TECHNOLOGY | WOOD-PLASTIC COMPOSITES
Nevertheless, the weaknesses of WPC and NFC
remain impact strength and water uptake, particu- larly for outdoor applications. “We try to overcome these by using different types of fibres or even employing hybrid formulations with more than one type of fibre in the compounds,” says Haider. “Other hot topics are the circular economy, where there are issues of recycling and/or reuse of these materials as they contain more components. Increasingly, the need for home compostability is being requested for many applica- tions. This can be addressed by using degradable biopolymers and bio-based additives. However, it must be considered that such materials should also run several cycles
before they are composted, because significant amounts of energy is needed to produce them.
Finally, for injection moulding and 3D-FLM
printing, simulation of material processing behaviour as well as performance is of great
Above: Fraunhofer WKI developed these injection moulded vegetable crates that contain up to 25% wood fibres
interest at present, but has not yet been solved.” Wood KPlus says it has developed formulations for physical and chemical foaming to produce extruded profiles and pellets for injection mould- ing. Some success has also been achieved in the simulation of processing steps in collaboration with partners, but without suitable correction factors this is not yet considered to be sufficient.
Packing performance Germany’s Fraunhofer WKI (Institute for Wood Research) recently developed a crate for transport and storage of vegetables comprised of up to 25% wood fibres. Researchers claim the new crates are more sustainable, lighter and sturdier without increasing production costs. In the future, they intend to transfer the expertise in materials research and injection moulding technology to other products. The project aimed to create a replacement for conventional crates, which are made from PP, that made use of the highest-possible proportion of renewable raw materials. Both wood and cellulose fibres fulfilled this criterion, were regionally readily available and are relatively inexpensive. In addition, the use of wood fibres makes the crate lighter. “If we consider the entire life cycle of the vegetable crate, the majority of the emissions are not created during the production of the material or through disposal, but during the use phase due to repeated transport. The transportation of lighter vegetable crates would therefore be an advantage, as less carbon dioxide would be produced,” says Chris-
60 COMPOUNDING WORLD | June 2020
toph Habermann at Fraunhofer WKI. During the development of the material, Haber- mann and his team not only took into account environmental aspects but also improved a number of application properties, such as stacking capabil- ity and resilience. “We are experts in materials research and innovative injection moulding processes, both of which are hugely influential factors,” says project member Carsten Asshoff. “With the aid of computer simulations, for example for strength simulation, we are able to optimise the production time and the product quality. The vegetable crates are a good example. Through the wood fibres, the strength and rigidity of the crates is increased. As a result, the wall thicknesses could be reduced and the internal volume increased. Users could benefit from lower transport costs.” The researchers examined the entire life cycle of
the crates. “We can only achieve real sustainability within the packaging industry if we also take further use and recycling into account when addressing the material composition,” says Habermann. “Wood fibres are better suited for this than, for example, glass fibres, which are to some extent also com- bined with polypropylene. Vegetable crates made from wood-fibre-reinforced plastic can be melted down to make new transport containers.” The advantages of the new materials are not limited to vegetable crates; many other versatile possible applications are foreseen. “Our tests have been very successful and the acquired knowledge can, theoretically, be applied to all types of reusable containers and transport crates as well as all kinds of injection moulded parts,” Asshof says. “Further- more, it would also be conceivable to use the materials for disposable products, such as shampoo bottles. In the future, customers could then buy their organic shampoo in organic packaging.”
Additive options Additives to improve the performance and process- ing of wood-plastic composites have been essential to their continued development and more wide- spread use. Among the companies that are active in this area is Struktol, which has expanded its line of lubricants, as well as introducing a new coupling agent and additive to fortify capstock compounds for the wood-plastic composite market. The new Struktol TPW 813 coupling agent is said
to offer superior properties to traditional products. In addition to providing good flexural properties, it is said to be especially effective in reducing water absorption, resulting in a much more durable product that can withstand many more wetting and freeze-thaw cycles. TPW 813 can be used with any
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IMAGE: FRAUNHOFER WKI
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