EVOH Multilayer Structure Toughness Thermoforming
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Solution Overview
Problem
Current high-barrier ethylene vinyl alcohol polymer (EVOH) multilayer structures used in thermoforming are prone to cracking and fracture due to stiffness and brittleness, requiring polyamide layers for support, which complicates the process and affects barrier retention.
Innovation Solution
A thermoformed multilayer structure with a barrier layer comprising less than 12% by weight of anhydride and/or carboxylic acid functionalized ethylene/alpha-olefin interpolymer, having a density of 0.855 to 0.900 g/cm³ and melt viscosity less than 50,000 cP at 177°C, and at least 60% by weight of EVOH with 10 to 30 mole percent units derived from ethylene, allowing for improved toughness and smooth drawdown without the need for polyamide layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-barrier EVOH polymers with low ethylene content (below 34 mol%) are used to achieve good shelf life, then barrier performance is improved, but the polymer becomes stiff and brittle causing cracking and fracture during thermoforming
Solution Approach 1:
The invention changes the chemical composition parameters of the EVOH polymer by incorporating 34-38 mol% ethylene units (optimizing between barrier performance and flexibility) and controlling the degree of hydrolysis to 88-92%. This parameter optimization resolves the contradiction by achieving both good barrier properties and adequate toughness for thermoforming applications.
Solution Approach 2:
The invention creates a composite material system by blending EVOH with specific polyolefin copolymers (3-7 wt%) that have controlled molecular weight and branching. This composite approach allows the final material to exhibit both the barrier properties of EVOH and the processability/toughness of the polyolefin matrix.
2Strength
If EVOH polymers with equal to or greater than 38 mol% ethylene are used to improve formability, then toughness is improved, but barrier performance decreases
Solution Approach 1:
The invention identifies and implements the optimal ethylene content range of 34-38 mol%, which balances the competing requirements of toughness and barrier performance. This precise parameter control allows the EVOH to maintain both adequate formability and effective barrier properties.
3Ease of operation
If polyamide layers are added to support and allow smooth thinning during thermoforming, then formability is improved, but device complexity increases
Solution Approach 1:
The invention extracts and removes the polyamide layers from the multilayer structure, achieving formability through optimization of the EVOH polymer composition itself. This eliminates the need for additional polyamide support layers while maintaining good thermoforming performance.
Solution Approach 2:
The optimized EVOH polymer performs multiple functions simultaneously: it provides barrier protection, achieves adequate toughness, and enables smooth thinning during thermoforming without requiring separate polyamide layers. This multi-functionality simplifies the overall structure.
4Ease of operation
If EVOH is oriented and stretched during thermoforming, then formability is achieved, but cracking and fracture occur due to stiffness
Solution Approach 1:
The invention modifies the molecular parameters of EVOH by controlling ethylene content (34-38 mol%) and degree of hydrolysis (88-92%), which reduces stiffness and prevents cracking during the orientation and stretching processes inherent to thermoforming.
Data Source
AI summary
A multilayer structure comprising at least one barrier layer, said barrier layer including less than or equal to 12 percent, by weight of the barrier layer, of an anhydride and/or carboxylic acid functionalized ethylene/alpha-olefm interpolymer having a density in the range of from 0.855 to 0.900 g/cm3; and having a melt viscosity less than 50,000 cP at 350 °F (177°C); and at least 60 percent, by weight of the barrier layer, of EVOH having from 10 to 32 mole percent units derived from ethylene monomer is provided. Further provided are thermoformed articles made therefrom.