On the other hand, when the content of high density polyethylene is less than 20 wt % (i.e. when the content of diluent is more than 80 wt %), the compoundability of polyethylene with diluent is reduced, and thus, polyethylene is not thermodynamically blended with the diluent but extruded in a gel state, bringing about problems, such as a breakage and a thickness nonuniformity during the stretchin