Rice and Einkorn wheat husks reinforced poly(lactic acid) (PLA) biocomposites: Effects of alkaline and silane surface treatments of husks

This paper investigated specific surface treatments, aimed to improve the adhesion between PLA and rice and Einkorn wheat husks. In the first part, husks were treated by alkaline solutions at three concentrations (2, 5 and 10%) at room temperature for different times between 6 and 48 h. Results revealed that the alkaline treatment dissolved a fraction of waxes, lignin and hemicellulose, so that the polarity of their surface was increased and therefore alkaline treated husks were more sensitive to moisture. Moreover the alkaline treatments have more influence on wheat than on rice husks, as shown by chemical composition determination, FTIR measurements and ESEM observations. In the second part, husks were treated by two kinds of organosilanes (γ-aminopropyltriethoxysilane (APS) and γ-glycidoxypropyltrimethoxysilane GPS)). These silane treatments were applied either alone or on previously alkaline treated husks (NaOH 5% for 24 h). The results showed that silane treatments reduced the moisture sensitivity and raise the energy surface of the husks. In the last part, treated husks were incorporated into polylactic acid (PLA) to produce biocomposites. Biocomposites reinforced by husks treated by alkaline solution and silane have higher bending moduli and stresses than those reinforced by untreated husks and husks treated by silane alone. It can be supposed that the PLA/husks adhesion was enhanced. No difference was observed according to the silane nature.