Polyethylene Copolymer Composition Barrier Properties
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Solution Overview
Problem
Current polyethylene compositions for applications requiring good barrier properties, such as bottle closures and films, often prioritize molecular weight over barrier performance, resulting in suboptimal oxygen and water vapor transmission rates.
Innovation Solution
A polyethylene copolymer composition comprising a blend of two ethylene copolymers with specific molecular weight distributions, density ranges, and short chain branching ratios, along with the inclusion of a nucleating agent, to enhance barrier properties and processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If polyethylene compositions use relatively low and high molecular weight homopolymers to achieve good barrier properties in films, then barrier properties are improved, but the composition is not suitable for molding applications requiring good environmental stress crack resistance
Solution Approach 1:
The invention changes the molecular parameters by using copolymers with controlled molecular weight distributions (Mw/Mn < 3.0), specific densities (0.910-0.970 g/cm³), and short chain branching ratios (SCB1/SCB2 > 1.0) to simultaneously achieve good barrier properties and environmental stress crack resistance that were not attainable with traditional homopolymer blends
Solution Approach 2:
The invention creates a composite polyethylene composition by blending two specific ethylene copolymers with different molecular weights and densities, where the first copolymer (10-70 wt%) provides barrier properties and the second copolymer (90-30 wt%) provides processability and stress crack resistance, achieving a synergistic effect that neither component alone can provide
2Object-affected harmful factors
If polyethylene copolymer compositions are designed with specific molecular weight distributions and density ranges to improve barrier properties, then oxygen and water vapor transmission rates are reduced, but the complexity of composition design and manufacturing increases
Solution Approach 1:
The invention establishes specific parameter ranges for the copolymer components (molecular weight distribution Mw/Mn < 3.0, density 0.910-0.970 g/cm³, short chain branching ratio SCB1/SCB2 > 1.0) that define the optimal composition for achieving good barrier properties while maintaining manufacturability
Solution Approach 2:
The invention assigns different local qualities to each copolymer component: the first copolymer (10-70 wt%) is optimized for barrier properties with specific molecular weight and density characteristics, while the second copolymer (90-30 wt%) is optimized for processability and stress crack resistance, allowing each component to excel in its specific function
3Ease of manufacture
If polyethylene compositions prioritize molecular weight for processing, then processability is improved, but barrier properties deteriorate with suboptimal oxygen and water vapor transmission rates
Solution Approach 1:
The invention optimizes the molecular weight distribution parameter (Mw/Mn < 3.0) and density parameters (0.910-0.970 g/cm³) of the copolymer components to achieve a balance where the composition remains easy to process while simultaneously achieving excellent barrier properties with optimized oxygen and water vapor transmission rates
Data Source
AI summary
A dual reactor solution polymerization process gives polyethylene compositions containing a first ethylene copolymer and a second ethylene copolymer and which has a balance of barrier properties, toughness and environmental resistance. The polyethylene compositions are suitable for end use applications which may benefit from low oxygen transmission rates such as closures for bottles or barrier film.