Single-Site Catalysed Ethylene Pipe for Flexibility and Pressure Resistance
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Solution Overview
Problem
Existing crosslinked polyethylene pipes for hot and cold water applications face issues with stiffness, poor processability, and insufficient melt strength, leading to reduced production speed and increased crosslinking agent consumption.
Innovation Solution
A peroxide crosslinked ethylene polymer pipe is developed using a single-site catalysed ethylene polymer with low density and narrow molecular weight distribution, allowing for improved flexibility, reduced energy consumption, and enhanced crosslinkability, achieved through metallocene catalysts and controlled peroxide addition for long-chain branching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high density polyethylene is used to meet HDPE-X norm requirements, then pressure resistance is improved, but pipe stiffness increases and flexibility deteriorates
Solution Approach 1:
The patent changes the molecular weight distribution parameters of the polyethylene from unimodal to bimodal, combining HMW fraction (≥3500) for strength with LMW fraction for flexibility. This parameter change allows achieving required pressure resistance without using high density polyethylene, thereby maintaining pipe flexibility
Solution Approach 2:
The patent creates a composite molecular structure by blending two distinct polyethylene fractions with different molecular weight characteristics. The HMW fraction provides mechanical strength and pressure resistance, while the LMW fraction provides flexibility and processability, resulting in a composite material that balances both requirements
2Reliability
If low MFR polymer is used to improve crosslinking response, then crosslinking efficiency is improved, but processability deteriorates and production speed decreases
Solution Approach 1:
The patent segments the polymer into two distinct molecular weight fractions that can be independently optimized for different functions. The HMW fraction (≥3500) ensures good crosslinking response and mechanical properties, while the LMW fraction provides excellent processability and high production speed, allowing both requirements to be met simultaneously
Solution Approach 2:
The patent changes the molecular weight distribution from a single peak (unimodal) to a bimodal distribution with distinct HMW and LMW peaks. This parameter change enables the material to exhibit both high crosslinking efficiency (from HMW fraction) and high processability (from LMW fraction), resolving the contradiction between reliability and productivity
3Productivity
If high MFR polymer is used to improve processability, then production speed is improved, but melt strength deteriorates and dimensional stability is lost
Solution Approach 1:
The patent segments the polymer into HMW and LMW fractions where the HMW fraction (≥3500) provides melt strength and dimensional stability during processing, while the LMW fraction ensures good processability and high production speed. The synergistic combination resolves the contradiction between productivity and stability
4Ease of manufacture
If high MFR polymer is used to improve extrudability, then processability is improved, but crosslinkability deteriorates and crosslinking agent consumption increases
Solution Approach 1:
The patent segments the polymer into two fractions with complementary properties: HMW fraction (≥3500) that ensures excellent crosslinkability and reduces crosslinking agent consumption, and LMW fraction that provides good extrudability and processability. This segmentation allows both ease of manufacture and high reliability to be achieved
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 results in a more flexible pipe with improved pressure test performance, reduced crosslinking agent requirements, and increased production speed, while maintaining or exceeding the performance of traditional higher-density materials.
Implementation Method 1
an ethylene polymer prepared by single-site catalysed polymerisation
Implementation Method 2
Peroxide crosslinking of polyethylene is previously known. In peroxide crosslinking, the crosslinking takes place by the addition of peroxide compounds, such as dicumyl peroxide, which form free radicals.
Implementation Method 3
achieved through metallocene catalysts and controlled peroxide addition for long-chain branching
Data Source
AI summary
A peroxide crosslinked ethylene polymer pressure pipe and a method for the preparation thereof are described. The pipe is characterized in that it comprises an ethylene polymer with a density of less than 950 kg/m3 obtained by polymerization with a single-site catalyst and having a shear thinning index, SHI5/300 of less than 20 and a MWD of <10. The method is characterized in that it comprises polymerizing ethylene, optionally together with at least one comonomer, with a single-site catalyst to provide the above defined ethylene polymer, forming the ethylene polymer into a pipe by extrusion and crosslinking it.