Investigation of thermoplastic polymers with regard to their suitability as mold material in the FRP manufacturing process

Abstract

Context: The choice of material, manufacturing process, and molding tool significantly effects the quality, environmental impact, and cost efficiency of fibre reinforces polymer (FRP) components. Producing one-piece hollow profiles with smooth inner surfaces and undercuts presents major challenges for conventional mold concepts. A promising solution are shape memory polymers (SMP) as tooling material. Objectives: This study aims to identify thermoplastic polymers which are suitable as mold material in the FRP manufacturing process. The overarching objective is to develop an high-rate manufacturing process for onepiece FRP hollow profiles with undercuts. This process should omit residual cores, wash- or melt-out cores which are associated with dirt an multi-part cores. Methods: First a manufacturing and curing process for a FRP is introduced. From this, boundary conditions for the mold material are defined. An assessment of the properties of thermoplastic polymers from literature research is carried out. An evaluation matrix allows the preselection of three polymers. PET, PPS, PA6 and PA6.6 are further analyzed by DSC and DMA. The results are used to tune the manufacturing process. Results: Semi-crystalline thermoplastics are more suitable as mold material than amorphous ones. When heated above their glass transition temperature (Tg) the elastomeric state allows for one-piece demolding. The material properties of 31 semi-crystalline polymers are assessed. PET, PPS, PA6 and PA6.6 are found as most likely suitable as mold materials for the introduced curing process. Their Tg is evaluated by DSC and DMA. Conclusion: PET, PA6 and PA6.6 meet the process parameters of the defined FRP production process. Further research has to be carried out regarding their shape memory behaviour and demolding capabilities.