| Microcellular polypropylene(PP)materials have the advantages of being lightweight,heat resistant,and environmental friendliness,but pure PP foams have obvious brittle fracture characteristics,which limits their widespread application.In order to improve the toughness of foamed PP,this paper uses elastic particles(OBC,TPU,and SEBS)to toughen PP foamed materials.The synergistic toughening mechanism of the elastomers are also investigated by combining theoretical analysis,physical tests,and multi-scale simulations.Firstly,solid and foamed PP composites were respectively prepared by injection molding(CIM)and foaming injection molding(FIM),and the laws of elastomer on the crystallization,rheological properties,micromorphology,and toughness of PP were investigated.The crystallization behavior showed that OBC and SEBS had a good effect on PP in promoting crystallization,and the best crystallization ability was achieved when the content of both reached 20wt%.The rheological behavior showed that the addition of OBC and SEBS could increase the melt viscosity of PP.The microscopic morphology of the particles in solid and foamed samples showed that the particles diameter of foamed PP0/TPU and PP0/SEBS decreased,while the particles diameter of foamed PP0/OBC increased.The cellular structure of PP composites showed that the addition of elastomer effectively improved the cellular structure parameters of PP.When 20wt% SEBS was added,the cellular structure of transition layer in the vertical section was optimal,with a cell size of 29.47μm and a cell density of 26.77 × 105 units/cm3.At this time,the impact toughness and fracture toughness of the foamed samples were optimal at 86.43 k J/m2 and 825%,respectively,which were increased by 1.8 and 6.2 times compared to solid PP0.Secondly,the influence of the diameter,volume fraction,and matrix ligament thickness of cells and particles on the stress concentration of the PP was quantitatively studied through representative volume elements(RVE)simulation.The results show that,compared to the cell diameter,the cell void fraction and ligament thickness have the most significant effect on the stress concentration and yield point of the matrix.Research on the effect of elastomer particle size and volume fraction on the stress concentration of the matrix showed that the stress concentration factor of the representative volume element increased with decreasing OBC particle size and volume fraction.In addition,when the elastic particles were filled,the toughness of the matrix is related to the particle size and ligament thickness,but not to the volume fraction.It was consistent with the experimental trend that the toughness of PP0/OBC materials gradually increased with decreasing OBC particle size and ligament thickness as well as the increasing content.Then,the synergistic toughening mechanism of elastomer and cell on PP was investigated by combining theoretical analysis,physical experiments and RVE simulations.The toughening mechanism of elastomer and cell on PP can be explained by the theory of ligament thickness,when the ligament thickness of the matrix reached the critical ligament thickness,the percolation of stress field and the brittle-tough transition occurred.Among them,the agglomeration or dispersion of elastomer occurred due to function of cell;Elastomer directly affected the cellular structure parameters of PP.Finally,a prediction model between process parameters and cellular structure parameters is established by the PSO-BP neural network.The training results show that the maximum error of the prediction value does not exceed 0.2%.Then,the genetic algorithm is used to optimize and obtain the best combination of process parameters.Simulation validation has shown the effectiveness of the method. |
PDF Full Text Request