Development of green composites based on activated spent coffee grounds waste and epoxy resin

This study investigates the development of green composites from epoxy resin and spent coffee ground waste (SCGW). The SCGW was subject to two chemical activations, the former is alkali activation using potassium hydroxide (KOH) and the latter is hydrogen peroxide/sulfuric acid (H 2 O 2 /H 2 SO 4 ) activation system. The raw and the activated SCGW were classified using a Retsch AS 200 shakers. The particle size of ≤250 µm was selected. The successful removal of amorphous hemicellulose and lignin was monitored by Fourier transform infrared spectra (FTIR) through the disappearance of the ester carbonyl band (C = O) at 1730 cm −1 . The X-ray diffraction (XRD) analysis revealed that these treatments significantly increased the structural order and molecular alignment of the bio filler. The raw and modified SCGW powder was added to commercial epoxy resin at a fixed loading of 10 wt.%. Based on the applied various pretreatments, the formulations were designated as epoxy with untreated control (EC), the sample with acid-hydrolyzed activated SCGW as (EH), and the sample with alkali-activated powder as (EK) composites. Mechanical testing demonstrated obvious reinforcement effect over the EC. EK yielded the highest ultimate flexural strength of 23 ± 1.4 MPa, a flexural modulus of 1.51 ± 0.09 GPa, and percentage elongation at break (% EB) of 1.51 ± 0.09%. Simultaneously, the EH formulation yielded the highest Impact Energy of 14 ± 0.9 J. It maintained high environmental stability with a low diffusion coefficient of 27.80 × 10 −3 mm 2 /h. The scanning electron microscope (SEM) micrographs of the fractured sample validated these results. It showed a transition from a brittle, glassy fracture in neat epoxy to a rough, energy-consuming topography in the EH counterpart. Finally, the achieved results prove that acid hydrolysis combined with physical size refinement is an effective practice for converting SCGW into sustainable, load-bearing engineering materials.