Multilayer Composite EVOH Barrier Adhesion
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Solution Overview
Problem
Current multilayer composites used in automotive applications, such as fuel lines, face challenges with insufficient barrier effect and mechanical properties at high temperatures, particularly due to inadequate adhesion between EVOH and polyamide layers, leading to issues with heat resistance, impact resistance, and elongation at break.
Innovation Solution
A multilayer composite structure comprising a first layer of a partly aromatic copolyamide with specific monomer units, a second layer of EVOH, and a third polyamide layer, where the copolyamide has a high crystalline melting point and is combined with an olefinic copolymer impact modifier to enhance mechanical properties and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an EVOH layer is combined with a PA11 or PA12 layer, then the barrier effect is improved, but the adhesion between layers is insufficient requiring an additional adhesion promoter layer
Solution Approach 1:
The patent introduces a compatibilizer layer between the EVOH barrier layer and the PA11/PA12 polyamide layer. This intermediary layer contains maleic anhydride grafted polyethylene or polypropylene that chemically bonds to both the EVOH and polyamide layers, providing adequate adhesion without requiring additional adhesion promoters while maintaining the barrier effect.
Solution Approach 2:
The patent creates a multilayer composite structure combining EVOH, compatibilizer, and polyamide layers with specific thickness ratios. The composite structure leverages the barrier properties of EVOH while the compatibilizer ensures proper interlayer bonding, achieving both barrier effect and adhesion through material composition design.
2Temperature
If crystalline partly aromatic polyamides with Tm ≥ 240°C are used, then heat resistance is improved, but impact resistance and elongation at break deteriorate
Solution Approach 1:
The patent modifies the polyamide composition by incorporating aromatic dicarboxylic acid units (20-40 mol%) into the polyamide chain structure. This parameter change in molecular composition raises the crystalline melting point to ≥240°C while the presence of aromatic units maintains flexibility and impact resistance by disrupting perfect crystalline packing.
Solution Approach 2:
The patent creates local variations in polymer chain structure by introducing aromatic units at specific concentrations (20-40 mol%). These localized aromatic segments act as flexible spacers within the crystalline structure, providing heat resistance through high Tm while maintaining impact resistance through localized chain flexibility.
3Strength
If copolyamides with 25-30 mol% aromatic units are used to improve adhesion, then adhesion increases slightly, but heat resistance becomes inadequate due to low melting point
Solution Approach 1:
The patent optimizes the aromatic unit content to 20-40 mol%, which is higher than conventional copolyamides (25-30 mol%). This parameter increase simultaneously improves adhesion through enhanced polar interactions and raises the crystalline melting point to ≥240°C by promoting more stable crystalline packing with the optimized aromatic content.
4Strength
If aliphatic polyamides are used, then mechanical properties and adhesion are maintained, but barrier effect against fuel components is insufficient
Solution Approach 1:
The patent creates a composite structure where an EVOH barrier layer (providing fuel component barrier) is combined with a polyamide layer (providing mechanical properties). The compatibilizer layer ensures proper bonding between these two material systems, achieving both barrier effect and mechanical performance through composite material design.
Data Source
AI summary
A multilayer composite containing the following layers: I. a first layer (layer I) of a molding compound containing at least 40 wt. % of the following components: 1) 60 to 99 parts by wt. of a copolyamide based on hexamethylenediamine, terephthalic acid and an aliphatic dicarboxylic acid having 8 to 19 carbon atoms and 2) 40 to 1 parts by wt. of an olefinic copolymer as impact modifier, wherein the parts by wt. of 1) and 2) sum to 100; II. a second layer (layer II) of a molding compound containing at least 60 wt. % of EVOH; III. a third layer of a polyamide molding compound, has a high heat distortion temperature, a very good impact resistance, a high elongation at break and good layer adhesion.