Dose-dependent effects of gamma irradiation on PVC/spent coffee grounds composites

Abstract

This study presents the first systematic investigation of polyvinyl chloride (PVC) composites reinforced with gamma-irradiated spent coffee grounds (SCG), addressing a significant gap in the development of sustainable material systems. Novel composites containing 20 wt% SCG, in both untreated and irradiated forms at 25 and 70 kGy, were fabricated using a lab-scale two-roll calender. Comprehensive characterization was conducted via FTIR spectroscopy, X-ray diffraction (XRD), tensile testing, thermogravimetric analysis (TGA/DTG), density and water absorption measurements, and environmental scanning electron microscopy (ESEM). FTIR and XRD revealed that irradiation induced significant modifications in the SCG surface chemistry and crystalline structure. These modifications altered composite performance in a dose-dependent manner: at 25 kGy, ESEM confirmed improved filler dispersion and interfacial adhesion. Mechanical testing at this dose showed notable gains in tensile strength (21.6 ± 2.05 MPa, a 25.1% increase), tensile modulus (263.06 ± 5.75 MPa; an 18.8% increase), and elongation at break (68.24 ± 1.54%; a 21.5% increase) compared to the base composite. These improvements were accompanied by reduced water absorption and higher density. Furthermore, thermal analysis confirmed enhanced stability, with decomposition temperatures shifting to higher values. While 70 kGy exposure led to a partial reduction in properties, the resulting composites remained superior to those prepared with untreated SCG. These findings establish controlled gamma irradiation as a viable pathway for valorizing agricultural residues into functional reinforcements, enabling eco-friendly PVC composites with superior performance and sustainability.