S. Basu, S. Malik, G. Joshi et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100050
Our research team have been dedicatedly working in the field of carbohydrate chemistry as well as functional modification of cellu- lose to promote sustainable and environment friendly measures in pulp and paper technology ( Gupta et al., 2020 ; Joshi et al., 2019 , 2015 ; Joshi, Naithani, Varshney, Bisht & Rana, 2017 ; Rana, Das, Gogoi & Ku- mar, 2014 ; Rana, Malik, Joshi, Rajput, & Gupta, 2021 ). The purpose of the present review is to bring together and explicitly discuss the pro- duction, functional-chemistry and applications of bio-based polymers as substitutes of harmful chemical additives and depleting fossil based chemicals ( Shen et al., 2014 ) used in pulp and paper industries. This review mainly covers the topic for the duration of last two and half decades i.e., studies carried out from 1995 to 2020.
tion parameters with varying raw material, due to their difference in fibre morphology and chemical makeup ( Gao et al., 2016 ). Al- though many processes have been reported regarding the production of cationic cellulose, alkalization-cationization dual step conversion has been the most effective one ( Moral, Aguado, Ballesteros & Ti- jero, 2015 ). Alpha cellulose extracted from a cellulosic biomass can be etherified with 2 ‑hydroxy-3-trimethyl ammonium propyl group by the reagent 2,3-epoxypropyltrimethyl ammonium chloride (EPTAC). Since this chemical is toxic and highly unstable, alternatively 3 ‑chloro-2- hydroxypropyltrimethyl ammonium chloride (CHPTAC) can be used. The cationization process is preceded by an essential alkali medi- ated charging procedure of the hydroxyl groups of cellulose ( Fig. 1 ) ( Khalil, Beliakova & Aly, 2001 ; Liu, Ni, Fatehi & Saeed, 2011 ; Rana et al., 2021 ; Su et al., 2016 ). The degree of substitution of quaternary ammo- nium group on the cationic cellulose can be confirmed by determina- tion of nitrogen content before and after modification ( Moral et al., 2015 ). Since the cationic modification of cellulose makes its surface positively charged, the same when used as an additive while paper making results in high filler retention, surface homogeneity, improved drainage property, improved absorption of anionic fines and strength enhancement ( Halab-Kessira& Ricard, 1999 ; Montplaisir, Chabot & Daneault, 2006 ; Sain & Boucher, 2002 ; W. Xie, Feng & Qian, 2008 ). Gao et al. (2016) have specifically emphasized on the production and utilization of cationized cellulose fibrils (CCF). CCF additive has com- parable influence of paper strength enhancement (2–3% tensile index improved) as done by popular cationic starch (CS) additive. Tensile in- dex is the maximum force per unit width developed in a paper specimen before rupture under prescribed conditions divided by grammage (gsm) of paper. The authors also found that CCF confers slightly improved ( ∼ 12%) tear strength in paper than CS at low (2–4%) concentrations. Hence cationic cellulose can be considered as a promising alternative of conventional synthetic cationic poly-electrolytes used for paper strength enhancement.
2. Cellulose and derivatives
Cellulose is the most abundant polysaccharide available in nature as a primary structural constituent of plant cell wall composed of 𝛽 - (1–4) linked d -glucose units ( Fig. 1 ). Apart from plants, cellulose is also found in bacteria from various genera like Aerobacter, Agrobac- terium, Gluconacetobacter, Acetobacter, Azotobacter, Achromobacter, Es- cherichia, Sarcina, Salmonella and Rhizobium . Since cellulose is mechan- ically strong, renewable and biodegradable, it has been in focus for di- verse small to large scale applications ( Rangaswamy, Vanitha & Hun- gund, 2015) . Cellulose is the backbone of pulp and paper products. To further broaden its application domain, the multiple hydroxyl groups of the cel- lulose can be modified with chemical agents. Typically, cellulose deriva- tives are resultants of esterification and/or etherification of hydroxyl groups of cellulose. Apart from these, nano-cellulose has gained atten- tion as an application tool in material science innovations as well as bio- medical applications in recent times ( Gao et al., 2016 ; Lahtinen et al., 2014 ; Shaghaleh, Xu & Wang, 2018 ). The chemical and physical properties of cellulose derivatives depend upon the type of substituting group, the degree of substitution (DS), the uniformity of substitution and the length of the cellulose molecules. In practice, it is very difficult to completely replace all the hydroxyl groups present in cellulose by other functional groups due to steric factors. The steric crowding may inhibit complete reaction. Accessibility, another factor may restrict the complete replacement of hydroxyl groups. Since the reactions are conducted under heterogeneous reaction environment, not all the hydroxyl groups may be accessible to the reaction, principally those in the crystalline regions. In overall, not all the accessible hydroxyl groups are equally reactive. The three hydroxyl groups of glucose units differ in their reactivity and the relative rates are not necessarily the same for other reagents. Most of the commercial cellulose derivatives are the products of only partial reaction, i.e. they contain a definite pro- portion of unsubstituted hydroxyl groups. The physical and chemical properties of cellulose derivatives are strongly affected by the DS and the degree of polymerization (DP). Properties that are mostly influenced by fluctuating the DS are the solubility, swelling and plasticity. Derivatives of low DS are more sensitive to water. Derivatives having high DS with nonpolar substituents, the water solubility is decreased, the sorption of water is decreased, and the solubility in organic solvents is increased. On the other hand, the plasticity is increased by the substitution of non- polar groups. If the mechanical properties are important in the final end product, a balance must be struck between a low DP, which will confer ease of fabrication, and the somewhat higher DP crucially required for adequate mechanical properties ( Mcginnis & Shafizadeh, 1979 ). Some common derivatives of cellulose and their route of synthesis are pre- sented in Fig. 1 ( Abdel-Halim, 2014 ; De Carvalho Oliveira et al., 2010 ; Joshi et al., 2015 , 2019 ; Rana et al., 2021 ).
2.2. Carboxymethyl cellulose (CMC)
There has been rigorous research and commercial applications when it comes to carboxymethyl cellulose. It is a versatile cellulosic product that can be synthesized from plant based biomass and/or recycled fi- bres and finds its use beyond traditional paper science ( Fatehi, Kitit- erakun, Ni & Xiao, 2010 ; Joshi et al., 2015 ). CMC is an anionic poly- mer with high surface charge (negative) that has been identified as a potential strength enhancer in papermaking. Its absorption onto fibres enhances under acidic conditions ( Jokinen, Niinimäki & Ämmälä, 2006 ; Watanabe, Gondo & Kitao, 2004 ). The synthesis of carboxymethyl cellulose ( Fig. 1 ) proceeds in the same manner as that of cationic cellulose i.e. alkali mediated acti- vation of hydroxyl group followed by etherification (carboxymethy- lation) [Williamson’s ether synthesis followed by carboxymethylation in S N 2 mechanism]. The commonly used carboxymethylating agent is sodium monocloroacetate under optimized conditions of temperature, time and chemical concentration depending upon raw material type ( Joshi et al., 2015 ; Tijsen, Kolk, Stamhuis & Beenackers, 2001 ; Varshney & Naithani, 2011 ; Varshney et al., 2006 ). In a general context, car- boxymethyl cellulose improves the hydrophobicity of paper based (cel- lulosic) products, enhances surface strength, improves oil resistance, de- creases porosity (increased air resistance) and thickens coating materi- als (rheology modifications) etc. ( Dulany, Batten, Peck & Farley, 2011 ; Holik, 2006 ; Shen & Qian, 2012 ; Tang, Zhou, Zhang & Zhu, 2013 ). Delv- ing deeper into the properties of CMC, the work of Taggart, Schuster and Schellhamer (1991) offers a clear picture of CMC when used along- side conventional starch derivatives. CMC (with DS ∼ 1.4 M/AGU) in an aqueous solution (0.1–5%) has been specifically utilized as a retention aid and strength enhancer alongwith cationic starch onto a paper fur- nish. Interestingly, the adsorption of starch increases by ∼ 60% when added in combination to CMC and by ∼ 30% when CMC is added after
2.1. Cationic cellulose
Standardized procedures have been devised for the production of cationic cellulose; however, the same requires unique optimiza-
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