LyondellBasell Icorene LMDPE 1877 is a linear medium density polyethylene powder supplied for rotational moulding. The model designation LMDPE places the material between butene-based linear low density polyethylene and high density polyethylene rotomoulding grades. Supplier-published typical values list a nominal density of 0.938 g/cm³ measured in accordance with ISO 1183-1 and a melt flow rate of 7.0 g/10 min at 190 °C under 2.16 kg load measured in accordance with ISO 1133-1:2022. These two indices are the primary sorting criteria for rotational moulding powder selection.

The grade is distributed as a ground powder with bulk density typically in the range 0.35–0.45 g/cm³. Particle size distribution is controlled by sieve analysis; rotomoulding powders in this density class commonly use a 35 mesh (500 µm) maximum screen retention. The exact fine fraction below 75 µm is lot-dependent and should be checked against the certificate of analysis because it affects electrostatic behaviour and powder flow from storage hoppers.

These values are supplier-published representative values, not release specifications. Batch-specific values may vary within the manufacturer’s control limits.

The linear backbone of Icorene LMDPE 1877 is produced by copolymerisation of ethylene with a short-chain alpha-olefin. The comonomer type and distribution determine the density and slow crack growth resistance. The medium density of 0.938 g/cm³ reflects a controlled reduction in crystallinity relative to HDPE, yielding a crystalline melting peak near 123–126 °C under ISO 11357-3. The molecular weight distribution is not reported in the supplier-published data sheet and is normally characterised indirectly through melt flow rate and dynamic oscillatory shear measurements.

What Limits the Use of a 7.0 g/10 min Melt Flow Rate in Deep-Cavity Moulds?

A melt flow rate of 7.0 g/10 min is higher than the 3.0–5.0 g/10 min range common for HDPE rotomoulding grades. The higher MFR corresponds to lower zero-shear viscosity and faster flow into ribs, inserts, and wall sections thinner than 6 mm. On shuttle-type rotational moulding machines with biaxial rotation ratios of 4:1, oven residence time can be reduced by 10–20 % relative to a 4.0 g/10 min LMDPE when the internal air peak temperature is held at 190–200 °C.

The processing conflict is bubble release. Lower zero-shear viscosity shortens the time required for trapped gas bubbles to escape during densification, but it also narrows the margin for error. If internal air temperature rises too quickly, the melt at the mould surface may seal before the powder bed has fully densified, producing pinholes. Field troubleshooting on shuttle machines has associated surface porosity with insufficient venting and excessive internal air temperature ramp rates rather than with resin flow alone.

Deep-cavity moulds with sharp internal corners are particularly sensitive. At 7.0 g/10 min, the resin can fill narrow channels, but the lower melt strength may produce local thinning when rotation is not uniform. Moulders using steel or cast aluminium tools should verify wall thickness distribution with ultrasonic gauging after the first article. The internal air temperature ramp should be limited to 5–8 °C/min between 150 °C and 190 °C to allow powder adhesion and bubble removal to occur sequentially.

Environmental Stress Cracking Resistance and Density-Driven Property Trade-offs

The density of 0.938 g/cm³ produces lower crystallinity than HDPE rotomoulding grades of 0.945–0.955 g/cm³. This lower crystallinity reduces stiffness and hardness but increases slow crack growth resistance under environmental stress. The supplier-published ESCR value of >1000 h under ASTM D1693 condition B in 100 % Igepal at 50 °C is the principal difference from generic HDPE rotomoulding grades, which often fall in the 50–200 h range under the same conditions. For containers exposed to detergents, agricultural chemicals, or hot water, this difference is more relevant than short-term modulus.

The density trade-off appears in flexural modulus. The nominal flexural modulus of 650 MPa under ISO 178 is approximately 30–40 % lower than that of conventional HDPE rotomoulding grades. Cylindrical water tanks designed for static head pressure may require increased wall thickness or external ribs when migrating from HDPE to LMDPE 1877. The tensile yield strength of 18 MPa under ISO 527-2 and elongation at break above 500 % indicate ductile behaviour at room temperature.

Compared with butene-based linear low density polyethylene grades of density 0.918–0.925 g/cm³, the 0.938 g/cm³ density raises flexural modulus and heat resistance while reducing low-temperature impact. Compared with higher-flow LMDPE grades, the 7.0 g/10 min MFR balances mould fill against impact retention. Lower-flow grades may provide marginally higher ESCR but require longer oven cycles and may not fully fill intricate tool details.

When Replacement of HDPE Rotomoulding Grades Becomes Technically Defensible

Substitution of HDPE with Icorene LMDPE 1877 is justified when the dominant failure mode is environmental stress cracking or low-temperature brittle fracture rather than excessive deflection under load. In cold-climate agricultural tanks, a stiff HDPE wall of density 0.950 g/cm³ may fail by brittle cracking at -20 °C or under detergent exposure; LMDPE 1877 maintains greater ductility under these conditions. The technical case should include comparative ESCR data under ASTM D1693 and low-temperature impact data under ISO 6603-2 or the ARM impact method for rotomoulded parts.

Where stiffness is the primary design requirement, replacement is not appropriate. The lower flexural modulus requires thicker walls, which increases material consumption and cycle time. Load-bearing parts such as structural bases, pallets, or unsupported decks should retain HDPE or be redesigned with ribbing and thickened sections. The solid-state shrinkage of LMDPE 1877 is between that of low density PE and HDPE; typical rotomoulding shrinkage in this density class is 2.5–3.5 % on steel moulds and can be slightly higher on aluminium tooling. Shrinkage must be measured after 24 h at 23 °C and again after thermal ageing because post-mould crystallisation can alter dimensions.

Chemical compatibility for Icorene LMDPE 1877 covers dilute aqueous acids, alkalis, alcohols, and non-oxidising salt solutions at temperatures below 40 °C. The material is not recommended for strong oxidising acids, ketones, aromatic hydrocarbons, or halogenated solvents because swelling and strength loss occur. For food contact applications, the base resin may meet FDA 21 CFR 177.1520(c) and European Regulation (EU) No 10/2011 as amended, but the final article must be tested for overall migration and organoleptic properties before commercial use. Potable water applications may require article-level certification to NSF/ANSI 61 or equivalent national standards; such certification is not automatically conveyed by resin selection.

Against high-density polyethylene grades of density 0.945–0.955 g/cm³, Icorene LMDPE 1877 exchanges approximately 30–40 % flexural modulus for a step change in ESCR from 50–200 h to >1000 h. Against linear low density polyethylene of density 0.918–0.925 g/cm³, it provides higher modulus and lower mould sticking but slightly lower dart impact at freezer temperatures. Within the LMDPE class, a 7.0 g/10 min melt flow rate is biased toward flow and cycle time, whereas a 4.0–5.0 g/10 min grade is biased toward melt strength and impact retention.

Oven cycle limits are defined by internal air temperature, not oven set point

Rotational moulding of Icorene LMDPE 1877 is typically performed in forced-air ovens at set points of 260–320 °C. The critical control variable is the internal air peak temperature measured through the mould vent, not the oven set point. For wall sections of 3–12 mm, an internal air peak of 190–210 °C is appropriate. At internal air temperatures above 210 °C, oxidative degradation accelerates, producing carbonyl species and increasing yellowness index. This risk is amplified in thick sections above 10 mm because the outer surface remains at elevated temperature for a longer period while the core cools.

The antioxidant package is designed for typical rotomoulding thermal cycles, but extended overheating may deplete stabilisers. Oxidative induction time under ISO 11357-6 can be used as a quality control tool on moulded parts when long service life is required. Full densification requires the internal air temperature to exceed the crystalline melting range and reach 190 °C. Compared with HDPE rotomoulding grades, the lower melting point and lower zero-shear viscosity of LMDPE 1877 allow a lower internal air peak temperature, typically 190–200 °C versus 200–220 °C for many HDPE powders. This lower peak reduces thermal exposure and can shorten cooling time, but it also means that ovens calibrated for HDPE may overheat the LMDPE if settings are not adjusted.

Cooling rate after fusion affects shrinkage and impact. Air cooling followed by water mist at 10–15 °C/min is standard for this density class. Quenching can produce slightly higher impact by reducing crystallinity, but it also increases residual stress and can induce warpage in flat panels. On aluminium moulds with wall thickness 5 mm, excessive quench rates have been associated with corner lift and dimensional instability. Moulders should verify post-mould dimensions on a temperature-controlled granite surface plate after conditioning for 24 h at 23 °C and 50 % relative humidity.

On carousel machines with three to five arms, the higher MFR of 7.0 g/10 min can reduce total cycle time when combined with thinner walls. On rock-and-roll machines used for long, narrow parts, faster melt flow may cause thickness variation if rotational speed is too low or the internal air temperature ramp is not controlled. Operators should reduce internal air peak temperature to 185–190 °C and increase minor-axis oscillation frequency until thickness variation measured by ultrasonic gauge is below ±10 % of nominal wall.

Dry powder flow is a processing variable that is not captured by melt flow rate. At relative humidity below 35 %, electrostatic charging may cause LMDPE powder to cling to mould vents and feed tubes, leading to uneven powder distribution. Conditioning the powder to 40–50 % relative humidity and grounding all metal tooling reduces charge accumulation. The fine fraction below 75 µm is the main contributor to electrostatic adhesion; if the fine fraction exceeds 8 %, screening or blending may be required. Published data for this specific configuration is limited, and powder flow should be verified with a standardised dry-flow cup method on each lot.

Mould venting design is critical with this grade. Vent tubes should be 8–10 mm internal diameter and extend through the tool wall to prevent blockage. In closed moulds, the 7.0 g/10 min MFR resin can trap gas at internal corners if the vent path is too long. A vent diameter of 8 mm per 500 cm³ of mould volume is a common starting point, but published data for this specific configuration is limited.

Incoming resin quality control should include melt flow rate under ISO 1133-1:2022, density by gradient column or displacement under ISO 1183-1, and sieve analysis. A density shift of more than 0.001 g/cm³ from the nominal value can alter flexural modulus and ESCR sufficiently to affect part approval. A melt flow rate shift of more than 0.5 g/10 min may change oven residence time and surface finish.

Documented failure modes in rotomoulded LMDPE parts include pinholes from incomplete bubble release, weld lines from insufficient fusion at tool joints, and oxidative embrittlement from excessive internal air temperature. Pinholes appear as circular voids in the wall; oxidative embrittlement is associated with carbonyl growth and reduced elongation at break to below 50 % under ISO 527-2.

Outdoor exposure is a standard condition for rotomoulded tanks and furniture. The UV-stabilised version of Icorene LMDPE 1877 is intended for weatherable parts; accelerated weathering under ISO 4892-2 method A with 0.51 W/m² irradiance at 340 nm and a 102 min dry/18 min water spray cycle can be used to assess colour shift and impact retention. Published data for this specific configuration is limited, so lot-specific weathering tests are required before approving extended outdoor service.

For European market compliance, the final article falls under the framework of REACH. Polymers are exempt from registration as substances under REACH Article 2(9); monomers and additives are registered by the polymer manufacturer. RoHS Directive 2011/65/EU applies only to electrical and electronic equipment and is not a general resin certification. Flame retardancy and electrical properties are not primary design properties of this grade.