The product category LLDPE Film Grade Granules: High Tensile Strength for Stretch Film denotes a polymer class based on ethylene copolymerized with 1-butene, 1-hexene, or 1-octene in gas-phase, solution, or slurry processes. The granules exhibit a density range from 0.918 to 0.935 g/cm³ when measured according to ASTM D1505 or ISO 1183-1, with melt indices between 0.8 and 2.0 g/10 min at 190 °C/2.16 kg under ISO 1133-1:2022. The linear backbone and randomly distributed short-chain branches reduce crystallinity relative to HDPE while maintaining sufficient tie-chain density for elevated tensile strength in thin-gauge stretch wrap. ASTM D882 tensile testing on 20–25 µm cast film from these granules typically records machine-direction ultimate tensile strength in the 25–45 MPa range, with elongation at break above 350%. These values are not fixed product data; they reflect industry-wide technical datasheet ranges for film-grade LLDPE and vary with comonomer type, molecular weight distribution, and additive loading.

Film-grade LLDPE pellets are distinguishable from injection or rotomoulding grades by their lower gel content and narrower melt-index band. Bulk density measured under ASTM D1895 Method A is typically 0.45–0.55 g/cm³. Pellets are transferred by vacuum loader rather than dense-phase pressure conveying because fracture of the waxy granules during conveying generates fines that accumulate on screening packs and create melt-pressure fluctuations. Production audits on cast film lines have shown that fines content above 200 ppm correlates with increased melt-pressure variation of ±0.5–1.0 MPa and a higher frequency of gauge bands below 12 µm when the extruder is operated above 100 kg/h per die width.

How Does Short-Chain Branch Distribution Control the Stretch-Film Tensile Response?

Short-chain branching frequency and distribution govern crystalline morphology and tie-molecule formation in LLDPE film granules. Octene-based grades with branch lengths of six carbon atoms typically produce more effective tie molecules than butene-based grades because longer branches disrupt lamellar organization while maintaining high molecular weight sections between crystalline lamellae. The result is higher machine-direction tensile strength and greater resistance to dart impact at equivalent density. Gel permeation chromatography data from commercial film resins show polydispersity indices between 3.0 and 4.5 for blown film grades; broader distributions enhance shear thinning but can reduce ultimate tensile properties if excessive low-molecular-weight tails are present. Under ASTM D882, tensile strength at break is measured on 25 mm wide film strips with a gauge length of 50 mm and a crosshead speed of 500 mm/min; reported values for LLDPE stretch film typically range from 25 to 45 MPa in the machine direction and 20 to 35 MPa in the transverse direction. High tensile strength is not solely a function of comonomer; the granule must retain a low gel level and a consistent melt index to avoid draw resonance on cast film lines.

On cast stretch-film lines, LLDPE granules are extruded through a flat die with die gaps of 0.5–0.8 mm onto a chill roll held at 15–30 °C. The melt temperature at the die exit is typically maintained between 240 °C and 280 °C to ensure homogeneous melt quality while avoiding thermo-oxidative degradation. Twin-screw compounding is not required for film-grade LLDPE because the resin is pelletized with additives during finishing; a single-screw extruder with 30:1 L/D and a barrier screw provides sufficient melting and melt-temperature uniformity at outputs up to 1,500 kg/h on wide cast lines. Melt pressure before the screen pack should remain below 35 MPa; sustained pressure above this threshold indicates poor melt homogeneity or contamination and can lead to gel streaks in machine-direction stretch film. Air-knife quenching and vacuum box edge pinning are used to stabilize the web at line speeds exceeding 250 m/min. The granules must be free-flowing and contain an antiblock masterbatch; otherwise surface blocking on the secondary chill roll causes web breaks that are detected as thickness deviation beyond ±1.0% using a capacitance gauge.

When Blown Film Lines Require Higher Melt Strength and Bubble Stability

In blown film extrusion, LLDPE film grade granules with melt index below 1.2 g/10 min are preferred to maintain bubble stability at blow-up ratios between 2.0:1 and 3.0:1. The frost line height is typically set at 6–10 times the die diameter for LLDPE, but the exact position depends on cooling air temperature and internal bubble pressure. Equipment data from monolayer blown lines show that die gaps for LLDPE must be wider than for LDPE because the higher shear viscosity of LLDPE increases die lip pressure and can induce melt fracture at narrow gaps below 1.0 mm. Stable operation is achieved with die gaps of 1.2–2.5 mm and a melt temperature of 170–210 °C. High tensile strength in the bubble is developed through a combination of draw-down ratio and stalk cooling; low-stalk or pocket cooling configurations are generally unsuitable for high-molecular-weight LLDPE because they reduce melt orientation and yield lower machine-direction tensile strength. The granules should be evaluated for melt extensibility using a capillary rheometer at an apparent shear rate of 100 s⁻¹ and 190 °C; melt strength values for film-grade LLDPE are lower than for LDPE, which imposes process limits on maximum bubble diameter and gauge uniformity.

Representative film-grade LLDPE property ranges from public technical datasheets

Property	Test method	Typical range	Process relevance
Melt index	ISO 1133-1:2022, 190 °C/2.16 kg	0.8–2.0 g/10 min	Controls extruder backpressure and orientation
Density	ASTM D1505 /ISO 1183-1	0.918–0.935 g/cm³	Sets modulus and puncture resistance
Tensile strength at break, MD	ASTM D882, 20–25 µm film	25–45 MPa	Direct stretch-film load-bearing requirement
Elongation at break, MD	ASTM D882	350–650%	Pre-stretch capacity on wrapper
Elmendorf tear, MD	ASTM D1922	2–8 N	Puncture propagation resistance
Dart impact, F50, 25 µm	ASTM D1709, Method A	80–250 g	Impact toughness of thin film
Haze	ASTM D1003	2–15%	Optical clarity requirement

Additive Systems, Surface Cling, and Unwinding Force Management

Film-grade LLDPE granules are frequently formulated with erucamide slip, synthetic silica antiblock, and polyisobutylene or ultra-low-density ethylene copolymers as cling additives. The amount of slip additive is typically kept below 500 ppm in cast stretch film to avoid loss of cling; antiblock loadings between 1,000 and 3,000 ppm are common for films below 20 µm gauge. Surface cling force is measured by ASTM D5458; machine-grade stretch films generally require peel cling values between 50 and 200 g, depending on wrapper type and load stability. Protrusion puncture resistance tested under ASTM D5748 should be specified for hand wrap and pre-stretch films, with typical values at 23 °C above 1.0 kg for 20 µm film. Excessive cling additive above 2 wt% can plasticize the LLDPE matrix, reduce tensile strength, and transfer residue to stainless steel rollers on automatic wrappers. The granule form must be dry-blended or compounded so that additive distribution variance across production lots remains below ±10%; otherwise cling levels drift and cause unwinding force fluctuations during high-speed wrapping.

A production-scale failure mode associated with low-melt-index LLDPE film granules is neckdown during high-ratio pre-stretch on powered roller stretch wrappers. Neckdown is the transverse width reduction of the film when elongated between pre-stretch rollers set to elongation ratios from 150% to 300%. Compounds with narrow molecular weight distribution and low branching show less neckdown but may sacrifice puncture resistance. The gradient of tensile modulus with elongation is assessed by secant modulus at 100% elongation according to ASTM D882; film-grade LLDPE typically exhibits secant modulus values of 80–150 MPa at 100% elongation. On a high-speed turntable wrapper operating at 30–40 wraps/min, film with neckdown exceeding 10% loses edge coverage on pallets and increases risk of load failure during transit. Published data for this specific configuration is limited; however, the relationship between pre-stretch ratio, residual stretch retention, and holding force is routinely monitored on production lines using load-cell feedback systems calibrated to ±5%.

Compliance Documentation Requires Migration Testing and SVHC Declarations

Food-contact stretch wrap produced from LLDPE film grade granules is evaluated under FDA 21 CFR 177.1520 for olefin polymers and, in the European Union, under Commission Regulation (EU) No 10/2011. The granule supplier must provide documentation that overall migration into food simulants does not exceed 10 mg/dm² and that specific migration of comonomer residues remains below the limits for 1-butene, 1-hexene, and 1-octene. Industrial films must comply with REACH Regulation (EC) No 1907/2006; restricted substances under REACH Annex XVII must not be present above the stated concentration limits. RoHS Directive 2011/65/EU applies when stretch film is used as packaging for electrical and electronic equipment; lead, cadmium, mercury, hexavalent chromium, PBB, and PBDE are limited to 1,000 mg/kg for lead and 100 mg/kg for cadmium at the homogeneous material level. Heavy metals in pigments or processing aids used in pellet coating should be absent or below REACH candidate list thresholds of 0.1% w/w.

Regulatory and standard references for LLDPE film grade granules

Requirement	Standard or regulation	Numerical limit or test condition
US food-contact olefin polymer	FDA 21 CFR 177.1520	Extractables limits per paragraph
EU food-contact plastics	Commission Regulation (EU) No 10/2011	Overall migration 10 mg/dm²
REACH SVHC declaration	(EC) No 1907/2006	0.1% w/w per article
RoHS restricted substances	Directive 2011/65/EU	Pb 1000 mg/kg, Cd 100 mg/kg
Melt mass-flow rate	ISO 1133-1:2022	190 °C/2.16 kg
Tensile properties of film	ASTM D882 /ISO 527-3	25–45 MPa MD range for typical LLDPE stretch film

In warehouse processing trials, LLDPE film grade granules stored at ambient temperatures above 35 °C for periods longer than 6 months have shown increased gel flecks in cast stretch film. Pre-drying is not normally required for LLDPE because moisture absorption is below 0.01% at 23 °C and 50% RH; however, condensation on pellet surfaces at relative humidity above 80% should be removed with a dry-air hopper at 60 °C for 2 h before extrusion. The failure mechanism under high storage temperature is oxidative degradation at unsaturated sites and additive migration, which can generate gel particles that block screen packs and produce film breaks at gauge bands below 15 µm. Extruders fitted with 80–100 mesh screen packs exhibit rapid pressure buildup when gel counts exceed 5 particles/m²; film producers monitor pressure differential across the screen pack and replace filters when differential pressure rises above 10–15 MPa. Storage of regrind beyond 12 months under ambient warehouse conditions has been associated with increased gel counts and erratic cling performance; film-grade LLDPE granules should be consumed within 9–12 months of packaging date unless inert-gas storage is used. Avoid blending with oxidized PE recyclate above 20 wt% because oxidized species accelerate chain scission and reduce machine-direction tensile strength under ASTM D882. Avoid combination with copper-based thermal stabilizers in downstream recycling streams, because copper ions catalyze oxidative degradation and lower elongation at break.