Biopolímeros à base de ágar com adição de nanofibras de celulose e nanoplaquetas de grafeno

Abstract

Agar stands out as a promising biopolymer for the production of sustainable polymeric films; however, it presents limitations in some physicochemical properties. The incorporation of nanoparticles, such as nanocellulose and graphene, has emerged as a strategy to improve the performance of these materials. Despite the potential of these combinations, comparative studies systematically evaluating their effects remain scarce. In this context, the development and investigation of these composites are relevant for advancing new sustainable, highperformance materials. The aim of the present study was to develop sustainable agar-based polymeric films and incorporate different concentrations (0.5, 2, and 4 wt%) of cellulose nanofibers (CNF) and graphene nanoplatelets (GNP) as reinforcing fillers. The films were produced by the casting method and characterized regarding their properties, with statistical analysis of the results. The films containing graphene exhibited a darker appearance, whereas nanocellulose did not alter the visual appearance of the films. Optical microscopy and SEM analyses revealed dense, pore-free structures, with CNF showing generally good dispersion despite the presence of some aggregates, while GNP exhibited a more heterogeneous distribution with a tendency toward agglomeration. Film thickness was not influenced by CNF addition but increased with GNP incorporation, presenting higher values than CNF-containing films at concentrations above 0.5 wt%. Film coloration increased with the addition of nanofillers from 2 wt% for CNF and 0.5 wt% for GNP, with a more pronounced effect for GNP. Transparency decreased as the concentration of both nanofillers increased, with GNPcontaining films exhibiting lower transparency values. The swelling degree was not affected by CNF incorporation but increased with the addition of 4 wt% GNP. Contact angle values generally decreased with CNF, indicating greater hydrophilicity, and increased with GNP, suggesting enhanced hydrophobicity. Surface energy showed no significant variation with the incorporation of either nanofiller. Water solubility decreased with GNP addition up to 2 wt%, with the film containing 0.5 wt% GNP presenting lower solubility than CNF-containing films, while CNF did not significantly affect this property. FTIR analysis indicated the formation of more stable structural networks through hydrogen bonding and physicochemical interactions between the polymer matrix and the additives. The addition of nanofillers reduced the tensile strength and elastic modulus of the films, whereas elongation at break remained unchanged. Films reinforced with CNF exhibited higher tensile strength than those containing GNP at 0.5 wt%, greater elongation at break, and lower elastic modulus at concentrations above 0.5 wt%. Thermal analyses (TGA and DSC) demonstrated improved thermal stability in nanofillercontaining films, evidenced by shifts of degradation and transition peaks toward higher temperatures. Water vapor permeability was not affected by the incorporation of nanofillers. Graphene exhibited antimicrobial activity against Escherichia coli and Staphylococcus aureus. Shelf-life testing demonstrated the stability of the films over time. Accelerated weathering exposure indicated that the photochemical stability of agar films was enhanced by the incorporation of nanofillers, particularly graphene. Biodegradability tests showed that the addition of nanofillers did not impair the biodegradable nature of the films. Comparing the two reinforcing nanofillers, CNF addition is promising for applications requiring preservation of the original film appearance and greater flexibility. In contrast, GNP stands out due to its lower opacity, reduced water solubility, antimicrobial activity, and superior protection against UVinduced degradation. [resumo fornecido pelo autor]