Jiutai Group LLDPE 7042 is a pelletized film-grade linear low-density polyethylene produced with butene-1 as the short-chain branching comonomer. The material belongs to the 7042 melt-index family widely referenced in China’s polyolefin trade, supplied as free-flowing white granules and used primarily in blown film conversion. Typical melt mass-flow rate is 2.0 g/10 min at 190 °C under a 2.16 kg load when determined according to ISO 1133-1:2022; nominal density is 0.920 g/cm³ measured by ISO 1183-1:2019. The grade is intended for monolayer and coextruded films in agricultural mulch, collation shrink, protective packaging, lamination, and heavy-duty sacks. Because the 7042 designation is not proprietary to Jiutai Group and is also produced by other Chinese and regional licensors under different catalyst and comonomer addition strategies, incoming inspection should verify lot-specific melt index, density, and film appearance before substituting lots in an established formulation.

Molecular architecture of Jiutai Group LLDPE 7042 is based on ethylene copolymerization with butene-1 in a gas-phase or slurry process depending on the production train. The resulting polymer contains linear backbones with ethyl short-chain branches; the absence of long-chain branching distinguishes it from high-pressure LDPE. The resin is supplied with antioxidant and acid scavenger packages, but not with antiblock or slip additives in the base grade unless specified by the converter. Additive incorporation occurs by masterbatch dilution at the hopper or by pre-compounding in downstream modification. The flow rate ratio I21/I2 is commonly reported between 25 and 30, indicating moderate shear thinning but less than high-pressure LDPE at equivalent melt index.

Which Physical and Rheological Specifications Govern Film-Grade Classification?

Film-grade classification for Jiutai Group LLDPE 7042 is controlled by the combination of melt flow stability, density, tensile yield response, and thermal transition values. Table 1 presents the typical property envelope for this grade as generically reported for butene-1 linear low-density film resins with the 7042 family designation; these ranges are not contractual specifications and must be confirmed against the producer’s certificate of analysis. Melt mass-flow rate, measured by ISO 1133-1:2022 procedure A, is typically 1.8–2.2 g/10 min. Density, determined by ISO 1183-1:2019 method D on compression-moulded plaques, is commonly 0.918–0.922 g/cm³. Tensile stress at yield measured on ISO 527-2:2012 type 1B specimens is not less than 8.0 MPa, and elongation at break exceeds 500%. Melting peak temperature by differential scanning calorimetry according to ISO 11357-3:2018 falls between 120 °C and 124 °C, and the Vicat softening temperature by ISO 306:2022 Method A50 is generally 95–105 °C.

On monolayer blown-film lines equipped with a grooved-feed extruder of L/D 28:1 and screw diameter between 45 mm and 65 mm, Jiutai Group LLDPE 7042 is routinely converted at barrel temperature settings from 160 °C in the feed zone to 195 °C at the metering zone, with adapter and die zones held at 190–200 °C. A die gap of 1.2–2.0 mm, blow-up ratio between 2.0:1 and 3.0:1, and frost line height of 3–8 die diameters have been used to maintain stable bubble geometry. When ambient relative humidity exceeds 60% and pellets are stored below 20 °C, surface condensation can introduce moisture-related pinholes and melt fracture; hopper-air temperature of 40–60 °C or a desiccant feeder is recommended before extrusion. The melt strength of this butene-1 LLDPE is lower than that of high-pressure LDPE at equivalent melt index, so external air-ring adjustment or internal bubble cooling is normally required to prevent bubble sag and flutter above 3.0:1 blow-up ratio. Output stability is also sensitive to feed-throat temperature because premature pellet sintering can cause screw slip and melt-pressure fluctuation. Purging with a 2.0 g/10 min LDPE grade before shutdown reduces oxidized heel formation, and residence time above 200 °C should be limited to 10 min to avoid cross-gel generation.

Film Property Comparisons Against High-Pressure LDPE and Metallocene LLDPE

Comparative selection between Jiutai Group LLDPE 7042, high-pressure LDPE, and metallocene LLDPE depends on extrusion stability, seal performance, and mechanical toughness. At equivalent melt index, the butene-1 Ziegler-Natta LLDPE has higher dart impact and tensile strength than autoclave LDPE but lower melt elasticity and lower bubble stability. Because the molecular weight distribution and short-chain branching distribution are narrower than those of LDPE but broader than those of a typical metallocene octene-1 LLDPE, the 7042 product occupies an intermediate processability window. Seal initiation occurs at approximately 95–105 °C, which is lower than many high-pressure LDPE grades but higher than metallocene grades that initiate below 90 °C. The butene-1 comonomer yields lower hot-tack strength and lower dart impact than octene-1 metallocene LLDPE at the same density, but the Ziegler-Natta product generally exhibits lower extruder torque fluctuation and less melt fracture on standard air-ring lines. Compared with high-density polyethylene film grades, Jiutai Group LLDPE 7042 has lower secant modulus and higher elongation, making it suitable for stretch and soft packaging but not for stiffness-critical liners or thermoformed trays. Table 2 compares representative blown-film value ranges for 40 µm film; values are published ranges and should not be used as direct lot acceptance criteria.

For agricultural mulch film and heavy-duty packaging, converter qualification of Jiutai Group LLDPE 7042 should reference tensile, tear, dart, and seal-strength measurements made on the finished film rather than on resin plaques. Tensile strength at break and elongation under ASTM D882-18 typically fall not less than 20 MPa in the machine direction and 18 MPa in the transverse direction for a 40 µm monolayer film, with elongation at break above 500% in both directions. Dart impact measured by ASTM D1709-16ae1 Method A is typically 80–150 g, and Elmendorf tear by ASTM D1922-15(2020) remains in the 200–400 gf machine-direction and 300–600 gf transverse-direction ranges. For lamination structures, corona treatment to 38–42 mN/m surface energy is required before adhesive application; without treatment, solventless polyurethane systems exhibit poor wetting and reduced peel strength. The oxygen permeability of a 40 µm monolayer LLDPE film is high, typically above 2000 cm³/(m²·day·atm) at 23 °C and 0% RH by ASTM D3985-17, limiting shelf life in oxygen-sensitive packaging unless a barrier layer is incorporated. The resin is not inherently UV-stable; agricultural film exposed for more than 6 months requires carbon black or hindered amine light stabilizer masterbatch addition. For food-contact use, converters should verify compliance with China GB 4806.6-2016 and EU Regulation (EU) No 10/2011 on the finished structure, because converter-added slips, antiblocks, and processing aids affect overall migration and specific migration limits.

When Processing Deviations Produce Bubble Instability or Gel-Related Defects

Field observations on high-output lines indicate that bubble instability with Jiutai Group LLDPE 7042 is most commonly induced by melt temperatures in excess of 210 °C, low melt temperatures below 160 °C, or excessive blow-up ratio above 3.5:1. At die temperatures above 210 °C, oxidative chain scission and crosslinked gel particles form in the die lip region; the resulting hard gels appear as arrowhead defects in thin film. At melt temperature below 160 °C, the resin does not fully melt, producing melt fracture and poor bubble symmetry. Moisture-related pinholes are mitigated by hopper-air temperature above 40 °C and by reducing compressed air dew point below -20 °C. The resin is incompatible with high levels of recycled polypropylene contamination; as little as 3 wt% PP can reduce tear strength by more than 30% and cause visible gels. For shutdown and changeover, the extruder should be purged until melt pressure stabilizes, and the screw should be run at low speed below 15 rpm before stopping to avoid carbonized heel formation. In applications requiring prolonged outdoor exposure above 24 months, the absence of adequate light stabilizer leads to embrittlement and loss of more than 50% of initial elongation before failure; published data for this specific configuration is limited, so film testing under the intended UV dose is required.