In thin-gauge T-shirt sack production, USI Corporation HDPE LH606 is processed on single-screw blown-film lines with a 24:1 to 30:1 L/D barrier screw and a spiral mandrel die. Each incoming lot is characterized by melt-flow index per ISO 1133-1 at 190 °C / 2.16 kg and density per ISO 1183-1. The melt temperature at the die is kept within 200–225 °C; excursions above 225 °C produce bubble flutter and surface roughness, while excursions below 200 °C raise melt pressure beyond 35 MPa on a 65 mm extruder. The die gap is set at 0.8–1.2 mm. A blow-up ratio of 3:1–5:1 and a stalk height of 6–10 die diameters are required to align the high-molecular chains. The long stalk is not decorative; it creates the machine-direction tear resistance necessary for 10–18 µm sack film. Film is converted on rotary sealing machines with seal temperatures between 150–170 °C. Tear and impact are measured according to ASTM D1922 and ASTM D1709 Method A because these methods respond to different failure modes. If 10–20 wt% linear low-density polyethylene is dry-blended, dart impact rises but film stiffness falls; beyond 20 wt% LLDPE, the film becomes too extensible for automated bag indexing. Regrind is accepted up to 20–30 wt% only when the melt filtration pack is at least 60/80/100 mesh. Higher regrind fractions create gel specks at 25 µm thickness. The terminal sack is non-food grocery carryout. No pre-drying is required because the polymer is non-polar and supplied with moisture below 0.05 wt% according to incoming plant data.

What Limits Bubble Stability When LH606 Is Run on a Low-Neck Coextrusion Line?

The core-layer viscosity mismatch is not a laboratory observation. In three-layer coextruded film for dry-food pouches and bag-in-box liners, LH606 is used as the stiffening core at 25–40 % of total film thickness. The total film thickness ranges from 35 µm to 60 µm, and the LH606 core is enclosed by LLDPE or LDPE skins. Core melt temperature is held at 210–225 °C, while skin melt temperatures are typically 170–200 °C to protect heat-sensitive additives. When the viscosity difference between core and skins exceeds the equipment design limit, wavy die-lines and interfacial instability appear at line speeds above 80 m/min. A melt pump after the core extruder reduces surge and maintains layer thickness within ± 1 µm. The die gap is set at 1.5–2.0 mm because the larger gap prevents molecular-weight buildup and reduces melt fracture in the HDPE layer. Blow-up ratio is limited to 2.5:1–3.5:1 with a low stalk height of 2–4 die diameters; this configuration minimizes bubble cooling demands but reduces MD transverse balance. Seal strength is checked to ASTM F88 because the final pouch must survive drop transport without seal delamination. For dry-food contact, final packaging is evaluated under EU Regulation (EU) No 10/2011 overall migration limit of 10 mg/dm²; EU simulant selection depends on final food type, not on resin alone. Published line data for LH606 in this exact three-layer structure is limited, so most converters qualify the structure by film thickness profile and seal strength rather than theoretical viscosity matching.

Unlike thin-gauge high-stalk production, heavy-duty liner conversion on conventional blown-film towers uses a low stalk height of 2–4 die diameters and a blow-up ratio of 2.5:1–3.5:1. LH606 is fed neat or with 10 wt% LLDPE. The die gap is set at 1.5–2.0 mm, and total film thickness is 80–200 µm. Melt temperature is maintained at 215–235 °C. Internal bubble cooling is added when the frost line climbs above 70% of the tower height; chilled air at 10–15 °C increases output by reducing the cooling-air residence time. Tear and tensile properties are measured to ASTM D882, while puncture resistance is characterized to ASTM D4833. For construction debris and asbestos abatement liners, project-specific minimums are often written around ASTM D4833 because it measures index puncture rather than film tensile elongation. If the liner is specified for outdoor storage, a UV masterbatch is added at 2–4 wt%; for exposures beyond 30 days, accelerated weathering per ASTM G154 is used to validate carbon black or HALS packages. The terminal product is a non-food liner for construction, demolition, and containment use. Regrind from edge trim is usually limited to 20 wt% to avoid reducing puncture resistance; converters who exceed this limit report more frequent star-seal failures at the bottom fold, especially when film thickness falls below 100 µm.

When 20 wt% LLDPE Is Dry-Blended for Tear-Balance Modification in Refuse Sacks

A dry blend of 80 wt% LH606 and 20 wt% LLDPE is hopper-fed into a single-screw extruder to shift the Elmendorf tear balance toward the transverse direction. The film is produced at 25–40 µm. The screw must include a Maddock mixing element; without it, low-viscosity LLDPE pools form and produce irregular gauge bands at the frost line. Melt temperature is held at 210–230 °C. The die gap is 1.2–1.5 mm, and the blow-up ratio is 3:1–4:1. The LLDPE fraction modifies tear anisotropy. If LLDPE exceeds 25 wt%, the film becomes excessively ductile for automatic bag insertion and MD tensile yield falls below internal specifications, so the ratio is not a convenience variable. Dart impact is checked to ASTM D1709 Method A; Elmendorf tear is checked to ASTM D1922; tensile yield is checked to ASTM D882. Published data for this specific dry blend under LH606 is limited, so converters set the final blend ratio through plant trials with the exact extruder screw and die configuration. Terminal products are star-sealed wave-cut refuse sacks and drawstring bags. No pre-drying is required for either component unless the LLDPE arrives with surface moisture from contaminated conveying air; condensation is drained from hopper loaders and the feed throat is kept above 30 °C in high-humidity plants.

Reclaim Compounding with Post-Consumer HDPE Letdown for Non-Food Sacks

For non-food refuse sacks containing post-consumer HDPE, LH606 is fed into a co-rotating twin-screw extruder with 40:1 L/D and vacuum venting at -0.08 MPa to -0.095 MPa. Post-consumer HDPE regrind is let down at 30–50 wt%; LH606 constitutes the balance at 50–70 wt%. The melt is filtered through 100–150 mesh screens before water-ring pelletizing. Melt temperature at the die plate is kept at 200–220 °C to limit degradation of unknown contaminants in the recycle stream. The objective is not tensile strength alone; LH606 restores stress-cracking resistance and dilutes gels that would otherwise tear in thin films. Pelletized blend is then converted on a blown-film line with a 60/80/100 mesh pack. Stress-cracking resistance is measured to ASTM D1693 Condition B; gel count has no universal standard, so converters use camera-based gel scanners calibrated at 25 µm. Each reclaim lot must be qualified separately because post-consumer HDPE varies in ash, density, and contamination. A film trial with 50 µm thickness is the final acceptance gate; dart impact to ASTM D1709 and tear to ASTM D1922 are recorded on every lot. The terminal product is a heavy-duty non-food refuse sack for municipal and commercial waste. If regrind content exceeds 50 wt%, bubble stability deteriorates and the frost line drops, requiring lower output and a wider die gap of 1.8 mm or more.

Extraction Profile Shifts When the Seal Layer Is Thinned to 12 µm

When monolayer food-contact film is thinned from 30 µm to 12 µm, the surface-to-volume ratio changes, and the extraction profile under food simulants shifts. LH606 is processed in this configuration for bakery bags, cereal liners, and lightweight produce film. The film is run at 200–225 °C melt temperature; the die exit is kept below 230 °C to minimize oxidative degradation products that would raise total extractables. Slip and antiblock masterbatches are used at 0.5–1.5 wt% only when the additive system is covered by a supplier food-contact statement referencing FDA 21 CFR 177.1520(c) and EU Regulation (EU) No 10/2011. The die gap is 0.8–1.0 mm. No pre-drying is required at relative humidities up to 60% because the resin is non-hygroscopic, but condensation from cold pellets transferred directly from outdoor silos into the feed throat causes die-hole streaks. The final film is evaluated under the applicable food simulant conditions; dry-food applications may require only Simulant E testing at 40 °C for 10 days under EU Regulation (EU) No 10/2011, whereas fatty-food contact requires higher-temperature simulants. The terminal products are food-contact bags and liners. The table identifies the relevant compliance references used during import and conversion.