Characterization and foaming of cellulosic nano/macro filler reinforced styrene maleic anhydride (SMA) composites

Natural filler-based composites have generally been reinforced using various forms of fillers in polymer matrices, but the resulting composites typically exhibit high densities. For improving this attribute, composites can be foamed to decrease their density by using different blowing agents (chemical or physical agents). In this study, styrene maleic anhydride SMA was used as a polymer matrix (ratio of using is at %66). The grafting ratio of maleic anhydride in SMA was 10%. Wood flour, starch, ?-cellulose, microcrystalline cellulose and cellulose nano fibrils as reinforcing agents in the polymer matrix were added at 30% filler loading. The lubricant loading of 4% was also used in preparing the composites to prevent sticking during reactive extrusion. After the materials were dried, SMA was mixed with nano/macro fillers through extrusion compounding. During the extrusion mixing process, the polymer-reinforcing material melts were foamed using the water by-product which is obtained from the esterification reaction between maleic anhydride and the hydroxyl groups of the cellulose. The water by-product initially started the bubble formation (cell nucleation) and with completion of mixing, provided growing of bubbles in the composite melt. The resulting bubbles continued to grow with the help of low pressure as the composite exited the foaming die. After the cooling process, the SMA matrix thermoplastic composites were produced at 60 rpm for 220oC with twin screw extruder. According to the results obtained, the best foaming was determined for starch reinforced SMA composite. Whereas it can be found that microcrystalline cellulose-SMA composite was partially foamed after extrusion. This status was found to cause since microcrystalline cellulose which has high crystallinity (about %80) cannot adequately react. According to expansion ratio, the best result was found to starch-SMA composites. Scanning electron microscopy results demonstrated that the foamed cell distribution is heterogeneous and composed of two sections. It was found that there are cells with different diameters and dimensions in the center of the sample and the cell size and dimensions through core decreased, but amount of cells increased through the skin of the sample. As seen as mechanical properties and thermal analysis, properties of the all SMA matrix composite were found to be low as compare with pure SMA polymer composites.