Reversible Crosslinked Foam for Recyclable Polyolefin Reprocessing
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Solution Overview
Problem
Conventional crosslinked polyolefin elastomer foams are not recyclable or reusable due to their stability under heating and mechanical shearing, limiting their recyclability and re-useability, which is a challenge in the context of global efforts towards carbon neutrality and plastic recyclability.
Innovation Solution
A crosslinked foam composition formed from ethylene-based polymers and 2,2,6,6-tetramethyl-4-piperidyl methacrylate disulfide (BiTEMPS) methacrylate, allowing the foam to be heated and reshaped into a re-processable polymer composition, which can then be cooled and re-crosslinked to form a re-processed article.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional crosslinking is used (peroxide or irradiation), then mechanical properties and stability are enhanced, but recyclability and re-useability are limited or non-existent
Solution Approach 1:
The patent changes the chemical nature of crosslinking bonds from permanent C-C bonds to reversible disulfide bonds. This parameter change in bond type allows the material to maintain crosslinked structure and mechanical properties at normal temperatures, while enabling bond dissociation at elevated temperatures for recycling. The disulfide bonds provide thermally reversible crosslinking, transforming the material from non-recyclable to recyclable without sacrificing mechanical performance.
Solution Approach 2:
The patent introduces dynamic reversibility to the crosslinked network through disulfide bonds. These bonds can dynamically break and reform: remaining intact at processing and use temperatures to provide structural stability, but dissociating at recycling temperatures to enable reprocessing. This dynamic behavior allows the same material structure to serve multiple functions across different temperature regimes, resolving the contradiction between stability and recyclability.
2Stability of the object's composition
If conventional crosslinked foam is heated, then the structure remains stable, but the foam cannot be reshaped or reprocessed
Solution Approach 1:
The patent utilizes a thermal phase transition in the disulfide crosslinks. At normal temperatures, disulfide bonds remain intact providing structural stability. When heated to recycling temperatures (e.g., above 100°C), the disulfide bonds undergo dissociation, transitioning from a stable crosslinked state to a mobile, reprocessable state. This thermally activated phase transition enables the foam to be reshaped only when intended for recycling, while maintaining stability during normal use.
Solution Approach 2:
The patent enables periodic reprocessing cycles through reversible disulfide crosslinking. The foam can be heated to dissociate crosslinks for reshaping, cooled to reform crosslinks and stabilize the new shape, and this cycle can be repeated. This periodic heating-cooling-dissociation-reformation sequence allows multiple reprocessing operations while maintaining structural integrity between cycles, resolving the contradiction between stability and reprocessability.
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 process enables the recyclability and re-useability of polyolefin elastomer foams by allowing them to be reprocessed and reshaped without losing mechanical properties, aligning with the goals of carbon neutrality and plastic recycling.
Implementation Method 1
heating the foam article to a reprocessing temperature... forming, at the reprocessing temperature, the foam article into a re-processable polymer composition
Implementation Method 2
cooling the re-processed pre-form to below the reprocessing temperature and forming a second article composed of a re-crosslinked polymer composition
Data Source
AI summary
The present disclosure is directed to a foam article. In an embodiment, the foam article includes a crosslinked foam composition formed from starting materials comprising (i) a polymer selected from the group consisting of an ethylene-based polymer, a polar ethylene-based polymer, and combinations thereof, and (ii) 2, 2, 6, 6-tetramethyl-4-piperidyl methacrylate disulfide (BiTEMPS) methacrylate. This yields a foam article that is composed of a crosslinked composition comprising (i) the polymer selected from the group consisting of the ethylene-based polymer, the polar ethylene-based polymer, and combinations thereof, and (ii) linkages having a Structure (2) below