Incorporating lignin into chitosan-based bioplastics enhances the tensile properties and provides control of swelling and opacity

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Abstract This study focuses on obtaining and characterizing bioplastics prepared with different mass amounts of commercial chitosan and lignin extracted from guava seed cake. The chitosan-lignin bioplastics were produced using the casting technique, and characterized through thermogravimetric analysis, tensile tests, swelling (water absorption), water solubility, and moisture. All bioplastics containing lignin exhibited moisture percentages higher than the only-chitosan sample (15.7%); the formulation with the lignin maximum content (10%) reached the highest content (19.4%). Water solubility did not show significant statistical differences; the average value was 17.4%. The increasing lignin content revealed a strong positive linear correlation ( R = 0.95) with opacity, with the maximum one (4.92 mm − 1 ) found in the formulation with the highest lignin content. Conversely, the increasing lignin content revealed an inverse linear correlation ( R = 0.83) with swelling, reducing it from 276.6% (only chitosan formulation) to 133.5% (formulation with the highest lignin content). The tensile strength of formulations containing lignin was higher than that of the only-chitosan specimen (12.5 MPa). However, the breaking elongation of formulations with lignin (except the formulation with 2% lignin content) was lower than that of the only-chitosan bioplastic (36.6%). According to thermogravimetric analysis, all samples had their mass losses in four distinct steps, the lignin incorporation raised the temperature at which the bioplastics showed their maximum mass losses, and the lowest mass loss rate was observed in the formulation with the highest lignin content. The cryofracture cross-section image for the formulation with the highest lignin content did not exhibit layer formation, therefore the chitosan-lignin in the study condition can originate blends.

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