Chevron Phillips Chemical HDPE HMN TR-945 / 945G is a hexene-copolymer high-density polyethylene designed for high-molecular-weight blown film extrusion. The base resin is available as pelletized TR-945 and granular 945G; both share the same nominal density of 0.945 g/cm³ when measured according to ASTM D1505 or ISO 1183-1:2019. Melt index under 190 °C/2.16 kg loading is typically 0.06 g/10 min by ASTM D1238 or ISO 1133-1:2022. The high-load melt index at 190 °C/21.6 kg is typically 6.0 g/10 min, yielding a melt flow ratio of approximately 100.

The combination of low melt index, high-load melt index, and density places the resin in thin-gauge high-strength HDPE film applications, including grocery sacks, trash can liners, and industrial liners. The broad molecular weight distribution indicated by the 100 melt flow ratio contributes to bubble stability and drawdown on high-shear single-screw extruders fitted with barrier screws and grooved-feed sections. These processing characteristics are not specification limits but are used by converters to select extrusion equipment and line conditions.

Mechanical Property Benchmarks and Test Method Alignment

Specifications for HMN TR-945 are reported under the following test designations. Film property values are gauge-dependent and line-condition dependent, so the current technical data sheet should be used for absolute values.

Mechanical values published by the manufacturer for tensile properties follow ASTM D882, Elmendorf tear follows ASTM D1922, and dart drop impact follows ASTM D1709-16a. Laboratory film blowing conditions such as die gap, blow-up ratio, and melt temperature modify orientation and crystallinity; therefore, mechanical values from a 25 µm laboratory film are not directly transferable to a 12 µm production film without accounting for draw ratio and frost-line history.

The density of 0.945 g/cm³ corresponds to a crystalline weight fraction lower than that of 0.952–0.955 g/cm³ HDPE film grades. Under ASTM D882 tensile testing, this generally lowers yield stress and secant modulus because the amorphous interlamellar regions contribute less resistance to low-strain deformation. Under ASTM D1922 Elmendorf tear testing, the same structural shift raises tear energy because crack propagation is retarded by tie-chains in the amorphous layer. These differences are relative and should not be interpreted as absolute specification limits.

Relative to 1-butene-copolymer HMW-HDPE grades at equivalent density and melt index, the hexene comonomer in HMN TR-945 provides a higher concentration of load-bearing tie-chains because the longer short-chain branch length allows amorphous chains to link adjacent lamellae. This structural feature is detected in standardized tests as higher Elmendorf tear and dart drop impact, but published data for this direct comparison is limited. Relative to higher-density HMW-HDPE film grades, the 0.945 g/cm³ density point reduces tensile yield stress and secant modulus measured by ASTM D882 while improving impact and tear. Relative to linear low-density polyethylene, HMN TR-945 produces higher modulus and lower moisture vapour transmission measured by ASTM E96/E96M, but the processing window is narrower because the low melt index requires high-shear extrusion.

What Limits the Processing Window for a 0.945 g/cm³ HMW-HDPE Film Resin?

The limiting variables in direct film extrusion are melt temperature, residence time, die gap, and bubble stability. A typical barrel temperature profile begins at 160 °C in the feed zone and increases to 220 °C in the metering section, with adaptor and die set between 210 °C and 230 °C. Operations above 240 °C are considered a thermal boundary because oxidation and gel formation can occur when the stabilizer package is depleted during long residence time. Nitrogen blanketing of the feed hopper and low freeboard resin storage are practical controls for this limitation.

The low 0.06 g/10 min melt index demands grooved-feed single-screw extruders with screw L/D ratios of 24:1 to 30:1 and barrier or barrier-Maddock mixing sections. On production-scale lines with 75 mm screw diameter, output rates for this resin class are commonly reported in the 90–130 kg/h range, but published data for this specific configuration is limited. High-shear screw designs generate viscous heat that must be removed through water-cooled grooved-feed sections, particularly when extruder throughput is raised above the design maximum.

Die gap selection below 0.9 mm may initiate sharkskin melt fracture in high-molecular-weight HDPE, while gaps above 1.5 mm reduce orientation and can lower machine-direction tensile properties measured by ASTM D882. The typical range for HMN TR-945 is therefore 1.0–1.5 mm, with blow-up ratios between 3.5:1 and 5:1 and frost-line height adjusted between 300 mm and 600 mm on high-stalk lines. Dual-lip air rings and internal bubble cooling are required to stabilize bubble diameter at high blow-up ratios; without internal cooling, gauge uniformity measured by ASTM D374 tends to deteriorate.

The shear-thinning behaviour of HMW-HDPE produces high apparent viscosity at low shear in the melt pool, but viscosity decreases at the high shear rate in the die lip. This is why die gaps as low as 1.0 mm are feasible for thin film, whereas the same resin would appear unpumpable if judged only by the 0.06 g/10 min melt index. Capillary rheometry at 210 °C is recommended to confirm lot-to-lot consistency; shear viscosity data are generated according to ISO 11443:2021.

Pre-drying is not generally required for film extrusion when the resin is stored below 60 % relative humidity. If surface moisture is present, a desiccant dryer at 70–80 °C for 2–4 hours is applied before processing. The presence of water at these temperatures can produce surface splay and microvoids in drawn film, particularly at gauge below 15 µm. Head pressure is monitored against baseline rather than against an absolute universal value because die design and extrusion rate change the backpressure. A gradual pressure increase at constant screw speed and temperature indicates screen pack blinding or resin contamination; sudden pressure reduction can indicate melt fracture or temperature override.

In thin-gauge grocery sack and trash liner applications, film from HMN TR-945 is typically drawn to 12–25 µm gauge on high-stalk HMW-HDPE blown film lines. The high molecular weight fraction stabilizes the stalk, allowing drawdown ratios of 3:1 to 6:1 depending on die diameter and lay-flat width. Converted bags are evaluated for dart impact according to ASTM D1709-16a, Elmendorf tear according to ASTM D1922, and seal strength according to ASTM F88/F88M-21. Because the lower density point reduces crystalline orientation, heat seal initiation typically shifts to a lower temperature than higher-density HDPE film grades; exact seal initiation values must be measured by ASTM F1921 on the specific film structure.

For heavy-duty industrial liners and can liners, gauge is increased to 50–75 µm. The lower density improves dart drop impact absorption at equivalent thickness compared with 0.952–0.955 g/cm³ high-density film grades; this comparison is only valid when films are tested under ASTM D1709-16a with the same conditioning protocol and gauge. Tear performance measured by ASTM D1922 is also influenced by orientation balance; higher blow-up ratios generally increase transverse tear.

When the 945G Granular Form Replaces the Pelletized TR-945 in Compounding

The 945G granular morphology is intended for masterbatch producers and compounders who require free-flowing granules for gravimetric feeding into co-rotating twin-screw extruders. Unlike pelletized TR-945, the granular form is typically produced without the final pelletizing step, which can reduce the total heat history. Processing on twin-screw lines with 32:1–44:1 L/D ratio and side-feed ports is typical; pigment dispersion is controlled by screw configuration, melt temperature, and specific energy input rather than by the viscosity of the film resin alone.

Formulators should avoid amine-based processing aids in 945G-based concentrates intended for high-temperature film lines because amines can react with residual catalyst residues to produce discoloration. This incompatibility is not unique to HMN TR-945 but is a practical boundary for HDPE concentrates processed above 220 °C. For let-down into HMN TR-945 film extrusion, a let-down ratio of 3–5 % is typical for colour concentrates; the exact ratio is determined by pigment loading and final film opacity measured according to ISO 2471.

Food-contact status for HMN TR-945 should be confirmed against FDA 21 CFR 177.1520 and Regulation (EU) No 10/2011 for olefin polymers. The manufacturer’s food-contact statement identifies specific conditions of use, including temperature and food type limitations. REACH obligations are addressed in the Safety Data Sheet under Regulation (EC) No 1907/2006. The resin is typically supplied with an antioxidant package; processing at sustained melt temperatures above 240 °C may consume the stabilizer and increase oxidation products, so the processor should monitor melt pressure and gel count in the finished film.