posted on 2024-02-21, 17:16authored byChris Rader, Patrick W. Fritz, Timur Ashirov, Ali Coskun, Christoph Weder
Cellulose
nanocrystals (CNCs) are bio-based, rod-like, high-aspect-ratio
nanoparticles with high stiffness and strength and are widely used
as a reinforcing nanofiller in polymer nanocomposites. However, due
to hydrogen-bond formation between the large number of hydroxyl groups
on their surface, CNCs are prone to aggregate, especially in nonpolar
polymer matrices. One possibility to overcome this problem is to graft
polymers from the CNCs’ surfaces and to process the resulting
“hairy nanoparticles” (HNPs) into one-component nanocomposites
(OCNs) in which the polymer matrix and CNC filler are covalently connected.
Here, we report OCNs based on HNPs that were synthesized by grafting
gradient diblock copolymers onto CNCs via surface-initiated atom transfer
radical polymerization. The inner block (toward the CNCs) is composed
of poly(methyl acrylate) (PMA), and the outer block comprises a gradient
copolymer rich in poly(methyl methacrylate) (PMMA). The OCNs based
on such HNPs microphase separate into a rubbery poly(methyl acrylate)
phase that dissipates mechanical energy and imparts toughness, a glassy
PMMA phase that provides strength and stiffness, and well-dispersed
CNCs that further reinforce the materials. This design afforded OCNs
that display a considerably higher stiffness and strength than reference
diblock copolymers without the CNCs. At the same time, the extensibility
remains high and the toughness is increased up to 5-fold relative
to the reference materials.