EVOH Resin Composition Moisture Management for Retort Stability
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Solution Overview
Problem
EVOH resin compositions used in multilayer films for packaging face degradation and loss of gas-barrier performance during hot water treatments like retort processes due to hydrogen bond disruption, leading to decomposition and foaming at high temperatures, especially when used in coinjection molding processes where higher temperatures and pressures are involved.
Innovation Solution
A resin composition comprising EVOH resin, polyamide-based resin, and a hydrate-forming tricarboxylate metal salt drying agent, which absorbs moisture and maintains hydrogen bonds, reducing weight loss by 5-35% at 250°C, thereby enhancing thermal stability and preventing decomposition and foaming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If EVOH resin is used to provide gas-barrier performance, then oxygen barrier property is improved, but gas barrier performance deteriorates after hot water treatment due to hydrogen bond destruction
Solution Approach 1:
A drying agent (such as calcium sulfate, magnesium sulfate, or silica gel) is introduced as an intermediary substance that preferentially binds water molecules, preventing water from disrupting the hydrogen bonds in EVOH resin. The drying agent acts as a mediator that sacrifices itself by absorbing water, thereby protecting the EVOH resin's hydrogen bond network and maintaining its gas-barrier performance after hot water treatment.
Solution Approach 2:
The chemical environment within the resin composition is modified by adding basic metal salts (such as calcium stearate, magnesium stearate, or zinc stearate) that alter the local pH and chemical interactions. This parameter change prevents acid-catalyzed degradation and stabilizes the hydrogen bonds during hot water treatment, allowing the EVOH resin to maintain its gas-barrier properties.
2Ease of operation
If temperature is increased to 250°C or higher for coinjection molding, then fluidity is improved, but decomposition and foaming occur leading to loss of long-run stability
Solution Approach 1:
Antioxidants and heat stabilizers are added to the resin composition in advance to prevent decomposition before it occurs during high-temperature processing. These preventive additives neutralize free radicals and inhibit thermal degradation reactions, allowing the resin to maintain its stability even when processed at 250°C or higher temperatures required for coinjection molding.
Solution Approach 2:
The resin composition is formulated as a composite system combining EVOH resin with polyamide resin, drying agents, basic metal salts, and stabilizers. This composite material approach allows each component to contribute specific functions: EVOH provides gas barrier, polyamide provides toughness, drying agents protect against moisture, and stabilizers prevent thermal degradation, collectively enabling high-temperature processing without decomposition.
3Reliability
If hydrate-forming metal salt drying agent is added to suppress gas barrier degradation, then gas barrier performance is improved, but weight loss increases due to water absorption
Solution Approach 1:
The drying agent is used as a sacrificial, consumable component that temporarily holds water through hydration. Although the drying agent itself gains weight by absorbing water, this prevents the EVOH resin from losing its gas-barrier properties. The weight increase of the drying agent is acceptable and even desirable, as it indicates the drying agent is actively protecting the resin structure during hot water treatment.
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 composition maintains excellent gas-barrier performance and long-run stability even after hot water treatment, suitable for high-temperature processes like coextrusion and coinjection molding, ensuring the integrity of packaged goods.
Implementation Method 1
a hydrate-forming tricarboxylate metal salt drying agent, which absorbs moisture and maintains hydrogen bonds
Implementation Method 2
a hydrate-forming tricarboxylate metal salt drying agent, which absorbs moisture
Implementation Method 3
the resin composition may decompose partially under a condition of high temperature selected from the range of 250 °C to 280 °C
Data Source
AI summary
Provided is a resin composition which has excellent gas barrier performance after hot water treatment and which both has long-run stability and suppress decomposition and foaming in operations conducted at a high temperature. This resin composition comprises a saponified ethylene-vinyl ester-based copolymer (A), a polyamide-based resin (B), and a drying agent(C), wherein the reduction in weight of the resin composition after being kept at 250 °C in a nitrogen atmosphere for 1 hour is 5 % by weight or more but 35 % by weight or less.