Propylene Copolymer Sterilization Resistance
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Solution Overview
Problem
Existing soft heterophasic propylene copolymers have low melting temperatures, which are detrimental for sterilization, and lack good optical properties that remain after sterilization, as well as adequate temperature resistance and flowability.
Innovation Solution
A propylene copolymer with a high comonomer content and xylene cold soluble (XCS) fraction, featuring a high propylene content and intrinsic viscosity, specifically with a comonomer content range of 7.5 to 12 wt.% and intrinsic viscosity of 1.8 to 3.0 dl/g, balancing the properties between the xylene cold soluble and insoluble fractions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the comonomer content is increased to improve softness and impact strength, then the melting temperature decreases, which is detrimental for sterilization
Solution Approach 1:
The propylene copolymer is segmented into two distinct phases: a crystalline polypropylene matrix phase and an amorphous elastomeric copolymer inclusion phase. This segmentation allows the matrix to provide high melting temperature for sterilization resistance, while the dispersed elastomeric inclusions provide softness and impact strength. The phases are physically separated rather than uniformly mixed, resolving the contradiction between these opposing properties.
Solution Approach 2:
The invention creates a composite heterophasic system where a crystalline polypropylene matrix contains dispersed elastomeric copolymer inclusions. The matrix phase provides thermal stability and high melting point for sterilization, while the elastomeric inclusions contribute softness and impact resistance. This composite structure combines materials with complementary properties to simultaneously achieve both high temperature resistance and mechanical toughness.
2Strength
If the elastomeric copolymer content is increased to improve impact behavior, then the optical properties deteriorate after sterilization
Solution Approach 1:
The elastomeric copolymer is localized as finely dispersed inclusions within the crystalline matrix, rather than being uniformly distributed. This local concentration of elastomeric material provides impact resistance at specific sites without compromising the overall optical clarity of the bulk material. The inclusions are small enough and sufficiently dispersed to minimize light scattering while maintaining mechanical performance.
3Strength
If the comonomer content is increased to achieve soft material properties, then the flowability during injection molding deteriorates
Solution Approach 1:
The segmented heterophasic structure allows the crystalline matrix to dominate the melt flow behavior during injection molding, while the elastomeric inclusions remain dispersed and do not significantly hinder flow. The matrix phase has good flow characteristics that enable easy manufacturing, while the dispersed soft inclusions provide the desired softness in the final product without compromising processability.
Data Source
AI summary
Propylene copolymer having a melt flow rate MFR2 (230°C) in the range of 2.5 to 12.0g/10min, a xylene cold soluble content (XCS) in the range of 20.0 to 45.0 wt.-%, a comonomer content in the range of more than 7.5 to 12.0 wt.-%, wherein further the comonomer content of xylene cold soluble (XCS) fraction of the propylene copolymer is in the range of 16.0 to 28.0 wt.-%.