The Circularity of Rings: Chemical Recycling of Polyesters
Time: Fri 2025-10-10 13.00
Location: F3 (Flodis), Lindstedtsvägen 26 & 28
Video link: https://kth-se.zoom.us/j/63931291702
Language: English
Subject area: Fibre and Polymer Science
Doctoral student: Vincent Nieboer , Polymerteknologi, Karin Odelius
Opponent: Associate Professor Will Gutekunst, Georgia Institute of Technology, USA
Supervisor: Professor Karin Odelius, Polymerteknologi, Wallenberg Wood Science Center; Docent Peter Olsén, Linköpings universitet; Doktor Jakob Wohlert, Fysik, Wallenberg Wood Science Center, Biokompositer
Abstract
To mitigate the generation of plastic waste, chemical recycling strategies andchemically recyclable polymers need to be developed. Equilibrium ring-openingpolymerization (ROP) has emerged as a promising approach to recycle polymersdue to the inherent ring – polymer equilibrium nature, facilitating ring-closingdepolymerization of polymers to recyclable rings. This thesis delves into theassociated thermodynamics of ROP to accelerate the development of closed loopchemical recycling to ring strategies.To provide an alternative to experimental wet lab trial and error approaches, acomputational model based on molecular dynamics was created to theoreticallydetermine the thermodynamics of ROP for different monomers. The atomisticinsight that the model provided, supported by experimental data and literatureobservations, led to a newly proposed understanding of the enthalpy andentropy of ROP. Particularly, the enthalpy of polymerization is hypothesized tocontain an energy term that accounts for polymer conformations in addition tothe already established ring-strain energy. Next, to enhance chemical recycling,thermodynamic terms that describe the full ring-chain equilibria (RCE)involving rings of different sizes was developed. The benefit of including all ringsand RCE thermodynamics was exemplified through the efficient chemicalrecycling of polymers under conditions that are inconceivable using ROPequilibrium thermodynamics. The RCE was further studied using random walkstatistics from which a method to calculate the involved equilibriumthermodynamics from theory was established. A drawback of RCE systems, isthe necessity of active catalysts, which cause an abundance in backbitingreactions. Such side reactions make it hard to control the architecture ofcopolymers. To provide the necessary conditions to create block, tapered, orrandom copolymers at will, despite abundant backbiting, an equation based onpolymerization kinetics was derived. The equation was validated experimentallyand copolymers of various copolymer architectures were synthesizedaccordingly. The theories developed in this thesis may assist in theunderstanding of ROP and technological advancement for chemical recycling.