From Science & Research
From Science & Research Biobased filler for SMC Introduction and motivation: In the market of glass-fiberreinforced polymer composites (GFRPC), Sheet Molding Compound (SMC) has high market relevance, as 20 % of all the glass fibers produced in Europe are handled in SMC processes [1]. Normally, SMC consists of a highly filled thermoset resins system, mostly based on unsaturated polyester resin, glass fi-bers, application specific additives and filler materials, see Figure 1. SMC is, based on its me-chanical properties, predestinated for the use in semi-structural parts or hang-on parts – e.g. for automotive applications. By a variation of the specific additives and the directly linked change of the composition of the semi-finished product, the scope of application can be diversified. The properties of the material itself can be changed from e.g. electrical applications for cabi-nets to parts with an equal thermal expansion coefficient as steel. Further advantages of the material are the advantageous price for the semi-finished product and the possibility for cost-efficient large-scale processing of the material in a parallel regulated compression molding pro-cess. Project approach: In a standard SMC, based on UP resin systems, approximately 40 % of the total weight of the SMC semi-finished product consists of mineral filler materials (Figure 1). These fillers can be divided into functional filler materials, e.g. aluminum hydroxide (Al(OH)3 as flame retardant with a density of 2.4 g/cm³) and non-functional filler materials, e.g. calcium carbonate ((CaCO3) with a density of 2.71 g/cm³). Within the scope of this research work, which was carried out at the Institute for Composite Materials (IVW) and the Institute for Bio-technology and Drug Research (IBWF) (both Kaiserslautern, Germany), the use of renewable and biobased filler materials replacing conventional filler materials was examined. Here, attention was paid to the fact that the biobased materials are a by-product of food industry and for-estry and should not be in direct contradiction. As biobased filler materials, wood flour out of regional soft- and hardwood, rapeseed meal, rice hulls and sunflower hull meal were used. The different fillers were subjected to different test series regarding their density, particle size distri-bution, dispensability, wettability, influence to resin paste viscosity and their tendency to fungus growth. This work will show an extract of the results which were achieved using grinded sun-flower hulls as a filler material for a standard SMC. In different test series, the non-functional filler material was replaced by an increasing proportion of biobased filler materials. Hereby, the focus was on the processability of the semifinished products. The semi-finished products should be processable with a conventional SMC production line and pressed with a conven-tional press cycle, see Table 1. Liquid components Figure 1: Composition of a typical SMC formulation (data in weight percent) Production and processing of SMC with biobased filler materials: The production of the SMC resin paste was carried out on a laboratory scale circular disc dissolver. The amount of biobased filler materials, replacing conventional filler materials, was raised in different test se-ries by steps of 25 %. The resin paste was processed to a SMC semi- Thermoplastic additiv 8 % UP-resin 15 % Glass fibers 30 % Application specific additives 7 % Filler materials 40 % Powedery compomets 34 bioplastics MAGAZINE [03/18] Vol. 13
From Science & Research By: Florian Gortner 1 ; Anja Schüffler 2 , Jochen Fischer 2 , Peter Mitschang 1 1: Institut für Verbundwerkstoffe GmbH (IVW) 2: Institut für Biotechnologie und Wirkstoff-Forschung gGmbH (IBWF) (both) Kaiserslautern, Germany finished material on the institutes’ own SMC production line under industry-oriented processing parameters. After a maturing time of 4 to 6 days, the semi-finished material was processed to specimen plates with conventional SMC processing parameters, see Table 1. Fungus/microorganism growth testing: All material samples with differing biobased filler concentrations were cut into square pieces (15 x 15 mm). The samples were photographed using a reflected-light microscope and afterwards incubated in microbiological growth medium inoculated with a Trichoderma species (Figure 2 A1), a mixture of airborne organisms (Figure 2 A2) and a standardized humus soil (Figure 2 A3), respectively. All samples were incubated at 27°C in a laboratory incubator at 40 rpm to ensure oxygen supply. The samples were surface-analyzed for possible degradation after 6 weeks. Additionally the square pieces were incubated based on the “Mildew Resistance Test Procedure GMW3259” but incubation temperature was 37 °C, 45 ml PS tubes with lamella stopper as containers and supports made of plastic were used. Results of mechanical properties and density reduction: By the replacement of the con-ventional non-functional fillers with biobased fillers, a reduction of the density of the semi-finished products up till 9,4 % could be realized. The mechanical properties given in this work were determined on tensile test according to DIN EN ISO 527-4 specimen type 2 (250x15x4 mm³) and decrease slightly with increasing share of the biobased filler materials. With a content of biobased filler materials of 75 %, Young’s modulus was decreased by 18 %, tensile strength was decreased by 20 % (Figure 2). Taking the specific mechanical properties into account, the new materials are very well comparable to standard SMC. Results of fungus/microorganism growth testing: Although the cut edges of all material samples were covered with a biofilm (Figure 2 C) in the cultures inoculated with Trichoderma, airborne microorganisms and humus soil sample, no degradation was observed even when 100 % biofiller were used (exemplarily a sample with 75 % bio-filler is shown before (Figure 2 B) and after incubation with airborne organisms for six weeks (Figure 2 D)). Furthermore, the mate-rial samples incubated based on “GMW3259” did not possess any fungal growth nor moldy odor after two weeks. Conclusion: The good mechanical results and the biological durability show that the use of biobased materials as filler materials for SMC is a realistic option. By using a former by-product of food industry or forestry as a raw material in a composite material an ecological useful upcycling is enabled. www.ivw.uni-kl.de | www.ibwf.de Table 1: Processing parameter for the production and processing of SMC Figure 2: Influence of the biobased filler materials to the mechanical properties according to DIN EN ISO 527 Manufacturing: 14.000 — Tensile strength Young‘s Modulus — 100 Resin paste viscosity for the processing on a SMC-line Processing: 15 – 45 Pa∙s Tool temperature 135 – 145 °C Cycle time approx. 1 min per mm thickness of the part Pressure inside the mold 100 – 120 bar Young‘s Modulus [MPa] 12.000 — 10.000 — 8.000 — 6.000 — 4.000 — 2.000 — 0 — 100 % CaCO 3 0 % bio-filler 75 % CaCO 3 25 % bio-filler 50 % CaCO 3 50 % bio-filler Variation of filler materials — 100 — 80 — 60 — 40 — 20 — 0 25 % CaCO 3 75 % bio-filler Tensile strength [MPa] A B C D 1 2 3 Figure 3: Material samples incubated with Trichoderma sp. (A1), airborne organisms (A2) and humus soil (A3); magnification of a sample with 75 % bio-filler before (B), with biofilm after (C) and washed after incuba-tion with airborne organisms for 6 weeks bioplastics MAGAZINE [03/18] Vol. 13 35
