Polyolefin Composition Stiffness Impact Balance
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Solution Overview
Problem
Propylene homopolymers exhibit poor impact resistance and elongation values, and the addition of a rubbery phase to improve impact resistance typically compromises stiffness and optical properties, leading to unsatisfactory stress whitening resistance.
Innovation Solution
A polyolefin composition comprising 50-80 wt% of a propylene polymer with high isotactic pentad content, 5-20 wt% of a first ethylene copolymer, and 10-40 wt% of a second ethylene copolymer, prepared using a Ziegler-Natta catalyst system, which maintains stiffness and impact resistance while improving stress whitening resistance and optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rubbery component is added to propylene homopolymers to improve impact resistance, then impact resistance is improved, but stiffness is impaired
Solution Approach 1:
The patent applies parameter changes by precisely controlling the ethylene content in two different copolymers (first copolymer: 8-30 wt%, second copolymer: 30-85 wt%) and their respective weight ratios (5-20 wt% and 10-40 wt%). This systematic variation of compositional parameters enables optimization of both impact resistance and stiffness, resolving the contradiction between these properties.
Solution Approach 2:
The patent creates a composite material system consisting of three distinct polyolefin components: propylene homopolymer, first ethylene-propylene copolymer, and second ethylene-propylene copolymer. Each component contributes different properties, and their synergistic combination achieves both high impact resistance and maintained stiffness, effectively resolving the contradiction through material composition design.
2Strength
If a rubbery phase is added to improve impact resistance, then impact resistance is improved, but optical properties deteriorate
Solution Approach 1:
The patent controls the optical properties by adjusting the ethylene content parameters and the amounts of each copolymer in the composition. By optimizing these parameters, the patent achieves a balance where impact resistance is improved while gloss is maintained above 40%, resolving the contradiction between mechanical and optical properties.
3Strength
If a rubbery phase is added to improve impact resistance, then impact resistance is improved, but stress whitening resistance deteriorates
Solution Approach 1:
The patent addresses stress whitening resistance by optimizing the ethylene content and molecular characteristics (intrinsic viscosity) of the copolymers. The specific parameter ranges defined for each component work together to maintain stress whitening resistance above 80% while achieving improved impact resistance, resolving this contradiction.
Data Source
AI summary
The present invention provides polyolefin composition comprising a 50-80 wt% of propylene omopolymer or copolymer and a first and a second ethylene/alpha-olefin copolymer, said composition having good stress whitening resistance and gloss, in combination with a good balance of mechanical properties.