Recyclable EVA Foam via Thermally Degradable Urethane Linkages
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Solution Overview
Problem
EVA foams used in footwear are not recyclable and undergo yellowing during thermal processing, limiting their applications due to uncontrolled color change and lack of durability.
Innovation Solution
Introduction of a thermally degradable urethane linkage using a TEMPO derivative in EVA systems, allowing for the creation of a recyclable crosslinked polymeric foam with controlled yellow index, enabling recyclability and desirable properties for various applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If EVA foam is highly crosslinked to enhance durability, then strength is improved, but recyclability deteriorates
Solution Approach 1:
The patent changes the chemical parameter of the crosslinking agent from conventional non-degradable types to thermally degradable urethane linkages formed by TEMPO derivatives. This allows the crosslinked structure to maintain strength during use but break down under specific thermal recycling conditions, enabling both durability and recyclability
Solution Approach 2:
The invention creates a composite crosslinked structure where EVA polymer chains are connected through reversible urethane crosslinks formed by TEMPO radicals. This composite approach combines the durability of crosslinked networks with the recyclability enabled by the specific chemical reversibility of urethane bonds under thermal processing
2Strength
If conventional crosslinking is used to improve durability, then strength is improved, but yellowing during thermal processing increases
Solution Approach 1:
The patent changes the chemical structure of the crosslinking mechanism to use TEMPO-derived urethane linkages that are less prone to thermal degradation and yellowing. The specific parameter changed is the chemical stability of the crosslink under thermal processing conditions, maintaining both strength and color stability
3Adaptability or versatility
If alternative raw materials such as TPU are used to improve recyclability, then recyclability is improved, but cost increases
Solution Approach 1:
The patent changes the chemical parameter of EVA by introducing controlled crosslinking with thermally degradable urethane linkages, allowing conventional EVA (a cost-effective material) to gain recyclability properties previously associated with more expensive alternatives like TPU
Solution Approach 2:
The invention copies the desirable recyclability feature of alternative materials like TPU by implementing a reversible crosslinking mechanism in EVA, achieving similar functionality while maintaining the cost advantages of using EVA as the base polymer
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 solution results in a recyclable crosslinked polymeric foam with a low yellow index, enhancing its flexibility for applications such as footwear, athletic equipment, and furniture, while maintaining performance characteristics like cushioning and durability.
Implementation Method 1
a reaction product of 0.1 to 10 parts by weight of a crosslinking agent and 0.1 to 5 parts by weight of a radical initiator
Implementation Method 2
a reaction product of 0.1 to 10 parts by weight of a crosslinking agent and 0.1 to 5 parts by weight of a radical initiator
Implementation Method 3
EVA (Ethylene Vinyl Acetate) foam is a commonly used material for the midsoles of footwear since it is light-weight and provides ideal cushioning properties
Data Source
AI summary
A recyclable crosslinked polymeric foam includes a reaction product of 0.1 to 10 parts by weight of a crosslinking agent and 0.1 to 5 parts by weight of a radical initiator, based on 100 parts by weight of a polymeric material. The crosslinking agent is represented by the following formula:wherein R is an alkylene group having 2 to 10 carbon atoms, an arylene group having 6 to 18 carbon atoms, or a cycloalkylene group having 6 to 18 carbon atoms.