'Yes' to natural fibers, 'no' to drying them

Natural-fiber reinforcements can prove an inexpensive, lightweight, and ecologically friendly alternative to conventional reinforcing materials. However, these materials’ users usually need a solution to handle the high moisture content in the fibers, typically necessitating pre-drying (both expensive and time-consuming) before the fibers can be used.

But extruder manufacturer KraussMaffei Berstorff (Munich, Germany), working together with the Hanover (Germany) University of Applied Sciences, says it has developed a twin-screw extruder that helps eliminate these fibers’ drawbacks. The patented Berstorff Multi-Process-Elements (MPE) technology is said to ensure gentle and cost-effective incorporation of the natural fibers. In addition, MPE allows the line to be tailored to the moisture content of the material to be processed, be it wood flour, wood fibers, flax, hemp, rice husks, or palm fibers. An additional advantage, says the company, is that by eliminating the need for pre-drying, the risk of explosion is eliminated.

As KraussMaffei Berstorff describes the process, first polymer is introduced into the feed zone by gravimetric dosing equipment and melted in the plasticizing zone. In addition to the polymer, various additives are fed into the feed section to improve material properties. The natural fibers are supplied via downstream side feeders and incorporated into the melt by means of the MPEs. Openings arranged along the processing section help remove moisture released from the natural fibers. After these have been mixed in, the melt is degassed under vacuum to further remove moisture and volatiles. During a final step, the melt pressure is built up and it is sent through the die. —[email protected]