Research Of PP/Inorganic Particles Composites In Hybrid In-Mold Decoration And Microcellular Foaming Injection Molding

Microcellular injection molding could improve the weight reduction,impact strength and thermal insulation of plastic products.But the decrease of tensile strength,flexural strength and bad surface quality restrict the application of this process.A combined process of microcellular injection foam and in-mold decoration was used to improve the surface quality of foamed parts.The inorganic particle was added into the polymer to enhance the mechanical properties of foamed parts.With experiments and tests,the effects of particle size,type and content on the properties of foamed parts were investigated.Combining experimental results and theoretical analysis,reveal the mechanism that inorganic particle reinforce and toughening the foamed parts,and the improvement of surface quality.The effects of inorganic particle on the cells structure and distribution were discussed.In the composite process,the effects of particle size,type and content on the properties of foamed parts were investigated.The experiment results of foamed parts’mechanical properties,surface quality and crystallinity were discussed respectively.Results showed that adding smaller particle could improve the mechanical properties of foamed parts.The mechanical properties were optimum when the content of nano-CaCO₃ was 6 wt%,the tensile strength,flexural strength and impact strength were22.02MPa,26.0MPa and 38.1kJ/m² respectively.Comparing the mechanical properties of foamed parts and solid parts,the mechanism that inorganic particles improve the mechanical properties of foamed parts was discussed.With the addition of inorganic filler,both improving the strength of polymer matrix and affecting the cell structure could improve the mechanical properties of foamed parts.The surface quality was affected by the inorganic particle,because of the cell nucleation in the filling stage and improvement of melt strength,and adding a proper content nano-CaCO₃ could improve the surface quality of foamed parts.The effects of inorganic filler on the cell structure and distribution were investigated.The parallel and vertical sections were discussed to investigate the cell structure with the addition of different particle.The results showed that the cell density increased and cell size decreased with the decrease of particle size and proper addition of nano-CaCO₃,when the content of nano-CaCO3 was 6wt%,the cell density was3.14×10¹⁰cells/cm³,and the cell diameter was 37.6μm.The asymmetric distribution of cells were discussed in the combined process.With the addition of nano-CaCO₃,the offset distance of core layer decreased,but the cell structure in the transition layers didn’t improve.The analysis of cell structure could explain the reason that inorganic particle improved the mechanical properties better.Based on the theoretical model,the nucleation,growth,deformation and distribution of cells with adding inorganic particles were analyzed,in the composite process.The more potential nucleation sites improve the cells structure with the addition of inorganic particle.The improvement of melt viscosity leads to the increment of the cells deformation.The existence of film leads to the asymmetric distribution of temperature and viscosity,thus leading to the asymmetric distribution of cells.