WPC compounding with planetary roller extrusion
Wood-plastic composite (WPC) compounding combines thermoplastic matrix resin — polyethylene, polypropylene, or PVC — with wood flour at loadings of 40–65% by weight to produce pellets for downstream extrusion into decking, cladding, fencing, window components, and automotive interior parts. WPC is simultaneously one of the highest-volume filled-compound applications and one of the most demanding in terms of process control.
The challenge is specific: wood flour is hygroscopic (3–8% moisture content depending on storage conditions), thermally sensitive above approximately 200°C (cellulose begins to discolour and degrade), and mechanically fragile under high shear (fibre shortening reduces composite mechanical properties). Achieving adequate dispersion of high wood flour loadings without exceeding the thermal or mechanical damage thresholds is not achievable on conventional high-shear equipment at competitive throughput rates.
Planetary roller extruders address this through their geometry. The PLATEX by Takımsan uses a low-shear film-forming mechanism that distributes wood flour through the matrix at barrel temperatures of 160–190°C, well below cellulose degradation onset. The thin melt film (0.5–2 mm) maximises the surface area available for moisture evaporation, and stage 2 vacuum degassing removes the steam generated from wood flour moisture at processing temperature. The result is a void-free, consistently coloured pellet at throughput rates competitive with twin-screw WPC lines.
For the full range of PLATEX models suitable for WPC, see the PLATEX system overview. For PE matrix compounds with high CaCO3 addition (which some WPC formulations include), see PE+CaCO3 compounding.
Why planetary outperforms twin-screw for WPC
Fibre preservation: Co-rotating twin screw extruders process WPC effectively but generate significant shear stress in the screw flight gaps, which shortens wood fibres. Fibre shortening from 400 µm to 150 µm mean length causes a measurable reduction in composite tensile strength and stiffness. The PLATEX’s rolling-contact mechanism applies lower specific shear stress to the wood fibres, preserving mean fibre length 20–35% longer than twin screw processing at equivalent loading levels (estimated). This translates to higher composite flexural modulus at the same formulation.
Temperature control at high loading: At 60% wood flour by weight, the heat capacity of the composite is dominated by the wood component. Twin screw extruders generate significant viscous dissipation even at medium screw speeds, raising melt temperature rapidly at high wood loading. At 60% loading, twin screw melt temperatures of 200–210°C are common in practice — above the 190°C threshold for cellulose discolouration. The PLATEX maintains melt temperature below 185°C at equivalent loading and throughput (estimated).
Moisture handling: Stage 2 vacuum degassing is standard on all PLATEX models. At 50% wood flour with 3% moisture, the PLATEX evaporates approximately 15 kg/hr of water at 600 kg/hr throughput — a water load that twin screw vacuum vents handle with more difficulty due to shorter vacuum contact time.
Homogeneity at high loading: At 60–65% wood flour, achieving uniform wood flour distribution in the polymer matrix is more demanding than at 40–50%. The PLATEX’s multiple roller contacts across the full barrel length distribute the filler through successive thin-film forming events. Twin screw intermeshing provides efficient mixing up to 55% loading; above this, the PLATEX geometry outperforms twin screw on dispersion uniformity (estimated).
See PLATEX vs twin-screw for the full technical comparison across all compound classes.
Recommended PLATEX models
For WPC production in the 450–800 kg/hr range, the PLATEX 155 (55 kW, PR 150) is the standard entry specification. At 600–1,100 kg/hr, the PLATEX 165 (75 kW) covers the production band for medium-to-large WPC decking lines. At 750–1,500 kg/hr for large WPC extrusion parks, the PLATEX 185 (90 kW, PR 250 or PR 150) is specified.
WPC throughput on PLATEX models is typically 15–25% lower than rigid PVC throughput at the same motor draw, due to higher melt viscosity. Plan capacity on WPC-specific throughput data, not PVC-rated figures.
For WPC formulation development and pilot production before committing to a production line, the PLATEX 80 lab extruder (max 45 kg/hr) allows testing of wood species, particle size, coupling agent type, and processing temperature ranges before scale-up.
Run your formulation in our lab
Send a 5–10 kg sample of your WPC premix (matrix resin + wood flour, pre-dried to below 3% moisture) to Takımsan’s İstanbul facility. Our team runs it on the PLATEX 80 lab extruder and report melt temperature, vacuum degassing effectiveness, coupling agent reaction completeness (by tensile test on pressed plaque), and pellet quality. Contact Takımsan to arrange a sample run.
