Recyclable High Performance Thermosets from Biobased Rigid Building Blocks
Time: Thu 2020-09-24 10.00
Subject area: Fibre and Polymer Science
Doctoral student: Yunsheng Xu , Fiber- och polymerteknologi, Royal institute of technology KTH, Minna Hakkarainen
Opponent: Lead Scientist Youssef Habibi, LIST, Materials Research and Technology, Luxembourg
Supervisor: Professor Minna Hakkarainen, Fiber- och polymerteknologi; Associate Professor Karin Odelius, Polymerteknologi
The finite petroleum resources and increasing polymer waste have given rise to concerns associated with the origin and end of life management of polymer materials. Developing biobased and recyclable thermosets is an important and still underexplored part of this process, especially as thermosets also possess inherent recycling issues caused by their crosslinked structure. In this thesis, several thermosets with high performance and enhanced recyclability were designed, starting from biobased rigid building blocks i.e. isosorbide, vanillin and lignin. First, unsaturated polyester resins were developed by utilizing isosorbide as a rigid diol for unsaturated polyesters synthesis and methacrylated isosorbide as a reactive diluent. The presence of isosorbide-units in the unsaturated polyester and as the reactive diluent imparted the resins with good miscibility, while the viscosity of the resins and thermomechanical properties of the cured resins could be modulated by the content of isosorbide. Due to the rigid bicyclic structure of isosorbide, the fabricated thermosets with high isosorbide content portrayed high modulus, comparable with commercial petroleum-based analogue. Second, vanillin-based vinyl ester resins containing imine bonds were prepared through a two-step chemical modification of vanillin i.e. methacrylation and imination. The obtained resins could be photo-cured into thermosets within merely 10 minutes, due to the high reactivity of vinyl bond. Owing to the presence of dynamic imine bonds in thermosets, they exhibited typical vitrimer behavior of stress relaxation, which allowed them to be recycled several times by thermal reprocessing. Last, Kraft lignin, and its solvent extracted or microwave processed fractions were directly utilized as multifunctional hydroxyl-group containing building blocks to fabricate polyester thermosets via a one-pot synthesis method. The lignin content and fractionation process had large influence on the mechanical and thermal properties of the thermosets. Chemical recycling of these thermoset was achieved via microwave assisted hydrolysis, and the degraded products could be recured into thermosets achieving near closed-loop process. The biobased nature of the fabricated thermosets together with the accessible synthesis routes, recyclable and tailorable properties contribute to building more sustainable material systems for high performance.