For heavy-duty form-fill-seal sack production on a three-extruder blown film line with grooved feed sections and L/D ratios from 25:1 to 30:1, Clearflex MDPE TF6 OK is typically processed at melt temperatures between 185 °C and 210 °C. The grade’s density of 0.934 g/cm³ and MFR of 0.6 g/10 min under ISO 1133-1:2022 supply the stiffness required to down-gauge from 180 µm to 140 µm without losing creep resistance in stacked pallet loads. Production-scale trials on 65 mm extruders show that die-lip build-up remains controlled when the die gap is set at 1.4–1.8 mm and the blow-up ratio is held between 2.5:1 and 3.0:1. A formulated core layer containing 15–20 wt% of this MDPE, 70–80 wt% LLDPE C6, and 5 wt% carbon-black masterbatch yields film with machine-direction tensile yield strength above 18 MPa under ASTM D882-18 and transverse-direction Elmendorf tear resistance above 8 g/µm under ASTM D1922. Terminal articles are 25 kg and 50 kg petrochemical resin sacks, mineral filler bags, and compacted waste liners. For non-food industrial use, REACH Annex XVII restrictions on PAH and phthalate content apply to the masterbatch, while food-contact variants require total migration below 10 mg/dm² under Regulation (EU) No 10/2011, Annex III. The operational boundary is rheological: increasing LLDPE content above 25 wt% reduces bubble stability and raises motor load, while reducing LLDPE below 10 wt% leads to film splitting at transverse-direction seals during cold warehouse transport below −10 °C. Pre-drying is not required below 60% RH; above 80% RH, silo condensation must be removed by a 70 °C hopper-air purge to avoid surface moisture streaks.

What limits heat-seal strength retention after frozen food distribution?

Blown film for frozen food packaging uses a symmetrical three-layer structure with MDPE in the outer layers to resist puncturing at low temperatures. The typical formulation is 30 wt% Clearflex MDPE TF6 OK in each outer layer and 40 wt% LLDPE C4 in the core, with the balance consisting of a low-gel polyolefin plastomer. Seal initiation temperature is recorded in the range 110–118 °C using ASTM F88/F88M-21 with a 25.4 mm specimen and a dwell time of 0.5 s. A critical processing limitation appears during high-speed vertical form-fill-seal filling at 80 packages/min: hot tack strength must remain above 2.0 N/25 mm at the moment the product drops from the filling tube, but MDPE’s slower crystallisation rate compared with HDPE reduces hot tack unless cooling air temperature is kept below 12 °C and frost line height is raised to 10–12 die diameters. Cold-brittleness testing according to ASTM D1709-A on 80 µm film shows puncture resistance above 120 g after conditioning at −18 °C for 48 h, which supports use in frozen vegetable and seafood packs. Compliance for direct food contact is evaluated under Regulation (EU) No 10/2011, Annex I and FDA 21 CFR 177.1520, with specific migration tests performed on the final printed laminate. The grade is not suitable for ultra-clear frozen fish display packs because haze typically exceeds 10% at 80 µm under ASTM D1003-21; this limitation should be confirmed by spectrophotometric measurement on the actual line.Because the tubular film process for collation shrink uses a high-stalk bubble configuration, melt rheology must be matched to the stretching forces generated at the nip. In a typical three-layer collation line with die diameter 350 mm and die gap 1.2 mm, Clearflex MDPE TF6 OK is blended at 20–30 wt% with LLDPE C6 in the core layer to increase shrink force. The extruder temperature profile is set from 175 °C in the feed zone to 210 °C at the die, and the bubble is frost-lined at 8–10 die diameters. Blow-up ratio is maintained at 3.2:1 to 3.6:1, producing transverse-direction orientation; machine-direction orientation is controlled by nip speed differential. The final film thickness of 35–50 µm gives transverse-direction shrink force values in the range 0.8–1.2 N/cm when tested according to ISO 14616 after 15 s at 130 °C in hot air. Terminal uses are bottle multipacks, can trays, and printed shrink bundling for beverage distribution. The main operational failure mode on commercial lines is bubble instability during ambient temperature fluctuations above 6 K/h in the extrusion hall, which creates gauge bands; closed-loop die-bolt control with at least 8 circumferential heating zones is therefore required.

Coextruded lamination film interlayer rheology and autoclave pouch conversion

Lamination structures for retortable pouches use a biaxially oriented PET or BOPA outer layer, an aluminium foil barrier, and a blown PE sealant film. Clearflex MDPE TF6 OK is incorporated into the sealant film as a stiffness modifier at 10–20 wt% in the skin layers, with the core consisting of LLDPE or metallocene LLDPE. The extrusion line is operated at 190–215 °C melt temperature with a die gap of 1.8 mm; the contact layer must be free of surface oxidation because peel strength to polyurethane adhesive is measured at 2–4 N/15 mm after 24 h curing. In retort processing at 121 °C for 30 min, the sealant film must retain at least 70% of its pre-retort seal strength; converter-reported data indicate that MDPE-containing sealants show lower delamination at the foil-sealant interface than LDPE-only sealants when the blown film was exposed to corona treatment above 42 mN/m wetting tension. Terminal articles are ready-to-eat rice pouches, pet food retort packs, and medical device peel pouches. Compliance is controlled under ISO 11607-1 for medical packaging and under FDA 21 CFR 177.1395 for laminates in contact with aqueous and fatty food above 121 °C. A known limitation is that the MDPE layer increases seal initiation temperature by 5–8 K compared with LDPE-rich sealants, narrowing the heat-seal operating window on high-speed pouch machines to approximately 20 K between seal and seal-through. Published data for this specific grade in retort sealant films is limited; the described values are converter-reported ranges rather than datasheet maxima.

Agricultural silage cover oxygen transmission limits

Silage clamp covers require puncture resistance and resistance to UV-assisted oxidation during six to nine months of outdoor exposure. MDPE is used as a core layer in coextruded covers because its higher density reduces oxygen ingress relative to LDPE at equal thickness. The blend contains 40 wt% Clearflex MDPE TF6 OK, 55 wt% LLDPE C4/C6, and 5 wt% of a UV-stabilizer masterbatch containing HALS and carbon black. The film is extruded at 150–200 µm thickness with a blow-up ratio of 2.8:1 and a frost-line height of 9–11 die diameters. Oxygen transmission rate measured at 23 °C and 0% RH on 150 µm film is typically in the range 1,200–1,800 cm³/(m²·day·bar) under ASTM D3985-17, which is lower than LDPE of the same thickness but not a substitute for EVOH or PA barrier layers. Terminal uses are silage clamp covers, grain storage liners, and agricultural fumigation tarpaulins. The main limitation in service is contact with silage acids; prolonged exposure to lactic and acetic acids at pH below 4.0 can extract low-molecular-weight additives and slightly increase surface tack, so the outer layer must be compounded with a suitable acid-neutralising stabilizer package. Published data for this specific MDPE grade under silage leachate exposure is limited; therefore, converter trials with the final UV masterbatch are mandatory before commercial supply.

Application	Regulatory or test anchor	Critical parameter
FFS industrial sacks	REACH Annex XVII; ASTM D882-18	Tensile yield, elongation at break
Frozen food packaging	Regulation (EU) No 10/2011; FDA 21 CFR 177.1520; ASTM F88/F88M-21	Seal strength, hot tack
Collation shrink film	ISO 14616	Transverse-direction shrink force
Retort pouch sealant	FDA 21 CFR 177.1395; ISO 11607-1	Peel strength after retort
Agricultural silage cover	ASTM D3985-17; REACH Annex XVII	Oxygen transmission, UV stabilizer content

When post-consumer recyclate is blended into the core layer

Mechanical recycling of LDPE-rich film waste generates a heterogeneous feedstock with density fluctuations between 0.920 g/cm³ and 0.935 g/cm³. Adding Clearflex MDPE TF6 OK at 15–30 wt% to post-consumer recyclate restores die-lip shear stress uniformity and reduces gel-induced film break frequency on a single-screw grooved feed extruder with L/D 30:1. The melt temperature is controlled at 200–220 °C; at the upper end, residence time must not exceed 90 s to avoid odour generation. Screens are specified at 100–120 mesh because PCR loadings above 20 wt% raise screen-pack differential pressure from 35 bar to 60 bar within 6 h of continuous operation. Terminal films are refuse sacks, construction temporary films, and low-specification carrier bags. The recycled blend is not suitable for food contact unless the PCR is certified under a closed-loop process meeting Regulation (EU) No 10/2011 and FDA 21 CFR 177.1520(c). The main operational boundary is gel dispersion; if the PCR contains more than 5 wt% of HDPE contamination, the melt index drops by 0.2–0.3 g/10 min and bubble stability deteriorates, which can be compensated by increasing MDPE content but at the cost of dart impact.Direct substitution of this MDPE grade into conventional carrier bag formulations at 40–60 µm gauge improves yield strength but reduces machine-direction Elmendorf tear resistance; converter trials should begin at 30 wt% with the balance LDPE and verify seal strength on rotary bag lines before full substitution.