Designing Soft and Transparent Films Based on Multi-Phase Polypropylene Copolymers and Styrene Block Copolymers

Concerns about the environmental and health impacts of plasticized PVC have created a clear demand to find alternative packaging materials for medical and pharmaceutical use. As polyolefin-based alternative, we blended polypropylene-ethylene copolymers of different, ethylene content-controlled, phase structure, with styrene-ethylene/butylene-styrene block copolymer (SEBS), as modifier, the latter being elastomeric and mechanically acting as cross-linked rubber due to a unique microphase separated morphology of hard spherical PS domains dispersed in the soft EB phase. Tests with injection-molded samples and cast films demonstrated promising combinations of flexibility, durability, and transparency—qualities essential for soft medical packaging like infusion pouches and blow-fill-seal bottles. For the desired level of flexibility (reflected by a flexural modulus of about 150 MPa), blends with two random-heterophasic (RAHECO) copolymers achieved this with only 15–25 wt.-% SEBS, compared to 37 wt.-% needed for a single-phase random copolymer (RACO); these blends also exhibited greater toughness. In contrast, a standard impact copolymer (HECO), with its more crystalline structure, required a higher modifier content of 45 wt.-% SEBS. Film morphology analysis indicated a gradual shift in disperse phase structure and orientation, leading to phase inversion at the highest SEBS content—without negatively affecting transparency.