The Study Of High Toughness Polyolefin Microcellular Foaming Structural Materials

The polyolefin microcellular foaming structure materials possess excellent performance and broad application prospects. Microcellular polyolefin foam injection molding compared to conventional injection molding with a reduced amount of polymer materials to improve dimensional stability and low injection pressures etc.. Those studies in industry and academia have caused a wide range of research interests.As we all know, the mechanical properties which is the main performance indicators of polyolefin microcellular foaming structure materials and mainly determined by the cell shape, diameter, density, distribution and material composition and structure.In this paper, polyolefin microcellular foaming structure materials were prepared by the volume controlled injection molding equipment and its mechanical properties was tested. The relationship between impact properties and impact fracture morphology of the microcellular polyolefin foams were analyzed. In order to give toughening mechanism of orientation microstructure, the oriented behavior and the relationship between oriented microstructure and notched impact strength were analyzed by etching technology.Therefore, the main research contents of the following three aspects:(1) the polypropylene / rubber particle microcellular foams were prepared by melt blending and the dispersion behavior of rubber particles also be analyzed by chemical etching and scanning electron microscopy(SEM). Moreover, to explore the toughening mechanism of rubber particles and investigate the effect of polypropylene grafting maleic anhydride(PP-g-MAH) on foaming behavior and mechanical properties polypropylene microcellular foams also be prepared.(2) The four kinds of elastomers and a high density polyethylene(HDPE) were used to produce different high-toughness polypropylene/elastomer microcellular foams which foaming behavior and mechanical properties affect by those different elastomers. Meanwhile, the relationship between impact strength and impact fracture morphology of polypropylene/elastomer microcellular foams were investigated by SEM.(3)Polypropylene(PP) matrix, ethylene- octene elastomer(POE) and HDPE in microcellular foams were investigated by chromic acid and dimethylbenzene in different temperature. The analysis of mechanical properties of the cell wall oriented microstructure and the investigation of the relationship between PP / HDPE / POE composites impact strength and fracture morphology at different temperatures were carried out. Additionally, the effect of oriented microstructure on toughening mechanical was profoundly investigated.The result indicated that:(1) NBR and NBR rubber particles can significantly improve the cell structure of microcellular foamed polypropylene, reducing the cell diameter, increasing cell density and enhancing notch impact strength. Furthermore, dispersity of rubber particles in PP matrix and the crystallization initiation temperature of PP matrix can be improved by adding compatibilizer PP-g-MAH. So, uniform and refinement cell structure of microcellular polypropylene foams can be obtained and toughness can be further improved.(2)The elastomer could improve cell structure and significantly improve the impact strength of polypropylene /elastomer composites, 2095 and POE elastomers are the best toughening agent for PP in four kinds of elastomers. The impact strength could be profoundly enhanced while the HDPE added into PP /elastomer composite. When PP/HDPE/2095 and PP/HDPE/POE mass ratio is 50/30/20, their notched impact strength of microcellular foams is 5.38 times and 5.63 times higher than that of pure PPT30 S microcellular foams.(3)In the cell rapidly grew process, POE elastomer in the cell wall was still small particle size distribution, while the matrix of PP and HDPE can be oriented along the cell walls formed a unique microstructure of microfiber and two-dimensional sheet oriented structure, respectively.(4)Microfiber and two-dimensional sheet oriented structure in cell wall of PP/POE and PP/HDPE/POE microcellular foams make the tensile yield point move to low strain. Moreover, the tensile strength, Young's modulus, flexural strength and flexural modulus of PP/POE microcellular foams lowering speed slower than that of unfoams with POE content increase. Furthermore, the impact strength of microcellular foams higher than that of unfoams when the polyolefin materials exhibit brittle properties.