Research On Condensed Structure And Aging Property Of Isotactic Polypropylene Parts

Polymer manufactures have been widely used in aerospace,automobile,ship,electrical and architectural fields,however,the aging problem of the polymer parts becomes serious in such applications for various servicing conditions,which usually reflected as the property of the parts greatly reduced and even been out of their function.It could be confirmed that the polymer aging is strongly related to internal condensed structure,and the condensed structure is mainly determined by the modeling conditions.In terms of the aging problem of isoplastic polypropylene parts,studying the relationship between the condensed structure and aging property on different molding parameters and ultrasonic vibration is very important.It is expected to provide effective technical support for the forming of high quality,high performance,high strength and long life parts and their application in practical engineering.Firstly,the rectangular shell part with standard tensile samples at the bottom was selected based on the isoplastic polypropylene material,and the injection mold with ultrasonic assisted vibration system was designed and manufactured.The single factor experiments under different technological parameters and ultrasonic field were carried out.And then salt spray aging experiment,low temperature aging experiment and natural climate aging experiment were carried out on the molded parts.Meanwhile,X-ray diffraction analysis,tensile test,quality test,Fourier transform infrared spectrometer analysis and scanning electron microscope observation were carried out on the samples before and after aging.Secondly,the effects of the molding process parameter as well as the ultrasonic field on the forming of the condensed state structure were studied.And the tendency of the crystallinity changing with the difference of the melt temperature,mold temperature,holding pressure and ultrasonic power was analyzed.The results show that the crystallinity of the samples(no matter before or after aging testing)decrease gradually with the melt temperature increase;on the contrary,the crystallinity will increase by increasing the holding pressure and mold temperature;with the enhancing of ultrasonic power,at lower ultrasonic power,the crystallinity will increase slowly,and if the ultrasonic power would exceed a certain higher value,the crystallinity of samples decreased gradually.Finally,the effects of condensed state structure on the aging properties of the products were studied.By means of tensile property test,quality test,Fourier transform infrared spectrum and scanning electron microscope before and after aging,the internal molecular structure and microstructure of the samples were analyzed and observed.The results show that the molded product had the best resistance to salt fog aging when the melt temperature was 190?which result in its condensed state structure.When the ultrasonic power is 200 W,the product has the best resistance to low-temperature aging and natural climate aging,which also owe to its condensed state structure.Furthermore,comparing to other process parameters,we could notice that at those preferable molding process conditions,the tensile strength of the aged samples still stay high,and retain a higher crystallinity,even a lower damage degree of the surface microstucture.