Microfibrillated cellulose-reinforced hemp non-wovens: Engineering functional pre-forms for sustainable composites

This study investigates the mechanical enhancement of long-fibre hemp non-woven mats—utilising both epoxy and bicomponent polypropylene/polyethylene (PP/PE) binders, through the incorporation of microfibrillated cellulose (MFC) processed at varying energy levels. The research provides a systematic evaluation of these modified mats, demonstrating their feasibility as sustainable pre-forms for hybrid automotive composites. MFC integration was assessed via a water-diluted wet-spraying process at doses of 1%, 2%, and 3%, resulting in significant improvements in mechanical performance. Successful incorporation was confirmed through scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). A key contribution of this work is the identification of a mechanical saturation limit governed by MFC fibrillation levels; notably, highly fibrillated MFC with high aspect ratio and degree of fibrillation (Hp-M) reached the tensile saturation threshold at lower loading levels compared to coarser, lower-aspect-ratio MFC (Lp-M, prepared via low-energy processing). Findings also indicate that gravimetric estimation of actual MFC retention is complicated by in situ selective leaching of non-structural components, particularly in mats with epoxy binders. Normalised tensile analysis showed that despite 3% Lp-M achieving the highest absolute mechanical performance, a 2% applied dosage of medium-energy MFC (Mp-M) represents the optimal techno-economic limit. This configuration mitigates excessive binder consumption while delivering substantial structural enhancements, specifically yielding an ∼80% increase in mass normalised tensile strength for thermoplastic-bonded networks (T2, T4) and a 600% improvement for epoxy-based architectures (T5) compared to untreated baseline controls. Ultimately, this study demonstrates that optimising the MFC–fibre interface at low applied dosages can transform agricultural side-streams into high-performance, carbon-sequestering constituents for lightweight vehicle components.