Shandong Yulong HDPE 2500HW is a high-density polyethylene resin supplied in pellet form for blown film and extrusion applications. The model designation 2500HW identifies a high-molecular-weight film grade with a melt mass-flow rate of 0.25 g/10 min measured at 190 °C under a 2.16 kg load according to ISO 1133-1, and a nominal density of 0.950 g/cm³ at 23 °C according to ISO 1183-1. The resin is formulated for high-stalk bubble configurations used in carrier bag, bin liner, and heavy-duty sack film. Table 1 lists typical physical properties reported in producer technical documentation.

In converter practice, the 2500HW designation is selected where bubble stability and stiffness are limiting factors. The high-molecular-weight fraction raises extensional viscosity in the melt, stabilises the bubble under high blow-up ratios, and permits down-gauging to 15 µm or thinner on modern lines. It is not formulated for injection moulding or high-speed thin-wall packaging. Conversion trials that replace a lower-MFR film grade with 2500HW may require an increase in melt temperature of 5–10 °C to reduce die pressure and a reduction in screw speed to avoid melt fracture. The grade is shipped in 25 kg bags or bulk containers. Pellets should be stored in clean, dry conditions at ambient temperature below 40 °C and protected from ultraviolet degradation. HDPE is not hygroscopic, but condensation on cold pellets transferred into a warm processing area can introduce surface moisture; hopper dryers are used only when visible condensation or ambient humidity exceeds 60 % RH.

The material is compatible with standard polyethylene purging compounds. Transition from a previous HDPE or LLDPE grade can be performed by purging with a commercial PE purge compound or the incoming resin at 10–15 % of barrel capacity until melt pressure stabilises. Avoid mixing with polyamide or PET regrind without adequate purge and separation because incompatible melt phases reduce film clarity and tear resistance.

What Differentiates 2500HW from Other HDPE Film and Extrusion Grades?

The most direct differentiation is melt mass-flow rate. The 2500HW grade is positioned below standard HDPE monofilament and extrusion grades and above very-low-MFR film grades. A typical 5000S-type HDPE is reported at 0.90 g/10 min and 0.954 g/cm³; a 7000F-type HDPE film grade is reported near 0.04 g/10 min and 0.953 g/cm³, both measured under ISO 1133-1 and ISO 1183-1. The intermediate MFR of 2500HW provides higher melt strength than the former and lower melt pressure than the latter. Density differences of 0.004–0.006 g/cm³ alter film stiffness, moisture vapour transmission rate, and seal initiation temperature in multi-layer structures. The grade should not be considered a drop-in replacement for LLDPE in high-puncture stretch or cling film; published data for 2500HW in those configurations is limited.

The molecular architecture of 2500HW also affects extensional flow behaviour. In a high-stalk process, the melt undergoes planar extensional deformation before the frost line. Higher molecular weight fractions increase strain hardening, which delays bubble rupture at high draw ratios. This is why 2500HW can be blown at a blow-up ratio of 4:1 with a 20 µm film, whereas an HDPE with an MFR of 0.90 g/10 min would show excessive bubble chatter and gauge variation under similar conditions on a 150 mm die. However, the strain-hardening component also increases die lip pressure; converter reports for high-molecular-weight HDPE on a 150 mm die indicate pressure increases of 10–20 % relative to lower-molecular-weight film grades at the same output. Published data for this specific configuration is limited, and start-up settings should be adjusted from the lower end of the pressure range.

When High-Stalk Blown Film Processing Encounters Melt Fracture Limits

The processing window is controlled by melt temperature, die gap, and frost line height. For high-stalk HDPE lines with a 120 mm die and a 1.8–2.5 mm die gap, the melt temperature is typically maintained between 190 °C and 210 °C. Below 180 °C, the high-molecular-weight fraction raises melt pressure and can induce sharkskin melt fracture at high output. Above 220 °C, oxidative chain scission increases gel count and reduces bubble strength. A blow-up ratio of 3:1 to 5:1 and a frost line height of 6–10 die diameters are typical starting conditions. The use of a barrier screw with L/D ≥ 24:1 and a Maddock or pineapple mixing section is recommended; low-shear general-purpose screws with insufficient mixing produce temperature heterogeneity and localised gel formation.

Melt temperature profile should be set with a reverse or flat profile. A typical profile for a 90 mm extruder with 30 L/D and a barrier screw is: feed 170–180 °C, compression 190–200 °C, metering 200–210 °C, die 200–210 °C. Higher metering temperatures reduce melt pressure but may increase degradation if residence time exceeds 5–7 min. Screen pack combinations of 80/100/80 mesh are used, but high back pressure from fine screens can raise melt temperature and cause gel formation. Die pressure fluctuations of more than ±2 % during a run indicate screw feeding instability or melt temperature variation, and require adjustment of feed zone cooling or screw speed.

Transition from a standard HDPE film resin to 2500HW may require a die gap increase of 0.3–0.5 mm to compensate for higher die pressure. The frost line should be raised if bubble instability occurs, but raising it above 12 die diameters reduces the high-stalk orientation that contributes to film stiffness. The material is not predried under normal storage below 60 % RH; if stored in humid conditions, surface moisture can be removed with a hopper dryer at 70–80 °C for 2 h. Avoid mixing with polyamide or PET regrind without adequate purge and separation because incompatible melt phases reduce film clarity and tear resistance.

On a production line with a 90 mm grooved-feed extruder and 150 mm die, the highest output is obtained when barrel cooling water is maintained at 50–60 °C in the feed zone. If the feed zone temperature rises above 65 °C, pellet bridging can occur at the feed throat, resulting in screw speed fluctuations. The melt pressure at the die inlet should be recorded and compared with the extruder manufacturer’s maximum allowable head pressure; sustained operation above 85 % of that maximum reduces screw bearing life and increases the risk of screen pack blowout.

Melt fractures in high-stalk HDPE film often appear as helical haze bands rather than complete bubble rupture. In 2500HW, these bands are usually observed when output exceeds the cooling capacity of the air ring or when the die gap is below 1.5 mm. The corrective action is to increase die gap, raise melt temperature by 5 °C, or reduce screw speed by 5–10 %. If haze persists, the screw may be generating excessive shear heat; inspection of the screw and barrel for wear or polymer build-up is required.

Mechanical Test Data for 20 µm Grocery Sack Film

Film test values are sensitive to blow-up ratio, frost line height, and screw design. For a 20 µm HDPE film produced at a blow-up ratio of 3:1 and conditioned at 23 °C and 50 % RH, tensile properties are commonly measured according to ISO 527-3 or ASTM D882. Stiffness-driven applications benefit from the density of 0.950 g/cm³, which increases secant modulus relative to LLDPE films of the same thickness. Dart impact values for comparable high-molecular-weight HDPE film resins fall typically between 150 g and 220 g F50 using ASTM D1709A, but published data for 2500HW film specifically is limited, and converter validation is required. Elmendorf tear results using ISO 6383-2 or ASTM D1922 should be obtained from the certificate of analysis because orientation effects in high-stalk films make tear directionality highly dependent on line configuration.

Common film applications range from 12 µm to 40 µm. For heavy-duty sack film at 40 µm, the grade provides high stiffness and low elongation under load. For a 15 µm carrier bag film, high-stalk processing at a frost line height of 8 die diameters enhances MD tear resistance. The material can be used in multi-layer coextrusion with LLDPE skin layers for heat sealing; the HDPE core increases modulus while the LLDPE skin improves seal strength. In such structures, the seal initiation temperature is influenced by density; the HDPE layer may increase seal initiation temperature by 10–15 °C compared with an LLDPE-only film, requiring higher seal bar temperatures in converting. Coextrusion with LDPE improves bubble stability but reduces stiffness; the mixing ratio must be determined by end-use stiffness targets.

In heavy-duty sack production on a 120 mm extruder with a 250 mm die, film thickness control is usually maintained within ±3 % at a layflat width of 800 mm. The resulting sacks are evaluated for drop impact and tear propagation; the high density of 2500HW contributes to a higher modulus than low-density polyethylene but may reduce impact resistance at sub-zero temperatures. Applications requiring low-temperature drop performance below -10 °C should blend 2500HW with LLDPE or select a lower-density PE grade.

Moisture vapour transmission rate should be measured by ASTM F1249 or ISO 15106-1. Published data for 2500HW at a given film thickness is limited; converter trial data is the basis for shelf-life calculations.

Regulatory Status and Food-Contact Boundary Conditions

Compliance is grade-specific. Polyethylene homopolymers and copolymers intended for food contact are generally addressed by FDA 21 CFR 177.1520 in the United States and by EU Regulation 10/2011, Annex I, Table 1 in the European Union if end-use migration testing is satisfied. Shandong Yulong HDPE 2500HW may be suitable for food-contact packaging only when the converter validates the finished article under the applicable migration conditions, as the pellet compliance statement does not cover additives or masterbatch added downstream. The grade is subject to REACH registration obligations under EC 1907/2006, and a current safety data sheet should be consulted for handling limits. Halogenated flame retardants, lead, cadmium, and mercury are not intentional additives, but the product should not be represented as automatically compliant with RoHS 2011/65/EU because packaging applications fall outside that directive’s scope unless incorporated into electrical or electronic equipment as a packaging component. Published data for specific food-contact configurations is limited; migration testing remains the responsibility of the converter.