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.