Structural changes in microfibrillated cellulose submitted to redispersion methods

Abstract

Microfibrillated cellulose (MFC) represents a material of great interest for several industries, such as composites, pharmaceuticals, electronics and many others. Due to its structure and size, it has different properties compared to macrofibers. However, drying causes aggregation of these particles, which makes it lose its unique characteristics. Therefore, the present study seeks to elucidate different approaches to MFC drying and to present possible drying methods. In the first article presented, the relationship between the number of drying cycles and temperature, and their consequent influence on the MFC structure was studied. The results show that the greater number of drying cycles and a higher temperature cause a greater aggregation in the MFC, growth of the particles, loss of stability in water and loss of mechanical properties. Once-dried at room temperature (20°C) was the most promising, with morphology and particle size close to never-dried MFC; which makes this treatment the most suitable when using the oven-drying method. In the second article, the presence of additives to aid redispersion of freeze-dried MFC was analyzed. The sample dried with no additive obtained the worst result, with great formation of aggregates, larger particle size and considerable loss in mechanical properties. The presence of sodium chloride helped the redispersion, but it still showed a considerable difference in relation to never-dried MFC. The use of the surfactant sodium dodecyl sulfate has assured redispersion to the point of being compared, in terms of morphology and structure, to never-dried MFC. Trace amount of the surfactant caused the mechanical properties to surpass the never-dried MFC, causing the treatment not only to carry out the redispersion but also the interaction between MFC and the surfactant to improve the properties.