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Designing Soft and Transparent Films Based on Multi-Phase Polypropylene Copolymers and Styrene Block Copolymers
Summary
Scientists have developed a new plastic material that could replace PVC in medical products like IV bags and bottles, which are known to shed plasticizers and microplastics into the fluids and medications they hold. By blending different types of polypropylene plastic with a rubber-like additive, they created a film that's flexible, durable, and clear—like PVC—but without needing potentially harmful chemical softeners. This matters because it offers a promising, safer alternative for medical packaging that reduces the risk of plastic and chemical contamination in healthcare settings.
Concerns about the environmental and health impacts of plasticized poly (vinyl chloride) (PVC), from plasticizer loss to microplastic formation, have created a clear demand to find alternative packaging materials for medical and pharmaceutical use. As a possible polyolefin-based alternative, we blended polypropylene-ethylene copolymers with different ethylene content-controlled phase structures with styrene-ethylene/butylene-styrene block copolymer (SEBS), as modifier. SEBS is elastomeric and performs mechanically like a cross-linked rubber due to its unique microphase-separated morphology of hard spherical polystyrene (PS) domains dispersed in the soft elastomeric ethylene-butylene copolymer (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 150-250 MPa), blends with two random-heterophasic (RAHECO) copolymers achieved the lower limit with only 15-25 wt.-% SEBS, compared to the 37 wt.-% needed for a single-phase random copolymer (RACO). These blends also exhibited greater toughness and excellent transparency. In contrast, a standard impact copolymer (HECO), with its more crystalline matrix, 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.