Essay: Cellulose nanocrystal, nanowhiskers, micro-fibrillated cellulose…

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Cellulose nanocrystal, nanowhiskers, micro-fibrillated cellulose, micro-fibril aggregates or nanofibers are the names other than nanocellulose (Karim et al., 2015) . Cellulose can be found in abundance from plant biomass, tunicates, algae and few bacteria (Chowdhury & Abd Hamid, 2016). Chemical formula for cellulose is (C6H10O6)n. Cellulose are composed of β-1,4-linked anhydro-D-glucose units and hydroxyl groups (-OH) that cause it become hydrophilic polymer and create a strong hydrogen bonds (Kumar et al., 2014). Generally, its play roles in maintaining the structure of plant cell walls since it is fibrous, tough and water insoluble (Habibi, Lucia, & Rojas, 2010). Typical preparation of nanocrystalline cellulose including three stages: pre-treatment of raw materials, acid hydrolysis and microwave assisted treatment.
 
The role of hemicellulose and lignin in biomass substrate are to strengthen the cell walls of plant residues and shield cellulose from chemical breakdown (Chowdhury & Abd Hamid, 2016). Lignin is a bond that strengthening cellulose and hemicellulose. Bonds that involve are ester bond that sensitive to alcohol and ether bond that not sensitive to alcohol (Kumar et al., 2014). NCC is usually produced from native cellulose by isolation of its crystalline regions, whereas the amorphous regions are hydrolysed and degraded into soluble products (Kos et al., 2014).

Physiochemical treatments such as ultrasonic wave or microwave were applied to the plant fiber materials to obtain high efficiency in virtue of intensification of heat and mass transfer (Lu et al., 2013). By using microwave assisted technique, it will generate heat by direct conversion of electromagnetic energy which will help in reducing energy consuming and reaction time compared to conventional heating (Lu et al., 2013). While by using ultrasonic wave, a strong mechanical oscillating energy will be produced and effectively breakdown interaction force between cellulose (Karim et al., 2015).

Figure 1.1 Schematic diagram for tree hierarchical structure (Moon et al., 2011)

Numerous preparations methods had been evaluated to obtain stable and usable material for NCC. Based on previous work, nano-crystalline cellulose was prepared by sulphuric acid hydrolysis of cellulose raw materials in aqueous solution, and then freeze-dried (Yu et al., 2013). During acid hydrolysis, amorphous regions are removed leaving only crystalline cellulose (Jasmani & Adnan, 2017). In general, the sulphate group will be attached to the surface of the NCC during the hydrolysis that will bring a decrease in thermal stability. NCC dominates more advantages than cellulose fibers. Such as high surface area, specific strength and modulus and having unique optical properties (Peng et al., 2011). NCC has great strength because of its dense and ordered crystalline structure while its elasticity for the perfect crystal of native cellulose had been estimated between 130 and 250 GPa and tensile strength between 0.8 and 10 GPa (Kos et al., 2014).

Demand of products that made from renewable and sustainable resources had been increasingly needed by consumers industry and government. For the past thousand years, our society had been used natural cellulose as based materials and it is still on going. They develop functionality, flexibility and high mechanical strength by

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