Effect of cold plasma treatment on the characteristics of waste coffee grounds reinforced HDPE composites

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The present work involved the surface modification of waste coffee grounds (WCG) via cold plasma using Ar as the precursor gas. The untreated and plasma-treated WCG particles were mixed with high-density polyethylene (HDPE) at a 20/80 wt% ratio of filler to polymer by using a two-roll mill followed by a hydraulic press. The effect of plasma surface treatment on the performance of composites was investigated using various analytical techniques, including tensile and izod impact strength tests, thermogravimetric analysis (TGA), contact profilometry analysis, density measurements, and scanning electron microscopy (SEM). The incorporation of WCG resulted in a reduction in both the impact strength and tensile strength of the composite material. Nevertheless, plasma surface treatment resulted in significant improvements in both impact strength and tensile strength compared to WCG composites that had not been subjected to cold plasma. The TGA results demonstrated that cold plasma treatment increased the thermal stability of WCG/HDPE composites, as the onset temperature of decomposition of plasma-treated WCG composites was higher than that of untreated WCG composites. The SEM images revealed modifications at the fiber-matrix interface, corroborating the improved mechanical properties after treatment with cold plasma. The contact profilometry analysis showed an enhancement in surface roughness, affirming the effect of plasma treatment on the WCG surface. These findings suggest that cold plasma can be utilized as an effective method for the modification of agro-waste materials and the production of high-performance, eco-friendly composite materials.