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Polymers and Polymer Composites

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Title: Heterogeneous surface wear models for the prediction of the specific wear rate of woven carbon fibre reinforced epoxy composites
Page Range: p.359-368
Author(s): Cheng B; Kortschot M
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.6

Abstract
Heterogeneous surface wear (HSW) models have been derived to predict the specific wear rates of woven carbon fibre reinforced epoxy composite materials. The specific wear rates of unidirectional carbon fibre/epoxy composites, with fibres orientated both parallel and antiparallel to the direction of sliding, are used as input variables. The first model (EW mode) is based on an assumption of uniform thickness reduction during wear, but uneven surface pressure. The second model (EP mode) is based on an assumption of even surface pressure throughout the test. The specific wear rates of plain and 5HS woven composite panels were measured to validate the accuracy of the models. It was found that the EW model was able to accurately predict the specific wear rates of the two types of woven composites under mild abrasive conditions (120 grit sandpaper). However, under more severe abrasive conditions (36 grit sandpaper), the woven panels exhibited a new wear mechanism caused by tearing of the out-of-plane fibres at the crossover points of warp and weft fibres. This mechanism caused both models to under-predict the specific wear rates of the woven composites in severe abrasive conditions. However, the EW model can be used with confidence under less abrasive conditions, where the asperities do not have significant interactions with the out of plane fibres. 19 Refs.

Title: Comparative study of polyethylene composites containing industrial lignins
Page Range: p.369-374
Author(s): Lei Hu; Tatjana Stevanovic; Rodrigue D
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.6

Abstract
In this work, free-radical grafting was investigated in order to enhance the compatibility between lignins and polyolefins. High density polyethylene (HDPE) was used as the matrix and two types of industrial lignins were selected as eco-friendly fillers: Kraft lignin which represents most of the global lignin production, but lacks adequate applications; and organosolv lignin which has received increasing attention for its low molecular weight, homogeneity and sulphur-free characteristics. The compounds were produced by batch mixing, and were compression moulded. From these samples, morphological, tensile and thermal properties were studied. The results show that incorporation of different lignins into HDPE yielded materials of different tensile behaviour, but improvement in morphological and mechanical properties through free-radical grafting was obtained. Furthermore, free-radical grafting was found to decrease the thermal oxidation resistance and the crystallinity of the composites. 22 Refs.

Title: Modeling of voids evolution in the encapsulation process of photovoltaic modules
Page Range: p.375-388
Author(s): Heng-Yu Li; Yun Luo; Ballif C; Laure-Emmanuelle Perret-Aebi
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.6

Abstract
Being void-free is an important criterion for the quality control of photovoltaic (PV) modules after encapsulation. The encapsulation process of PV modules with Ethylene Vinyl Acetate (EVA) polymer is complex, due to the time-dependent processing conditions and the material properties caused by continuous heat transfer and chemical reactions such as crosslinking. Hence, an in-depth understanding on the void evolution mechanism is challenging yet critical for obtaining high-quality, durable void-free PV modules and improving their production throughput. Towards this goal, a void evolution model is proposed in order to reveal the most appropriate processing parameter windows for eliminating voids during the EVA encapsulation process. Firstly, the types and origins of the voids in PV modules are discussed. Then the pressure balance in-/outside the void is considered, to evaluate the void stability as a function of temperature and pressure in the actual encapsulation cycle. Finally, a diffusion-controlled model for the evolution of void of wet air is adapted and implemented to predict the void evolution and interpret the experimental observations throughout the encapsulation process. In the conclusion, the critical processing parameters affecting the void evolution during the encapsulation process of PV modules are highlighted. 20 Refs.

Title: An evaluation of the compression response of high-performance prepregs for AFP applications
Page Range: p.389-398
Author(s): Rao S; Umer R; Cantwell W J
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.6

Abstract
In this study, the compaction response of unidirectional out-of-an autoclave (OOA) prepreg tape has been evaluated experimentally at 25 deg, 45 deg and 65 deg C. Instantaneous and incremental displacement compaction experiments have been carried out in a universal testing machine until a compressive strain of 0.42 plus/minus 0.02 was achieved. The fibre-bed stress was determined by transposing the results of displacement-controlled experiments onto data from corresponding load-controlled experiments. The material was then modelled as a viscoelastic material using a third order exponential decay function, based on a generalised Maxwell model. This procedure enabled the extraction of the relaxation time constants and the peak stress. The results highlight a linear relationship between the operating temperature and the load/stress relaxation response of the prepreg/tape, suggesting that if the fibre placement procedure is performed at 65 deg C, the effect of roller stiffness on tape/fibre laying is negligible. The maximum contribution of fibre stress to the overall relaxation is approximately 6% at 45 deg C and 65 deg C, indicating the formability to be matrix dependent. A minimum spring-back is observed in specimens that were tested under incremental displacement conditions. The difference in thickness of the as-laid laminate and the cured laminate at 45 deg C and 65 deg C were similar. The linear stress relaxation model has been shown to be capable of predicting the maximum stress accurately using the viscosity values of the dashpots and the moduli of the springs. 42 Refs.

Title: Fracture behaviour of epoxy resins modified with liquid rubber and crosslinked rubber particles under mode I loading
Page Range: p.399-406
Author(s): Makoto Imanaka; Keisuke Ikeda; Yoshinobu Nakamura; Masaki Kimoto
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.6

Abstract
Three-point bending tests were conducted with two kinds of rubber-modified epoxy resins: a liquid rubber-modified epoxy resin and a nano-elastomer particle-modified one. In most studies on rubber-toughened epoxy resins, fracture toughness has been evaluated by critical stress intensity factor or critical energy release rate, where the crack is assumed to propagate rapidly, and stable crack propagation has not been considered. However, stable crack propagation was observed for the present rubber-modified epoxy resins. To take into account crack propagation, fracture toughness was characterised using the crack-growth resistance curves (R-curve). In the present study, the evolution behaviour of the damage zone near the crack tip was observed using a video-microscope for the two kinds of rubber-modified resins. Furthermore, to investigate microscopic fracture mechanisms, the fracture surfaces were observed by scanning electron microscopy, and side views near the crack tip were also observed by a confocal laser scanning microscopy. 6 Refs.

Title: Concept of tercet molecular nanocomposites and preliminary studies on [PPTA /(PA -6/PA -66)] system of miscible blend of polyamide-6/polyamide-6,6 molecularly reinforced at nano level by poly(pphenylene-terephthalamide)
Page Range: p.407-414
Author(s): Sanjay Palsule; Anuja Baijal; Sampat Singh Bhati
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.6

Abstract
A tercet molecular nanocomposite is a ternary miscible polymer system in which a miscible blend of two flexible polymers is molecularly reinforced at nanometre level by a rigid-rod macromolecule and the tercet molecular nanocomposite demonstrates properties better than those of the constituent flexible polymers and their blend. A tercet molecular nanocomposite of a blend of flexible polyamide-6 (PA6) and polyamide-6,6 (PA6,6) molecularly reinforced at the nanometre level by a rigid-rod poly-p-phenylene-terephthalamide (PPTA) has been processed by coagulating a sulphuric acid solution of the components in water. This study reports miscibility, structure and properties of PPTA/[PA6/PA6,6] tercet molecular nanocomposites. Miscibility has been established by recording single intermediate glass transition temperatures by differential scanning calorimetry. Homogeneous morphology and dispersion of PPTA in [PA-6/PA-6,6] below 5 nanometre level has been established by scanning electron microscopy. Intermolecular interactions dispersing PPTA in [PA-6/PA-6,6] below the 5 nm level by imparting miscible homogeneous morphology and have been identified by Fourier transform infra red (FTIR) spectroscopy. Improved tensile mechanical properties of the tercet molecular nanocomposite, compared to those of the constituent flexible polymer blend, have been established by universal testing machine. 22 Refs.

Title: Synthesis of poly (styrene-block-vinyl alcohol) by successive photo-induced charge transfer polymerization and molecular dynamics simulation of its compatibility for the blend system
Page Range: p.415-426
Author(s): Fangzhuan Liu; Lingyu Wang; Qinjian Yin; Bo Jiang
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.6

Abstract
In the present work, a rapid and novel route to prepare a diblock copolymer consisting of styrene and vinyl acetate (VAC) units was performed by successive photoinduced charge-transfer polymerisation (CTP) under UV irradiation, and then a series of objective products PSm-b-PVAn bearing different ratios of PS and PVA was obtained by the hydrolysis of PSm-b-PVACn with sodium ethoxide as the catalyst. Additionally, the influences of the reaction time, concentration of monomer and photoinitiator and kinetics of copolymerisation were investigated. Good linear relationships of ln([St] 0/[St]) and ln([VAc]0/[VAc]) with the polymerisation time indicated a first-order control/'living' process. The copolymers were characterised in detail by means of Fourier transform infrared (IR) spectrometry, 1H NMR and gel permeation chromatography (GPC). Furthermore, the miscibility of the originally incompatible blend system was improved quite significantly, so a full atomistic molecular dynamics simulation was applied to discuss the binary and ternary systems through the Flory-Huggins parameters, enthalpy of mixing and Tg. 38 Refs.

Title: Studies on physical and mechanical properties of silica fume-filled nylon 66 polymer composites for mechanical components
Page Range: p.427-434
Author(s): Raja V L; Kumaravel A
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.6

Abstract
Enhancement of mechanical and wear-resistant properties of polymer composites is important because they are widely used in tribological environments. The properties can be enhanced by reinforcement with particulates in the polymer matrix. Nylon is used in many engineering applications, and silica fume is used as a filler material in civil-oriented applications. In this paper, the properties of Nylon 66 reinforced with silica fume particulates are investigated. The reinforcement by silica fume at 5%, 10%, 15%, 20% and 25% weight fraction is considered. Nylon 66 and silica fume were compounded in a twin screw extruder and the test samples were produced in 60 ton L and T injection moulding machine. Heat distortion temperature (HDT), tensile, flexural, compression and impact strength tests were carried out in accordance with ASTM standards. The test results confirmed the improved mechanical and HDT properties of the Nylon 66-silica fume composites. Observations made using scanning electron microscopy revealed good physical adhesion and uniform dispersion of silica fumes in the Nylon 66. 27 Refs.

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