NaFiTech - Reliable use of natural fiber-reinforced thermoplastics in technical plastic components

Challenges, limits and potentials of natural fiber-reinforced plastics

The use of sustainable materials and substances is not only a decision with high ecological and social relevance, but also a strategic step.

With this in mind, one goal is to replace classically injection moulded, reinforced materials (e.g. short glass fiber-reinforced polymers (GFRPs)) with natural fiber-reinforced polymers (NFRPs). However, a direct one-to-one substitution is not possible in many applications.

Natural fiber-reinforced thermoplastics may differ from short glass fiber-reinforced plastics considerably. The mechanical properties are at a lower level and, as a result of the natural origin of the natural fibers, have a higher degree of fluctuation. Natural fibers have a higher thermal sensitivity, which must be taken into account during processing, and tend to produce more odors and emissions at higher temperatures. Furthermore, natural fibers are sensitive to moisture absorption. Their behavior under long-term loading in highly stressed applications and possible changes in material behavior due to external influences are also not yet sufficiently known. The scientific and technical literature contains studies on these dependencies using different examples of natural fiber-reinforced plastics. Solutions and approaches for the targeted optimization of individual properties can also be found. However, many of the approaches are still at an early stage of development, which is why natural fiber-reinforced polymers are currently still rarely used in structural components.

Therefore, it is necessary to know and understand the challenges, limitations and potentials of natural fiber-reinforced plastics. From this, suitable strategies can be derived to enable application-specific and requirements-oriented use of this class of materials.

The goal of the industrial joint project NaFiTech is to delop a solid database for evaluating the possibilities and perspectives of natural fiber-reinforced composites.

Project focus & approach

The joint project includes the following work items:

• Definition of representative requirement profiles for materials and components from the group of participants
• Research based on scientific literature and the market with regard to natural fibers from the national and European area, commercial natural fiber-reinforced plastics as well as application examples of components made of natural fiber-reinforced thermoplastics. The focus of this research is:
  • Available materials (polymer, fibers, possibly other additives)
  • Material properties
  • Fiber post-treatment
  • Process factors influencing material properties
• Comparison of the mechanical properties of commercially available short-fiber-reinforced NFRPs with short-glass-fiber-reinforced plastics based on different selected polymers (e.g. polypropylene (PP), polylactide (PLA), low-melting polyamide (PA)) with the aim of defining selected references (maximum 5) for a comparative evaluation of the material properties within the project with the following contents:
  • specification of the materials in consultation with the participants
  • provision of the materials by participants
  • production of test specimens
  • Characterization
    • Mechanical characterization
    • Gravimetric moisture absorption
    • Thermal properties (TGA, DSC)
• Production and testing of short natural fiber-reinforced plastics: In consultation with the participants, several campaigns regarding compounding and injection molding (approx. 60 variations) will be carried out iteratively to narrow down the relevant parameters and identify fundamental dependencies between composition, process variables and selected material properties.
  
  • Definition of the parameters to be investigated and experimental design:  based on research and test results, e.g. with regard to material/formulation (fiber type, volume fraction, fiber post-treatment, influence of selected other additives, etc.), process (processing temperature, speed, fiber dispersion)
  • Implementation of the test campaigns
    • Processing (fiber treatment, compounding, injection molding)
    • Characterization of the individual compounds
      • Mechanical characterization (quasi-static tensile tests)
      • Moisture absorption
      • Thermal resistance
    • Structural characterizations are carried out on selected compounds to derive structure-property relationships, e.g. microscopic examination of the interface (SEM) or fiber orientation investigations using CT
• Summary and evaluation of the results for natural fiber-reinforced plastic compounds:
  • Summary of the main factors influencing the mechanical properties of natural fiber-reinforced plastics as a function of thermal load and humidity and comparison with the jointly defined requirements profile
  • Assessment of the future potential of natural fiber-reinforced composites compared to short glass fiber-reinforced plastic compounds currently in use