Multimodal Ethylene Polymer Crosslinking Processability
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Solution Overview
Problem
Existing polyethylene pipes for hot and cold water applications face challenges in achieving a balance between cross-linking ability and processability, particularly in screw extrusion, resulting in stiffness and poor extrudability due to high density and crystallinity, which affects flexibility and production efficiency.
Innovation Solution
A cross-linked multimodal ethylene polymer with a density of less than 950 kg/m³, produced using a single-site catalyst, exhibiting a melt flow rate (MFR) of 10-20 g/10min and a shear thinning index of at least 4, comprising a lower molecular weight ethylene homopolymer and a higher molecular weight ethylene copolymer, enhancing cross-linking response and flexibility while maintaining good processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyethylene of relatively high density is used to meet HDPE-X norm requirements, then heat deformation resistance and structural integrity are improved, but pipe stiffness increases and flexibility deteriorates
Solution Approach 1:
The patent uses a multimodal polyethylene composition combining homopolymer and copolymer components with different molecular weights and densities. The homopolymer provides structural integrity and heat resistance, while the copolymer component contributes flexibility and processability, creating a composite material system that balances opposing properties.
Solution Approach 2:
The patent creates different molecular weight distributions within specific portions of the polymer structure. The homopolymer fraction provides local regions of high strength and heat resistance, while the copolymer fraction creates local regions of enhanced flexibility and processability, allowing different parts of the material to excel at different functions.
2Reliability
If polyethylene of relatively low melt flow rate (high molecular weight) is used to improve crosslinking response, then cross-linking degree increases, but processability and extrusion line speed deteriorate
Solution Approach 1:
The patent segments the polymer into two distinct molecular weight populations: a high molecular weight homopolymer component that provides excellent crosslinking response and a lower molecular weight copolymer component that ensures good processability and extrusion speed. This segmentation allows each component to optimize its specific function without compromising the other.
Solution Approach 2:
The patent changes the molecular weight distribution parameters by combining polymers with different M w values. The multimodal distribution with specific M w and M w /M n ratios enables the material to exhibit both high crosslinking capability (from high M w component) and good processability (from lower M w component) simultaneously.
3Productivity
If single-site catalyst is used to produce multimodal polyethylene with good processability, then MFR is improved, but crosslinking ability may be compromised
Solution Approach 1:
The single-site catalyst system produces a composite polymer structure containing both homopolymer and copolymer fractions with controlled molecular weights. This composite approach ensures that the catalyst's precision in controlling molecular architecture is maintained while achieving the desired balance between processability and crosslinking ability through the multimodal composition.
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 polymer achieves improved cross-linking degree of at least 60% with enhanced flexibility and pressure test performance, allowing for more efficient pipe production with reduced energy consumption and lower cross-linking agent usage, while maintaining excellent surface quality and reduced ash content.
Implementation Method 1
polymerising ethylene in a first stage in the presence of a single site catalyst... polymerising ethylene and at least one comonomer in a second stage in the presence of the same single site catalyst
Implementation Method 2
a shear thinning index SHI 2.7/210 of at least 4
Data Source
AI summary
A multimodal ethylene polymer with a density of less than 950 kg/m3 obtained by polymerisation with a single-site catalyst and having an MFR21 in the range of 10 to 20 g/10min; a shear thinning index SHI2.7/210 of at least 4; and preferably a crosslinkability of at least 60%.