Combined effects of acacia tannin and Prosopis juliflora biochar on the structural and crystallisation behaviour of PLA sheets

Conventional polyethene mulch sheets contribute substantially to the accumulation of permanent agricultural plastic waste, emphasising the need for sustainable and biodegradable alternatives. Biodegradable Polylactic acid (PLA)-based bio-composite sheets were made using waste-derived Acacia Tannin (AT) and Prosopis juliflora Biochar (PJBC). Four formulations were evaluated, namely S1 (neat PLA), S2 (PLA + AT), S3 (PLA + PJBC), and S4 (PLA + AT + PJBC). Water contact angle measurements showed increased surface hydrophobicity, with the contact angle rising from 67.56 ± 3 ° (S1) to 84.25 ± 3 ° (S4), indicating a transition towards near-hydrophobic behaviour. Differential Scanning Calorimetry (DSC) and X-ray Diffraction (XRD) analyses suggested that PJBC acted as a heterogeneous nucleating agent, thereby enhancing crystallisation and improving structural ordering within the composite matrix. Raman spectroscopy showed a reduction in the D -band-to-G-band intensity ratio (ID/IG) from 1.13 (S3) to 0.66 (S4), suggesting improved graphitic ordering in the ternary composite. FE-SEM and EDS analysis confirmed the homogeneous distribution of the hybrid filler system, representing efficient integration of Acacia Tannin and Prosopis juliflora biochar without significant elemental segregation. The combined incorporation of AT and PJBC improved the thermal transition behaviour and surface properties of PLA compared with neat PLA. The utilisation of biomass-derived Acacia Tannin and invasive-species-derived Prosopis juliflora biochar represents a sustainable waste-valorisation strategy for developing biodegradable agricultural mulch materials with the potential to reduce environmental plastic accumulation.