Bimodal Polyethylene Pipe Resin for Thick-Wall Extrusion
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Solution Overview
Problem
Metallocene-based and chromium-based catalyst systems face challenges in producing ethylene polymers suitable for large diameter and thick wall pipe products due to issues with extrusion processability and melt strength.
Innovation Solution
Development of high molecular weight ethylene polymers with specific density, zero-shear viscosity, and relaxation time ranges, achieved by contacting a base resin with a peroxide compound, enabling the production of large diameter, thick wall pipes without slump or sag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallocene-based catalyst systems are used to produce ethylene polymers, then impact strength, tear resistance, and optical properties are improved, but extrusion processability and melt strength deteriorate
Solution Approach 1:
The patent employs a bimodal polyethylene composition comprising two distinct polyethylene components with different molecular weight distributions. The first component provides impact strength and tear resistance, while the second component provides extrusion processability and melt strength. This composite approach allows both metallocene-based and chromium-based catalyst advantages to be combined in a single material system, resolving the contradiction between mechanical properties and processing characteristics.
2Ease of manufacture
If chromium-based catalyst systems are used to produce ethylene polymers, then extrusion processability and polymer melt strength are improved, but impact strength and optical properties deteriorate
Solution Approach 1:
The bimodal polyethylene composition combines two polyethylene components produced by different catalyst systems. The chromium-based component provides extrusion processability and melt strength, while the metallocene-based component provides impact strength and optical properties. This composite material strategy allows the final product to exhibit both good processability and mechanical performance.
3Strength
If high molecular weight ethylene polymers are produced to improve melt strength, then slump resistance is improved, but extrusion processability deteriorates
Solution Approach 1:
The patent segments the polyethylene material into two distinct molecular weight distribution components. The high molecular weight component (broad MWD) provides melt strength and slump resistance, while the low molecular weight component (narrow MWD) provides extrusion processability. This segmentation allows each component to fulfill its specific function without compromising the other.
Solution Approach 2:
The patent changes the molecular weight distribution parameters by combining two polyethylene components with different MWD characteristics. The broad MWD component has higher average molecular weight for melt strength, while the narrow MWD component has lower average molecular weight for processability. By adjusting the ratio and properties of these two components, the patent optimizes both melt strength and extrusion processability simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The resulting ethylene polymers exhibit excellent melt strength and slump resistance, allowing for the production of pipes with diameters up to 24 inches and wall thicknesses of at least 2 inches, with improved processability and durability.
Implementation Method 1
contacting a base resin with a peroxide compound to produce the ethylene polymer
Implementation Method 2
contacting a base resin with a peroxide compound to produce the ethylene polymer characterized by a density of at least about 0.94 g/cm3, a HLMI (I21) in a range from about 4 to about 20 g/10 min, a zero-shear viscosity (η0) at 190° C. in a range from about 20,000 to about 400,000 kPa-sec, and a relaxation time (τη) at 190° C. in a range from about 225 to about 3000 sec
Data Source
AI summary
Disclosed herein are ethylene-based polymers generally characterized by a density of at least 0.94 g/cm3, a high load melt index from 4 to 20 g/10 min, a zero-shear viscosity at 190° C. from 20,000 to 400,000 kPa-sec, and a relaxation time at 190° C. from 225 to 3000 sec. These ethylene polymers can be produced by peroxide-treating a broad molecular weight distribution Ziegler-catalyzed resin, and can be used in large diameter, thick wall pipes and other end-use applications.