Polymorphic transformation of cellulose I to cellulose II by alkali pretreatment and urea as an additive

► Cotton linter was treated with NaOH with and without urea as an additive. ► At 15 wt% NaOH sudden transformation from cellulose I to II polymorph. ► On addition 5 wt% urea this transformation decreased largely. ► The crystallinity index showed a gradual decrease with increasing concentration.