Recycled LLDPE (rLLDPE): what post-industrial and post-consumer streams deliver is a short-chain-branched polyolefin feedstock whose converting behavior is controlled less by base resin selection than by thermal history, contamination profile, and melt-filtration burden. Post-industrial rLLDPE originates from pre-consumer edge trim, slit-roll waste, transition film, start-up lumps, purgings, and off-spec rolls generated during polymerization finishing, film conversion, or sheet extrusion. Post-consumer rLLDPE is recovered after service from stretch wrap, collation shrink film, agricultural silage film, pallet hoods, logistics mailers, and thin packaging. Under ISO 14021:2016, the point of discard defines the stream category: post-industrial material has not reached the final user, whereas post-consumer material has completed its intended application. The distinction is operationally critical because post-consumer film introduces adhesives, paper labels, soil, silage liquor, oxygenated plant debris, inorganic fillers, and mixed polyolefin fractions that alter melt-flow-rate stability and pellet quality. No single commercial specification covers all rLLDPE grades; each lot must be qualified against the intended converting process and final article requirements.

What Distinguishes Post-Industrial rLLDPE from Post-Consumer rLLDPE at the Molecular and Contaminant Level?

Post-industrial rLLDPE from edge trim and slit-roll waste normally retains a thermal history limited to one or two processing operations. The molecular weight distribution remains close to the original LLDPE, and the carbonyl concentration is typically low because exposure to ultraviolet radiation, oxygen, and agricultural chemicals has not occurred at the same intensity as in post-consumer film. Post-consumer rLLDPE from silage wrap and stretch film carries a more complex contaminant load. Silage film may contain soil particles, silage liquor residues, oxygenated harvest debris, and calcium carbonate filler from white or tinted films. Stretch wrap may contain polyisobutylene-based cling additives, low-molecular-weight tackifiers, and label adhesive fragments. These components modify the measured melt flow rate because low-viscosity fractions plasticize the melt, while fillers and fibrous debris raise density and increase filtration pressure. Published data for specific mixed post-consumer feedstock compositions is limited because regional collection systems vary widely; however, the ranges in the table below summarize typical pelletized rLLDPE received at converting plants after melt filtration and blending with virgin LLDPE.

Because post-industrial rLLDPE is frequently generated from known grades, its density and melt flow rate are more stable across lots. Post-consumer rLLDPE exhibits batch-to-batch variation of ±0.3 g/10 min within a single lot and up to 0.8 g/10 min across lots when collection streams shift seasonally. The presence of oxidized post-consumer film also reduces environmental stress-cracking resistance. In notched constant-strain testing conducted according to ASTM D1693-15, post-consumer rLLDPE with elevated gel content can exhibit failure times 20–50% shorter than virgin LLDPE at equivalent density, depending on gel distribution and comonomer type.

Filtration requirements for rLLDPE are determined by the particle size that a downstream process can tolerate without bubble instability, surface defects, or die-lip build-up. For cast film and sheet, hard particles of 50–100 µm are often visible as pits or specks. For blown film below 30 µm, melt filtration of 60–120 µm is commonly specified. Heavy-duty sacks and agricultural films above 70 µm may tolerate filtration of 150–250 µm, but large particles still create local stress concentrations at the haul-off nip. Continuous screen changers are specified for post-consumer rLLDPE because screen blockage from soil and fibre is non-linear; a pressure rise from 40 bar to 90 bar across a 120 µm screen at 220 °C indicates that screen replacement is required.

When Post-Consumer rLLDPE Is Incorporated into Blown Film Lines Above 20 Weight Percent

Because post-consumer rLLDPE from stretch wrap often contains polyisobutylene-based cling additives and low-molecular-weight tackifiers, its melt phase can exhibit lower extensional viscosity than virgin LLDPE at equivalent density. At addition levels above 20 wt%, bubble stability may decline on high-stalk blown film lines, particularly when the die gap is below 1.6 mm and the blow-up ratio exceeds 2.8:1. The addition of 5–15 wt% LDPE or the use of a grooved-feed extruder with barrel cooling in the feed zone can restore melt extensibility. For thin-gauge film below 20 µm, converter trials should begin with post-consumer rLLDPE addition at 10–20 wt% and increase only after the gel count and bubble stability are confirmed on the production line. Published data for this specific configuration is limited because bubble stability is highly dependent on die geometry, frost-line height, and air-ring design. In pilot-line evaluations on a 45 mm blown film line with a 2.0 mm die gap, tensile strength at break in the machine direction measured by ASTM D638-14 decreased from approximately 35 MPa to 28 MPa when 30 wt% post-consumer rLLDPE was incorporated, while transverse elongation at break decreased from 650% to 450%. Dart impact resistance measured by ASTM D1709-16a is commonly reduced by 10–30% at 30 wt% post-consumer content because gels and unmelts initiate puncture.

Post-consumer rLLDPE containing ethylene-vinyl alcohol or polyamide barrier fragments must be processed with flat temperature profiles and a melt temperature below 220 °C to avoid transient crosslinking and carbonized specks. Polypropylene contamination from labels or seals remains solid at LLDPE processing temperatures of 190–230 °C; a 100 µm filtration screen retains some PP film fragments but not fine PP fibres. Vacuum venting in the metering zone removes low-molecular-weight volatiles, but strongly oxygenated silage residues may still generate acrid degradation by-products at melt temperatures above 230 °C.

Injection Moulding Feedstock and Shrinkage Thresholds

For injection moulding, post-consumer rLLDPE is usually dry-blended with virgin HDPE or PP because neat rLLDPE has a flexural modulus below 400 MPa when measured by ISO 178:2019. A blend of 70 wt% HDPE and 30 wt% rLLDPE reduces shrinkage anisotropy in deep-draw parts. Mould shrinkage determined by ISO 294-4:2018 ranges from 2.0–3.0% for unfilled rLLDPE and falls to 1.2–1.8% when the feedstock contains 15–25 wt% calcium carbonate filler from reclaimed opaque film. Clamp force calculations for a 1,200 mm × 600 mm mould use an estimated cavity pressure of 300–400 bar; a rLLDPE blend with melt flow rate of 1.0 g/10 min typically requires injection pressures of 800–1,200 bar depending on flow length-to-wall-thickness ratio. Gate seal time is 10–20% longer than for HDPE at equivalent part mass because rLLDPE crystallizes more slowly, and premature gate freeze is avoided by maintaining gate diameters above 1.5 mm.

Traceability of recycled LLDPE under EN 15343:2007 requires the supplier to document input material categories, process losses, and recycled content on a mass-balance basis. A certificate of analysis should include melt flow rate per ISO 1133-1:2022, density per ASTM D792-20, ash content per ISO 3451-1:2019, moisture content per ISO 15512:2019, and a filtration pressure value from a standard screen pack. Moisture content above 0.05 wt% requires pre-drying at 70–80 °C for 2–4 h; higher moisture produces splay on injection moulded surfaces and bubbles in sheet. For food-contact applications, post-consumer rLLDPE is generally not accepted for direct food contact unless produced through a recycling process with a U.S. FDA letter of no objection or an EU process validated under Regulation (EU) No 10/2011. Even then, migration testing under the specified food simulant must be performed. Non-food rLLDPE must comply with REACH Annex XVII and RoHS Directive 2011/65/EU for hazardous substance restrictions, but those regulations do not verify mechanical recyclability or process stability.

Melt Filtration Pressure and Vacuum Venting Govern rLLDPE Pelletizing Operations

During pelletizing of reclaimed rLLDPE, a single-screw extruder with L/D ratio of 30:1 to 44:1 and vacuum venting in the metering zone removes residual moisture and low-molecular-weight volatiles. Melt filtration pressure before the screen changer is monitored as a surrogate for contaminant load. A pressure increase from 40 bar to 90 bar across a 120 µm screen at 220 °C signals screen blockage and requires a screen change. Continuous screen changers permit screen replacement without line stops and are preferred for post-consumer feedstocks containing soil and fibre. For higher-contamination streams, a co-rotating twin-screw extruder with L/D 40:1 and vacuum venting can disperse fillers and homogenize melt flow rate, but the additional shear raises melt temperature and must be controlled below 230 °C to avoid oxidative chain scission. Melt temperature limits are process-critical: above 230 °C, oxygenated post-consumer residues accelerate chain scission, increasing melt flow rate and reducing melt strength, which later compromises film bubble stability and moulded part toughness.