TECHNOLOGY | WOOD PLASTIC COMPOSITES
Right: A 3Dprinted sample produced at Fraunhofer WKI for evaluation in construction and building applications
variable in [coloured] compounds could be different additives [such as] the amount of additive for UV stabilisation. UV resistance is one of the primary requirements of the product standard and the complete range of different com- pounds used must be considered in the evaluation,” he says. Recycled plastics can potentially have
more variability than virgin plastics, which is another consideration in testing. “A trend that we’re seeing in the use of recycled plastics is manufacturers getting into the plastics recycling business to gain greater control over the materials they use in their products,” says Wagner. One of the most challenging requirements for WPC decking is the structural performance needed for use as stair treads, says Wagner. “This is primar- ily due to a deflection limit under a 300lb concen- trated load required in ASTM D7032. Manufacturers often need to limit stair tread spans to something less than what you’d find in typical deck construc- tion or develop installation details that provide some additional support for the stair tread,” he says.
3Dprint ideas While most WPC products are produced using extrusion, Germany’s Fraunhofer WKI (Institute for Wood Research) has initiated a new project that aims to demonstrate what is possible in novel light-weight 3D-printed designs for building and construction applications that incorporate wood- based filaments and as much bio-based content as possible. Project lead Dr Arne Schirp says the researchers are exploring wood particles, pure cellulose and lignin, and mixtures of these in PLA (polylactic acid, a biobased thermoplastic polyes- ter) compounds with 20 and 40% fibres by weight. The compounds will be made into filaments and 3D-printed. “One of the main challenges is to find the right balance between printing speed and quality when it comes to large parts. This summer, the first prototypes will be designed and printed by our project partners,” says Schirp.
Additive manufacturing has the potential to save
material and cost in the production of complex, customised components, according to the Fraun- hofer team. The project will look at simplifying production of existing architectural components, such as facade elements and partition walls, as well as development of new and innovative designs. PLA reinforced with wood or cellulose fibres has
already been used in 3D-printed parts but (so far) rarely in building applications, says Schirp. PLA is, however, desirable as a material based on renew- able resources.
68 COMPOUNDING WORLD | August 2022
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.fiberondecking.com �
www.oldcastleapg.com �
www.trex.com �
www.teknorapex.com �
https://laniercolor.com/ �
www.dow.com �
www.mitsui.com/de/en/ �
www.mixaco.com �
www.intertek.com �
www.wki.fraunhofer.de
www.compoundingworld.com
Researchers are working to improve fire-retar- dancy and heat resistance of the materials, which is particularly challenging in the PLA matrix. “We are currently investigating the benefits of electron beam irradiation, which can be used to crosslink thermoplastics (in our case, PLA and bio-based polyamides). The crosslinking takes place in the amorphous regions of the polymer,” he says. “The crosslinked systems also include [phosphi-
nate] FR additives. The idea is to find out if a combination of the crosslinking agent and FR can achieve the same performance as with the use of FR only. At present, we try to understand the interaction between FR additive and cross-linking agent better. We [can] confirm that increased heat resistance can be obtained using irradiation, while the effects on fire-retardancy are still under investigation. Tests such as the UL-94, glow wire test and comparative tracking index are in pro- gress,” says Schirp. The researchers are also working on continuous
fibre filaments based on hemp, flax and used in conjunction with bio-based thermoplastics. “We are currently working on achieving a homogene- ous coating of the fibres with PLA prior to 3D-print- ing. Our project partners have been working on modifying a printer specifically for this long-fibre material, and they are also designing and imple- menting a cutting mechanism,” Schirp says.
IMAGE: FRAUNHOFER WKI/MANUELA LINGNAU
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