Haile et al. Bioresour. Bioprocess.
(2021) 8:35
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for the outstanding mechanical properties of the poly- mer. Cellulose as macromolecule is composed of many cellobiose repeat units which themselves are made up of glucose monomeric units (β-glucose) via β-1,4- glycosidic linkages. The individual extended cellulose chains are parallel to each other and the inherent stabil- ity and crystallization of cellulose polymers are due to the presence of extensive intramolecular and intermo- lecular hydrogen bonds. In pulp and paper mills different conventional pro- cesses are used to recover cellulose from wastewater. The process of separation of cellulose from dried sludge is done using ionic liquid-based segregation techniques which involve cellulose precipitation from the sludge (Gibril et al. 2018). Direct extraction and utilization of cellulose from sawdust and woody matters are also possible. The production of CNC from cellulose is an emerging possibility for the diversified utilization of trees for bio- materials (Fig. 12). A biorefinery approach can be used to convert cellulose from pulp and paper mill waste into nanocrystalline cellulose (Souza et al. 2017). The pro- duction of nanocellulose is attained by a two-step pro- cess (Clemons 2016). In the first step, the pretreatment process of native cellulose biomass is done which yields treated cellulose fibers. While in the second step, pre- treated cellulose fibers are converted into nanocellulose using various routes, e.g., high-pressure homogeniza- tion, micro fluidization, micro grinding, high-intensity ultra-sonication, electrospinning, and steam explosion.
techno-feasible and cost-effective, and also reduces effluent production (Clemons 2016). Nanocellulose has retained significant attention due to its tremendous functionality, i.e., greater surface chemistry, extraor- dinary biotic possessions, low toxicity, low cost, lower density, and significant mechanical properties. Cellulose Nanocrystals have many important physical properties Nanocrystalline cellulose has high heat stability which makes it suitable as a potential engineering material for aggressive temperature environments and its morphol- ogy with regards to small size and shape can be managed for different applications in solutions (Feng et al. 2015; Aguayo et al. 2018). The cellulose from the different waste sources in pulp and paper mills can be converted into cel- lulose nanocrystals (CNC) for wider application as a bio- material in diversified fields of application (Fig. 11). CNC is needle-shaped and highly crystalline material produced from cellulose pulp (Clemons 2016). The out- looked application of CNC is very wide and mostly its use in medical and industrial fields is tremendous. CNC can be used for the fabrication of medical products such as artificial skin, breast implants, versatile hygiene products, tissue-engineered materials, wound dressings, and drug delivery biomaterials. Industrially CNC can be used for the automotive interior, cosmetics industry, acoustics/ photonics, build-tech, and different packaging materials. Cellulose fiber is a key and characteristic component in pulp and paper mill sludge and is also constituted by sawdust and other woody residues (Aguayo et al. 2018). Cellulose is an important biopolymer that con- sists of semicrystalline regions which are responsible
Fig. 11 Multitude application of CNC biomaterial
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