LyondellBasell Icorene LMDPE 3650 is a linear medium density polyethylene rotational moulding powder classified within the Icorene polyolefin portfolio as a stiffness-modified grade for single-layer and multi-layer rotational moulding. The material is characterised by a nominal density of 0.936 g/cm³ when determined according to ASTM D1505-18 or ISO 1183-1:2019 and a melt flow rate of 5.0 g/10 min at 190°C under a 2.16 kg load according to ASTM D1238-20 Procedure A or ISO 1133-1:2022 Method A. The numeric designation 3650 differentiates the product from lower-density linear low density polyethylene and higher-density high density polyethylene rotational moulding powders within the same manufacturing range. The grade is designed for closed-tool rotational moulding of hollow parts in which a combination of higher flexural stiffness, moderate melt flow, and low-temperature impact retention is required.

The base polymer is a linear polyethylene with short-chain branching introduced through comonomer incorporation. This structure produces a density and crystalline fraction that lie between conventional LLDPE rotational moulding grades in the 0.918–0.925 g/cm³ range and HDPE rotational moulding grades above 0.940 g/cm³. The consequence is a property balance that shifts away from the high dart impact behaviour of very low-density PE grades and away from the high creep resistance but lower stress crack tolerance of some high-density grades. Specific datasheet values should be verified with the manufacturer; published data for this exact configuration are limited to typical property tables and processing guidance.

How Does LMDPE 3650 Compare With Standard Linear Low Density Rotational Moulding Powders?

At a nominal density of 0.936 g/cm³, the grade exhibits greater flexural modulus, higher surface hardness, lower permeability, and improved environmental stress crack resistance than most LLDPE rotational moulding powders. The melt flow rate of 5.0 g/10 min provides lower viscosity during powder sintering than fractional-melt or 3.0 g/10 min grades, which can improve wall-thickness uniformity in tools with deep draw, ribs, or narrow channels. The difference in property profile is quantified in the following representative data set.

These values are typical and should not be read as specification limits. The increase in flexural modulus relative to a 0.920 g/cm³ LLDPE rotational moulding powder is commonly reported in the range of 25–30% when measured under identical laboratory conditions, while elongation at break remains above 300%. The retained elongation is significant because higher-density PE grades can lose ductility rapidly when cooling rates are not controlled. LMDPE 3650 therefore occupies an intermediate position in which stiffness is raised without the full low-temperature impact penalty of a high-density homopolymer or low-comonomer copolymer.

When the powder is charged into a closed single-piece tool on a shuttle-type, carousel, or rock-and-roll rotational moulding machine, the lower zero-shear viscosity associated with a 5.0 g/10 min melt flow rate reduces the time required for particle coalescence and bubble removal. Production-scale experience on shuttle machinery with forced-air oven temperatures of 280–300°C indicates that this grade can produce smooth inner surfaces when the peak internal air temperature is maintained in the range of 190–205°C. Tool rotation ratios are typically set at 4:1 for near-symmetrical parts and may be adjusted to 1:5 for elongated parts. Powder dry-flow consistency and bulk density should be monitored because lot-to-lot variation in ground powder particle size distribution can alter the fill weight and wall thickness in narrow tool sections.

When Peak Internal Air Temperature Exceeds 210°C During LMDPE 3650 Moulding

Thermal exposure during rotational moulding is the principal boundary condition for this grade. If the peak internal air temperature exceeds 210°C, the inner surface can enter an oxidative degradation regime in which carbonyl species form, polymer melt viscosity increases unevenly, and impact strength declines. The issue is not merely discoloration; accelerated oxygen uptake in the air space inside the mould can generate surface pinholes, bubble entrapment, and a brittle inner skin that fails under low-temperature impact. At the opposite boundary, peak internal air temperatures below 170°C are associated with incomplete sintering, residual powder particles, and low weld-line strength at thin-wall intersections. These are not uniquely product-specific thresholds but are observed process limits for LMDPE rotational moulding powders on production-scale shuttle equipment.

Processors measure peak internal air temperature using a thermocouple inserted through the mould vent. The thermocouple reading should be recorded every cycle because oven set-point changes do not translate linearly to internal air temperature when mould mass, tool thickness, and part wall thickness vary. In tools with steel thickness above 6 mm, the oven residence time required to reach a given internal air temperature can be 20–30% longer than in aluminium tools of equivalent size. Cooling rate after demoulding is equally influential. Forced-air cooling at an initial rate of 10–15°C/min followed by water mist is preferred over immediate water quench because rapid cooling across the crystalline solidification range can induce warpage, internal stress, and impact failure at mould parting lines.

Environmental stress crack resistance is a primary differentiator in chemical containment and fuel tank applications. In a rotationally moulded diesel fuel tank, the polymer is exposed to constant hydrostatic pressure, weld-line stress concentrations, and hydrocarbon contact. The >1000 h ESCR value reported under ASTM D1693-21 Condition A with 100% Igepal CO-630 indicates resistance to slow crack growth under this type of service. By comparison, standard LLDPE rotational moulding powders may fail before 100 h in the same test, while high-density homopolymers with higher density may exhibit lower ESCR due to reduced tie-molecule concentration. The comonomer distribution in LMDPE 3650 is therefore the controlling variable that permits simultaneous stiffness and stress crack tolerance.

Environmental Stress Crack Resistance, Additive Stability, and Regulatory Conformance

For outdoor tanks, agricultural chemical containers, and water treatment vessels, the polymer must resist ultraviolet degradation, oxidation, and environmental stress cracking over a service life that may exceed 10 years. The product is supplied as a stabilised powder, and the ultraviolet package can be adjusted for specific exposure categories. Where outdoor weathering is specified, validation should be conducted under ASTM D2565-23 or ISO 4892-2:2013 using the final part geometry rather than only compression-moulded plaques. Accelerated weathering on rotational moulded parts has shown that surface microcracking can initiate earlier on corners and weld lines than on flat sections, so test specimens should be cut from actual moulded parts.

Food-contact assessments for this grade should be completed on the final moulded article, because processing aids, pigment systems, and mould release agents can alter overall migration results. The base polyolefin may meet the chemical identity requirements of 21 CFR 177.1520, but end-use testing under the relevant food simulant and time-temperature condition is required before commercial food-contact use. No conclusion as to global food-contact approval is stated here; supply-chain documentation from LyondellBasell technical service should confirm the specific grade and lot.

Where moisture uptake on cold powder is suspected, particularly after storage in an unheated warehouse at relative humidity above 60%, the powder should be pre-dried at 60–70°C for 2–4 h before charging. The drying step does not hydrolyze the polymer but removes surface condensation that otherwise produces steam pinholes during the early heating stage. The material should not be stored in direct sunlight or near strong oxidising agents, chlorinated hydrocarbons, or aromatic solvents under stress. Contact with these agents can accelerate environmental stress cracking in the moulded part. Published data for this specific configuration is limited with respect to long-term chemical resistance across all service fluids, so immersion testing under the intended chemical environment is required.