S. Basu, S. Malik, G. Joshi et al.
Carbohydrate Polymer Technologies and Applications 2 (2021) 100050
Fig. 2. Different starch products as paper additives.
activation followed by acetylation with reagents like acetic acid or acetic anhydride or ketene or vinyl acetate or a combination of all ( Fig. 2 ). Acetylation of starch prevents its retrogradation, reduces enthalpy or ∆ H (which depicts the alteration of amylopectin helices) and subse- quently reduces crystallinity (improves reactivity). These properties in- voke acetylated starch to be an excellent surface sizing agent in paper industry ( Ayucitra, 2012 ; Bello-Pérez, Agama-Acevedo, Zamudio-Flores, Mendez-Montealvo & Rodriguez-Ambriz, 2010 ; Chen, Kaur & Singh, 2017 ; Halal et al., 2015 ; Khalil, Hashem & Hebeish, 1995 ; Rutenberg & Solarek, 1984 ). Hydroxypropyl starch , another starch derivative used
for paper coating and surface engineering, is commercially produced in presence of alkali and propylene oxide. Hydroxypropylation again reduces gelatinization temperature, increases swelling power, solubility and improved freeze-thaw stability of starch ( Jonhed, 2006 ; Kaur, Singh & Singh, 2004 ; Rastogi & Samyn, 2015 ).
5. Chitosan
Chitosan is a deacetylated derivative of chitin ( Fig. 3 ), which hap- pens to be the second most abundant polymer after cellulose in na-
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