Identification of suitable Parameter Combinations for the Production of flax-fiber-reinforced Organic sheets

The Project Durobast – Durable and resource-saving composite structural components based on novel pretreated and processed bast fibers (funding reference: 2220NR090C) – pursues a holistic approach for the development and the production of bast fiber-reinforced polymer composites. Primary objective is the selection of locally available natural fibers (particularly hemp fibers cultivated in Germany) and pretreatment to reduce moisture absorption. The project follows the entire process chain from fiber selection and pretreatment to yarn and textile as well as to the production of semi-finished products, so-called organic sheets, and component manufacture.

One research focus at Leibniz-Institut für Verbundwerkstoffe (IVW) is the production of natural fiber-reinforced organic sheets (NF-OB). The impregnation behavior of bast fiber fabrics with different thermoplastic matrix polymers is investigated on a laboratory scale in order to identify suitable process parameter combinations for production on an industrial scale. In addition, different variants of combination of textile and polymer are considered – film stacks and powder prepregs, but also hybrid yarns and hybrid fabrics. The selection of suitable parameter combinations for NF-OB production is particularly crucial with regard to process temperatures. On the one hand, a sufficiently high temperature must ensure complete impregnation of the fibers with the matrix polymer. On the other hand, individual fiber components decompose when certain temperatures are exceeded. Increasing process pressures facilitate macro impregnation but also reduce the onset temperatures of this behavior. In addition to reducing the mechanical properties, this decomposition also influences the formation of odors by the fibers. Especially for interior applications in the automotive industry, odor formation must be prevented.

IVW’s investigations form the basis for the production of NF-OB on an industrial scale with continuous hot pressing processes. The flat thermoplastic semi-finished products can be transformed into the final part geometry by using efficient thermoforming processes. Optimization of the forming process can be achieved by process simulation. For this purpose, the characteristic drape behavior at the process temperature is determined in shear tests and simulated in a FE-model. This minimizes the experimental effort and thus the material input.

Durobast project is funded by the Federal Ministry of Food and Agriculture on the basis of a decision by the German Bundestag (funding reference: 2220NR090C).

Project partner:

• Fraunhofer LBF
• Institut für Textiltechnik (ITA) der RWTH Aachen
• Nova-Institut GmbH
• Eta Ressourcenmanagment
• Hübner GmbH & Co. KG
• Wagenfelder Spinnereien
• DST Dräxlmeier Systemtechnik GmbH
• Lehrstuhl für Werkstoffprüftechnik (WPT) der Technischen Universität Dortmund
• Rhenoflex GmbH
• Silbaerg GmbH
• Gustav Gerster GmbH & Co. KG