Linear low-density polyethylene SK LLDPE FU149M is a pelletized film-extrusion resin supplied for blown-film processing. The grade’s nominal melt flow rate is 1.0 g/10 min measured at 190°C under a 2.16 kg load in accordance with ISO 1133-1, and its nominal density is 0.918 g/cm³ determined under ISO 1183-1. The base polymer is a 1-butene-based LLDPE; its short-chain branches are predominantly ethyl branches distributed along the polyethylene backbone. This structural feature separates the grade from hexene-based and octene-based LLDPE resins in terms of tie-molecule formation, low-gauge film toughness, seal performance, and processing behavior. The product is intended for general-purpose packaging, agricultural film, and industrial liner structures where a balance of processability, seal initiation, and controlled optical properties is required. It is not formulated for injection moulding or rotomoulding.

Within the producer’s film-extrusion grade portfolio, FU149M occupies the medium-viscosity 1.0-g/10 min range. The generic polyethylene CAS registry number is 9002-88-4. Because film performance is inseparable from line configuration, die geometry, and cooling conditions, direct substitution into an existing package should be revalidated on the target blown-film line rather than assumed from resin data alone. Published data for comparative performance of this specific grade against metallocene or higher alpha-olefin resins is limited; end users should generate film samples on the actual production line and test the relevant packaging failure modes before changing the resin specification.

When Blown Film Lines Are Operated Below 25 µm Die Gap

Processing on a 55 mm single-screw extruder with a 28:1 L/D barrier screw generally uses barrel zone set points of 170°C to 190°C and adapter/die zones of 185°C to 205°C. A stable bubble is typically held at a blow-up ratio of 2.0:1 to 2.5:1, with the frost-line height maintained at 3 to 6 die diameters. Reducing the die gap below 1.2 mm for film gauges below 25 µm increases shear rate and die pressure. On fixed-geometry spiral mandrel dies of 150 mm diameter, melt pressures below 200 bar can produce non-uniform gauge because the spiral channels are not fully filled. Melt temperatures below 170°C may limit homogenization of slip and antiblock additives, while temperatures above 220°C increase oxidative chain scission and gel formation. These boundaries define the practical operating window and are more restrictive than for some higher-melt-strength hexene-based LLDPE resins.

The downgauging limit is not solely rheological. At film thickness below 20 µm, butene-based LLDPE frequently loses dart impact and Elmendorf tear more rapidly than hexene-based or octene-based LLDPE because the shorter ethyl branch is less effective at generating interlamellar tie molecules. Processors should establish the low-gauge limit for the specific die and bubble configuration using film samples tested under ISO 7765-1 and ASTM D1922. A gauge coefficient of variation above ±4% across the layflat can introduce misleading dart impact and tear results; therefore capacitance or beta gauge verification should precede mechanical testing. Specimens should be conditioned for at least 40 h at 23°C and 50% relative humidity according to ISO 291 before testing.

Capillary rheometry under ISO 11443 is used to assess lot-to-lot shear viscosity. The specific shear viscosity curve is not a fixed resin property because it shifts with additive package, lot history, and measurement temperature. For extrusion-scale evaluation, shear viscosity at 100 s⁻¹ and 1000 s⁻¹ is typically monitored to predict die pressure and screw torque. However, the producer’s certificate of analysis generally provides only melt flow rate and density; additional rheological data must be generated by the converter or requested from the supplier.

What Distinguishes Butene-Based Short-Chain Branching from Hexene or Octene LLDPE?

In LLDPE, comonomer type controls the length of the short-chain branch attached to the ethylene backbone. 1-Butene introduces a branch of 2 carbons, 1-hexene introduces 4 carbons, and 1-octene introduces 6 carbons. Longer branches are more effective at connecting adjacent crystallites through tie molecules at equal density and branch content. For FU149M, the shorter butene branch therefore provides lower low-gauge toughness than hexene-based or octene-based grades, but it often offers a wider stable bubble and lower extruder torque on lines with limited back-pressure capability. This is a structural trade-off rather than an additive effect.

Tensile, tear, and optical properties are not fixed resin attributes; they depend on gauge, die gap, blow-up ratio, melt temperature, and additive package. Therefore, film properties must be generated on the target blown-film equipment. Cast film testing cannot replicate the biaxial orientation and cooling history of a blown-film bubble, and the resulting data may overestimate or underestimate performance. When comparing FU149M with a hexene or metallocene grade, the test specimens should be produced at the same blow-up ratio and die gap, and conditioned under the same environment before testing.

Because density is 0.918 g/cm³, the resin provides lower modulus and lower tensile yield strength than LLDPE film grades with densities of 0.925 g/cm³ or higher. This can be useful in liners and overwrap where flexibility and puncture tolerance are more important than stiffness. The melt flow rate of 1.0 g/10 min places the grade in the medium-viscosity film-extrusion range; lower-MFR grades are often selected when higher melt strength is needed for large-bubble stability, while higher-MFR grades are selected for low-energy extrusion or coating. These differences are not absolute and should be confirmed by side-by-side extrusion trials.

Seal initiation and hot-tack behavior differ from metallocene-catalysed LLDPE. Metallocene grades typically show lower seal initiation temperature and a wider hot-tack window at the same density. FU149M is therefore less likely to be suitable for high-speed horizontal form-fill-seal packaging machines that require a hot-tack window below 110°C. Hot-tack performance should be verified according to ASTM F1921, and heat-seal strength according to ASTM F88, on the actual package substrate and at production sealing pressures.

Extrusion Purging, Additive Compatibility, and Melt Temperature Boundaries

FU149M does not require predrying under normal storage conditions because the base polyethylene is non-hygroscopic. If a hygroscopic filler masterbatch or recycled fraction is introduced, the mixture should be dried to a moisture content below 0.05% to prevent steam streaks and bubble defects. Purging should use a low-viscosity polyethylene or commercial purging compound with a melt flow rate of 2 to 5 g/10 min; these products displace high-viscosity residues more efficiently than the product itself. The purge temperature should remain below 220°C to avoid carbon formation on the die lip.

The resin is not compatible with strong oxidizers or high peroxide levels. Melt blending with peroxides can induce radical crosslinking or chain scission and create unacceptable gel formation. Environmental stress-cracking resistance should be evaluated under ISO 22088-2 when the package is intended for contact with surfactants, polar liquids, or industrial chemicals. The grade is also not designed for continuous service above 60°C under load unless the specific application is validated by creep or ESCR testing.

Avoid combining FU149M with high levels of regrind containing unknown processing aids, release agents, or printing inks. Such diluents can alter coefficient of friction, seal strength, and additive migration behavior in ways that are not visible until the package reaches the filling line. Where post-consumer recyclate is used, the blend should be tested for gel level, film appearance, tear propagation, and seal response before production release. The additive package of the base grade may also contain slip and antiblock agents; these levels are formulation-dependent and should be confirmed from the lot-specific certificate of analysis because they influence the seal curve and hot-tack window.

For storage, the resin should be kept in closed, dry silos or sealed containers away from direct sunlight and sources of heat. Exposure to ultraviolet radiation can induce photo-oxidation over extended storage periods, altering melt flow rate and color. Inventory rotation of 6 months to 12 months is commonly applied for film-grade polyethylene under ambient conditions, but the producer’s storage recommendation should be followed. If the resin has been stored in high-humidity conditions, condensation should be removed by drying the pellets with warm air before extrusion, although the primary polymer is not hygroscopic.

Regulatory Status Is Governed by Food-Contact and Packaging Test Frameworks

Polyethylene copolymers of the olefin class may be evaluated for food-contact use under FDA 21 CFR 177.1520, subject to end-use temperature and food-type limitations. In the European system, the governing framework is Commission Regulation (EU) No 10/2011, which sets an overall migration limit of 10 mg/dm² of food contact surface and includes specific migration limits for additives and monomers. Compliance cannot be established by resin certification alone; the finished package must be tested under the intended food simulant, contact time, and temperature conditions.

For packaging strength, seal initiation and seal strength are commonly measured with ASTM F88 on 25 µm to 50 µm films sealed at jaw temperatures from 110°C to 130°C and a dwell time of 0.5 s at 2 bar jaw pressure. The presence of slip and antiblock additives influences the seal curve and hot-tack window; these additive levels are part of the producer’s formulation and should be confirmed from the lot-specific certificate of analysis. The film’s optical haze is typically measured under ASTM D1003, while dart impact is measured under ISO 7765-1 or ASTM D1709. The dart impact test method is sensitive to dart diameter, drop height, and specimen clamping; method A uses a 38 mm dart and method B uses a 51 mm dart. Comparisons across film structures are valid only when the same method and film gauge are used.

In a frozen food packaging application using 25 µm blown film, the product is typically evaluated by measuring dart impact, tear propagation under ASTM D1922, and optical haze under ASTM D1003. The film’s performance is highly sensitive to die gap and frost-line height; a film produced at a 0.8 mm die gap may show lower dart impact than one produced at 1.5 mm even when the final gauge is identical. This dependence must be controlled during scale-up. For heavy-duty sack liners, FU149M is sometimes blended with 10% to 20% low-density polyethylene to improve bubble stability and reduce dart impact variability. The blend’s overall density and melt flow rate should be verified as a mixture because the secondary resin changes the comonomer balance and seal response.

In coextruded agricultural film, FU149M is often used as a core or skin layer and combined with a UV-stabilized outer layer. The butene-based core contributes processability and transverse-direction tear resistance, while longitudinal tear may remain lower than in hexene-based structures. The final film should be tested after weathering under the intended field exposure, because UV stabilization resides primarily in the additive package rather than in the base polyethylene. If the film is intended for silage wrap or greenhouse film, adhesion, blocking resistance, and retained tear strength after 1000 hours of accelerated weathering under ISO 4892-2 should be evaluated before commercial approval.

Substitution of FU149M into a plant that previously ran a hexene-based LLDPE should include a two-stage validation: first, a short extrusion trial to define melt pressure and bubble stability; second, a full-scale packaging trial with seal testing at the filling line. This sequence is necessary because resin data sheets do not capture the interaction between butene-based short-chain branching and the existing die geometry, air ring, and downstream haul-off. Lot-to-lot variation in additive addition and pellet morphology can also influence conveying, feeding, and film appearance; these variables are minimized by routine incoming inspection of melt flow rate, density, and visual pellet cleanliness.