Micro-ondas como um método alternativo para a oxidação de celulose bacteriana

Abstract

Bacterial cellulose (BC) is a natural polymer whose specific properties enable its application in a multitude of different areas, mainly for high value products. Chemical modification can introduces new functionality to the material, increasing its potential for specific applications. In this context, sodium periodate oxidation is a popular and simple chemical modification that generates 2,3-dialdehyde cellulose. However, the process is often quite long. As a means of optimizing the process, microwave radiation was applied as a heat source to reduce reaction times and the products chemical and physical properties were evaluated. BC membranes were oxidized with two concentrations of NaIO4 (0.75% or 1%) under controlled conditions of time and temperature. Microwave oxidized CB was characterized by SEM, FTIR, TGA and XPS and by determining oxidation degree and the results obtained were contrasted with oxidized CB under conventional thermal heating. Results demonstrated that microwave-assisted oxidized membranes had oxidation levels significantly higher than those oxidized in a water bath under the same conditions. The use of a high concentration of NaIO4 and microwave irradiation allowed to convert 73% of the cellulose in 30 minutes. FTIR and XPS confirmed that the microwave-assisted oxidation was effective, for there was formation of aldehyde groups in the polymer’s structure. XPS also exhibited an additional formation of carboxylic acids for all samples, indicating a second oxidation of aldehyde groups. TGA indicated that microwave oxidized CB has better thermal stability than its convencionally oxidized couterpart. SEM images reported less degradation of CB microstructure in microwave oxidized samples than conventionally oxidized samples. Ultimately, microwave-assisted oxidation is a good vehicle for the modification of bacterial cellulose, generating greater oxidation in the same intervals of time, temperature and oxidizing agent concentration compared to conventional oxidation.