LLDPE 1002AY and 1002XBU: Film Codes with an “LL” Prefix Explained

The film codes LLDPE 1002AY and 1002XBU are supplier-specific designations for film-grade linear low-density polyethylene resins. The “LL” prefix in commercial polyolefin nomenclature denotes the low-pressure reactor family used to produce linear polyethylene with controlled short-chain branching; it separates the products from high-pressure low-density polyethylene, which contains both short-chain and long-chain branching. The full supplier designation is often written as LLDPE LL 1002AY or LLDPE LL 1002XBU, where the first LLDPE identifies the polymer class and the second LL is the product-slate shorthand for linear low-density material. LLDPE resins are ethylene/α-olefin copolymers, typically incorporating butene, hexene, or octene at comonomer weight fractions between 2 and 8 weight percent. The density range for film-grade LLDPE is normally 0.915 g/cm³ to 0.940 g/cm³ when tested under ASTM D1505-18.

In the two code strings, the numeric sequence 1002 is not an ISO 1872-1 melt-flow designation; it links the resins to a nominal melt index of 2.0 g/10 min at 190 °C and 2.16 kg when measured according to ASTM D1238-20. The suffixes AY and XBU differentiate additive packages, catalyst lineage, and plant-specific finishing conditions. Public technical data for the exact additive split between 1002AY and 1002XBU is limited because the formulations are proprietary, but the base-resin density and melt-flow class are the same. The 1002AY grade is commonly cited in supplier literature as a butene-based film resin for general-purpose blown film; 1002XBU is supplied with a formulated surface additive package for higher-slip packaging films. The designation itself does not state the comonomer type or additive concentrations.

What Does the “LL” Prefix Signify in Commercial Polyethylene Nomenclature?

The term “linear” refers to the absence of long-chain branching on the ethylene backbone. Short-chain branches introduced by the comonomer interrupt crystallisation and reduce density. In conventional LLDPE, butene, hexene, or octene is inserted at intervals along the chain; branch length increases with the α-olefin chain length. Under identical density and melt index, hexene-based grades generally exhibit higher dart impact and tear resistance than butene-based grades because the C₆ branch produces a more homogeneous distribution of tie molecules in the amorphous region. This effect is measured by gel permeation chromatography and differential scanning calorimetry, not by the “LL” label alone.

The target density of 0.918 g/cm³ is achieved by adding sufficient comonomer to reduce crystallinity to approximately 45 to 55 percent. Medium-density polyethylene of similar short-chain branching has higher crystallinity, while high-pressure LDPE of the same density can show lower crystallinity because long-chain branching further restricts crystallisation. The melt flow ratio measured under ASTM D1238-20 at 190 °C using 21.6 kg and 2.16 kg loads is an indirect indicator of molecular weight distribution. For film-grade LLDPE with a nominal MI of 2.0 g/10 min, the I₂₁/I₂ ratio commonly falls between 24 and 30; higher values indicate broader distribution and generally improve bubble stability but can increase extractable content and surface roughness.

There is no ISO standard that assigns the prefix “LL” to a polymer grade; the prefix is commercial shorthand. ASTM D4976-12a classifies polyethylene plastics by density and flow rate rather than by “LL” labels. Consequently, 1002AY and 1002XBU must be interpreted through the supplier’s technical literature, not through a universal code convention.

For a 90 mm single-screw blown-film extruder with a 28:1 L/D screw and a 250 mm die, a 2.0 g/10 min LLDPE typically runs at a barrel profile of 180 °C to 210 °C, with die temperature maintained between 200 °C and 220 °C. Melt pressure at the breaker plate normally falls between 200 bar and 320 bar at an output of 180 kg/h to 220 kg/h. Blow-up ratio is usually held between 2.2:1 and 3.0:1; at ratios below 2.0:1, machine-direction tear strength deteriorates sharply, while ratios above 3.5:1 reduce bubble stability and increase gauge variation.

Processing Window Conflicts on Blown Film Lines

The processing window for LLDPE 1002AY and 1002XBU is bounded at the upper limit by thermal oxidation and gel formation, and at the lower limit by incomplete melting and screw wear. At melt temperatures above 230 °C, antioxidant consumption accelerates and gel particles may appear in the film; below 185 °C, the same melt index class can retain unmelted polymer or produce high screw torque. Internal bubble cooling permits lower frost-line heights and higher output, but excessive cooling can produce condensation on the inner bubble surface and blocking. Frost-line height is normally maintained between 500 mm and 800 mm for 25 µm to 50 µm monolayer film. Die gap selection is coupled to melt index: a 2.0 g/10 min resin generally tolerates a die gap of 1.6 mm to 2.2 mm; a gap below 1.2 mm increases shear rate and melt fracture risk unless molecular-weight distribution is narrow.

Surface additive migration creates a secondary process limit. Slip agents such as erucamide or oleamide reduce film-to-film friction only after migration to the surface. Freshly blown film may exhibit kinetic coefficient of friction above 0.50, while the same roll after 24 h at 23 °C and 50 % relative humidity may fall to 0.10 to 0.25. This time-dependent change must be accounted for in bag-converting operations because static blocking and coefficient of friction vary with storage conditions.

Where 1002XBU is selected instead of 1002AY, the practical distinction is typically in the surface-additive package rather than in the base polymer density or melt index. The suffix “XBU” customarily denotes a slip/antiblock formulation; “AY” may indicate a base stabilised grade. Because additive composition is proprietary, converters should obtain the supplier’s food-contact declaration and migration data rather than infer additive loadings from the suffix. Blocking force under ASTM D3354-18 is time-, temperature-, and winding-tension dependent; published data for 1002XBU film blocking force is product-specific and must not be transferred across line configurations without trial verification.

When Optical Requirements Restrict the Use of Standard Butene LLDPE

If the selected film code is formulated from butene comonomer, optical performance is constrained by the crystalline morphology of the butene-branched polymer. Butene-based LLDPE generally produces higher haze and lower gloss than hexene-based grades at the same density. Haze under ASTM D1003-21 for 25 µm monolayer blown film from a butene-based 0.918 g/cm³, 2.0 g/10 min resin can exceed 8 %, whereas metallocene-catalysed hexene resins in the same density class can approach 4 %. Gloss at 45° under ASTM D2457-19 follows an inverse relationship; values below 65 are common for butene grades, while high-clarity grades can exceed 75. Reducing die gap from 2.0 mm to 1.4 mm and increasing melt temperature to 215 °C can lower haze by 1 to 2 percentage points, but the same adjustment narrows the melt-fracture window.

Film processors seeking clarity below 5 % must either blend LLDPE with high-pressure LDPE or select a metallocene-catalysed hexene/octene grade. The code string 1002AY or 1002XBU does not itself state the comonomer type or catalyst technology; therefore, optical potential cannot be deduced from the designation alone.

Raising frost-line height from 600 mm to 800 mm can increase haze by 1 to 2 percentage points in some butene-based formulations because slower cooling promotes larger spherulite growth. Conversely, use of chilled-air cooling and low drawdown improves clarity but may sacrifice bubble stability at high output. Atomic force microscopy on blown film surfaces shows surface roughness can be 20 nm to 80 nm for butene grades, which is sufficient to scatter visible light and contribute to diffuse transmission. Slip-additive bloom can initially increase surface roughness and haze before the additive layer becomes uniform.

Interpreting Film Tear Data Across Comonomer Lengths

Dart impact under ASTM D1709-22 is a thickness-weighted failure test; for a 25 µm monolayer film produced from a 0.918 g/cm³, 2.0 g/10 min LLDPE, values in the range of 90 g to 150 g are typical. Increasing density to 0.925 g/cm³ lowers dart impact to approximately 60 g to 100 g because higher crystallinity reduces the energy-absorbing amorphous fraction. Elmendorf tear under ASTM D1922-15 is measured in both machine direction and transverse direction. Machine-direction tear is typically lower because processing orients the polymer chains and lamellae along the take-off direction. A transverse-direction to machine-direction tear ratio above 2.0 is common in blown film; a ratio below 1.5 indicates excessive drawdown or low blow-up ratio, which can cause directional weakness in bag drop tests.

The choice between 1002AY and 1002XBU within the same base-resin class does not materially alter tensile yield or elongation unless the additive package introduces nucleating or processing aids. Tensile strength at break under ASTM D882-18 for 0.918 g/cm³ LLDPE typically falls between 40 MPa and 55 MPa in the machine direction and 30 MPa to 42 MPa in the transverse direction; elongation at break exceeds 600 % in both directions for most film grades. The viscosity curve of a 2.0 g/10 min LLDPE measured by capillary rheometry at 190 °C typically shows shear viscosity of 400 Pa·s to 800 Pa·s at 100 s⁻¹ and 120 Pa·s to 200 Pa·s at 1000 s⁻¹; the power-law index from the Carreau-Yasuda fit is normally 0.50 to 0.60. These values explain why die pressure increases less than proportionally with output.

Regulatory compliance for 1002AY and 1002XBU film applications is determined by the finished article and additive package, not solely by the base resin. In the United States, olefin polymers may be used in food-contact articles under FDA 21 CFR 177.1520(c) provided the polymer is manufactured with permitted catalysts and the finished article meets extraction specifications appropriate for the food type and use condition. EU Regulation No 10/2011 establishes an overall migration limit of 10 mg/dm² or 60 mg/kg for food-contact plastics, with lower specific migration limits for any authorised additives. REACH Regulation (EC) No 1907/2006 places the obligation on the manufacturer or importer to register the polymer and confirm no intentionally added substances of very high concern above 0.1 wt %. RoHS Directive 2011/65/EU restricts cadmium, lead, mercury, hexavalent chromium, PBB, and PBDE in electrical and electronic equipment; packaging is outside the direct scope but is frequently tested to the same limits by supply-chain agreements.

Coextrusion layouts use these resins as core or skin layer in heavy-duty sacks, agricultural film, and lamination film. In such structures, the base-resin density and melt index of 1002AY or 1002XBU often determine the rheology match with adjacent layers; a melt index mismatch greater than 1.0 g/10 min between skin and core can create interfacial instability. The final compliance of the laminate is judged on the finished structure, not on the individual pellets. Published data for the exact additive composition and for all end-use performance combinations is limited; converters obtain supplier certificates and run trial runs on the intended line geometry.