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

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/cm(3)) 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 degrees. 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.