SCLAIR MDPE 13-10A is a hexene-1 medium density polyethylene resin supplied by NOVA Chemicals for injection moulding, thin-wall technical parts, and selected rotational moulding applications after grinding to powder. The grade falls within the medium density range of 0.926–0.940 g/cm³ defined by ASTM D1248. Published representative values include a nominal density of 0.934 g/cm³ measured by ASTM D1505 and a melt index of 10 g/10 min at 190 °C/2.16 kg under ASTM D1238. The moulded tensile yield strength is 18.0 MPa when evaluated on ASTM D638 type IV specimens at 50 mm/min, with elongation at break exceeding 600 %. Flexural modulus is reported at 550 MPa under ASTM D790. The hexene-1 comonomer introduces ethyl short-chain branches that reduce lamellar thickness, lower the crystalline fraction relative to HDPE homopolymers, and improve environmental stress crack resistance while maintaining sufficient modulus for structural industrial parts. The product is typically supplied as a pelletized resin; rotational moulding converters use a powder ground to controlled particle size distribution to achieve uniform sinter densification.

What Distinguishes SCLAIR MDPE 13-10A from High Density and Linear Low Density Polyethylene?

The principal differentiation is the combination of density, melt flow, and comonomer type. A general-purpose injection or rotational moulding HDPE homopolymer commonly exhibits a density of 0.942–0.955 g/cm³ and a melt index of 3–8 g/10 min, while SCLAIR MDPE 13-10A is specified at 0.934 g/cm³ and 10 g/10 min. The 0.934 g/cm³ density lowers the crystalline mass fraction, which increases slow crack growth resistance in wetting-agent environments. ASTM D1693 condition B testing on medium density moulded plaques typically produces F50 values above 500 h; the grade-specific result should be confirmed against the current certificate of analysis because ESCR is sensitive to moulding cooling rate and test plaque preparation. At the same time, the 10 g/10 min melt index provides lower zero-shear viscosity than conventional MDPE grades with melt indices of 3–5 g/10 min. This flow level reduces injection pressure, improves reproduction of fine tool surface features, and allows shorter oven residence time in rotational moulding, but it also reduces melt strength and narrows the processing window in large flat panel sections. The hexene-1 comonomer produces ethyl branches that interrupt crystallinity more effectively than butene branches in many LLDPE resins, giving a different balance of tensile elongation, puncture resistance, and creep performance. The grade therefore does not replace HDPE where maximum top-load stiffness is required, nor does it replace a LLDPE film resin where dart impact and tear resistance dominate. It is specified when the converter requires improved ESCR over HDPE and higher flow than standard medium density resins.

In injection moulding, the resin is processed on a general-purpose polyethylene screw with an L/D of 20:1 to 24:1 and a compression ratio of 2.5:1. Melt temperatures are maintained between 190 °C and 220 °C, and mould temperatures are held at 15–40 °C to accelerate solidification and reduce cycle time. For rotational moulding, the pelletized resin is ground to a powder with less than 10 % below 125 µm to reduce dusting and improve charge uniformity. Oven air temperatures of 260–315 °C are used, with mould surface temperature at oven exit controlled between 210 °C and 230 °C. The 10 g/10 min melt index permits peak internal air temperature targets to be lowered by 10–20 °C relative to a 4 g/10 min MDPE, but the lower melt strength demands a controlled cooling cycle. Forced-air cooling followed by water mist cooling at a rate no faster than 15 °C/min reduces warpage in flat panels and improves dimensional stability. On shuttle-type rotational moulding machines with a swing diameter of 3.6 m, production-scale trials have shown that oven residence time can be shortened by approximately 15 % when the 13-10A powder is moulded at a nominal wall thickness of 4.0 mm, compared with a 5 g/10 min MDPE under identical tooling and oven setpoint conditions. The exact cycle reduction depends on tool mass, oven air turnover, and part thickness; published data for this specific configuration is limited.

When the Grade Is Specified for Large Chemical Storage Vessels

In large chemical storage vessels, design loads combine hydraulic hoop stress, long-term chemical exposure, and environmental stress cracking. SCLAIR MDPE 13-10A is evaluated for these applications through ASTM D1693 ESCR, ASTM D638 tensile yield, and ASTM D2837 hydrostatic design basis testing where applicable. The density reduction from 0.955 g/cm³ to 0.934 g/cm³ lowers flexural modulus by approximately 15–20 % relative to HDPE and increases time to slow crack growth in wetting-agent environments. Fabricators processing the grade into 5000 L to 15000 L vertical tanks report that moulded wall thickness in the 5.0–6.5 mm range requires post-mould dimensional inspection after 24 h conditioning at 23 °C and 50 % relative humidity because the lower crystallinity permits additional contraction after demoulding. The material is not recommended for continuous exposure to strong oxidizing acids or aromatic hydrocarbons; polyethylene in this density range swells in toluene and xylene, and design stress must be derated according to ISO 9080 or ASTM D2837 when aggressive media are present. For potable-water contact, compliance to NSF/ANSI 61 or AS/NZS 4020 is product-specific and must be verified on the finished rotationally moulded article. The base resin falls within the polyolefin family described by FDA 21 CFR 177.1520 for food-contact use, but additive loading and end-use extraction testing remain the converter’s responsibility.

Pre-drying of the powder is required when storage humidity exceeds 60 % RH or when the powder has been subjected to repeated freeze-thaw cycles. Moisture levels above 0.1 wt% can generate steam bubbles at the mould surface and reduce impact strength. The powder should be stored in sealed containers at temperatures below 40 °C and away from direct UV exposure. If storage exceeds 12 months, the antioxidant package may be partially consumed; a melt flow stability check under ASTM D1238 should be performed before production. The material is combustible and produces electrostatic charge during pneumatic transfer; all hoppers, silos, and vacuum receivers must be bonded and grounded. Dust controls should maintain airborne respirable dust below the lower explosive limit, and fine powder fractions below 125 µm should be minimized to reduce dusting during charging.

Melt Index Ratio and Short-Chain Branching: A Processing Window Metric

The melt index ratio of the grade, measured as the high-load melt index at 190 °C/21.6 kg divided by the standard melt index at 190 °C/2.16 kg under ASTM D1238, provides a qualitative indication of molecular weight distribution and shear thinning. Medium density resins with a melt index of 10 g/10 min and a melt index ratio of 25–30 exhibit moderate shear thinning and rapid sinter densification. The high-load flow is relevant when the melt must fill deep ribs, undercut inserts, and bridged tool features; low zero-shear viscosity allows the melt to coalesce at lower internal air temperature, but it also shortens the temperature interval between complete densification and oxidative degradation. The processing window is therefore narrower than for lower-melt-index MDPE grades. The recommended maximum melt temperature is 230 °C, measured at the inner mould surface in rotational moulding or at the melt front in injection moulding. Sustained temperatures above 240 °C accelerate chain scission and increase carbonyl formation; the stabilizer package is designed for short-duration oven exposure but not for prolonged melt residence times above 15 min.

On production-scale injection moulding operations, the grade has produced consistent wall thickness in parts with nominal 2.0–6.0 mm walls when barrel temperature zones are set from 180 °C at the feed throat to 215 °C at the nozzle. The screw back pressure should be kept between 0.5 MPa and 1.0 MPa to avoid excessive shear heating. In rotational moulding, the powder charge should be adjusted to avoid fines segregation; a particle size distribution with less than 10 % below 125 µm reduces dusting and makes charge weight more uniform. Data from NOVA Chemicals technical bulletins should be used to define the specific barrel temperature profile for the available machine configuration; published data for this configuration is limited.

Compliance Verification for Rotationally Moulded Products

The regulatory status of a finished injection moulded or rotationally moulded article depends on the additive package, processing temperatures, and service exposure. The following matrix identifies the verification routes commonly applied to medium density polyethylene parts made from this product.

Combination of 13-10A with high levels of unsaturated oils or transition-metal stearates can accelerate thermomechanical degradation during injection moulding or rotational moulding. Addition of colourants or UV masterbatch at levels above 5 wt% should be validated for impact and ESCR because the diluent effect reduces the effective molecular weight fraction and may shift the brittle transition temperature. The resin is not recommended for parts requiring sustained service above 60 °C under mechanical load; modulus decreases with increasing service temperature, and creep resistance must be evaluated using ISO 899-2 or ASTM D2990.