LyondellBasell Icorene 3546 GRN 6669 is a precoloured green linear low-density polyethylene rotational moulding powder. The natural Icorene 3546 base resin is identified in LyondellBasell technical literature by a nominal density of 0.938 g/cm³ when tested to ISO 1183-1:2019 and a nominal melt mass-flow rate of 4.0 g/10 min at 190°C/2.16 kg when tested to ISO 1133-1:2022. The GRN 6669 designation denotes a green colour package; pigment loading, ultraviolet stabiliser content, and the shift in density or melt-flow rate relative to the natural Icorene 3546 grade must be confirmed against the certificate of analysis. Published data for the complete precoloured configuration are limited, and laboratory verification on retained powder samples is required before process start-up. The material is supplied as a free-flowing powder for rotational moulding, and incoming inspection should include particle-size distribution, bulk density, dry-flow time, and colour measurement because these variables affect shot-to-shot consistency.

Which melt-flow and density boundaries define this grade in rotational moulding?

The combination of 0.938 g/cm³ density and 4.0 g/10 min melt mass-flow rate places the material in the low-density segment of rotomoulding polyethylene, below conventional high-density rotomoulding grades that typically lie between 0.945 g/cm³ and 0.955 g/cm³. In rotational moulding, the melt-flow rate governs the rate of bubble dissolution and the time required for the powder to coalesce into a void-free wall. At 4.0 g/10 min, the melt viscosity is low enough to release trapped air during the heating cycle, but high enough to resist excessive sagging on vertical mould surfaces. The density below 0.940 g/cm³ reduces crystalline content, which lowers tensile modulus but increases environmental stress cracking resistance and low-temperature impact performance. Processors should not substitute this grade with film-extrusion LLDPE of similar density, because rotomoulding grades are ground to controlled particle-size distributions and do not contain slip or antiblock additives that can interfere with interfacial sintering.

On shuttle-type and carousel rotational moulding machines with forced-air or direct-fired ovens, the controlling variable is the internal air temperature inside the mould cavity, not the oven set point. Industrial practice for LLDPE powders of this melt-flow class is to target a peak internal air temperature between 210°C and 230°C and to maintain every cold-spot thermocouple above 200°C for at least 2 min before initiating cooling. Unmelted powder, pinhole porosity, and poor drop-impact resistance are observed when the peak internal air temperature is below 195°C, while prolonged exposure above 240°C can accelerate thermo-oxidative degradation and shift colour in the green part. Cooling rate is a further control variable: forced-air cooling followed by water mist can reduce crystallinity and improve impact, but rapid differential cooling across thick and thin sections increases warpage. Moulders should set cooling profiles and mould-release chemistry against the part geometry and the final dimensional tolerance specified on the drawing.

When the green 6669 masterbatch is dispersed into the natural Icorene 3546 powder

Colour concentrates and precoloured powders can alter the rheology, crystallisation, and mechanical response of rotomoulding LLDPE. The green pigment package in GRN 6669 is typically a blend of organic and inorganic colourants selected for heat stability at rotomoulding peak temperatures; however, the exact pigment chemistry and loading are not fully disclosed in public literature. Inorganic green pigments based on chromium or cobalt-chromium systems can increase density and reduce melt-flow rate slightly, while organic green pigments may decompose if the internal air temperature exceeds 230°C for extended cycles. The moulder should verify colour consistency and delta E after oven ageing using ISO 11664-4:2008 CIELAB measurement and should check dispersion by preparing a 100 µm microtome section and inspecting for pigment agglomerates larger than 50 µm. Undispersed pigment agglomerates act as stress concentrators and reduce low-temperature impact strength in rotomoulded parts.

Because rotomoulded parts are fabricated without external pressure, the mechanical properties measured on compression-moulded plaques may overestimate the performance of thick-walled mouldings unless the moulding cycle has fully coalesced the powder. Tensile yield stress, flexural modulus, and elongation at break for the natural Icorene 3546 base resin are commonly listed in supplier data using ISO 527-2:2012 and ISO 178:2019; nominal public values include a tensile yield stress of 18 MPa, a flexural modulus of 550 MPa, and an elongation at break above 600%. These values should be considered reference points for the natural powder and not acceptance limits for the precoloured GRN 6669 variant. The moulded part should be tested by cutting specimens from flat sections of a rotomoulded cube or plaque, because skin-core morphology and residual porosity influence failure. Low-temperature impact testing is commonly performed according to ISO 6603-2:2000 or the ARM low-temperature dart impact method; a drop in brittle failure energy of more than 20% between natural and precoloured powder indicates inadequate pigment dispersion or an incompatible stabiliser package.

Rheological fingerprint, sintering kinetics, and residual porosity

During the heating phase, the powder bed densifies and individual particles coalesce by neck growth. The rate of neck growth is inversely proportional to zero-shear viscosity and particle radius; for a 4.0 g/10 min LLDPE at 220°C, zero-shear viscosity is typically below the range where bubble release is hindered, but local cold spots can remain if oven airflow is non-uniform. Sintering proceeds only after the particle surface reaches the crystalline melting range. The base resin exhibits a peak melting temperature near 127°C by differential scanning calorimetry; the green pigment may act as a nucleating agent and raise the crystallisation temperature by 1°C to 3°C. Residual porosity is assessed by density gradient columns or by polished cross-sections through the moulded wall; more than 2% void area in a 6 mm wall is associated with reduced drop-impact energy. Moulders can adjust the heating time and peak internal air temperature only after thermocouple mapping has confirmed the slowest-heating point in the tool.

Compared with metallocene-catalysed LLDPE rotomoulding powders of similar density, the base Icorene 3546 chemistry is generally understood to be a conventional Ziegler-Natta-catalysed copolymer, although the supplier technical data sheet should be checked for the specific catalyst and comonomer type. Ziegler-Natta copolymers tend to have heterogeneous comonomer placement, which broadens the melting range and can improve creep resistance while reducing the ultimate low-temperature impact ceiling relative to metallocene grades. Published data for this specific configuration is limited, so direct substitution into a mould designed for a metallocene grade should be preceded by instrumented dart-impact testing on rotomoulded samples. Against high-density rotomoulding powders, the 0.938 g/cm³ density provides lower tensile creep modulus and higher environmental stress cracking resistance, making the grade more appropriate for large chemical tanks than for load-bearing structural components.

Environmental stress cracking resistance separates this grade from high-density rotomoulding powder

For storage tanks and agricultural chemical vessels, environmental stress cracking resistance is often the limiting design property. The lower density and linear low-density comonomer distribution of Icorene 3546 provide longer failure times in contact with surface-active agents than typical high-density rotomoulding grades of similar melt-flow rate. Supplier literature for the natural base resin lists an environmental stress cracking resistance value above 1000 h when tested to ASTM D1693-15, Condition B, in 100% Igepal CO-630; however, the result is statistical and should be specified as an F50 failure-time value. The green 6669 pigment package may reduce environmental stress cracking resistance if pigment agglomerates create local stress concentrations, so qualification should include specimens cut from a rotomoulded wall rather than compression-moulded sheet. Chemical storage applications require compatibility testing with the specific fluid, because LLDPE is susceptible to swelling in aliphatic and aromatic hydrocarbons, chlorinated solvents, and some surfactant formulations at elevated temperature.

Before charging the powder to the moulding machine, the warehouse should store Icorene 3546 GRN 6669 in sealed containers at 5°C to 35°C and below 60% relative humidity. Cold powder moved into a warmer moulding hall can condense moisture; surface water introduced into the mould cavity produces steam porosity and internal blisters at rotomoulding peak temperatures. If condensation is suspected, the powder should be allowed to reach ambient temperature while still sealed, and the container headspace should be purged with dry air. The material is not hygroscopic in the manner of polyamide or PET, but condensed water at the particle surface is a process hazard. Safe handling requires extraction of dust generated during powder transfer to control combustible dust concentrations below the relevant lower explosive limit; the powder can form flammable dust clouds and should be grounded during pneumatic conveying.

At the compliance stage, the base resin and the green colour package must be assessed separately because the food-contact and potable-water status of natural polyethylene does not automatically extend to a precoloured rotomoulding powder. The operational boundary for direct food contact and potable water is not established by the base resin compliance alone, because the green 6669 colour package and any processing aids must be cleared for the intended contact temperature and extraction simulant. The powder should not be dry blended with calcium carbonate or mineral fillers above 5 phr without revalidating impact and environmental stress cracking resistance, because rigid filler particles increase viscosity and reduce melt coalescence. Avoid contact with strong oxidising agents and halogenated solvents during cleaning and service, and confirm that the moulded part is not exposed to sustained tensile stress above the design strain limit in the presence of wetting agents.