Bio flame retardant for Polylactic acid by combining phytic acid and lignin nanoparticles from lignosulphonate

Abstract

Lignosulphonate nanoparticles/Phytic acid bio-flame retardant for PLA is a novel and environmentally friendly flame retardant that has the potential to revolutionize the fire safety industry. This research paper provides a comprehensive overview of the background, possible applications, process conditions, key results, and novelty of this innovative bio-flame retardant. The background of this dissertation stems from the growing concern over the use of traditional flame retardants, which often contain harmful chemicals that can pose serious health and environmental risks. In response to this, researchers have been exploring alternative, sustainable flame-retardant materials, and the combination of lignosulphonate nanoparticles and phytic acid has emerged as a promising candidate. Polylactic acid (PLA) is a biodegradable polymer with applications in engineering, electronics, transportation, and aerospace due to its excellent properties; however, because it has an organic matrix, its thermal and fire retardancy needs improvement. Lignin has a high aromatic content and therefore offers a chance to use bio-based materials as nanoscale intumescent flame retardants. However, because of its structural heterogeneity, lignin requires modification with a material that has flame-retardant qualities. It has already been proven that combining lignin and PLA causes the matrix of a polymer to degrade during melt-processing. Phosphorous functionalized lignin nanoparticles, on the other hand, appear to reduce PLA degradation during melt-processing. Our goal was to create a high-functionality, bio-based phosphorus-containing flame-retardant that could be reactively incorporated into the PLA matrix to enhance flame retardant efficacy in a way that is sustainable. Through the combination of phytic acid and lignosulfonate, bio-based flame retardant was formulated. Functionalized lignin nanoparticles were synthesized by first combining lignosulfonate with phytic acid at 80ºC for 4hrs with magnetic stirring, followed by 1 hour of ultrasonication at a frequency of 20Hz with a cavitation probe of 3.175 mm, to give a nanoparticle dispersion, LNP-PA. The LNP-PA dispersion was spray-frozen on aluminium plate cooled with liquid nitrogen and kept frozen at -80ºC, followed by lyophilization. Key results presented in this paper demonstrate the successful synthesis of functionalized lignosulphonate nanoparticles, superior flame-retardant properties of the lignosulfonate/Phytic acid bio-flame retardant compared to traditional flame retardants. The bio-flame retardant exhibits excellent fire resistance, low toxicity, and minimal environmental impact, making it a highly desirable alternative for various applications.X-ray powder diffraction (XRPD) spectrum showed that the pristine lignin and the functionalized NPs both have an amorphous structure, and the broadening of the spectra of the phosphorylated lignin after sonication shows the formation of nanoparticles, whose sizes were confirmed by dynamic light scattering (DLS). According to the vi DLS measurements, the average particle diameter was 238 nm. However, scanning electron microscopy (SEM), revealed that there was agglomeration of particles after freeze drying but a significant particle size reduction of lignin was observed. Fourier transform infra-red spectroscopy (FTIR) spectrum showed a reduced intensity due to the loss of hydroxyl functional groups resulting from homolytic cleavage during ultrasonication, and phosphorylation. This was confirmed by 31P-NMR, which shows the loss of hydroxyl functional groups, indicating that they reacted with the phosphate groups in PA. The appearance of peaks in LNP-PA's FTIR spectrum corresponding to P=O and P-O-R ester bonds proved that phytic acid had been chemically and successfully linked to lignosulfonate. The fire-retardant effect of the bio-flame retardant formulation was examined using a modified UL-94 tests. The control sample, pristine PLA burned more vigorously in the vertical method. Melting drips were observed in pristine PLA, PLA/LNP, and PLA/5LNP-PA, all of which were classified as V-2.PLA/10LNP-PA and PLA/15LNP-PA samples that had higher weight percentages of the bio-flame retardant additive demonstrated better fire behaviour and were classified as V-1 and V-0 respectively. All samples were classified as HB in the horizontal mode, and as the loading ratio of LNP-PA additives increased, the rate of burning decreased. The results are credited to the presence of lignosulfonate whose highly aromatic composition forms a carbon-based char layer which inhibits the diffusion of oxygen to the combustion site. Phytic acid also forms a char layer when it degrades due to the six phosphate groups within its structure, that produce phosphoric acid. This forms a protective layer which reduces the amount of fuel needed to sustain the combustion process and restricts heat flow in the material. The novelty of this research lies in the development of a sustainable and effective bio-flame retardant that addresses the shortcomings of conventional flame retardants. Previously published research on this subject has reported on the use of pristine or phosphorous based macro-scale lignin to synthesize bio-flame retardants, and there has been few reports involving lignin nanoparticles or their combination with phytic acid. The combination of lignosulfonate and phytic acid offers a unique and innovative solution to fire safety concerns, paving the way for a more sustainable and eco-friendly approach to flame retardancy. Possible applications of lignosulfonate nanoparticle/Phytic acid bio-flame retardant include its use in various industries such as construction, textiles, and electronics, where fire safety is of utmost importance.