Melt processing of wood cellulose tissue and ethylene-acrylic acid copolymer composites
Artikel i vetenskaplig tidskrift, 2013
The difficulty of feeding cellulose fibers together with the polymer into the melt processing equipment is a serious disadvantage for the production of cellulose-containing composites on a large scale. In the present work, a continuous method of feeding cellulose in the form of a tissue into a twin-screw extruder through an opening downstream of the extruder cylinder was studied. With this method, composites with different fiber contents were obtained. The tissues used were one made mainly of softwood fibers and another mainly of hardwood fibers. In order to better understand how to improve the fiber dispersion by melt mixing, a second extrusion was performed with a single screw extruder with a barrier-flighted screw and also with the twin-screw used to compound the tissue with the polymer. The compounds produced were then injection molded into test bars. The test bars containing the softwood tissue exhibited some fiber aggregates also after a second extrusion, whereas no fiber aggregates were observed in samples made with the tissue containing hardwood fibers and two passes through the twin screw. The fiber length was in general reduced by each melt processing stage and the shortest fiber length was observed after two extrusions with the twin-screw and injection molding. The tensile modulus increased with increasing fiber content. A higher stiffness was obtained with more softwood fibers in the tissue whereas more hardwood fibers gave a higher tensile strength and greater elongation at break.