Metallocene Polyethylene Copolymers for Low-Density Moisture Barrier Films
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Solution Overview
Problem
Polyethylene (PE) films exhibit permeability to gases such as oxygen and moisture, limiting their barrier properties, and high-density PE films with improved barrier properties compromise mechanical properties like impact and tear resistance.
Innovation Solution
Development of metallocene-catalyzed polyethylene copolymers with lower densities, formed using various polymerization methods and catalyst systems, including metallocene compounds and chemically-treated solid oxide supports, to enhance barrier properties while maintaining or improving mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high density polyethylene is used to improve barrier properties, then moisture vapor transmission rate decreases, but impact and tear properties deteriorate
Solution Approach 1:
The patent changes the molecular weight distribution parameters of polyethylene by using metallocene catalysts to produce copolymers with specific Mz/Mw ratios (2.5-5.0), achieving improved barrier properties at lower densities without sacrificing mechanical strength
Solution Approach 2:
The patent creates a composite molecular structure by incorporating comonomers (1-butene, 1-hexene, or 1-octene) into the polyethylene chain, forming copolymers that combine the barrier properties of high-density PE with the mechanical flexibility of lower-density PE
2Strength
If low density polyethylene is used to improve impact and tear properties, then mechanical strength increases, but barrier properties deteriorate
Solution Approach 1:
The patent optimizes the molecular weight distribution parameters, specifically controlling the Mz/Mw ratio between 2.5-5.0 and Mn between 10,000-100,000 g/mol, to achieve a balance where lower density provides mechanical strength while the controlled molecular architecture maintains barrier properties
Solution Approach 2:
The patent creates local variations in polymer chain structure through comonomer incorporation at specific positions along the chain, resulting in regions with different crystallinity and packing densities that simultaneously provide mechanical strength and barrier properties
3Strength
If metallocene-catalyzed copolymers with lower densities are developed, then mechanical properties are maintained or improved, but traditional high-density barrier performance is compromised
Solution Approach 1:
The patent fundamentally changes the molecular weight distribution parameters achieved by metallocene catalysts, producing copolymers with Mz/Mw ratios of 2.5-5.0 (compared to traditional 10-20), and Mn of 10,000-100,000 g/mol, which enables lower density while maintaining both mechanical strength and barrier properties
Solution Approach 2:
The patent creates composite molecular structures by incorporating 1-butene, 1-hexene, or 1-octene comonomers at controlled levels (0.5-10 mol%), forming copolymers that combine the crystalline barrier properties of polyethylene with the amorphous flexibility provided by comonomer units
Data Source
AI summary
A metallocene-catalyzed polyethylene copolymer having a zero shear viscosity (η ° ) of from about 1X102 Pa-s to about 5X103 Pa-s and a ratio of a z-average molecular weight to a number average molecular weight (Mz/Mn) of from about 4 to about 15, and when tested in accordance with ASTM F1249 displays a moisture vapor transmission rate of less than or equal to about 0.9 g-mil/100 in2/day. A metallocene-catalyzed polyethylene copolymer which when tested in accordance with ASTM F1249 has a moisture vapor transmission rate (MVTR) that is decreased by at least 5% when compared to an MVTR determined in accordance with ASTM F1249 of an otherwise similar metallocene-catalyzed polyethylene homopolymer.