Structure And Properties Of Vibration Injection Molded Polyolefin Blends

A vibration injection molding machine was used to investigate structure and properties of polyolefin blends. The melt was subjected to a low-frequency and high-amplitude vibration pressure during the period of injecting and packing. The orientation, crystallization behavior and phase morphology of the melt can be changed under the shear stress field. All of these alterations would be kept when the melt cooled down. Conventional injection molding and vibration injection molding were used to mold samples of HDPE/LLDPE, PP/LLDPE and PP/HDPE blends. The relationship between mechanical properties and orientation, crystallization behavior and phase morphology was explored. Main results are as following:1) Compared to samples injection molded in conventional way, the tensile strength and notched impact strength of the vibration injection molded samples are improved. The percentage increase of tensile strength is depending on the macromolecular structure. More increase of tensile strength is obtained in blends with HDPE matrix than blends with PP and LLDPE matrix. The reason is that there is less chain branching in HDPE than in PP and LLDPE, it's easier for HDPE to obtain more orientation under shear stress field. For example, when vibration injection molded, the HDPE/LLDPE (80/20) blend got a 100% increase in tensile strength while the HDPE/LLDPE (20/80) blend just got a 14.1% increase.2) The notched impact properties of PP/HDPE and PP/LLDPE blends are greatly...