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Remarkable enhancement of the stability against aging of nanocellulose films by the incorporation of boron compounds
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Resumo(s)
Sulfated cellulose nanofibril (S-CNF) films are promising sustainable materials, yet their properties can deteriorate under moist-heat exposure, limiting their long-term performance. Here, the aging behavior of S-CNF films at 80 °C and 65% relative humidity was investigated and the addition of sodium borohydride (NaBH4) as a chemical stabilization strategy is proposed. Neat S-CNF films underwent rapid acidification and cellulose depolymerization with aging, with pH decreasing from 3.7 to 1.9 and the degree of polymerization (DP) of cellulose dropping from 569 to 80 after only two days of aging. Concomitant changes in crystallinity and morphology were observed, which together culminated in the deterioration of several properties after eight days of aging, including a tensile strength reduction from 123 to 3 MPa and very high color changes (∆E = 39.6). These poor results were attributed to hydrolysis of sulfate ester groups, which intensified acidification, thus leading to accelerated cellulose chain scission and chromophore generation reactions. In contrast, NaBH4 addition resulted in films with a buffered pH of ca. 9, which suppressed cellulose depolymerization (DP going from 801 to 761 after eight days of aging) and preserved the chemical and microstructural integrity of the films during aging. Consequently, the NaBH4-treated films showed a superior mechanical performance (tensile strength of 39 MPa) and exhibited minimal color changes (∆E = 1.7) after aging. Overall, NaBH4 addition prior to film formation effectively improves the resistance of S-CNF films against moist-heat aging, extending their applicability for long-term and high-performance applications.
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Palavras-chave
Accelerated aging Cellulose degradation Cellulose nanopapers Deep eutectic solvent Sodium borohydride Sulfation General Chemistry Environmental Chemistry Biochemistry General Chemical Engineering Polymers and Plastics Materials Chemistry