Fully bio-based films based on purified biopolymer fractions from hydrothermal extraction of discarded carrots

Abstract

Flexible 100 % bio-based films were produced from discarded carrots fractions. The main ingredient was purified high molecular weight fractions of hemicelluloses and pectins previously obtained by hydrothermal treatment and ultrafiltration/diafiltration. A fraction of lignin-containing cellulose nanofibers was used as an additive. These nanofibers were obtained from the residual pulp of the hydrothermal treatment after a mechanical treatment. Low content of lignin-cellulose nanofibers (< 5 % w/w) improved oxygen permeability (up to 29 %) but worsened water vapor permeability and tensile properties. A higher addition of lignin-cellulose nanofibers (5-25 % w/w) allowed to recover the properties of the reference film (without fibers) and provided a higher hydrophobicity, increasing the water contact angle from 79.9° to 125.8°. The study of the influence of the molecular weight (67.77-102.75 kDa) and composition of the hemicellulose and pectin fraction in films containing 1 % lignin-cellulose nanofibers showed that a higher molecular weight decreased oxygen permeability (from 48.18 to 41.14 cm3·µm/m2/kPa/day), increased water vapor permeability (from 21.56 to 24.01 g·mm/m2/kPa/day) and decreased hydrophobicity (from 86.84° to 71.10°). Tensile stress was higher with higher pectin content and lower molecular weight (from 1.13 to 2.84 MPa), while elongation was higher with higher hemicellulose content (from 5.92 to 15.28 %). The obtained films had acceptable properties for food packaging and high hydrophobicity, with the great advantage of being 100 % from agri-food waste by applying environmentally friendly processes and without the need for chemical modification.