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Polymers and Polymer Composites

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Title: Global sensitivity analysis for the elastic properties of unidirectional carbon fibre reinforced composites based on metamodels
Page Range: p.205-222
Author(s): Chao Zhu; Ping Zhu; Jiahai Lu
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 26
Issue No: No.3

Abstract
A fast and effective numerical method to predict mechanical properties of carbon fibre reinforced polymer (CFRP) composites, even elastic properties, is complicated due to the mismatch of mechanical properties among the constituents. Furthermore, it is not possible to completely characterise the influence of multiple parameters including mechanical and structural parameters on the bulk properties of CFRP by experiments. In this study, a three-phase finite-element model consisting of matrix, carbon fibre and interface was developed to predict the elastic mechanical behaviour of unidirectional CFRP. The elastic properties in terms of two Young's moduli, two Poisson's ratios and a shear modulus were calculated by means of a homogenisation method. High-accuracy Kriging surrogate models were constructed to fast-calculate the elastic responses for a large number of samples. Combining Kriging and high dimensional model representation (HDMR) methods, a global sensitivity analysis was performed to study how the microscopic parameters influence the elastic responses to get a deeper understanding of elastic property-structure relationship. Eleven parameters, including mechanical and geometry properties of constituent phases, were chosen as inputs. Independent and cooperative effects of input parameters on the elastic properties of the studied composites were surveyed via first- and second-order sensitivity indices, respectively. An importance ranking of these parameters for each elastic response was derived directly by these indices. The procedure proposed in this work could serve as a theoretical guide for further design optimisation of CFRP. 35 refs.

Title: Accelerated ageing of alkali treated olive husk flour reinforced polylactic acid (PLA) biocomposites: physico-mechanical properties
Page Range: p.223-232
Author(s): Samra Isadounene; Dalila Hammiche; Amar Boukerrou; Rodrigue D; Hocine Djidjelli
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 26
Issue No: No.3

Abstract
In this study, olive husk flour was added to poly(lactic acid) (PLA) to produce fully biosourced and biodegradable composites. In particular, untreated and alkali treated particles were used to produce the biocomposites at 20 wt.% via melt extrusion followed by injection moulding. The samples were then subjected to accelerated ageing (UV irradiation and water spray at 50 deg C) for different amounts of time (120, 240, 360 and 480 h). The results show that accelerated ageing decreased the tensile strength (TS) and Young's modulus (YM) for both untreated and alkali treated biocomposites, but the treated particles presented a lower reduction. Further comparison was made via differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) to detect any changes in the samples. 46 refs.

Title: Polypyrrole-Fe2O3 nanocomposites with high dielectric constant: in situ chemical polymerisation
Page Range: p.233-242
Author(s): Bashir T; Shakoor A; Ahmed E; Niaz N A; Saeed Akhtar M; Rafi Raza M; Azad Malik M; Foot P J S
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 26
Issue No: No.3

Abstract
Novel nanocomposites of polypyrrole (PPy) dispersed with iron oxide (Fe2O3) particles have been synthesised by in situ chemical oxidative polymerisation of pyrrole in the presence of ammonium persulphate (APS) as an oxidising agent. The concentration of Fe2O3 was varied between 10-50wt% of PPy. The simultaneous polymerisation of pyrrole and oxide addition led to the complete synthesis of nanocomposites. A maximum dielectric constant of ~28500 was observed at 20wt% of Fe2O3. The nanocomposites were characterised by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD analysis confirmed the structure and crystallinity of the nanocomposites, and a strong interaction between PPy and Fe2O3 particles was observed by FTIR technique. SEM and TEM images showed that Fe2O3 particles had been coated with PPy by establishing a network during the polymerisation process. The values of dielectric constant were obtained from capacitance measurements. The value of dielectric constant for nanocomposites with 20wt% of Fe2O3 was observed to be almost 12 times that of the pure PPy matrix. The high value of dielectric constant indicated a high packing density of Fe2O3 particles in PPy matrix. These nanocomposites have potential applications in electronic or biomedical devices. 57 refs.

Title: Evaluation of short-term creep behavior of PE-HD after aging in oil derivatives
Page Range: p.243-250
Author(s): Ayrton Alef Castanheira Pereira; Moraes d'Almeida J R; Thiago Motta Linhares Castro
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 26
Issue No: No.3

Abstract
The creep behaviour of a high density polyethylene (PE-HD) was evaluated before and after ageing in contact with gasoline and diesel oil. Four viscoelastic models were used to assess changes in creep properties of the material: three parameters model, four parameters model, stretched Burgers model and Findley Law. Viscoelastic properties, stationary creep rate and compliance were used to analyse and compare the behaviour between samples. A strain increase could be seen in aged samples in comparison with as-received ones, caused by plasticisation due to ageing effects. An increase in flexibility and decrease in stiffness in aged samples was also noted. This work also shows that the effects of ageing on the creep response of a polymeric material can be analysed using short term creep tests. 24 refs.

Title: Polymer composites with enhanced thermal conductivity and mechanical properties for geothermal heat pump pipes
Page Range: p.251-258
Author(s): Haihong Ma; Fanglin Xu; Zhengfa Zhou; Weibing Xu; Fengmei Ren
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 26
Issue No: No.3

Abstract
In this article, we report a robust strategy to prepare polymer composites with enhanced thermal conductivity and mechanical properties for geothermal heat pump pipes, in which high density polyethylene (HDPE) used as matrix, various inorganic fillers including zero-dimensional (0D) aluminium spherical particles (Al-SPs), one-dimensional (1D) carbon fibres (CF) and two-dimensional (2D) graphite platelets (GPs), used alone or blended as modifier. The as-prepared polymer composites are GPs/HDPE, GPs/CF/HDPE, GPs/Al-SPs/HDPE and GPs/CF/Al-SPs/HDPE. Thermal conductivity and mechanical properties of these polymer composites were characterised. The results indicate that of all these as-prepared polymer composites, GPs/CF/Al-SPs/HDPE composites are the only one which possesses preferable and comprehensive properties both in thermal conductivity and mechanical properties due to the synergistic effect of filler. The thermal conductivity, elongation at break and tensile strength of GPs/ CF/Al-SPs/HDPE composites prepared with GPs (9 wt%), CF (3 wt%) and Al-SPs (3 wt%) were 0.803 W m-1K-1, 70.6 % and 26.69 MPa, respectively, which could meet the commercial requirements of the geothermal heat pump pipes. 24 refs.

Title: The effect of flocculent, dispersants, and binder on wet-laid process for recycled glass fiber/PA6 composite
Page Range: p.259-269
Author(s): Pritesh Yeole; Haibin Ning; Ahmed Arabi Hassen; Vaidya U K
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 26
Issue No: No.3

Abstract
The papermaking industry has been using the wet-laid process to suspend paper pulp-derived fibres in water and drain the solution through a forming mesh. This process has recently been adopted to produce non-woven, wet-laid fibre-reinforced polymer matrix composite mats. The mats can be post moulded into different complex shapes using compression moulding or related processes. The objective of this study was to produce composite panels from wet-laid mats and observe the effect of chemicals used during the process on the mechanical and thermal characteristics of the resulting composite. Two sets of mats were processed using recycled glass fibre with Polyamide 6 (PA6). Flocculent, dispersant and binder (poly(vinyl alcohol) (PVOH)) were added to one of the mats, and the second mat was processed without these chemicals. The addition of these chemicals enhanced the fibre distribution and reduced processing defects in the mats. This was reflected in the mechanical properties of the final product. It was noticed that the flocculent, dispersant and binder volatilized during the compression moulding step. Hence, the additives were found not to affect the thermal properties of the consolidated part. 29 refs.

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