Carboxymethylation of alkali extracted xylan for preparation of bio-based packaging films

• Alkali-extracted birch pulp xylan was carboxymethylated.
• Carboxymethylxylans formed cohesive and flexible films.
• Carboxymethyl groups seemed to act as inner plasticizers of xylan films.
• Low degree of substitution yielded higher tensile strength and Young's modulus.
• Carboxymethylation is a potential way to upgrade birch xylan to packaging films.

This study describes the synthesis of carboxymethylxylan (CMX) and investigates its suitability as a film for packaging applications. High-purity polymeric xylan was extracted from commercial bleached birch kraft pulp and converted to CMX with three different degrees of substitution (DSs). The water vapor sorption, mechanical, and barrier properties of the films prepared from CMX were tested. Increasing DS of CMX films resulted in an increase in elongation at break and a decrease in tensile strength and Young's modulus. The DS also affected the barrier properties of the films. CMX films with higher DS showed improved (reduced) oxygen permeability (OP), and the water vapor permeability (WVP) increased with DS. It was demonstrated that the carboxymethylation of xylan recovered from industrial side-streams and its conversion to packaging films could be a viable option to valorize xylan.