Engineering Polyhydroxyurethane Nanocomposites with Cellulose and Chitin Nanomaterials
Time: Tue 2025-10-14 10.00
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Video link: https://kth-se.zoom.us/j/63944377485
Language: English
Subject area: Chemistry
Doctoral student: Pavithra Wijeratne , Glykovetenskap
Opponent: Professor Kristiina Oksman, Luleå tekniska universitet
Supervisor: Professor Qi Zhou, Glykovetenskap, Wallenberg Wood Science Center; Professor Jean-Marie Raquez, University of Mons, Belgien
QC 20250917
Abstract
The transition toward sustainable polymers requires alternatives to conventional isocyanate-based polyurethanes that retain performance while reducing environmental and health concerns. Polyhydroxyurethanes (PHUs), synthesized via cyclic carbonate aminolysis, represent a promising isocyanate-free polyurethane platform, but their development has so far been limited by relatively low mechanical performance and challenges in processing. This thesis addresses these limitations through the design of bio-based PHUnanocomposites reinforced with polysaccharide nanomaterials, with emphasis on interfacial chemistry, nanofiller morphology, and processing strategy.
The first part focuses on interface engineering through epoxy hybridization and polysaccharide reinforcement. Incorporation of epoxy resins into PHU matrices significantly increased modulus and tensile strength, though at the expense of ductility, leading to brittle behavior at higher epoxy contents. Complementary reinforcement with cellulose nanocrystals (CNCs) provided a more synergistic improvement, enhancing both modulus and strength while maintaining a strain-to-failure above 240%, a key advantage for applications requiring both strength and toughness. A second system based on segmented PHUs reinforced with CNCs and partially deacetylated chitin nanocrystals (ChNCs) demonstrated the critical role of interfacial interactions. CNCs, engaging primarily through hydrogen bonding, tripled the modulus (up to 1.2 MPa), while ChNCs, capable of covalent grafting to the PHU matrix, showed over 140-fold modulus enhancement (58.8 MPa) and a ~20-fold increase in tensile strength compared to neat segmented PHU.
The second part explores processing strategies for PHU-based nanocomposites. Reactive extrusion was employed as a solvent-free route to synthesize PHU/ChNC nanocomposites, achieving homogeneous nanocrystal dispersion and improved thermomechanical stability. These nanocomposites exhibited a storage modulus up to three orders of magnitude higher than neat PHU rubbery state and displayed ferroelectric-like polarization switching, demonstrating potential for energy-harvesting applications. In parallel, an aqueous one-pot synthesis was developed to prepare PHU hydrogels reinforced with chitin nanofibers and form double-network (DN) architectures. These DN hydrogels achieved compressive modulus up to 0.39 MPa in the wet state and tensile Young’s modulus above 20 MPa after drying. The ability to tailor performance through nanofiber surface chemistry and loading demonstrated the versatility of this approach for designing high-performance, sustainable hydrogels.
In summary, this work establishes systematic strategies to improve the mechanical performance of PHUs by combining interfacial engineering with processing control. The findings demonstrate that renewable nanofillers, integrated into tailored PHU matrices through scalable methods, can significantly expand the property profile of these isocyanate-free polymers and open new pathways toward sustainable, high-performance materials.