LyondellBasell Icorene 3560 G GRY 7223 is a linear low-density polyethylene supplied as a pre-compounded grey powder for rotational molding. The base resin designation, Icorene 3560 G, identifies an LLDPE with a manufacturer-reported nominal density of 0.935 g/cm³ when tested under ISO 1183-1:2019 and a melt flow rate of 6.0 g/10 min at 190 °C and 2.16 kg when characterized by ISO 1133-1:2022. The suffix GRY 7223 is a commercial colour reference for a grey pre-coloured grade, not a separate resin modification. The product is delivered in pulverized powder form rather than pelletized compound. The powder form is essential for rotational molding equipment, including carousel, shuttle, and rock-and-roll machines, because the material must flow freely inside a rotating mould and then sinter into a continuous wall. The measured density places the product in the linear low-density class; it therefore provides lower tensile modulus and higher environmental stress cracking resistance than a high-density rotomolding powder of equivalent melt flow rate. The powder is directly charged into the mould cavity without screw-driven plastication. Batch-to-batch consistency of particle size, bulk density, and colour depends on the compounding and grinding operation, not on the reactor resin alone.

Typical property values for the material are usually generated on compression-moulded plaques, not on rotomoulded parts. That distinction is relevant because rotational molding produces cooling rates, shrinkage histories, and contact surface patterns that are not reproduced in a compression mould. The values in the following table are manufacturer-published representative data for comparison, not guaranteed part-level specifications.

The tensile yield stress of 14 MPa and flexural modulus of 700 MPa indicate a moderately soft polyethylene. When the same powder is rotomoulded into a curved or flat panel, the actual part stiffness depends strongly on wall thickness; flexural modulus is a material property, but bending stiffness scales with the cube of wall thickness. A designer comparing this LLDPE to a high-density rotational molding grade with a flexural modulus above 1000 MPa must increase wall thickness or add ribs, kiss-offs, or metal stiffening frames to maintain equivalent load-bearing performance. The compensation is enhanced stress-crack resistance: the >1000 h F50 result under ASTM D1693-21 supports service conditions in which the part is subjected to low-level flexural strain and chemical contact, such as agricultural tanks and water-storage vessels.

What separates the GRY 7223 grey pre-compound from uncolored rotational-molding powders?

Uncolored linear low-density polyethylene powders used in rotational molding typically require either dry-blending of pigment masterbatch at the moulding shop or compounding of colourant at the extrusion stage before grinding. Dry-blended systems can exhibit particle segregation because the pigment masterbatch and resin powder differ in bulk density and particle size distribution. On a four-arm carousel machine, this segregation may appear as colour drift when the hopper level changes after refilling. With a pre-compounded grade such as GRY 7223, the pigment is dispersed before the final particle-sizing step, so the hopper contains a single coloured powder population rather than a bimodal dry blend. This reduces the colour-shift mode associated with particle segregation but also restricts the moulder to one colour reference; dilution to a lighter shade is not possible without selecting a different commercial reference.

An additional process distinction concerns radiant heat absorption. Grey pigmented powder may absorb and emit radiant energy differently from natural powder during oven residence. The surface temperature response measured by an infrared pyrometer can therefore differ from that of uncolored Icorene 3560 G. Moulders should not transfer a natural-powder cycle profile to the grey pre-compound without confirmation by internal air temperature measurement and demould inspection. The pre-coloured grade also requires control of regrind percentage. If used powder is dry-blended back into the charge, the overall particle shape, colour, and dry-flow behaviour change, and the added regrind should be quantified rather than introduced intermittently.

Processing boundaries in rotomolding oven cycles and mould surface thermocouples

The conversion of a loose powder bed into a continuous melt film involves overlapping stages of powder sticking, sintering, bubble dissolution, and densification. Oven air temperature alone is an incomplete control variable because the powder and melt interface temperature lags the air temperature. Production rotomolders measure either the internal air temperature inside the mould or the mould surface temperature, usually with a slip-ring thermocouple or a wireless data logger. For LLDPE with a melt flow rate of 6.0 g/10 min, the forced-air oven is commonly operated at 260 °C to 330 °C. The primary process target is a peak internal air temperature of 165 °C to 185 °C. The lower boundary is determined by the need to remove interstitial voids and achieve full coalescence at the mould surface. The upper boundary is set by oxidative stability; extended exposure above 200 °C internal air temperature can shift colour, reduce ESCR, and generate odour. Because GRY 7223 contains a grey pigment, the absorption of radiant energy may differ from that of natural 3560 G, so the heating cycle should be re-qualified with the actual coloured powder.

Cooling rate is the second independent process variable. Fast cooling produces finer spherulites and lower crystallinity in quenched zones, but it may also increase shrinkage anisotropy and warpage. Slow cooling increases crystallinity and stiffness but can reduce impact resistance and extend cycle time. In air-cooling stations on shuttle and carousel machines, rotation is typically maintained until the melt has solidified sufficiently to resist deformation. For parts with wall thickness between 3 mm and 8 mm, a staged air-cooling sequence of 15 min to 35 min is often used. Thicker sections require longer cooling and may require a reduced cooling-air velocity to prevent surface collapse. Water mist cooling is available on some machines, but it increases the shrinkage differential between the mould surface and the inner core. If water mist is applied too early, the part may develop sink marks or internal voids. The powder should be stored in sealed containers and allowed to reach workshop temperature before charging. If condensation is visible or bulk bags have been stored in high-humidity conditions, pre-drying at 80 °C for 2 h may be applied, although polyethylene moisture uptake is generally below 0.1 % under normal dry conditions.

Powder particle size and bulk density are controlled because they govern shot weight, dry flow, and wall thickness repeatability. Quality-control laboratories commonly use ASTM D1921 for sieve analysis and ASTM D1895 Method B for apparent density. Excessive fines from over-grinding can reduce dry-flow and cause bridging in hoppers, while oversized particles can delay sintering and create pinholes. A finer powder can pack more densely and produce a slightly higher shot weight at constant volume; a coarser powder can reduce contact surface and delay coalescence. On production lines with rotary carousels, lot changes should be accompanied by a shot-weight check and a first-article wall-thickness scan. If regrind is used above approximately 20 % by weight, the dry flow and particle size distribution should be re-tested because regrind particles are often angular and may behave differently from virgin powder.

Rotomoulded parts manufactured from the 0.935 g/cm³ LLDPE class are typically selected for service where environmental stress cracking resistance and low-temperature ductility govern. Chemical storage tanks, agricultural sprayer tanks, water treatment vessels, hoppers, and outdoor equipment housings are process-compatible with the grade when wall thickness and support ribs are designed for the lower flexural modulus of LLDPE relative to HDPE. In corrosive or solvent-containing service, compatibility should be confirmed by immersion testing under ASTM D543-21 at the service temperature. The material should not be specified as inherently weather-resistant on the basis of colour alone; a UV stabilizer package must be confirmed and supported by accelerated weathering data under ISO 4892-2 or ASTM D2565. Published weathering data specific to GRY 7223 is limited, so outdoor service life projections should be derived from a supplier-authorized testing program rather than generic LLDPE outdoor exposure tables.

Rheological characterization also matters beyond the melt flow rate. In rotational molding, the material is not pumped through a screw; the viscous response at low shear is more relevant to sintering and bubble dissolution. The DSC melting peak of the base LLDPE typically occurs near 127 °C under ISO 11357-3, but the process target of 165 °C to 185 °C requires considerable superheating to reduce viscosity sufficiently for bubble removal. Higher internal air temperature accelerates densification but also increases the risk of oxidation and colour shift. Lower-flow grades can deliver higher toughness but may require longer oven dwell and may produce pinholes in complex moulds because the molten film cannot densify quickly enough. Higher-flow grades may wet the mould surface faster and produce sharper internal corners, but they often have lower entanglement density, which reduces ESCR and impact.

When melt flow index and part wall thickness interact

A melt flow rate of 6.0 g/10 min places the 3560 G powder in the intermediate flow region for rotational molding. Higher-flow LLDPE grades, often above 10 g/10 min, may improve internal detail and reduce cycle time but typically display lower tear strength and reduced ESCR. Lower-flow grades, typically below 3 g/10 min, may improve toughness but require longer oven residence and may not distribute evenly in complex mould geometry. The 3560 G balance is intended for medium-complexity parts with wall thicknesses from 3 mm to 10 mm. Wall thickness below 2 mm may be difficult to control because the powder charge is small and the sintered film may cool too quickly during rotation; wall thickness above 12 mm may require extended cycles and can develop internal voids if the peak internal air temperature is reached too quickly. These limits are processing boundaries rather than product specifications; part-specific trials on the target machine and mould are required.

Compared with high-density rotomolding grades, Icorene 3560 G GRY 7223 has lower tensile yield stress and flexural modulus but higher ESCR and low-temperature impact. Compared with uncolored Icorene 3560 G, the pre-coloured version removes dry-blend segregation but requires re-qualification of the heating cycle because of possible differences in radiant heat absorption. Compared with higher-flow LLDPE rotomolding powders, the 6.0 g/10 min melt flow rate shifts the balance toward toughness and stress-crack resistance rather than short cycles and very thin walls. The grade is therefore evaluated through a part-specific trial that includes internal air temperature profiles, wall thickness mapping, ESCR or drop-impact testing on cut specimens, and outdoor weathering validation where relevant. Specific published data for GRY 7223 in long-term outdoor service are limited, and final performance is a function of part design, mould surface condition, grinding consistency, and cycle control more than resin property tables alone.