Technology for Wood and Natural Fiber-Based Materials

Research Project

BioFla – Halogen-free flame retardance for bioplastics and biocomposites in electronics and logistics

Products in electrical engineering, electronics and logistics must fulfil high flame-retardancy requirements. Furthermore, they must be heat resistant and impact resistant. The biomaterials currently available on the market do not satisfy these requirements. In this project, we are developing bioplastics and biocomposites which have the necessary properties and which can be processed by means of injection molding and 3D printing. Products such as light switches, sockets, motion detectors, cable ducts or charging stations for electric vehicles could soon be produced from biomaterials. 

A bundle of white and brown filaments lies on a piece of wood.
© Fraunhofer WKI | Manuela Lingnau
Flame-retardant bio-filaments for 3D printing.

As a first step, we are working in collaboration with the Fraunhofer IAP on the development of a halogen-free bio-flame retardant. In a second step, this will be reactively bound to the bioplastic polylactide (PLA). For its production, we will use sugar-based alcohol and will synthesize fully esterified organophosphoric acid esters. The phosphorus group is responsible for the flame-retardant effect. The contained acrylate or meth(acrylate) groups serve the binding to the PLA. The binding of the reactive flame retardants and the partial crosslinking of the PLA is achieved through electron irradiation.

By adding impact modifiers, we try to achieve the required impact strength. We also add wood fibers. Based on our research experience, we surmise that the wood fibers have a positive effect on heat resistance and flame retardancy. The heat resistance of PLA depends on its crystallization. Crystallization can be accelerated or increased by injecting into a hot tool and subsequently annealing. The faster crystallization occurs, the faster the workpiece can be ejected and the shorter the cycle time - which is of considerable economic importance in practice. In our tests, we determine the optimum crystallization time for PLA as well as appropriate processing conditions using flame retardants and wood fibers.

Parallel to the developments with self-synthesized flame retardants, we use commercially available flame retardants in the compounding of PLA and wood fibers. In addition, we are also examining further bioplastics: polyhydroxybutyrate (PHB), various polyamides (PA 6.10, PA 10.10 and PA 11) and polyethylene terephthalate (PET).

All the compounds are processed by means of injection molding and additive manufacturing (FDM) to form test specimens for the following tests: UL94, heat resistance, glow-wire test, tracking resistance, tensile strength and modulus of elasticity, impact resistance, water absorption and swelling. 

Testing apparatus in which a small bioplastic test specimen is clamped. The wire in contact with the specimen is white-hot.
© Hager Electro GmbH
Glow-wire test: A test specimen made from bioplastic is tested for flammability. A preheated glow wire thereby remains in contact with the test specimen for 30 seconds whilst various characteristic values are measured.
Testing apparatus with two electrodes touching a small test specimen made from bioplastic which is positioned in the center.  A drop-dispensing unit is suspended at a short distance above
© Hager Electro GmbH
Testing for tracking resistance: Two electrodes touch a test specimen made from bioplastic onto which a drop falls every 30 seconds.

Results (intermediate status)

During the first year of the project, it was possible to develop PLA-based formulations, extrude them into filaments and print them, thereby achieving the classification V0 according to UL94 at a test-specimen thickness of 1.6 mm. Flame-retardant PLA as well as a flame-retardant, wood fiber-reinforced PLA-PBS blend successfully withstood the glow-wire test at 960° C. With regard to tracking resistance, the flame-retardant, wood fiber-reinforced PLA-PBS blend achieved at least 175 V; in a single test, 200 V and 250 V were also achieved. Flame-retardant PLA without wood content achieved 600 V. 

The heat distortion temperature of the flame-retardant, printed and annealed test specimens reaches values of over 100° C, according to initial tests. In contrast, unfilled, annealed PLA test specimens exhibited severe deformation as early as during annealing. The addition of flame retardants and/or wood fibers therefore improves not only the flame-retardant effect but also the heat deflection temperature of PLA.

With regard to bio-based PA 6.10, PA 10.10 and PA 11, formulations with the classification V0 (UL94) at a thickness of 1.6 mm have also been developed.

In the second year of the project, we will conduct investigations with PHB and PET as well as the new bio-flame retardant. In cooperation with our project partners from industry, the formulations will then be compounded on a larger scale and processed for applications in electrical engineering and electronics (E&E) and logistics. 

Project partners

  • Fraunhofer IAP
  • Clariant Plastics & Coatings (Deutschland) GmbH
  • Linotech GmbH
  • Hesco Kunststoffverarbeitung GmbH
  • Kabel Premium Pulp & Paper GmbH
  • Hager Electro GmbH
  • BGS Beta-Gamma-Service GmbH & Co. KG
  • Rettenmaier & Söhne GmbH
  • Georg Utz GmbH

Funding

Official project title: Erschließung von neuen Anwendungen für Biokunststoffe und Bioverbundwerkstoffe in Elektronik und Logistik unter Verwendung von halogenfreien Flammschutzsystemen  

Funding body: German Federal Ministry of Food and Agriculture (BMEL)

Funding reference: 22022717

Project management: Fachagentur Nachwachsende Rohstoffe e. V. (FNR)

Duration: 1.2.2019 to 31.1.2022

Funded by the Federal Ministry of Food and Agriculture by decision of the German Parliament
Fachagentur Nachwachsende Rohstoffe e. V. (Agency for Renewable Resources)