Polylactic acid coating of cellulose/chitosan insulating foams as a strategy for enhancing mechanical properties and hydrophobicity

Abstract

The production of cellulose-based foams directly from cellulose pulp has become a novel and interesting alternative to traditional fossil-based foams, such as expanded/extruded polystyrene (EPS/XPS) or polyurethane foams. However, there are some limitations regarding these bio-based materials, such as their high sensitivity to water and their low mechanical strength. In this work, different PLA coatings were developed for the hydrophobization of cellulose- and cellulose/chitosan-based foams. The resulting foams showed apparent densities (0.12–0.16 g/cm3) that were comparable to those of commercial foams, which is important for packaging and building applications. The PLA-coated foams exhibited improved mechanical properties (elastic modulus: 1.01–3.02 MPa) compared to the uncoated ones (elastic modulus: 0.29–0.78 MPa). The compressive strength of the PLA-coated foams (0.09–0.20 MPa) was similar to that of commercial foams (0.05–0.40 MPa). Also, the PLA coating of the foams significantly reduced the water absorption and improved the hydrophobicity of the surface. PLA-coated cellulose/chitosan foams exhibited water absorptions of 0.33–0.52 g water/g of dry foam and water contact angles of 94–110°. The addition of both PLA and chitosan to the foam formulations did not affect their thermal insulation ability, and the obtained thermal conductivity values (0.035–0.037 W/mK) were comparable to those of commercial insulating materials. Finally, the developed foams could serve as a bio-based alternative to traditional materials for packaging and building industries.