LyondellBasell Icorene 3546 UV+ GRN 6414 is a linear low-density polyethylene powder produced for biaxial rotational molding of hollow parts. The grade is pre-stabilized and pre-compounded with a green 6414 color package, placing it outside the natural LLDPE powder category. Supplier typical property documentation reports a density of 0.934 g/cm³ measured by ISO 1183-1 and a melt flow index of 4.0 g/10 min at 190 °C under 2.16 kg load in ISO 1133-1. The resin is used in outdoor chemical storage, agricultural tanks, playground enclosures, marine flotation devices, and industrial covers. The principal difference from unpigmented Icorene grades is the elimination of dry-blended masterbatch at the molding machine and the associated color segregation; the principal difference from HDPE rotomolding grades is a lower flexural modulus and higher environmental stress-crack resistance.

Why Does a Pre-Colored UV+ Grade Reduce Rotomolding Pigmentation Variance?

When natural rotomolding powder is dry-blended with a granular pigment masterbatch at the hopper, the two components have different bulk densities, particle sizes, and flow behaviors. Vacuum conveying, auger feed, and mold rotation can stratify the mixture before the powder reaches the heated mold wall. The result is color streaking, local pigment agglomeration, and shot-to-shot ΔE variation that is often measured with a spectrophotometer against the CIELAB L*a*b* reference. In contrast, the 3546 UV+ GRN 6414 grade is compounded under high-shear twin-screw mixing before grinding, which wets pigment particles with polyethylene and stabilizes the colorant distribution in the final powder. On carousel machines running multiple aluminum molds from a common hopper, the pre-compounded grade reduces the manual weigh-up error and segregation that occur when operators add 2–3 wt% masterbatch to natural powder. The incorporated pigment also affects infrared absorption during oven heating; green colorants can reflect a different fraction of the incident IR spectrum than natural powder or carbon black, so the grade and final wall thickness should be temperature-profiled together.

The mechanical design envelope for this LLDPE grade includes tensile yield strength near 18 MPa per ISO 527-2/1A, elongation at break above 700%, and flexural modulus in the range of 550–750 MPa per ISO 178. The environmental stress-crack resistance under ASTM D1693 condition B, 10% Igepal CO-630 at 50 °C, is typically reported above 1,000 h for the base resin family; actual values for green-compounded powder should be confirmed by lot certificate. Low-temperature resistance is commonly assessed by impact testing on rotomolded plaques rather than by neat resin tests, because cooling rate, wall thickness, and internal stress dominate field performance. Published data for the specific GRN 6414 configuration at sub-−20 °C service is limited; final-part testing under ISO 179-1 Charpy or equivalent is required before use in cold-climate structural parts.

Powder Morphology, Sieve Retention, and Machine Feed Consistency

Rotational molding powder is characterized by dry-flow time, bulk density, and particle-size distribution, not simply by melt flow index. The Icorene 3546 family is typically supplied as a ground powder with a 35-mesh profile; sieve analysis per ASTM D1921 is used to control the fraction retained on 500 µm, 250 µm, and 150 µm screens. Fines below 150 µm can create dust during mold charging and tend to melt prematurely, producing small pits on the outer surface. Oversized particles above 500 µm may not fully coalesce in short oven residence times and can leave pinholes at the inner surface. Dry-flow values below 35 s/100 g by ASTM D1895 Method A are typical for clean feed through 25-kg bag dumping stations and flexible screw conveyors. The bulk density of this type of rotomolding powder is commonly between 0.38 g/cm³ and 0.42 g/cm³; a lower bulk density changes the shot weight that fills a given mold volume, and processors should recalculate fill ratios whenever the powder source changes.

At the low shear rates encountered in rotational molding—typically below 10 s⁻¹—the melt viscosity of LLDPE is shear-rate-sensitive but not as temperature-sensitive as that of HDPE. The zero-shear viscosity of a 4.0 g/10 min LLDPE at 190 °C is commonly in the range of 2 × 10⁴ Pa·s to 5 × 10⁴ Pa·s, which is high enough to allow the powder to densify and sinter before flow fills the mold. In thick sections, trapped air bubbles must escape through the melt; bubble removal is governed by melt viscosity, surface tension, and mold surface temperature. The green pigment particles can act as nucleating sites or as local viscosity modifiers, so bubble-entrapment behavior should be established using sectioned plaques.

On shuttle and carousel rotational molding machines, the recommended mold surface temperature is between 260 °C and 320 °C. The peak internal air temperature for LLDPE of this density is typically maintained between 190 °C and 210 °C; falling below 190 °C can leave partially coalesced particles and lower ESCR, while exceeding 230 °C for extended periods accelerates thermo-oxidative degradation and may darken the green color. Cooling must be controlled because LLDPE crystallization continues below 80 °C; forced-air cooling followed by water mist is common, but rapid quenching of thick sections can increase amorphous orientation and distort large flat panels. The biaxial rotation ratio is set by mold geometry; ratios of 4:1 primary to secondary are a starting point on shuttle machines, but rock-and-roll machines for long tanks may use a single-axis rock with approximately 30° to 45° swing. Rotational molding tooling is typically fabricated from cast aluminum or stainless steel. Aluminum molds provide higher heat transfer and shorter cycle times but are more prone to surface wear from filled or abrasive powders; 3546 UV+ GRN 6414 is unfilled, so tool wear is not a primary concern. Mold release agents based on silicone or PTFE should be applied to thin cross-sections sparingly, because excessive release agent can be entrapped at the inner surface and reduce weld-line strength.

When ESCR and Low-Temperature Impact Govern Tank Design over Density

For outdoor liquid storage, rotomolding engineers often choose a lower-density LLDPE because slow crack growth resistance is more important than the higher stiffness of an HDPE grade. Icorene 3546 UV+ GRN 6414 has a density below 0.940 g/cm³; the lower crystallinity leaves a larger fraction of amorphous tie molecules between lamellae. Under constant hoop stress in a filled tank, the tie-molecule network resists crack opening at stress concentrations such as weld lines, insert bosses, and the liquid fill line. This behavior is measured by ASTM D1693 and by ISO 22088-3 bent-strip methods, and for long-term hydrostatic design by ISO 9080 regression of pipe-grade data. The trade-off is reduced flexural modulus relative to HDPE: the same sidewall deflects more under head pressure, so tank walls are often thickened by 10–20% or reinforced with rotationally molded ribs. The low-temperature impact of the finished part is a function of section thickness and mold surface finish; brittle transitions are evaluated by impact testing at −20 °C and −40 °C on samples cut from the actual moldings, not solely on compression-molded plaques.

Outdoor service degrades polyolefins through free-radical oxidation initiated by ultraviolet radiation, leading to surface chalking, loss of gloss, and tensile elongation loss. The UV+ package in Icorene 3546 contains a hindered amine light stabilizer and a UV absorber, dispersed during pellet production to survive the grinding step. Accelerated weathering per ISO 4892-2 cycle 1, with a 0.51 W/m² irradiance at 340 nm and black panel temperature of 65 °C, is used to compare stabilized grades against unstabilized controls. Unstabilized LLDPE can lose more than 50% of its original elongation within 3,000 h of xenon-arc exposure; stabilized rotomolding grades are expected to retain the majority of their elongation over the same interval, although actual retention depends on wall thickness, cooling rate, and pigment loading. The green pigment can elevate surface temperature under solar exposure by absorbing visible and near-infrared radiation, so the service temperature at the exposed surface is somewhat higher than for white or natural parts. Published data for GRN 6414 after 5,000 h of xenon-arc exposure is limited; requesting supplier weathering curves is advisable before specifying a multi-year outdoor service interval.

A Comparative Table for Stiffness, Stress-Crack Resistance, and UV Stability

The table below compares the general property envelope of Icorene 3546 UV+ GRN 6414 with a natural LLDPE rotomolding powder and an HDPE rotomolding grade. The values are typical ranges and should not be read as specification limits.

The practical difference in rotational molding is that the precolored grade removes a manual compounding step and its attendant lot-to-lot drift, while the HDPE alternative gains stiffness at the cost of ESCR and low-temperature ductility. MDPE grades occupy an intermediate position with density near 0.940 g/cm³ to 0.945 g/cm³, but their processability window is often narrower because the higher crystallinity can produce more shrinkage and warpage in asymmetric molds. Crosslinkable PE grades offer higher heat distortion and creep resistance, but they cannot be reground and reprocessed as readily as a linear low-density grade.

Regulatory Status When the Finished Article Contacts Food or Potable Water

The base polyethylene is typically manufactured to meet FDA 21 CFR 177.1520 for olefin polymers, but that clearance applies to the base polymer and specified end-use extractive conditions, not automatically to a green pigmented finished article. The UV stabilizer and pigment package must be evaluated under the relevant national or regional food-contact framework. For European Union food contact, plastic materials and articles must comply with Regulation (EU) 10/2011, including overall migration limits of 10 mg/dm², and the pigment must be listed or authorized. For drinking-water components in North America, NSF/ANSI 61 certification is article-specific and depends on formulation, surface-to-volume ratio, and exposure temperature. The grade is therefore more commonly specified for non-food outdoor chemical storage and agricultural tanks than for direct potable-water contact. Metal release and heavy-metal restrictions under REACH and RoHS Directive 2011/65/EU can be addressed by supplier declarations, but these are not substitutes for article-level compliance testing.

Field applications for Icorene 3546 UV+ GRN 6414 include rotationally molded agricultural sprayer tanks, water storage tanks, outdoor playground components, marine buoys, road barriers, and machinery covers. The green color serves as a visual designation for chemical compatibility or asset ownership without secondary painting; polyethylene surfaces require flame, corona, or plasma treatment before coating, so precompounded color avoids that process step. Agricultural chemical contact can induce environmental stress cracking even at low concentrations because surfactants and emulsifiers act as ESC agents. Tanks used for glyphosate, paraquat, or ester-based formulations should be tested under ASTM D2561 or by internal pressurization after contact with the formulation. The high ESCR of LLDPE is advantageous, but the rotational molder must ensure complete fusion of weld lines; any undercured region becomes a preferential crack-initiation site. Wall-thickness mapping of rotomolded tanks with ultrasonic gauges is often specified at 18–25 points to verify minimum wall thickness before the tank enters service. Processors should not expose the grade to strong oxidizing acids, aromatic solvents, or low-boiling hydrocarbons at elevated temperature without chemical resistance data for the exact fluid, concentration, and service temperature. Cold-climate installations below −20 °C require final-part impact testing because weld-line quality, wall-thickness distribution, and UV history override neat resin ductility. Dimensional stability after demolding is improved by cooling fixtures for large flat panels, especially when the green pigment raises the surface temperature during outdoor storage.