The Experts below are selected from a list of 45 Experts worldwide ranked by ideXlab platform
Jie Zhang - One of the best experts on this subject based on the ideXlab platform.
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effects of ultrahigh molecular weight polyethylene and mould temperature on morphological evolution of isotactic polypropylene at micro injection Moulding Condition
Polymer Testing, 2015Co-Authors: Xiang Xu, Xinpeng Li, Tao Wang, Jie ZhangAbstract:Abstract The effects of ultrahigh molecular weight polyethylene (UHMWPE) and mould temperature (Tmould) on an isotactic polypropylene (iPP) matrix moulded via micro-injection were investigated via polarized light microscopy, scanning electron microscopy, differential scanning calorimetry, wide-angle X-ray diffraction and small-angle X-ray scattering. Results showed that the complex viscosity of the system increased significantly when the UHMWPE content was more than 5%; however, this viscosity decreased when the UHMWPE content was less than 5%. In addition, the addition of UHMWPE increased the onset of crystallisation temperature and the relative crystallinity of the β-form crystals in micro-injection moulded specimens. Moreover, the UHMWPE phase induced the formation of fan-shaped β crystals in iPP/UHMWPE blends. When mould temperature was 50 °C, the degree of orientation of microparts increased and the crystalline structures were highly compact. However, the relative crystallinity of the β-phase form (Kβ) was lower than those prepared at 130 °C Tmould. Most importantly, well-oriented, bundle-like β crystals have been discovered for the first time in 5 wt.% UHMWPE/iPP blends obtained at 130 °C Tmould owing to the “orientation-maintenance” and “shear-amplification” effects of UHMWPE.
Noëlle Billon - One of the best experts on this subject based on the ideXlab platform.
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The Tensile Behaviour of an Injection‐Moulded Propylene–Ethylene Copolymer: the Effect of the Local Thermomechanical Processing Conditions
Polymer International, 1997Co-Authors: Júlio C. Viana, António M. Cunha, Noëlle BillonAbstract:In this paper the mechanical behaviour of a propylene-ethylene copolymer was characterised as a function of the local processing Conditions using injection-moulded axisymmetrical dumbbell-like specimens of diameter 1.5 mm. The Moulding programme, designed according to the central composite face technique, included variation of the injection and mould temperatures and the flow rate. The local thermomechanical environment associated with each Moulding Condition was determined by filling simulations and quantified by the local bulk temperature and the maximum shear stress. Based on these parameters, thermal and thermomechanical indexes were defined to quantify the morphology of the Mouldings, which was evaluated experimentally by the skin ratio. The tensile tests were carried out at two different constant velocities: 2mmmin -1 (0.56 x 10 -6 ms - ') and 3ms -l , in order to assess the tangent modulus, the strain and the energy at rupture. The results concerning processing-structure and processing-properties relationships are presented as 3D plots, based on polynomial interpolations of the experimental data.
Xiang Xu - One of the best experts on this subject based on the ideXlab platform.
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effects of ultrahigh molecular weight polyethylene and mould temperature on morphological evolution of isotactic polypropylene at micro injection Moulding Condition
Polymer Testing, 2015Co-Authors: Xiang Xu, Xinpeng Li, Tao Wang, Jie ZhangAbstract:Abstract The effects of ultrahigh molecular weight polyethylene (UHMWPE) and mould temperature (Tmould) on an isotactic polypropylene (iPP) matrix moulded via micro-injection were investigated via polarized light microscopy, scanning electron microscopy, differential scanning calorimetry, wide-angle X-ray diffraction and small-angle X-ray scattering. Results showed that the complex viscosity of the system increased significantly when the UHMWPE content was more than 5%; however, this viscosity decreased when the UHMWPE content was less than 5%. In addition, the addition of UHMWPE increased the onset of crystallisation temperature and the relative crystallinity of the β-form crystals in micro-injection moulded specimens. Moreover, the UHMWPE phase induced the formation of fan-shaped β crystals in iPP/UHMWPE blends. When mould temperature was 50 °C, the degree of orientation of microparts increased and the crystalline structures were highly compact. However, the relative crystallinity of the β-phase form (Kβ) was lower than those prepared at 130 °C Tmould. Most importantly, well-oriented, bundle-like β crystals have been discovered for the first time in 5 wt.% UHMWPE/iPP blends obtained at 130 °C Tmould owing to the “orientation-maintenance” and “shear-amplification” effects of UHMWPE.
Júlio C. Viana - One of the best experts on this subject based on the ideXlab platform.
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The Tensile Behaviour of an Injection‐Moulded Propylene–Ethylene Copolymer: the Effect of the Local Thermomechanical Processing Conditions
Polymer International, 1997Co-Authors: Júlio C. Viana, António M. Cunha, Noëlle BillonAbstract:In this paper the mechanical behaviour of a propylene-ethylene copolymer was characterised as a function of the local processing Conditions using injection-moulded axisymmetrical dumbbell-like specimens of diameter 1.5 mm. The Moulding programme, designed according to the central composite face technique, included variation of the injection and mould temperatures and the flow rate. The local thermomechanical environment associated with each Moulding Condition was determined by filling simulations and quantified by the local bulk temperature and the maximum shear stress. Based on these parameters, thermal and thermomechanical indexes were defined to quantify the morphology of the Mouldings, which was evaluated experimentally by the skin ratio. The tensile tests were carried out at two different constant velocities: 2mmmin -1 (0.56 x 10 -6 ms - ') and 3ms -l , in order to assess the tangent modulus, the strain and the energy at rupture. The results concerning processing-structure and processing-properties relationships are presented as 3D plots, based on polynomial interpolations of the experimental data.
Fengzhou Fang - One of the best experts on this subject based on the ideXlab platform.
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Precision replication of microlens arrays using variotherm-assisted microinjection Moulding
Precision Engineering, 2021Co-Authors: Haoyang Zhang, Nan Zhang, Wei Han, Michael D. Gilchrist, Fengzhou FangAbstract:Abstract Injection Moulding is ubiquitous in the production of plastic optical components, the functionality of which depends on minimising residual stress and on precisely replicating surface forms. In this study, variotherm-assisted microinjection Moulding is used to manufacture a practical microlens array designed for light-field applications in order to achieve satisfactory geometric accuracy, surface quality and stress birefringence of the microlenses, all of which are difficult to achieve by conventional microinjection Moulding. Based on in-line process monitoring and a comprehensive evaluation regarding the quantitative and qualitative aspects of the aforementioned factors, the replication is shown to correlate well with machine settings and dynamic machine responses. Screw movements are found to be crucial in the replication process. Compared to an optimised conventional microinjection Moulding Condition, the general residual stress level and uniformity of the microlens array area are improved by 5.08% and 88.11%, respectively, when the warm circuit temperature is 135 °C and enhanced by 2.73% and 84.32%, respectively, by a delayed switch from the warm circuit to the cold circuit. It is concluded that variotherm-assisted microinjection Moulding can significantly reduce residual stresses while maintaining excellent geometric accuracy and surface quality.