LyondellBasell Icorene 3560 A1 ATC 9816 Polyethylene, Linear Low Density is a rotomoulding-grade ethylene/α-olefin copolymer powder. The grade designation identifies a low-pressure catalytically polymerised linear low density polyethylene with a short-chain branching distribution that places it in the intermediate stiffness range commonly used for hollow industrial parts. The ATC 9816 suffix refers to a specific additive configuration; the lot-specific certificate of analysis from the manufacturer takes precedence over generic trade compilations, and published data for this specific configuration is limited to supplier-controlled technical bulletins. The material is supplied as a ground powder rather than as pellets, which permits dry charging into closed or semi-closed mould cavities and promotes particle coalescence during the heating stage of biaxial rotation. In comparison with high-pressure autoclave low density polyethylene, the linear backbone of this product type reduces long-chain branching and produces higher tensile strength and environmental stress crack resistance for a given density.

Specification control for this product class should include melt mass-flow rate measured according to ISO 1133-1:2022 at 190 °C under 2.16 kg; density determined by ISO 1183-1:2019; particle size distribution by ASTM D1921; bulk density and dry flow by ASTM D1895; and tensile properties by ISO 527-2:2012. For linear low density polyethylene powders in the 0.930–0.940 g/cm³ density band, tensile yield stress commonly falls between 14 MPa and 20 MPa, elongation at break is generally above 600%, and flexural modulus ranges from 500 MPa to 800 MPa depending on comonomer type, test speed, and moulded skin effects. These ranges are class descriptions rather than lot-specific guarantees; final part qualification must be made on moulded plaques or cut specimens because rotomoulding produces anisotropic crystalline structures influenced by cooling rate and wall thickness.

Why Does the Powder’s Particle Size Distribution Govern Wall Thickness Uniformity?

Rotational moulding powders are not free-flowing thermoplastics in the sense of injection moulding granules; they exhibit bulk shear, angle of repose, and segregation behaviour that directly affect wall thickness consistency. For Icorene 3560 A1 ATC 9816 and similar linear low density polyethylene powders, the dry charge is heated while the mould rotates biaxially, and heat transfer through the powder bed controls the sintering rate. A screen cut with a maximum near 500 µm and controlled fines below 150 µm is normally maintained because coarse particles require longer residence time to densify, while excessive fines can segregate toward the inner free surface and create porosity or uneven layer growth. Production-scale carousel machines with arm ratios of 4:1 and 2:1 frequently show wall thinning at rib intersections when the hopper charge contains a broad particle size distribution; the finer fraction flows preferentially into narrow features before the coarser fraction is fully consolidated. Dry-flow time measured by ASTM D1895 should be recorded on incoming lots, and the powder should be kept dry during transfer. Condensation on cold powder is a process risk because surface moisture can generate steam porosity during the heating stage; if bulk powder has been stored in uncontrolled outdoor conditions, conditioning at 80 °C for 1 h may be applied before charging.

Mechanical characterisation of rotationally moulded specimens from this grade should be performed on flat panels cut from a controlled moulding trial, not on compression-moulded plaques alone. The reason is that rotomoulding produces a different crystalline morphology: slow cooling from the melt creates spherulitic growth that is interrupted by wall thickness constraints, and the inner surface can contain residual bubble patterns if peak internal air temperature is too low. These microstructural features influence tensile yield stress, flexural modulus, and impact behaviour more than the base resin melt flow rate alone. For parts assembled by fusion welding, the weld line should be tested according to ISO 13953 or the relevant pressure vessel code because weld strength in rotomoulded linear low density polyethylene can remain below parent material strength if oxidation has occurred at the weld zone.

Thermal Processing Envelope and Bubble Dissolution Kinetics

Heating and densification of rotomoulding-grade linear low density polyethylene follow a sequence of particle adhesion, sintering, melt film formation, and bubble dissolution. The processing window for Icorene 3560 A1 ATC 9816 is controlled less by melt mass-flow rate than by peak internal air temperature and oven residence time. Typical oven air temperatures for this product class are 250–320 °C, with peak internal air temperature commonly targeted between 190 °C and 220 °C. If the peak internal air temperature remains below 180 °C, residual undissolved gas bubbles may remain in the wall, reducing impact strength and producing a coarse inner surface. If it exceeds 240 °C for prolonged periods, antioxidant depletion accelerates and the inner surface may yellow or embrittle. Bubble dissolution is also rate-dependent: viscosity at the processing temperature must be low enough to allow gas diffusion, but excessive melt fluidity can cause localised wall thinning on vertical surfaces. A useful in-process check is the absence of visible pinholes in a translucent section, followed by a drop-weight impact test on a test piece cut from the same moulding.

Demoulding temperature is another operational boundary. Linear low density polyethylene rotomoulded parts should be cooled below 80 °C before ejection when dimensional tolerances are tight. Cooling rate is an independent variable: forced-air cooling in the range of 8–15 °C/min generally gives a better balance of crystallinity and warpage control, while water-mist cooling at 15–30 °C/min can shorten cycle time but increases differential shrinkage between thick and thin sections. Warpage is also influenced by mould release, wall thickness distribution, and the temperature of the mould surface at charging. Moulds with narrow ribs or internal inserts may require higher release agent dosage, but zinc stearate above 0.2–0.5 wt% can interfere with melt film formation and create pinholes. When dimensional stability is critical, the part should be fixtured during cooling or annealed at 100–120 °C for a time proportional to wall thickness.

When the Part Is Destined for Outdoor Service and Chemical Contact

Outdoor rotomoulded parts made from Icorene 3560 A1 ATC 9816 are typically specified for agricultural tanks, industrial containment basins, outdoor seating, and playground components where the part must tolerate sunlight, temperature cycling, and occasional chemical exposure. The ATC 9816 additive package is usually selected for extended weathering resistance, but the exact ultraviolet stabiliser type and loading should be confirmed from the manufacturer’s technical datasheet because additive packages with similar trade suffixes can differ by production site and regulatory region. Accelerated weathering should be conducted according to ISO 4892-2 with failure criteria based on retained elongation at break rather than colour change alone. A retained elongation of 50% after a specified xenon-arc exposure interval is a common screening criterion for outdoor structural parts, but this value must be agreed between the moulder and end user for each formulation.

Chemical resistance testing should follow ISO 4433-1 or ASTM D543 for the specific contact fluid. Linear low density polyethylene of intermediate density is generally resistant to aqueous salt solutions, dilute alkalis, and many polar solvents at ambient temperature, but strong oxidising acids, chlorinated solvents, and certain hydrocarbons can swell or degrade the polymer. Environmental stress crack resistance measured by ASTM D1693 is a better indicator of long-term failure in detergent or wetting-agent environments than tensile strength. When the part is used for potable water or food contact, compliance must be verified under the relevant regulation: FDA 21 CFR 177.1520 for olefin polymers in the United States, EU Regulation (EU) No 10/2011 within the European Union, and applicable national migration limits elsewhere. Compliance depends on final part construction, contact temperature, and food simulant; the resin supplier’s regulatory statement is not a substitute for finished article testing.

The Substitution Decision Depends on ESCR, Stiffness, and Mould Shrinkage

Compared with a high-pressure autoclave low density polyethylene of the same melt flow rate, the linear low density polyethylene used in Icorene 3560 A1 ATC 9816 has a narrower molecular weight distribution and short-chain branches rather than long-chain branches. This molecular architecture raises tensile strength, modulus, and environmental stress crack resistance but can increase mould shrinkage anisotropy. When a converter replaces autoclave LDPE with this grade in an existing tool, the part may require a slightly higher peak internal air temperature or a longer cooling cycle because linear low density polyethylene can exhibit more differential shrinkage at sharp corners. Compared with high density polyethylene rotomoulding grades, the intermediate density of this product provides lower flexural modulus and higher impact resistance at low temperatures, which is important for large flat panels that would otherwise crack at -20 °C to -30 °C. High density polyethylene may be preferable when greater stiffness or heat resistance is required, but it often sacrifices environmental stress crack resistance and low-temperature ductility.

Blending with other polyethylenes should be approached as a formulation change, not as a routine adjustment. Adding more than 30 wt% of high-pressure low density polyethylene may improve dry flow and surface gloss but can reduce tensile yield stress and environmental stress crack resistance below the value required by the part specification. Adding high density polyethylene can raise modulus but may create a processing mismatch if the two powders sinter at different rates. Pigment masterbatches and ultraviolet masterbatches should be dry-blended in a low-shear mixer because high-shear mixing can generate fines and alter the particle size distribution. The mould charge should be homogenised immediately before each cycle to prevent pigment segregation during hopper residence. Lot-to-lot variation in stabiliser content and particle size distribution is possible; incoming inspection should therefore include dry flow, bulk density, melt flow rate, and a small-scale moulding trial when the part wall thickness is below 4 mm or when the part is safety-critical.

Icorene 3560 A1 ATC 9816 is positioned for rotational moulding applications in which the converter needs linear low density polyethylene toughness without moving to a high-density stiffness class. The material is not intended for film extrusion, injection moulding, blow moulding, or pipe extrusion, and it should not be processed at melt temperatures above the supplier’s stated limit. Because published data for this specific configuration is limited, all critical values should be obtained from the LyondellBasell lot certificate and confirmed by moulded plaque testing before production release.