High Density Polyethylene Composition for Impact and Stress Crack Resistance
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Solution Overview
Problem
There is a need for high-density polyethylene resins that simultaneously exhibit good impact resistance and environmental stress crack resistance properties, which existing polyethylene resins have not adequately addressed.
Innovation Solution
A polyethylene composition comprising a blend of two ethylene copolymers with specific molecular weight, branching, and density characteristics, including a first ethylene copolymer with higher weight average molecular weight and short chain branches, and a second ethylene copolymer with lower molecular weight and fewer short chain branches, achieving a density of ≥0.945 g/cm3 and enhanced melt strength, impact resistance, and environmental stress crack resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single polyethylene resin is used, then the density and processing properties can be controlled, but it is difficult to simultaneously achieve high impact resistance and environmental stress crack resistance
Solution Approach 1:
The patent uses a composite material system consisting of two different polyethylene resins (first and second polyethylene resins) with distinct molecular weight and density characteristics. The first resin has higher molecular weight and provides environmental stress crack resistance, while the second resin has lower molecular weight and provides impact resistance. By blending these two resins in specific ratios, the composition achieves both impact resistance and environmental stress crack resistance simultaneously, which cannot be achieved with a single resin type.
Solution Approach 2:
The patent applies local quality by assigning different functional roles to different components of the blend. The first polyethylene resin (higher molecular weight, 0.93-0.96 g/cm³ density) is optimized for environmental stress crack resistance, while the second polyethylene resin (lower molecular weight, 0.96-0.97 g/cm³ density) is optimized for impact resistance. Each component contributes its specific property to the overall composition, allowing the final material to exhibit both properties simultaneously.
2Reliability
If high molecular weight polyethylene is used to improve environmental stress crack resistance, then impact resistance improves, but melt flow and processing become difficult
Solution Approach 1:
The patent changes the molecular weight parameter by using a blend of two polyethylene resins with different molecular weights. The first resin has higher molecular weight (providing environmental stress crack resistance) while the second resin has lower molecular weight (providing good melt flow and processing). By adjusting the ratio of these two resins and controlling their respective molecular weights within specific ranges, the composition achieves both good environmental stress crack resistance and adequate processability.
Solution Approach 2:
The patent creates a composite material system where the lower molecular weight polyethylene resin acts as a processing aid for the higher molecular weight resin. The second resin (lower molecular weight) improves the melt flow characteristics of the blend, enabling adequate processing, while the first resin (higher molecular weight) provides the environmental stress crack resistance. This composite approach allows both requirements to be met simultaneously.
3Strength
If polyethylene composition is optimized for impact resistance, then environmental stress crack resistance decreases, and vice versa
Solution Approach 1:
The patent employs a composite material system comprising two polyethylene resins with complementary properties. The first resin (higher molecular weight, 0.93-0.96 g/cm³ density) contributes environmental stress crack resistance, while the second resin (lower molecular weight, 0.96-0.97 g/cm³ density) contributes impact resistance. The synergistic effect of blending these two resins in appropriate ratios enables the composition to achieve both impact resistance and environmental stress crack resistance simultaneously, overcoming the trade-off that exists when using single resin systems.
Data Source
AI summary
A polyethylene composition has a density of ≥0.945 g/cm3, a melt index. I2 of from 0.8 to 4.0 g/10 min. an environmental stress crack resistance, an ESCR of greater than 400 hours as determined by ASTM D1693 in 100% IGEPAL CO-630 under conditions A or B. and a melt strength of ≥3.0 cN.