TECHNOLOGY | WOOD PLASTIC COMPOSITES
Right: Mixaco’s HM/KM Wood mixing system is designed for the specific challenges of WPCs
bonding between the wood fibres and polymer matrix. Matthias Stuecke, Deputy General Manager at Mitsui in Germa- ny, says that maleic anhydride (MAH)- grafted coupling agents are the “gold standard” in polyolefin-based WPC compounds. “We have received quite positive feedback from the market [on Mitsui’s coupling agents]. Never- theless, we hope to present some more new developments at this year’s K2022,” he says. The WPC product
portfolio from Dow extends to capstock formulations, lubricants, compatibilis- ers, and what is describd as a “next-generation” product that provides both lubrication and compatibilisation. “Historically, process and performance aids have been independent prod- ucts that sometimes interacted with each other in negative ways,” says Jim Keenihans, Senior Technical Service & Development Scientist, Dow Consumer Solutions. “The most common chemistries of lubricants can actually inhibit wood-polymer compatibilisers such that the full properties cannot be reached. Because of this, formulators have been forced to make compromises on lubrication—which is critical to quality, stability, and rate—and compatibilisation, which is critical for mechanical strength, moisture stability, and melt strength,” Keenihans says. Dow says that its Amplify Si PE 1000 product was developed with the intention that both lubrication and performance work at their peak performance. Keenihans claims that the product can “achieve a whole new echelon in WPC additives.” Dow’s research has shown that the Si PE 1000 additive is more thermally stable than metallic stearates and will not degrade as quickly as
process temperatures and rates are increased. “One of our most interesting findings is
that mechanical perfor- mance is improved so significantly that strength can be achieved with lower cost materials, for example utilising linear low density polyethylene instead of, or blended with, high density polyeth- ylene,” he says.
Mixing ideas Mixing the high volume of natural
fillers required in WPC compounds is a challenge, according to Nicolas Gehring, Global Sales Manager at equipment manufacturer Mixaco. He explains that in the mixing process in general, it is easier to homogenise materials and to prevent post-mixing separation if the particle sizes and shapes of the components are similar. In WPC compounds, however, the fine low
bulk-density wood flour or fibres are very different from the polymer powders or granules. “Mixing is a matter of moving particles consistently in order to create a uniform blend. However, particles with different bulk densities behave very differently. Lighter products need less power to get moved, while heavier products need more energy,” Gehring says. Dispersing the additives into the blend is also challenging because of the high loading of natural fillers. Achieving a uniform blend is key for the produc-
tion of the WPC end-product. “Uniformity can affect the intake behavior of an extruder, or the material transport handling,” says Gehring. “The smallest change in the [mixing] process can affect the further processing of the product.” He adds
Figure 1: To create a blend of 60% PLA with 40% cellulose fibre, such as that shown above, Mixaco’s HM/KM Wood system regulates parameters including hot mixer rpm (blue), hot mixer temperature (red), and hot mixer torque (green)
64 COMPOUNDING WORLD | August 2022
www.compoundingworld.com
SOURCE: MIXACO
IMAGE: MIXACO
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