). Various reaction models have been tested for probable reaction mechanism using hybrid genetic algorithm (HGA). Diffusion model and nucleation & growth with n = 2/3 has prominent role in thermal decomposition of P3HT. A plausible degradation route is proposed based on the experimental details acquired from gas chromatography (GC), Raman spectroscopy, FTIR spectroscopy, powder X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Degradation of P3HT starts at around 195 °C with release of lighter units like CS. Further increase in the temperature results in detachment of the hexyl chain from P3HT and the residue obtained at 1050 °C contains fullerenes mixed with amorphous carbon.
Keywords: Poly (3-hexylthiophene); Thermal degradation; Fullerene; Model free kinetic analysis; Model fitting method; Kinetic parameters;
Poly (ethylene terephthalate) thermo-mechanical and thermo-oxidative degradation mechanisms by Wanderson Romão; Marcos F. Franco; Yuri E. Corilo; Marcos N. Eberlin; Márcia A.S. Spinacé; Marco-A. De Paoli (1849-1859).
1H NMR and MALDI-TOF MS measurements were used to study the thermo-mechanical and thermo-oxidative degradation mechanisms of bottle-grade PET (btg-PET). In the thermo-oxidative degradation, the concentration of low molar mass compounds increased with time and the main products were cyclic and linear di-acid oligomers. In the thermo-mechanical degradation, the main-chain scission reactions affect the stability of the cyclic oligomers. One of the most important bottle-grade PET co-monomers is diethylene glycol (DEG), which is a “reactive site” in the thermal degradation of btg-PET. The DEG co-monomer was shown to be the precursor to colour changes in btg-PET, owing to the attack by molecular oxygen on the methylenic protons adjacent to the ether oxygen atoms of DEG. This behaviour was observed in the thermo-oxidative degradation process in which the degradation of DEG causes the release of hydroxyl radicals in the polymeric matrix, thereby producing mono- and di-hydroxyl substituted species. This was also observed in the thermo-mechanical degradation process.
Keywords: Poly(ethylene terephthalate); Thermo-oxidative degradation; Thermo-mechanical degradation; Diethylene glycol; 1H NMR; MALDI-TOF MS;
Synthesis and kinetics of non-isothermal degradation of amide grafted high density polyethylene by M.A. Semsarzadeh; V. Poursorkhabi (1860-1866).
The grafted structures from the reaction of high density polyethylene with maleic anhydride (PEgMA) was reacted further with 1,4-diaminobutane to synthesize amide grafted polyethylenes. Grafted amic-acids were partially converted to imide groups during the reaction. Grafted products were identified by titration, elemental analysis and FTIR. DSC analysis indicated that Cp for amide grafted product increased about 47% with respect to PEgMA, its crystallinity increased 50% with respect to PE and 18% with respect to PEgMA. Analysis of kinetics of degradation was performed by thermogravimetry; degradation kinetic parameters of these amide grafted products have not been evaluated or reported. The degradation of Amide grafted polyethylene is similar to HDPE but with smaller activation energy indicating that it is the most stable product. Fn and An kinetic models seemed more suitable than diffusion models.
Keywords: Polyethylene grafted amide; Maleic anhydride; Isoconversional methods; Stability; Thermal properties; Kinetics of thermal degradation;
High-molar-mass hyaluronan degradation by Weissberger's system: Pro- and anti-oxidative effects of some thiol compounds by Eva Hrabárová; Katarína Valachová; Jozef Rychlý; Peter Rapta; Vlasta Sasinková; Marta Malíková; Ladislav Šoltés (1867-1875).
Pro- and anti-oxidative effects of two thiol compounds, d-penicillamine and reduced l-glutathione, on the kinetics of degradation of high-molar-mass hyaluronan samples were monitored via rotational viscometry. The degradation was induced under aerobic condition by the so-called Weissberger′s system [ascorbate plus Cu(II)]. Electron paramagnetic resonance spectroscopy was used to confirm the presence of free radicals generated during the biopolymer degradation. Infrared spectroscopy and non-isothermal chemiluminometry were used to characterize the biopolymers after processing.
Keywords: Hyaluronan degradation; d-Penicillamine; l-Glutathione; EPR; Rotational viscometry; Chemiluminometry;
Mechanical properties and biodegradability of poly-ɛ-caprolactone/soy protein isolate blends compatibilized by coconut oil by Seung In Hong; Won Young Choi; Seung Yong Cho; Se H. Jung; Boo Y. Shin; Hyun Jin Park (1876-1881).
This study was performed for the mechanical properties, adhesion properties and biodegradability depending on the coconut oil content based on poly-ɛ-caprolactone (PCL):soy protein isolate (SPI) blends. Coconut oil was capable of forming the PCL:SPI blend. Tensile strength (TS) of the blend decreased and elongation at break (EAB) increased when the concentration of coconut oil increased. Lap shear strength of all samples was observed in the values of the general formulated hot-melt but in particularly, high adhesive strength was shown at 20 mL of coconut oil. The improvement of surface hydrophilicity and biodegradation resulted from the addition of SPI rather than coconut oil. Consequently, coconut oil acted as a plasticizer and compatibilizer although it did not enhance in biodegradation and surface hydrophilicity.
Keywords: Hot-melt adhesive; Biodegradability; Soy protein isolate; Poly-ɛ-caprolactone; Coconut oil;
Pyrolysis behaviour of titanium dioxide–poly(vinyl pyrrolidone) composite materials by Rohan L. Holmes; Jonathan A. Campbell; Robert P. Burford; Inna Karatchevtseva (1882-1889).
Inorganic–organic hybrid materials are studied due to the unique properties they exhibit. As these materials become more widely applied, particularly as precursor materials for forming inorganic materials, it is essential that the pyrolysis behaviour is understood. Transparent yellow hybrid materials consisting of titanium dioxide and poly(vinyl pyrrolidone) were prepared using sol–gel processing techniques. The hybrids maintained their transparency up to the highest achieved inorganic loading of 57 wt.%. These materials were characterised using thermogravimetric analysis in which the organic component was pyrolysed. The resultant chars were then investigated using optical microscopy, x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The inorganic loading had an effect on char formation, with higher loadings leading to the formation of pyrolysis intermediates which were less apparent in samples of lower inorganic content. The pyrolysis intermediates were found to be carbon-rich.
Keywords: Pyrolysis; Titanium dioxide; Hybrid; Nanocomposite; Microstructure;
Porosity development in chars from thermal decomposition of poly(p-phenylene terephthalamide) by Alberto Castro-Muñiz; Amelia Martínez-Alonso; Juan M.D. Tascón (1890-1894).
The main objective of this work was to investigate the development of porosity in solid residues from the thermal decomposition of the polymer, poly(p-phenylene terephthalamide) (PPTA). PPTA chars were prepared at different temperatures and characterized by X-ray diffraction and physical adsorption of CO2 at 0 °C. The carbonization temperatures were selected on the basis of thermogravimetric analysis results. The effect of introducing an isothermal treatment at 500 °C on the characteristics of the resulting chars was also studied. It was found that this pre-treatment lowers the decomposition temperature of PPTA and yields a somewhat less ordered material than in the case of pyrolysis under a constant heating rate. The micropore volume increases with increasing heat treatment temperature for both series of samples. The mean micropore size decreases for the two series of chars until the 700–800 °C interval; above these temperatures, this evolution is reversed. The micropore volume of the samples submitted to the isothermal treatment is higher than when PPTA is treated under a constant heating rate. Likewise, the pore size distribution is more heterogeneous when the intermediate isothermal treatment at 500 °C is introduced during PPTA pyrolysis. Some differences between porosity development in chars from PPTA and other high thermal stability polymers were explained on the basis of different mechanistic features in polymer pyrolysis.
Keywords: Poly(p-phenylene terephthalamide); Chars; Porosity; Adsorption;
Preparation of chitooligosaccharides by the enzymatic hydrolysis of chitosan by Yu Xie; Jingang Hu; Ya Wei; Xiaowei Hong (1895-1899).
Chitosan of 80% degree of deacetylation was depolymerised by the cellulase of Aspergillus niger to prepare chitooligosaccharides. MALDI-TOF MS analysis of the enzymatic hydrolyzates indicated that the products were mainly chitooligosaccharides with degree of polymerization (DP) in the 3–11 range. By fractionation of the hydrolyzates with acetone–water, products of DP below 6 and DP above 6 were separated in good yield.
Keywords: Chitoogliosaccharides; Cellulase; Hydrolysis; Chitosan;