Applications of biodegradable lignin-g-PLGA and lignin-g-PCL polymers for sustainable agriculture

"The dissertation explores the applications of grafted biodegradable lignin-polyesters (LN-PCL and LN-PLGA) in sustainable agriculture, specifically for controlled agrochemical delivery via nanoparticles and films. Alkali lignin (ALN) and lignosulfonate (SLN) were modified using acylation and ring opening polymerization (ROP) onto PCL, and acylation onto PLGA at various (A/S)LN ratios. Amphiphilic LN-PCL polymers formed nanoparticles (NPs) with a core-shell structure, loaded with MFZ, exhibiting a hydrophilic LN outer layer and a hydrophobic PCL core. The grafting methods and degree of polymerization (DP) influenced NP diameters, ranging from 80.21±0.2 nm (acylation) to 245.0±1.5 nm (ROP). Lignin NPs (LNPs) from the acylation reaction grafting method showed a cumulative release of MFZ of only 36.78±1.23%, over 192 hours, while an increase in DP through ROP grafting method reduced cumulative release from 92.39±1.46% to 70.59±2.40% over the same time frame. Furthermore, PCL films incorporating LN-PCL synthesized by ROP were studied for delivering hydrophobic atrazine (ATZ) and hydrophilic metribuzin (MTZ). The incorporation of LN-PCL into PCL films led to hydrogen bond formation, increased crystallinity, and a ~2-fold increase in Young’s modulus. Lower DPs (≤57) in LN-PCL decreased the contact angle from 78° (PCL) to 68° (LN-PCL/PCL composites). UV evaluations showed over 98.0±0.1% UVA and 94.5±0.0% UVC light absorbance by LN-PCL films. Release studies revealed that 27.9% of ATZ and 75.0% of MTZ were released in the first four weeks, with a slight increase in cumulative ATZ release and potential MTZ reabsorption. Additionally, the study synthesized and characterized 1-octadecanethiol (ODT) surface-modified CuS NPs, which were entrapped in (A/S)LN-PLGA NPs for controlled release of Cu and S ions. CuS NPs were synthesized via the citrate method, and their surfaces were modified with ODT. (A/S)LN:PLGA ratios (1:1 and 2:1) facilitated CuS-ODT NPs entrapment, with SLN-PLGA NPs being smaller (122-130 nm) than ALN-PLGA NPs (132-162 nm). Cu and S release in aqueous solutions was controlled over 168 hours, with a total dissolution of 30.50% and 28.21% for S, higher than 0.76 and 4% for Cu for ALN-PLGA1:1 and ALN-PLGA2:1. Overall, this dissertation highlights the potential of LN-based NPs and films for controlled agrochemical delivery, emphasizing their role in sustainable applications."