Reactive Thermoplastic Prepregs

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Despite numerous positive properties, the application of thermoplastic matrices for fiber-reinforced polymer composites (FRPC) is hindered by at least one significant process-related drawback. The high melt viscosity of thermoplastics poses a technical challenge in rapidly and efficiently impregnating dry fiber structures, which intensifies with increasing width and thickness of the semi-finished product [1, 2]. To manufacture FRPC, the high-viscosity polymer must penetrate the smallest spaces between the fibers, wet them and simultaneously displace any existing air from the fiber structure. Any failure in completing these steps during the process negatively impacts the properties of the FRPC. In order to produce high-quality thermoplastic FRPC, high process temperatures and pressures are necessary, leading to correspondingly high equipment costs [2, 3]. To minimize polymer flow paths during processing, various semi-impregnated products are available on the market, ranging from partially impregnated powder prepregs to fully impregnated tapes. While the use of these semi-finished products may reduce processing time for manufacturers, the materials exhibit drawbacks in terms of drapability and cost efficiency [2, 4]. Additionally, the multiple melting cycles of the polymer during semi-finished product manufacturing and subsequent processing into the final component may even have a negative impact on the properties and the environmental footprint of the FRPC.

One approach to overcoming the challenges of thermoplastic impregnation is the use of reactive thermoplastic resin systems. These systems exhibit significantly lower viscosity than pre-polymerized thermoplastics, enabling a time- and energy-efficient impregnation of fiber structures. One such system is Arkema’s Elium® resin. It is a liquid acrylic polymer diluted with a reactive methyl methacrylate (MMA) monomer mixture [5, 6]. The system is available in multiple configurations, tailored to various manufacturing processes such as vacuum infusion, resin transfer molding (RTM), wet winding or pultrusion. By adding an initiator, the resin can be polymerized after impregnation by either temperature [7] or UV irradiation.

Based on the Elium® resin system, reactive glass fiber reinforced (twill weave, 580 g/m²) thermoplastic prepregs are manufactured and processed at Leibniz-Institut für Verbundwerkstoffe GmbH (IVW). Using two initiators provides the option to polymerize the resin with both temperature and UV irradiation. In the process route investigated at IVW, the prepregs are partially polymerized by UV irradiation, offering advantages in handling while providing flexibility in adjusting properties related to drapability and tack. The complete polymerization of multiple prepreg layers to a FRPC component is subsequently achieved by a hot pressing process. The first results indicate that high quality laminates in terms of impregnation quality, fiber-matrix adhesion and monomer conversion rate can be achieved from reactive prepregs. Prepolymerization exhibits a positive influence on the hot pressing process, with the exothermicity of the polymerization reaction decreasing as prepolymerization increases, thereby reducing the formation of pores due to resin overheating in the hot press tool. Currently, the effects of prepolymerization on prepreg and component properties are further investigated.

[1]        W. Obande, D. Mamalis, D. Ray, L. Yang and C. M. Ó Brádaigh, „Mechanical and thermomechanical characterisation of vacuum-infused thermoplastic- and thermoset-based composites“, Materials & Design, vol. 175, p. 107828, 2019, doi: 10.1016/j.matdes.2019.107828.

[2]        K. van Rijswijk and H. E. N. Bersee, „Reactive processing of textile fiber-reinforced thermoplastic composites – An overview“ (en), Composites Part A: Applied Science and Manufacturing, vol. 38, no. 3, p. 666–681, 2007, doi: 10.1016/j.compositesa.2006.05.007.

[3]        M. Hou, „Stamp forming of continuous glass fibre reinforced polypropylene“, Composites Part A: Applied Science and Manufacturing, vol. 28, no. 8, p. 695–702, 1997, doi: 10.1016/S1359-835X(97)00013-4.

[4]        F. N. Cogswell, “Thermoplastic aromatic polymer composites: A study of the structure, processing and properties of carbon fibre reinforced polyetheretherketone and related materials”. Oxford: Butterworth-Heinemann, 1992.

[5]        Technical Data sheet ELIUM® C595 E“, Arkema, 2023.

[6]        S. K. Bhudolia, P. Perrotey and S. C. Joshi, „Enhanced vibration damping and dynamic mechanical characteristics of composites with novel pseudo-thermoset matrix system“, Composite Structures, vol. 179, p.. 502–513, 2017, doi: 10.1016/j.compstruct.2017.07.093.

[Translate to English:] Prozesskette zur Prepregherstellung

[Translate to English:] Schliffbild eines mehrlagigen Laminats, hergestellt aus reaktiven Prepregs

[Translate to English:] REM-Aufnahme eines hergestellten Laminats nach kryogenem Bruch

Kontakt

M.Sc.

Andreas Krämer

Wiss. Mitarbeiter Press- & Fügetechnologien

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