Liquid acrylic thermoplastic composites make advances
Arkema is advancing its Elium liquid acrylic thermoplastic technology for molding composite parts with mechanical properties similar to thermoset composites, but with the weldability and recyclability of conventional thermoplastics. The latest grade addition to its portfolio, FC703T, boasts a cure time of three minutes at 150°C for prepreg compression molding of a carbon fiber-reinforced part measuring 1 x 1 m in area and 3 mm thickness.Arkema’s Cledat: Liquid acrylic-based composites are inherently recyclable.
The acrylic composite part also features enhanced toughness. And according to Guillaume Cledat, Business and Development Manager for Elium at Arkema, the net-shape part generates no scrap but features superior weldability without the surface activation required for conventional thermoset SMC components. The Elium material can also endure E-coating at 200°C for 40 minutes, making it suitable for use in automotive structural parts. Grade FC703T also delivers a shelf life of four weeks at room temperature.
Elium MC grades, meanwhile, can readily be thickened with magnesium oxide in sheet molding compounds to improve surface smoothness and fire retardancy. A processing aid package is available from BYK Chemie for this purpose and processing times are reportedly faster than those achievable with unsaturated polyester resins. The volatility of the MMA monomer is, however, higher than that of styrene and processors are thus advised to check the efficiency of their carrier films to block emissions.
Arkema has also joined forces with French processor Mäder Composites and French filament winding equipment provider MF TECH to develop a resin system, especially for the filament winding process. The system employs Elium 591 and a UV initiator from Mäder’s Nucorad range together with a peroxide. The resin is continuously pre-gelled via UV irradiation while winding, then post-cured, typically at 30 min/cm @80°C.
The technology has been employed for fabrication of a 60-L carbon fiber composite pressure vessel. Winding speed is 1 m/sec, and the pressure vessel features higher toughness and impact resistance, lower crack propagation, and improved durability.
Elium technology also lends itself to recycling. Composites parts made from Elium can be easily ground and then compounded with thermoplastic resins such as ABS, whose properties can be enhanced by the recycled material. Polycarbonate, acrylic resin, and some polyesters are also suitable for such usage.
The resin can also be depolymerized into recycled monomer that can then be reused in virgin Elium resin production. To further such technology, Elium is part of a 13-company consortium that plans to design a recycling process and construct a 30,000-tonnes/year acrylic resin depolymerization plant to be operated by Dutch recycler Heathland. The plant is scheduled for commercial operation soon after 2022.