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4186554 - Molecular design of capping agents for efficient chemical recycling of thermoplastic polyurethanes using blocked isocyanate chemistry | Poster Board #M26
4:00 PM - 6:00 PM EDT
Wednesday, March 26, 2025Room: Pacific Ballroom Foyer (San Diego Marriott Marquis)Parent Session
Chemical Recycling & Upcycling of Polymers:
Room: Pacific Ballroom Foyer (San Diego Marriott Marquis)
DIVISION/COMMITTEE: [PMSE: Division of Polymeric Materials Science and Engineering]
Credits
0.00 CE
Organizers
- Konstantinos Alexopoulos, The Pennsylvania State University
- Mark Dadmun, Univ of Tennessee
- Brett Helms, Lawrence Berkeley National Lab
- Brian Long
- Tomonori Saito, Oak Ridge National Laboratory
- Hilal Ezgi Toraman, The Pennsylvania State University
Poster - In-person
PMSE: Division of Polymeric Materials Science and Engineering
Overview
Polyurethanes are the 6th most used synthetic polymer with reported annual production of 26MMT in 2022. Thermoplastic polyurethanes (TPU) are a class of polyurethanes that distinguishes itself by its capacity to be melted and reshaped, unlike thermoset polyurethanes. The widespread use of TPU has resulted in substantial waste accumulation in landfills and the environment, necessitating effective recycling solutions to address environmental concerns. Chemical recycling of TPUs, where the polymer is broken down into its constituents, offers opportunities towards a sustainable approach for circular reuse of waste polyurethanes.
The present work focuses on utilizing blocked isocyanate chemistry as a strategy for TPU depolymerization. In this approach, reactive isocyanate groups get capped during depolymerization in order to passivate them and enable separation, followed by thermal decapping (or “deblocking”) to regain their reactivity for repolymerization. Overall, the envisioned chemical recycling strategy thus comprises four steps: 1) catalytic depolymerization and capping of TPU; 2) separation of the capped hard and soft segments; 3) thermal dissociation to recover the capping agent and (uncapped) hard segment segments; and 4) repolymerization of fresh TPU from the recovered hard and soft segments. In order to make this scheme feasible, efficient, and economic, the selection of capping agents is critical. A suitable capping agent needs to decap at low temperature to minimize the energy intensity of the process while remaining stable at the temperature of the depolymerization step. Understanding and tailoring the decapping temperatures of different capping agents is hence critical.
Based on a thorough literature review of potential capping agents, we synthesized capped 4,4'-methylene diphenyl diisocyanate (MDI) using select capping agents, determined decapping temperatures of these model compounds using thermogravimetric analysis (TGA), and derived correlations between decapping temperature and physicochemical properties of the capping agents, such as nucleophilicity, pKa, and chain length. The results reveal clear trends, with specific functional groups and molecular characteristics determining the decapping temperature. The results hence yield a guideline for the molecular design of effective capping agents for blocked isocyanate chemistry, guiding the path towards effective TPU depolymerization and promoting circular economy practices in polymer recycling.
The present work focuses on utilizing blocked isocyanate chemistry as a strategy for TPU depolymerization. In this approach, reactive isocyanate groups get capped during depolymerization in order to passivate them and enable separation, followed by thermal decapping (or “deblocking”) to regain their reactivity for repolymerization. Overall, the envisioned chemical recycling strategy thus comprises four steps: 1) catalytic depolymerization and capping of TPU; 2) separation of the capped hard and soft segments; 3) thermal dissociation to recover the capping agent and (uncapped) hard segment segments; and 4) repolymerization of fresh TPU from the recovered hard and soft segments. In order to make this scheme feasible, efficient, and economic, the selection of capping agents is critical. A suitable capping agent needs to decap at low temperature to minimize the energy intensity of the process while remaining stable at the temperature of the depolymerization step. Understanding and tailoring the decapping temperatures of different capping agents is hence critical.
Based on a thorough literature review of potential capping agents, we synthesized capped 4,4'-methylene diphenyl diisocyanate (MDI) using select capping agents, determined decapping temperatures of these model compounds using thermogravimetric analysis (TGA), and derived correlations between decapping temperature and physicochemical properties of the capping agents, such as nucleophilicity, pKa, and chain length. The results reveal clear trends, with specific functional groups and molecular characteristics determining the decapping temperature. The results hence yield a guideline for the molecular design of effective capping agents for blocked isocyanate chemistry, guiding the path towards effective TPU depolymerization and promoting circular economy practices in polymer recycling.
