Pyridinium-grafted-cellulose nanocrystals were prepared by a simple one-pot reaction using 4-(1-bromoethyl/bromomethyl)benzoic acid, pyridine and cellulose nanocrystals (CNCs). The grafting consists of an esterification reaction between 4-(1-bromoethyl/bromomethyl)benzoic acid and CNCs and a nucleophilic attack on the C-Br bond of 4-(1-bromoethyl/bromomethyl)benzoic acid by pyridine. This reaction simplifies existing cationization methods, which leads to a higher grafting density while retaining the CNC crystallinity.
Flexible composite films with a high cellulose nanowhisker (CNW) content of up to 75% by weight were produced by casting from aqueous solution with water soluble cellosize (CS). The surface topography of the films displayed an aggregated morphology influencing the surface roughness and light transparency properties of the blends. Using fluorescently labelled CS, we were able to determine the extent of aggregation in the composites which indicated that up to 13% of CNWs can be homogeneously blended with CS, above which larger CNW aggregates occur. However, even in a somewhat aggregated form, the CNWs still form a percolated network and appear to be homogeneously dispersed as larger aggregated entities. The composite CNW-CS films further exhibited improved thermal stability compared to both the CNWs and CS alone with decomposition temperatures shifting from 261 C for CNWs and 313 C for CS to 361 C for blends containing 75% CNWs. Surface induced crystallisation of CS by CNWs was also found with higher crystallinity for the composite films than for the individual constituents. Due to the reinforcing effect of CNWs within the matrix, an increase in the tensile strength (294%) and modulus (2004%) was observed for the blend containing 75% CNWs compared to the pure CS film (tensile strength $12.23 MPa and modulus $0.39 GPa). The storage modulus of all the flexible blends/films investigated also revealed an increasing trend with the CNW content across the temperature region explored. The swelling kinetics of the CNW-CS blends in phosphate buffered saline (PBS) media at 37 C were also investigated and CNWs were shown to have a strong influence on reducing the equilibrium swelling capacity and initial swelling rate of the blends.
This
article reports on the successful preparation and characterization
of cellulose nanocrystals (CNCs) surface-modified with polylactide
(PLA) and poly(butylene succinate) (PBS) binary mixed homopolymer
brushes. Their synthesis was designed as a three-step procedure combining
polyester synthesis and surface-modification of CNCs with simultaneous
polyester grafting via a heterogeneous copper(I)-catalyzed azide–alkyne
cycloaddition reaction. For comparison, single homopolymer brushes
tethered to CNCs (PLLA-g-CNC and PBSBDEMPAM-g-CNC) were obtained applying the same procedure. The hairy
nanoparticles were characterized in terms of chemical composition
and thermal properties. Spectroscopic analyses suggested “rippled”
microphase separation of both immiscible homopolyesters in the mixed
brushes, while others showed impeded homopolyester crystallization
after surface-grafting. A synergistic relationship between the polyesters
and CNCs was also suggested, i.e., the polyester grafting increases
the CNC thermal resistance, while CNC presence imparts char formation.
The as-obtained binary homopolymer brushes tethered to nanoparticles
makes these surface-modified cellulosic nanomaterials attractive as
compatibilization/reinforcement agents for PLA/PBS blends.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.