Literature has shown that cellulose nanocrystals (CNCs) which are produced through hydrochloric (HCl) acid hydrolysis catalyzed by inorganic chlorides can enhance the mechanical properties of organic polymers further than CNCs by pure HCl acid hydrolysis. Existing studies reported that CNCs' size may have an impact on the level of mechanical enhancement of natural polymers. However, the correlation between the hydrolysis reaction and the size distribution of CNCs by catalyzed hydrolysis is not well documented. Many factors, such as hydrolysis temperature, acid type, catalyst type, degree of polymerization of the raw materials, the mass of raw materials to acid ratio (v/m ratio), and reaction time can affect the CNCs' size. In this study, CNCs are extracted from microcellulose crystals (MCC) by HCl acid hydrolysis catalyzed by titanium tetrachloride under hydrothermal conditions. Past research has explored inorganic chlorides, including ferric chloride hexahydrate, copper chloride dihydrate, aluminum chloride, and manganese chloride tetrahydrate. The results have shown that the level of reinforcement may be closely related to the dissociation constant of the inorganic chlorides.  However, titanium tetrachloride’s dissociation constant is 1.3, lower than that of ferric chloride, 2.2, which is the lowest dissociation constant among the four inorganic chlorides that have been studied. Therefore, for this study, titanium tetrachloride was investigated. The only two variables in this study are reaction time and v/m ratio. A set of six samples was produced with a v/m ratio of 50, and varying reaction times from 1.75 to 3 hours with increments of 0.25 hours. Another four samples were produced with a reaction time of 3 hours and varying v/m ratios from 30 to 60 with a 10 v/m ratio increment. The molecular structure of CNCs and size distribution were analyzed using Fourier transform-infrared spectroscopy (FTIR) and a laser diffraction (LD) particle size analyzer. The results of LD show that, even when the hydrolysis process produces nanosized cellulose crystals (CNs), micro-sized CNs still exist. This observation has not been reported by existing articles. The resulting solutions with variation in reaction time exhibit white, ivory, brown and black color and the average size of the CNs decreases with increasing reaction time. However, the sample color is not an indication of particle size. With increasing v/m ratio and 3 hours of reaction time, the average size of the CNs will also decrease, but the color of the solution is consistently black. The FTIR results of CNCs showed that the catalyzed hydrolysis preserved the molecular structure of MCC. However, the size of the OH and CH peaks decreased after completing hydrolysis when compared to MCC, but the amount of reduction was not correlated to the v/m ratio and the reaction time. In conclusion, increasing reaction time and v/m ratio will cause cellulose nanocrystals size reduction. The color of the resulting solution after hydrolysis is not an indication of cellulose nanocrystals size. Prolonged hydrolysis, time up to three hours, did not show signs of dehydration and carbonization.


The Size Distribution of Cellulose Nanocrystals in the Variation of Acid-to-Microcellulose Crystals Ratio and Reaction Time Through Catalyzed Acid Hydrolysis

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Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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