The product designation LyondellBasell Icorene 3560 GRN 6181 identifies a color-compounded linear low-density polyethylene rotational molding powder. The base grade is classified as a PE-LLD with a nominal density of 0.935 g/cm³ determined by ISO 1183-1 and a melt mass-flow rate of 5.5 g/10 min at 190 °C under 2.16 kg load per ISO 1133-1:2022. The suffix GRN 6181 defines a green color and additive package. Published data for this exact color-compounded variant is limited; therefore, the values in Table 1 are drawn from the uncolored base-grade technical data sheet and should be treated as representative fingerprints rather than guaranteed specifications.

Under ISO 1872-1, linear low-density polyethylene is designated by the format PE-LLD, followed by density and melt flow codes. For the uncolored base resin, the nominal density of 0.935 g/cm³ places the material at the upper end of the LLDPE density range and separates it from very low-density polyethylene grades below 0.915 g/cm³ and from medium-density grades above 0.940 g/cm³. The digit string 3560 is an internal grade identifier; the GRN 6181 suffix is a color-compound code. In rotational molding, the grade number should not be interpreted as a melt index multiplied by ten or as a direct density indicator because proprietary nomenclature differs across polyethylene families.

The material is supplied as a powder for rotational molding rather than as pellets, which separates it from injection-molding and film-extrusion LLDPE grades. The grade is specified where medium-sized hollow parts require a balance of low-temperature ductility, stiffness, and environmental stress-crack resistance. Typical application categories include agricultural tanks, storage bins, outdoor furniture, buoyancy components, and playground structures. The green 6181 package is normally selected for outdoor visibility, part identification, or UV-stabilized green exterior surfaces.

What Limits Cycle Time When This Grade Is Processed by Rotational Molding?

Because rotational molding imposes low shear on the melt, the MFR window is a primary cycle-time control. With oven air temperatures of 280–300 °C and mold rotation ratios between 4:1 and 8:1, the powder sinters into a continuous layer and entrapped air diffuses through the melt at a rate controlled by melt viscosity. Peak internal air temperature should reach 180–190 °C for complete densification; sustained temperatures above 200 °C tend to accelerate thermo-oxidative chain scission and surface discoloration, particularly in green-pigmented parts. If the MFR falls below 3 g/10 min, the elevated melt viscosity restricts bubble removal and can leave pinholes in splash zones. If the MFR exceeds 7 g/10 min, vertical-wall sag and wall-thickness variation increase on larger molds. At 5.5 g/10 min, the grade is positioned for nominal wall thicknesses from 3 mm to 10 mm, with thinner sections requiring higher oven temperature or longer dwell.

The rate of powder densification depends on particle size, oven air velocity, mold thermal mass, and melt surface tension. Laboratory hot-stage microscopy of LLDPE powders with MFR near 5 g/10 min typically shows initial particle adhesion at 125–130 °C and full densification at 170–180 °C. These temperatures are lower than the oven air setting because the mold surface and melt act as a heat sink. The oven must therefore be hot enough to overcome heat transfer resistance, but excessive oven air can degrade the outer skin before the inner surface reaches full densification. This is why rotational molders monitor peak internal air temperature rather than oven setpoint alone.

With the green 6181 concentrate, color-related differences in infrared absorption may slightly change heating rates compared with natural or black powders. Green pigments can absorb in the near-infrared region, but the magnitude of the shift is mold-dependent and should be determined by instrumented run trials on the actual mold. Pre-drying is normally not required unless the powder has been stored under condensation risk at relative humidity above 60%. In that case, pre-drying at 60 °C for 1–2 h before mold filling reduces surface defects. On shuttle and carousel machines, published processing guides for LLDPE rotational molding report cycles of 18–25 min for 6 mm nominal wall sections at oven settings near 280 °C, though part geometry and mass distribution can shift this range by several minutes.

In rotational-molded parts above 12 mm, compression-molded tensile values do not translate directly because the cooling rate across the wall is nonuniform. The outer surface quenches against the mold and develops a finer crystalline structure; the inner surface cools more slowly against trapped air and may remain partially molten longer. That differential produces a crystallinity and density gradient across the wall and can lower tensile modulus in the inner layer while raising impact resistance. Published processing guidance recommends demolding at internal air temperatures below 120 °C and using forced-air cooling before water mist. Rapid water quench from above 150 °C can induce bow, especially in flat panel areas. Regrind addition should be validated for each part because pigment dispersion and environmental stress-crack resistance can shift when reprocessed material is added to primary cosmetic surfaces.

The density gradient can be characterized by cutting a cross-section and performing differential scanning calorimetry at multiple depths. A surface layer may show a crystallinity of 60–65%, while the inner layer may remain in the 50–55% range for thick sections. This is not a defect but a consequence of nonisothermal solidification. The gradient influences shrinkage: outer and inner layers do not contract identically, producing residual stress. If the part is exposed to aggressive cleaning agents or agricultural chemicals, the inner surface may be more susceptible to environmental stress cracking because lower crystallinity can allow greater permeation. Therefore, ESCR values measured on compression-molded specimens should be supplemented with chemical immersion tests on prototype parts using the actual fluid mixture.

The base-grade datasheet values in Table 1 are generated on compression-molded specimens. In thick rotomolded sections, the practical modulus and yield strength may be lower than the datasheet because of the density gradient and residual stresses. Structural calculations should therefore use a design factor based on part thickness, service temperature, and chemical environment rather than defaulting to single-point room-temperature data.

When the GRN 6181 Color Package Is Specified for Outdoor Exposure

Ultraviolet exposure of the green 6181 variant is evaluated under accelerated weathering methods such as ISO 4892-2 or ASTM G154, typically with an irradiance of 0.75 W/m²/nm at 340 nm and a black-panel temperature of 63 °C. Published data for this specific green concentrate is limited; therefore, end users should request lot-specific accelerated weathering results from the supplier. The service limit for polyethylene under UV is generally a decline in elongation at break rather than tensile strength at break. A part is often considered to have reached its weathering limit when elongation at break falls below 50% of the unexposed value. Green pigments can screen part of the 300–400 nm band but do not prevent surface oxidation. For prolonged external use, design thickness allowance and UV stabilizer concentration must be verified against the application’s solar load and cleaning chemistry.

Polyethylene photodegradation follows a hydroperoxide-mediated radical chain mechanism. Carbonyl groups form in the surface, causing embrittlement and loss of elongation. The green pigment can reduce light transmission but also introduces inorganic oxide pigments that may accelerate or stabilize photodegradation depending on surface treatment. Therefore, lot-specific xenon-arc testing is required. A common acceptance criterion for rotomolded agricultural tanks is retention of at least 70% of original elongation after 2,000 h of ISO 4892-2 exposure, but the specific requirement depends on the end-use specification.

The color package should not be modified with amine-containing antistatic or antifog additives unless compatibility testing is performed, because amine chemistry can interfere with phenolic antioxidants and alter color stability. The same restriction applies to blending with ionomer regrind or unapproved color concentrates unless melt-state compatibility is confirmed by differential scanning calorimetry or rheological testing.

Comparative positioning against LDPE and HDPE rotational molding powders is based on density, MFR, and comonomer architecture. LDPE contains long-chain branching and often offers lower warpage and better surface clarity, but its tensile modulus and ESCR are lower at equivalent density. HDPE offers higher stiffness and heat deflection temperature but lower low-temperature impact and ESCR. This LLDPE grade at 0.935 g/cm³ occupies a middle position: its alpha-olefin short-chain branches produce a higher tensile modulus than LDPE of the same density and better ESCR than many HDPE grades. Against conventional Ziegler-Natta LLDPE rotational molding grades, the base resin may show a narrower molecular weight distribution and lower extractables; however, no universal claim can be made without the manufacturer’s specification sheet for the exact lot.

Compared with cast-film LLDPE grades having MFR values near 1.0 g/10 min, this rotational-molding grade has higher melt flow and lower melt strength. It is not suitable for blown-film bubble stability at low shear. Compared with HDPE rotomolding grades, the lower density and lower peak melting temperature can allow processing at slightly lower oven temperature or shorter cycle, but the trade-off is lower modulus and greater susceptibility to creep under sustained load. Pigment loading in GRN 6181 can reduce dart impact slightly when compared with natural or black grades, with a supplier-documented shift that is normally below 10% if the concentrate is properly dispersed. Because pigment agglomerates can act as stress concentrations, ESCR values for green compounds may require separate determination under ASTM D1693 in 100% Igepal CO-630.

Compliance Verification Matrix for Regulated End Uses

For food-contact and toy applications, the base resin and color concentrate must be approved separately. Base-resin compliance with FDA 21 CFR 177.1520 does not automatically extend to the green concentrate. End users must obtain a letter of conformity from LyondellBasell and the colorant supplier for the specific product lot. Table 2 summarizes the typical regulatory framework; inclusion in the table is not a certification for this specific lot.