LyondellBasell Icorene 3560 BWN 8903 is a black, UV-stabilised linear low density polyethylene powder intended for rotational moulding. The product is supplied as a free-flowing powder rather than pellets, and its particle-size distribution is controlled for consistent dry-flow hopper discharge and uniform melt densification. The numeric designation 3560 identifies the melt-flow and density set within the Icorene linear low density polyethylene range; BWN denotes a black weathering grade, and 8903 identifies the specific stabiliser and pigment formulation. The material is used in outdoor agricultural tanks, chemical storage vessels, utility ducting, and rotationally moulded industrial housings where carbon black pigmentation and long-term weathering resistance are required. Compared with high-pressure LDPE homopolymer, the linear low density backbone provides higher environmental stress-crack resistance and higher tensile yield stress at similar density. Compared with HDPE rotomoulding powder of typical melt flow rate 4.0 g/10 min, the 6.0 g/10 min melt flow rate of this grade provides lower melt viscosity and permits more uniform wall-thickness distribution in complex ribs, although the lower density 0.935 g/cm³ also lowers flexural stiffness. Compared with metallocene-catalysed LLDPE grades, the product tends to show a broader processing window and lower sensitivity to peak internal air temperature variation, although published comparative data for this exact grade against metallocene grades is limited. Representative property data are summarised below.

Representative values are lot averages, not minimum specifications. The ESCR value is a typical category value for a black LLDPE rotomoulding grade with carbon black and weathering additives; actual values vary with moulded wall thickness, cooling rate, and regrind content.

Processing Boundaries Are Defined by Sintering, Not by Melt Index Alone

On shuttle-type rotational moulding machines with a 4:1 arm ratio and oven air velocity of 7–12 m/s, the powder undergoes a sequence of tackification, sintering, bubble dissolution, and densification. The melt flow rate of 6.0 g/10 min is sufficiently low in viscosity to allow the melt to coat the mould surface, but the actual process window is controlled by peak internal air temperature, not by melt index alone. A minimum PIAT of 190 °C is required to eliminate trapped air; however, sustained PIAT above 240 °C accelerates oxidative chain scission at the air-polymer interface and can produce amber discolouration even in black parts. Observed failure modes include pinholes when PIAT remains low, powder bridging in narrow ribs when the mould surface is heated too rapidly, and flat-spot warpage when cooling is stopped before the part drops below 60 °C. Recommended heating ramps for wall sections from 4 mm to 8 mm bring the mould surface to 150 °C at 8–10 °C/min, then hold at PIAT 210 °C for 8–12 min before forced-air cooling at 10–15 °C/min to demould at 70 °C or lower. Pre-drying is required when powder moisture exceeds 0.05 wt% or when storage humidity has exceeded 60% relative humidity, because absorbed water leads to steam bubbles and pitted inner surfaces. The black pigment increases radiative heat absorption compared with natural LLDPE; infrared pyrometer settings should be adjusted for emissivity 0.92–0.96 or mould surface temperature will be underestimated.

These values are typical starting points for a shuttle machine with wall thickness 4–8 mm and should be adjusted by trial because mould geometry and oven characteristics shift the actual optimum. Batch-to-batch variation is normally controlled by the supplier’s internal specification, but segregation during silo discharge can produce a higher density fraction and a lower melt-flow fraction in the final packaging; rotational moulders should sample from multiple bags when auditing a delivered lot. Incoming powder should be tested for melt flow rate by ISO 1133-1 and density by ISO 1183-1 on each lot. Sieve analysis by ISO 4610 or ASTM D1921 should be conducted at the silo outlet, not at the bag, because fines migration during transport can change the distribution by 2–5%. On a vertical ribbon blender with capacity 1,000 kg, the dry blend should be mixed for 10–15 min after any regrind addition. Overmixing can generate fines and static charging, which reduces flowability in deep cavity moulds.

On open-flame equipment, black powder requires a gentler heating programme than natural LLDPE because the pigment increases radiative absorption. Flame impingement on uncoated mould surfaces can create hot spots above 260 °C and rapid local oxidation. The flame should be adjusted to a soft luminous flame with a reducing tip rather than an oxidising blue flame, and the operator should keep the flame moving across the rotating mould. Published data for this exact grade on open-flame equipment is limited; the practice described is common for black LLDPE rotational moulding powders.

What Limits Weathering Resistance in Carbon Black-Modified LLDPE Rotomoulding Grades?

The outdoor service life of LyondellBasell Icorene 3560 BWN 8903 is governed by carbon black dispersion, stabiliser activity, and the surface temperature history of the moulded part. In black LLDPE, carbon black acts as a UV absorber and free-radical scavenger, but its protective value is lost if agglomerates exceed approximately 20 µm in primary particle size because microcracks initiate at agglomerate-polymer interfaces. The proprietary 8903 stabiliser formulation is added to protect the melt during the long heating phase and to retard photo-oxidation after installation. Accelerated weathering should be screened according to ISO 4892-2 method A or ASTM G154 cycle 2; however, published outdoor multi-year data for this specific grade is limited, and xenon or QUV hours cannot be converted directly into years of service. Black parts in tropical sunlight may reach surface temperatures above 70 °C, which increases the rate of hindered amine stabiliser consumption and can cause local oxidation at weld lines and sharp corners. A converter should not assume that the presence of carbon black alone confers UV protection; dispersion must be confirmed by optical microscopy on 20 µm microtomed sections. Thermo-oxidative stability should be evaluated by ASTM D3895 or ISO 11357-6 on samples taken from moulded parts, not from powder. Dry-blending with additional phenolic antioxidant or phosphite stabiliser masterbatches is not recommended without compatibility testing, because additive interactions can reduce the oxidative induction time rather than raise it.

In outdoor agricultural spraying equipment and site-built chemical tanks, the grade is selected over natural LLDPE because the black weathering package suppresses chalking and surface embrittlement after intermittent exposure to fertiliser solutions, UV radiation, and cleaning agents. The linear low density backbone provides environmental stress-crack resistance in the presence of non-ionic wetting agents; however, silicone-based surfactants and some ester-containing crop oils can plasticize the polymer, and the converter must test the specific formulation under ISO 175 or ASTM D1693 after moulding. Field experience in subtropical and temperate environments indicates that black LLDPE rotationally moulded tanks with minimum wall thickness 6 mm retain impact toughness after three to five years; published multi-year data for this exact grade is limited. Regrind from rejected agricultural parts should be limited to 20 wt% or lower because repeated grinding shifts the particle-size distribution toward fines and the carbon black distribution becomes less uniform. Chemical storage service also requires ISO 175 immersion testing in the intended medium at maximum use temperature. LLDPE is generally resistant to dilute aqueous acids and alkalis, but aromatic and chlorinated hydrocarbons can plasticize the amorphous phase and reduce stress-crack resistance.

When Black LLDPE Replaces Natural LLDPE in Multi-Station Carousel Tooling

When a multi-station carousel machine is converted from natural LLDPE to LyondellBasell Icorene 3560 BWN 8903, the oven settings require adjustment because the black surface absorbs infrared energy faster. Oven temperature should be reduced by 5–10 °C or the heating time shortened by 1–3 min to avoid exceeding the 240 °C PIAT limit. On a 500 L agricultural tank mould, cycle time is typically limited by the need to achieve 190 °C minimum PIAT in the thinnest wall while keeping the thickest boss below 230 °C. Heating delay after mould release is set to 30–45 s to allow the black powder to flow into narrow ribs before tackification begins. Compared with HDPE rotomoulding powder, the lower modulus of this LLDPE grade means structural parts should use 10–15% thicker walls or additional ribbing when equivalent stiffness is required. The lower density of 0.935 g/cm³ reduces part weight relative to HDPE at the same wall thickness. Compared with LDPE homopolymer, the grade yields a higher tensile yield stress and better ESCR, which is relevant for moulded-in threaded inserts and metallic nut inserts where stress concentrations initiate cracks. When the part includes brass or steel inserts, the thermal expansion mismatch between metal and black LLDPE should be accommodated by insert preheating to 100 °C or by using rounded bosses; sharp insert geometries increase localized stress and lower the failure threshold.

Food-contact compliance is not automatically established by the resin grade and must be validated under the applicable national regulation for the finished article. Regulatory declarations for REACH and RoHS should be confirmed from the supplier safety data sheet before export. No statement in this document replaces the LyondellBasell product specification, and the converter is responsible for process validation on the production machine.