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Polymers and Polymer Composites

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Title: Determination of optimum process parameters for cutting hole in a randomly-oriented glass fiber reinforced epoxy composite by milling process: maximization of surface quality and cut-hole strength
Page Range: p.81-90
Author(s): Hussain G; Al-Ghamdi K A; Bijanrostami K; Alehashemi A J
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
The epoxy based randomly-oriented glass fibre reinforced polymer (GFRP) composites are used to construct structures intended to support multi-directional loading. Due to random orientation of the fibres, cutting of high quality hole is a difficult task in such composites. In the present study, a composite with 60% glass and 40% epoxy (by volume fraction) was fabricated by hand lay-up. To begin with, the performance of two machining processes, namely twist-drilling and end-milling, was compared to cut hole in the composite. It was found that the milling performed better than the drilling process. Later, a design of experiments following the response surface methodology was conducted to determine the effect of milling parameters (i.e., feed rate and speed) on the surface quality and cut-hole strength of composite. The results showed that the parameter-response relationship was not straight rather the parametric effects were interactive and complex. Further, the relative value of speed and feed rate was observed to have controlling influence on the process performance. To predict the process performance for a given set of conditions, empirical models were proposed. Finally, the optimal parameters minimising the surface roughness and maximising the tensile strength, employing desirability function approach, was carried out so as to provide guidelines to the users. 40 Refs.

Title: The mechanical behaviour and failure mode of FRP composite steel casing joints
Page Range: p.91-100
Author(s): Zhen-shan Wang; Xiao-ming Ma; Yun-he Liu; Hui Ma; Hong-chao Guo
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
Fibre reinforced plastic (FRP) composite has been widely used in engineering due to its light weight, high strength, and corrosion resistance. Joint behaviour is important in structural design. This research investigated the ultimate tensile and compressive bearing capacities of bonding joints of i200 mm x 10 mm steel casing. By conducting full-scale tests, the load-displacement curve and strain distribution in joints in an FRP composite steel casing were analysed, and the ultimate bearing capacity, stiffness, and failure mode were obtained. The research showed that under axial compression, joints underwent brittle failure, and the steel casing exerted a greater lateral restraint to the composite pipe, which resulted in a decrease of bearing capacity of its components. While under axial tension, the failure mode of joints was such that the FRP composite pipe was pulled off and the bearing capacity of its joints was determined by the strength of the binders used. This study forms an experimental basis for engineering application. 16 Refs.

Title: Preparation and characterization of a phenol-formaldehyde resin adhesive obtained from bio-ethanol production residue
Page Range: p.101-106
Author(s): Wei Qiao; Shujun Li; Fengying Xu
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
Enzymatic hydrolysis (EH) lignin was utilised to replace phenol partially for preparing phenol-formaldehyde (PF) resin adhesives. The influence of the degree of lignin substitution on the properties of the lignin phenolformaldehyde (LPF) resin adhesive was investigated. The results demonstrated that up to 50% of phenol in the resin could be replaced by EH lignin without damaging the bonding strength of the adhesive, and a lower free phenol content was observed in LPF resin adhesives. Fourier transform infrared spectroscopy spectra of the resins revealed that the introduction of lignin did not appreciably change the final chemical structure of the adhesive, but did negatively impact the resin's thermal ultimate stability. Furthermore, compared to bio-ethanol production residue-modified phenol-formaldehyde (ERPF) resin, the LPF resin exhibited higher bonding strength at the same level of the phenol substitution. This result of the comparison indicated that the raw biomass extraction process improved the performance of the bio-based PF resin. 24 Refs.

Title: The design optimisation of the co-extrusion of a wood-like grain surface composite polymer profile
Page Range: p.107-114
Author(s): Wang Qi-bing
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
A wood-like grain surface composite polymer profile (or wood-like profile) was fabricated by the extrusion moulding of melting multi-component polymers through a co-extrusion die, with two extruders feeding the co-extrusion die simultaneously. To improve the extrusion velocity uniformity of melting composite polymers, and decrease the distortion of wood-like grain profiles, this study treats the velocity equality among sub-regions in the wood-like profile cross-sections at the exit of the co-extrusion die as its optimisation objective. Meanwhile, the compression section gap, which exerts a significant influence on flow uniformity is selected as the design variable. Finite element numerical simulation and an ERP system are adopted to optimise the design in combination with a CAD/CAE network system co-extrusion die expert database of concurrent engineering. The optimisation design of case studies confirms that the velocity uniformity of the optimised wood-like grain profile melts presents a significant improvement in each sub-region at the exit of the co-extrusion die. Moreover, the distortion of composite profiles is decreased. The structural dimensions and performance of the composite profiles meet industrial demands. 21 Refs.

Title: Effect of process conditions on ILSS of carbon fiber / epoxy composites stepwise curing with low-energy E-beam
Page Range: p.115-120
Author(s): Xinming Zhao; Yugang Duan; Dichen Li; Jingjing Zhang; Ben Wang
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
Electron beam (E-Beam) curing technology has become increasingly applied in modern composite manufacturing industry. Comparing to conventional thermal curing, E-Beam curing provides an efficient solution to fabricate integrated composite structures of a wide range of dimensions with a minimal consumption of energy. Currently, the majority of E-Beam curing systems use high-energy E-Beams. However, high construction cost, high radiation, and low operational flexibility hinder the further expansion of applications of this technique. In this study, a prototype of novel dual-emitter low-energy E-Beam curing system was built, which was energy efficient and radiation safe. The minimum E-Beam energy that could satisfy the stepwise curing of carbon fibre/epoxy composites was investigated through detailed analysis of effects of the irradiation dose, the post cure temperature, and roller materials on the inter-laminar shear strength (ILSS) with microstructure characteristics. The results indicate that carbon fibre/epoxy (CF/EP) composites can be adequately cured by 150 keV E-Beams using our system, with an optimal irradiation dose which could enhance the ILSS as largely as 44.6 % (from 34.2 MPa to 61.7 MPa). It was also observed that laminates irradiated by 50 kGy and post-cured at 180 deg C would reach the optimised ILSS of 64.7 MPa. An anti-sticking silicon rubber with low surface energy could effectively reduce interlayer defects, resulting in higher ILSS. 9 Refs.

Title: Carbon fiber/epoxy interfacial bonding improvement by microwave pretreatment for low-energy electron beam curing
Page Range: p.121-126
Author(s): Xinming Zhao; Yugang Duan; Dichen Li; Jingjing Zhang; Wang B
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
In this paper, the prepreg of carbon fibre/epoxy (CF/EP) was pretreated by microwave radiation, and the effect of microwave radiation on the interfacial performance of the composite cured by low-energy electron beam (E-Beam) was investigated. By a rather short time microwave irradiation, the atomic ratio of O/C on the CF surface was increased, so did the oxygen-containing functional groups which helps strengthen the chemical bonding between the fibre and resin matrix. The CF surface became rougher after the microwave radiation, which would improve the bonding surface and mechanical interlocking. Compared with the untreated composite, the interlaminar shear strength (ILSS) of laminate fabricated with microwave radiated prepreg was increased by 9.6%. The SEM images showed that the resin distributed uniformly and adhered to the CF surface tightly. The interlaminar shear fracture morphology by SEM further indicated that the bonding strength between CF and EP resin was effectively improved by the microwave radiation. 11 Refs.

Title: Dynamic compressive behavior of FRP-confined concrete under impact and a new design-oriented strength model
Page Range: p.127-132
Author(s): Yang Hui; Song Hengwen
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
The dynamic mechanical properties of fibre-reinforced polymer (FRP) confined concrete were experimentally and theoretically studied using a 100-mm-diameter split Hopkinson pressure bar (SHPB) apparatus. As test results turned out, the dynamic strength of FRP-confined concrete was improved significantly. Within the mean strain rate range of 50-130 s-1, the dynamic strength increased with the rise in strain rate. With same strain rate, the strengthening effect was influenced by confining ratio. The optimal confining ratio of AFRP-confined concrete is 0.264, once beyond this limit, the failure pattern will be changed, and the dynamic strength will be decreased. In addition, a modified model was proposed for dynamic strength of FRP-confined concrete, which agrees with the test results well. 15 Refs.

Title: Morphological, mechanical and thermal properties of chemically bonded graphene oxide nanocomposites with biodegradable poly(3-hydroxybutyrate) by solution intercalation
Page Range: p.133-142
Author(s): Jun Bian; Hai Lan Lin; Gang Wang; Qiang Zhou; Zheng Jun Wang; Xing Zhou; Yun Lu; Xin Wei Zhao
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
Chemically covalent bonded graphene oxide (MGO)/Poly(3-hydroxybutyrate) (PHB) nanocomposites were fabricated successfully through solution blending. Morphological observations indicated that MGO was dispersed well in the nanocomposites during solution intercalation. The mechanical and thermal property characterisations indicated that incorporation of 2.0 wt.% MGO resulted in the increasing of up to 101% and 46% in tensile strength and tensile modulus of nanocomposites, respectively, compared to neat PHB; while the maximum thermal decomposition temperature improved about 15.5 degC higher than that of PHB. Differential scanning calorimetric (DSC) analysis showed that the crystallisation process of PHB accelerated, resulting in an increasing in crystallinity with the incorporation of MGO due to its' "nucleating effect". Electrical conductivity analysis indicated that the electrical conductivity of MGO/PHB nanocomposites has increased by 14 orders in comparison to that of pure PHB, especially for r-MGO filled PHB nanocomposites (4 wt.% r-MGO loading). It was concluded that the formation of graphene-graphene network structure in the nanocomposites, the increases in homogeneous dispersion of graphene and interfacial interactions contributed to the enhancements of properties. 36 Refs.

Title: A study on degradation of composite material PBS/PCL
Page Range: p.143-148
Author(s): Jitao Huang; Chunna Cui; Guiyang Yan; Jianhua Huang; Min Zhang
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
systematic study on the degradation and mechanism of composite materials based on polybutylenes succinate/ polycaprolactone (PBS/PCL) was conducted by putting composites of different ratios into the local soil culture solution and cured compost culture solution to observe the microbial reaction. The surface morphologies, crystallinities, and structures of the composites before and after degradation were characterised by FTIR, XRD, and SEM. The results revealed that the original functional groups of the composites were retained perfectly after the mixing and fusing of PBS and PCL, and hydrogen bonds were formed between these two phases. The composite based on PBS and PCL degraded well in the compost culture solution. The weight of this composite was reduced by 32.67% after 60 d. Degradation of the composite in the soil culture solution was indicated by a weight loss up to 8.76%. PCL degraded much faster than PBS did, while the PBS/PCL composite degraded even faster. Crystallinity was improved after degradation, and the non-crystalline area degraded first. The viscosity analysis showed that the degradation of the composite was achieved by the simultaneous processes of breaking big molecules into small molecules and by the degradation of small molecules. Biodegradable and environmental friendly PBS that belongs to aliphatic series polyester is one of the most promising environmental-friendly and biodegradable polymer materials; PCL is a kind of thermal plastic crystalline polyester with good bio-degradability, drug permeability, and biocompatibility. Meanwhile, the raw materials for PCL preparation are cost-effective and accessible. Due to the wide application of bio-degradable materials, the relationship between the degrading rate and the molecule design of bio-degradable material is becoming a key research topic in the area of biodegradable materials1-10.. Zhang et al. studied the relationship between the chemical structure of PBS and its degradable structure11-16; the influences of microorganism quantity, humidity, temperature, metal ions, and pH on the degradable property were also studied17-21. In addition to the factors mentioned above22-26, adding other materials also greatly influences degradation performance. In practical applications, the mechanical properties of biodegradable materials are not as good as conventional plastics; the uncontrollable degradation rate of the biodegradable materials is another issue that prevents their wider promotion. In this project, PBS/PCL composites of different ratios were prepared. Good mechanical properties and good biodegradability were expected for these composites. A systematic study on the degradation of these composites is presented, which provides good reference for the controllable application of biodegradable plastics. Furthermore, the degradation mechanism of the composites is rationally inferred, which is well supported by reported data. This study facilitates further research on the controlling of degrading rate of PBS/PCL. 26 Refs.

Title: Defects characterization in CFRP using x-ray computed tomography
Page Range: p.149-154
Author(s): Xueshu Liu; Fei Chen
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
Although carbon fibre reinforced plastic (CFRP) is ideally high mechanical performance, manufacturing induced defects are hardly avoidable and their appearances generally result in a loss of mechanical properties. To accurately characterise this kind of defects is a foundation to estimate mechanical performance of a CFRP structure. Compared to the traditional defect assessment methods, X-ray computed tomography (CT) has been approved a promising method due to its ability to provide spatial information of defect. In this study, the effect of resolution on the accuracy of defects estimation was investigated in details. Scanning data obtained by using two different resolutions were comparatively studied based on delamination characterisation. In addition, an image processing based method for porosity estimation was discussed as well. It is concluded that it is possible for us to enlarge our region of interest by selecting a reasonable resolution not at cost of losing too much desired details. 19 Refs.

Title: Curing process-induced internal stress and deformation of fiber reinforced resin matrix composites: numerical comparison between elastic and viscoelastic models
Page Range: p.155-160
Author(s): Xiaoxia Wang; Yaru Zhao; Hao Su; Yuxi Jia
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
Curing process-induced internal stress and deformation are major problems that restrict the wildly used of carbon fibre/epoxy composites in aerospace and vehicle industry. The finite element simulations of the evolution of cure-induced internal stress and curing deformation of the AS4/3601-6 composites are carried out using both elastic and viscoelastic models. The differences between these two kinds of numerical results are analysed. The numerical results show that the difference between the two decreases with the increase of the fibre volume fraction or the decrease of the resin curing shrinkage. The comparative analysis is helpful for clearly understanding the deformation mechanism and then optimally designing the processing conditions in accordance with the specific needs. 17 Refs.

Title: Erosion resistance and interface properties of epoxy composite filled with graded silicon carbide
Page Range: p.161-166
Author(s): Yaming Zhang; Haihong Zhang; Jianfeng Yang; Gangqiang Geng
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
In the present study, the effect of graded aggregate on the erosion resistance and interface performance of SiC/EP (epoxy resin) composite was investigated. The graded aggregate (84% 550(mu)m and 16% 110 (mu)m) SiC particles was designed by the modified coarse aggregate void filling approach from the theory of concrete. The erosion mechanism of obtained composite was discussed through the microstructure analysis. Obtained results from different erosion tests showed the graded structure contributed to increasing the hard spots and density, which significantly reduced erosion rate. The mechanical properties and wear fraction indicated that the preferred interface could be obtained using migration with KH-550. 12 Refs.

Title: Effect of annealing temperatures and time on structural evolution and dielectric properties of PVDF films
Page Range: p.167-172
Author(s): Yunfei Zhu; Huijian Ye; Li Yang; Lixiang Jiang; Liang Zhen; Jianguo Huang; Zilong Jiao; Jipeng Sun
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
In this paper, we investigate the effect of thermal annealing on the degree of crystallinity, the fraction of electroactive phase (p-phase) and the dielectric properties, such as dielectric constant and loss tangent. Through control the thermal annealing conditions, dramatic improvements have been achieved. The degree of crystallinity is greatly enhanced up to 45.2%. The relative content of electro-active phase increases remarkably by 61% and the dielectric constant is improved greatly by 17.8% and reaches its maximum value of 9.9 meanwhile the dielectric loss being as low as 0.026. 16 Refs.

Title: Structural foamed concrete with lightweight aggregate and polypropylene fiber: product design through orthogonal tests
Page Range: p.173-178
Author(s): Yuexiu Wu; Xianjun Tan; Quansheng Liu; Weizhong Chen; Xiangjun Meng; Xiaolin Deng; Weiqing Li
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 24
Issue No: No.2

Abstract
In order to optimise the mix ratio design for structural foamed concrete with lightweight aggregate (LWA) and polypropylene fibre, orthogonal test approach with an L32 (49) orthogonal array have been carried out, with nine factors (fly ash, perlite, foam, water, waterproof agent, antifreeze, polypropylene fibre, water reducing agent and accelerating agent) and four levels for each factor. Seven responses (quality of sample moulding, distribution of fibres, dry density, water absorption, compression strength, tensile splitting strength and the ratio of tensile splitting strength to compression strength) of each formula have been measured. According to the analysis of test results, an optimal mix ratio of foamed concrete with the desired engineering properties is obtained. 22 Refs.

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