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Title: INSIGHTS INTO THE ENCAPSULATION PROCESS OF PHOTOVOLTAIC MODULES: GCMS ANALYSIS ON THE CURING STEP OF POLY(ETHYLENE-CO-VINYL ACETATE) (EVA) ENCAPSULANT
Page Range: p.665-672
Author(s): Heng-Yu Li; Theron R; Roder G; Turlings T; Yun Luo; Lange R F M; Ballif C; Laure-Emmanuelle Perret-Aebi
File size: 290K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
Appropriate encapsulation schemes are essential in protecting the active components of the photovoltaic (PV) module against weathering and to ensure long term reliability. For crystalline cells, poly(ethylene-co-vinyl acetate) (EVA) is the most commonly used PV encapsulant. Additives like peroxides and silanes are formulated in EVA encapsulants to obtain the desired properties, e.g. the desired gel content value and sufficient adhesion after the encapsulation process etc. The identification and control of volatile organic compounds (VOCs) released by the polymeric encapsulant during PV module encapsulation is important for understanding and optimizing processes in order to enhance the encapsulation quality of the manufactured modules. The authors demonstrate how gas chromatography and mass spectrometry (GC-MS) techniques can be used to help understand the curing process, mainly by identifying the VOCs emanating from EVA under the effect of temperature and pressure. The results provide chemical insights into the EVA encapsulation process, which are valuable for further optimisation of the PV module manufacturing process and evaluation of its environmental impact. 26 Refs.

Title: FRICTION AND WEAR OF EPOXY COMPOSITES CONTAINING SILICA NANOPARTICLES GRAFTED BY HYPERBRANCHED AROMATIC POLYAMIDE
Page Range: p.673-682
Author(s): Ying Yu; Min Zhi Rong; Ming Qiu Zhang
File size: 408K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
Nano-sized SiO2 particles grafted with hyperbranched aromatic polyamide were employed as fillers for fabricating epoxy based composites. The hyperbranched aromatic polyamide was selected because its terminal amine groups could take part in the curing reaction of epoxy resin and covalently connect silica nanoparticles with the matrix. The experimental results proved the occurrence of this reaction, and indicated that the presence of the grafted SiO2 in epoxy does not change the overall curing mechanism of epoxy. In comparison to the composites filled with untreated nano-SiO2 particles, the composites with the grafted nano-SiO2 exhibited significantly improved sliding wear resistance and reduced frictional coefficient owing to the strong filler/matrix interfacial bonding. Moreover, hyperbranched aromatic polyamide grafted nano-SiO2 was more effective to enhance tribological properties of epoxy than linear polymers grafted versions. 23 Refs.

Title: DYNAMIC MECHANICAL CHARACTERIZATION OF THE CROSSLINKED AND CHAIN-EXTENDED HTPB BASED POLYURETHANES
Page Range: p.683-692
Author(s): Nadeem Ahmad; Khan M B; Xiaoyan Ma; Noaman Ul-Haq; Ihtasham-Ur-Rehman
File size: 301K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
The viscoelastic response of two different polyurethane (PU) systems (crosslinked and chain-extended) based on hydroxyl terminated polybutadiene (HTPB) were analysed and compared. The PU elastomers were fabricated by reacting HTPB with isophorone diisocyanate. A tri-functional alcohol (1,2,6 hexanetriol) and a bi-functional aliphatic diol (1,4 butanediol) were used as the crosslinking agent and the chain extender respectively. Hydrogen bonding between the hard segments is identified by the IR spectroscopy. The segregation of these segments was manifested by dynamic mechanical analysis at characteristic frequency over a wide range of temperature. The intensity and temperature location of the relaxation peaks was identified and discussed. The phenomenon of viscous dissipation was evaluated by recording the viscoelastic parameters as a function of temperature across a series of frequencies. The results obtained indicate that the chain-extended polymer is phase segregated and more sensitive to temperature rise via viscous dissipation as compared to crosslinked polymer. Both the polymers showed similar glass transition temperature (Tg) and characteristic relaxation times. Master curves for the polymer systems investigated are produced and discussed. 31 Refs.

Title: SYNTHESIS AND CHARACTERIZATION OF MONTMORILLONITE-CARBON NANOTUBES HYBRID FILLERS FOR NANOCOMPOSITES
Page Range: p.693-700
Author(s): Madaleno L; Ryszard Pyrz; Jensen L R; Pinto J J C; Lopes A B; Dolomanova V; Schjodt-Thomsen J; Rauhe J C M
File size: 428K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
Montmorillonite-carbon nanotubes hybrids were prepared by growth of carbon nanotubes (CNT) on five different types of iron-montmorillonite clays using the chemical vapour deposition (CVD) method. Microscopy studies revealed the presence of carbon nanotubes protruding from clay surfaces and linking the clay layers in a network structure. X-ray diffraction results showed changes in the clay interlayer spacing induced by growth of carbon nanotubes within the layers of iron-montmorillonites. The quality of the resulting carbon nanotubes was evaluated by Raman spectroscopy and thermogravimetric analyses were used to evaluate the amount of carbon nanotubes and its thermal stability. The method used for the preparation of the iron-montmorillonites appeared to be critical for the quality and quantity of carbon nanotubes obtained in each hybrid. In a preliminary study the hybrids were used to reinforce polyurethane nanocomposite foams. 23 Refs.

Title: THE STRUCTURE AND NONISOTHERMAL CRYSTALLIZATION KINETICS OF HDPE NANOCOMPOSITES FILLED WITH MG2AL-LDH
Page Range: p.701-710
Author(s): Jun Qin; Xiaolang Chen; Jie Yu; Tian Xie; Yaozhu Tian; Qing Lv; Pu Xie
File size: 476K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
High-density polyethylene (HDPE)/Mg2Al-layered double hydroxide (Mg2Al-LDH) nanocomposites with an ethylene-acrylic acid random copolymer (EAA)/Mg2Al-LDH master batch were prepared by melt-mixing. The structure of the nanocomposites was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results demonstrate the formation of the nanocomposites with exfoliated/intercalated layered double hydroxides well distributed in the HDPE matrix. The nonisothermal crystallisation behaviour of master batch-based HDPE nanocomposites was studied by using differential scanning calorimetry (DSC). The crystallisation behaviour of HDPE/Mg2Al-LDH nanocomposites was well defined by the Avrami analysis and Jeziorny method, as well as the combined Avrami and Ozawa analysis (MO's model). The results reveal that a very small amount of Mg2Al-LDH (1%) accelerates the crystallisation process in comparison with the neat HDPE, and the high crystallisation rate is attributed to the nucleating effect of the exfoliated nanoparticles. Overall, the exfoliated Mg2Al-LDH particles act as the nucleating agent, and therefore distinctly change the type of nucleation, growth and geometry of HDPE crystals. 36 Refs.

Title: FRACTURE TOUGHNESS OF LAMINATED COMPOSITES - A NON-LINEAR ANALYSIS
Page Range: p.711-716
Author(s): Rizov V; Mladensky A
File size: 280K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
Non-linear fracture behaviour of laminated composite materials under mode I (crack opening) loading conditions was studied experimentally and theoretically. For this purpose, single edge notched tension (SENT) tests were carried-out using displacement-controlled loading under room temperature dry conditions. It was found that the load-displacement diagram had non-linear character prior to onset of macroscopic crack propagation. Thus, the main objective of this paper was to study the fracture properties using non-linear fracture mechanics. A two-dimensional finite element model was set-up in order to analyse the non-linear response of the SENT test specimen. Non-linear deformation due to damage was simulated using the Tsai-Hill failure criterion. The failure analysis revealed that the damage was localized in the vicinity of the crack tip. The fracture response was characterized using a J-integral. It was shown that a realistic appraisal of the potential for crack growth should include the effects of non-linear material deformation. It was found that taking into account the non-linear deformation increased the fracture resistance. This finding was attributed to the increased strain energy dissipation due to the damage induced non-linear behaviour of the SENT test specimen. 32 Refs.

Title: PERFORMANCE OF GRAPHITE FILLED COMPOSITE BASED ON BENZOXAZINE RESIN. II. DECREASING THE MOULDING TIME OF THE COMPOSITE
Page Range: p.717-724
Author(s): Hajime Kimura; Keiko Ohtsuka; Akihiro Matsumoto
File size: 355K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
To put the fuel cell to practical use, it is necessary to reduce its cost for the production of the bipolar plate as one of the components in the cell. Decreasing the moulding (cure) time of the graphite filled composites as a bipolar plate can increase its productivity. In this study, we aimed to decrease the moulding (cure) time of graphite-filled composites based on benzoxazine resin for the bipolar plate. Therefore, phenol novolac resin was added to benzoxazine resin as a curing accelerator. Expanded graphite was used for the preparation of the graphite-filled composites. The composites were prepared by means of the compression moulding of mixtures of graphite and benzoxazine resin containing phenol novolac as a curing accelerator. The properties of the graphite filled composites based on benzoxazine resin containing phenol novolac as a curing accelerator were characterised by mechanical properties, gas permeability and electrical conductivity. As a result, the curing reaction of benzoxazine resin containing phenol novolac as a curing accelerator could proceed more rapidly than that of only benzoxazine resin, and the moulding (cure) time of the composite was decreased. It was found that phenol novolac was an effective moulding accelerator of the graphite filled composites based on benzoxazine resin, and that it could increase the productivity of the bipolar plate using the graphite filled composite based on benzoxazine resin. It was also found that graphite filled composites based on benzoxazine resin containing phenol novolac as a curing accelerator showed good gas impermeability, electrical conductivity and mechanical properties compared with those of the graphite-filled composites based on the conventional phenolic resins. 22 Refs.

Title: EFFECT OF MOLECULAR WEIGHT OF POLYCARBOXYLATE-TYPE SUPERPLASTICIZER ON THE RHEOLOGICAL PROPERTIES OF CEMENT PASTES
Page Range: p.725-736
Author(s): Xiongyi Peng; Conghua Yi; Xueqing Qiu; Yonghong Deng
File size: 413K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
In order to study the effect of molecular weight of polycarboxylate-type superplasticiser (PC) on the rheological properties of cement pastes, PCs with different molecular weights (low, medium, high) were synthesised, and used as superplasticisers for cement suspensions. The effect of molecular weight of PC on the zeta potential, adsorption, and rheological behaviour of the corresponding cement suspensions were investigated systematically. Among the PCs, PC with a medium molecular weight always produced the lowest apparent viscosity for cement pastes at the same shear rate. Compared to PC with a low molecular weight, PC with a high molecular weight presented a stronger initial dispersing ability and a weaker dispersing stabilising ability for cement pastes. In addition, PC with a low molecular weight had an advantage over PC with a high molecular weight for reducing the viscosity of paste in the low added dosage or low water/cement ratio, but the latter had the advantage of reducing the viscosity of the paste when the added dosage or water/cement ratio was high. This understanding of the rheological properties of cement pastes incorporating PC will provide an important reference for the application and synthesis of PC with high efficiency. 28 Refs.

Title: EFFECT OF NANOCLAY ON QUASI STATIC PERFORATION OF THIN-WALLED POLYMER COMPOSITE LAMINATES
Page Range: p.737-748
Author(s): Javad Moftakharian Esfahani; Masoud Esfandeh; Ali Reza Sabet
File size: 422K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
In this study, the penetration and perforation performance of nanoclay reinforced unsaturated polyester resin/ fibreglass nanocomposite laminates have been investigated via quasi-static indentation tests using a hemispherical nose indenter. Unsaturated polyester resin (UP) was mixed with 1.5 and 3 wt.% nanoclay using a homogeniser stirrer to prepare a homogeneous mix. UP reinforced nanocomposite was then utilized to manufacture 150 x 150 mm2 laminated composite panels using 400 g/m2 glass fibre woven roving via a hand lay-up process. X-ray diffractometry, transmission electron microscopy analysis, energy-dispersive X-ray (EDXA) analysis and measurement of viscosity changes in the liquid state resin confirmed the exfoliation and the intercalation of the nanoclay by the unsaturated polyester resin system used. Quasi-static perforation tests were conducted using a surface-hardened steel indenter with a hemispherical tip at 5 and 500 mm/min load rates on nanocomposite laminated plates. Measurement of the quasi-static force as a function of indenter displacement for all the specimens showed four distinct regions, namely penetration, perforation, exit and residual frictional force. The results indicated a clear role being played by the nanoclay filler as a secondary reinforcement, in terms of higher energy absorption in all four regions. 42 Refs.

Title: STUDIES ON THERMOMECHANICAL CHARACTERISTICS OF POLY(METHYL METHACRYLATE) AND ETHYLENE-METHYL ACRYLATE COPOLYMER BLENDS
Page Range: p.749-754
Author(s): Poomalai P; Varghese T O; Siddaramaiah
File size: 206K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 20
Issue No: No.8

Abstract
Blends of poly(methyl methacrylate) (PMMA) with ethylene - methyl acrylate (EMA) copolymers of different compositions, viz. 95/05, 90/10, 85/15 and 80/20 wt.% were prepared by a melt mixing technique using a twinscrew extruder. The blends were characterized by thermo-analytical methods, viz. differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The TGA of PMMA/ EMA blends show that thermal degradation takes place in two steps and the temperature of the decomposition rate maximum is proportional to the compositions of the blends. The DSC studies reveal two glass-transition temperatures (Tg) for all the blends corresponding to their individual components which indicates that the blends are incompatible. The DMA thermograms exhibit two steps in the dynamic modulus-temperature curves for higher EMA content, which is characteristic of immiscible polymers in a two phase system. 27 Refs.

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