LyondellBasell Icorene 3545 GRN 6659 Polyethylene, Linear Low Density is a dry-flow rotational moulding powder based on a linear low-density polyethylene backbone. The LLDPE backbone is produced by low-pressure copolymerization of ethylene with an alpha-olefin, giving short-chain branching along a linear main chain. The suffix GRN 6659 designates a pre-compounded green colour package, not a surface coating or post-mould pigmentation. Typical values from the manufacturer’s product data sheet place the melt flow rate at 4.5 g/10 min when measured at 190 °C under 2.16 kg load in accordance with ISO 1133-1:2022, and the base density at 0.934 g/cm³ at 23 °C in accordance with ISO 1183-1:2019. The material is designed for rotationally moulded tanks, agricultural containers, refuse bins, and outdoor equipment in which low-temperature impact resistance, environmental stress crack resistance, green colour identity, and outdoor weathering resistance are simultaneously demanded. Because the product is supplied as a dry-flow powder, it is conveyed, weighed, and charged directly into closed moulds on carousel, shuttle, clamshell, or rock-and-roll rotational moulding machines. It is not intended for injection moulding or single-screw extrusion without prior compounding or pelletising. The base resin is not hygroscopic in the bulk, but surface moisture adsorption can occur in storage at relative humidity above 60 %, and this condition should be checked when silo loading occurs from outdoor bulk bags.

What Limits Peak Internal Air Temperature and Cycle Time for This Rotomoulding LLDPE?

The controlling variable in production-scale rotational moulding of this LLDPE is peak internal air temperature, not oven set-point. For this class of linear low-density polyethylene, the peak internal air temperature is typically held in the interval of 190–210 °C. Below 190 °C, the moulded layer may retain sintered microvoids, appear rough on the internal surface, and show reduced tensile elongation when tested per ISO 527-2:2012. Above 210 °C, thermo-oxidative chain scission can proceed rapidly, producing yellowing of the green part, pitting at the inner wall, and a measurable decline in elongation at break. A drift of ±5 °C around the validated peak internal air temperature can be sufficient to move a thin-walled part from ductile low-void performance to brittle, oxidised performance, particularly where wall sections are below 4 mm.

Oven set-points between 260 °C and 300 °C are commonly used for LLDPE rotomoulding powders, but they are not a substitute for internal air temperature measurement. Mould metal thickness, part mass, mould release geometry, and charge weight all alter the time-temperature history at the inner wall. An air probe should be placed away from the mould surface and logged at intervals no greater than 1 s so that the true peak internal air temperature is recorded. On construction-scale carousel machines with multiple arms, the same set-point may yield a PIAT variation of 5–10 °C between arms if airflow is not balanced. Production-scale qualification should include temperature mapping across all arms.

Rotation ratio influences wall thickness uniformity and local densification. Cylindrical tanks are often moulded at a ratio of 4:1 between major and minor axes, while rectangular bins may require 2:1 or a variable ratio programme that changes during the cycle. If the ratio is incorrect, powder residence time at the extremities of the mould changes, producing thin corners, heavy ribs, or visible parting-line porosity. For complex inserts and shut-outs, a deliberate pause or dwell may be introduced to allow the melt to coalesce at the inside edge. Such dwells also extend the heat history and require PIAT compensation.

Densification is governed by melt rheology. The melt flow rate of 4.5 g/10 min indicates a moderate-viscosity LLDPE. It requires more time or a slightly higher PIAT to eliminate trapped air than higher-flow rotomoulding grades with melt flow rates of 6–8 g/10 min. Trapped gas that does not escape before the inner surface freezes becomes subsurface porosity, which is difficult to detect by visual inspection and is best evaluated by sectioning the part or by density measurement. At the same time, the lower melt flow rate supports higher environmental stress crack resistance and better low-temperature impact, so cycle time and property retention must be balanced by experimental validation.

Cooling after sintering is equally important. Slow cooling in still air lowers residual stress but may reduce stiffness. Rapid forced-air cooling shortens cycle time but can increase warpage in flat panels. Water-mist cooling gives the highest productivity but can freeze the surface before the core has contracted, causing internal voids or visible cooling lines. For the green-coloured grade, excessive quench cooling may also produce non-uniform colour reflectance because the pigment particles reside in a semicrystalline matrix with a surface skin that forms under a steep temperature gradient. Published data for this specific configuration is limited, so each mould should be evaluated for warpage, colour uniformity, and impact retention on production-scale parts before rate increases are approved.

At incoming inspection, rotomoulding powders of this class are evaluated for particle-size distribution, dry flow, and bulk density because these powder characteristics determine how uniformly the charge spreads across the mould. Typical rotomoulding powders are controlled through a 35 mesh (500 µm) screen and exhibit bulk densities commonly in the range of 0.35–0.42 g/cm³. A high fine fraction below 75 µm can promote dusting, feed hopper bridging, and uneven melting, whereas an excessive coarse fraction can settle prematurely and create thin upper walls. On shuttle machines with divided moulds, powder flow differences between lots are sometimes observed as uneven wall thickness even when the rotation ratio is unchanged. This has been traced to changes in bulk density or electrostatic charging. The powder should therefore be sampled from each lot and tested with a standard dry-flow funnel before large runs.

Mechanical Property Profile and Comparative Positioning

Typical mechanical values for the base LLDPE powder are obtained from the manufacturer’s published product data sheet and are reproduced in the table below. These are typical values, not specification limits. Batch-release values appear on the certificate of analysis.

The density of 0.934 g/cm³ places the product in the lower-stiffness region of rotational moulding polyethylene. Compared with high-density polyethylene rotomoulding grades at 0.940–0.946 g/cm³, this LLDPE exhibits lower flexural modulus, greater elongation, and generally better environmental stress crack resistance, but it also has a lower modulus and a greater tendency to swell in contact with hydrocarbon solvents. Compared with low-density polyethylene made in high-pressure autoclave or tubular reactors, the linear short-chain branching of LLDPE increases tensile yield strength and puncture resistance while reducing long-chain branching and melt strength. Those differences are relevant when a mould carries deep ribs or sharp corners: the LLDPE can fill the geometry but requires more care in densification than a long-chain branched LDPE.

High-flow LLDPE rotomoulding powders with melt flow rates of 6–8 g/10 min densify faster and fill narrow details more readily, but they tend to sacrifice ESCR and low-temperature impact. In contrast, the 4.5 g/10 min melt flow rate of Icorene 3545 GRN 6659 shifts the balance toward toughness and chemical stress crack resistance. The difference is most apparent in large, thick-walled chemical tanks and agricultural storage units, where a cycle-time increase is often accepted in exchange for longer service life. Conversely, in small, intricate parts with thin ribs, a high-flow grade may be preferred for processability. The green colourant of GRN 6659 is another differentiator: it provides product identity and UV opacity, but the pigment phase may act as a mild stress concentrator, so impact retention should be confirmed on pre-coloured parts and not assumed from natural-grade data.

When Outdoor Weathering and Chemical Exposure Overlap, What Specification Data Apply?

Rotomoulded polyethylene parts in outdoor service are subjected to ultraviolet photo-oxidation, cyclic temperature, and chemical attack. Accelerated weathering is commonly performed under ISO 4892-2:2013 or ASTM G154-16, with retained tensile elongation measured by ISO 527-2:2012 or ASTM D638-14. The green GRN 6659 pigment package absorbs part of the incident radiation and changes the weathering profile compared with unpigmented LLDPE. Therefore, data generated on natural resin cannot be transferred directly to this coloured grade. Published data for this specific configuration is limited, so long-term outdoor exposure on cut sections from production parts remains the most reliable basis for service-life claims.

Environmental stress crack resistance is critical for tanks storing detergents, agricultural formulations, and exhaust-gas aftertreatment fluids. The typical ESCR value of >1000 h under ASTM D1693-15 applies to a standard crack agent and a defined stress level. It does not guarantee compatibility with every chemical at all temperatures. Immersion testing under ASTM D543 at the intended service temperature is required for applications involving oxidizers, chlorinated solvents, aromatic hydrocarbons, or strongly acidic formulations. If the part is intended for food contact, the base olefin polymer is generally assessed under FDA 21 CFR 177.1520, but the green colorant in GRN 6659 must be assessed separately because pigment carriers and heat stabilisers are not automatically covered by the base resin status.

Regulatory obligations remain application-specific. Under REACH Regulation (EC) No 1907/2006, the polymer itself is exempt from registration under Article 2(9), but imported monomers and additives require coverage. The RoHS Directive 2011/65/EU may be relevant if the rotomoulded article is incorporated into electrical or electronic equipment. Heavy metals in pigments should be verified even though the polyethylene matrix is not a restricted material. The following matrix summarises the main regulatory touchpoints, but written compliance confirmation for the specific grade and colour code should be obtained from the supplier.

Storage, contamination control, and operational boundaries are often as significant as resin selection. The powder should be kept dry and shielded from direct sunlight because prolonged UV exposure in storage can pre-degrade the outer layer of the powder bed and shift the green colour. Silos and grinding lines should be segregated from polypropylene, polyamide, and PVC because trace contamination can generate pinholes and delamination during rotomoulding. Field failures in moulded tanks have been associated with incompatible polymer residues that do not coalesce within the LLDPE processing window. If surface condensation is present, drying at 60–70 °C for 1–2 h before charging is prudent. Drying above 80 °C for extended periods is not recommended because of possible additive migration or pigment degradation.

In thin-walled parts below 3 mm, the peak internal air temperature should be held near the lower end of the 190–210 °C window to avoid overcure. In thick sections above 8 mm, cooling rate rather than heating rate may dominate cycle time and void formation. Forced-air cooling should be staged so that surface-to-core temperature differences do not exceed 20 °C unless mould geometry has been designed to tolerate post-mould warpage. Each tool qualification should record peak internal air temperature, oven residence time, ambient relative humidity, wall thickness distribution, tensile elongation retention per ISO 527-2:2012, and falling-weight or instrumented impact behaviour so that lot-to-lot shifts can be separated from process drift.