Linear low-density polyethylene (LLDPE) is produced by low-pressure ethylene copolymerisation with an α-olefin—but-1-ene, hex-1-ene, or oct-1-ene—over Ziegler-Natta or metallocene catalyst systems. The resulting short-chain branch distribution controls density, crystalline fraction, melt rheology, tear anisotropy, and environmental stress-cracking resistance. Within Lotte Chemical’s LLDPE portfolio, the designations UR644 and UF414 occupy distinct fabrication positions in common supplier literature: UR644 is associated with rotational moulding service where long oven residence times and wall-thickness uniformity dominate, while UF414 is associated with blown film extrusion where gauge reduction, dart impact resistance, and optical quality define the processing window. The suffixes are not specifications by themselves. Grade-specific melt flow rate, density, comonomer identity, and additive loading must be taken from the active technical datasheet or certificate of analysis because reactor campaigns, additive formulations, and lot-specific values change.

What Physical Property Matrix Separates UR644 from UF414?

Property separation is best performed on a common test-method basis. Melt flow rate is determined by ASTM D1238 or ISO 1133-1:2022 at 190 °C under 2.16 kg. Density is measured by ISO 1183-1:2019 or ASTM D1505. Tensile properties are measured by ISO 527-2 or ASTM D638. For LLDPE film, dart impact and optical haze are measured by ASTM D1709 and ASTM D1003, respectively, while tear resistance is measured by ASTM D1922. For rotational moulded parts, instrumented impact is assessed by ISO 6603-2 or ASTM D3763, and environmental stress-cracking resistance is assessed by ASTM D1693 or ISO 16770. The separation between UR644 and UF414 is therefore not a single property but a composite of melt index, density, comonomer type, and stabiliser package. Published data for this specific configuration is limited; a processor should not transfer values from one production campaign to another without a matching lot number.

On a 45 mm single-screw blown-film line with an L/D of 30:1 and a 100 mm die, UF414-class linear film resin is processed at barrel temperatures from 165 °C to 205 °C, adapter and die temperatures from 190 °C to 215 °C, and blow-up ratios between 2.2:1 and 3.0:1. The frost-line height is maintained at 4–6 die diameters to stabilise the bubble. At gauge below 20 µm, the lower melt tension of linear chains can produce bubble flutter and gauge variability. In such cases, processors add 10–30 wt% high-pressure LDPE or raise the die gap from 1.6 mm to 2.2 mm. The characteristic MD/TD tear imbalance of linear film is evaluated by ASTM D1922; dart impact is evaluated by ASTM D1709; haze is evaluated by ASTM D1003. These settings are process indicators rather than grade-specific prescriptions, and they should be tuned against the active datasheet.

The Role of Comonomer Type in Film Performance Metrics

The comonomer type selected for film-grade LLDPE changes short-chain branch length and distribution. But-1-ene generally produces a higher optical clarity and lower dart impact relative to hex-1-ene at equivalent density; hex-1-ene or oct-1-ene grades provide higher toughness and better MD/TD tear balance at the same melt index. For a film resin such as UF414, the datasheet should be checked for comonomer identity and density target. At a nominal density of 0.918 g/cm³, a Ziegler-Natta LLDPE may show a crystalline melting peak between 121 °C and 126 °C by ISO 11357-3; crystallisation onset may lie between 105 °C and 112 °C. These thermal transitions define seal initiation behaviour and heat-resistance in downstream converting. LLDPE commonly retains ductility in instrumented impact tests down to -40 °C, as evaluated by ISO 6603-2, although the precise transition depends on density and testing speed. For film converters, the practical consequence is that UF414 should be evaluated in the exact gauge, frost-line height, and winding tension used on the production line; laboratory values alone do not predict bubble stability or slitting performance.

When UR644 Is Sintered in Biaxial Rotational Moulding

Rotational moulding of LLDPE requires powder with a narrow particle size distribution, low fines content, and sufficient melt flow to densify against atmospheric oxygen. The powder is ground to a nominal particle size below 500 µm; retention on a 35-mesh sieve is typically kept below 2% to ensure wall-thickness uniformity. Dry flow and apparent density are measured by ISO 6186 or an equivalent bulk-density method. In a shuttle or carousel moulding machine, the mould is rotated at a ratio of 4:1 on the primary axis and 1:1 on the secondary axis, with oven air temperature between 260 °C and 320 °C and peak internal air temperature between 200 °C and 230 °C. For a wall thickness of 6 mm, total cycle time is commonly 25–40 min. UR644 must maintain oxidative stability during this residence time; oxidative induction time is measured by ASTM D3895 or ISO 11357-6. Insufficient stabilisation appears as pinholes, yellowish core layers, and brittle failure at the inner surface. The part should be tested for low-temperature impact by ISO 6603-2 and tensile yield strength by ISO 527-2.

Biaxial rotational moulding trials on production carousels have shown that a pure LLDPE powder can develop a tacky inner surface if peak internal air temperature exceeds the stabiliser ceiling. To reduce this failure mode, processors blend 10–30 wt% HDPE or MDPE into UR644 to stiffen the wall and reduce surface tack; however, the ESCR performance of the blend must be re-qualified by ASTM D1693. Pre-drying is not generally required for neat LLDPE powder at relative humidity below 60%, but wet regrind or condensation during warehouse storage can introduce surface moisture. A desiccant hopper at 80 °C for 2–3 h is used when the moisture content exceeds 0.1% as measured by ISO 15512. Compatibility with carbon black masterbatch for UV protection should be assessed by weathering tests under ISO 4892-2 for outdoor tanks and enclosures.

Additive Durability, Purging Boundaries, and Moisture Thresholds

The additive package in LLDPE film and rotomoulding grades typically includes a phenolic primary antioxidant, a phosphite secondary antioxidant, and an acid neutraliser. These additives migrate slowly to the surface. In film-grade UF414, additive bloom can reduce surface tension and corona treatment wetting. Corona-treated film should be laminated or printed within 48–72 h because wettability can decay below 38 dyn/cm on high-slip formulations. In UR644, additive bloom can reduce interlayer adhesion in multi-layer rotomoulded structures; sanding or flame treatment may be required before secondary layering. Purging from LLDPE to a polar resin requires an intermediate LDPE purging compound because residual LLDPE can form gels or streaks in subsequent runs. The screw and die should be purged at 200–230 °C until the melt is clear. Barrel temperatures must not exceed 250 °C to avoid chain scission, crosslinking, and gel formation.

Does Food-Contact Compliance Transfer Across Lotte LLDPE Grades?

Food-contact status is registered by grade, not by polymer class. Under FDA 21 CFR 177.1520, olefin polymers may be cleared if the density and extractables limits are met. Under Regulation (EU) No 10/2011, a specific migration limit applies for total migration and for any restricted additives. A grade used for a cereal pouch liner cannot be assumed compliant for acidic or fatty food simulants unless the supplier’s compliance statement covers the intended conditions of use. For UR644 in potable water tanks, NSF/ANSI/CAN 61 certification is evaluated on the finished rotomoulded article, not on the raw powder alone. Processors should request a migration test report performed under the appropriate food simulant—ethanol 10%, acetic acid 3%, or vegetable oil as defined in the EN 1186 series. The absence of heavy metals and hazardous substances is documented by IEC 63000 and REACH SVHC certificates. Compliance documentation must be matched to the exact Lotte grade, production site, and revision status of the datasheet.