Bimodal Polyethylene Crosslinking for Pipe Sagging Resistance
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Solution Overview
Problem
Current polyethylene compositions for pipe production face challenges in sagging resistance and gel level, particularly for large diameter pipes, despite previous attempts using peroxide-based methods.
Innovation Solution
A process involving the use of bimodal or multimodal polyethylene with additives and controlled peroxide addition in an extruder device, where the polyethylene powder is mixed with non-organic additives and then melted with organic peroxide at specific conditions to reduce gel levels and enhance sagging resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If peroxide-based methods are used to improve sagging resistance, then sagging resistance is improved, but gel level increases
Solution Approach 1:
The patent changes the physical state of peroxide from solid to liquid form, and controls the addition timing and temperature parameters during extrusion. By maintaining lower temperatures and using liquid peroxide solution, the patent achieves crosslinking for sagging resistance while minimizing excessive gel formation that occurs with conventional solid peroxide methods.
Solution Approach 2:
The peroxide is added in liquid form before the extrusion process begins, and is distributed throughout the polyethylene powder in advance. This preliminary distribution ensures uniform crosslinking during extrusion while controlling the reaction to minimize gel formation, rather than adding peroxide during the extrusion process itself.
2Ease of manufacture
If conventional peroxide addition methods are used, then processing is simplified, but gel level increases and sagging resistance is insufficient
Solution Approach 1:
The patent uses a liquid peroxide solution that can be easily pumped and distributed through hydraulic systems during the extrusion process. This liquid form allows for precise control of peroxide addition rates and uniform distribution throughout the polyethylene material, achieving both ease of manufacture and improved sagging resistance.
3Strength
If high peroxide dosage is used to improve sagging resistance, then sagging resistance is improved, but gel level increases
Solution Approach 1:
The patent changes from solid peroxide to liquid peroxide solution form, and precisely controls the concentration and addition rate parameters. This allows for optimized peroxide dosage that achieves the necessary crosslinking for sagging resistance while minimizing waste and excessive gel formation through better control of the crosslinking reaction.
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 process results in polyethylene compositions with improved sagging resistance and reduced gel levels, suitable for producing pipes with uniform wall thickness and superior mechanical properties.
Implementation Method 1
a) supplying a bimodal or multimodal polyethylene... d) adding an organic peroxide... e) melting and homogenizing the mixture to form a molten polyethylene composition
Implementation Method 2
e) melting and homogenizing the mixture to form a molten polyethylene composition
Implementation Method 3
melting and homogenizing the mixture
Data Source
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AI summary
A process for preparing a polyethylene composition comprising bimodal or multimodal polyethylene in an extruder device comprising mixing a bimodal or multimodal polyethylene having a density from 0.940 g/cm3 to 0.968 g/cm3 in form of a polyethylene powder and one or more additives in a mixing device at a temperature from 10°C to 100°C without melting the polyethylene powder; melting and homogenizing the mixture within the extruder device to form a molten polyethylene composition; and pelletizing the molten polyethylene composition, wherein a liquid comprising an organic peroxide is added in an amount from 20 ppm to 200 ppm of organic peroxide with respect to the polyethylene powder, and the liquid is added to the polyethylene powder at a position where mixing occurs and where the polyethylene powder has a temperature of from 10°C to 100°C.