Improvement of the mechanical and thermal properties of cellulose triacetate (CTA) films is required without sacrificing their optical properties. Here, poly(ethylene glycol) (PEG)-grafted cellulose nanofibril/CTA nanocomposite films were fabricated by casting and drying methods. The cellulose nanofibrils were prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, and amine-terminated PEG chains were grafted onto the surfaces of the TEMPO-oxidized cellulose nanofibrils (TOCNs) by ionic bonds. Because of the nanosize effect of TOCNs with a uniform width of ∼3 nm, the PEG-TOCN/CTA nanocomposite films had high transparency and low birefringence. The grafted PEG chains enhanced the filler-matrix interactions and crystallization of matrix CTA molecules, resulting in the Young's modulus and toughness of CTA film being significantly improved by PEG-grafted TOCN addition. The coefficient of thermal expansion of the original CTA film was mostly preserved even with the addition of PEG-grafted TOCNs. These results suggest that PEG-TOCNs are applicable to the reinforcement for transparent optical films.
Freeze-dried microfibrillated cellulose (MFC) was directly dissolved in 8.0% w/w lithium chloride/N,N-dimethylacetamide (LiCl/DMAc), and MFC/LiCl/DMAc solutions with accurate MFC concentrations were prepared. The different MFC solutions were diluted to 1.0% and 0.5% w/v LiCl/DMAc, and subjected to size-exclusion chromatography with multiangle laser-light scattering and refractive index analyses (SEC/MALLS/RI), and off-line RI analysis to determine their refractive index increments (dn/dc). Chitin, cellulose triacetate, a poly(styrene) standard, and cellobiose were used for comparison. Each of the two determination methods gave different dn/dc values for MFC and chitin but similar dn/dc values for cellulose triacetate and poly(styrene). The anomalously small dn/dc values of MFC and chitin were explainable in terms of stable cellulose-LiCl and chitin-LiCl structures (i.e., formation of apparent covalent bonds between hydroxyl groups and LiCl) in the solutions. Thus, the SEC/MALLS/RI method provides reliable molecular mass parameters for cellulose and chitin.
Careful design of the structures
of interfaces between nanofillers
and polymer matrices can significantly improve the mechanical and
thermal properties of the overall nanocomposites. Here, we investigate
how the grafting density on the surface of nanocelluloses influences
the properties of nanocellulose/cellulose triacetate (CTA) composites.
The surface of nanocellulose, which was prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl
oxidation, was modified with long poly(ethylene glycol) (PEG) chains
at different grafting densities. The PEG-grafted nanocelluloses were
homogeneously embedded in CTA matrices. The mechanical and thermal
properties of the nanocomposites were characterized. Increasing the
grafting density caused the soft PEG chains to form denser and thicker
layers around the rigid nanocelluloses. The PEG layers were not completely
miscible with the CTA matrix. This structure considerably enhanced
the energy dissipation by allowing sliding at the interface, which
increased the toughness of the nanocomposites. The thermal and mechanical
properties of the composites could be tailored by controlling the
grafting density. These findings provide a deeper understanding about
interfacial design for nanocellulose-based composite materials.
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.