Braskem LL5405S is a blown film extrusion grade linear low density polyethylene with a nominal melt index of 1.0 g/10 min when measured under ASTM D1238 at 190°C and 2.16 kg and a nominal density of 0.918 g/cm³ under ASTM D792. In heavy-duty shipping sacks, the resin is processed at 100 wt% or in dry blends containing 10 wt% to 20 wt% low-density polyethylene. The LDPE fraction reduces melt pressure and stabilises the bubble at low film thickness. On a 70 mm single-screw extruder with 28:1 L/D and a 100 mm blown film die, the die gap is set between 1.6 mm and 2.0 mm. The blow-up ratio is held at 2.2:1 to 2.8:1. Frost line height is maintained between 450 mm and 650 mm for a 120 µm monolayer sack. Melt temperature at the die is controlled between 195°C and 220°C to suppress oxidative gel formation. Edge trim regrind is used up to 20 wt% in the core layer of a three-layer sack because gel count increases beyond this level. Terminal sacks for polymer granules, mineral fillers, and fertiliser are tested for dart drop impact under ASTM D1709 Method B. Tensile properties are recorded under ASTM D882. Elmendorf tear propagation is measured under ASTM D1922. Where the sack is used as UN certified packaging, the performance follows drop and stacking tests described in Chapter 6.5 of the UN Model Regulations. The converter must run batch-to-batch melt index checks because variation above ±0.1 g/10 min alters bubble stability at 120 µm and shifts the frost line into a lower neck region that reduces transverse tear resistance.

What Limits Seal Initiation Temperature in Frozen Food Sealant Layers?

In frozen food packaging, LL5405S is placed into the sealant layer of a three-layer or five-layer polyethylene blown film. The sealant layer typically occupies 20% to 30% of the total gauge. At total film thickness of 50 µm, the sealant layer is 10 µm to 15 µm. The film is produced on a 250 mm multi-layer die with 1.8 mm die gap and 2.0:1 blow-up ratio. Melt temperature at the sealant extruder is kept at 200°C to 215°C because a higher sealant-layer melt temperature narrows the hot tack window and promotes seal-surface irregularity. The slip additive concentration in the sealant layer is held below 1,000 ppm because migration above this level can reduce seal strength under ASTM F88 by more than 10%. The terminal bags are used for IQF vegetables, seafood, and portion-controlled frozen prepared food. Heat seal characteristics are evaluated under ASTM F2029. For butene LLDPE of 0.918 g/cm³ density, the seal initiation temperature is generally observed in the 95°C to 105°C band when jaw pressure is 2.7 bar and dwell time is 0.5 s. Hot tack is measured under ASTM F1921. Seal strength is measured after 24 h conditioning under ASTM F88. Compliance for food contact requires verification under EU 10/2011 and FDA 21 CFR 177.1520. The overall migration limit is 10 mg/dm² under EU 10/2011 for plastic materials in contact with food. Converters must confirm that antioxidants or slip additives in the final formulation do not exceed the specific migration limits of Annex I of that regulation. The operational boundary is the seal bar temperature. Below 90°C, seal strength is not sufficient for frozen distribution. Above 115°C, the film can shrink at the seal jaw and produce pleats that compromise pack integrity.

Collation shrink films containing LL5405S are formulated in a narrow blending window of 70 wt% to 80 wt% LLDPE and 20 wt% to 30 wt% LDPE. The LDPE component is not added for cost control only. It increases machine-direction shrink tension and accelerates bubble cooling. A monolayer or three-layer line with a 1.2 mm die gap and 3.0:1 blow-up ratio is used. The high stalk is maintained at a frost line height of 350 mm to 500 mm. Film thickness is 40 µm to 70 µm. Under ASTM D2732, unrestrained linear thermal shrinkage in the machine direction is typically in the 60% to 75% range at 160°C, while transverse direction shrinkage remains below 15%. Shrink force is checked under ISO 14616. The terminal product is bottle multipack collation and printed film overwrap for cans. A processing boundary exists at LDPE addition above 30 wt%. The bubble enters a less stable corridor because the high-molecular-weight LDPE fraction increases melt strength but reduces the dart drop of the final shrink film. Below 20 wt% LDPE, the machine-direction shrink tension is insufficient to hold bottle groups under transit vibration. The converter adjusts the collapsing frame angle and uses a low-pressure dual-lip air ring to avoid gauge variation above ±8% because shrink force is proportional to local gauge. Batch-to-batch LDPE melt index changes above 0.4 g/10 min shift the required frost line height and can produce irregular shrink windows.

Low-Tunnel Greenhouse Film and Blown Film Gauge Uniformity

For agricultural low tunnels and silage cover film, LL5405S is used in monolayer and three-layer structures at total thickness between 50 µm and 150 µm. The film is blown through a 200 mm die with 2.0 mm die gap at 2.4:1 blow-up ratio. A frost line height of 500 mm to 700 mm is maintained. The extruder barrel profile is set from 180°C at the feed throat to 210°C at the adapter. UV stabiliser masterbatch is let down at 4 wt% to 6 wt% in the core layer, and anti-fog additive masterbatch is introduced at 2 wt% to 3 wt% in the inside skin layer only. For three-layer film, the layer ratio is 30% skin / 40% core / 30% skin. Tensile strength is tested under ASTM D882. Impact resistance is verified under ASTM D1709 Method B. The finished film is used as low-tunnel cover, silage clamp cover, and overwintering film for nursery stock. Compliance is linked to EN 13206 for covering films used in agriculture and horticulture. The standard requires minimum tensile and impact properties after weathering exposure. The film must be stored in a temperature-controlled warehouse below 35°C because uncontrolled UV masterbatch dispersion can produce local thinning when regrind is reused above 10 wt%. The major operational boundary is film gauge uniformity. A variation greater than ±10% across the web reduces the weathering life of thin sections and creates premature failure under wind load on low-tunnel structures.

Monolayer can liners are produced at 20 µm to 35 µm from LL5405S as a 100 wt% resin or as a blend with 10 wt% to 30 wt% HDPE. The HDPE fraction increases the secant modulus for easy bag opening but reduces dart drop impact. On a 60 mm extruder with 24:1 L/D and 120 mm die, the die gap is set at 1.0 mm to 1.4 mm. The blow-up ratio is 2.5:1 to 3.0:1. Melt temperature is held at 200°C to 225°C. At 20 µm, bubble stability is the primary bottleneck. The frost line height is kept below 400 mm to prevent the bubble from wandering. Above take-off speeds of 35 m/min, draw resonance may appear as alternating thick and thin bands. Terminal products are refuse can liners and retail produce bags. Film is tested for dart drop under ASTM D1709 Method A. At 25 µm, dart drop values in the 90 g to 160 g range are typical for this density class. The lower limit is governed by the film gauge. Elmendorf tear is measured under ASTM D1922. Machine-direction tear is usually lower than transverse direction tear because molecular orientation is higher in the machine direction. The converter must monitor ambient air temperature. Below 15°C, the film cooling rate increases and film stiffness increases, which can generate poor bag opening and static cling. Blending above 30 wt% HDPE is not recommended because the dart drop falls below the level required for heavy refuse load retention.

When Die Gap Is Reduced Below 1.2 mm, Melt Curtain Stability Changes in Lamination Base Films

Lamination base film made from LL5405S is blown at 15 µm to 25 µm for subsequent adhesive lamination to biaxially oriented polyester or biaxially oriented polypropylene. The film is corona treated in-line to a wetting tension of 38 mN/m to 42 mN/m measured by ASTM D2578. The die gap is set at 0.8 mm to 1.2 mm. The blow-up ratio is held at 2.0:1 to 2.3:1. Cooling air is directed through a dual-lip air ring at low velocity to limit haze. The extruder melt temperature is kept at 195°C to 210°C. At die gaps below 1.2 mm, the thin melt curtain becomes sensitive to changes in die lip cleanliness and melt temperature variation. The terminal laminate is used in wrap-around labels, snack packaging, and coffee pouches. For food contact, the final laminate must comply with EU 10/2011 and FDA 21 CFR 177.1520. The converter runs the lamination substrate at 0.3% to 0.5% slip additive by weight only when the downstream converter confirms that the slip additive has no adverse effect on lamination bond strength after 24 h curing. The lamination bond strength is checked under ASTM F904 using a heat-seal bond tester. Surface treatment must be re-verified before winding because corona decay can reduce wetting tension by 4 mN/m to 6 mN/m within 72 h on untreated film. Film is wound with taper tension of 12–15 N/100 mm width to prevent blocking. The primary failure mode on the laminator is poor wet-out when the wetting tension drops below 38 mN/m, causing the adhesive to de-wet on the LLDPE surface and reducing bond strength below the acceptable 60 g/25 mm seal-strength threshold used in flexible packaging quality control.