Research On Anti-aging Properties Of Polypropylene Based On Crystal Structure Control

Recently,the ecological management of mine slope has raised lots of concerns,with the enhancement of people's awareness of environmental protection.The slope repair technology in the internation has developed to the fourth generation of soft slope,which employs functional component of polypropylene(PP)with low price,excellent mechanical properties,corrosion resistance to acid and alkali,but the presence of tertiary carbon atoms leads to bad anti-aging performance,which limits its widespread use.So it has become an urgent problem to improve the aging resistance of polypropylene.Polypropylene is a kind of polycrystalline polymer,in which the ? and ? crystals are of practical value.The crystalline structure influences the anti-aging performance,the crystal grain of ?crystal is larger than that of ? crystal,the light is not easy to pass through?crystal,the ? crystal has better anti-aging performance than?crystal.In this study,aiming at improving the anti-aging performance of fiber grade of polypropylene by controlling its crystalline structure.Multi methods to controlling the crystalline structure has been studied in this paper,such as changing the materials system,preferring the process conditions,adding ultrasonic field.This paper focus on the possibility of controlling the crystalline structure and exploring the internal mechanism.Based on the research above,this thesis has finished the following works,and gains the research results as following:(1)The effect of materials system on the crystalline structure.The result implys that the content of nucleating agent can influence it's self-assembly by altering the interation between nucleating agent,the different structure of self-assembly can lead to diverse crystalline structure.The crystallinity of PP increases first and then decreases with rising content of nucleating agent,it is found that ?crystal riches in the content of 0.4%.Also,the content of nucleating agent can effect the hierarchical crystalline structure.In order to have richer ?crystal in skin layer,it is reasonable to add 0.4%(W/W)nucleating agent;Based on the content of 0.4%,interfacial modification can further enhanced the content of ? crystal.It is proved thatsilane coupling agent has significant effect,which lead to33% increases.And after interfacial modification,the ratio of ?-crystal content between the skin and core layers increased by 14%,which make it true to have richer ?crystal in skin layer.(2)The effect of process condition on the crystalline structure.The result implys that the melting temperature of 220 ? leads to the best solubility of nucleating agent,and ?crystal riches at this melting temperature,while melting temperature has no effect on the hierarchical crystalline structure;High cooling temperature leads to more content of ?crystal and crystallinity,also high cooling temperature enhances the content of ? crystal in the skin layer.Based on the finite element analysis of PP cooled at different cooling temperature,it is proved that the effect of cooling temperature on the crystalline structure is due to the residence time in the temperature range for formation of ?crystal;The draw ratio has two effects to the crystalline structure,the content of ? crystal increases first and then decreases with rising draw ratio,it riches in the draw ratio of 4.And the draw ratio can enhances the hierarchical structure.(3)The effect of ultrasonic field on the crystalline structure.The result implys that the effect of ultrasonic frequency on the crystalline depends on the temperature.Hign ultrasonic frequency with high temperature can enhances the crystallinity and the content of ? crystal.Also,while at low temperature,the untrasonic frequency only effect the skin layer,instead of the intermediate layer and the core layer,when at high temperature,the effect of ultrasonic frequency can reach to the intermediate layer,but still not to the core,this effect weaken the hierarchical structure at high ultrasonic frequency with high temperature.(4)Regulation of crystal structure can realize the anti ageing polypropylene modified to a certain extent,when the content of ? crystal increased 47.13%,the carbonyl index decreased 16.28%.And with the content of ? crystal increased,carbon index The ?crystal in the skin layers can effectively prevent the transmission of light and slow down the aging process of radial polypropylene.