Pilot-scale biorefinery of agri-food residual biomass oriented to valuable bioproducts

Abstract

Chapter 6 focused on the formation of biodegradable films whose main ingredient was the purified solid fractions of hemicelluloses and pectins obtained in Chapter 4 and 5.The residual pulp obtained from the two hydrothermal treatments (140 and 180 °C) applied in Chapter 4 was studied as an additive in the films. A small percentage of residual pulp addition (< 5 %) decreased the oxygen permeability through the film (up to 29 %) but increased the water vapor permeability and worsened the tensile properties. Higher residual pulp content (5-25 %) allowed the film to regain properties similar to those of the reference film (the one without residual pulp) and significantly improved the surface hydrophobicity by increasing the water contact angle from 79.9° (0 % residual pulp) to 125.8° (25 % residual pulp). Glycerol was used as a plasticizing agent in the films at a content of 35 %. The influence of the molecular weight (67.77-102.75 kDa) and the composition of the purified hemicellulose and pectin fractions on films containing 1 % residual pulp was studied. Higher molecular weight decreased oxygen permeability (from 48.18 to 41.14 cm 3 •µm/m 2 /kPa/day), increased water vapor permeability (from 21.56 to 24.01 g•mm/m 2 /kPa/day), and decreased hydrophobicity (from 86.84° to 71.10°). Tensile strength was higher for higher pectin content and lower molecular weight (from 1.13 to 2.84 MPa), and elongation was higher for higher hemicellulose content (from 5.92 to 15.28 %). The films had acceptable properties for application in the food packaging industry, their main strengths being: 1) 100 % origin from an agri-food waste, 2) production through environmentally friendly processes, 3) non-toxicity, 4) high hydrophobicity without the need for chemical modification, and 5) predictable high biodegradability due to no chemical modification.