Abstract
Rice straw cellulose was completely defibrillated via aqueous counter collision (ACC) at a low energy input of 15 kWh/kg, then fractionated by differential centrifugation into four increasing weight fractions of progressively thinner cellulose nanofibrils (CNFs): 6.9% in 80–200 nm, 14.4% in 20–80 nm, 20.3% in 5–20 nm, and 58.4% in less than 5 nm thickness. The 93.1% less than 80 nm or 78.7% less than 20 nm thick CNFs yields were more than double those from wood pulp by other mechanical means but at a lower energy input. The smallest (3.7 nm thick and 5.5 nm wide) CNFs were only a third or less in lateral dimensions than those obatined through ACC processed from wood pulp, bamboo, and microbial cellulose pellicle. The less than 20 nm thick CNFs could self-assemble into continuous submicron (136 nm) wide fibers by freezing and freeze-drying or semitransparent (13–42% optical transmittance) film by ultrafiltration and air-drying with excellent mechanical properties (164 MPa tensile strength, 4 GPa Young’s mo...
Highlights
Rice straw consists of similar extents of cellulose, i.e., 36.5− 46.6%,1−4 as wood and can be pulped using traditional processes,[3,5,6] extracted for long fibers by high pressure steam[7] and alkaline/enzyme[8] processes, as well as hydrolyzed into microcrystalline cellulose by hydrochloric acid[9] and enzymes.[10]
After 30 aqueous counter collision (ACC) passes, only a few of the smallest microfibers remained visible at the same concentration, indicating that most of the original microfibers were significantly defibrillated into dimensions less than the visible light wavelengths (Figure 1b)
Rice straw cellulose was mechanically defibrillated via ACC by processing 0.8 wt % aqueous dispersion at 180 MPa in 30 passes, differentially centrifuged into four increasing weight fractions of progressively thinner cellulose nanofibrils (CNFs): 6.9% 80−200 nm, 14.4% 20−80 nm, 20.3% 5−20 nm, and 58.4% less than 5 nm in thickness
Summary
Rice straw consists of similar extents of cellulose, i.e., 36.5− 46.6%,1−4 as wood and can be pulped using traditional processes,[3,5,6] extracted for long fibers by high pressure steam[7] and alkaline/enzyme[8] processes, as well as hydrolyzed into microcrystalline cellulose by hydrochloric acid[9] and enzymes.[10]. Rapid freezing 0.1 wt % aqueous ACC processed suspensions in liquid nitrogen and lyophilizing at −50 °C caused CNFs to self-assemble into a fluffy fibrous mass containing submicrometer to micrometer wide and over one hundred micrometer long fibers in all cases (Figure 4 and Table 2).
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