Fully biodegradable, hydrophobic, enhanced barrier starch bio-composites with sandwich structure by simulating wood

Through a single-sided cavity free-form foaming process, composites with open cell structures similar to wood cells were obtained by using corn starch, pulp fiber, and sisal fibers, which was used as the middle layer of the sandwiched composites. Afterwards, more hydrophobic lignin-containing nanocellulose fibrils from pine bark were coated on the surfaces of the open cell composites by high-pressure gun spraying, simulating the bark of wood to impart barrier property to the final product. The water barrier, mechanical property, apparent density, heat insulation, and biodegradability of the sandwich structured bio-composites were characterized. Experimental results indicated that the water contact angle on the surface of the bio-composite was as high as 92 degrees. The apparent density of the bio-composite was very low, at 0.107 g/cm3. The tensile strength of the bio-composites reached 5.3 MPa. After conducting biodegradability tests in soil for 60 days, the bio-composites lost 87 % of its mass.