Microalgal proteins: a new source of raw material for production of plywood adhesive

Microalgae have attracted increasing interests due to their potential as an alternative to land crops to produce renewable fuels, chemicals, foods, and personal care products. In this study, we demonstrate the feasibility of producing type II plywood adhesive using total proteins extracted from Spirulina platensis and Chlamydomonas reinhardtii. Denaturation with NaOH and chemical cross-linking improved tensile strength and water resistance of the adhesive. Among the three aldehydes tested, glyoxal was found to be the best cross-linker. The optimum concentration of NaOH was approximately 50 mM and of glyoxal was 2 % (w/w). Glyoxal (2 % w/w) improved the tensile strength of plywood samples up to 55, 270, and 650 % of dry, soak/dry, and soak/dry (60 °C), respectively, for S. platensis proteins. Increase in hot pressing temperature and time also improved tensile strength. The optimum hot pressing conditions were 120 °C for 5 min after 10 min assembling time. Of the two algae sources tested, C. reinhardtii UTEX 2337 proteins had better adhesive strength and water resistance than S. platensis proteins and showed comparable adhesive properties to soy proteins. Notably, bioadhesives made from both algal proteins had lower viscosity than soy proteins. This feature should allow easier spreading of adhesive on wood surfaces and deeper penetration into veneers. Our results suggest that algal proteins are a promising resource for the production of bioadhesive for type II plywood.