Evaluation of the Flexural Strength, Sorption, Rheological and Thermal Properties of Corncob Plastic Composites

Abstract

Plastic composites were made from corncobs and high density polyethylene (HDPE) by extrusion and evaluated. The composites were manufactured using two different screened corncob particle size fractions (<2 mm and <0.5 mm) and tested for flexural properties, water sorption, melt flow and thermal properties. The melt viscosities at 190 o C were 18.0 ± 0.8 kPa•s (<2 mm) and 24.0 ± 0.6 kPa•s (<0.5 mm). The results obtained indicated that the composites made with the smaller particle size fraction had higher flexural strength (31.7 ± 1.7 MPa) and modulus of elasticity (1.4 ± 0.1 GPa) than those made with the larger particle size fraction (21.2 ± 1.4 MPa and 1.1 ± 0.1 GPa). Also, the composites made with the smaller particles and were more dimensionally stable. Corncob composites had thermal stability range of 259 -274 o C (onset degradation temperature). The corncob composites made with smaller sized particles possessed better properties in comparison with those made from the <2 mm. Particle size and density significantly affected the mechanical, physical and thermal properties of the composites evaluated.

Evaluation of the Mechanical, Thermal and Rheological Properties of Hop, Hemp and Wood Fiber Plastic Composites

“…Pine fiber was shown to have the lowest density at 1.46 g/cm 3 while hop fiber was the highest at 1.53 g/cm 3 . These cell wall density values are consistent with the literature for wood and natural fibers (approximately 1.5 g/cm 3 ) [8,24].…”

“…This process did not use chemicals to produce the fine fiber as in other studies [14]. Natural fibers (bamboo, rice husks, and corn cob) produced using the 0.5 mm sized screen have been shown to produce fibers suitable for use in thermoplastic composites, while large screen sized fibers (<1 mm or <2 mm) produced composites with reduced properties [5,6,8]. The fiber size distribution for pine, hemp and hop fibers was determined by light scattering (Figure 2a).…”

“…In geographical locations where wood residues are not available, alternative natural fibers can be used in WPC applications [3]. There are various natural fibers available regionally, such as wheat straw [4], rice husks [5], bamboo [6], rattan canes [7], corn cobs [8] and banana stalks [9] that could be used as alternatives to wood fiber [10]. In the USA there are new fiber sources available, notably from hemp and hops, that could be used as a wood replacement.…”