Polyethylene Pipe Composition for Pressure Resistance and Homogeneity
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Solution Overview
Problem
Current polyethylene compositions for high-pressure pipes face challenges in achieving a balance between mechanical properties, processability, and homogeneity, particularly when incorporating ultra-high molecular weight fractions, which often result in surface defects and reduced homogeneity due to compatibility issues.
Innovation Solution
A polyethylene composition with a density of 952.0 kg/m3 to 960.0 kg/m3, produced through a multistage process involving multiple reactor stages with a solid Ziegler-Natta catalyst, achieving improved complex viscosity, slow crack propagation resistance, and maintaining suitable processability and mechanical properties while minimizing white spots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultra-high molecular weight fractions are incorporated into polyethylene composition, then pressure resistance and slow crack propagation resistance are improved, but homogeneity deteriorates and white spots appear on surface
Solution Approach 1:
The patent applies parameter changes by precisely controlling the complex viscosity within 750-1900 kPa·s and molecular weight distribution (Mw/Mn of 25-65) to optimize the dispersion of ultra-high molecular weight fractions. This parameter optimization ensures that the high molecular weight components integrate uniformly into the matrix without phase separation, resolving the contradiction between improved pressure resistance and maintained homogeneity.
Solution Approach 2:
The patent creates a composite polyethylene system by combining ultra-high molecular weight fractions (providing pressure resistance and slow crack propagation resistance) with base resin fractions (ensuring homogeneity and processability). The controlled molecular weight distribution and viscosity parameters enable these different molecular weight components to form a unified composite material structure without visible defects.
2Strength
If complex viscosity is increased to improve pressure resistance, then slow crack propagation resistance is enhanced, but processability deteriorates
Solution Approach 1:
The patent optimizes processability by controlling the melt flow rate MFR21 within 1.0-7.5 g/10 min, which corresponds to the complex viscosity range of 750-1900 kPa·s. This parameter window allows the material to have sufficient viscosity for pressure resistance while maintaining adequate flow characteristics for extrusion and molding processes, resolving the contradiction between strength and processability.
3Strength
If molecular weight distribution is broadened to enhance mechanical properties, then pressure resistance is improved, but manufacturing precision deteriorates due to increased white spots
Solution Approach 1:
The patent controls the molecular weight distribution by limiting Mw/Mn to 25-65 and adjusting the molecular weight average to achieve complex viscosity of 750-1900 kPa·s. This controlled distribution ensures that ultra-high molecular weight fractions are dispersed uniformly throughout the matrix, preventing white spot formation while maintaining enhanced pressure resistance and mechanical properties.
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 solution significantly enhances pressure resistance and slow crack propagation resistance at elevated temperatures while maintaining good mechanical properties and homogeneity, addressing the compatibility issues associated with ultra-high molecular weight fractions.
Implementation Method 1
produced through a multistage process involving multiple reactor stages with a solid Ziegler-Natta catalyst
Data Source
AI summary
The present invention relates to a polyethylene composition comprising a base resin having a density of from 952.0 kg/m3 to 960.0 kg/m3, determined according to ISO 1183, wherein the polyethylene composition has a melt flow rate MFR21 (190° C., 21.16 kg), of from 1.0 to 7.5 g/10 min, determined according to ISO 1133, a complex viscosity at a frequency of 0.05 rad/s eta0.05 of from 750 kPa #s to 1900 kPa #s, determined according to ISO 6721-1 and ISO 6721-10, and a white spot rating of not more than 12.0, determined according to ISO 18553, a polyethylene composition obtainable by a multi-stage process, a process for producing said polyethylene composition, an article, such as a pipe or pipe fitting, comprising said polyethylene composition and the use of said polyethylene composition for the production of an article.