On production-scale three-layer blown film lines, CHN Energy Xinjiang LDPE 2426H is processed in heavy-duty sack outer and middle plies where a nominal melt flow rate of 2.0 g/10 min at 190°C/2.16 kg (ISO 1133-1:2022, ASTM D1238-20) and density of 0.923 g/cm³ (ISO 1183-1:2019, ASTM D1505) provide sufficient melt strength for bubble diameters up to 900 mm. Formulation practice for industrial sacks requiring a minimum dart impact of 180 g under ASTM D1709-16a Method A uses 70–80 wt% 2426H, 20–30 wt% butene-grade LLDPE with a melt flow rate of 1.0 g/10 min, and 0–15 wt% internal regrind; a fluoropolymer process aid at 300–600 ppm is added to suppress die lip fouling. On a three-layer line with 65 mm/90 mm/65 mm extruders, 30:1 L/D barrier screws, a 350 mm die, and a 2.0 mm die gap, melt temperatures between 175°C and 185°C, blow-up ratio of 2.2:1 to 2.6:1, and frost line height maintained 600–900 mm above the die permit output of 280–420 kg/h. Internal bubble cooling with adjustable iris stabilises the bubble; a shift from BUR 2.5:1 to 2.8:1 without raising frost line height produces transverse direction gauge variation above ±12%, which raises dart impact failure at gusseted corners. Compliance for the sack structure is verified through tensile properties per ISO 527-3:2018 and ASTM D882-18, Elmendorf tear per ASTM D1922-15, and seal strength per ASTM F88/F88M-15. Terminal products include FIBC liners, heavy-duty shipping sacks, fertilizer and peat sacks, and outer plies for laminated paper sacks. Operational boundary: regrind above 20 wt% lowers measured dart impact below 180 g in thin sections and generates unmelted gels from degraded regrind; resin stored at RH above 70% can develop surface condensation that produces bubble pinholes.

Layer distribution on three-layer heavy-duty sack lines is usually maintained at 25/50/25 or 20/60/20, with the middle layer carrying regrind and the outer layers containing the highest 2426H fraction. Melt filtration with screen packs of 80–120 mesh is required because printed trim and low-gel recycled film can raise screen pressure by 10–15% within 8 h of continuous operation when contaminant loading exceeds 500 ppm; screen pressure above 80 bar changes die lip pressure and produces longitudinal gauge bands of 5–8% deviation. Corona treatment of the outer layer at 38–42 mN/m surface tension is applied before flexographic printing or lamination, and roll tension is maintained below 100 N/m to prevent blocking of unprinted film during warehouse storage above 30°C.

What Limits BUR Above 2.8:1 in Agricultural Greenhouse Film Lines?

Greenhouse cover and low tunnel film producers running CHN Energy Xinjiang LDPE 2426H in the outer layer observe that die lip plate-out from hindered amine light stabilisers becomes the limiting variable before melt strength when UV masterbatch addition exceeds 8 wt% of the total formulation. Three-layer agricultural film formulations typically allocate 60–75 wt% 2426H, 20–30 wt% LLDPE, 5–10 wt% UV masterbatch, and 1–3 wt% anti-fog/anti-dust concentrate, with some formulations replacing up to 10 wt% of the LLDPE portion with EVA to improve low-angle light transmission and low-temperature flexibility. This formulation is processed on 1.6–2.2 mm die gaps at melt temperatures of 180–195°C and BUR 2.0:1 to 2.4:1, producing 150–200 µm film. The frost line height is kept between 500 mm and 800 mm; above BUR 2.8:1 the bubble shows slow helical oscillation and thickness variation of ±10% at the edges. Climate-aging performance is evaluated under ISO 4892-2:2013 with UV irradiance of 60 W/m² at 340 nm and under EN 13206:2017 for thermoplastic covering films; tensile properties are measured after 1500 h to ASTM D882 / ISO 527-3. Terminal products include greenhouse covers, low tunnel film, silage covers, and mulch film. Operational boundary: high HALS loadings above 10 wt% masterbatch can deposit on the die lip and require purging with low-MFI LDPE; anti-fog concentrates containing glycerol esters can reduce film coefficient of friction but may cause roll blocking in warm storage above 35°C.

Multi-span greenhouse film records in high-UV regions indicate that an outer layer with 8 wt% HALS masterbatch retains 60–70% of initial elongation after 1500 h under ISO 4892-2:2013, whereas the same formulation at thickness below 120 µm embrittles earlier at frame contact points. For mulch film below 25 µm, the LLDPE fraction is raised to 35–40 wt% to maintain puncture resistance under EN 13206:2017; the 2426H portion is correspondingly reduced to 50–55 wt% and the UV masterbatch is limited to 5–7 wt% to avoid bubble instability at thin gauge.

Where single-layer clarity and seal integrity are specified in bread bags and frozen food liners, 2426H is processed without LLDPE dilution because the resin’s long-chain branching supplies sufficient melt strength for thin-gauge operation at 30–70 µm. Food-contact film lines blend 99.0–99.7 wt% 2426H with a slip masterbatch at 500–1200 ppm and a silica antiblock at 1000–3000 ppm; a fluoropolymer process aid at 200–400 ppm is included when running die gaps below 1.4 mm to reduce melt fracture. Single-layer blown film extrusion on a 65 mm, 25:1 L/D grooved-feed extruder with a 200 mm die, 1.2–1.8 mm die gap, and dual-lip air ring operates at melt temperatures of 165–180°C, BUR 2.8:1 to 3.2:1, and frost line positioned at 7–9 die diameters above the die. Output of 120–200 kg/h is typical; batch-to-batch MFI shift of ±0.15 g/10 min changes die lip pressure by approximately 4% and shifts frost line position by 50 mm, requiring air ring adjustment to maintain gauge uniformity. EU Regulation 10/2011 and FDA 21 CFR 177.1520(c)(2.2) apply when the film is used for food contact; total migration testing under EN 1186-1:2002 and specific migration of additives follow the packaging converter’s composition documentation. Terminal products include bread bags, frozen food liners, textile overwrap, and general-purpose transparent poly bags. Operational boundary: slip addition above 1500 ppm reduces printing ink adhesion and lamination bond strength, while antiblock above 3000 ppm elevates haze beyond typical specification for clear packaging.

Moisture condensation on cold regrind is a known source of bubble pinholes; pre-drying at 60°C for 2 h is applied when regrind has been stored in RH above 60%. Air ring chilled air inlet temperature is controlled at 7–12°C to stabilise frost line and maintain haze below 7% for transparent grades; higher frost line height above 9 die diameters increases crystallinity and reduces film clarity but improves impact resistance.

Carrier Resin Compounding at 40 wt% TiO₂ Loadings

Compounding lines handling CHN Energy Xinjiang LDPE 2426H as a carrier for white and black masterbatch depend on the resin’s melt flow rate of 2.0 g/10 min and broad molecular weight distribution to wet pigments without excessive torque. A 40 wt% TiO₂ white masterbatch formula combines 58–62 wt% 2426H, 40 wt% rutile TiO₂, and 1–2 wt% PE wax lubricant; in black masterbatch the carbon black loading is held at 40 wt% with 58–60 wt% carrier and 2 wt% wax. Compounding is performed on a co-rotating twin-screw extruder with 44:1 L/D, side feeding at zone 6, screw speed 500–600 rpm, barrel profile 150–190°C, and die melt temperature 190–200°C; underwater pelletizing with water temperature below 35°C is used to prevent pellet agglomeration. At 60 wt% total filler, die pressure typically remains between 45 bar and 60 bar; above 70 wt% filler, die pressure exceeds 80 bar and strand breaks become frequent. Published data for die pressure values at exactly 70 wt% filler in all screw configurations is limited; the quoted ranges derive from single-screw compounding technical bulletins and should be confirmed by pilot trials. The carrier satisfies EU Regulation 10/2011 and FDA 21 CFR 177.1520 for colour masterbatch used in food-contact packaging, provided the pigment and wax components are permitted; end-product converters require migration testing under EN 1186-1:2002 when final packaging is not excluded by functional barrier. Terminal products include white masterbatch, black masterbatch, additive masterbatch, and custom colour compounds. Operational boundary: batch mixing before the main feed is necessary when using above 4 wt% wax to prevent screw slip and uneven pigment dispersion.

Feeding sequence influences colour strength: TiO₂ is side-fed after polymer melting to minimise abrasive screw wear, while PE wax is pre-blended with the resin to reduce screw slip. A gear pump before the screen changer maintains die pressure fluctuation below ±2 bar; melt temperature measured by immersion probe is kept under 200°C to avoid LDPE crosslinking and gel formation. Strand pelletizing is preferred over underwater pelletizing when the batch contains above 2 wt% wax because water absorption reduces pellet hardness and causes feeding problems in downstream packaging lines.

When 2426H Is Tandem-Foamed Below 115°C Melt Temperature

Tandem foam extrusion of polyethylene sheet uses CHN Energy Xinjiang LDPE 2426H as the primary resin when a density range of 30–70 kg/m³ is specified for protective packaging and expansion joint filler. The formulation consists of 95–97 wt% 2426H, 3–5 wt% endothermic/exothermic blowing agent masterbatch with active content 0.6–1.5 wt%, and 0.5–1.0 wt% nucleator masterbatch. A primary extruder of 65 mm with 32:1 L/D feeds a secondary 90 mm extruder with 20:1 L/D; melt temperature at the die is held between 105°C and 115°C to prevent pre-expansion inside the die. Sheet thickness of 1–6 mm is controlled by a calender stack downstream; foam density is tested under ISO 845:2006, and compression set under ISO 7214:2012. REACH registration for blowing agent decomposition products and ISO 7214:2012 test methods for polyethylene cellular plastics govern the product; flame-retardant variants require testing to ISO 4589-2 for oxygen index when used in construction. Terminal products include PE foam sheets, protective packaging, automotive interior padding, and expansion joint filler. Melt temperature above 120°C causes gas to evolve inside the die and produces surface melt fracture; below 103°C the melt freezes at the die lip and generates high die pressure. No direct food contact is claimed for foamed sheet containing chemical blowing agent decomposition residues unless specific migration testing demonstrates compliance.

Property testing of foamed sheet includes apparent density under ISO 845:2006, compression stress at 10% deflection to ISO 7214:2012, and residual blowing agent content by GC headspace if the product is supplied for enclosed automotive interior use. The calender stack gap is set 10–15% narrower than the final sheet thickness to limit post-extrusion expansion and surface waviness. For sheet widths above 1200 mm, die lip adjustment and edge trimming remove edge beads where density can be 15–20% higher than the centre.

Shrink Film High-Stalk Bubble Cooling and Free Shrink Targets

The high-stalk bubble configuration for heavy-duty shrink film uses CHN Energy Xinjiang LDPE 2426H when the formulation requires 65–75% free shrink in the machine direction at 150°C under ASTM D2732-14. A typical shrink formulation contains 70–80 wt% 2426H, 20–30 wt% butene LLDPE, and in some cases 10–20 wt% EVA replacing the LLDPE portion to increase transverse shrink and reduce sealing temperature. Processing uses die gaps of 1.2–1.8 mm and BUR 3.5:1 to 4.5:1; the stalk is maintained at 12–15 die diameters above the die before bubble expansion, and melt temperatures are kept at 170–190°C. The resulting oriented film is collapsed and wound with controlled tension; free shrink is measured at 130°C and 150°C to ISO 14616:2004, while seal strength is tested to ASTM F88/F88M-15. Shrink force and free shrink are controlled under ISO 14616:2004; film thickness is measured to ASTM D6988-13, and tensile properties to ISO 527-3:2018. Terminal products include collation shrink film, pallet shrink hood, bottle bundling film, and industrial shrink bundling. Operational boundary: high stalk heights above 15 die diameters raise MD free shrink above 75% but lower Elmendorf tear below 20 g in the machine direction; residual stresses decay within 24 h and can alter shrink performance if film is stored above 30°C before use.

Free shrink values for high-stalk 2426H/LLDPE shrink film are typically non-uniform across web width unless air ring temperature is held within ±2°C; centre-to-edge shrink variation above 5% causes bottle bundling film to lift at package corners. The bubble is collapsed at a haul-off speed ratio of 3.0:1 to 4.0:1 relative to die velocity to set machine direction orientation; higher ratios increase MD free shrink but reduce TD free shrink below 10% at 130°C and lower seal seam integrity under ASTM F88/F88M-15. Shrink tunnel residence time of 8–12 s at 160–180°C is used for pallet hood applications to achieve 60–70% final MD shrink without burning the film surface.