MATERIALS | WOOD PLASTIC COMPOSITES
Right: The Basajaun project aims to produce a WPC-based alternative to high pressure laminates
improve this issue, the addition of antistatic agents is one of the solutions. Adeka has launched a new antistatic additive
— ADK STAB AS-301E — that can overcome this. ADK STAB AS-301E is described as a permanent antistatic additive suitable for polyolefin (the company says antistatic agents for plastics are either primary types, such as surfactants, or permanent, such as hydrophilic polymers). Anti- static performance is generally represented by surface resistivity. Materials with a surface resistivity of 1011-14
materials with a surface resistivity of 108-11
Ω/sq can provide anti-dust performance; Ω/sq
provide anti-electrostatic discharge performance. According to Adeka, the AS-301E additive offers anti-dust performance in polyolefins at a 5-10% loading and anti-electrostatic discharge perfor- mance at a 15-20% loading. It is said to provide very good efficiency when used in WPCs. For example, 10% of AS-301E can offer anti-dust level in HDPE-based WPCs containing 30-50% of wood flour (Figure 1). Antistatic performance is main- tained even in low humidity conditions (20% RH), which it says confirms that WPCs additivated with AS-301-E will show high antidust performance.
Compounding challenges Some of the challenges experienced when compounding wood fibres or powders arise from their sensitivity to heat and shear, as well as residual moisture. While twin-screw extruders are used for compounding highly filled compounds with low bulk density fillers, using equipment such as downstream side feeders and venting, continu- ous mixers can also be beneficial due to their use of lower temperatures and lower energy, says Slayton Altenburg, application specialist at TPEI. In addition, he says volatiles can escape more readily from a continuous mixer because the compound is not under pressure.
Italian twin screw extruder maker Bausano, which specialises in custom extrusion lines, has tested several twin screw extruder configurations for processing a variety of WPC and NFC formula- tions. The company says one project using the company’s MD series twin-screw extruder achieved an output of 100 kg/h when running formulations with 60-80% PLA and 20-40% sawn wood dust. Other projects have investigated recycled plastics — ABS derived from electronic waste in one test and LDPE bottle caps in another test — as the polymer component of the WPC. Bausano notes that processing materials from
renewable sources poses handling challenges and results in a limited thermal processing range. In addition, post-consumer recycled waste challenges include higher variability and greater risk of degraded material that can lead to negative changes in physical and mechanical properties.
Wood fillers Research is ongoing into new ways to use wood fibres or particles, particularly from waste or recycled wood sources. At the Fraunhofer Institute for Wood Research (Wilhelm-Klauditz-Institut, WKI), researchers are investigating the use of wood particles in bio-based plastics to create a bio-based, thermoplastic sheet for interior wall panels or furniture. The research is part of the European Basajaun project for sustainable building with wood and is operating under a grant from the EU’s Horizon 2020 programme. The bio-composite sheet is envisioned as
Figure 1: Antistatic performance of PP/wood flour WPCs containing Adeka’s Addstab AS-301E permanent antistat additive Source: Adeka
14 PIPE & PROFILE EXTRUSION | November/December 2023
providing an alternative to high-pressure laminate (HPL) used as the surface layer of a plywood or other wood-based panel structure. HPL has high
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IMAGE: FRAUNHOFER WKI
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