ExxonMobil HDPE HTA-002 is a high-density polyethylene homopolymer supplied as pelletized injection-moulding resin. The grade is not a compound or masterbatch; it contains no mineral filler, glass fibre, or flame retardant. The nominal density is 0.964 g/cm³ when measured according to ASTM D1505, and the melt index is 7.5 g/10 min at 190 °C under 2.16 kg load when tested according to ASTM D1238. These values position the material in the medium-flow, high-density segment of polyethylene injection grades. Intended end uses include rigid crates, pails, caps and closures, housewares, and thin-section technical mouldings where surface hardness, tensile strength, and dimensional consistency are valued after demoulding. It is not intended for film extrusion, blow moulding, rotomoulding, or pipe extrusion; those processes require melt strength and parison or bubble stability that are deliberately narrowed in this injection-moulding molecular weight distribution. Pellet handling follows standard polyolefin practice: moisture pickup is low at ambient storage below 60 % RH, but cold pellets moved into a warm production hall can condense surface moisture and should be conditioned before dry-air conveying or hopper loading. The values quoted in this technical description are typical values, not specification limits, and lot-specific certificates of analysis should be reviewed before process parameters are fixed.

Typical property values reported in public datasheets for the neat resin are shown below.

On hydraulic or electric injection machines fitted with general-purpose polyolefin screws of 20:1 to 25:1 L/D and compression ratio 2.5:1 to 3.5:1, the melt temperature for HTA-002 is normally set between 180 °C and 230 °C. Mould temperature is typically 10–40 °C, although 50 °C may improve gloss and reduce flow-mark visibility at the expense of cooling time. Screw rotation should be selected to keep melt temperature below 260 °C; above this boundary the stabilising package may be depleted, visible yellowing can occur, and the melt may release oxidative degradation products. In open cold-runner tools, switchover cavity pressures of 30–50 MPa are common for HDPE of this density. Hold pressure and cooling time should be established by gate-seal and part-weight studies, not by barrel residence time alone. Extended residence times above 15 min at high melt temperature increase the risk of molecular weight reduction and should be avoided during production interruptions. Published data for optimal holding profiles in specific mould geometries is limited; processing windows are best established by short-shot and gate-freeze experiments on the target production tool.

Because the density of 0.964 g/cm³ indicates a semicrystalline microstructure with relatively high crystalline content, mould shrinkage is typically between 1.5 % and 2.5 % in the flow direction and 1.5 % and 2.0 % transverse to flow when measured after 48 h at 23 °C according to ASTM D955. Shrinkage is anisotropic and is strongly influenced by packing pressure and gate freeze-off. Raising hold pressure from 30 MPa to 50 MPa can reduce shrinkage variation by 0.3–0.8 percentage points depending on wall thickness and gate geometry. Ribs and bosses with thickness greater than 60 % of the adjoining wall increase the probability of sink marks and voids; gas-assisted injection or foaming is required if surface class is critical. The narrow molecular weight distribution of HTA-002 accelerates solidification and may reduce post-mould warpage compared with broad-distribution HDPE, but it shortens the effective packing phase and makes delayed switchover less forgiving. Dimensional checks should use conditioned specimens, and measurement should not be performed immediately after ejection because cooling continues for several hours after demoulding.

What Limits Injection Speed When Running HTA-002 in Thin-Wall Tooling?

A melt index of 7.5 g/10 min does not by itself define maximum injection speed. The limiting factor in thin-wall parts is flow-front solidification produced by rapid heat loss to the mould wall. HDPE of density 0.964 g/cm³ has a high crystalline fraction, and the latent heat released during crystallisation must be removed before ejection. In nominal wall thickness below 1.2 mm, flow-front freeze can stop filling before pack pressure is transmitted to the cavity end. The difference between HTA-002 and high-flow HDPE grades of 16–20 g/10 min is expressed primarily as higher required injection pressure and reduced maximum flow-length-to-thickness ratio, not simply longer injection time. On injection machines with clamp force between 1,200 kN and 2,500 kN, increasing injection speed above 80 mm/s can generate shear heating and reduce apparent viscosity, but it can also produce gate blush or jetting if the cold-runner diameter and gate land are not matched to the volume flow rate. Thermocouple feedback at the nozzle should be monitored because shear heating at thin gates can raise local melt temperature by 15–30 °C, temporarily improving flow while increasing degradation risk at the gate surface. A spiral flow mould can rank materials under a specific wall thickness and temperature, but no published HTA-002 spiral-flow curve appears in the general technical datasheet; the production tool therefore remains the only reliable predictor of injection speed limit.

Comparative Position Against Higher-Melt-Index HDPE and Lower-Density Copolymers

In comparison with HDPE injection grades of higher melt index, HTA-002 exhibits lower fluidity but higher stiffness. A high-flow HDPE grade with a nominal melt index near 16 g/10 min reduces fill pressure in thin-wall tools and permits lower barrel temperatures; that fluidity is usually accompanied by lower density, lower flexural modulus, and lower Vicat softening temperature. The selection between HTA-002 and such a grade is therefore a balance between mould-filling capability and stiffness-driven dimensional or thermal performance. A lower-density HDPE copolymer near 0.952 g/cm³ demonstrates better notched impact and environmental stress crack resistance because the amorphous tie-chain population is higher, but this structural difference lowers flexural modulus and surface hardness. Blow-moulding HDPE grades with melt index below 1.0 g/10 min possess greater melt strength and are preferred for parison hang and wall-thickness control; they are not equivalent to HTA-002 in reciprocating-screw injection moulding because their higher viscosity increases screw torque, recovery time, and shear heating. Within the ExxonMobil HDPE range, selecting HTA-002 instead of a lower-melt-index injection grade generally shifts the process toward shorter fill times and lower clamp force while retaining the high-density crystallinity that produces hardness and modulus. Direct comparisons with other commercial grades should be made using current seller datasheets and identical test standards, because production-site values can vary.

Stress-Crack Resistance Falls as Crystallinity Increases Above 0.960 g/cm³

Environmental stress crack resistance is a known boundary for high-density homopolymers. Because HTA-002 is an unfilled homopolymer with density 0.964 g/cm³, its ESCR under ASTM D1693 is generally lower than that of HDPE copolymers or medium-density polyethylene. In applications involving detergents, wetting agents, oils, or alkaline cleaning fluids, stress-crack testing should be conducted at 50 °C with the actual end-use contact fluid, because the standard Igepal test may not correlate with field failure. Publicly available technical datasheets for HTA-002 do not provide ESCR values for all Igepal concentrations and sample preparation histories; assigning a universal ESCR number without specifying moulding condition, cooling rate, and test geometry would be inaccurate. Slow cooling, overpacking, and sharp radii can reduce ESCR by an order of magnitude in practice. The resin is not recommended for deep-draw closures that carry continuous compressive assembly stress unless part geometry and applied-stress testing have been validated. Chemical resistance to dilute mineral acids, alkalis, alcohols, and many polar solvents is generally consistent with high-density polyethylene, but aromatic and chlorinated hydrocarbons swell the amorphous phase and accelerate cracking. Strong oxidising acids at elevated temperature should be avoided because the stabiliser package can be consumed. The material is not flame-retardant and is not suitable for UL 94 V-0 applications without modification; it is also not inherently antistatic.

When Food-Contact Compliance and Heavy-Metal Limits Govern Material Acceptance

For food-contact parts, HDPE homopolymer can be evaluated under 21 CFR 177.1520, which covers olefin polymers. End-use migration testing is required according to the food type, contact temperature, and contact time; the regulation does not provide automatic approval without lot-specific documentation. For electrical or electronic components, EU RoHS directive 2011/65/EU restricts lead, mercury, cadmium, hexavalent chromium, specific brominated flame retardants, and specific phthalate plasticisers listed in Annex II. A typical unfilled HDPE such as HTA-002 would not contain these substances as intentional additions, but the moulder’s color masterbatch, additive package, or processing aid may. REACH candidate list obligations apply at the article level and to European importers, not to the neat resin alone. Suppliers should be asked for a compliance statement or safety data sheet reflecting the production site and grade. The resin is not radiopaque, not UV-stabilised for long-term outdoor exposure, and not formulated for direct contact with strong oxidising agents or high-temperature hydrocarbon streams. In regulated applications, the most important difference between HTA-002 and other HDPE grades is not the polymer density but the available lot-specific documentation, supplier change-management discipline, and the consistency of the additive package across production campaigns.

For parts with wall thickness less than 1.0 mm, high-speed closures, or long flow paths from central gates, moulding trials should compare HTA-002 against higher-melt-index HDPE because the product can generate injection-pressure peaks that exceed machine hydraulic capacity. The material performs more predictably in section thickness of 1.5–3.0 mm, where cooling time and melt flow are balanced. Gate land length, runner size, and venting should be designed according to cavity volume and expected flow front velocity; inadequate venting at the end of fill can cause diesel burning and surface deposits. In such cases, reducing injection velocity may be required, but this reduction further increases the risk of early flow-front freeze. The processing boundary therefore lies at the intersection of melt temperature, injection speed, and part geometry, and no single datasheet value can define acceptable performance without a structured injection-moulding trial on the intended production machine.