Abstract
To expand the application field of the pulping industry, this study conducted a series of sample preparations for processing cellulose nanocrystals (CNCs) from a dry hardwood pulp to achieve optimal sulfuric acid hydrolysis. The properties of laboratory-prepared pulp CNCs (P-CNCs) were investigated with different preparation conditions including sulfuric acid concentrations, hydrolysis temperatures, and hydrolysis durations. Results showed a gradient of color changes observed with the increase of hydrolysis duration and temperature. Under certain conditions, the derived P-CNCs exhibited nanoscale dimensions, detected by transmission electron microscopy, and a crystallinity index similar to commercial products. In addition, the surface sulfate groups were assumed to be contributed by sulfuric acid hydrolysis. However, a high acid concentration and long hydrolysis processing duration introduced more sulfate groups on the derived P-CNCs, which may have acted as flame retardants and, thus, increased the amount of char residue.
Highlights
Cellulose is a sustainable bioresource and is abundant in nature
With the numbering system of carbon atoms, the locations of hydroxyl groups are determined in an anhydroglucose unit of cellulose
Hydroxyl groups on the surface of cellulose can react with various chemicals and become derivatives with designed functions
Summary
Because of the hydroxyl groups, intra- and inter-molecular hydrogen bonds are formed, and cellulose chains are arranged in a highly ordered crystalline region, whereas the remaining disordered structure is called an amorphous region. With the nanometric size effect, the crystalline regions, extracted to be cellulose nanocrystals (CNCs), have recently been studied in the development of biocomposites [1]. For the design of a CNC composite, CNCs have the potential to serve as a functional reinforcement material, providing enhanced thermal, mechanical, optical, and gas-barrier properties, as a result of their highly ordered nanostructure [2]. Owing to the steric effect, the hydroxyl groups on cellulose chains exhibit different reactivity characteristics. Hydroxyl groups on the surface of cellulose can react with various chemicals and become derivatives with designed functions. The CNC extraction procedure plays an essential role in modifying the surface chemistry of the particles; ideal hydrolysis conditions are important for consistently producing high-quality CNC products
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