LyondellBasell Icorene 3546 YEW 2912 Polyethylene, Linear Low Density is a linear low-density polyethylene rotational moulding powder. The base resin is characterised by a density of 0.935 g/cm³ when tested in accordance with ISO 1183-1 or ASTM D1505 and by a melt mass-flow rate of 5.0–5.5 g/10 min at 190 °C under 2.16 kg load per ISO 1133-1. The YEW 2912 suffix is a producer-specific article code rather than a generic resin designation; such suffixes commonly identify a defined stabilizer and/or colour package in rotational moulding supply practice. The exact additive formulation must be confirmed from the lot certificate of analysis and safety data sheet rather than from the general technical data sheet.

The material is supplied as a ground powder rather than as pellets because rotational moulding requires controlled particle size distribution, apparent density, and dry-flow behaviour matched to biaxial tool filling. Published data for this specific YEW 2912 powder configuration is limited for particle size distribution and additive masterbatch composition; lot-specific values must be verified before production scale-up. The polymer backbone is an ethylene/α-olefin copolymer with short-chain branches that reduce crystallinity below that of a high-density polyethylene and provide a balance of stiffness, low-temperature impact, and slow crack growth resistance.

How does YEW 2912 compare with a standard rotational moulding MDPE?

Compared with a typical rotomoulding medium-density polyethylene of 0.940 g/cm³, the 0.935 g/cm³ LLDPE base shows lower flexural modulus and Vicat softening temperature but generally longer environmental stress-crack resistance and better retention of low-temperature impact. The following representative values are drawn from producer technical literature for the resin class; the certificate of analysis for the specific lot remains the governing document.

The lower density and modified comonomer distribution also affect shrinkage and warpage. Parts moulded from the 0.935 g/cm³ grade typically exhibit lower differential shrinkage in thick-to-thin transitions than equivalent MDPE parts because the reduced crystalline fraction generates less post-demoulding crystallisation stress. This is not a property specification; prototype mouldings must be measured for a given tool geometry and cooling protocol.

Mechanical characterisation of rotomoulded parts should not rely solely on compression-moulded plaques. The biaxial rotation creates knit lines, internal voids, and thickness variation; tensile specimens cut from flat tool sections and tested under ISO 527-2 may show lower elongation at break than resin data-sheet values. The Association of Rotational Molders low-temperature impact method or instrumented puncture per ISO 6603-2 provides part-relevant impact data because falling-dart tests and Izod values from compression-moulded sheets do not fully capture weld-line and void effects.

Densification and bubble removal require a defined internal air-temperature plateau

On shuttle or carousel rotational moulding machines carrying steel tools, the external oven-air temperature is generally set between 280 °C and 300 °C. The critical control parameter for this resin class is the internal air temperature measured inside the rotating mould. Complete densification for a 6 mm nominal wall is observed when the internal air temperature reaches 190–200 °C. Removal below 185 °C is associated with residual microvoids, poor inner-surface definition, and reduced low-temperature impact. Extended plateaus above 205 °C accelerate antioxidant consumption, increase carbonyl index, and can produce colour shift or embrittlement. The processing window is therefore narrow in the internal air-temperature domain, even when oven-air temperature remains constant.

For a 230 mm cubic steel tool on a three-arm shuttle machine with forced-air cooling, oven residence times in the range of 25–35 min are typically reported for this density class, depending on wall thickness, shot weight, and tool thermal mass. Cooling rate through the crystallisation region from 125 °C to 95 °C affects crystallite size, part warpage, and inner-surface stress. Air cooling followed by water mist shortens cycle time but can increase bowing on flat panels; the lower crystallinity of this LLDPE grade reduces but does not eliminate such distortion. The melt mass-flow rate of 5.0–5.5 g/10 min supports faster sintering and bubble migration than a fractional-melt HDPE rotomoulding grade, but it also reduces melt strength on vertical walls; excessive oven residence can produce inner-wall sagging in deep-draw tools.

During powder densification, individual grains undergo contact-neck growth driven by surface tension. The characteristic time for void disappearance scales with melt viscosity and particle radius; coarser powder fractions therefore increase the required plateau time. For thin-wall work, sieve retention above 500 µm is a practical upper limit because coarse particles may remain as partially sintered inclusions. Fine particles below 150 µm densify quickly but can undergo thermal degradation near the mould wall when the oven setpoint exceeds 300 °C. Production-scale failures on shuttle equipment are frequently caused by premature demoulding before the internal air-temperature plateau, by uneven heating from blocked oven ducts, or by cold spots at tool supports. Darkened inner surfaces after demoulding indicate antioxidant depletion from excessive oven residence or local overheating; this failure mode develops in the powder layer and is not visible in the bulk pellet.

Because the material is supplied as powder, dry-flow characterisation by ASTM D1895 Method A apparent density and sieve analysis per ISO 4610 is relevant to hopper feeding and mould fill. A narrow particle size distribution reduces segregation and dust; excessive fines below 150 µm lower apparent density and may cause bridging in bulk handling equipment. The producer's certificate of analysis provides lot-specific sieve retention data, which should be compared against the handling equipment capability before silo transfer.

Where rigid chemical tanks, agricultural water troughs, marine buoys, and below-ground utility enclosures require a combination of toughness, slow crack growth resistance, and outdoor service, this resin class is specified for rotational moulding. The stabilizer package associated with the YEW 2912 code is intended for prolonged outdoor exposure, but the producer documentation must be consulted for ultraviolet weathering warranties and colour retention data. The grade is not automatically approved for potable-water contact in all regulatory jurisdictions; compliance with FDA 21 CFR 177.1520, EU Regulation (EU) No 10/2011, or NSF/ANSI 61 must be confirmed for the specific additive package and the extraction profile of the finished moulding. Food-contact statements apply only to the base polyolefin and are invalid if post-moulding operations introduce non-compliant surface treatments or colourants.

Environmental stress-crack resistance and chemical exposure boundaries

Slow crack growth resistance is a defining property for rotomoulded LLDPE tanks and enclosures. The typical ESCR for this density class exceeds 1000 h in 10% Igepal CO-630 under ASTM D1693 condition B. This supports use in parts that experience tensile stress at internal corners, around moulded-in inserts, and in thick-to-thin transitions. By comparison, a rotomoulding HDPE of 0.945 g/cm³ typically provides higher flexural modulus but significantly shorter ESCR in the same test; the 0.935 g/cm³ LLDPE grade is therefore selected for fatigue-prone liquid containment rather than for high top-load structural stiffness.

The polymer absorbs very little water and resists dilute mineral acids, alkalis, aqueous salt solutions, and many polar solvents up to approximately 60 °C. Continuous immersion in strong oxidising acids such as 98% sulfuric acid or concentrated nitric acid is outside the operating limit. Aromatic hydrocarbons, chlorinated solvents, and high-octane gasoline blends with oxygenates can swell the polymer; when the stored fluid produces more than 1–2% mass gain at service temperature, design stress should be reduced and permeation losses assessed. For outdoor chemical storage, the rotational moulded part should be tested with the intended fluid at the upper service temperature because ESCR ranking changes with chemical environment and residual stress from moulding.

Operational limitations include the following. Powder pre-drying is generally not required at ambient relative humidity below 60%, but moisture contamination from bulk handling should be avoided because vaporisation during oven residence can generate pores. Reprocessed material from the same resin should not exceed 20 wt% without validation, because higher addition levels reduce impact and can raise the minimum internal air temperature required for densification. The grade should not be dry-blended with pigment or antistatic masterbatches that lower thermal stability unless oven-aging data confirm that the 280–300 °C peak temperature remains tolerable. Storage should be away from direct sunlight and at temperatures below 50 °C; prolonged storage beyond the producer-specified shelf life can alter dry-flow even when the stabilizer package remains effective.