PetroChina Guangdong HDPE 5704F — Technical Introduction

PetroChina Guangdong HDPE 5704F is a high-density polyethylene resin produced at the Guangdong Petrochemical complex of PetroChina. The grade is supplied as a pelletized feedstock for blown-film extrusion and is positioned in the low-melt-index, high-density segment of HDPE film resins. Supplier technical data for this grade list a nominal density of 0.957 g/cm³ determined by ISO 1183-1:2019 and a melt flow rate of 0.45 g/10 min measured at 190 °C under 2.16 kg load in accordance with ISO 1133-1:2022. The combination of elevated density and low melt index increases melt strength, tensile stiffness, and resistance to creep under sustained loading compared with lower-density LLDPE or LDPE film resins, while also raising extrusion head pressure and reducing low-shear flow. The resin is therefore directed toward blown-film applications where film gauge reduction, stiffness, and bubble stability are more important than clarity or low-temperature ductility.

The representative property envelope for this grade is summarized below. The values are typical values from supplier technical information and should not be read as specification limits; lot-specific processing and film performance should be confirmed against the certificate of analysis for the actual batch.

Because the resin has a melt flow rate below that of general-purpose HDPE film grades, extrusion equipment must be selected for sufficient low-speed torque and melt-pressure capability. The grade is not intended for thin-wall injection molding or for processes requiring high-flow spiral-fill behavior.

What distinguishes 5704F from conventional blown-film HDPE resins?

The main differentiation of 5704F from more general-purpose HDPE film grades lies in its low melt flow rate combined with a density at the upper end of the film-grade range. A melt flow rate of 0.45 g/10 min corresponds to a higher average molecular weight than HDPE film resins with melt flow rates of 0.7–1.0 g/10 min. The higher molecular weight increases entanglement density and low-shear viscosity, which stabilizes the blown-film bubble at high blow-up ratios and permits down-gauging in sack and liner applications where tensile strength per unit thickness is a limiting parameter. However, the same property raises screw torque, melt pressure, and die residence time at constant output. Compared with HDPE film grades of density 0.948–0.952 g/cm³, the 0.957 g/cm³ density of 5704F increases crystallinity and flexural modulus. This shifts the property balance toward stiffness and tensile yield, while reducing environmental stress-crack resistance and low-temperature impact toughness, as is typical for higher-density HDPE film resins.

Relative to high-melt-strength film grades with melt flow rates below 0.2 g/10 min, 5704F retains a degree of processability on standard blown-film lines because its melt flow rate is not so low as to require specialized low-output extruder screw designs. Relative to injection-grade or blow-molding-grade HDPE, the low melt index of 5704F makes it inappropriate for rapid cavity filling or high-flow blow molding. In multi-layer film structures, 5704F commonly appears as a stiffening core layer or as a high-strength back layer; its use in skin layers can reduce sealing performance unless blended with a lower-density polyolefin or a sealant resin.

Blown-film processing parameters, melt pressure, and line-speed limits

On commercial blown-film lines, 5704F is typically processed with a barrier screw in an extruder having a length-to-diameter ratio of 25:1 to 30:1. Melt temperature setpoints are normally held between 190 °C and 220 °C at the adapter and die, with barrel profile setpoints increasing from approximately 180 °C in the feed zone to 210 °C in the metering zone. Die gap is commonly set from 1.8 mm to 2.4 mm, with blow-up ratios from 2.5:1 to 4.0:1. Frost-line height is normally maintained between six and ten die diameters, depending on ambient temperature and cooling-air delivery, to control film haze, blocking, and tensile balance. At blow-up ratios above 3.0:1, the low melt flow rate of 5704F contributes to bubble stability, but the die head pressure rises more rapidly with output than it does for lower-viscosity film grades. Extended runs on 50–70 mm extruders with die diameters of 150–250 mm generally operate under torque-limited rather than melt-temperature-limited conditions. Published data for this specific configuration is limited, and the optimum output window must be established on the individual line.

Pre-drying is not normally required for storage in dry ambient conditions, but pellet surface moisture can develop when bags are stored at relative humidity above 60%. In such cases, drying at 80 °C for 2 h is recommended before extrusion to reduce surface splay and melt-pressure fluctuation. The resin should not be processed in equipment containing degraded PVC or PVDC, because acidic residues can accelerate surface oxidation and produce visible gel defects. Purge procedures should be completed when transitioning from high-MFI color concentrates or polar polymers; a low-MFI HDPE purge transition may require longer residence time than transitions between LLDPE grades of similar density.

Film converters report that the grade’s low melt flow rate narrows the processing window for thin films below 15 µm because excessive drawdown rates can induce melt resonance or film-thickness variation. The risk is reduced by increasing melt temperature within the 200–220 °C range, reducing haul-off speed, or blending with an LLDPE of melt index 0.5–1.0 g/10 min. In such blends, the viscosity ratio between 5704F and LLDPE influences layer stability in coextrusion, and screw speed must be adjusted to prevent interfacial flow instabilities.

For monolayer heavy-duty sacks and industrial liners, the grade is run at film thicknesses from 25 µm to 70 µm, where its puncture resistance and stiffness support load-bearing requirements. The tensile yield stress of 23 MPa in the resin is increased by orientation in the machine direction, but the degree of orientation depends on drawdown ratio and frost-line height. A balanced tensile profile is obtained by adjusting the blow-up ratio and die gap; higher blow-up ratios increase transverse orientation, while higher drawdown ratios increase machine-direction orientation.

When measuring film quality in production, dart impact testing under ASTM D1709-16a Method A is commonly used as a release criterion for 25 µm film. Typical values in supplier literature fall within the range of 120–170 g, but the observed value changes with die gap, cooling rate, blend level, and test temperature. The grade’s higher density reduces impact toughness relative to lower-density HDPE film grades, so end-use specifications requiring high puncture resistance at freezer temperatures may require blending with LLDPE or EVA. Published data for this specific configuration is limited, and converters should generate capabilty data on their own lines before setting final specifications.

The resin’s Vicat softening temperature of 127 °C under ISO 306:2013 A50 indicates a heat resistance suitable for warm-fill bag applications, although the continuous-use temperature is lower and depends on mechanical load. In applications where the film is heat-sealed, the sealing initiation temperature should be determined on the final film rather than on the pellet, because surface additives and corona treatment shift seal initiation.

Additive compatibility should be evaluated with the specific masterbatch carrier. 5704F accepts standard HDPE-compatible white and color masterbatches, but high-loading filler masterbatches may increase melt pressure because of the low base-resin melt index. The use of fluoropolymer processing aids at low addition levels can reduce die build-up and melt-pressure variation, but the addition level should be confirmed by film-surface testing because excess processing aid can interfere with printing or sealing.

Film produced from 5704F at 25 µm thickness is used in high-stiffness T-shirt carrier bags, refuse sacks, and industrial liners where down-gauging is required to reduce material consumption. The resin is also used in agricultural film structures and in stiff overwrap film where high modulus and moderate moisture-vapor transmission are acceptable. The film has a characteristic HDPE crinkle and lower clarity than LLDPE or LDPE film; applications requiring optical clarity or high low-temperature dart impact are generally served by blends or alternative chemistries. For food-contact applications, the base resin may be evaluated under FDA 21 CFR 177.1520 for olefin polymers and under EU Regulation (EU) No 10/2011, but final compliance depends on the complete film formulation, pigment systems, processing conditions, and end-use migration testing under the applicable exposure regime. 5704F should not be considered a food-contact-approved grade without specific formulary and migration verification.

When a converter co-extrudes 5704F with LLDPE in high-bag-volume applications

In high-volume carrier-bag production, 5704F is often blended with an LLDPE phase to recover low-temperature dart impact and tear resistance lost by the high-density phase. In a typical blend of 70–80 wt% 5704F with 20–30 wt% LLDPE, the LLDPE contributes lower crystallinity and better puncture resistance, while 5704F contributes stiffness, melt strength, and downgauging capacity. The blend is processed on the same blown-film line but with a slightly wider die gap or a lower blow-up ratio than neat 5704F because the LLDPE phase can lower bubble stability. The optimum ratio is not universal; it depends on the LLDPE comonomer type, melt index, and density. Published data for this specific configuration is limited, but plant-scale experience shows that die-head pressure decreases as the LLDPE content increases, while ambient-temperature dart impact increases.

In coextruded films, 5704F is used as the high-stiffness inner or middle layer in three-layer constructions where the outer layers provide sealability or slip. The low melt index of 5704F can create a viscosity mismatch with thin skin layers of low-density polyethylene, leading to encapsulation of the lower-viscosity skin at high output. This is controlled by adjusting skin-layer melt temperature upward or by selecting a skin resin with lower melt index. The practical upper output for such structures is usually determined by interfacial instability rather than by screw torque. The resulting films meet stiffness specifications without the full cost or toughness penalty of a monolayer high-density film.

For film processors evaluating 5704F against high-density film grades of similar density, the primary selection variables are melt-pressure capability, torque capacity, gauge target, and the need for low-temperature toughness. The lower melt flow rate of 5704F supports bubble stability at high blow-up ratios but demands more robust extrusion hardware than a film grade with a melt flow rate of 1.0 g/10 min. The higher density compared with 0.950 g/cm³ film grades provides a measurable increase in flexural modulus and tensile yield, but the same density increase reduces environmental stress-crack resistance under conditions involving polar liquids or surfactants. In such cases, performance should be verified under end-use conditions using ASTM D1693-15b or an equivalent bend-strip test, because laboratory tensile data alone do not predict long-term cracking under stress.