Scale-up production viability of biobased flame-retardant composites

Abstract

The polymer industry is in the middle of transitioning from conventional fossil fuel-based materials to more biobased environmentally compatible biopolymers for the sake of a more sustainable future. Most biopolymers are very flammable, and it is a necessity to make them flame retardant for commercial use. Use of conventional flame retardants is increasingly discouraged due to their environmental and health impacts, creating a need for scalable, bio-based solutions. A better alternate is needed to be developed that can be used at large scale to make a completely sustainable bio compatible solution. This study investigates the development and characterization of bio-based flame-retardant polylactic acid (PLA) composites using lignin nanocapsules (LNCs) with ammonium polyphosphate (APP) as the cargo. The performance of this core–shell system was compared to direct incorporation of APP into PLA. To enhance sustainability and scalability, emulsion formulation optimization was performed by reducing waste generation and increasing production. Emulsion preparation and drying processes such as sonication, rotor stator homogenization, microfluidization, freeze drying and spray drying were investigated to potentially determine the best fit processes for scale up. Comprehensive characterization, including Microscale Combustion Calorimetry (MCC), Thermogravimetric Analysis (TGA), Gel Permeation Chromatography (GPC), mechanical testing, UL94, LOI, and SEM-EDX were conducted to select the best loading for the composite sample prepared using twin screw extrusion. Results showed that direct incorporation of APP at 1 wt% modestly improved flame retardance but only achieved a V-2 UL-94 rating, insufficient for commercial standards. PLA composites achieved a V-0 rating at ≥3 wt% APP loading or ≥5 wt% LNC loading. While higher additive concentrations reduced heat release rate (HRR) and increased LOI, they also led to molecular weight reduction and mechanical property loss. SEM-EDX images confirmed improved dispersion of phosphorus in the LNC composites compared to APP based ones. LNC composites were found to retain mechanical properties better than APP ones at higher loadings. The LNC system was found to offer a more sustainable pathway to flame-retardant PLA by utilizing less APP and better conserving the inherent properties of the biopolymer. There is a need to further investigate LNC system to make it more biobased and universally compatible with polymers. Further, validation on the post processing survival of LNC particles is needed. This research highlights LNCs as a promising bio-based flame-retardant system with industrial scalability potential.