Green composites based on avocado seed starch and nano- and micro-scale cellulose

Nonedible avocado (Persea americana) seed starch (AVS) was developed as resin for green composites. AVS was cross-linked using a green cross-linker, 1,2,3,4-butane tetracarboxylic acid to prepare a rigid thermoset resin having improved water stability. Two cellulose fiber reinforcements, micro-fibrillated cellulose (MFC) with average diameter of 50 nm and a common weed velvet leaf (Abutilon therophrasti) stem-derived microfibers (VLF) with average diameter of 12 mu m, were used to fabricate green composites by solution casting method. MFC/AVS and VLF/AVS green composites were characterized for tensile, thermal, and dynamic mechanical properties and water absorption. Results showed that mechanical properties of VLF/AVS composites were comparable to MFC/AVS composites at same volume fraction. The tensile strength, fracture strain, and Young's modulus of AVS composites with 30% VLF microfibers and 15% sorbitol (plasticizer) were 27.8 MPa, 10.2%, and 1614 MPa, respectively. Both strength (36.7 MPa) and Young's modulus (2303 MPa) increased significantly with 40% VLF fiber content. Good reinforcement by VLF microfibers was realized due to its high aspect ratio and good dispersity in AVS matrix. It would be advantageous to replace MFC with inexpensive VLF to reduce the cost. These composites may be further reinforced to fabricate hybrid green composites using continuous fibers.