Mechanical, dynamic and tribological characterization of HDPE/peanut shell composites

Polymer composites reinforced with natural fibres are more appealing than conventional materials due to their accessibility, renewability, low weight and price, low density, and biodegradability. There are a wide variety of different natural fibres, such as nutshells, flax, and palm, which can be applied as reinforcements or fillers, showing potential as replacements for inorganic fibres. Plastics are often somewhat economical when producing complex shapes, and the possibility of obtaining composite materials with reduced demoulding times, as no chemical reaction is required, makes them very interesting from an industrial point of view. Moreover, polymers are increasingly used for tribologically stressed components, whereby plastic components replace metallic bearings, gear wheels, or sliding elements. In this regard, this work's objective was to produce composites of high-density polyethylene (HDPE) with different proportions (2, 4, 6, 8. and 10 wt%) of peanut shell (PS) filler and evaluate the influence on the dynamic mechanical and tribological properties of the addition of different amounts of filler. The strain (%) increases with fibre contents of 2 and 4 wt%, but at higher fibre contents, a considerable reduction, approximately 4 times for a fibre content of 6 wt% and an even more substantial reduction for fibre contents of 8 wt% and 10 wt%, could be observed. From the Dynamic Mechanical Analysis (DMA) tests, it could be observed that E' is practically constant for composites for all fibre contents between -20 degrees C and similar to 50 degrees C at 1.5 Hz and 10 Hz, which is similar to 6 times higher than that of neat HDPE under the same conditions. The tribological assays were carried out by the reciprocating sliding wear test with loads of 10, 20, and 30 N. Although the wear rate (k) and wear volume (V) increased with increasing applied load, these values were similar for fibres with different wt% contents. Thus, the addition of fibre does not modify the tribological properties of HDPE. By Raman spectrum analysis, similar intensities and positions of the bands of the HDPE vibrational mode before and after wear tests could be observed.