Study On Preparation And Properties Of Polypropylene Microporous Membrane

Isotactic polypropylene(iPP)is one of the most common semi-crystalline polymers exhibiting pronounced polymorphisms and morphologies.Microporous membrane prepared by iPP is widely used in the fields of medical treatment,chemical industry,electronics,environmental protection and so on.However,due to the lack of research on the relationship between the preparation process and the structure and performance,the microporous membrane still has some problems of poor consistency,difficult production control and high cost.Therefore,studying the relationship between preparation process and structure and performance,and putting forward the scientific preparation process,is important to improve the comprehensive performance of microporous membrane.Firstly,this paper prepared film using iPP as material by extrusion casting,and then microporous membrane was obtained as a result of annealing and stretching.And the relationship between crystallinity,orientation,elastic recovery rate,pore distribution and preparation process was studied.Under the condition of general processing,iPP exists in a crystal.To study the effect of extrusion temperature on crystalline of a-iPP film,the relationship between extrusion temperature and crystallinity was analyzed by measuring crystallinity of films prepared under different extrusion temperatures.And the reasonable extrusion temperature was obtained.To reveal the influence of extrusion temperature on the mechanical properties of a-iPP film,the tensile strength and elongation at break and some other properties were investigated by tensile test.The relationship between casting ratio and hard-elastic and orientation was determined by calculating the the elastic recovery ratio and orientation of a-iPP film prepared under different casting ratio.And by studying the periodic structure,the effect of casting ratio on long period and crystal thickness was discovered.The a-iPP film with high crystallinity and high orientation is easier to form micro pores.The crystallization of film was improved by annealing,the crystallinity of different annealing temperatures was calculated,and the relationship between the annealing temperature and the crystallinity was determined.Cold and hot stretching ratio have a direct impact on the size and distribution of micro pores.The mechanical behaviors of cold stretching and hot stretching process were analyzed,and by observing the microporous structure,the stretching parameters of preparing of a-iPP were obtained.? crystal is the metastable crystalline of iPP,which can be obtained under certain conditions.The density of ? crystal is smaller than a crystal.In the stretching process,? crystal will transform to a crystal,and the micro pores are formed because of the density difference.It is often used in the production of microporous membrane.In this paper,?-iPP film was obtained by adding ? crystal nucleating agent.By studying the effect of the ratio of nucleating agent on the relative content of ? crystal and crystallinity,the optimum ratio was determined.The mechanical behaviors of ?-iPP film during cold stretching and hot stretching were analyzed,and the relationship between stretching parameters and micropore-forming of ?-iPP film was obtained by counting the size and distribution of micro pores.