Effect of processing conditions and functional silica/lignin content on the properties of bio-based composite thin sheet films

Functional silica/lignin dual fillers were obtained via mechanical grinding of the components (Syloid 244 silica and kraft lignin). The novel bio-component dual fillers were characterized with its dispersive-morphological and thermal properties. SiO2/lignin hybrids with different biopolymer content were used as a bio-based additive into the film grade, low density polyethylene. The composites with 2.5%, 5% and 7.5% by weight of SiO2/lignin were melt mixed via co-rotating twin screw extruder. Thin sheet films were produced with single screw extruder and chill roll device equipped with air knife. For the measurement of the seal strength, the impulse heat sealer was applied and the seal strength of welded sheets was tested. Mechanical tests performed on specimens cut from extruded films revealed, that a drawing speed during film forming is the key parameter to enhance the material strength during film preparation. Moreover, it was noticed, that addition of dual fillers influences the mechanical properties of films for samples prepared with the highest chill roll speed. The highest tensile strength in machine-direction (MD) orientation was reported for composite filled with 2.5% of hybrid filler with silica/lignin content (10:1 wt/wt.). Tensile test of welded joints showed that films prepared from composites revealed slightly lower sealed properties compared to films obtained from original PE-LD.