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Polymers and Polymer Composites

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Title: Preparation and properties of core-shell particles filled beta-nucleated polypropylene random copolymer composites
Page Range: p.1-10
Author(s): Youchen Li; Guixin Zhang; Xiaowei Fu; Weihong Guo
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.1

Abstract
To provide polypropylene random copolymer (PPR) with excellent toughness without lowering its rigidity, a novel kind of core-shell particles (CSP) and beta-nucleating agent (beta-NA) were incorporated into PPR by melt blending. The CSP, in which nano-CaCO3 acted as the core and polyethylene (PE) formed the shell, was also prepared through melt blending. The effects of different proportion of PE shell and nano-CaCO3 core on the properties of p-modified PPR composites were investigated. The dispersion and morphology of CSP were studied by transmission electron microscopy (TEM) and the results showed that the CSP dispersed fairly well in the PPR matrix and the core-shell structure was successfully formed. The nano-CaCO3 core was completely encapsulated by PE, especially at the 50/50 weight ratio. The crystallisation behaviour of the PPR composites was characterised by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarised optical microscopy (POM). All the results showed that the relative content of beta-form crystal was greatly enhanced with the incorporation of beta-NA. Furthermore, the weight ratio change of PE/nano-CaCO3 could also increase the relative content of the beta-form crystal. Under the combined effects of beta-modification and CSP, the mechanical properties of the PPR composites were greatly enhanced without reducing its rigidity. 40 refs.

Title: Temperature distribution and curing behaviour of carbon fibre/epoxy composite during vacuum assisted resin infusion moulding using rapid heating methods
Page Range: p.11-20
Author(s): Yizhuo Gu; Xing Qin; Min Li; Kaomin Zhang; Zuoguang Zhang
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.1

Abstract
This paper designs two kinds of rapid heating methods for vacuum assisted resin infusion moulding (VARIM) process aiming to reduce the cycle time of carbon fibre/rapid curing epoxy composite fabrication. One utilizes the silicone rubber heating sheet containing thin resistance wires, and the other takes advantage of carbon fibre conductivity to produce internal resistive heating. Conventional oven heating VARIM was performed as a reference. The heating rates and temperature distributions in carbon fibre preform heated by the three heating methods with and without epoxy resin injection were investigated and compared. The curing degree and glass transition temperature of laminates fabricated by different VARIM processes were determined. The heating rate of silicone rubber heating sheet was 26 deg C/min, while the carbon fibre internal resistive heating reached 30 deg C/ min, which was much higher than the heating rate of 2 deg C/min in oven. Unlike the highly uniform temperature distribution in the oven heating process, there was a slight temperature gradient within 5 deg C in the silicone rubber heating process and a relatively large gradient within 13 deg C in internal resistive heating process for dry fibre preform. When epoxy resin was injected, the temperature gradients obviously increased along the resin flowing direction especially for the rapid heating methods. However, the temperature gradient seemed not to affect the curing degree and its uniformity of laminates for all studied VARIM processes. The cycle time of composite fabrication by the rapid heating VARIM processes was reduced by over 40% compared to oven heating VARIM. 24 Refs.

Title: Impact fracture study of laminated composite using single edge notched bend specimens
Page Range: p.21-28
Author(s): Rizov V
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.1

Abstract
The results of an investigation of impact fracture in laminated composite material are presented in this paper. Low velocity impact fracture tests were carried out on single edge notched three-point bending (SENB) specimens using a drop-weight rig. An inclined notch was introduced in the SENB specimen in order to generate mixed mode I/II crack loading conditions. Different mixed-mode ratios were obtained by varying the notch inclination from 10 deg to 90 deg with a step of 10 deg. The SENB specimens were subjected to various impact potential energies by varying the drop-height in order to determine the critical impact potential energy at which the crack growth initiates from the initial notch tip position for each of the considered notch inclinations. The mechanical response of the SENB specimen to impact loading was analysed using a two-dimensional linear-elastic finite element model. Good agreement was obtained between the predicted contact force - time curve and the measured one at various impact potential energy levels and notch inclinations. The strain energy release rate mode components were computed by the virtual crack closure technique. The composite fracture toughness under impact loading was characterised in terms of the critical dynamic strain energy release rate at the onset of crack growth. It was found that the fracture toughness under impact loading increases with decreasing the notch inclination. This finding was attributed to the increase of mode II component of crack loading. A comparison of the fracture behaviour under impact and static loading was performed. It was found that the fracture toughness under impact loading was between 19% and 23% lower than the static one for the different notch inclinations. Therefore, it was concluded that static fracture toughness should not be used in the fracture mechanics based design of composite structures which are subjected to impact loading during their lifetime. 28 Refs.

Title: Investigation on mechanical properties of OCC fiber-HDPE composite containing different types of coupling agents
Page Range: p.29-36
Author(s): Mohebi Damabi R; Rashno A; Ahmadi S
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.1

Abstract
In this study, the effects of adding different coupling agents, e.g. maleic anhydride-grafted polyethylene (MAPE), silane (3-aminopropyltrimethoxy silane) (silane1189) and isocyanate (hexamethylenediisocyanate) (HDI) on mechanical and morphological properties of composite samples of high density polyethylene/old corrugated container fibres (HDPE/OCC) were studied. The amounts of OCC fibre and coupling agents used were 30% and 2% of dry composite weight, respectively. Mixing of materials was carried out by a two-screw counter extruder and samples were prepared by injection moulding. In order to compare the results of the use of mixture coupling agents, their effects were studied independently, as well. Mechanical properties of prepared composite samples containing coupling agents were measured and the results were compared with those of pure high density polyethylene and those of composite samples without coupling agent. The measured mechanical properties showed that maximum values of tensile and flexural strengths and tensile and flexural modulus could only be obtained in composites containing a mixture of silane1189 and MAPE coupling agents. It was also observed that the Izod impact strength values of composites with coupling agents increased significantly. SEM micrographs of failure surfaces of samples showed that the best homogeneity of composites and bonding between OCC fibres and polymer matrix were obtained for the sample containing 1 wt.% silane and 1 wt.% MAPE. 32 refs.

Title: The tribological and mechanical properties of PDCPD/PEW composites prepared by reaction injection moulding
Page Range: p.37-42
Author(s): Liping Wang; Bingli Pan; Jinping Du; Yumei Cheng; Jichun Liu; Sanming Du; Bao Shangguan; Yongzhen Zhang
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.1

Abstract
In order to improve mechanical performance and wear resistance of polydicyclopentadiene (PDCPD) by convenient methods and technologies, novel PDCPD/polyethylene wax (PEW) composites were prepared by in-situ polymerisation in a simulated reaction injection moulding. Studies on the mechanical and tribological properties of the composites were carried out. The bending strength and hardness of PDCPD/PEW composites significantly improved compared with neat PDCPD. The incorporation of PEW in PDCPD greatly enhanced the wear resistance and reduced the friction coefficients. The wear mass loss and friction coefficients for PDCPD/ PEW composites decreased continuously in the range of our experiments. The SEM micrographs of the worn surface showed the friction and wear mechanism of PDCPD. 17 Refs.

Title: Mechanical constitutive relation model of expanded polyvinyl alcohol
Page Range: p.43-50
Author(s): Dongmei Wang; Hong Zhu
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.1

Abstract
The compression stress-strain response of expanded polyvinyl alcohol under different influence factors had been studied by static compression experiments. The constitutive relation model of expanded polyvinyl alcohol was established based on the Sherwood-Frost model, including density, temperature, strain rate and strain, and the factor of relative humidity was added to improve the model. Finally, the accuracy of the constitutive relation model was validated by comparing calculated curves according to the constitutive relation model and experimental data; the results were in good agreement. The model can easily predict compressive stress of expanded polyvinyl alcohol under various environmental conditions, and is also meaningful to offer reference data for product packaging. 13 Refs.

Title: The orientational order of the alpha-helical backbone of poly(gamma-benzyl l-glutamate) - a molecular dynamics simulation
Page Range: p.51-58
Author(s): Zhiping Zhou; Lu Tao; Wenming Yang
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.1

Abstract
For a Poly(gamma-benzyl L-glutamate) (PBLG) segment with 30 monomers, molecular dynamics simulation was carry out in the Amber forcefield, by the software package InsightII/Discover. The geometrical structure of the backbone of the model molecule in the minimized energy state is in close agreement with that in the solid polypeptides. In the dynamic equilibrium state, the structure becomes slightly flabby and has a potential ca. 4800kJ/mol higher than that in the minimized energy state for the model molecule. On the average, the alpha-helical backbone architecture of PBLG remains quite stable during the molecular dynamic process, though the fluctuation of the bond and dihedral angles. The observed D NMR spectra for the quadrupolar splittings are reproduced and the previous architecture analysis was verified by the simulation calculations. 16 Refs.

Title: Cocrystallization behavior of HDPE/UHMWPE blends prepared by two-step processing way
Page Range: p.59-64
Author(s): Jiandong Zuo; Shumei Liu; Jianqing Zhao
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Journal: Polymers and Polymer Composites
Issue Year: ppc
Volume: 23
Issue No: No.1

Abstract
Blends of high density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE) were prepared by two-step processing way. Middle molecular weight polyethylene (MMWPE) as the lubricant was added into UHMWPE in the first processing step. Cocrystallisation behaviour of the blends was examined by DSC, XRD and light microscope (LM). A single endotherm peak in DSC curves revealed that cocrystallisation probably formed between HDPE and UHMWPE. Moreover reducing heating rate didn't make the single endotherm separate. The enhancing of diffractive strength on 110 and 200 crystal face manifested that the UHMWPE molecular chains taken part in the crystallisation of the blends. Reducing of the diameter of the undissolved UHMWPE particles in LM manified that the dispersion of UHMWPE in the blends obviously improved. Therefore two-step processing way could improve the dissolved degree and contribute to form the cocrystallisation. 14 Refs.

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