Nanofillers with high mechanical strength and high aspect ratio have a potential to effectively reinforce polymer materials. Nanofiller-reinforced polymer composites have large interfacial areas between the nanofillers and polymer matrix. Various phenomena occur at the interfacial area, which governs bulk properties of the nanocomposites. Designing the structure and properties of the interfacial area is thus important for nanofiller-reinforced composites. However, it is difficult to minutely design the interfacial structure and properties without changing the dispersibility of nanofillers. We prepared TEMPO-oxidized cellulose nanofibrils (TOCNs) which have good dispersibility in polymer matrices, and investigated the contributions of the grafting density on the nanofiller surface using two types of TOCNs, or neat TOCNs and poly(ethylene glycol)-grafted TOCNs (PEG-TOCNs). The PEG-TOCNs were prepared by amine-terminated PEG onto TOCN surfaces via ionic bonds. The grafting density was controlled by changing the molar ratio between the TOCN carboxy group and the PEG amine group. Cellulose triacetate (CTA)/TOCNs or CTA/PEG-TOCNs composite films were prepared to investigate the influence of the grafting density on mechanical and thermal properties. Accordingly, Young’s modulus and tensile strength of CTA films were improved by the addition of TOCNs or PEG-TOCNs, and the reinforcing effect of TOCNs decreased with increasing the grafting density. The elongation at break and toughness of the nanocomposite films increased with increasing the grafting density. These results suggest that the soft PEG layers on the TOCN surfaces hindered stress transfer between TOCNs and CTA matrix and enhanced energy dissipation during deformation. Coefficients of thermal expansion of the CTA films decreased with the addition of TOCNs, and increased with increasing the grafting density. It is likely that the coefficients of thermal expansion of the nanocomposites resulted from both TOCN-induced dimensional stability and PEG-induced thermal expansion. In conclusion, the grafting density influences the mechanical and thermal properties of nanocomposites and should be controlled to exploit the favorable properties of the nanofillers.

Grafting density design of surface-modified nanocellulose for polymer composites

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.