Starch and Plant Fiber Reinforced Biodegradable Composites with Open Cell Structures

Abstract

In order to figure out the effect of different starches on the properties of starch-based composites, new biodegradable composites with open cell structure were prepared through thermo-cavity foam molding using four different type starches (corn starch (CS), wheat starch (WS), potato starch (PS), and sweet potato starch (SPS)) and sisal fibers as main raw materials. Mechanical properties of the biodegradable composites were tested. The order of tensile and compressive strength of the composites was as follows: SPS-based composite > CS-based composite > PS-based composite > WS-based composite. Following X-ray diffraction, the infrared spectrum analysis, scanning electron microscopy, and viscosity test were employed to gain comprehensive views on the effect of the different starch microstructures on the properties of the biodegradable composites. X-ray diffraction analysis showed that the crystalline index of the SPS and CS were lower than those of PS and WS. Amorphous starch more easily combined with the sisal fiber, which is the deep reason that the SPS-based composite had the best tensile strength. Moreover, the infrared spectrum analysis indicated that SPS molecules demonstrated more hydroxyl groups than the others. The hydroxyl group in the SPS molecules formed more hydrogen bonds with the hydroxyl group in the sisal fibers. Scanning electron microscopy images showed that SPS bonded tightly with sisal fibers uniform open cell structure in the biodegradable composites. The order of the viscosities of the different starch slurry was: WS slurry > PS slurry > CS slurry > SPS slurry. The lower the crystalline index of the starch, the larger the amorphous zone, the lower the viscosity of the starch slurry, and the better the rheological properties are. In this case, the SPS and sisal fibers can combine well, and the SPS-based composites offer improved mechanical properties.