Influence of sequential biaxial stretching parameters on the interior structure of polypropylene membrane

This study investigated the interior structures of sequential biaxially stretched membranes to determine how stretching parameters affect the interior membrane structure. The polypropylene sheets for stretching were made by injection moulding. Experimental results indicate that, in the sequential biaxial stretching process, increasing the orientation of the structure of membrane produced by machine direction (MD) stretching and then separating the interior structure of the membrane by tiny pre-stretching in the transverse direction (TD) at a low temperature would lead to a net-like interior structure after TD stretching. During MD stretching, the uniformity of the structure of membrane can be improved by increasing stretching temperature and the drawing ratio. During TD pre-stretching, increasing the stretching temperature significantly decreases the number of net-like structures. However, a high proportion of pre-stretching to total TD stretching increases the number of net-like structures and improves size consistency. During TD stretching, increasing the stretching temperature would make membranes tend to be more rubbery, and decreases the generation of the net-like structures. Also, higher drawing ratio in TD would cause the size of net-like structures to grow. A high drawing ratio in the TD also increases the size of net-like structures.