The LyondellBasell Icorene 3546 GRN 6686 grade is a pigmented linear low density polyethylene rotational moulding powder. The base designation 3546 identifies a resin designed for low-shear, closed-cavity powder processing, while GRN 6686 denotes the incorporated green color package. The material is supplied as a dry-flowable powder, not pelletized feed, and is therefore specified for rotational moulding rather than high-shear extrusion or injection moulding. Published LyondellBasell technical literature places the 3546 base resin in the density range of 0.932 g/cm³ to 0.936 g/cm³, with a melt flow rate near 5.0 g/10 min when determined under ISO 1133-1:2022 at 190 °C and 2.16 kg. The green-compounded GRN 6686 version carries a pigment concentrate that can shift stiffness, gloss, and shrinkage by small but measurable margins relative to the natural base resin. Typical application fields include rotationally moulded storage tanks, agricultural hoppers, outdoor cabinets, marine fenders, and recreational platforms. Because final article properties depend on wall thickness, cooling rate, pigment dispersion, and tool-specific processing history, the lot-specific certificate of analysis and first-article validation should prevail over nominal data-sheet values.

In rotational moulding, linear low density polyethylene occupies a defined position between low density polyethylene and high density polyethylene. Short-chain branching from an α-olefin comonomer disrupts crystallinity, lowering density and flexural modulus while improving environmental stress-crack resistance and low-temperature impact relative to an HDPE of similar melt flow rate. The 3546 base resin therefore supplies a wider and lower peak-temperature densification window than many high-density powders, but the resulting part is less stiff and more creep-active under sustained load. The GRN 6686 color package adds a further variable: organic or inorganic pigments can act as heterogeneous nucleation sites during slow cooling, potentially increasing crystallite density and altering warpage direction. Processors should not assume that the green grade will warp identically to an unpigmented lot.

What separates an LLDPE rotational moulding grade from LDPE and HDPE when the same tool is charged?

When the same closed-cavity tool is charged with different polyethylene powders, final part performance is governed by molecular architecture and crystallization kinetics more than by nominal wall thickness alone. Linear low density polyethylene in the 0.934 g/cm³ density class contains sufficient short-chain branching to reduce lamellar thickness and overall crystallinity, commonly into a range of 40 % to 45 %, compared with roughly 55 % to 60 % for an HDPE rotational moulding grade. The practical consequences are measurable: flexural modulus is lower than HDPE, while tensile strain at break and environmental stress-crack resistance are normally higher. In rotational moulding, the lower crystallinity reduces the peak internal air temperature required for densification, which can reduce thermo-oxidative stress on the stabilizer package. At the same time, lower crystallinity reduces heat deflection temperature and increases long-term creep under continuous load. A comparative data pattern for representative rotomoulding polyethylenes is shown in Table 1.

Table 1: Representative natural-grade comparisons for rotational moulding polyethylenes; not product-specific values for pigmented compounds.

The product-specific property envelope for Icorene 3546 GRN 6686 is summarized in Table 2. Values are representative of published LyondellBasell technical literature and are conditioned at 23 °C and 50 % relative humidity in accordance with ISO 291 unless otherwise stated. The green pigment adds a second phase; tensile modulus, hardness, and shrinkage may shift by up to 5 % in either direction depending on pigment loading and dispersion quality. Final article properties should be confirmed by first-article inspection on the production tool.

Table 2: Product-specific property envelope for Icorene 3546 base resin; confirm pigment effects from the grade-specific certificate of analysis.

On shuttle, rock-and-roll, or clamshell rotary rotational moulding lines, Icorene 3546 GRN 6686 is charged into a closed steel or cast aluminium tool at ambient temperature. The tool is rotated biaxially; typical machine settings use primary rotation speeds of 4 rpm to 10 rpm and a secondary-axis speed ratio near 4:1, although the optimum ratio depends on mould geometry and parting-line orientation. The powder distributes and densifies when the cavity reaches the melting range. Oven air set-points of 260 °C to 300 °C are common; the controlling variable is the peak internal air temperature, which should be held between 190 °C and 210 °C for an LLDPE of this density class. The mould should not be quenched rapidly. Cooling in forced air at 10 °C/min to 20 °C/min reduces warpage, while water mist may be introduced only after the part has cooled below 90 °C to prevent differential shrinkage between the outer skin and the inner semi-molten layer.

Unlike hygroscopic engineering resins, LLDPE does not require pre-drying for absorbed water. The practical boundary is surface condensation: cold powder brought into a warm moulding hall can condense atmospheric moisture and generate steam pinholes during densification. If the powder has been stored below 10 °C, it should be allowed to equilibrate in closed containers to ambient temperature before opening. Dry-flow consistency should be checked by bulk density and flow time; a shift in angularity or top-size can alter first-pass powder spread and create thin corners. Incoming lots should be tested for melt flow rate and particle size distribution, and the color concentrate should be verified for pigment dispersion under ISO 18553 or an equivalent microscopic dispersion rating.

When peak internal air temperature overshoots the stabilizer package

The most consequential processing failure in rotational moulding of LLDPE is not incomplete densification but thermo-oxidative degradation caused by excess oven residence. A thermocouple should be mounted in the cavity; for the 0.934 g/cm³ LLDPE class, the target peak internal air temperature of 190 °C to 210 °C should be maintained, and excursions beyond 230 °C are generally regarded as the threshold where antioxidant consumption accelerates. Above that threshold, phenolic stabilizers and phosphites are depleted, carbonyl species form, melt flow rate increases, and impact properties decline. The result may appear as a brittle inner surface, discoloration, or a sharp drop in oxidative induction time measured by ASTM D3895. Processors should establish an incoming-lot oxidative induction time baseline and reject material that shows a reduction greater than 50 % after 20 min at 200 °C in air unless the cavity thermocouple trace demonstrates a lower thermal exposure.

The GRN 6686 pigmentation introduces a second failure pathway related to infrared absorption. Dark green surfaces can absorb infrared energy more strongly than natural translucent powder, especially in gas-fired ovens with direct flame or exposed heating elements. Localized surface temperature can exceed the internal air temperature by 10 °C to 20 °C, shifting the effective processing window. This requires adjustment of oven residence or infrared shielding and validation with surface-temperature probes. Pigment dispersion also affects mechanical continuity: agglomerates act as stress concentrations that reduce environmental stress-crack resistance. The grade’s UV stabilization should be confirmed by accelerated weathering under ISO 4892-2 or ASTM D2565 for outdoor parts; natural and pigmented lots may weather differently because the pigment screens part of the UV flux. Published data for the specific GRN 6686 compound under all end-use exposure conditions are limited; outdoor service in high-UV geographies should be validated with the final part geometry.

Regulatory verification and end-use boundaries

The base olefin polymer may be assessed against FDA 21 CFR 177.1520 for olefin polymers in food-contact applications; however, a color-compounded grade such as GRN 6686 requires a specific compliance letter because the pigment and its carrier resin must also meet the same migration limits. In the European Union, plastic food-contact articles must comply with Regulation (EU) No 10/2011, including overall migration and specific migration limits for colorants and stabilizers. In the absence of a product-specific declaration, the grade should not be used in food-contact or potable-water service. For general industrial articles, the supplier provides a safety data sheet and REACH registration documentation under Regulation (EC) No 1907/2006. Heavy-metal restrictions under Directive 2011/65/EU are typically not relevant for polyolefins unless compounded with restricted pigments or contaminated in downstream processing. Each converter should verify raw material certificates against the final article’s regulatory scope; compliance is end-use and article-specific, not a single property of the polymer.

In rotationally moulded storage and agricultural components, the grade is specified where a balance of low-temperature impact and environmental stress-crack resistance is more important than maximum stiffness. A wall thickness of 4 mm to 6 mm is frequently used for moderate chemical duty, but continuous hydrostatic load at 40 °C requires a creep modulus or a service factor applied to the short-term tensile value. The product differs from high-density rotational moulding powders by a lower flexural modulus and higher environmental stress-crack resistance; it differs from low density polyethylene by higher yield stress and puncture resistance at equivalent melt flow rate. It is not a crosslinked polyethylene, and it should not be substituted for high-temperature or pressure-pipe applications without thermomechanical validation under ISO 9080 or equivalent. The material is also not recommended for prolonged contact with strong oxidizing acids, aromatic hydrocarbons, or chlorinated solvents at elevated temperatures; published data for this specific green-compounded grade under aggressive chemical combinations are limited. Final article testing under ASTM D1998 for tanks or ISO 16101 for chemical compatibility should be conducted on representative production rotomoulded parts before commercial use.