COSMOPLENE PP Terpolymer FS6612L is a propylene-ethylene-butene-1 terpolymer specifically engineered for use as a heat-seal layer in coextruded cast and biaxially oriented polypropylene (BOPP) film structures. The melt mass-flow rate, measured at 230 °C under 2.16 kg load per ISO 1133-1:2022, falls within a nominal range of 5.5–7.5 g/10 min, a window established through production-scale trials on single-screw extruders with a 30:1 L/D ratio and barrier screw profiles. Density at 23 °C is 0.895–0.905 g/cm³ (ISO 1183-1:2019). The comonomer distribution—specifically the incorporation of butene-1 into the propylene backbone alongside ethylene—depresses the melting peak temperature to approximately 126–132 °C when recorded via differential scanning calorimetry at a scan rate of 10 °C/min (ISO 11357-3:2018), a reduction of roughly 15–20 °C relative to a standard propylene-ethylene random copolymer of comparable ethylene content. This thermal shift forms the basis for the material’s differential positioning in film-converting operations.
Sealing Initiation Temperature and the Onset of Hermetic Closure
The most operationally significant consequence of the terpolymerization chemistry is a sealing initiation temperature (SIT) that consistently ranges between 98 °C and 105 °C as determined by laboratory heat-seal tests conforming to ASTM F88/F88M-21 with a dwell time of 0.5 s and a jaw pressure of 0.275 MPa. This SIT band is typically 12–17 °C lower than that of propylene-ethylene random copolymers containing 3–4 wt% ethylene comonomer. On horizontal form-fill-seal (HFFS) packaging lines running at linear speeds above 60 m/min, the extended thermal window between SIT and the onset of film distortion permits a 8–12 °C increase in seal-bar temperature setpoint without inducing wrinkle defects or burn-through. A critical threshold observed in high-speed vertical form-fill-seal (VFFS) equipment is that when dwell time falls below 0.3 s, the seal strength of FS6612L still exceeds 400 g/25 mm at 105 °C, whereas random copolymer comparators require temperatures exceeding 118 °C to achieve equivalent hot-tack performance. This behavior is linked to the broadening of the melting endotherm caused by the ternary monomer sequence distribution, a phenomenon documented in temperature-rising elution fractionation profiles that show a significant mass fraction eluting below 90 °C.
During extrusion lamination onto aluminum foil and paperboard substrates, the reduced seal-initiation temperature presents both an advantage and a processing conflict. On one hand, the lower required seal-bar energy input reduces thermal cycling of the substrate, limiting paper fiber dehydration and curl. On the other hand, if the extruder barrel temperature profile is not optimized—particularly in the feed zone—the low melting point of the terpolymer phase increases the risk of pellet bridging in the hopper throat when ambient plant temperatures exceed 32 °C. Operators on cast-film lines have observed batch-to-batch variance in screw feeding stability that correlates with storage conditions; pre-conditioning of resin in a climate-controlled silo at ≤ 25 °C and ≤ 50 % relative humidity is recommended, though published data for this specific configuration is limited. The necessity for hopper cooling may be eliminated when lines are equipped with grooved-feed extruders with water-cooled throat sections.
What Differentiates FS6612L from Standard Propylene-Ethylene Random Copolymers?
The structural divergence arises from the incorporation of butene-1 as a third monomer species during gas-phase or bulk polymerization, a process route that modifies the crystallizable sequence length of propylene more effectively than ethylene alone. A direct comparison of physical properties between FS6612L and a representative propylene-ethylene random copolymer (MFR 7.0 g/10 min) can be tabulated, drawing on data generated via standard test protocols.
| Property | Test Method | COSMOPLENE FS6612L | Propylene-Ethylene RACO (Reference) |
|---|---|---|---|
| Melt mass-flow rate (230 °C/2.16 kg) | ISO 1133-1:2022 | 5.5–7.5 g/10 min | 6.0–8.0 g/10 min |
| Melting temperature (peak) | ISO 11357-3:2018 | 127–131 °C | 143–148 °C |
| Seal initiation temperature (0.5 s, 0.275 MPa) | ASTM F88/F88M-21 | 98–105 °C | 113–122 °C |
| Haze (1 mm plaque) | ASTM D1003-21 | 2.0–3.5 % | 3.5–6.0 % |
| Flexural modulus (1% secant) | ISO 178:2019 | 650–800 MPa | 850–1050 MPa |
| Hot-tack strength at 110 °C | ASTM F1921-20 | 250–350 g/25 mm | 80–150 g/25 mm |
Beyond these aggregate differences, the rheological fingerprint of FS6612L under processing-relevant shear rates reveals a lower onset of shear thinning in capillary rheometry at 230 °C. The apparent viscosity at a shear rate of 1000 s⁻¹ measures approximately 65–75 Pa·s, which is 15–20 % below that of the random copolymer reference. This viscosity depression assists in wet-out on chill rolls during cast-film quenching but can contribute to die-lip build-up if the die gap is set below 0.5 mm and melt temperature exceeds 260 °C. In such instances, the measured die-lip deposit formation rate on a 2.4 m wide cast-film line was observed to be 1.7–2.3 g/h at 270 °C melt temperature, an increase over the 0.8–1.2 g/h typical of a random copolymer film grade. The comparative data point toward a processing window bounded at the upper end by 260 °C for continuous operation exceeding 72 h without die cleaning.
Optical Clarity and Organoleptic Compliance in Food Contact Layers
The combination of reduced crystallite size—induced by the heterogeneous comonomer incorporation—and the absence of high-activity Ziegler-Natta catalyst residues at levels above 15 ppm titanium results in haze values below 3.5 % on 50 µm cast films. Gloss, measured at a 60° angle per ISO 2813:2014, exceeds 90 GU. These optical benchmarks are maintained after corona treatment to a surface energy of 38–42 mN/m, provided the treatment is applied within 24 h of extrusion to prevent post-treatment decay that can degrade wetting properties and compromise lamination bond strength. Migration testing under EU Regulation 10/2011 (simulant D1, 40 °C, 10 days) yields overall migration values below 5 mg/dm², positioning FS6612L for direct food contact in multilayer laminates where the seal layer is not in direct contact with fatty foodstuffs. The specific compliance matrix references the positive list under Regulation (EU) No. 10/2011 Annex I and the associated migration modeling performed at a food-contact surface-to-volume ratio of 1 dm²/kg for aqueous and acidic simulants. For fatty food applications above 60 °C, a functional barrier layer of at least 10 µm of homopolymer PP must separate FS6612L from the food side, in line with FDA 21 CFR 176.170(c) conditions of use B through H.
A limitation that emerges from the terpolymer architecture is its incompatibility with certain slip- and anti-block-additive masterbatches based on primary amide waxes (erucamide/oleamide) when added at let-down ratios exceeding 2 %. At concentrations above this threshold, the relatively lower melting point and broader melting range of the terpolymer matrix enable migration kinetics that can cause surface bloom saturation within 72 h of film winding, leading to a progressive drop in coefficient of friction from an initial 0.25–0.30 to a terminal value below 0.15. This ultra-low COF, while beneficial for certain horizontal form-fill-seal applications, compromises film stacking stability and ream integrity in high-speed converting. Pre-compounded masterbatch concentrates with a PP carrier and controlled particle-size distribution of synthetic silica (D50 ≤ 5 µm) are the preferred anti-block system.
When Corona Discharge Energy Density Exceeds 15 W·min/m²—Surface Functionalization and Film Handling
Surface treatment for adhesion promotion reveals a secondary interaction with the butene-1 component. X-ray photoelectron spectroscopy (XPS) data on films treated at discharge energy densities between 10 and 25 W·min/m² indicate a peak oxygen incorporation of 8–12 at%, saturated at the higher energy level. However, when the treatment intensity exceeds 15 W·min/m², the terpolymer surface exhibits increased low-molecular-weight oxidized material migration, detectable via atomic force microscopy as a shift in surface roughness from a baseline Ra 12 nm to Ra 28–35 nm within 48 h of treatment. This roughness increase correlates with a loss in clarity and a measurable decline in peel-strength values when laminated with solvent-based polyurethane adhesives. Lamination lines operating with inline corona treaters are advised to set power density at 10–15 W·min/m² and to process the treated film within the subsequent 8 h shift, unless a nitrogen-purging system is employed to minimize post-treatment oxidation. The film’s modulus, being 15–25 % lower than that of random copolymer films, also necessitates adjustment of tension control parameters during secondary processing (e.g., slitting, printing). Unwind tension on a central-impression flexographic press is typically set to 0.05–0.08 N/mm² of web cross-section, a reduction from the 0.10–0.12 N/mm² used for RACO films, to prevent elongation set and register errors exceeding 0.2 mm.
In BOPP tenter-frame processes, FS6612L is employed as a coextruded skin on a homopolymer core. The stretch ratios applied in machine and transverse directions—typically 4.5–5.0 MD and 8.0–9.0 TD—interact with the low melting point of the terpolymer to depress the effective stretching temperature to 148–152 °C, compared to 155–160 °C for RACO skins. The lower process temperature diminishes the risk of core layer cavitation when using calcium carbonate-filled cores, but necessitates tighter control of the transverse stretching profile to avoid thickness variation exceeding ±5 % in the seal layer. Gauging data from a 8.4 m wide BOPP production line producing a 20 µm film with a 1.5 µm FS6612L skin layer show that deviation bands tend to widen outside ±4% when the tenter oven zone-2 setpoint deviates by ±3 °C. This sensitivity is a direct consequence of the broad melting range, which, while beneficial for sealing, reduces the crispness of the solid–liquid transition during orientation. The operational solution is not resin-side modification but a tighter temperature control algorithm implemented on the tenter’s PLC, with PID loop tuning that reduces integral action time in zones 2 and 3.
In extrusion coating applications onto paper and aluminium foil at line speeds from 150 to 300 m/min, the melt curtain stability of FS6612L is influenced by the narrow molecular-weight distribution characteristic of the grade. The polydispersity index (Mw/Mn) is typically 3.0–3.5 as determined by gel permeation chromatography relative to polystyrene standards. This relatively narrow distribution, while promoting low volatiles and a clean draw-down, can reduce the draw resonance threshold when the die-to-chill-roll gap exceeds 200 mm. Coating trials on a pilot line with a 600 mm variable-gap die indicate that at a line speed of 250 m/min and a gap of 250 mm, periodic thickness variation of 8–12 % amplitude appears, synchronized with the web’s natural frequency. Reducing the gap to 150 mm eliminates the resonance. This places an equipment-specific constraint on older coating lines with fixed-geometry die supports, a limitation documented in site acceptance test reports for multiple high-speed laminators. No chemical reformulation is required; the constraint is purely configurational.
The terpolymer’s low stiffness relative to random copolymer also finds utility in reduction of noise and boardiness in multilayer flexible packaging for powdered goods where the package must conform to irregular contents without stress-whitening. The resistance to stress-whitening is quantified by a Gardner impact test (ASTM D5420-21) in which a 50 µm cast film formed from FS6612L shows no visible whitening at impact energies up to 1.5 J, whereas an equivalent RACO film demonstrates haze increases of 4–7 % at 1.0 J. This characteristic is traced back to the lower crystallinity (28–33 % by DSC enthalpy relative to a fully crystalline PP reference of 207 J/g) and the consequent reduced volume of cavitation-prone spherulitic boundaries.
Regulatory and End-of-Life Boundaries
FS6612L does not contain phthalate-based catalysts or additives; the catalyst system is a fourth-generation Ziegler-Natta type supported on magnesium chloride, with a triethylaluminum co-catalyst and a silane-based external donor. Residual aluminum content in the final pellet is below 50 ppm, and residual titanium is below 2 ppm, both measured by inductively coupled plasma optical emission spectrometry. Total volatiles, as per the headspace gas chromatography method at 180 °C, remain below 120 µg/g. The grade complies with the heavy-metal limits specified in EU Directive 94/62/EC (packaging and packaging waste) and the concentration limits for cadmium, hexavalent chromium, lead, and mercury defined in EN 13432:2000 Annex A. For mechanical recycling streams, FS6612L is compatible with mixed polyolefin reprocessing at recycled content incorporation up to 15 wt% in non-food high-clarity film applications, where the terpolymer acts as a minor component that marginally lowers the crystalline melt point of the reclaimed blend. Reprocessability trials on a twin-screw extruder (25 mm diameter, 40:1 L/D) with three reprocessing loops show an MFR shift from 6.2 to 8.5 g/10 min, attributable to chain scission, a magnitude of drift that remains within the usable range for many non-critical blown-film processes.
In controlled lamination structures intended for retort applications, FS6612L is not recommended as the sole sealing layer. Exposure to steam sterilization conditions at 121 °C for 30 min causes partial melting of the terpolymer skin and can result in blocking of sealed pouches and delamination forces reaching below 2 N/15 mm. Where retortability is required, a sealing layer of cast polypropylene random copolymer with a melting point above 140 °C should be placed between the terpolymer and the product contact side, or the terpolymer layer must be located as a buried tie layer rather than the primary sealant. This limitation is intrinsic to the low melting temperature that otherwise defines the product’s value proposition in ambient and chilled packaging.
