Energy-efficient manufacturing with SMCs

Composite material Hemp fiber replaces fiberglass in many applications

2024-09-30 Source: | Translated by AI 3 min Reading Time

Hemp fibers instead of fiberglass: Biogenic residues can replace synthetic fibers in Sheet Molding Compounds (SMCs), whose manufacturing process is energy-intensive. The Fraunhofer IWU Zittau and Zittau/Görlitz University of Applied Sciences are researching which biological alternatives to fiberglass in composite materials are feasible.

Close-up of a component made from natural fiber SMCs (interior trim panel). The fiber orientation and the geometric freedom allowed by the material are clearly visible.(Image: Fraunhofer IWU) — Close-up of a component made from natural fiber SMCs (interior trim panel). The fiber orientation and the geometric freedom allowed by the material are clearly visible.
(Image: Fraunhofer IWU)

Sheet Moulding Compounds (SMCs) are long fiber-reinforced semi-finished products used to produce complex molded parts with high surface quality through the compression molding process. The applications for SMC components are diverse: they serve as interior linings in trains and railways, exterior cladding for trucks and agricultural machinery, or protect electrical distribution boxes and switchgear.

Gallery

Dr. Rafael Cordeiro is researching composite materials with natural fibers at the Fraunhofer IWU in Zittau.(Image: Fraunhofer IWU)

Coarser hemp fibers on the conveyor belt before defibrillation and bonding with the matrix.(Image: Fraunhofer IWU)

Dr. Rafael Cordeiro is a research associate at the Fraunhofer Plastic Center Oberlausitz and involved in the LaNDER³ project at the Zittau/Görlitz University of Applied Sciences. He specifically works on train interior linings where glass fibers are replaced with natural fibers combined with resin. Hemp, specifically the coarser fibers that are a byproduct of textile production using hemp, serves as the natural fiber. The natural fiber content in the newly developed SMC is about 15 percent; with the planned use of bio-based resin as the matrix, the component in which the fibers are embedded, the "natural" portion is expected to rise to up to 38 percent in the future. Additionally, 55 percent of the composition comprises minerals such as calcium carbonate (known as limestone or chalk) or hydrated aluminum hydroxide, which naturally occurs as bauxite. The remaining 7 percent are predominantly petrochemical additives, for which there is currently no bio-based replacement.

High humidity as a challenge for production

A challenge for production is that natural fibers particularly absorb moisture, and in countries with high humidity, preliminary drying may be necessary to prevent blister formation. Blister formation also depends on the impregnation. Dr. Cordeiro stated, "The natural fiber SMC is developed in such a way that only very minor additional equipment investments and minimal changes in process parameters are required for the production of larger quantities."

Energy consumption in manufacturing

In the production of semi-finished products and components by compression molding, there are no significant differences in terms of processes and energy requirements between natural fiber and glass fiber SMCs. The production of semi-finished products occurs at room temperature, which results in relatively low energy demand for the facility. The forming of components takes place in a hot pressing process in hydraulic presses, at temperatures between 110 °C and 150 °C. This temperature range is lower than that for thermoplastic components and does not require cooling or heating cycles of the tools, which has a positive impact on energy requirements.

Impacts on humans and the environment: Reduced skin and respiratory irritations

Like all plastic products, there is a possibility of microplastic formation through abrasion in these materials as well. However, the natural fiber SMCs developed at Fraunhofer IWU in Zittau are intended for applications where intensive abrasion does not occur. The substitution of glass fibers with hemp fibers reduces skin and respiratory irritations among employees involved in material and product manufacturing, as well as when handling damaged parts or during disposal. In addition, the production of hemp fibers results in lower CO2 emissions compared to glass fibers, significantly reducing environmental impacts.

The typical lifespan of natural fiber SMCs is up to 30 years, depending on whether the material is used for indoor or outdoor applications. For instance, weather resistance can be enhanced by adjusting the matrix resin specifically.

Biodegradability, recyclability

Similar to conventional SMCs, natural fiber SMCs cannot be recycled. Although they are not entirely biodegradable, promising experiments are underway to separate the natural fiber from the matrix and filler, allowing the natural fiber component to be composted and the filler to be reused. After separation, the fibers are too small to be reused in SMC applications. Further research is needed to explore the technological reuse of the extracted short fibers.

Dr. Rafael Cordeiro: "The sustainability record of natural fiber SMCs is not perfect yet. But it is already much better than that of fiberglass-reinforced composite materials. The material costs are also right. Thus, the alternatives to traditional fiberglass SMCs that we have developed are definitely marketable. Manufacturing more sustainable SMC components is possible."

“This article was first published on our sister portal "konstruktionspraxis" (German Edition), Vogel Communications Group.“

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