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Polymers and Polymer Composites

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Title: EXTRUSION OF CNT-MODIFIED POLYMERS WITH LOW VISCOSITY - INFLUENCE OF CRYSTALLIZATION AND CNT ORIENTATION ON THE ELECTRICAL PROPERTIES
Page Range: p.473-482
Author(s): Steinmann W; Vad T; Weise B; Wulfhorst J; Seide G; Gries T; Heidelmann M; Weirich T
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 21
Issue No: No.8

Abstract
Several polymers were modified with multiwalled carbon nanotubes (CNT) to study the influences of the crystallisation in the polymeric matrix and of the CNT orientation during extrusion on the electrical conductivity. Experiments were carried out with common semi-crystalline polymers (polypropylene, polyethylene, polyamide 6) and compared to an amorphous polymer (ethylene vinyl acetate). All polymers were grades with low viscosity, so that the CNT could be oriented well during extrusion. For all materials, the percolation threshold was determined, and the lowest value of 3% was found in polypropylene. The percolation threshold was correlated to the degree of crystallinity of the matrix polymers, so that crystallites could be seen as an excluded volume for CNT. The crystallisation itself was analysed by differential scanning calorimetry (DSC), whereby nucleation effects and changes in the crystallisation temperature were found. The shear rate during extrusion had a large influence on the electrical conductivity. This effect was analysed by transmission electron microscopy (TEM), with which the orientation of CNT in the direction of extrusion was visualized and differences between the polymer matrices were explained. 37 Refs.

Title: PROCESSING AND CHARACTERIZATION OF CONTINUOUS FIBRE TAPES CO-MOULDED WITH LONG FIBRE REINFORCED THERMOPLASTICS
Page Range: p.483-494
Author(s): Balaji Thattaiparthasarathy K; Selvum Pillay; Dhruv Bansal; Haibin Ning; Vaidya U K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 21
Issue No: No.8

Abstract
An important advantage when designing with plastics is the ability to incorporate features such as ribs, grids and bosses in the part. Rib stiffened polymer matrix composites have been widely used in aerospace, automobile, and civil infrastructure applications due to their high impact and fatigue resistance, high strength and stiffness to weight ratio, and damage tolerance. However, for long fibre-reinforced polymer composites, the processing complexity increases for features including ribs, grids and bosses. An innovative method of replacing ribs is the use of pre-consolidated continuous fibre reinforced thermoplastic (CFRT) tapes that can be co-moulded with long fibre thermoplastics (LFT). This work focuses on processing and performance evaluation in terms of the static and dynamic properties of LFTs co-moulded with pre-consolidated CFRTs, referred to as endless long fibre thermoplastic (E-LFT). The E-LFT approach is an alternative to rib stiffened composites. The effect of the thickness and fibre type in tape reinforced LFT is compared to LFT (with and without ribs) of equivalent flexural rigidity for static flexure and low velocity impact (LVI) response. In all these conditions, E-LFT samples performed better that the LFTs with and without ribs. LFT samples with and without ribs exhibited a brittle failure, as opposed to the progressive failure exhibited by E-LFT. 14 Refs.

Title: IMPROVEMENT IN MECHANICAL AND THERMO-MECHANICAL PROPERTIES OF CARBON FIBRE/EPOXY COMPOSITES USING CARBOXYL FUNCTIONALIZED MULTI-WALLED CARBON NANOTUBES
Page Range: p.495-508
Author(s): Salam M B A; Hosur M V; Jahan N; Rahman M M; Jeelani S
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 21
Issue No: No.8

Abstract
Investigations were carried out to optimize mechanical and thermal performances of carbon fibre/epoxy composites modified with functionalised carbon nanotubes. For fabricating carbon fibre/epoxy nanocomposites, 0.1-0.4 wt.% carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs-COOH) were incorporated in an epoxy system. Laminates were cured at a temperature of 65.55 degrees C. The effects of MWCNT on flexural, interlaminar shear strength (ILSS), tensile and thermo-mechanical properties of carbon fibre/epoxy composites were studied. The results obtained from flexural, ILSS, tensile and dynamic mechanical analysis (DMA) of carbon fibre/epoxy demonstrated a linearly increasing trend in properties up to 0.3 wt.% MWCNT loading. Results obtained from the thermal mechanical analysis showed a linearly decreasing trend in coefficient of thermal expansion up to 0.3 wt.% MWCNT loading. The properties were lower at 0.4 wt.%, due to agglomeration that may have resulted in poor wetting of the carbon fibres. 39 Refs.

Title: MODELLING AND PREDICTION OF BARRIER PROPERTIES OF POLYMER LAYERED SILICATE NANOCOMPOSITES
Page Range: p.509-518
Author(s): Vikas Mittal
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 21
Issue No: No.8

Abstract
Different permeation models have been compared with the experimental barrier performance of the polyethylene and polypropylene layered-silicate nanocomposites. It was observed that the models assuming the perfect orientation of filler platelets did not represent the nanocomposite system accurately, whereas the models incorporating the misalignment and incomplete filler exfoliation effects were more efficient. Such models also predicted reduction in the barrier performance of the nanocomposites due to saturation of the polymer matrix with the platelets at a particular filler fraction, an observation which was also experimentally confirmed. Further combinations of these models with each other generated additional insights into the nanocomposite systems such as average aspect ratio, extent of filler platelet randomness, relative platelets distance, shape factor and aggregate thickness etc. As a beneficial alternative, modelling and prediction of the barrier performance of the polymer nanocomposites was also demonstrated using the mixture and factorial design methods. Using factorial design methods, aspect ratio as well as percent randomness of the filler platelets in the nanocomposites could be quantified by knowing beforehand the permeation performance and filler volume fraction. Alternatively, by knowing either the aspect ratio or percent randomness revealed the average permeation behaviour in the nanocomposite of known filler volume fraction. 28 Refs.

Title: STUDY ON THE SYNTHESIS AND ANTIBACTERIAL PROPERTIES OF SILVER-CHITOSAN COMPOSITE
Page Range: p.519-524
Author(s): Yan Bao; Chengrong Wei; Enqi Su; Qi Zhang; Yongxiao Bai
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 21
Issue No: No.8

Abstract
The aim of this work was to synthesize a silver-chitosan composite to enhance the antibacterial properties of the composite by using as small an amount of silver as possible. The silver-chitosan composite was prepared using a facile method. The structure character of the silver-chitosan composite was characterized by X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FT-IR). Its antibacterial activities were evaluated by measurements of the minimal inhibition concentration (MIC), inhibition zone diameter and the kinetics of antibacterial activity. The results indicated that silver was connected with the chitosan homogeneously and stably after initiation by potassium persulphate. The composite exhibited high antibacterial activity to Candida albicans with low MIC and relatively low optical density; it also had good antibacterial activity to Escherichia coli with larger inhibition zone diameter. 44 Refs.

Title: FABRICATION, STRUCTURAL MORPHOLOGY AND THERMAL ENERGY STORAGE/RETRIEVAL OF ULTRAFINE PHASE CHANGE FIBRES CONSISTING OF POLYETHYLENE GLYCOL AND POLYAMIDE 6 BY ELECTROSPINNING
Page Range: p.525-532
Author(s): Yibing Cai; Xue Zong; Heng Ban; Qian Liu; Hui Qiao; Qufu Wei; Yong Zhao; Hao Fong
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 21
Issue No: No.8

Abstract
This study aimed at the development and characterization/evaluation of polyethylene glycol (PEG) encapsulated in supporting polymer matrices (e.g., electrospun nanofibres) as innovative form-stable phase change materials (PCMs) for storage and retrieval of thermal energy. Ultrafine phase change fibres consisting of PEG (acting as phase change materials) and polyamide 6 (PA6, acting as supporting materials) were successfully fabricated by electrospinning technique. The effects of PEG amount and two different molecular weights (Mn) of PEG on structural morphology and thermal energy storage/retrieval property of PEG/PA6 ultrafine phase change fibres were systematically studied by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The SEM images showed that neat PA6 nanofibres were smooth with cylindrical shape, but the tubercles and/or beads in fibres were observed for PEG/PA6 ultrafine phase change fibres with increasing PEG amount and higher molecular weight of PEG. The average fibre diameters ranged from about 80 to 150 nm and increased with increasing the PEG amount and molecular weight of PEG, which resulted from the increased viscosity and decreased conductivity of composite spin dopes. The DSC results indicated that the enthalpies of melting and crystallisation of PEG/PA6 ultrafine phase change fibres increased with increasing PEG amount, and were lower than those of neat PEG powders. 32 Refs.

Title: SHORT NYLON 6 FIBRE REINFORCED POLYSTYRENE/NATURAL RUBBER BLENDS: EFFECT OF MALEATED-POLYSTYRENE COMPATIBILISER
Page Range: p.533-542
Author(s): Jayalatha G; Kutty S K N
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 21
Issue No: No.8

Abstract
Nylon 6 short fibre was used to prepare composites based on blends of 85/15 Polystyrene (PS)/Natural rubber (NR) to study the effects of surface modification of the fibres and a compatibiliser based on PS. Initially, the loading of fibre, cut to 6 mm length, was varied from 0 to 3 wt.% in a 85/15 PS/NR blend. The composites were prepared on a Thermo Haake Rheocord mixer at 170 deg C and sheeted out on a two-roll mill. Tensile, flexural and impact test samples were punched out from sheets and tested to study the mechanical and dynamic mechanical properties. It was found that the tensile properties, flexural properties and impact strength increased with the fibre content up to 1 wt.%, above which there was a significant deterioration in the properties. The fibre surface was further modified by alkali treatment and a reactive compatibiliser based on maleic anhydride-grafted-polystyrene (MA-g-PS) was used in an effort to improve the performance of the composites. The treated Nylon fibre in conjunction with the compatibiliser improved the tensile properties, flexural properties and impact strength. Dynamic mechanical analysis showed that by using the modified fibre and the compatibiliser, the storage modulus of the composite could be significantly improved. The fibre-matrix morphology was studied by SEM analysis of the tensile fractured specimens. Examination of the fibre extracted from the treated fibre composites revealed that some fraction of the matrix was bonded to the fibre surface. These results suggest that a combination of hydrolysed fibre and MA-g-PS increases the interfacial adhesion between the fibre and the matrix. 41 Refs.

Title: EFFECT OF RAPID COMPRESSION ON THE CRYSTALLIZATION BEHAVIOUR OF POLYETHYLENE
Page Range: p.543-552
Author(s): Ranran Zhuo; Chunguang Shao; Qian Li; Chenggang Liu; Ruijing Zhang; Yang Zhang; Wei Cao; Changyu Shen
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 21
Issue No: No.8

Abstract
The crystallisation behaviour of PE samples with different molecular weight was investigated through two different processes, concerning rapid compression (RC) and quench cooling (QC). The scanning electron micrographs, wide angle X-ray diffraction and Raman results showed that all the recovered samples were composed of spherulites. For the QC process, the effect of molecular weight on the spherulites morphologies was slight, but for the RC process, with increased molecular weight (MW), the growth rate as well as the final average diameter of the spherulites decreased remarkably. Additionally, for samples with the same MW, the mass fraction of the rigid amorphous phase of RC samples was lower. Furthermore, the crystallinity distributions in the longitudinal and latitude directions of the RC samples were both more uniform than those of the QC samples, implying that in the RC process, the pressure distribution was quite uniform and there was no pressure decay. 51 Refs.

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