PEX Surface Coating on Expanded Polyethylene Without Oxidation
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Solution Overview
Problem
Current methods of cross-linking polyethylene (PE) and expanded polyethylene (ePE) alter their mechanical properties, such as tensile strength and durability, often leading to undesirable effects like chain scission and oxidation.
Innovation Solution
A cross-linked polyethylene (PEX) outer surface is formed on an ePE substrate using plasma enhanced chemical vapor deposition (PECVD) with ethylene gas, maintaining the ePE's microstructure and mechanical properties while enhancing abrasion resistance and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional cross-linking methods (γ irradiation or e-beam) are used for bulk polyethylene, then cross-linking is achieved, but mechanical properties of ePE are compromised
Solution Approach 1:
The patent applies cross-linking locally only to the surface layer (0.1-10 μm depth) rather than the entire bulk material. This localized cross-linking approach provides the desired cross-linked structure at the surface while preserving the mechanical properties of the bulk ePE substrate, resolving the contradiction between achieving cross-linking and maintaining mechanical strength.
Solution Approach 2:
The patent segments the cross-linking process into a surface-limited treatment rather than bulk treatment. By controlling the cross-linking depth to be shallow (0.1-10 μm), the invention separates the cross-linked surface layer from the uncross-linked bulk material, allowing each region to have optimized properties for its specific function.
2Reliability
If inert gas plasma is used to cross-link PE, then cross-linking is achieved, but tensile strength of ePE is destroyed
Solution Approach 1:
The patent uses an intermediary substance (organic vapor or liquid) as a mediator during the plasma cross-linking process. This intermediary allows energy transfer to occur through a medium that protects the ePE substrate from direct plasma damage, enabling cross-linking while preserving tensile strength.
Solution Approach 2:
The patent replaces direct plasma treatment with a plasma-enhanced process using organic vapor/liquid intermediaries. This substitution of the treatment mechanism allows cross-linking to occur without the harsh mechanical and chemical effects of direct plasma exposure that would destroy tensile strength.
3Reliability
If cross-linking is performed on ePE, then durability is improved, but microstructure and mechanical properties are altered
Solution Approach 1:
The patent applies cross-linking locally only to the surface layer (0.1-10 μm depth) rather than the entire bulk material. This localized cross-linking approach provides the desired cross-linked structure at the surface while preserving the mechanical properties of the bulk ePE substrate, resolving the contradiction between achieving cross-linking and maintaining mechanical strength.
Solution Approach 2:
The patent applies partial cross-linking only to the extent necessary for surface durability (shallow depth of 0.1-10 μm) rather than complete bulk cross-linking. This partial action is sufficient to achieve the desired durability improvement while avoiding the harmful effects of excessive cross-linking on the overall microstructure.
4Strength
If cross-linked PE surface is formed, then wear resistance is enhanced, but oxidation of ePE substrate occurs
Solution Approach 1:
The patent uses an intermediary substance (organic vapor or liquid) as a mediator during the plasma cross-linking process. This intermediary allows energy transfer to occur through a medium that protects the ePE substrate from direct plasma damage, enabling cross-linking while preserving tensile strength.
Solution Approach 2:
The patent employs an inert or reducing atmosphere during the plasma cross-linking process to prevent oxidation of the ePE substrate. By creating an oxygen-free environment during treatment, the invention enables cross-linking while protecting the substrate from oxidative damage.
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 method preserves the ePE's structural integrity and mechanical properties while providing a PEX outer surface that increases wear resistance and burst strength, maintaining porosity and tensile strength without substantial oxidation.
Implementation Method 1
A cross-linked polyethylene (PEX) outer surface is formed on an ePE substrate using plasma enhanced chemical vapor deposition (PECVD) with ethylene gas
Implementation Method 2
inert gas plasma can be used to cross-link PE
Data Source
AI summary
An article including expanded polyethylene (ePE) and cross-linked polyethylene (PEX) defining a surface that is conformal and continuous on the ePE, the surface including a thickness from about 10 nm to about 500 nm, the surface being about 5% or more weight percent of the ePE, wherein the ePE and the PEX are substantially free of any other element than hydrogen or carbon.