LyondellBasell Icorene 3545 ORE 3220 is a linear low density polyethylene rotational moulding powder. The ORE 3220 designation identifies a formulated variant of the Icorene 3545 base resin; because a standalone public data sheet for the suffix may not be available, the nominal values stated here are for the base family and should be checked against the batch certificate. The product is supplied as free-flowing powder for biaxial rotational moulding, not as pellet stock for injection moulding. The primary specification indicators are density 0.934 g/cm³ per ISO 1183-1 and melt flow rate 4.5 g/10 min at 190 °C under 2.16 kg per ISO 1133-1. These values place the grade in the medium-density LLDPE class, where low-temperature ductility and environmental stress crack resistance are weighted more heavily than stiffness.

The tabulated values are nominal and should not be interpreted as specification limits; pigment and stabiliser additions in the ORE 3220 formulation can shift density and melt flow rate. In rotational moulding, the powder must also be evaluated for bulk density, dry flow, and particle size distribution. Apparent density per ASTM D1895 Method A and particle-size distribution per ASTM D1921 are more informative for rotomoulding than melt flow rate alone. A bulk density between 0.38 g/cm³ and 0.45 g/cm³ is typical for this product class; values below that interval are associated with excessive fines, while values above it may indicate coarse, low-flowing material. The median particle diameter is generally observed between 150 µm and 250 µm. Coarse particles above 500 µm reduce inter-particle contact, delay full densification, and create surface irregularities.

The melt flow rate of 4.5 g/10 min is an incoming quality-control parameter, not a direct predictor of sintering. Rotational moulding takes place at nearly zero shear, where the molecular weight distribution and short-chain branching control melt viscosity and bubble dissolution. The Icorene 3545 family is produced with metallocene catalyst chemistry, which yields a narrower comonomer distribution than conventional Ziegler-Natta LLDPE. The melting peak, measured by ISO 11357-3, is narrow and lies near 126 °C for a density of 0.934 g/cm³. If the mould surface temperature remains below the melting endset, the inner powder layer does not fully sinter and the part fails by pinholes or delamination.

What distinguishes the ORE 3220 formulation from Ziegler-Natta LLDPE and HDPE rotomoulding powders?

Conventional Ziegler-Natta LLDPE powders have a broad comonomer distribution, producing mixed crystalline domains with different melting points. The metallocene-catalysed Icorene 3545 base resin distributes short-chain branches more uniformly along the chain and across the molecular weight distribution. On a differential scanning calorimetry trace per ISO 11357-3, the melting endotherm is narrow, and the interval between melting endset and crystallization onset is smaller than that of a broad-distribution Ziegler-Natta powder. In biaxial shuttle trials with mould surface thermocouples, this narrow interval allows full densification at a lower peak internal air temperature than a Ziegler-Natta powder of identical melt flow rate and density. The operational consequence is reduced cycle time and lower thermal-oxidative load, because the polymer spends less residence time at high oven temperature.

Impact performance is not controlled by tensile yield alone. Instrumented puncture tests per ISO 6603-2 at -20 °C are used to detect ductile-to-brittle transition; the LLDPE grade is selected when a sharp brittle failure at -20 °C is unacceptable. Environmental stress crack resistance, evaluated by ASTM D1693 condition B in a wetting agent, is also used to qualify tanks and containers exposed to detergents. The published ESCR value for natural Icorene 3545 should not be applied to the ORE 3220 formulation without confirmatory testing on a rotomoulded part, because colourants and stabilisers can act as stress concentrators or modify surface energy.

Compared with a 0.945 g/cm³ HDPE rotomoulding grade, the 0.934 g/cm³ LLDPE base resin has lower flexural modulus. A representative HDPE rotomoulding grade may exhibit flexural modulus above 800 MPa by ISO 178, while the tabulated value for the LLDPE is 550 MPa. HDPE is the appropriate choice when top-load strength and creep resistance dominate; the LLDPE grade is selected for low-temperature drop impact, environmental stress crack resistance, and flexural fatigue. Compared with low-density polyethylene homopolymer, the LLDPE grade offers higher tensile yield strength and stiffness, but its sharper melting interval demands closer control of oven residence time and peak internal air temperature. Older rotomoulding machines with uneven air circulation may handle LDPE with a wider process window; the ORE 3220 formulation is therefore not a universal drop-in for all rotomoulding resins.

Failure modes concentrated at the sinter-melt boundary during biaxial rotation

On biaxial shuttle and carousel machines, the powder bed undergoes repeated avalanching and heating. The primary process variables are oven air temperature, residence time, peak internal air temperature, and cooling rate. For this grade, industrial practice sets oven air temperature between 280 °C and 310 °C; peak internal air temperature is controlled between 190 °C and 210 °C. Oven temperatures above 330 °C accelerate oxidative degradation and produce a yellow, low-molecular-weight layer on the inner surface, detectable by reduced impact and increased solvent wipe discolouration. Oven temperatures below 270 °C may not generate sufficient heat flux through the mould wall, leaving an unfused inner surface and poorly defined weld line.

Residence time is wall-thickness dependent. For a 6 mm nominal wall section in a 2.4 m swing diameter shuttle machine, total oven dwell is typically 18–25 min. Thick sections above 12 mm require staged heating and slower cooling because the outer layer sinters first while the inner layer remains below the crystallization point; the resulting thermal gradient creates shrinkage porosity in the core. A rotational speed ratio of 4:1 is common for symmetrical parts, while 8:1 is used for elongated shapes. An incorrect ratio produces excessive thinning at the poles or accumulation of powder in the mould centre.

Weld-line weakness is evaluated on a panel containing an intentional knit line. A 3.2 mm drop-dart test at -20 °C per ASTM D5420 is more discriminating than a standard tensile test because rotomoulded failures often occur at particle boundaries. Processors report three recurring failure modes: pinholes at weld lines due to trapped gas or insufficient surface temperature; orange-peel inner surfaces due to incomplete densification of fine particles; and warpage due to uneven cooling. The first two are corrected by adjusting peak internal air temperature and powder particle distribution, but the third is controlled by cooling rate.

Cooling rate is the most common source of warpage. A forced-air cooling segment of 8–12 min followed by a water mist segment of 3–5 min is typical. Demolding temperature should be at least 10–15 °C below the Vicat softening point of 116 °C. Premature demolding or one-sided water spray produces residual stresses that cause post-mold distortion. The powder should be conditioned in the processing hall for at least 12 h before charging; condensation on the mould surface from cold powder is a common source of surface specks.

When pelletised injection moulding LLDPE is substituted without requalification

The powder morphology of Icorene 3545 ORE 3220 is essential to rotomoulding. A pelletised injection moulding LLDPE with the same melt flow rate and density cannot be used directly because the particle size distribution is too coarse and the material does not form a uniform powder bed. Processing pellets in a rotomoulding machine produces thin spots at the mould surface and incomplete fusion at weld lines, even when oven residence time is extended. Conversely, using this rotomoulding powder in injection moulding after pelletisation is not a direct substitution; the additive package is not optimised for high-shear screw plasticating, and the narrow molecular weight distribution may reduce melt strength relative to broad-distribution injection grades.

If pelletising is required, a twin-screw extruder with a length-to-diameter ratio of at least 30:1 is used. The screw should provide moderate shear; melt temperature above 230 °C increases the risk of degradation of the UV stabiliser package. The compounder should measure melt flow rate after extrusion because thermal history can shift the value by 0.5–1.0 g/10 min. This shift is not necessarily outside the rotomoulding specification, but it must be understood before requalifying a moulded part.

Verifying lot-to-lot consistency in powder flow and sinter densification

Incoming quality control should measure density, melt flow rate, apparent density, and particle size distribution for each silo or batch. The ORE 3220 suffix may shift density and melt flow rate relative to the natural base resin because inorganic pigments and UV stabilisers add mass without melting. Pigment and stabiliser loading in such formulations commonly falls between 2 wt% and 5 wt%; at these loadings, measured composite density can rise by 0.003–0.007 g/cm³. Colour concentrate carriers with lower viscosity can cause localised flow lines on the inner surface. Batch-to-batch variance in powder particle size has a larger effect on cycle time than a 0.5 g/10 min difference in melt flow rate; process adjustment should therefore use particle size and peak internal air temperature, not MFI alone.

For incoming inspection, a stack of a 500 µm sieve and a 35 mesh screen is used. The fraction retained on the 500 µm sieve should be below 1 wt%, while the fraction passing the 35 mesh screen is monitored to avoid excessive fines. Melt flow rate drift after thermal ageing at 210 °C for 30 min can indicate inadequate stabilisation. An increase above 1 g/10 min after ageing is cause for rejection in critical outdoor applications.

Sinter densification is evaluated by moulding a flat panel under a fixed cycle and measuring thickness profile, gloss, and impact. The panel is cut along its axis, and the wall thickness is measured at 10 mm intervals; a variation greater than ±10% of nominal wall indicates an incorrect rotational speed ratio or uneven oven airflow. Impact testing of the panel per ISO 6603-2 at -20 °C is performed with a 20 mm hemispherical striker and 50 mm support ring. The lot is not qualified if the failure mode remains brittle at -20 °C in more than 20% of specimens.

For UV-stabilised variants, retained elongation after accelerated weathering is used. A xenon-arc exposure of 2000 h per ISO 4892-2 should not reduce tensile elongation below 50% of the unexposed value; the criterion is adjusted to wall thickness and geographic exposure. The test plaque is rotomoulded, not injection moulded, because stabiliser migration and surface oxidation differ between processes.

For outdoor applications under continuous exposure, the ORE 3220 package is formulated to retard UV-induced chalking and loss of impact, but published data for this exact suffix is limited. Weathering qualification must be performed by xenon-arc exposure per ISO 4892-2 or ASTM D2565 at the intended wall thickness. For food-contact applications, base-resin compliance with 21 CFR 177.1520 and Regulation (EU) No 10/2011 must be confirmed for the specific colourant and stabiliser formulation; not every formulated grade is automatically cleared. For electrical and electronic equipment, RoHS Directive 2011/65/EU compliance should be verified because colourants may contain regulated substances. The product should not be blended with incompatible masterbatch carriers or high-melt-flow polypropylene regrind; the viscosity mismatch disrupts inter-particle sintering and creates visible inclusions. If bulk storage exceeds 60% relative humidity or condensation is observed, pre-drying at 70–80 °C for 1–2 h is recommended; drying above 90 °C can cause surface oxidation.

In agricultural chemical tanks and marine fenders, the shell stress distribution should be calculated from hydrostatic load or buoyancy load and compared with the tensile yield strength of 15 MPa after applying a safety factor of at least 1.5. Long-term creep under load should be assessed per ISO 899-2. For automotive fluid reservoirs, permeability should be measured by weight loss at 60 °C over 14 days, because LLDPE barrier properties are lower than those of HDPE. For thin-wall parts below 3 mm, particles greater than 500 µm can produce localized lumps and incomplete fusion; a 35 mesh screen is used to remove oversize material before charging. Mold release agent must be applied at the minimum effective loading; excess release agent migrates to the part surface and reduces weld-line impact strength. Lot acceptance for critical applications should therefore include density, melt flow rate, particle size distribution, and an instrumented puncture test on a rotomoulded panel containing a weld line, rather than compression-moulded plaques alone.