Production and characterisation of novel sustainable composite particleboards from cellulosic waste of pineapple peduncles and hybrid tannin-epoxy adhesives

The use of cellulosic agricultural residues and tannin-rich forestry waste for the production of particleboards offers a sustainable alternative to conventional construction materials. This study develops bio-based composite panels by combining particles derived from pineapple peduncles (containing 45.8–49.3 wt% cellulose) with a partially biobased hybrid adhesive composed of Okan tannin and epoxy resin. The peduncles were transformed into particles with high porosity (75.7 %), significant water absorption capacity (224.3 wt%) and moisture absorption (58.3 wt%). The tannin, extracted via maceration and evaporation, was characterised using ¹³C NMR spectroscopy and MALDI-TOF mass spectrometry, revealing a composition rich in flavonoids, carbohydrates, and phenolic acids, enhancing its interaction with the epoxy matrix. Panels were manufactured using two particle size ranges (600–1000 μm and 1000–1500 μm) and two adhesive formulations, namely a tannin-epoxy hybrid system (7.5 + 7.5 vol% and 10 + 10 vol%) and pure epoxy (15 and 20 vol%). These fractions were selected to ensure uniform impregnation of the lignocellulosic particles. Characterisation included gravimetric tests, mechanical testing (tensile, three-point bending, internal bonding, Charpy impact). Statistical analysis (ANOVA) confirmed that particle size and adhesive type significantly ($p<$ 0.05) affect density, dimensional stability, and mechanical performance. The resulting panels exhibited moderate water absorption ($<$ 50 wt%), good dimensional stability, and robust mechanical properties (tensile strength: 48–50 MPa; flexural strength: 13–14.6 MPa; impact strength: 6–19 J cm⁻²; hardness: 90 ± 2 HC; internal bonding: 0.62–0.89 MPa), meeting the EN 312 standard requirements for P2-grade boards used in partitioning and furniture manufacturing. This work paves the way for the development of eco-friendly composites and the optimisation of bio-based hybrid adhesives in materials science.