Polypropylene Composition with Low-Styrene Elastomer for Sterilized Packaging
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Solution Overview
Problem
Standard heterophasic polypropylene systems exhibit inadequate seal strength performance after sterilization, which limits their use in packaging applications, and have high haze values unsuitable for medical packaging.
Innovation Solution
A polymer composition comprising a heterophasic propylene copolymer and a styrenic-based elastomer with low styrene content, specifically a styrene-ethylene/butylene-styrene (SEBS) block copolymer or hydrogenated styrene-vinyl isoprene (SIS) block rubber, where both components have similar melt flow rates, enhancing seal strength and maintaining low haze and toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the amount of rubber dispersed within the polypropylene matrix is increased to improve impact strength, then impact strength is improved, but seal strength after sterilization deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the rubber phase by specifying that it must be a styrenic block copolymer with styrene content of 10-40 wt% and specific comonomer ratios. This parameter optimization allows achieving sufficient impact strength while maintaining seal strength after sterilization, resolving the contradiction between these two properties.
Solution Approach 2:
The invention creates a composite material system consisting of polypropylene matrix combined with specifically formulated styrenic block copolymer rubber phase. This composite structure enables the material to simultaneously exhibit high impact strength from the rubber dispersion and good seal strength from the optimized polymer composition, overcoming the limitations of conventional impact-modified polypropylenes.
2Strength
If standard heterophasic polypropylene systems are used to achieve sufficient stiffness and impact strength, then mechanical properties are improved, but haze values become too high for medical packaging applications
Solution Approach 1:
The invention optimizes the comonomer composition parameters of the rubber phase by specifying exact ranges for ethylene (20-80 wt%), 1-butene (10-40 wt%), and other α-olefins. This precise parameter control enables tuning of the rubber phase properties to achieve both high impact strength and low haze values, making the material suitable for medical packaging where transparency is critical.
3Stability of the object's composition
If the styrene content in the styrenic based elastomer is increased to improve elastomeric properties, then rubber elasticity is improved, but seal strength after sterilization deteriorates
Solution Approach 1:
The invention identifies and optimizes the critical parameter of styrene content in the styrenic block copolymer, specifying it should be 10-40 wt%. This parameter optimization balances the elastomeric properties needed for impact modification with the seal strength required after sterilization, resolving the contradiction between these two requirements.
Data Source
AI summary
Polymer composition comprising - a heterophasic propylene copolymer comprising a polypropylene matrix and an elastomeric propylene copolymer comprising at least one comonomer selected from the group consisting of ethylene and C4 to C20 a-olefine, and - a styrenic based elastomer(s) (B), wherein the styrene content in each styrenic based elastomer (B) is equal or below 15 wt.-%,, and the total amount of the styrenic based elastomer(s) (B) based on the total amount of polymers present in the polymer composition is of 16.0 to 46.0 wt.-%.