Commercial T-shirt sacks in the 10.5–14.0 µm range are produced from Chevron Phillips Chemical HDPE HHM TR-131 on conventional HMW-HDPE blown film lines with grooved-feed extruders of 45–65 mm diameter and 24:1–30:1 L/D. The resin’s nominal melt index of 0.12 g/10 min at 190°C/2.16 kg per ASTM D1238 and density of 0.950 g/cm³ per ASTM D1505 position it as a high-molecular-weight film-grade HDPE. Melt temperature at the die is maintained between 216°C and 232°C, die gap is set at 1.2–1.5 mm, and blow-up ratio is operated at 3.0:1–4.0:1 to balance machine-direction and transverse-direction tear. Frost line height is held at 4–6 die diameters; shorter heights reduce bubble cooling and produce uneven gusset folding at the collapsing frame. Finished sacks commonly require Dart Drop Impact values of 120–180 g by ASTM D1709 Method A, Elmendorf tear above 40 g MD and 250 g TD by ASTM D1922, and tensile strength at break above 35 MPa MD and 30 MPa TD by ASTM D882. Edge trim regrind is limited to 20 wt% because higher addition reduces dart impact below the 120 g threshold and raises gel counts. On a 65 mm extruder fitted with a 250 mm die, output is generally 160–220 kg/h when internal bubble cooling is used. The terminal products are grocery carrying sacks, produce bundling sacks, and small retail merchandise bags.

What Limits Downgauging Below 8 µm in High-Speed Bag Converting?

Below 8 µm, HHM TR-131 transitions from a thickness-limited regime to a bubble-stability-limited regime. On high-stalk extrusion lines, the die gap is widened to 1.8–2.0 mm to reduce shear stress at the die land and suppress sharkskin; the bubble neck height is then held between 6 and 8 die diameters to allow melt strain recovery. Barrel temperature profiles are flat from 210°C to 220°C except for the grooved-feed throat, which is maintained at 40–50°C to prevent pellet bridging. Melt temperature at the die is allowed to rise to 221–232°C. If internal bubble cooling air velocity falls below 15 m/s, bubble flutter appears as crescent-shaped gauge bands, and online capacitance gauging shows thickness variation exceeding ±10%. Coefficient of friction is modified with 1.5–2.5 wt% slip/antiblock masterbatch; levels above 3 wt% cause die-lip plate-out and increased backpressure. Dart impact at 8 µm is often specified at 80–120 g by ASTM D1709 Method A, but the balance between dart impact and tear is strongly dependent on blow-up ratio; raising BUR above 3.5:1 increases TD tear while degrading MD tear. The converted film is used as lightweight refuse can liners and over-the-counter retail bags. Published data for this specific configuration is limited; the stated operating ranges are drawn from standard HMW-HDPE extrusion practice rather than grade-specific design data.

Three-layer spiral mandrel coextrusion of shipping sack films uses HHM TR-131 in the outer skin to increase secant modulus and surface hardness. A typical structure is 30%/50%/20% HDPE outer, recycled HDPE core, and LLDPE sealant inner skin, produced through a spiral mandrel die with die gap of 1.5 mm and total output of 350–450 kg/h on a 350 mm die. The HDPE outer layer is fed from a 60 mm grooved-feed extruder at 210–226°C, while the LLDPE skin is run at 190–205°C to preserve heat-seal initiation temperature below 110°C. The recycled core is metered by gravimetric feeders because calcium carbonate masterbatch loads of 20–30 wt% can otherwise cause screw surging and gauge fluctuation. Final film thickness of 50–80 µm is tested for tensile strength at break per ASTM D882, tear propagation per ASTM D1922, and puncture resistance per ASTM D5748. The outer HDPE skin of HHM TR-131 improves resistance to snagging on sharp container edges during bulk filling of mineral fillers, granular fertilizers, and powdered construction additives. Seal integrity is checked with heat-seal strength per ASTM F88 and hot-tack per ASTM F1921.

Dry-Food Liner Extrusion with HHM TR-131 and Slip/Antiblock Packages

Dry-food carton liners use HHM TR-131 at 18–30 µm because the high-density film yields a moisture vapor transmission rate below 6 g/m²·day at 37.8°C and 90% RH when measured by ASTM F1249. The film is processed with a 55–65 mm grooved-feed extruder, melt temperature 210–227°C, die gap 1.4–1.6 mm, and blow-up ratio 2.8:1–3.5:1. Slip and antiblock are added as 1.0–2.0 wt% masterbatch to control blocking force below 30 g/cm² by ASTM D3354 and kinetic coefficient of friction below 0.3 by ASTM D1894. Compliance with US FDA 21 CFR 177.1520 is required for cereal, cracker, and biscuit liners; the regulation covers high-density olefin polymers and sets extractable fraction limits under conditions of use that do not exceed 60°C. For EU applications, overall migration into food simulants must remain below 10 mg/dm² under Regulation (EU) No 10/2011. Converted liners are heat sealed with dwell times of 0.5–1.0 s at 150–170°C; higher temperatures cause film thinning at the seal interface and loss of seal strength. Because HHM TR-131 does not contain slip or antiblock as polymerized, the converter must control additive dispersion by measuring film haze per ASTM D1003 and by monitoring melt pressure stability during extrusion.

When Is HHM TR-131 Preferred over LLDPE in Heavy-Gauge Industrial Skins?

In heavy-gauge industrial skins, HHM TR-131 is selected over LLDPE when flexural stiffness and creep resistance dominate stretch resistance. In monolayer extrusion of 80–120 µm industrial sheeting, the HDPE film exhibits a 1% secant modulus above 900 MPa per ASTM D882, compared with typical LLDPE values below 350 MPa. The processing window is narrower than LLDPE: melt temperature must be held within ±5°C of the 218–227°C setpoint to avoid surface melt fracture from high shear stress. Die gap is set at 1.6–1.8 mm, blow-up ratio at 2.5:1–3.0:1, and frost line height at 5–7 die diameters. The high stiffness enables down-gauging of industrial wrapping films by 20–30% relative to LLDPE, but tear propagation resistance in the machine direction remains the critical limitation, with Elmendorf MD values rarely exceeding 50 g at 25 µm. For that reason, the film is often laminated or coextruded with LLDPE to restore tear resistance. Continuous operation beyond 24 h without die-lip cleaning can produce visible die lines due to oxidized resin buildup, especially when regrind levels exceed 15 wt%. The terminal use is as temporary containment sheeting, concrete curing covers, and equipment dust covers.

For retail bag film containing post-consumer recycle (PCR), HHM TR-131 is compounded with up to 35 wt% of washed HDPE flake in a twin-screw reprocessing line. The twin-screw extruder is configured with L/D 36:1, vacuum venting at 600–800 mbar, and melt filtration with a 125–180 µm screen pack to remove gel particles. The blend is pelletized and then re-extruded into blown film at 18–25 µm. Virgin HHM TR-131 contributes melt strength and broad molecular weight distribution, which helps stabilize the bubble against viscosity fluctuations from the PCR fraction. However, dart impact per ASTM D1709 Method A decreases by approximately 10–15% for every 10 wt% increase in PCR flake above 20 wt%. This limits practical PCR incorporation in thin-gauge sacks to below 30 wt% unless the film is thickened to 25 µm. The finished film is used for retail merchandise bags, newspaper sleeves, and commercial laundry packaging.