Linear low-density polyethylene marketed under the Relene name represents a butene-comonomer film resin family supplied by Reliance Industries Limited. The technical scope of this review is LLDPE Relene Grades: Reliance's Code Range and Film Applications. Property data for these materials are generated according to ASTM D1238 for melt flow rate at 190 °C/2.16 kg, ASTM D1505 for density, and ASTM D882 for tensile properties of thin film. The molecular architecture contains short-chain branches from but-1-ene, reducing crystalline density and melting point relative to high-pressure low-density polyethylene at equivalent melt flow rate.

How Does the Relene Designation Encode Density and Melt Flow?

The alphanumeric code of film-grade Relene LLDPE carries density, melt flow, and end-use information. The leading two digits indicate nominal density: 18 corresponds to 0.918 g/cm³, 20 to 0.920 g/cm³, 24 to 0.924 g/cm³, and 26 to 0.926 g/cm³. The terminal three digits represent melt flow rate as tenths of a gram per 10 min; thus 010 denotes 1.0 g/10 min and 020 denotes 2.0 g/10 min. The letter position in the trade designation identifies film end-use and additive modification; FS is associated with film-slip/antiblock packaging in published trade literature. Verification against current Reliance technical datasheets is required because commercial grade availability varies by region and product rationalization.

Cast stretch film lines running 75 mm to 90 mm extruders with L/D 28:1 to 32:1 and die gaps of 0.5 mm to 0.8 mm require polymer with a melt flow rate high enough to limit draw resonance at thin gauges. Relene LLDPE grades with nominal melt flow rate 2.0 g/10 min are therefore selected for high-line-speed cast film to maintain melt curtain stability and reduce edge neck-in. Puncture resistance and elongation measured under ASTM D5748 and ASTM D882 are primary acceptance criteria; the higher short-chain branching of butene LLDPE improves puncture relative to LDPE at equal gauge but remains below hexene or octene copolymers when extreme elongation is specified.

Blown Film Die Gap, Frost-Line Height, and Bubble Stability Limits

Monolayer blown film extrusion of Relene LLDPE film grades on single-screw extruders of 45 mm to 75 mm diameter and L/D 24:1 to 30:1 typically uses a die gap of 1.8 mm to 2.5 mm. A melt temperature between 180 °C and 230 °C is maintained to prevent gels and to limit oxidative degradation in the die lip region. The bubble configuration is stabilised at blow-up ratios of 2.0:1 to 3.0:1, with frost-line height adjusted between 5 and 9 die diameters. Processing below 180 °C raises melt pressure and may produce melt fracture at high screw speeds; processing above 240 °C encourages crosslinking and gel particle formation in butene LLDPE, particularly in stagnant regions of the spiral mandrel die. Field data from blown film lines indicate that bubble instability increases when melt temperature variation exceeds ±5 °C, causing gauge bands at ±10 % or greater.

Heavy-duty sack film produced from 0.924 g/cm³ Relene LLDPE with 1.0 g/10 min melt flow rate is processed at a thickness of 80 µm to 150 µm. The selection of 0.924 g/cm³ density over 0.920 g/cm³ raises secant modulus measured under ASTM D882 and lowers water vapor transmission rate tested under ASTM E96 at 38 °C and 90 % RH. Dart impact and Elmendorf tear values at these gauges vary with frost-line height and draw-down ratio; a lower frost-line height increases transverse direction tear but may degrade machine-direction tear symmetry. Production-scale lines report lower melt pressure and better melt homogeneity when the extruder barrel profile is set with a reverse temperature zone in the feed section to prevent pellet bridging in the hopper throat.

When High-Stalk Bubble Geometry Demands Lower Melt Flow Variation

High-stalk bubble geometry, used to orient LLDPE film for stretch and heavy-duty packaging, requires sufficient melt tension to maintain a stable stalk height of 6 to 10 die diameters. Melt flow rate variation of more than ±0.2 g/10 min across a batch destabilises the stalk because draw force varies with molecular weight distribution. Relene LLDPE grades designated 010 or 020 are specified with a maximum lot-to-lot melt flow rate variation of ±0.2 g/10 min in producer technical bulletins; converters should confirm this because secondary distribution and silo blending can widen the variation. The extruder gear pump suction pressure should remain above 20 bar to avoid cavitation when running 1.0 g/10 min material at high screw speeds. In high-stalk operation, bubble breaks occur most often at the frost line transition when draw-down ratio exceeds 30:1; reducing die gap or increasing melt temperature widens the apparent melt strength window but can lower machine-direction tear.

In extrusion lamination, a low-density peelable sealant web based on 0.918 g/cm³ Relene LLDPE with 2.0 g/10 min melt flow rate is coated at 10 g/m² to 25 g/m² onto paper, aluminium foil, or oriented polyester. Seal initiation temperature measured according to ASTM F88 at 0.5 s dwell and 2.8 bar jaw pressure typically falls between 105 °C and 115 °C for butene LLDPE sealants; hot tack is measured by ASTM F1921. Lower density improves sealability but reduces melting point and increases blocking tendency on the reel. For extrusion coating, melt temperature at the die is held at 280 °C or below to limit odour and smoke; edge trim is reprocessed at levels not exceeding 15 wt% to avoid gel specks in the thin coating.

What Role Do Antiblock and Slip Additive Packages Play in Seal Initiation Temperature?

Film-grade Relene LLDPE can be supplied with silica antiblock, erucamide slip, or non-migratory slip packages depending on end-use. Erucamide migration to the film surface reduces coefficient of friction to 0.10–0.25 measured under ASTM D1894 over a 24 h to 72 h ageing period. The same migratory slip additive can reduce seal initiation temperature by 2–5 °C and can lower hot tack by 5–15 % if bloomed slip contaminates the seal bar. High-slip grades are therefore unsuitable for printing, lamination, or medical packaging without corona treatment because surface energy drops below 38 mN/m. Antiblock packages increase surface roughness and reduce blocking but raise haze; the balance is tested under ASTM D1003 for haze, ASTM D2457 for gloss, and ASTM D3354 for blocking load.

Agricultural greenhouse film based on 0.920 g/cm³ Relene LLDPE is compounded with hindered amine light stabilizers and nickel quenchers at 0.3 wt% to 0.8 wt%. The service lifetime claim requires weathering testing under ISO 4892-2 cycle conditions with UV irradiance of 0.55 W/m² at 340 nm and black-standard temperature 65 °C. Film tensile retention after 12,000 h accelerated weathering is the acceptance criterion; published data for specific Relene stabilizer masterbatches is limited and must be generated by the converter.

Mechanical and Optical Test Methodology Anchors Film Selection

Film selection for Relene LLDPE requires a test matrix that separates resin performance from extrusion process effects. The following methods are used for batch acceptance and application qualification:

For food-contact applications, the base olefin polymer must comply with FDA 21 CFR §177.1520 or Regulation (EU) No 10/2011; specific additive packages and migration limits must be validated under EN 1186 and EC 1935/2004. Relene LLDPE is not recommended for continuous service above 60 °C in thick sections because oxidative life falls sharply. In blown film, regrind containing moisture above 60 % RH should be dried at 65 °C for 2 h to prevent surface pitting. The use of amine-based antifog agents can interfere with erucamide slip migration and alter heat seal performance; compatibility must be confirmed per ASTM F2029.