Engineering Polyhydroxyurethane Nanocomposites with Cellulose and Chitin Nanomaterials

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 isocyanatefree
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 PHU
nanocomposites 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 modulus and strength while maintaining 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 nanocrystals dispersion
and improved thermomechanical stability. These nanocomposites exhibited
storage modulus up to three orders of magnitude higher than neat PHU in
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
II
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.