The effect of acid aging on the mechanical and tribological properties of coir–coconut husk-reinforced low-density polyethylene composites

Abstract

The present study investigates the physical, thermo-mechanical and tribological properties of coir–coconut husk particulate-reinforced polymer composites subjected to a corrosive environment. The composites were prepared by the conventional facile hot compression molding method. The composite was immersed in a strongly acidic environment of pH 2.2 for a period of 3, 6, and 9 days. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used to elucidate the structure and morphology of the composites. The thermal analysis using differential scanning calorimetry, water absorption, hardness, coefficient of friction and wear rate was performed as per the ASTM standards to characterize the as-prepared and aged composites. The experimental test results revealed that with an increase in acid aging time, the acid aged samples lost surface matrix such that the fiber was seen on the surface. The effects of corrosion seemingly reduced the crystallinity of the acid aged samples allowing amorphous regions to be trapped within the crystals. Water absorption of the samples increased with aging time due to inherent voids in the specimens as weight gain values were 5.27, 16.80, 19.33 and 19.91%, respectively for control and acid aged samples. Hardness values initially decreased with immersion time and increased which was attributed to the crystallinity of the specimens and to some extent the elemental carbon present in the specimens before and after aging. The measured hardness values of the control and acid aged composites were 2.98, 7.27, 14.40 and 9.07 HV, respectively. From the thermal analysis, it was noticed that the glass transition temperature (Tg) of the polymer shifts to higher temperatures as the aging time in the acidic medium increased, which can be attributed to cross-linking of the polymer chains. The control specimen shows higher coefficient of friction (CoF) because they are more rigid than the acid aged samples, and hence under dry sliding can cause more friction leading to increased heat and CoF.