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Polymers and Polymer Composites

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Title: CURE KINETICS OF AN EPOXY-ANHYDRIDE-IMIDAZOLE RESIN SYSTEM BY ISOTHERMAL DSC
Page Range: p.445-454
Author(s): Wang C S; Choongyong Kwag
File size: 208K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
Liquid composite moulding is used to manufacture automotive structural composites, and epoxies have been used in vehicle mass production programs. N order to meet the automotive processing and performance requirements, it is necessary to optimise the moulding cycle times. This necessitates an understanding of the curing behaviour of the resin. This study, therefore, examines the curing behaviour of a dimethyl imidazole catalysed diglycidyl ether of bisphenol A-methyltetrahydrophthalic anhydride resin system using isothermal data obtained from differential scanning calorimetry. The system was selected as a potential automotive liquid moulding resin based on its favourable moulding characteristics and thermomechanical properties. The kinetic data were analysed using both n^th order and autocatalytic kinetic models. The results indicated that the epoxy curing process could be described satisfactorily by Kamal's four-parameter generalised autocatalytic model, modified with an exponential function of conversion defined as the diffusion factor. 19 refs.

Title: APPLICATION OF THE ‘THEORY OF MIXTURES' TO TEMPERATURE – STRESS EQUIVALENCY IN NONLINEAR CREEP OF THERMOPLASTIC/AGRO-FIBRE COMPOSITES
Page Range: p.455-472
Author(s): Pramanick A; Sain M
File size: 390K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
A study is made of thermoplastic/agro-fibre composites based on HDPE (40%) and rice husk (60%) in terms of the ability to predict creep. In order to characterise the viscoelasticity of this biocomposite, it was necessary to predict creep by establishing a relationship between deformation, time, temperature and stress. An extended ‘theory of mixtures' is used to describe creep-related parameters in two-phase materials. The stress- and temperature-related shift factors were estimated in terms of the activation energy of the constituents. The combined effect of temperature and stress on creep strain was accommodated in a single analytical function, where the interaction was shown to be additive. The model is claimed to be unique because it describes creep, not through curve fittings, but in terms of the creep constants of the constituents. This constitutive model is described not only as a vanguard in the prediction of long term creep of many biocomposites, but also in the modelling of creep under step loading of temperature. The impact of humidity was explored for the first time for the creep of agro-based composites. 20 refs.

Title: EFFECT OF INTERFACIAL MODIFICATION ON THE RHEOLOGICAL PROPERTIES AND NUCLEATION BEHAVIOUR OF PP-BaSO”4 COMPOSITES
Page Range: p.473-481
Author(s): Ke Wang; Jingshen Wu; Hanmin Zeng
File size: 295K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
The effect of surface treatment of barium sulphate filler particles on the rheological behaviour of PP composites was studied. The polypropylene-barium sulphate composites were prepared by pretreating the filler with stearic acid, silane and polypropylene-g-maleic anhydride, respectively. The effects of the PP-barium sulphate interfacial interaction on the rheological properties and nucleation behaviour of the composites were studied. It was shown that once the polymer-filler interfacial interaction had been enhanced by reactive coupling agents, the fillers acted as temporary physical crosslinking points, effectively restricting the motion of polymer chains neighbouring the filler particles. As a result, the tendency of the polymer chains to undergo intermolecular slippage was reduced, and the melt viscosity was enhanced. However, when the filler surface was modified with non-reactive coupling agents such as stearic acid, the reduced particle-particle interaction and lubricating effect of the stearic acid decreased viscosity. With the modification of the interface, the barium sulphate dispersion in PP was improved and the thermodynamic potential barrier for the formation of primary nuclei was reduced by the adsorption mechanism. 16 refs.

Title: FRACTURE AND FAILURE BEHAVIOUR OF JUTE FABRIC REINFORCED POLYPROPYLENE. EFFECT OF THE INTERFACE MODIFICATION
Page Range: p.483-493
Author(s): Acha B A; Karger-Kocsis J; Reboredo M M
File size: 600K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
The tensile fracture and failure behaviour of jute cloth (25 wt.%) reinforced PP composites were studied as a function of the interface modification. Although jute appears to be promising candidate as a reinforcement for PP, the lack of adhesion between the hydrophilic cellulose fibres and the hydrophobic PP results in unsatisfactory properties for the composite. In this study, the jute fabric was subjected to esterification and lignin and maleated PP were used as modifiers. The tensile and fracture mechanical characteristics of the composites were determined. Analysis of the emitted acoustic signals, together with fractographic inspection served to determine the failure and damage development. The best property improvements were achieved by using maleated PP. the observed notch sensitivity for the specimens was attributed to missing reinforcement homogeneity, owing to the presence of insufficient jute cloth layers. 29 refs.

Title: PREPARATION AND SURFACE PROPERTIES OF SILOXANE-ACRYLATE COPOLYMER WITH HIGH SILOXANE CONTENT
Page Range: p.495-502
Author(s): Xiaobo Deng; Shunsheng Cao; Bailing Liu; Rong Luo; Hualin Chen
File size: 157K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
Latices of siloxane-acrylate copolymer find wide application due to their non-toxic and non-contaminating character, and interest has been shown to combine acrylate with siloxane in order to obtain stable polymer latices and other polymer materials with improved performance. It is known that the more siloxane in the copolymer, the better the properties, but since the polymerisation temperature of the acrylate is higher than 80 deg.C and under such conditions the Si (OCH”3)”3 groups are easy to hydrolyse, forming siloxane bonds and then proceeding to form a network structure and coagulum. This is the main reason that the siloxane content of the copolymer could not be enhanced during polymerisation. To overcome this, an oxidation-reduction initiator was introduced into the system, which could initiate the reaction at relatively low temperatures. In addition, sodium bicarbonate was added when the pH fell below 6.5. Under these conditions, the acrylate-siloxane copolymers were prepared by emulsion polymerisation in which the siloxane content could reach 30%. The latex properties of the copolymer were characterised by FTIR spectroscopy and the use of a surface tension analyser. It was shown that almost all the monomer had participated in the copolymerisation. Results of characterisation by the surface tension analyser showed that the introduction of organic siloxane could decrease the surface tension values greatly. Surface properties were also studied by the static contact angle method. Compared with the acrylate homopolymer, the copolymer containing 3-(methacryloxypropyltrimethoxysilane) was capable of making an increase in water repellency. 29 refs.

Title: SINTERING OF NON-SPHERICAL POLYETHYLENE PARTICLES
Page Range: p.503-513
Author(s): Torres F G; Cubillas M L; Quintana O A
File size: 346K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
Powder sintering has been well studied for metals and ceramics, but not many fundamental studies have been carried out in order to understand the nature of the underlying processes which take place during the formation of a dense material when a polymer powder is sintered as occurs during the rotational moulding process. This work reports on experimental observations of polymer sintering with non-spherical particles. The evolution of neck formation during sintering was studied by two-particle experiments in a temperature-controlled oven. Shrinkage and change in surface area were also measured using image analysis. Melt densification studies using powder particles were included to complement the two-particle experiments. It was found that ground polymer particles show an important shape recovery stage at the beginning of the sintering process. Comparisons with sintering models available in the literature were made, and deviations from the behaviour predicted by such models were discussed. 28 refs.

Title: NANOCOMPOSITES BASED ON THERMOPLASTIC ELASTOMERIC BLENDS OF STYRENE ACRYLONITRILE AND ETHYLENE VINYL ACETATE: EFFECT OF NATURE AND LOADING OF NANOCLAYS AND DYNAMIC VULCANIZATION
Page Range: p.515-525
Author(s): Patel J; Maiti M; Naskar K; Bhowmick A K
File size: 193K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
A thermoplastic elastomer based on a 30:70 w/w/ styrene-acrylonitrile: ethylene vinyl acetate blend was prepared. In order to improve the strength of the blend, two types of nanoclay (grades of Cloisite) were added in variable loading levels. Improved levels of mechanical properties were achieved with Cloisite NA at 4 phr loading. These results were explained in terms of the morphology of the nanocomposites as studied by X-ray diffraction, atomic force microscopy and X-ray dot-mapping. The dynamic mechanical properties and the diffusion behaviour of acetone through the resultant nanocomposites corroborated the observations on the static mechanical properties. It was demonstrated that dynamic vulcanisation significantly improved the mechanical properties of nanoclay reinforced SAN/EVA blends. 40 refs.

Title: COATED NANO-SIZED CACO”3 REINFORCED SEMI-CRYSTALLINE EPDM
Page Range: p.527-536
Author(s): Yabin Zhou; Shifeng Wang; Yong Zhang; Yinxi Zhang
File size: 339K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
Nano-sized calcium carbonate modified with stearic acid was used to reinforce semi-crystalline EPDM and for comparison, micron-sized calcium carbonate was also studied. It was found that both nanosized and micron-sized calcium carbonate fillers improved the mechanical properties of the EPDM vulcanisates and that the nanofiller exhibited better reinforcement than the microfiller. The difference in reinforcement effects was explained in terms of the filler particle size and the crosslink density of the vulcanisates. The nanofiller was also modified by titanate, borate, and aluminate-titanate complex coupling agents and used to reinforce EPDM vulcanisates. Results showed that the titanate coupling agent-coated nanosized filler exhibited the best reinforcement ability. FE-SEM showed that stearic acid, titanate and aluminate-titanate coupling agents improved the dispersion of the filler in the rubber matrix, whereas borate coupling agents could not. The effect of modified nano-sized calcium carbonate on the dynamic mechanical properties was also studied. Incorporate of calcium carbonate was found to reduce the glass transition temperature of the vulcanisates, with micro-sized calcium carbonate depressing the TG to a greater extent. 21 refs.

Title: ON-LINE MONITORING OF RESIN CONTENT AND VOLATILE CONTENT IN CARBON/PHENOLIC RESIN PREPREG CLOTH BY NEAR-INFRARED SPECTROSCOPY
Page Range: p.537-543
Author(s): Wei Li; Yu Dong Huang; Li Liu; Bo Jiang
File size: 129K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 14
Issue No: No. 5

Abstract
NIR diffuse reflectance spectroscopy is demonstrated to be a suitable on-line monitoring technique during the manufacture of carbon/phenolic resin prepreg cloth in terms of resin and volatile contents. Calibration models were generated using partial least square regression to relate the on-line spectral data to the components' content. Due to its rapid and non-destructive nature, the NIR spectroscopic method is proposed as an alternative to traditional chemical analysis. 31 refs.

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