振动注塑PP的拉伸蠕变研究

分别通过改变机械振动注塑机的频率(5~25 Hz)和压力(10~18 MPa)获得不同条件下成型的PP样条,然后在各种成型条件下的PP样条上分别施加相同的拉伸力(F=125 N),进行24 h拉伸蠕变实验.结果表明,在相同的振动频率(10 Hz)和不同的振动压力下成型的PP试样,其24 h蠕变量随着压力的增大而减小;在相同振动压力(12 MPa)和不同的振动频率下成型的PP试样,其24 h蠕变量随着频率的增大而增大.当振动频率达到f=10 Hz的时候,其24 h拉伸蠕变量的变化趋于平缓.同时,也对不同振动条件下注塑的PP试样进行拉伸实验,冲击实验和动态力学性能测试,讨论了成型条件对性能的影响.

STUDIES ON TENSILE CREEP OF POLYPROPYLENE MOULDED IN VIBRATION FIELD

A custom-made dynamic injection molding machine was adopted to obtain PP specimens via changing the vibration frequency(5～25 MPa) and vibration stress(10～18 MPa).The specimens were characterized by tensile tests,notched Izod impact tests,dynamic mechanics analysis and creep measurements under a tensile load of 12 kg.For specimens prepared under a vibration frequency of 10 Hz their 24 h creep strain decreased from 7.4% to 4.5% with an increase of vibration stress from 10 MPa to 18 MPa.While for specimens prepared under a vibration stress of 12 MPa their 24 h creep strain increased with vibration frequency first,and after 10 Hz its variation became very slow.It was also found for these specimens that the Izod impact strength increased from 3.2 kJ/m~2 to 4.2 kJ/m~2,when the vibration stress changes from 10 MPa to 18 MPa,and,at the same time,the Izod impact strength decreased with increasing vibration frequency first and showed a minimum around 20 Hz.The influence of processing conditions on tensile elongation and dynamic mechanical properties were also observed.All the results indicated that within the experimental conditions used in this work increasing the vibration stress and decreasing the vibration frequency during processing could improve the long-term mechanical performance and impact ductility of PP specimens.