Bio-based cationic waterborne polyurethane dispersions from high oleic soybean oil

Abstract

Polymeric materials are under tremendous pressure for improving their greenness: despite their important role in several essential aspects of human life, in public opinion they are mostly associated with single-use plastics pollution and use of fossil resources. Sustainable polymer-based materials may be prepared from biobased monomers and polymers, through photoinduced processes. Owing to low energy requirements, high reaction rates at room temperature, and low VOC emissions, photoinduced polymerization is recognized as a green technology. Among the biobased monomers explored in this field, those derived from cardanol (a natural phenolic lipid obtained from cashew nutshell liquid) and from unsaturated vegetable oils, such as soybean oil, are interesting for industrial applications, being commercially available. However, polymers obtained by photoinduced polymerization of biobased monomers often have low thermomechanical properties; biobased monomers are thus typically used as co-monomers to increase the biobased content of fossil-based polymers, in non-structural applications, such as coating or adhesives, or are added with reinforcements to obtain composite materials. The latter option is particularly interesting when natural fillers, such as cellulosic fibers, are used, thus obtaining fully biobased composites. In our group we exploited photoinduced reactions to produce composites from biobased monomers, using wood-based microfibrillated cellulose and nanocellulose from hemp waste fibers as reinforcements. Two routes were explored: (i) epoxidized and (meth)acrylated monomers derived from cardanol and from soybean oil, were polymerized by photoinduced radical or cationic chain growth reactions; (ii) copolymer latexes obtained from derivatives of eugenol and coumarin were crosslinked through a photocycloaddition reaction. In the latter case, the potential reversibility of the crosslinking was explored in view of recyclability. The photoinduced polymerization and crosslinking reactions were studied by Fourier Transform Infrared (FTIR) and UV-visible spectroscopies; high degrees of conversion were obtained. The thermal, mechanical, and functional properties of these composites make them interesting for e.g., packaging applications.