Peroxide-Treated Bimodal Polyethylene for Thick-Wall Pipe 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 applications due to issues with extrusion processability and melt strength, leading to problems with slump or sag during pipe production.
Innovation Solution
Development of high molecular weight ethylene polymers with specific density, melt index, zero-shear viscosity, and relaxation time ranges, achieved by contacting a base resin with a peroxide compound, which enhances melt strength and processability, allowing for the production of large diameter and 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 combines metallocene-catalyzed polyethylene (providing excellent impact strength, tear resistance, and optical properties) with a small amount of high-density polyethylene (HDPE) containing long chain branches (providing melt strength and extrusion processability). This composite resin composition achieves both good mechanical properties and excellent extrusion processability for large diameter pipe applications.
2Ease of manufacture
If chromium-based catalyst systems are used to produce ethylene polymers, then extrusion processability and polymer melt strength are improved, but the ability to produce polymers for large diameter and thick wall pipe products deteriorates
Solution Approach 1:
The patent introduces a specific component with long chain branches (LCB) that constitutes 5-50 wt% of the total resin composition. This LCB-containing component locally provides the melt strength and extrusion processability needed for large diameter pipe applications, while the majority metallocene polyethylene maintains its superior mechanical properties. The localized addition of LCB component resolves the contradiction between general processability and specific large diameter pipe suitability.
3Strength
If high molecular weight ethylene polymers are produced, then melt strength is improved, but slump or sag during pipe production increases
Solution Approach 1:
The patent carefully controls the molecular weight and long chain branch content of the HDPE component within specific ranges (Mw: 200,000-1,000,000 g/mol, LCB: 5-50 wt%). By optimizing these parameters, the resin achieves sufficient melt strength for large diameter pipe extrusion while avoiding excessive slump or sag. The balanced composition allows the polymer to maintain structural integrity during processing without excessive deformation.
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, enabling the production of pipes with diameters up to 24 inches and wall thicknesses of at least 2 inches, with improved commercial production rates and reduced gel content.
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
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.