IMPROVING THE DISPERSIBILITY OF CELLULOSE MICROFIBRILLATED STRUCTURES IN POLYMER MATRIX BY CONTROLLING DRYING CONDITIONS AND CHEMICAL SURFACE MODIFICATIONS

摘要

The aim of this paper was to investigate some possibilities to improve the compatibility of cellulose microfibrillated structures at the fibre-polymer matrix interface level, when they are used as reinforcement in polymer composite materials. The cellulose microfibrillated structures isolated from bleached softwood pulp by chemical-mechanical methods were subjected to surface modification by acetylation, aiming to reduce their hydrophilic character. Fourier transform infrared spectroscopy (FTIR) analyses indicated the acetylation of the hydroxyl groups of cellulose; the increase of the elastic modulus of the polymer composite materials was due to the good dispersion of the surface modified cellulose microfibrillar elements in the polymer matrix. Another method that was tested to reduce the hydrophilic character of cellulose microfibrillated structures in contact with a polymer matrix was the spray drying, using the atomization of cellulose microfibrils. This method produces particulate materials with unchanged size and very good potential as reinforcement in composite manufacturing, utilizing conventional thermoplastic compounding techniques. The improvement in the mechanical properties of the composites reinforced with spray dried cellulose microfibrillar elements shows that this drying method is the most suitable for cellulose fibres that are used as reinforcement in hydrophobic polymer matrix, because this procedure reduces the advanced irreversible hornification phenomenon, which occurs during the oven drying process.