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Abstract:
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Abstract: The sustained release of agrochemicals in agriculture is a promising solution to reduce eco-toxicological and increase the effectiveness of agrochemicals administration. Although agrochemicals are necessary to the agricultural scenario, due to, e.g., voluminous production, devastating fungal diseases and soil depletion, the indiscriminate use of fertilizers and pesticides has contributed to the development of harmful impacts in the environment, pest resistance and human health. Biopolymer nanocarriers are environmentally friendly alternatives due to their renewable origin and biodegradability, which enable their integration into biogeochemical cycles. Lignin and cellulose are worldwide available biopolymers produced as waste in millions of tonnes every year and therefore are interesting inexpensive renewable raw materials suitable, after chemical modification, for macromolecular nanostructures syntheses. Kraft lignin was esterified with methacrylic anhydride with > 90 % of functionalisation to yield lignin methacrylate. Lignin nanocarriers (NCs) were produced by aza-Michael click addition in miniemulsion and several fungicides ? namely azoxystrobin, pyraclostrobin, tebuconazole, and boscalid ? were encapsulated in situ, thereby demonstrating the wide-ranging applicability of the method. NCs with average particle size of 200 ? 300 nm were obtained, with 70 to 99% encapsulation efficiencies. The crosslinking, using the biobased amines spermine and spermidine as crosslinking agents, was monitored by the decrease in the band at 950 cm-1 in the infrared spectra. Native cellulose, 45 % of crystallinity, was submitted to transesterification of cellulose to produce colza oil cellulose esters and to esterification to produce undec-10-enoic cellulose esters (UACEs), for such, two different systems were used, DBU/CO2 switchable solvent, a novel environmentally friendly approach for cellulose solubilisation, and DMAc/LiCl, the classical method. The obtained degrees of substitution were up to 2.4, and chemical modification has entailed some changes in molecular weight, thermal properties and crystallinity to cellulose esters. Cellulose nanocarriers were synthesized from UACEs by thiolene addition in miniemulsion and the crosslinking was qualitatively monitored by the double bond consumption observed at 907 cm-1 in infrared spectra. NCs in the size range of 150 ? 250 nm were obtained. Captan and pyraclostrobin were encapsulated in high efficiency, > 70 %, measured by HPLC. Overall, NCs formulations presented lower minimum inhibitory concentrations than their bulk counterparts against phytopathogenic fungi. Lignin NCs successfully inhibited the growth up to ca. 90 % of Phaeomoniella chlamydospora and Phaeoacremonium minimum, fungi associated to the worldwide occurring fungal grapevine trunk disease Esca. In addition, cellulose NCs have successfully inhibited spore germination and mycelial growth P. minimum and Neonectria ditissima up to 80 % of inhibition depending on the formulation and the fungus strain tested. Trunk diseases cannot be controlled by aspersion of fungicides on the crop and cause the dieback and death of plants, as well as decrease crop yields impacting on commercial trades. Novel strategies to fight these diseases on-field are still under development and biobased polymer nanocarriers loaded with fungicides are a promising approach to overcome destructive trunk diseases that affect crops globally by, for instance, trunk injection, which could keep the plant under protection over years by slow sustained release mediated by the presence of fungi |
