Influence of the form II/Form I crystal polymorphism of random copolymers of butene-1 with ethylene or propylene on the peel behavior of peel films

Peel films of blends of low density polyethylene (LDPE) and random isotactic copolymers of butene-1 with either ethylene (iPB-Eth) or propylene (iPB-Prop) were investigated regarding the effect of the copolymer composition on both the Form II mesophase to Form I crystal transformation of the copolymers, and the time-dependent peel behavior of their blends with LDPE in peel films. In general, there is observed a decrease of the peel force with increasing concentration of both ethylene and propylene co-units in random iPB-1 based copolymers and their blends with LDPE, after completion of the Form II to Form I transformation. Thus, to tailor the peel force, either the content of the peel component in the blends, or the concentration of ethylene or propylene co-units in the peel component may be varied. The effect of ethylene co- units in the random copolymers on the peel force is distinctly larger than that of propylene co- units. Parallel to the Form II to Form I transition of butene-1 based copolymers, the peel force decreases with a rate which depends on the copolymer composition. The Form II to Form I transition in iPB-Prop copolymers proceeds distinctly faster than in iPB-Eth copolymers of identical concentration of co-units.