This application section addresses the use of LyondellBasell POLYBATCH™ Treated Pine 60181U/4 Concentrate Based In LLDPE in polyethylene-rich wood-plastic composite manufacturing and related PE colouring operations. The concentrate is carried in LLDPE, which means the processor is not adding a neutral colour additive but a polyolefin phase that participates in melt rheology, shrinkage and solid-state modulus. The downstream corridors below are limited to PE-based profiles, coextruded capstock, and injection-moulded or extruded wood-plastic articles where treated-pine visual formatting is required. This concentrate is not suitable for rigid PVC, polypropylene, ABS or glass-filled engineering resins, because LLDPE carrier domains can remain as discrete low-crystallinity inclusions and reduce weld-line integrity. Lot-specific melt index should be verified according to ISO 1133-1:2022; pellets stored in a humid production hall with RH above 60% should be pre-dried at 70–80 °C for 2–4 h before the feed hopper. Where the final article is supplied to EU markets, RoHS Directive 2011/65/EU and REACH SVHC screening apply as product-level obligations rather than concentrate-level declarations.

In high-filled PE deck board extrusion, 60181U/4 is metered into the main feed throat after the wood fibre has been dried to 0.8–1.0 wt% moisture. The working let-down is typically set at 2.0–4.5 wt% in the cap layer of coextruded boards; for uncapped solid boards, the ratio is held at 1.5–2.5 wt% through the entire cross-section to avoid the low-viscosity LLDPE carrier altering the compound’s die swell and residual stress profile. On a conically tapered counter-rotating twin-screw extruder with a metering-zone screw diameter of 60 mm and L/D 32:1, the melt is typically shaped through a profile die at 155–180 °C; cooling is staged in water tanks at 20–40 °C with vacuum calibration held at −20 to −40 kPa. Die head pressure is monitored at 8–12 MPa; excursions beyond 14 MPa generally indicate filter clogging or insufficient moisture removal. The normative framework for exterior deck boards includes ASTM D7032-17, EN 15534-1:2014 and, where span ratings are submitted for evaluation, ICC-ES AC174. The principal processing conflict on production lines is plate-out on the die lips. Because the LLDPE carrier contributes lower melt strength than an HDPE carrier, high screw-shear conditions can generate low-molecular-weight wax-like fractions; die-lip build-up appears first at the edges of hollow profiles and alters embossing depth. Operators typically reduce screw speed rather than raise the zone set point when edge tear or surface streaking appears. The terminal articles are 22 mm × 140 mm solid or hollow-ribbed deck boards, grooved-edge boards and fascia boards.

What Limits Linear Output in Hollow Cladding Profile Extrusion?

Linear output in hollow PE cladding profiles is rarely limited by colour concentrate dispersion when 60181U/4 is pre-blended with the capstock resin before the cap extruder feed hopper; it is limited by calibrator heat transfer and residual heat in the internal webs. The capstock formula is compounded at 3.0–6.0 wt% concentrate in an LLDPE/LDPE-rich cap resin, while the core is typically 45–55 wt% wood fibre in recycled HDPE. Coextrusion equipment comprises a primary counter-rotating twin-screw extruder for the core and a single-screw cap extruder with a barrier screw of 25–35 mm diameter; cap thickness is maintained at 0.3–0.5 mm. The relevant normative anchors are EN 15534-1:2014 for material consistency and EN 13501-1 where exterior cladding is subject to a national reaction-to-fire classification; the concentrate itself does not confer a fire class. When the cap layer exceeds 6.0 wt% loading, field reports describe a reduction in scratch resistance and an increase in cap-layer stress whitening after cold impact, because the excess LLDPE carrier and pigment at the surface disrupt the co-crystallinity of the HDPE-rich cap. The production window is bounded at the upper end by calibration cooling: above 2.0–2.5 m/min on a 150 mm wide hollow profile, web collapse and edge rounding appear unless additional chilled-water calibrators are installed. The terminal products are tongue-and-groove rainscreen cladding boards, soffit boards, and hollow exterior wall battens.

If a fence picket line runs a fully pigmented solid profile without a cap layer, the entire cross-section carries 60181U/4 at 2.0–3.5 wt%, because surface streaking cannot be hidden by coextruding a pigmented shell. The compound is fed as a pre-mix of 50–60 wt% hardwood fibre, HDPE and additives into a counter-rotating twin-screw extruder with atmospheric and vacuum venting; vent vacuum below −60 kPa is retained to remove residual moisture and wood volatiles. The profile is embossed in-line with a deep wood-grain roller before cooling in stacked calibrators. For fence and privacy-screen products, procurement specifications frequently invoke EN 15534-1:2014 and ISO 4892-2:2013 xenon-arc weathering; a common project specification is ΔE ≤ 4.0 after 3000 h, but that value is system-dependent and must be validated on the full pigmented compound rather than on the concentrate alone. The main failure mode in this downstream corridor is residual thermal stress causing picket bow after installation in high-sun exposure. The LLDPE carrier reduces the flexural modulus of the solid profile more than an equivalent HDPE-carrier concentrate, so processors compensate by increasing profile wall thickness by 0.5–1.0 mm rather than increasing concentrate loading. The terminal parts are solid fence pickets, tongue-and-groove privacy slats, post sleeves and lattice profiles.

Thermal Gate Freeze-Off in Injection-Moulded Furniture Components

Injection-moulded PE wood-composite furniture components require a lower concentrate loading than extrusion profiles because the part surface is formed under high shear at the gate and prematurely cooled at the mould wall. 60181U/4 is let down at 2.0–4.0 wt% in LLDPE or HDPE wood-plastic compounds with 20–35 wt% cellulose fibre; the mixture is fed to a general-purpose reciprocating-screw injection machine with L/D 20:1 and compression ratio 2.5:1. Barrel temperatures are set from 170 °C at the feed zone to 195 °C at the nozzle, and mould surface temperatures are held at 20–40 °C. The critical processing defect is jetting from small edge gates followed by weld-line weakness in chair back frames; LLDPE carrier reduces shear viscosity but does not eliminate weld-line reduction in fibre-filled systems. The normative interface for outdoor furniture is EN 581-1:2017, with weathering stability verified under ISO 4892-2:2013. Load-bearing components that must retain a minimum safety factor under cyclic static load should not exceed 4.0 wt% concentrate without re-checking the compounded flexural modulus, because each incremental percentage of LLDPE and pigment lowers the composite modulus. The terminal articles are chair armrests, table slats, bench backs, and injection-moulded connector blocks used with extruded rail profiles.

Railing System Color Stability and Core–Shell Layer Economics

For railing systems, 60181U/4 is used primarily in the coextruded cap shell at 3.0–5.0 wt% to produce a treated-pine face colour without tinting the recycled HDPE core. The shell extruder is a single-screw cap machine with a barrier screw of 30–45 mm, while the core runs on a counter-rotating conical twin-screw extruder; shell thickness is maintained at 0.5–1.0 mm around a core containing 45–55 wt% wood fibre and recycled HDPE. The system is evaluated under ASTM D7032-17 for guard and handrail performance, and ICC-ES AC174 is commonly used where code-compliance submittals require independent load and weathering data. The processed article must pass baluster spacing, guard load and handrail graspability requirements without relying on the shell for structural strength. On-line color stability is controlled with a spectrophotometer using the D65/10° illuminant/observer pair; acceptable batch-to-batch colour tolerance is set by the brand owner and is usually tighter than ΔE ≤ 1.2 for visible surfaces. The differentiated constraint in railing assembly is the presence of injection-moulded connectors and brackets: if these connectors are produced from a separate batch of the same compound, the let-down must be matched to the shell to ±0.3 wt% to prevent visible colour shift at the joint line. Terminal products are top and bottom rails, balusters, post sleeves and retrofit handrail covers.

When Regrind Reintroduction Shifts the Effective Let-Down Ratio in PE Cladding Plants

When plants return trimmed cladding skeletons and start-up waste to the core extruder, the effective concentration of 60181U/4 in the final core can drift above the intended formulation because the regrind already contains colourant from the cap layer. The appropriate control method is to calculate the rework stream as a pre-coloured component rather than as neutral polymer: every 10 wt% of cap-containing regrind in the core introduces a fraction of the original 3.0–6.0 wt% shell loading into the bulk. When this drift is not accounted for, the core surface at cut ends becomes noticeably darker than the cap, and the overall modulus of the profile can decrease because the LLDPE carrier in the returned cap layer contributes additional lower-crystallinity material. The relevant process control standard is ISO 9001:2015 for documented rework traceability, while the physical material consistency is tested by ash content and melt-flow rate according to ISO 3451-1:2019 and ISO 1133-1:2022. Published data for this specific regrind configuration is limited because most extrusion lines vary their rework fraction between 5 and 20% depending on order length and colour changes. The terminal impact is the same as the primary cladding article: hollow cladding boards and soffit stock with cut-end aesthetics that must remain within the brand owner’s acceptance limit.