Polymer Degradation and Stability (v.94, #8)

Calendar (I-II).

Radical scavenging efficiency of different fullerenes C60–C70 and fullerene soot by Eldar B. Zeynalov; Norman S. Allen; Nazilya I. Salmanova (1183-1189).
This investigation was undertaken to determine the antioxidant activity of a range of fullerenes C60 and C70 in order to rank them according to their comparative efficiency. The model reaction of initiated (2,2′- azobisisobutyronitrile, AIBN) cumene oxidation was used to determine rate constants for addition of radicals to fullerenes. Measurements of oxidation rates in the presence of different fullerenes showed that the antioxidant activity as well as the mechanism and mode of inhibition were different for fullerenes C60 and C70 and fullerene soot. All fullerenes – C60 of gold grade, C60/C70 (93/7, mix 1), C60/C70 (80 ± 5/20 ± 5, mix 2) and C70 operated as alkyl radical acceptora, whereas fullerene soot surprisingly retarded the model reaction by a dual mode similar to that for the fullerenes and with an induction period like many of the sterically hindered phenolic and amine antioxidants. For the C60 and C70 the oxidation rates were found to depend linearly on the reciprocal square root of the concentration over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl radicals to the fullerene core. This is consistent with literature data on the more ready and rapid addition of alkyl and alkoxy radicals to the fullerenes compared with peroxy radicals. Rate constants for the addition of cumyl radicals to the fullerenes were determined to be k (333K) = (1.9 ± 0.2) × 108 (C60); (2.3 ± 0.2) × 108 (C60/C70, mix 1); (2.7 ± 0.2) × 108 (C60/C70, mix 2); (3.0 ± 0.3) × 108 (C70), M−1 s−1. The increasing C70 constituent in the fullerenes leads to a corresponding increase in the rate constant.The fullerene soot inhibits the model reaction according to the mechanism of trapping of peroxy radicals; the oxidation proceeds with a pronounced induction period and kinetic curves are linear in semi-logarithmic coordinates.For the first time the effective concentration of inhibiting centres and inhibition rate constants for the fullerene soot have been determined to be fn[C60−soot] = (2.0 ± 0.1) × 10−4 mol g−1 and k inh = (6.5 ± 1.5) × 103 M−1 s−1 respectively.The kinetic data obtained specify the level of antioxidant activity for the commercial fullerenes and scope for their rational use in different composites. The results may be helpful for designing an optimal profile of composites containing fullerenes.
Keywords: Model oxidation; Fullerene; Fullerene soot; Kinetics; Oxidation rate; Induction period;

Characterization of a mesophilic aliphatic–aromatic copolyester-degrading fungus by Ken-ichi Kasuya; Nariaki Ishii; Yoshio Inoue; Koji Yazawa; Tomoko Tagaya; Taro Yotsumoto; Jun-ichiro Kazahaya; Daisuke Nagai (1190-1196).
We isolated 5 mesophilic microorganisms that form clear zones around the colony on an opaque medium containing the aliphatic–aromatic copolyester poly(60 mol% butylene adipate-co-40 mol% butylene terephthalate) (PBAT). Among all strains, the fungal strain NKCM1712 degraded PBAT at the fastest rate (3.5 ± 0.3 μg cm−2 h−1). Genetic and morphological analyses revealed that this strain was closely related to Isaria fumosorosea (phylum Ascomycota). Mass spectroscopic analysis revealed that the degradation products were T, AB, TB, BAB, and ABT (T, terephthalic acid unit; A, adipic acid unit; B, 1,4-butanediol unit)] in the culture of the strain that used PBAT as the sole carbon source. Furthermore, the PBAT degradation ability of this strain in terms of BOD suggested that it could utilize the PBAT degradation products as growth substrates. This is the first report of a mesophilic strain that can mineralize an aliphatic–aromatic polyester into carbon dioxide on its own.
Keywords: Aliphatic–aromatic copolyester; PBAT; Biodegradation; Fungus; Mesophilic; Mineralization;

Biohydrolysis of nylon 6,6 fiber with different proteolytic enzymes by Mazeyar Parvinzadeh; Reza Assefipour; Amir Kiumarsi (1197-1205).
In recent years, the textile industry must go towards sustainable technologies and developing environmentally safer methods for textiles processing. One way is the processing with enzymatic system, rather than conventional chemical methods. The aim of this work was to investigate the changes induced on nylon 6,6 fiber by enzymatic system using different proteolytic enzymes. Technical measurements were studied including Fourier-transform infrared spectroscopy, scanning electron microscopy, thermal, dyeability, and fastness properties. For this purpose, nylon 6,6 fabrics were first treated separately with different concentrations of four protease enzymes. The dyeing process was then carried out on the treated fabrics with two reactive and acid dyes. The intensity of major peaks in FTIR spectra of the protease treated samples is in favor of chemical changes of the polypeptide functional groups in fabric. Thermal studies also show significant decrease in thermal degradation temperature of the treated polymer. Reactive and acid dyes showed higher dyebath exhaustion on the enzyme treated samples compared to raw material. The results of color measurements showed that the more concentration of enzyme used, the darker the color of dyed sample is. Interesting results were obtained in the studied topic.
Keywords: Nylon 6,6; Protease; Hydrolysis; FTIR spectroscopy; Thermal properties;

Chemical oxidative degradation of Polybenzimidazole in simulated environment of fuel cells by Zhihong Chang; Hongting Pu; Decheng Wan; Lu Liu; Junjie Yuan; Zhenglong Yang (1206-1212).
The chemical oxidative degradation process of poly [2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI) in simulated environment of fuel cells was evaluated. From the mechanical properties and the intrinsic viscosity of PBI, it was observed that the stress at break of PBI membranes decreased and the macromolecular chains of PBI were broken after the treatment in Fenton reagent for 24 h. From the photos of Scanning Electron Microscope, it was identified that there were lots of corroded holes in PBI membranes. By means of FTIR and 1H NMR analysis, it was shown that during the treatment of PBI in the presence of HO• or HOO• free radicals the hydrogen atom of N–H bond in imidazole ring was liable to be oxidized, and the phenyl was oxidized with the formation of quinine and dicarboxylic acid structures. In the end, the possible mechanism of the chemical oxidative degradation of PBI was proposed.
Keywords: Polybenzimidazole; Degradation; Free radical; Fuel cell; Fenton reagent;

A method for the determination of polymer additives like antioxidants, UV absorbers and processing stabilizers using liquid chromatography (LC) coupled with atmospheric pressure photoionization mass spectrometry (APPI–MS) is presented. Ion source parameters were optimized regarding temperatures, gas flow rates, and voltages applied. Detection limits were determined using APPI with or without dopant and were compared with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). Differences between APPI, ESI and APCI are pointed out and the effect of the dopant toluene and acetone is discussed. The optimized method yielded detection limits between 0.001 mg L−1 and 0.022 mg L−1 for 15 different analytes. Linear calibration plots could be obtained for all solutes over a wide concentration range showing satisfying repeatability with standard deviations of peak areas between 3.4% and 7.6%. The results indicate that the developed method can be regarded as suitable for the quantitative determination of polymer additives even at low concentration levels.
Keywords: Polymer additives; Liquid chromatography; Mass spectrometry; Atmospheric pressure photoionization; Atmospheric pressure chemical ionization;

Degradation of Mater-Bi®/wood flour biocomposites in active sewage sludge by R. Scaffaro; M. Morreale; G. Lo Re; F.P. La Mantia (1220-1229).
The mechanical properties of Mater-Bi® are, in general, not adequate for certain applications and the addition of a filler is therefore necessary. Among the different fillers, natural fibres are particularly interesting because they potentially allow improving the performance of the material without compromising its biodegradability.In order to improve the basic mechanical properties of a Mater-Bi grade and to obtain a new, fully biodegradable material, wood flour based composites were prepared by different processing methods. To simulate actual and not laboratory bacterial attack on the prepared materials, in this work we studied the biodegradation of the composites in a real active sewage sludge reactor. In particular, the biodegradation rates were investigated with reference to different pre-treatments of the materials and different environmental conditions (summer and winter). The results showed that wood flour enhances the biodegradability of the materials. The results indicated also strong relationships between the surface roughness and the biodegradation rates (in particular, higher roughness leads to wider bacterial attack). The different processing techniques had direct effects on the overall biodegradation rates. In particular, when higher smoothness and packing is achieved, the biodegradation rate is lower. The mechanical analysis indicated that adding wood flour to Mater-Bi has positive effects on the elastic modulus, but when the bacterial attack becomes critical, a general sudden drop of the mechanical properties is observed.
Keywords: Polymer composites; Environmental degradation; Extrusion; Injection moulding; Scanning Electron Microscopy;

Polyhedral oligomeric silsesquioxane as flame retardant for thermoplastic polyurethane by Serge Bourbigot; Thomas Turf; Séverine Bellayer; Sophie Duquesne (1230-1237).
In this work, the reaction to fire of thermoplastic polyurethane (TPU) containing polyhedral oligomeric silsesquioxanes (or POSSs) was investigated by mass loss calorimetry. This composite exhibits a large reduction of peak of heat release rate (PHRR) compared to virgin TPU. The protection occurs via an intumescent mechanism. Mechanism of protection is examined in chemical and physical ways. Solid state NMR of carbon and silicon on heat-treated materials reveals that there is no significant chemical interaction between TPU and POSS. Nevertheless the intumescent char is characterized as ceramified char made of silicon network in a polyaromatic structure. The expansion occurs because of the partial volatilization of the organic part of POSS and because of the evolving degrading products of TPU. The formation of this intumescent structure makes an efficient insulating material at the surface of the substrate limiting heat and mass transfer and then decreasing heat release rate.
Keywords: Reaction to fire; Flame retardant; POSS; Intumescence; Solid state NMR; Polyurethane;

Oxidative and photooxidative degradation of poly(acrylic acid) by Neelesh Bharti Shukla; Nagu Daraboina; Giridhar Madras (1238-1244).
The oxidative degradation of poly(acrylic acid) (PAA), a water soluble polymer, was studied at various temperatures with different concentrations of persulfates, potassium persulfate (KPS), ammonium persulfate (APS) and sodium persulfate (SPS). The photodegradation of PAA was also examined with APS as oxidizer. The degraded samples were analyzed for the time evolution of molecular weight distribution by gel permeation chromatography. A theoretical model based on the continuous distribution kinetics was developed that accounted for the polymer degradation and the dissociation of persulfate. The rate coefficients for the oxidative and photooxidative degradation of PAA were determined from the parametric fit of the model with experimental data. The rate of degradation increased with increasing amount of persulfate in both oxidative and photooxidative degradation. The rate of degradation also increased with increasing temperature in the case of oxidative degradation.
Keywords: Poly(acrylic acid); Oxidative; Photooxidative; Degradation; Persulfate;

The flame retardancy of poly(butylene terephthalate) (PBT) containing aluminium diethlyphosphinate (AlPi) and/or nanometric metal oxides such as TiO2 or Al2O3 was investigated. In particular the different active flame retardancy mechanisms were discovered. Thermal analysis, evolved gas analysis (TG-FTIR), flammability tests (LOI, UL 94), cone calorimeter measurements and chemical analyses of residues (ATR-FTIR) were used. AlPi acts mainly in the gas phase through the release of diethylphosphic acid, which provides flame inhibition. Part of AlPi remains in the solid phase reacting with the PBT to phosphinate-terephthalate salts that decompose to aluminium phosphate at higher temperatures. The metal oxides interact with the PBT decomposition and promote the formation of additional stable carbonaceous char in the condensed phase. A combination of metal oxides and AlPi gains the better classification in the UL 94 test thanks to the combination of the different mechanisms.
Keywords: Poly(butylene terephthalate); Flammability; Metal oxide nanocomposite; Metal phosphinate;

Poly[(3,3,3-trifluoropropyl)methylsiloxane] (PTFPMS) was treated with the solvents acetone, ethyl acetate and methanol and its degradation products were analyzed with multiple techniques. 1H, 29Si and 19F nuclear magnetic resonance (NMR) spectroscopy were useful for the characterization of the intact polymers and for the determination of cyclosiloxanes. Cyclosiloxanes with a ring size of up to 23 were quantified by gas chromatography. The only degradation products found were TFPmethyl-cyclosiloxanes. 1,3,5,7-Tetrakis(TFPmethyl)-cyclotetrasiloxane was predominant, and (TFPmethyl)cyclotri-, penta- and hexasiloxane could be detected at lower concentrations. The identity of cyclic degradation products with a ring size of up to 6 was unambiguously confirmed by direct infusion mass spectrometry. The TFPmethyl-cyclosiloxanes were successfully ionized by electrospray ionization in the negative mode. None of the techniques applied gave hints to other degradation products such as short linear oligomers. Almost complete degradation of PTFPMS occurred in acetone and methanol, while degradation is distinctly reduced in ethyl acetate.
Keywords: 29Si NMR spectroscopy; 19F NMR spectroscopy; Mass spectrometry; Degradation; Cyclosiloxanes; Stationary phases for GC;

The thermal performance of aromatic polyesters (poly(DPA–IPC), poly(MDP–IPC) and poly(EDP–IPC)) prepared from isophthaloyl chloride (IPC) with diphenolic acid (DPA) and its esters were studied with DSC and TG, and the decomposition mechanism of poly(DPA–IPC) were investigated using FTIR and integrated TG/FTIR analyses. As compared with ordinary aromatic polyesters, poly(DPA–IPC) has lower glass transition temperature (159 °C) and much lower thermal stability. It starts to decompose at about 210 °C and is characterized by two-stage thermal decomposition behavior, with active energies of decomposition of 206 kJ/mol and 389 kJ/mol, respectively. The analyses of the decomposition process and products indicate that the pendent carboxyl groups in poly(DPA–IPC) are responsible for its low thermal stability. Accordingly, a decomposition mechanism for the first stage is proposed. With this knowledge in mind, we capped the carboxyl groups in DPA with methyl and ethyl groups to prepare poly(MDP–IPC) and poly(EDP–IPC) from methyl diphenolate and ethyl dipenolate. As expected, these two polymers exhibit obviously improved thermal stability, with onset decomposition temperature of about 300 °C.
Keywords: Interfacial polycondensation; Aromatic polyester; Diphenolic acid; Thermal decomposition; Thermal stability;

A predictive model is formulated for the fire response of a glass reinforced plastic panel, consisting of two glass-fibre/polyester skins and Vermiculux sandwich material (core) in between. Polymer conversion takes place according to a first-order decomposition reaction and an n-order combustion reaction both with an Arrhenius-type dependence on temperature. Intrinsic kinetic parameters have been estimated by re-examination of thermogravimetric data at four heating rates, resulting in activation energies for the two steps of 128 and 150 kJ/mol, respectively. Physical processes are modelled by the unsteady, one-dimensional conservation equations taking into account heat transfer by convection and conduction, convective mass transfer, surface heat transfer, effective thermal conductivity, moisture evaporation, ablation of the heat-exposed surface at a critical temperature and property variation. Simulated process dynamics, using intrinsic values for all the model parameters, are highly influenced by the behaviour of the heat-exposed skin which shows three main regimes: I) very rapid conversion of a thin surface layer (fast heating regime), II) slowing down of the conversion processes following the formation of a thick insulating fibre glass layer (slow heating regime) and III) a new enhancement in the reaction rates as a consequence of surface collapse and ablation (ablation regime). Good agreement is obtained for the predicted and measured temperatures for both a single skin composite plate and a sandwich panel loaded with a hydrocarbon flame.
Keywords: Glass reinforced plastics; Sandwich panels; Mathematical modelling; Fire response;

The effect of basecoat pigmentation on mechanical properties of an automotive basecoat/clearcoat system during weathering by H. Yari; S. Moradian; B. Ramazanzade; A. Kashani; N. Tahmasebi (1281-1289).
The aim of this study is to elucidate the effect of basecoat pigmentation on mechanical aspects of an automotive basecoat/clearcoat (BC/CC) system during artificial weathering exposures. A silver basecoat as the most reflective and a black basecoat as the most absorptive basecoat were selected. These two extreme behaviored basecoats were chosen with hopes that other basecoats would behave somewhere between the silver and the black extremes. The structural and mechanical properties of the coatings were investigated after various weathering exposure times (0, 150, 300, 450, 600 h). Dynamic mechanical thermal analysis (DMTA) was carried out to study variations in structure and basic characteristics of the system such as cross-linking density and T g during weathering. In order to investigate variations in mechanical properties of the system, nano indentation, nano scratch, and tensile tests were also utilized.It was found that although both silver and black systems experienced post-curing reactions (dominant at earlier stages of weathering) and degradation reactions (dominant at later stages of weathering), but basecoat pigmentation affected the post-curing and degradation reaction rates of the BC/CC system, leading to variations in mechanical properties. It was concluded that post-curing occurred to a greater extent in the black pigmented system whilst in the silver pigmented system weathering degradation was much more sever.
Keywords: Weathering; Mechanical properties; Automotive coating; Nano-indentation;

Polystyrene/layered double hydroxides (PS/LDHs) nanocomposites were prepared by free radical polymerization of styrene monomer in the presence of LDHs intercalated with 4,4′-azobis(4-cyanopentanoate) anions (LDH–ACPA). XRD and ATR-IR are used to confirm that the materials produced are layered and the presence of the azo-initiator anions in these LDHs. These LDHs were used successfully to polymerize styrene and both XRD and TEM images of the composites support the formation of a mixed exfoliated-intercalated nanocomposite for ZnAl–ACPA but a microcomposite for MgAl–ACPA. The magnesium-containing LDHs decreased the glass transition temperature (T g) of the composites while ZnAl–ACPA did not affect T g significantly. The T g depression is related to enhanced polymer dynamics due to the extra free volume at the LDH additive-polymer interface. A reduction in the onset of thermal decomposition temperature was observed in PS/LDH compared to neat PS, likely due to the early decomposition of the LDH. The fire performance, as evaluated by the cone calorimeter, reveal that PS–ZnAl–ACPA shows enhanced fire properties compared to PS–MgAl–ACPA.
Keywords: Nanocomposites; Layered double hydroxides; Fire retardancy; Polystyrene;

Does organic modification of layered double hydroxides improve the fire performance of PMMA? by Calistor Nyambo; Dan Chen; Shengpei Su; Charles A. Wilkie (1298-1306).
The effect of modified layered double hydroxides (LDHs) on fire properties of poly(methyl methacrylate) is investigated. Organically-modified LDHs were prepared via rehydration of calcined hydrotalcite in a palmitate solution. Composites consisting of the organo-LDHs, unmodified hydrotalcite and calcined oxides were prepared with poly(methyl methacrylate) using melt blending. Thermal and fire properties of the (nano)composites were studied. The thermogravimetric analyses of the composites show an increase in thermal stability. Fire performance, evaluated using cone calorimetry, show that organically-modified LDHs composites give the best reductions in peak heat release rate, PHRR, i.e., 51% at 10% weight loading. Dispersion of the LDHs was characterized using transmission electron microscopy and X–ray diffraction. Nanocomposite formation was observed with organically-modified LDHs, while the unmodified LDH composites gave only microcomposites.
Keywords: Layered double hydroxide; Calcination; Thermogravimetric analysis; Poly(methyl methacrylate); Cone calorimeter;

Three-layer gelatin films, composed of sodium montmorillonite (MMt) – plasticized gelatin (Ge-5MMt) (inner layer) and dialdehyde starch (DAS) – cross-linked and plasticized gelatin films (Ge-10DAS) (outer layers), obtained by heat-compression molding, were submitted to degradation under indoor soil burial conditions for 14 days. Biodegradation of multilayer film as well as individual components and control gelatin films was evaluated by monitoring water absorption and weight loss. It was established that technological treatments performed on gelatin, such as cross-linking, compounding with clay and heat-compression molding have a major impact on the biodegradation rate and extent. The possible reasons are discussed. Weight loss results revealed that the susceptibility to microbial attack during soil burial varied in the order: Ge-10DAS < multilayer < Ge-5MMt < gelatin control film. The intermediate behaviour of the multilayer was associated with the presence of hydrogen-bonding interactions between layers, induced by processing. Scanning electron microscopy revealed that the multilayer was preferentially biodegraded by filamentous microorganisms and even larvae in the later stages of the process. The presence of holes and pits on the multilayer surface was more likely attributed to the preferential removal of glycerol and DAS as shown by thermogravimetric analysis.
Keywords: Gelatin; Multilayer; Biodegradation; Soil burial; Cross-linking; Bio-nanocomposite;