Linear low-density polyethylene resin DNDA8320 is a butene-comonomer LLDPE grade produced by low-pressure gas-phase polymerisation for blown-film conversion. The resin has a nominal density of 0.918 g/cm³ measured under ISO 1183-1:2019 and a melt flow rate of 2.0 g/10 min when tested at 190 °C with a 2.16 kg piston load in accordance with ISO 1133-1:2022. The grade is supplied as free-flowing pellets and is typically converted on monolayer and coextruded film lines at die gaps of 1.8 mm to 2.2 mm and blow-up ratios from 2.0:1 to 2.5:1. DNDA8320 is not a high-pressure LDPE; the molecular backbone is essentially linear with ethyl short-chain branches from butene incorporation, and the material lacks the long-chain branching that defines autoclave or tubular LDPE. The resulting rheological profile differs in shear viscosity, extensional behaviour, dart impact, tear propagation, and seal initiation temperature. Published data for DNDA8320-specific mechanical properties is limited; converter qualification therefore relies on mill certificates for density and melt flow rate combined with film testing under the standards listed below.

What Differentiates Butene-Based DNDA8320 from High-Pressure LDPE and Metallocene LLDPE?

At a density of 0.918 g/cm³, DNDA8320 produces films with higher tensile yield strength and higher dart impact than LDPE of equivalent melt index, but with lower melt strength and a narrower bubble-stability window. High-pressure LDPE carries long-chain branching and a broad molecular weight distribution; this yields high extensional strain hardening and stable melt drawing but limits film toughness. DNDA8320, by contrast, derives its mechanical performance from linear chains containing ethyl side branches. Compared with hexene-based and octene-based LLDPE, the butene comonomer is less effective at creating tie-chain density at the same molar comonomer content, so converters must often accept higher resin density or reduced low-temperature toughness. Metallocene grades possess a narrower molecular weight distribution and often lower seal initiation and higher dart impact, but they exhibit higher shear viscosity at equivalent melt index and may require wider die gaps and higher melt pressure on conventional single-screw film lines. DNDA8320 is therefore specified where processing robustness and cost are weighted above ultimate optical performance and low-temperature hot-tack.

Table 1 summarises class-level differences between butene-based DNDA8320 and higher-alpha-olefin LLDPE grades. The comparison is qualitative and is drawn from polymer science literature rather than from DNDA8320 mill certificates.

On a 45 mm single-screw extruder with an L/D ratio of 25:1 and a barrier screw, DNDA8320 typically exits the die at melt temperatures from 175 °C to 215 °C. Barrel settings are profiled from 160 °C in the feed zone to 210 °C at the adapter and die. Die pressure at output rates near 45 kg/h is strongly influenced by screen-pack configuration; a 40/80/40 mesh pack often produces pressures in the 15 MPa to 25 MPa range on a 200 mm die with a 1.8 mm die gap, but values shift with melt temperature and batch-to-batch variation in molecular weight distribution. Bubble stability for DNDA8320 depends on frost-line geometry and internal bubble air pressure. The frost line is commonly held at 1.0 m to 1.6 m above the die face, corresponding to 8 to 12 die diameters, to balance isotropy and opacity. If the frost line falls below 0.8 m, machine-direction orientation rises and transverse tear strength deteriorates; if it is raised beyond 1.8 m, output per unit die circumference becomes limited by bubble wander and gauge variation. The addition of 2.5 wt% high-pressure LDPE can increase bubble stiffness and reduce hole formation, but it raises seal initiation temperature and reduces dart impact energy.

Bubble stability breaks down when die pressure exceeds the resin’s critical wall shear stress

Surface melt fracture in DNDA8320 is observed as sharkskin near the die lips when the wall shear stress in the die land exceeds the resin critical value; for butene LLDPE class materials, this threshold is commonly in the range 0.14 MPa to 0.20 MPa depending on melt temperature and molecular weight distribution. Gross melt fracture appears at higher shear rates and degrades film transparency. To mitigate sharkskin without lowering output, converters widen the die gap from 1.2 mm to 2.0 mm and reduce the entrance angle of the die land. A wider die gap lowers wall shear stress but also reduces draw-down orientation and may require an increased blow-up ratio to compensate for gauge uniformity. Residence time distribution in extruders longer than L/D 30:1 promotes oxidative degradation and gel formation; gel counts above 20 gels/m² with particle diameter greater than 100 µm become visible in thin film and act as dart-failure initiation points. Melt filtration is therefore controlled with screen packs of 40/80/40 mesh or finer, and gel counts are measured by optical scanning of 1 m² film samples. If regrind is added above 20 wt%, localised gel accumulation in the screen pack becomes the limiting process variable for extended film runs.

Pre-drying of DNDA8320 is not generally required because the resin is hydrophobic. Surface condensation on pellets stored below dew point is addressed by a 60 °C hopper dryer for 0.5 h to 1.0 h; higher temperatures are not recommended because pellet agglomeration can occur above 80 °C. Moisture-induced lensing defects in film are not a bulk degradation mechanism but rather a function of air entrainment in the screw feed zone. Feed-throat cooling water can be set to 30 °C to 40 °C to prevent pellet sticking and unstable solids transport.

When Layer Ratios Shift Below 20% in Three-Layer Coextrusion

DNDA8320 is used in three-layer coextruded films as a skin layer for seal strength and puncture toughness. At total film thickness below 50 µm, the skin layer thickness is often reduced to 5 µm to 10 µm per side, equivalent to 20% or less of the total structure. Under these conditions, seal fusion becomes sensitive to interfacial defects and layer-thickness deviations. A skin layer gauge variation of ±1 µm can shift seal initiation temperature by 3 °C to 5 °C because heat transfer at the seal-bar interface is dominated by the skin thickness. Coextrusion feedblock instabilities and melt-temperature mismatches above 10 °C between skin and core layers produce interfacial waviness that is detectable as optical haze and seal-strength fluctuation. For DNDA8320, melt temperature at the die should be held within 200 °C to 215 °C because lower temperatures raise melt viscosity and promote interfacial instability. Published data for DNDA8320-specific coextrusion performance is limited, so the above temperature limits are derived from general butene LLDPE behaviour on three-layer lines. The resin is not optimised for cast-film quenching; chill-roll temperatures below 15 °C shift crystallisation kinetics and may increase roll-wrap and blocking.

Seal strength and hot-tack performance of DNDA8320 films are evaluated under ASTM F88/F88M-21 and ASTM F1921-18 using 25.4 mm wide specimens cut in the machine direction. For butene LLDPE class grades at 50 µm thickness, seal initiation is generally recorded between 95 °C and 110 °C, with maximum seal strength near 145 °C to 160 °C. Hot-tack peaks at 115 °C to 130 °C at a dwell time of 0.5 s and a seal pressure of 0.24 MPa. Above 160 °C, seal strength decreases because melt squeeze-out reduces weld thickness. DNDA8320’s broad molecular weight distribution makes hot-tack more tolerant to temperature fluctuation than a narrow metallocene grade, but it also tends to increase seal initiation temperature relative to C6 or C8 metallocene films. In high-speed vertical form-fill-seal operations, the sealing jaw is maintained at 140 °C to 160 °C and the dwell time is not to exceed 300 ms; if the film slips on the jaw surface due to low coefficient of friction, intermittent seal fusion is observed.

Register of Standards Used for Incoming Resin and Film Qualification

Qualification of DNDA8320 for flexible packaging requires a matrix of physical, mechanical, and optical test methods. Table 2 lists the principal standards invoked during incoming resin release and converted film evaluation. Food-contact conversion also requires compliance with 21 CFR 177.1520, EU Regulation 10/2011, and applicable GB 9685-2016 additive restrictions.

On a vertical form-fill-seal line producing 500 g frozen-food pouches at 80 pouches/min, film made from DNDA8320 is typically sealed at 145 °C to 155 °C with jaw pressure of 0.25 MPa to 0.35 MPa and dwell time of 180 ms to 250 ms. At speeds above 100 pouches/min, hot-tack strength becomes limiting because the pouch weight pulls the seal before solidification. The observed failure mode is seal peel at the bottom gusset, not film tear; this distinguishes DNDA8320’s seal performance from higher-alpha-olefin LLDPE grades that often exhibit film tear at the seal perimeter. In agricultural silage film applications, DNDA8320 is compounded with 1 wt% to 2 wt% carbon black masterbatch and converted at 150 µm to 200 µm. The carbon black raises melt temperature and die pressure, and the processing window narrows by approximately 5 °C; specific extrusion data for this formulation should be verified by line trials. The final allowable downgauging limit is therefore fixed by the measured transverse Elmendorf tear under ISO 6383-1:2015, not by tensile yield.