Braskem HDPE ES6007 is a high-density polyethylene extrusion grade specified for sheet extrusion and subsequent thermoforming. The product is identified by a nominal melt flow rate of 0.70 g/10 min measured at 190 °C under 2.16 kg in accordance with ASTM D1238, and a nominal density of 0.960 g/cm³ measured in accordance with ASTM D1505. These values place the grade in the high-stiffness, low-flow region of HDPE sheet materials. The 0.960 g/cm³ density contributes to flexural modulus values reported above 1,400 MPa under ASTM D790, while the 0.70 g/10 min melt flow rate provides sufficient low-shear viscosity for melt strength at the die exit. The designation separates ES6007 from injection-moulding and blow-moulding HDPE grades in the producer’s portfolio, which carry different melt-flow and density targets. The grade is used in monolayer sheet, coextruded cap-layer structures, and thick-gauge thermoforming stock.

Sheet extrusion of ES6007 is governed by the shear-viscosity curve rather than the single-point melt flow rate. The low-shear-rate viscosity controls sag, while the high-shear-rate viscosity controls extruder amperage and die pressure. At a die shear rate typical of polished-sheet production, the viscosity is lower than at zero-shear conditions; this shear thinning permits the grade to be pumped through a conventional sheet die without excessive melt temperature. The melt flow rate at 190 °C under 2.16 kg reports only a low-shear point and does not provide the complete flow curve. Capillary rheometry under ASTM D3835 should be used when designing a new die or changing equipment, because the slip and shear-thinning behaviour at the die wall affect gauge uniformity.

What Limits the Melt-Temperature Window During Sheet Extrusion of ES6007?

On monolayer sheet lines fitted with 75 mm single-screw extruders at 30:1 L/D, process stability is sensitive to melt temperature because the low flow rate generates shear heat. Head-pressure fluctuations above ±2.5% indicate that the screw is not operating inside its stable pumping region. For this grade, melt temperatures below 185 °C can produce poor melt homogenisation and visible pale streaks in thick sheet, while melt temperatures above 230 °C can initiate thermal-oxidative degradation that raises gel content and deposits degraded polymer at the die lip. The practical melt-temperature set point for rigid HDPE sheet extrusion in this density class is commonly maintained between 190 °C and 210 °C, but the exact value must be adjusted from lot-specific melt-flow data and the measured melt temperature at the feedblock.

Thermal degradation in HDPE follows a radical chain mechanism that shifts the molecular weight distribution and reduces elongational melt strength needed for thermoforming. The result is not a single-point failure but a narrowing of the draw window. Film edge trim and sheet edge bead may show increased sag sensitivity, and the sheet may exhibit more orientation in the machine direction. When die-lip deposit appears after a prolonged run, the first measurement should be the melt temperature at the screw exit rather than the die temperature, because the die probe often underestimates the peak shear-heated region. The use of a melt-temperature thermocouple inserted directly into the melt stream provides better indication of thermal excursions.

Screw Geometry, Screen-Pack Pressure, and Take-Off Stability

On a 90 mm extruder with an L/D of 32:1, a single-stage barrier screw with 3.0:1 to 3.5:1 compression ratio and a feed-zone length of approximately 5D has been used to reduce pulsation. A melt pump after the screen changer further isolates the die from screw-speed changes. Screen-pack differential pressure should be monitored with pressure transducers installed upstream and downstream of the breaker plate; when the differential rises beyond the line-specific baseline, the resulting energy input can increase melt temperature by several degrees and push the resin out of the established window. Published data for this specific equipment configuration is limited, so the differential-pressure limit should be established on the production line rather than copied from another installation.

Because ES6007 is more viscous than high-flow HDPE, the screw must provide positive feed-zone conveying. Feed-zone temperature that is too high can cause pellet slippage and output variation. The first barrel zone is typically set below the melting point to maintain a solid conveying bed, while downstream zones are raised to complete melting before the metering section. Differences in screw geometry across production lines prevent a single barrel profile from being valid. At the take-off, the sheet enters a vertical or horizontal polishing stack. Roll temperatures between 70 °C and 90 °C are typical for crystalline HDPE sheet because they control surface replication without causing sheet to stick to the rollers. Higher roll temperatures increase surface smoothness but reduce cooling-limited line speed. The die gap is normally set above the target thickness to allow draw-down; excessive draw-down, however, creates machine-direction orientation and can reduce the forming window in subsequent thermoforming.

Compared with a fractional-melt HDPE in the same density band, ES6007 lowers head pressure at an equivalent screw speed and allows a lower start-up melt temperature. This difference shifts output control from the extruder to the haul-off; the same screw speed can produce a thicker sheet if line speed is not adjusted. Compared with injection-moulding HDPE grades having melt flow rates near 7.0 g/10 min, ES6007 has higher extrudate strength and lower post-extrusion sag, but it is not suitable for thin-wall injection moulding under low clamp-force conditions. The molecular weight associated with the 0.70 g/10 min flow rate also reduces knit-line strength in complex flow channels; therefore, the grade is not interchangeable with high-flow HDPE in closed-mould processes. The selection of ES6007 is therefore limited to processes that exploit extrudate strength and sheet stiffness rather than melt-pressure reduction or rapid mould filling.

Interpreting Physical Property Data Without Overextrapolation

The values in Table 1 are typical published data for the grade; they are not contractual specifications. Lot-specific certificates of analysis should be obtained before production because melt-flow and density shifts as small as ±0.02 g/10 min or ±0.002 g/cm³ can move the sheet extrusion window and affect gauge control. Measurements are influenced by conditioning at 23 °C and 50% relative humidity as defined in ASTM D618 for tensile specimens.

The tensile strain at break of 800% is a uniaxial laboratory value measured on extruded or compression-moulded specimens; it should not be taken as the maximum forming ratio in production. Thermoforming draws stress the sheet in multiple directions and at varying strain rates, so the forming window is narrower than the uniaxial elongation value suggests. The Vicat softening point of 129 °C under ASTM D1525 is useful for ranking but is not a continuous-use-temperature limit. Above 80 °C, long-term oxidative stability and creep become design-limiting factors.

During thermoforming, ES6007 sheet is typically heated to a surface temperature between 130 °C and 160 °C for thin-gauge stock, but thick sheet requires slower heating to avoid surface oxidation. The crystalline melt transition of HDPE at this density occurs around 130 °C to 135 °C; therefore, the sheet must be brought through the melting range uniformly. Uneven heating creates cold spots that produce thinning or webbing. Quartz or ceramic radiative heaters with zoned control are used to profile the sheet surface; the edges require lower energy input because they cool faster. The depth of draw should be evaluated against the sheet’s measured thermal expansion and sag behaviour rather than the room-temperature tensile values.

When ES6007 Is Coextruded as the Cap Layer Over a Lower-Density Core

In coextruded sheet, ES6007 can serve as a high-modulus cap layer over a medium-density HDPE core. The melt-flow mismatch must be managed at the feedblock because the layers do not automatically maintain their thickness ratio. The higher viscosity of ES6007 relative to a 0.940 g/cm³ core grade can cause interfacial instability or layer non-uniformity if the melt streams are not temperature-adjusted. The core layer may require a slightly higher melt temperature to bring its viscosity closer to that of the cap layer; otherwise, the cap layer can encapsulate the core and create edge-trim waste with variable composition. Regrind from coextruded sheet therefore has a density lower than 0.960 g/cm³ and a melt-flow rate different from neat ES6007. A blend of cap-layer trim and core trim should be used only after the resulting melt-flow rate and density have been measured, because those values predict extruder back-pressure and final flexural modulus.

When the regrind fraction exceeds 30%, the risk of gel increase from thermally degraded edge trim becomes significant. Degraded HDPE does not plasticate uniformly at the same screw speed, and it may form visible gels in thin-gauge sheet. The screen pack should be checked at intervals; if the differential pressure rises rapidly, the regrind stream should be reduced or diverted. Film edge trim and start-up scrap should not be reintroduced without size reduction and blending, because large particle-size distribution can cause melt pump cavitation and surging. The melt-flow rate of the blended regrind is not linear with weight fraction when the components have very different molecular weight distributions, so it should be measured separately.

Compliance Testing Follows the Finished Article, Not the Neat Resin.

The neat resin may be assessed for compliance with FDA 21 CFR 177.1520 for olefin polymers in food-contact use. The finished article is not automatically compliant because the additive package, regrind stream, printing inks, and processing aids must be included in the assessment. For European Union food-contact applications, the relevant framework is Regulation (EU) No 10/2011, which requires overall migration testing of the finished article under specified food simulants. Under REACH Regulation (EC) No 1907/2006, the supplier certificate for the neat resin does not remove the downstream obligation to communicate substances of very high concern if they are introduced during conversion. For electrical and electronic applications, RoHS Directive 2011/65/EU limits on lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE must be verified on the final component.

Chemical exposure is a design parameter for HDPE sheet. The high crystallinity of a 0.960 g/cm³ grade improves resistance to water, aqueous salt solutions, and many polar solvents at ambient temperature, but it also increases notch sensitivity relative to medium-density polyethylene. Environmental stress cracking in HDPE is evaluated by ASTM D1693, and the resistance is strongly dependent on test condition and sheet orientation. This grade should not be specified for continuous contact with strong oxidizing acids, aromatic hydrocarbons, or chlorinated solvents at elevated temperatures. Detergent and silicone-based release agents can accelerate stress cracking in formed parts under load; therefore, the final part should be tested under actual service conditions rather than inferred from resin data. Published data for ES6007 in specific solvent environments is limited, so compatibility testing should be performed on the formed article.

As with most HDPE grades, drying is not required for moisture removal because the polymer is not hygroscopic. Surface condensation caused by moving cold pellets into a warm production area can introduce water into the feed throat and cause visible surface bubbles in thick sheet. When outdoor storage or cold-room storage is used, pellets should be brought to ambient temperature and blown with low-dew-point air before feeding. The feed throat should be kept cool enough to prevent bridging, but not so cold that condensation forms. For lines running above 500 kg/h, a hopper loader with a vented pickup and a low-dew-point air supply reduces moisture-related defects.