Linear low-density polyethylene (LLDPE) remains the dominant resin for machine-grade stretch film because its short-chain branching distribution, created by copolymerizing ethylene with 1-butene, 1-hexene, or 1-octene, provides a practical balance of tear resistance, puncture resistance, elongation, and load retention. Commercial stretch film grades typically exhibit density from 0.918 g/cm³ to 0.922 g/cm³ and melt mass-flow rate from 1.0 g/10 min to 2.5 g/10 min when measured at 190 °C under 2.16 kg load according to ISO 1133-1:2022. PCR Content Targets in Stretch Film: The Compliance Path for LLDPE Converters now places post-consumer recycled resin at the center of film formulation decisions, because non-contact-sensitive packaging is subject to minimum recycled content obligations in the European Union, the United Kingdom, and other jurisdictions. The practical challenge is not the chemical compatibility of PCR LLDPE with virgin LLDPE, but the control of contamination, gel formation, viscosity drift, and mechanical property loss at thin gauges.

For cast stretch film produced at 12–25 µm gauge, film performance is characterized by tensile elongation in the machine direction according to ISO 527-3 or ASTM D882, dart impact resistance according to ASTM D1709, Elmendorf tear resistance according to ISO 6383-2 or ASTM D1922, and cling performance according to ASTM D5458. In virgin LLDPE formulations, these properties are controlled by resin density, comonomer type, and additive package. With PCR addition, measured values can shift non-linearly because the recycled stream is a blend of multiple LLDPE generations, LDPE, metallocene polyethylene, and trace contaminants. The converter therefore needs a compliance path that separates regulatory chain-of-custody evidence from extrusion stability programs.

The regulatory driver for PCR in LLDPE stretch film is strongest in Europe and the United Kingdom. Stretch film is generally classified as transit packaging, which places it in the non-food-contact and non-contact-sensitive category for most extended producer responsibility schemes. Retailers and industrial accounts now require third-party certification from programs such as RecyClass or EuCertPlast that verifies the proportion of post-consumer resin. These schemes require documentation of input mass, output mass, and PCR allocation according to ISO 22095:2020 or EN 15343:2007. On the production floor, the compliance path commonly involves dedicated PCR storage silos, segregated feeding lines, and mass balance records rather than a complete redesign of the cast line.

Does 30 wt% PCR LLDPE Create Melt Pressure and Filtration Instability in High-Speed Cast Stretch Film?

In a typical cast stretch film line, a core extruder melts virgin LLDPE and feeds a flat die through a screen changer. The introduction of 30 wt% PCR LLDPE alters melt pressure stability when the recycled feedstock contains polypropylene labels, ethylene-vinyl acetate copolymers, paper fiber, or polyester fragments. On a 75 mm barrier-screw extruder with an L/D of 30:1 and a continuous screen changer fitted with 100 µm and 60 µm Dutch twill weaves, filter pack life may decrease from a normal 8–12 h for clean virgin LLDPE to 3–5 h for baled PCR stretch film containing label residue and adhesive. Pressure upstream of the filter pack can increase by 15–30% at constant screw speed, requiring a reduction in line speed or an increase in melt temperature. This is a production-scale failure mode rather than a laboratory property issue.

Melt mass-flow rate of PCR LLDPE can be shifted by ±0.3–0.8 g/10 min relative to the nominal virgin resin because of chain scission and crosslinking caused by repeated extrusion history. A broadened molecular weight distribution raises die pressure and reduces the smoothness of the melt curtain. For thin-gauge cast film below 15 µm, the die-zone processing window can narrow to ±5 °C; below that window, unmelts create die lines, and above it, oxidative degradation generates volatiles that form microvoids. The film producer should separate PCR-rich feedstocks from PP-contaminated regrind above 3 wt%, because polypropylene forms immiscible gel particles that are visible in the finished film and reduce tear resistance.

Oxidation induction time is determined by ISO 11357-6. Recycled LLDPE from post-consumer stretch film often shows oxidation induction time at 200 °C below 10 min compared with 20–40 min for virgin LLDPE. Converters respond by adding a phosphite and hindered phenolic stabilizer blend at 500–1,500 ppm into the core layer. Excessive stabilizer loading above 2,500 ppm can cause die lip build-up and surface defects. The stabilizer adjustment is more critical when the PCR supplier cannot provide a batch-specific melt flow curve or oxidation induction time certificate.

Blown film lines running LLDPE stretch grades at lower melt temperatures of 180–220 °C are generally less tolerant of PCR than cast lines because lower melt temperatures do not disperse polymer gels as effectively. In blown film, a higher frost line height and reduced internal bubble pressure may be required when the core layer contains 20 wt% or more PCR. Cast stretch lines, by contrast, operate with higher die temperatures and can tolerate moderate PCR loading in the core if melt filtration and screw design are adequate.

Table 1 summarizes representative property envelopes for 23 µm cast stretch film formulations. The values are drawn from supplier technical datasheets and converter trials; actual results vary with PCR source, layer distribution, and extrusion line configuration.

Because the data show that core-layer PCR incorporation is more resistant to haze and gel defects than full-layer PCR, many converters restrict PCR to the core layer of a three-layer or five-layer cast structure. In a typical A/B/C coextrusion, the core layer represents 60–80% of total thickness and can accept 30 wt% PCR without the same surface roughness penalty observed in full-layer PCR films. The skin layers remain virgin LLDPE plus a low-molecular-weight polyisobutylene or polyolefin tackifier, which preserves cling and surface gloss. This layer configuration is the main production-scale compliance path for LLDPE converters because it permits high recycled content claims by mass balance while maintaining downstream equipment performance.

Capillary rheometry according to ISO 11443 shows that PCR-rich LLDPE typically exhibits higher viscosity at low shear rates near 10 s⁻¹ and lower viscosity at high shear rates near 1,000 s⁻¹ than the virgin base when the recycled feedstock has a broad molecular weight distribution. This shear sensitivity affects die lip velocity and edge bead formation. The same rheological data can be used to set the core extruder profile, because the higher low-shear viscosity can increase melt residence time and accelerate degradation if barrel temperatures are too high.

Tensile Retention and Cling Force Boundaries at 20 wt% and 30 wt% PCR

Tensile retention is the most sensitive mechanical indicator for PCR-loaded stretch film. At 20 wt% core-layer PCR, cast film typically retains 85–95% of the virgin machine-direction elongation at break. At 30 wt% PCR, retention drops to 75–88% depending on gel count, comonomer distribution, and film thickness. Dart impact resistance decreases more steeply when dispersed gel particles exceed 600 µm; the gel acts as a stress concentrator and reduces F50 values by 20–40% relative to the same formulation without gel. Elmendorf tear in the cross direction is particularly sensitive to machine-direction orientation, and converters may compensate by increasing gauge by 1–2 µm or adjusting chill roll cooling rates. Published data for specific closed-loop stretch film PCR grades is limited, so the values above are offered as observed commercial ranges, not universal specifications.

Cling performance is not governed by the recycled content in the core layer because cling is supplied by skin-layer tackifiers. However, oxidized low-molecular-weight species from PCR can migrate into the skin and alter the rate of cling development. Peel cling testing according to ASTM D5458 is recommended after 24 h aging on stainless steel or cardboard, because surface energy changes may not appear immediately at the winder. Converters should also measure unwind force on automatic wrappers, because PCR-induced gel roughness can raise noise at high pre-stretch ratios above 200%.

Incoming PCR bales are characterized for melt mass-flow rate according to ISO 1133-1, density according to ISO 1183-1, and oxidation induction time according to ISO 11357-6. A high oxidation induction time alone does not guarantee good film performance, but a low value is a reliable predictor of odor, color shift, and brittle failure. Ash content and total contamination are also specified by the recycler. For film below 15 µm, total contamination above 0.5 wt% is associated with an increase in web breaks and die line defects.

When the UK Plastic Packaging Tax and EU Packaging and Packaging Waste Regulation Apply to LLDPE Stretch Film

The UK Plastic Packaging Tax creates a direct compliance cost for stretch film with less than 30% recycled content. Converters must keep audited evidence of the recycled proportion, often through a mass balance rule or a controlled blending system. Under EU Regulation (EU) 2025/40, Article 7 sets plastic packaging recycled content targets; for plastic packaging other than contact-sensitive packaging and single-use beverage bottles, the target is 35% by 1 January 2030 and 65% by 1 January 2040. LLDPE stretch film used for pallet wrapping and transit packaging falls within the non-contact-sensitive category when it is not designed to touch food directly. Importers and converters therefore require a documented chain of custody that separates PCR from technical regrind and post-industrial scrap.

Table 2 provides the compliance checklist matrix for a LLDPE converter entering a PCR-containing stretch film product.

On a three-layer cast stretch film line with a 90 mm core extruder and 65 mm skin extruders, the core extruder is typically run at 240–270 °C barrel temperatures and 260–280 °C die temperatures to disperse the higher-viscosity fraction of PCR LLDPE. The chill roll temperature is maintained between 15 °C and 25 °C to control crystallinity and film blocking. When PCR feedstocks contain paper fiber or high surface moisture, vented barrel sections or pre-drying at 60 °C for 2–4 h may be required above 60% RH storage conditions. The use of a gear pump before the screen changer reduces pressure surges caused by changing contamination loading. Trials on these lines show that stable 23 µm film can be produced at 250–500 m/min with 30 wt% PCR in the core layer when melt filtration is maintained below 80 µm and the PCR stream is screened for polypropylene content below 3 wt%.

Operational boundaries include the requirement to avoid mixing PCR-rich feedstock with ethylene-vinyl acetate-rich stretch film waste above 2 wt%, because EVA reduces thermal stability and changes tackifier response. When a PCR supplier cannot provide a batch-specific melt flow curve, the converter should limit the core-layer PCR fraction to 15–20 wt% until extrusion pressure variability is characterized. Published data for this specific equipment configuration is limited, but the described ranges are recurrent in equipment supplier start-up guidance and polymer recycler technical bulletins.