The influence of chain entanglement density on ultra-drawing behavior of ultra-high-molecular-weight polypropylene in the gel-casting method

The ultra-drawing behavior of ultra-high-molecular-weight polypropylene (UHMW-PP) in the gel-casting method has been investigated by using four kinds of gel-cast sheets prepared from four kinds of solutions of 1.0, 2.0, 4.0 and 6.0 wt.% of UHMW-PP. Consequently, it was found that the draw ratio during neck deformation (N.DR.) was related linearly to the inverse root of solution concentration of UHMW-PP. Since this phenomenon was similar to the relationship between the attained maximum draw ratio (λmax) and the solution concentration, it was considered that N.DR. was related linearly to the inverse root of chain entanglement density. And, it was also found that λmax could be defined by the maximum drawing stress (F) around yield point in the 2nd step drawing. On the other hand, no influence of solution concentration on the increasing behavior of strength and modulus with ultra-drawing was detected for the gel-cast sheet prepared from initial solution concentration of above 1 wt.%. The reason of this fact was inferred from the increase of the content of shishkebab structure in the gel-cast PE fiber from the high initial solution concentration.