Stress Transfer in Cellulose Nanowhisker Composites—Influence of Whisker Aspect Ratio and Surface Charge

Abstract

The mechanically induced molecular deformation of cellulose nanowhiskers embedded in subpercolation concentration in an epoxy resin matrix was monitored through Raman spectroscopy. Cellulose nanowhiskers isolated by sulfuric acid hydrolysis from tunicates and by sulfuric acid hydrolysis and hydrochloric acid hydrolysis from cotton were used to study how the aspect ratio (ca. 76 for tunicate and 19 for cotton) and surface charges (38 and 85 mmol SO(4)(-)/kg for sulfuric acid hydrolysis of cotton and tunicate, respectively; no detectable surface charges for hydrochloric acid hydrolysis) originating from the isolation process influence stress transfer in such systems. Atomic force microscopy confirmed that uncharged cellulose nanowhiskers produced by hydrochloric acid hydrolysis have a much higher tendency to aggregate than the charged cotton or tunicate nanowhiskers. Each of these nanowhisker types was incorporated in a concentration of 0.7 vol % in a thermosetting epoxy resin matrix. Mechanically induced shifts of the Raman peak initially located at 1095 cm(-1) were used to express the level of deformation imparted to the nanowhiskers embedded in the resin. Much larger shifts of the diagnostic Raman band were observed for nanocomposites with tunicate nanowhiskers than for the corresponding samples comprising cotton nanowhiskers. In the case of nanocomposites comprising nanowhiskers produced by hydrochloric acid hydrolysis, no significant Raman band shift was observed. These results are indicative of different modes of stress transfer, which in turn appear to originate from the different sample morphologies.

Benchmarking Cellulose Nanocrystals: From the Laboratory to Industrial Production

“…75 Using shorter particles as stabilizing agents produced more individualized droplets where as long CNCs bridged droplets creating network-like emulsions. Aspect ratio not only affects interfacial behaviour but impacts, rheological properties, 73 reinforcing capability, 76 and packing of CNCs. 118 Particles with higher aspect ratios, form gels and percolated networks at significantly lower concentrations than shorter particles, potentially reducing the amount of material required for specific applications.…”

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“…It was suggested that this was due to the higher aspect ratio of the tunicate nanowisker nanocomposite and the absence of charge on the tunicate related to the cotton nanowiskers. 75 When a polymethylmethacrylate nanocomposites with cellulose nanocrystal was prepared by the solution casting method a composite sheets formed from this material retained its transparency. By the thermogravimetric analysis showed to be thermal stable with a significant enhancement of its storage modulus compared with pure one.…”

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“…The procedure has been slightly modified from that described by Rusli et al (2011). NCC was obtained by partial hydrolysis of MCC with 2.4 M HCl solution in a 3 L 3-neck round bottom flask (RBF, equipped with a mixer, reflux condenser, and a glass needle adapter connected to a N 2(g) source) and heating/refluxing in an oil bath at *100°C for 2 h under a steady stream of N 2(g) .…”