2.3. Physical Properties of RH/CP Reinforced ABS Blend Composites

The density of biocomposites was evaluated according to ASTM D4018. The thickness and weight of the developed blend composites of RH/CP were recorded for tests. The samples were weighed to the nearest 0.001 g by using a close chamber EMS 300-3 precision balance (Kern and Sohn, Balingen, Germany).

Water absorption characteristics were conducted following the ASTM D570. The sample was initially dried in a circulation oven (CMH Ltd., Lancing, UK) at 80 °C for 2 h before the composites’ weight was obtained. In this study, five replicates of composite specimens with the dimension of 20 mm × 20 mm × 3 mm were immersed in distilled water at room temperature of 25 °C. The coupons were taken out from the moist condition, and all exposed surfaces were dried by using a microfiber cloth (Spontex, Worcester, Worcestershire). The moisture uptake data were recorded by using a weight balance EMS 300-3 (Kern and Sohn, Balingen, Germany) regularly at every 2 h of water immersion. The moisture absorption characteristic was evaluated by using the following equation:

where, W_t is the sample’s weight at a recorded immersion time, and W₀ is weight of the dried sample. The kinetic and diffusion mechanism was evaluated based on Fickian’s theory. Its relation is:

where M_t and M_∞ are water absorption at time, t and saturation point, respectively. k and n are constants.

The ability of moisture to penetrate the composite’s molecule, also known as diffusion coefficient, D is a primary parameter of Fick’s model [15]. The D value is obtained from initial linear portion of the moisture absorption percentage versus the square root of the time curve. The one-dimensional diffusion coefficient, D, can be determined from the following equation:

where h is the plate thickness, M₂, M₁ are the moisture content at time t₁ and t₂, respectively.