Polymer Degradation and Stability (v.96, #10)

Calendar (I).

A two-stage reaction process was used to convert polypropylene (PP) into multi-walled carbon nanotubes (MWCNTs) and hydrogen-rich gas. The proposed process consisted of two stages: catalytic pyrolysis of PP over HZSM-5 zeolite in a screw kiln reactor and the subsequent catalytic decomposition of pyrolysis gases over a nickel catalysts in a moving-bed reactor for producing MWCNTs and hydrogen. The resultant gas mainly consisted of hydrogen and methane. SEM and TEM images revealed that carbon products in the moving-bed reactor were in the form of MWCNTs. XRD and TGA characterization indicated that high decomposition temperature resulted in the formation of more highly crystalline nanotubes. The influence of pyrolysis temperature (550–750 °C) and decomposition temperature (500–800 °C) on the performances of the two-stage reaction system were investigated. The MWCNT yield and hydrogen concentration increased with an increase in the decomposition temperature and reached a maximum at 700 °C. With increasing pyrolysis temperature the yield of pyrolysis gas increased while the liquid yield decreased. The yield of MWCNTs in the moving-bed reactor was determined by both the quantity and quality of the pyrolysis gas.
Keywords: Carbon nanotubes; Catalysis; Hydrogen; Polypropylene; Pyrolysis;

One symmetric diamine (4) and two symmetric phenols (5) and (6) were synthesized as phosphorus-containing flame retardants. The synthesis comprised a two-step procedure: the condensation of p-phenylenediamine with benzaldehyde, 4-hydroxybenzaldehyde and 2-hydroxybenzaldehyde respectively, followed by the addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the imine linkage. The structures of (4)–(6) were characterized by FTIR, NMR and mass spectra. (4)–(6) served as co-curing agents of diaminodiphenylmethane for epoxy resins, and epoxy thermosets exhibited excellent flame retardancy, moderate changes in glass transition temperature (T g) and thermal stability. When the phosphorus content reached 1.0 wt.%, the epoxy resin system met the UL-94 V-0 classification and the limiting oxygen index (LOI) reached more than 35.6, probably because of the nitrogen–phosphorus synergistic effect.
Keywords: Epoxy resin; Flame retardancy; Thermoset; Phosphorus;

Flame retardant mixtures of carbon nanotubes (CNTs) and intumescent flame retardant (IFR) were embedded in polypropylene (PP) to investigate what will happen if the additives exhibit two different flame retardation mechanisms. TEM tests showed that CNTs dispersed homogenously in PP matrix without any visible agglomeration. The effects of CNTs on thermal stability and flammability of PP were investigated by thermogravimetry (TG) and cone calorimetry tests, respectively. Results indicated that the introduction of CNTs only enhanced thermal stability of materials in a certain temperature range, but caused a severe deterioration of flame retardancy due to the interaction of the network structure and the intumescent carbonaceous char. Furthermore, conditions for an intumescent flame retardation system to behave with high efficiency were also discussed by a secondary combustion test.
Keywords: Flame retardant; Carbon nanotubes; Intumescent flame retardant; PP;

The integration of the environmental problem in the design of industrial products leads us to incorporate vegetal fibres and recycled polymers into composite materials. The aim of this work is to study the behaviour and the environmental interest of a recycled PP/hemp fibre after several injection cycles. The mechanical and rheological behaviour of recycled PP/hemp composite was first studied by using tensile, dynamical mechanic analysis and rheological measurements. Then, to better understand the influence of the recycling, a morphology study was carried out on composites by using optical and electron microscopy. Finally, we investigated the environmental advantages of our composite thanks to a simplified environmental assessment. Our results highlighted the environmental interest of using a recycled matrix to prepare composites reinforced with vegetal fibres and the interesting properties of this material after recycling.
Keywords: Polypropylene; Hemp fibre; Recycling; Environmental analysis; Mechanical properties;

Photodegradation of isotactic poly(1-butene): Multiscale characterization by Lubomír Beníček; Lenka Chvátalová; Martin Obadal; Roman Čermák; Vincent Verney; Sophie Commereuc (1740-1744).
The effect of photodegradation in isotactic poly(1-butene) (PB-1) have been investigated using rheology, differential scanning calorimetry and infrared spectroscopy. Two commercially available grades of PB-1 with different average molecular weight were chosen. Specimens prepared by compression moulding were UV irradiated in the interval from 0 to 70 h. UV-induced changes in molecular structure have been followed by evolution of rheological properties, thermal properties and degradation by-products. Thermal analysis showed significant changes in crystallization behaviour influencing morphology and resulting thermal properties. Moreover it has been confirmed that the degradation significantly retards the phase transformation. Rheological measurement has been found as an effective method for determination of early stages of photodegradation of PB-1.
Keywords: Isotactic poly(1-butene); Rheology; Infrared spectroscopy; Thermal behaviour; Photodegradation;

Water-catalyzed racemisation of lactide by Lidong Feng; Xuesi Chen; Bin Sun; Xinchao Bian; Zhiming Chen (1745-1750).
The reactions of lactide racemisation, hydrolysis, or alcoholysis in the presence of water or anhydrous alcohol have been investigated separately. A small amount of water leads to lactide racemisation, hydrolysis, or both. Water acts as a catalyst for the racemisation of lactide. The racemisation mechanism has been studied by substituting D2O instead of H2O and measuring the substituent by gas chromatography–mass spectrometry (GC–MS). The experimental results show that the hydrogen atom on a chiral carbon of lactide is substituted by a 2H atom of D2O. The reaction of lactide with water is in good agreement with the mechanism of addition–elimination. The addition of water to the carbonyl group produces an intermediate with a pair of hydroxyls connected to a carbon atom. If a hydroxyl hydrogen atom is transferred to the ester bond (CO–O), the hydrolysis of lactide generally occurs. Any of these hydroxyls could also be dehydrated with the close methine, thus producing an enolate, and the transfer of hydrogen from the enolic hydroxyl group results in lactide racemisation. The conversion of d- or l-lactide into meso-lactide is a reversible and endothermic reaction when catalyzed by water. When lactide reacts with alcohol, its alcoholysis occurs more readily than its racemisation.
Keywords: l-lactide; Racemisation mechanism; Water catalysis; Alcoholysis;

Three commercial anti-oxidant systems have been studied regarding migration and chemical reaction in different polyethylene pipe materials during extraction in organic solvents and in hot water, 95–100 °C, under anaerobic and aerobic conditions. Materials made of crosslinked and non-crosslinked high density polyethylene, low density polyethylene and blends thereof were stabilized with different phenolic antioxidants: Irganox 1330, Irganox 1010, and Irganox 1076. The loss in stability with increasing extraction times was followed by oxidation induction time (OIT) measurements and by measuring the residual amounts of anti-oxidant by extraction. A gradual decrease in OIT and amount of anti-oxidant with increasing treatment time in water was observed for all samples. However, the behaviour of the three antioxidants was dissimilar. For materials containing Irganox 1330 three new species, possibly transformation products of the anti-oxidant, were found within the material. Larger decrease in anti-oxidant content in the polymer compared to corresponding loss in OIT indicates that the new species still have anti-oxidant capacity. On the other hand, corresponding transformation species could not be found within materials stabilized with Irganox 1010 or 1076. It is suggested that these antioxidants, which both contain ester groups, are hydrolyzed and that the new species migrate out into the surrounding water. Solvent extractions showed that crosslinking did not affect the extractability of the antioxidants. Actually, even with water as the extracting media, the network did not show any obstructive effect of the migration of the anti-oxidant. For peroxide crosslinked samples part of the anti-oxidant could not be extracted with solvent but we believe that grafting of antioxidants onto the polymer backbone is the most plausible explanation in this case. Additionally, we see a clear decrease in anti-oxidant loss with increasing crystallinity.
Keywords: Phenolic anti-oxidant; Migration; Polyethylene; HPLC-analysis; Drinking water;

Impact of formic/acetic acid and ammonia pre-treatments on chemical structure and physico-chemical properties of Miscanthus x giganteus lignins by Caroline Vanderghem; Aurore Richel; Nicolas Jacquet; Christophe Blecker; Michel Paquot (1761-1770).
Miscanthus x giganteus was treated with formic acid/acetic acid/water (30/50/20 v/v) for 3 h at 107 °C and 80 °C, and soaking in aqueous ammonia (25% w/w) for 6 h at 60 °C. The effects of these fractionation processes on chemical structure, physico-chemical properties and antioxidant activity of extracted lignins were investigated. Lignins were characterized by their purity, carbohydrate composition, thermal stability, molecular weight and by Fourier transform infrared (FTIR), 1H and quantitative 13C nuclear magnetic resonance (NMR), adiabatic broadband {13C–1H} 2D heteronuclear (multiplicity edited) single quantum coherence (g-HSQCAD). The radical scavenging activity towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) was also investigated. Formic/acetic acid pretreatment performed in milder conditions (80 °C for 3 h) gave a delignification percentage of 44.7% and soaking in aqueous ammonia 36.3%.Formic/acetic acid pretreatment performed in harsh conditions (107 °C for 3 h) was more effective for extensive delignification (86.5%) and delivered the most pure lignin (80%). The three lignin fractions contained carbohydrate in different extent: 3% for the lignin obtained after the formic/acetic acid pretreatment performed at 107 °C (FAL-107), 5.8% for the formic/acetic acid performed at 80 °C (FAL-80) and 13.7% for the ammonia lignin (AL). The acid pretreatment in harsh conditions (FAL-107) resulted in cleavage of β–O-4′ bonds and aromatic C–C. Repolymerisation was thought to originate from formation of new aromatic C–O linkages. Under milder conditions (FAL-80) less β–O-4′ linkages were broken and repolymerisation took place to a lesser extent. Ammonia lignin was not degraded to a significant extent and resulted in the highest weight average 3140 g mol−1. Despite the fact of FAL-107 repolymerisation, significant phenolic hydroxyls remained free, explaining the greater antioxidant activity.
Keywords: Miscanthus x giganteus; Ammonia pretreatment; Formic/acetic acid pretreatment; Lignin chemical structure; Lignin characterisation; Repolymerisation;

Melt stabilisation of Phillips type polyethylene, Part III: Correlation of film strength with the rheological characteristics of the polymer by János Kovács; Piroska Pataki; Ágnes Orbán-Mester; Gábor Nagy; Peter Staniek; Enikő Földes; Béla Pukánszky (1771-1779).
Different aspects of the melt stabilising effect of various antioxidant packages were studied in a Phillips type polyethylene in the work described in this series of papers. The polymer was stabilised with various combinations of a phenolic antioxidant with phosphite, phosphonite, and phosphine type secondary antioxidants and processed by multiple extrusions followed by film blowing. After determining the role of the antioxidants in the melt stabilisation process and the effect of antioxidant consumption on polymer properties the correlation of the rheological characteristics of polymer with the tear and impact strengths of films is discussed in this paper. The Elmendorf tear strength of films measured in transverse direction, which is sensitive to long chain branching, correlates closely with viscous compliance determined by creep recovery experiments and the ratio of melt flow indices measured at high and low loads. The relationships are independent of the type and amount of antioxidant added. This makes possible the prediction of the effect of various antioxidant packages on film properties on the basis of rheological measurements. The correlation between the dart drop impact strength of the films and the rheological characteristics of the polymer is less reliable.
Keywords: Polyethylene; Stabilisation; Rheological characteristics; Film strength;

The aim of this study was to investigate the thermal degradability, and in particular, the thermal degradation mechanism of organophosphorus flame-retardant poly(methyl methacrylate) (PMMA). For this purpose thermogravimetry and direct pyrolysis mass spectrometry analyses were used. Release of diethylphosphinic acid, melamine, and several products involving Al–O–P and N–P linkages were detected from the organophosphorus additive containing aluminium diethylphosphinate, melamine polyphosphate and zinc borate. When incorporated in PMMA, reactions of diethylphosphinic acid, melamine and/or their derivatives with the ester group affected the decomposition pathways by generation of (C2H5)2POOCH3 and HNCO at relatively high temperatures.
Keywords: Thermal degradation; Direct pyrolysis mass spectrometry; Organophosphorus flame retardant; PMMA;

Rapid internal bubble formation in a microwave heated polymer observed in real-time by X-ray scattering by J.B.A. Mitchell; E. Jerby; Y. Shamir; Y. Meir; J.L. Le Garrec; M. Sztucki (1788-1792).
A combined study of small-angle and wide-angle X-ray scattering (SAXS/WAXS) of the melting of a nylon-6 sample by localized microwave radiation has shown that this method can reveal the presence of bubbles forming and disappearing rapidly in real time in the interior of the sample due to its thermal decomposition.
Keywords: SAXS; WAXS; Melting; Polymer melting; Bubble formation;

Novel hybrid systems based on poly(propylene-g-maleic anhydride) and Ti-POSS by direct reactive blending by Mario Hoyos; Alberto Fina; Fabio Carniato; Mirko Prato; Orietta Monticelli (1793-1798).
Novel hybrid systems based on maleic anhydride-grafted polypropylene (PPgMA) and home-made Ti-containing amino polyhedral oligomeric silsesquioxanes (Ti-POSS-NH2) have been prepared by one-step reactive blending, and their properties have been compared with those of systems based on a non-reactive POSS (POSS). The occurrence of a reaction between PPgMA and the reactive POSS molecules has been assessed by Fourier Transform Infrared Resonance (FTIR) measurements, whereas dispersion of POSS into the polymer was evaluated by Scanning Electron Microscopy (SEM), showing a nanometric dispersion only for the reactive POSS. Thermo-oxidative behaviour was studied by Thermogravimetric Analysis (TGA), showing a delayed volatilization of the PPgMA/Ti-POSS-NH2 with respect to both PPgMA/POSS and pristine PPgMA, which is attributed to the chemical activity of Ti in Ti-POSS-NH2. To highlight the mechanism of the hybrid system decomposition, samples which underwent a thermal treatment at 250 °C, i.e. the onset temperature for polymer matrix decomposition in thermo-oxidative conditions, have been studied by FTIR and X-Ray Photoelectron Spectroscopy (XPS) measurements.
Keywords: Ti-POSS; Reactive blending; PPgMA; Thermal degradation; XPS;

The resistance to over-oxidation for polyaniline initiated by the resulting quinone-like molecules by Mingming Gao; Guohui Zhang; Gang Zhang; Xinhua Wang; Shuguang Wang; Ying Yang (1799-1804).
Polyaniline (PANI) suffers electrochemical over-oxidation at high anodic potentials, which leads to severe degradation, forming quinone-like molecules (hydroquinone/benzoquinone, HQ/BQ). A research area usually neglected is the influence of the newly-produced HQ/BQ on the over-oxidation of PANI. In this study, it has been examined by cyclic voltammetry (CV) and FT-IR spectroscopy. When HQ was intentionally added into sulfuric acid solutions, the cyclic voltammograms demonstrate that the rate of degradation turned to be lower as the concentration of introduced HQ increased. First-order rate constants obtained from kinetic study were shown to vary between 0.1399 and 0.1027 s−1 within the concentration range of HQ from 0 to 0.05 M. An important finding is that the quinone-like molecules may have a great electronic exchange with the nitrogen atoms of the intact PANI chain when adsorbed on it, which leads to the changes in PANI structure at the molecule level. Less pernigraniline (PEB) was finally obtained and thus slower degradation was observed. This conclusion is supported by the phenomenon that the peak potentials for emeraldine/pernigraniline (EM/PEB) transitions shifted to more positive values when HQ was added. Moreover, from FT-IR analyses, it seemed that the relative content of the reduced form of PANI ascended with the degradation. So, the existence of HQ/BQ enhances the stability of PANI structure, endows PANI with resistance to over-oxidation and protects it from further degradation to a certain extent.
Keywords: Polyaniline; Over-oxidation; Quinone-like molecule; Electronic exchange; Stability; Resistance;

Crosslinking investigation of polybutadiene thermal degradation by carbon-13 nuclear magnetic resonance by Mohamad Ronagh-Baghbani; Farshid Ziaee; Hosein Bouhendi; Farhood Ziaie (1805-1811).
Thermal degradation of polybutadiene (PBD) in anaerobic atmosphere at 250 °C had been studied by carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) before complete crosslinking. In this investigation four types of low molecular weight PBD with different 1,2-vinyl isomer content had been chosen, then pure and mixed samples of PBD were heated in different time periods. 13C NMR spectra showed that two kinds of crosslinking mechanisms occur that both of them produce methyl groups. The first mechanism is a reaction between 1,2-vinyl isomers of two PBD chains, and the second one occurs between 1,2-vinyl isomer of one chain via methylene carbon of cis or trans isomer in another chain. Also 13C NMR results showed that the presence of 1,2-vinyl isomer in the PBD structure is necessary and without it none of the mentioned reactions will occur. Furthermore isomers sequence is another important parameter which affects crosslinking. Results show that cis or trans isomer which is not adjacent to 1,2-vinyl isomer does not take part in crosslinking reaction. Moreover such cis or trans isomer can take part in second mechanism of crosslinking that 1,2-vinyl isomer was attached from head to cis or trans isomer, thus in this arrangement of isomers second mechanism of crosslinking will become dominant rather than first mechanism of crosslinking.
Keywords: Polybutadiene; Thermal degradation; NMR; Crosslinking; Microstructure;

Thermal degradation of elastomeric vulcanized poly(ethylene-co-vinyl acetate) (EVM): Chemical and kinetic investigations by Oriane Cérin; Sophie Duquesne; Gaëlle Fontaine; Andreas Roos; Serge Bourbigot (1812-1820).
The thermal degradation of vulcanized elastomeric poly(ethylene-co-vinyl acetate) (EVM) in inert and oxidative conditions was investigated. Based on the characterization of both condensed and gas phases during the thermal degradation it was possible to propose a reaction scheme of the EVM degradation. In addition, the determination of the kinetic parameters completed the chemical investigations. The thermo-oxidation of vulcanized EVM occurs in five steps, including the cleavage of some cross-linking bonds, the catalytic deacetylation forming polyenes and a charring step, followed by the decomposition and oxidation of the char. It appeared that the curing, and thus the cross-linking nodes, enhances the thermal stability of EVM by favouring the charring. On the other hand the pyrolysis of the polymer is quite not influenced by the vulcanization.
Keywords: Vulcanized EVM; Thermal degradation; Kinetic modelling; Solid state NMR;

The pyrolysis and fire behaviour of epoxy resin (EP) composites based on a novel polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-POSS) and diglycidyl ether of bisphenol A (DGEBA) have been investigated. The pre-reaction between the hydroxyl groups of DOPO-POSS and the epoxy groups of DGEBA at 140 °C is confirmed by FTIR, which means that DOPO-POSS molecules of hydroxyl group could easily disperse into the epoxy resin at the molecular level. The EP composites with the DOPO-POSS were prepared through a curing agent, m-phenylenediamine (m-PDA). The morphologies of the EP composites observed by SEM indicate that DOPO-POSS disperses with nano-scale particles in the EP networks, which implies good compatibility between them. The thermal properties and pyrolysis of the EP composites were analyzed by DSC and TGA, TGA-FTIR, and TGA–MS. The analysis indicates that the DOPO-POSS change the decomposition pathways of the epoxy resin and increase its residue at high temperature; moreover, the release of phosphorous products in the gas phase and the existence of Si–O and P–O structures in the residue Is noted. The fire behaviour of the EP composites was evaluated by cone calorimeter (CONE). The CONE tests show that incorporation of DOPO-POSS into epoxy resin can significantly improve the flame retardancy of EP composites. SEM and XPS were used to explore micro-structures and chemical components of the char from CONE tests of the EP composites, they support the view that DOPO-POSS makes the char strong with the involvement of Si–O and P–O structures.
Keywords: Epoxy resin; Pyrolysis; Flame retardancy; POSS; DOPO;

Modified graphite oxide (MGO)/Poly (propylene carbonate) (PPC) composites with excellent thermal and mechanical properties have been prepared via a facile solution intercalation method. An intercalated structure of MGO/PPC composites was confirmed by X-ray diffraction and scanning electron microscope. The thermal and mechanical properties of MGO/PPC composites were investigated by thermal gravimetric analysis, differential scanning calorimetric, dynamic mechanical analysis, and electronic tensile tester. Due to the nanometer-sized dispersion of layered graphite in PPC matrix and the strong interfacial interaction between MGO and PPC, the prepared MGO/PPC composites exhibit improved thermal and mechanical properties in comparison with pure PPC. Compared with pure PPC, the MGO/PPC composites show the highest thermal stability and the T g is 13.8 °C higher than that of pure PPC, while the tensile strength (29.51 MPa) shows about 2 times higher than that of pure PPC when only 3.0 wt.% MGO is incorporated. These results indicate that this approach is an efficient method to improve the properties of PPC.
Keywords: Poly(propylene carbonate) (PPC); Modified graphite oxide (MGO); Composites; Solution intercalation; Properties;

Stability of polystannanes towards light by Markus Trummer; Thomas Nauser; Marie-Luise Lechner; Frank Uhlig; Walter Caseri (1841-1846).
The influence of pendant side groups on the stability of polystannanes against light was studied; more specifically poly[bis(4-butylphenyl)stannane] and poly(dibutylstannane) in solutions of tetrahydrofuran and dichloromethane. In both solvents, the poly(diarylstannane) was found to be more resistant towards light than the poly(dialkylstannane). Degradation was particularly rapid in tetrahydrofuran (THF) but was markedly retarded in presence of the radical scavenger 2,6-di-tert-butyl-4-methylphenol (BHT). Experiments with laser flash photolysis indicated that the superior stability of poly[bis(4-butylphenyl)stannane] was not a result of more stable Sn–Sn bonds but due to recombination of relatively long-living radicals. By contrast there was no evidence for such a process in the case of poly(dibutylstannane). Different reaction pathways of the degradation of polymer molecules themselves were identified by gel permeation chromatography (GPC) analysis of irradiated polymer solutions, leading to the conclusion that two different decomposition mechanisms can occur: i.e. either random scission of polymer chains or unzipping, depending on the polymer architecture and the nature of the solvent.
Keywords: Polystannane; Laser flash photolysis; Polymer degradation; Unzipping;

Effect of moisture on copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole by Guillaume H.R. Messin; Kirk D. Rice; Michael A. Riley; Stephanie S. Watson; John R. Sieber; Amanda L. Forster (1847-1857).
In recent years, there has been concern in the soft body armor community that copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole can release hydrochloric acid, which is present in these fibers as a by-product of the manufacturing process. The presence of acids could potentially be detrimental to other fibers that might come in contact with these materials. In an effort to examine this issue, a study was designed to investigate the release of acid in different environments from these fibers. During the first phase of the study, fibers were exposed to water and pH decreases were observed. While immersed in deionized water, two of the fiber samples studied released a sufficient amount of acid to drop the pH of the solution from approximately pH 6.0 to approximately pH 3.0 in less than 10 d at room temperature. Further ion-selective electrode studies of chloride ion released from these fibers indicated that hydrochloric acid may not be the species responsible for this pH reduction. In a second phase of the investigation, fibers were exposed to water vapor in an elevated temperature environment (conditions were 65 °C, 80% RH). While the pH reduction released by the water vapor exposure was substantially less than observed in the submersion phase, a reduction in the yarn tensile strength of some of the fibers was observed during this phase of the study. In a third phase, fibers were exposed in a dry oven (less than 5% RH) at 65 °C. Almost no pH reduction or strength reduction was observed. Molecular spectroscopy was also performed to better understand the effect of elevated temperature and moisture environments on these fibers.
Keywords: Copolymer fibers; Body armor; Moisture; Acid release; Degradation; 5-Amino-2-(p-aminophenyl)-benzimidazole;

Moisture uptake of a polycarbonate blend exposed to hygrothermal aging by Mojtaba Haghighi-Yazdi; Jacky K.Y. Tang; Pearl Lee-Sullivan (1858-1865).
As an extension of an earlier study on aging of a polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend, this paper has explored the roles of two competing phenomena, physical aging and moisture diffusion, during hygrothermal aging. Moisture absorption experiments at four different relative humidity conditions were compared with full immersion condition. Uptake curves show two different diffusion behaviour including Fickian moisture absorption and anomalous peak overshoot. The equilibrium moisture uptake in the polymer system, the coefficient of diffusion of moisture and the dual glass transitions were characterized. In general, the uptake behaviour could be explained using free volume expansion and contraction concepts that are associated with diffusion and structural recovery theories, respectively. However, using statistical methods, it was found that the relationship between the effects of aging temperature and relative humidity is both complex and interactive, with either diffusion or relaxation processes dominating depending on the extent of hygrothermal exposure.
Keywords: Polycarbonate/acrylonitrile-butadiene-styrene blend (PC/ABS); Physical aging; Moisture diffusion; Coefficient of diffusion;

Photo-oxidation of nanoporous polymers is little studied. The high UV penetration depth and high surface concentration in these materials give unprecedented possibilities both in fundamental work on surface photochemistry and in nanotechnological applications related for example to patterned hydrophilicity or refractive index. This is a quantitative study of the photo-oxidation products of nanoporous gyroid 1,2-polybutadiene in air. Irradiation of the porous sample with UV in the wavelength range of 300–400 nm enables tuning of the hydrophilicity of the nanoporous polymer through formation of hydrophilic chemical groups, carboxyl and hydroxyls, mainly onto the large air–polymer interface. The nature and abundance of the chemical groups induced by photo-oxidation is identified by solid-state 13C-NMR and FTIR spectroscopy. The distribution of photo-oxidation groups, both relative to the nanometre-scale polymer–air interface, and as a function of irradiation depth in the sample, is studied by gravimetry, titrimetry, ATR-FTIR and energy dispersive X-ray spectroscopy in scanning electron microscopy.
Keywords: Nanoporous; 1,2-Polybutadiene; Photo-oxidation; Energy dispersive X-ray spectroscopy;

The thermal degradation of two high temperature epoxy adhesives has been measured in terms of weight loss and adhesion loss and the lifetime predictions are compared for the two independent measurements of thermal degradation. Weight loss measurements were performed at high temperature under accelerated thermal aging conditions. Adhesion loss measurements were performed at lower temperatures closer to typical continuous operating temperatures. An Arrhenius relationship is validated for the thermal degradation of the epoxy adhesives, and the extent of degradation in terms of weight loss and adhesion loss is modelled with an autocatalytic rate expression. The degradation kinetic parameters and models are compared between the two thermal degradation measurements and are found to give similar predictions for the lifetime of the adhesives. In addition, the relationship between network degradation and loss of adhesive strength is discussed.
Keywords: Epoxy; Degradation; Adhesion; Thermal aging;

Degradation kinetics of poly(lactic-co-glycolic) acid block copolymer cast films in phosphate buffer solution as revealed by infrared and Raman spectroscopies by Elisabeth Vey; Caroline Rodger; Jonathan Booth; Mike Claybourn; Aline F. Miller; Alberto Saiani (1882-1889).
Poly(lactic-co-glycolic) acid (PLGA) is an important copolymer used in drug delivery platforms where controlled release is required. In this work we investigated the in vitro degradation of four PLGA copolymers with L/G molar compositions of 50/50, 65/35, 75/25 and 95/5. ATR-IR and Raman spectroscopies were used to differentiate and quantify the degradation rates of glycolic and lactic units. Both techniques were used to determine the polymer composition as a function of degradation time and the degradation rate constants for the hydrolysis of glycolic and lactic units were calculated using a 1st order kinetics approach. Our results revealed a two stage process for the degradation of PLGA cast films in PBS in agreement with our previous work. The degradation rate constant for glycolic unit was found to be 1.3 times higher than for lactic units. In addition the degradation rate constants for L and G units were shown to decrease proportionally with increasing initial lactic content of the copolymer used to prepare the films.
Keywords: Degradation kinetics; PLGA; Cast films; Poly(lactic-co-glycolic) acid; Infrared spectroscopy; Raman spectroscopy;

One-step water-assisted melt-compounding of polyamide 6/pristine clay nanocomposites: An efficient way to prevent matrix degradation by F. Touchaleaume; J. Soulestin; M. Sclavons; J. Devaux; M.F. Lacrampe; P. Krawczak (1890-1900).
Polyamide 6 (PA6)/clay nanocomposites, based on organo-modified and pristine (i.e. purified but non-modified) montmorillonite, were prepared using a water-assisted extrusion process based on the injection of water during extrusion. The formation of a single PA6/water phase during extrusion (shown by High Pressure Differential Scanning Calorimetry (HPDSC)) improves the clay dispersion, decreases the PA6 melting temperature by 66 °C (so-called cryoscopic effect), and thus prevents the polymer matrix degradation during processing. This process enables the compounding of pristine clay-based nanocomposites whose dispersion state, thermal and mechanical performances are close to what is generally reported for organo-modified montmorillonite-based nanocomposites. Advantage was taken of water-assisted extrusion to optimize the clay dispersion by increasing shear rate and of the cryoscopic effect to limit the degradation by decreasing the processing temperature. Using these conditions PA6/pristine clay nanocomposites properties are similar to those of more conventional PA6/organomodified clay nanocomposites.
Keywords: Polyamide; Nanocomposites; Pristine clay; Water-assisted extrusion; Degradation;

Monitoring the influence of different weathering conditions on polyethylene pipes by IR-microscopy by Raquel Maria; Karsten Rode; Robert Brüll; Frank Dorbath; Benjamin Baudrit; Martin Bastian; Emmanuelle Brendlé (1901-1910).
Plastic pipes are often exposed to a range of environmental conditions which may lead to their degradation. The most important influence factors are UV radiation, humidity and temperature. These can cause leaching of long-term and light stabilisers and finally oxidation of the polymer. In this study we demonstrate how the elemental steps of the photooxidative degradation of polyethylene pipes can be monitored by IR-microscopy. In detail the influence of UV radiation leads to a depletion of the phenolic long-term stabiliser, Irganox 1010. Calibration of the spectroscopic data enables IR-microscopy to be carried out in a quantitative manner and the rate constants for the stabiliser loss to be calculated for the first time. The results obtained from IR-microscopy are well in agreement with those obtained by mechanical sample preparation and measurement of the oxidative induction time (OIT) as well as extraction coupled with chromatographic analysis (HPLC). A mechanism based on Norrish type cleavage is proposed. Also the formation of trans-vinylidene groups as unsaturated degradation products of the PE can be observed. In summary it can be shown that IR-microscopy is highly superior to the conventional approach of mechanical sample preparation with regard to spatial resolution and offers the advantage of being less labour intensive.
Keywords: Photodegradation; Stabiliser diffusion; IR-microscopy; Pipes; Poly(ethylene); Ageing;

Preparation and properties of thermally stable polyimides derived from asymmetric trifluoromethylated aromatic diamines and various dianhydrides by Qianqian Bu; Shujiang Zhang; Hui Li; Yanfeng Li; Chenliang Gong; Fengchun Yang (1911-1918).
A novel method for the preparation of an asymmetric fluorinated aromatic diamine, 3,4′-bis(4-amino-2-trifluoromethylphenoxy)-benzophenone was investigated. This new diamine containing trifluoromethyl side group was synthesized from the nucleophilic substitution reaction of 2-chloro-5-nitrobenzotrifluoride and 3,4′-dihydroxybenzo phenone in the presence of potassium carbonate, followed by catalytic reduction with SnCl2·6H2O and concentrated hydrochloric acid. This novel diamine was used to react with different commercially available aromatic tetracarboxylic dianhydrides to prepare polyimides via thermal or chemical imidization. The polyimide properties such as inherent viscosity, solubility, thermal and surface properties were investigated to illustrate the contribution of the trifluoromethyl group and the asymmetry structure of the polyimide. The polyimides obtained had good thermal stability and the glass transition temperature values ranged from 225 to 267 °C. All of these novel polyimides held 10% weight loss at the temperature above 543 °C in air and left more than 47% residue even at 800 °C in nitrogen. The inherent viscosities of the obtained polyimides were above 0.73 dL/g and were easily dissolved in both polar, aprotic solvents and some low-boiling-point solvents. Moreover, these PI films had dielectric constants of 2.94–3.53 (1 kHz), with moisture absorption in the range of 0.07–0.34 wt%. In comparison of the PIs (5) series with the analogous symmetric PIs (6) series based on 4,4′-bis(4-amino-2-trifluoromethylphenoxy)-benzophenone, the (5) series revealed better solubility, low dielectric constant and moisture absorption.
Keywords: CF3-containing polyimide; Unsymmetrical diamine monomer; Solubility; Polymer films;

Formulation selection of aliphatic aromatic biodegradable polyester film exposed to UV/solar radiation by Thitisilp Kijchavengkul; Rafael Auras; Maria Rubino; Susan Selke; Mathieu Ngouajio; R. Thomas Fernandez (1919-1926).
Aliphatic aromatic copolyester films, poly(butylene adipate-co-terephthalate) or PBAT, are susceptible to photodegradation, leading to main chain scission and crosslinking. The presence of crosslinked structures not only decreased the mechanical properties of the film due to embrittlement, but also hindered the biodegradation process by limiting access of water and microorganisms to the polymer chains. This has limited the use of PBAT for outdoor applications, such as mulch films. In this study, response surface methodology (RSM) was used to determine the optimal concentrations of carbon black (CB) and the chain breaking antioxidant butylated hydroxytoluene (BHT) for the design of mulch films that can prevent the formation of crosslinked structures from recombination of free radicals. An overlaid contour plot of suitable concentrations of CB and BHT for the formulation of mulch film for crop production in Michigan or regions with similar solar radiation was established using selection criteria of light transmission of less than 20%, final tensile strength of at least 6.35 MPa, maximum gel fraction of 0.30, and positive number average molecular weight reduction sensitivity in the early stage of degradation.
Keywords: Response surface methodology; Photodegradation; Poly(butylene adipate-co-terephthalate); PBAT; Biodegradation;

Poly[acrylamide-co-(2-acrylamido-2-methylpropane sodium sulfonate)] superabsorbents and superabsorbent composites (SAPCs) with zinc borate and/or melamine as fire retardants were synthesized. Water absorbencies decreased inversely to added amount of fire retardant. Thermal stability of SAPC/zinc borate increases with increasing zinc borate. Incorporating melamine improved thermal stability of the SAPC until 300 °C. Flammability analysis demonstrated that wood surface coated with SAP or SAPC emulsions extended time to ignition of the wood. Peak heat release rate and total heat release are smallest in specimens coated with SAPC/30% melamine. Wood coated with SAPC incorporating 20% zinc borate/10% melamine mixture gave the longest time to ignition at 4½ min.
Keywords: Superabsorbent; Zinc borate; Melamine; Fire retardant; Cone calorimetry;

Accelerated ageing to study the degradation of cellulose nitrate museum artefacts by Anita Quye; David Littlejohn; Richard A. Pethrick; Robert A. Stewart (1934-1939).
Cellulose nitrate is susceptible to hydrolysis as well as loss of plasticiser when left in a humid atmosphere. A comparison of the ageing behaviour of cellulose nitrate samples prepared from cotton linters was used to simulate the artefacts studied in a previous study. Certain artefacts were also subjected to accelerated ageing at 12%, 55% and 75% relative humidity at 70 °C. The rate of degradation was observed to vary with the RH, indicating the connection between the absorption of moisture and the hydrolysis process. The effect of varying the sulphate level on the rate of hydrolysis was studied using concentrations similar to those detected in artefacts. The study was carried out using <0.1 mg g−1, 2 mg g−1 and 5 mg g−1 of sulphate and distinct differences were observed which is consistent with the conclusions drawn for a study of a number of artefacts. The observed rates of degradation are consistent with previous studies on cellulose nitrate. The degradation was studied using a combination of infrared spectroscopy, ion chromatography and gel permeation chromatography. The analysis was complemented by a study of the weight changes which occur during ageing.
Keywords: Cellulose nitrate; Infrared spectroscopy; Ion chromatography; Gel permeation chromatography; Ageing; Degradation;

Preparation and mechanical behavior of PLGA/nano-BCP composite scaffolds during in-vitro degradation for bone tissue engineering by M. Ebrahimian-Hosseinabadi; F. Ashrafizadeh; M. Etemadifar; Subbu S. Venkatraman (1940-1946).
In this paper, the yield strength and elastic modulus of Poly (lactide-co-glycolide) (PLGA) and PLGA/nano-biphasic calcium phosphate (nBCP) composite scaffolds, before and during in-vitro degradation, have been evaluated. Composite scaffolds were made by using PLGA matrix and 10–50 wt.% nBCP powder as the reinforcement material. All scaffolds, with more than 89% porosity, were fabricated by thermally-induced phase separation (TIPS). During in-vitro degradation (0–8 weeks), the PLGA/nBCP scaffolds showed both more weight loss and better mechanical properties as compared to neat PLGA scaffolds. The PLGA/nBCP scaffolds with 30 wt.% nBCP illustrated the highest value of yield strength among the composite scaffolds, before and after degradation, until 6 weeks. After 8 weeks, the yield strength values were very poor and close to each other. The values of elastic modulus for all samples were less than the half of their initial values after 6 weeks. However, after 8 weeks, the elastic moduli of all samples reduced to negligible values.
Keywords: Nano composite scaffold(s); In-vitro degradation; Mechanical properties; Biphasic calcium phosphate;