Starch and cellulose being both carbohydrate polymers, thermoplastic starch (TPS) is expected to be a suitable compatibilizer for materials made of cellulosic fillers and polyesters. This paper investigates the interactions between TPS and cellulose in Poly(butylene adipate-co-terephthalate) (PBAT), melt-blended composites. For this, microfibrillated cellulose (MFC) were dispersed in a commercially available polymer (Mater-Bi, MB), containing TPS already dispersed in PBAT. Microscopic observations were performed on composites based on either MB or neat PBAT reinforced with microfibrillated cellulose (MFC). Tensile tests and dynamic mechanical analysis in solid and in the molten state revealed a percolating network of fillers. Results indicated interaction between TPS and cellulose as the origin of the adhesion of the components but also of biphasic agglomerates.
Dispersion in the melt is a very serious issue that affects properties of composites based on cellulosic fillers as these materials tend to form agglomerates. The aim of this study is to test the efficiency of various methods to improve the dispersion of cellulosic fillers in PBAT polymer. First, periodate oxidation treatment was carried out on the fillers in an attempt to reduce the amount of hydroxyl groups responsible of the agglomeration of cellulosic fillers in composite materials. Secondly, as several studies have demonstrated the positive effect of using tert-butanol (TB) as a freeze-drying medium for preventing the aggregation of cellulosic particles, this method was tested to produce composites with reduced amount of agglomerates. Finally, the addition of a third component as a compatibilizer which has a similar chemical structure to cellulose such as starch was also tested. No significant improvement of mechanical properties was noticed in using TB as a freeze-drying medium or with periodate oxidation treatment on the cellulosic fillers at least in improving dispersion in PBAT composites. However, the addition of starch as a compatibilizer has proved its effectiveness through the creation of a percolating network and a better dispersion of the fillers in the polymer matrix.
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