Braskem HDPE GP5550BK is a black-compounded high-density polyethylene supplied in pellet form for thick-wall pressure pipe extrusion and associated extruded profiles. The grade designation incorporates carbon black pigmentation directly in the compound, so the processor does not require a separate black masterbatch at the extruder throat. Typical density is 0.955 g/cm³ when measured according to ISO 1183-1:2019 or ASTM D1505-20. Melt flow rate at 190 °C under 5.0 kg load is reported as 0.5 g/10 min by ISO 1133-1:2022 or ASTM D1238-20. These values place the material in the high-molecular-weight HDPE range associated with slow-crack-growth resistance and elevated hydrostatic design stress. A single melt flow measurement at 2.16 kg is insufficient for pipe-grade quality control because the low shear rate rheology controls sag and wall-thickness stability during extrusion.

Specification Profile and Published Typical Values

The values below are typical published data, not guaranteed batch limits. Conversion trials and first article qualification should be based on the producer’s certificate of analysis and on pipe-scale tests rather than on resin plaque values alone.

Because pipe-grade performance is controlled by molecular architecture rather than by a single flow value, the producer typically reports melt flow rate at 5.0 kg rather than 2.16 kg. The higher load is necessary to differentiate batches in the high-molecular-weight range where standard-load values may be <0.1 g/10 min and have poor repeatability. Batch release testing also includes carbon black content, density, and oxidative induction time; pipe producers may request rheological curves from 0.1 rad/s to 100 rad/s to detect high-molecular-weight tails. A batch with equivalent melt flow rate but lower low-frequency complex viscosity can produce higher sag in thick-walled pipe and should be rejected for large-diameter applications. Batches with carbon black content near the upper end of the range may show slightly higher viscosity and lower elongation at break, although published data for this specific configuration is limited. Tensile yield stress and density are not independent variables; the 0.955 g/cm³ density is achieved through controlled comonomer content and molecular architecture.

On a grooved-feed single-screw extruder with an L/D ratio of 30:1 to 36:1, barrel profiles typically begin at 180 °C in the feed zone and progress to 215 °C in the metering zone, with the die head maintained at 210 °C to 220 °C. Pre-drying is unnecessary when the packaging remains sealed; if exposed to relative humidity above 60 %, drying at 80 °C for 4 h with a desiccant unit prevents surface splay and porosity. Melt temperature at the adapter should remain below 240 °C for continuous production, and residence time above 5 min at this temperature degrades oxidative induction time and increases gel counts. Carbon black typically raises melt pressure at a fixed throughput by 5 % to 15 % relative to natural HDPE of equivalent melt index because the filler increases low shear viscosity; screw designs with deeper feed channels and lower compression ratios are therefore preferred. Vacuum sizing tank water temperature should be held at 15 °C to 30 °C; lower temperatures may chill the outer skin too rapidly and create residual stresses that lower impact strength. Cooling length is governed by wall thickness, haul-off speed, and target outer skin temperature, and published line-specific values vary with tank design and ambient temperature.

How Is GP5550BK Distinguished From Unfilled HDPE Pipe Resins?

Three technical differences govern substitution decisions. First, carbon black at 2.0–2.5 wt% supplies ultraviolet screening and improves weathering resistance relative to unfilled natural HDPE, which requires an external UV stabilizer package if exposed above ground. Second, black pigmentation modifies melt rheology, increasing head pressure and reducing melt index by an amount that depends on carbon black particle size and structure. Third, the long-term hydrostatic strength of extruded pipe is not defined by resin density alone; it is evaluated under ISO 9080:2022 at multiple temperatures and converted to a minimum required strength classification under ISO 12162. In contrast, general-purpose HDPE injection moulding grades with melt flow rate above 4 g/10 min at 190 °C/2.16 kg show shorter environmental stress crack resistance and are unsuitable for pressure pipe under ISO 4427 or ISO 4437. Unfilled HDPE pipe resins may offer easier colour change and lower melt pressure but do not possess the same intrinsic carbon black dispersion unless a masterbatch is added earlier in the supply chain. Relative to a typical unfilled HDPE pipe grade, GP5550BK may exhibit a lower melt flow rate at equivalent density because carbon black increases energy dissipation in the die. The effect is not linear; high-structure carbon black grades increase viscosity more than low-structure grades at the same loading. Processors switching from natural to black compound often observe that the screw must run 5 rpm to 10 rpm slower to maintain die pressure within the extruder’s maximum rating. Published data for this specific configuration is limited; therefore, commissioning trials should begin with a 10 % output derating and gradually increase while monitoring melt temperature and surface quality.

Qualified pipe applications include potable water distribution networks, industrial fluid transport, and natural gas distribution pipes where the finished pipe meets the dimension and pressure requirements of ISO 4427-2:2014 or ISO 4437-2:2014. The resin is also applied in black outer layers of multi-layer pipes over recycled or foamed cores; the outer layer thickness is calculated from the local UV exposure class and the carbon black depth. Service temperature boundaries are application-specific. For water pipe, sustained pressure derating follows the temperature factors of the applicable national standard; installation below 0 °C requires impact verification because HDPE embrittles at low temperature. Published data for this specific configuration is limited for specialized chemical transport; immersion tests under ASTM D543-21 or ISO 175:2010 should be conducted before specifying the grade for aggressive media. Strong oxidizing acids, aromatic solvents, and some chlorinated hydrocarbons degrade HDPE; swelling, stress cracking, and loss of hydrostatic strength must be evaluated for each fluid composition.

When Carbon Black Dispersion Falls Below ISO 18553 Grade 3

Carbon black dispersion is not a cosmetic attribute; it is a structural variable that controls slow crack growth and hydrostatic failure. In compounded black HDPE, dispersion is rated by microtome section according to ISO 18553, with pipe specifications commonly requiring a rating of ≤3. Agglomerates larger than 60 µm behave as internal flaws that can reduce environmental stress crack resistance by an order of magnitude and initiate crack propagation at hoop stresses below 5 MPa. Compounding of GP5550BK should be performed on co-rotating twin-screw extruders with L/D ratios of 40:1 or higher, using kneading blocks after the melting zone and distributive mixing elements before the die. Specific energy input in the range of 0.15–0.25 kWh/kg is typical for dispersing carbon black in high-molecular-weight HDPE; values below 0.10 kWh/kg may leave undispersed aggregates. Melt temperatures above 260 °C cause oxidative chain scission and lower oxidative induction time, whereas temperatures below 190 °C produce visible die lines and poor dispersion. Incoming pellets should be tested for carbon black content by thermogravimetric analysis according to ISO 6964 and for dispersion by microtome or pressure-rise method before production runs.

Material safety and regulatory compliance are confirmed at the finished pipe level, not by resin data alone. For potable water contact, extruded pipe is tested under NSF/ANSI 61 or the national transposition of EU Drinking Water Directive 2020/2184; resin-level declarations under REACH 1907/2006 and RoHS 2011/65/EU do not replace end-article compliance. Gas pipe systems require pipe-level testing for minimum required strength, slow crack growth under ISO 13479, and rapid crack propagation under ISO 13477 at wall thicknesses above 63 mm. Failure to conduct pipe-level tests—particularly on large-diameter thick-wall pipe—can lead to field failures that are not predicted by melt flow rate or density alone. Pellet handling and storage affect conversion. Pneumatic conveying at air velocities above 25 m/s can generate fines that alter bulk density and feed stability; hopper magnets and 20 mesh screens are standard protective measures. Storage below 50 °C and away from direct sunlight reduces oxidative degradation of pellet surfaces. Because the black colour masks yellowing, oxidative induction time testing under ISO 11357-6 or EN 728 should be used as a diagnostic instead of visual inspection.

Melt Temperature and Residence Time Boundaries in Pipe Extrusion

Process control limits for this grade are set by thermal-oxidative stability and melt fracture thresholds. Adapter melt temperature should be maintained between 200 °C and 235 °C; the lower boundary prevents unplasticated high-molecular-weight fractions from producing surface roughness, while the upper boundary avoids premature antioxidant consumption. In production-scale pipe lines, thermocouple errors of ±5 °C are common, so a nominal set point of 215 °C provides a safe margin against both limits. Residence time distribution in a grooved-feed extruder is widened by screw speed reductions and high head pressure; at low throughput, resin held in dead zones can degrade and create intermittent gel particles. The use of a screen pack with 20/40/20 mesh and a breaker plate improves melt homogeneity and raises back pressure, but screen pressure above 25 MPa indicates carbon black agglomeration or foreign debris. Rheological data from capillary rheometry at 190 °C and shear rates from 10 s⁻¹ to 1,000 s⁻¹ show shear-thinning behaviour typical of high-density polyethylene. Power-law indices for similar high-molecular-weight pipe grades are generally near 0.4 to 0.6; published data for this specific configuration is limited. Melt pressure at the die is estimated from the pipe tooling and throughput; fluctuations greater than ±0.5 MPa at constant screw speed indicate feed bridging or incoming bulk density variation. In-line rheometers and melt pressure transducers provide better batch-to-batch control than periodic laboratory melt index checks because they capture the low-shear viscosity that governs sag and wall-thickness control.