Effect of silane-treated pine wood fiber (PWF) on thermal and mechanical properties of partially biobased composite foams

In this study, biobased thermoset composite foams were fabricated from epoxidized pine oil and pine wood fibers (PWF) using a siloxane-based foaming agent. The foam compositions were developed for pine wood fiber treated using a simple, scalable silane treatment. The delayed addition method was employed to arrest cell growth and the incorporation of PWF served as nucleation sites leading to a decrease in cell size and an increase in cell density. Silane treatment was also shown to influence cellular structure by further arresting cell growth by lowering the activation energy of curing and positively affecting the thermal properties, and mechanical properties by improving stress transfer between fiber and matrix and increasing crosslinking densities. Biobased composite foams containing 5 wt% and 10 wt% untreated and silane-treated PWF having densities between 0.60 – 0.75 g/cm3 were successfully prepared and their microstructure, thermal and mechanical properties were studied. Silane treatment was shown to improve thermal stability of the fiber by 31% and the 10 wt% treated PWF foamed composite by 26%, respectively. The addition of untreated and treated PWF resulted in significant alteration of cellular properties; cell size decreased from 217 to 107 and 80 µm while cell density increased 5-fold, from 10 to 40 and 56.5 cell/mm2 respectively. Compared to the baseline unfilled bioepoxy foams, incorporation of 10 wt% exhibited increased compressive strengths from 11.30 MPa to 18.21 and 24.66 MPa respectively. Lastly, Ashby-Gibson models were used to decouple the importance of the foam microstructure from reinforcement effect of PWF on compressive moduli of the foam.