On a 90 mm single-screw extruder with an L/D ratio of 30:1 and a barrier-screw/melt-pump configuration, Chevron Phillips Chemical HDPE HHM5502 is processed at barrel temperatures from 180 °C at the feed throat to 220 °C in the metering zone, with die zones held between 220 °C and 230 °C to produce 1.5 mm smooth black geomembrane for landfill cell and heap leach liner service. The pellet grade has a density of 0.955 g/cm³ under ASTM D1505 and a melt flow rate of 0.35 g/10 min at 190 °C and 2.16 kg under ASTM D1238-20; high-load melt flow measured at 21.6 kg supports full-width draw without edge tear. The pellet feed is dry-blended with a carbon black masterbatch to achieve 2.0 wt% to 2.5 wt% carbon black in the finished sheet. Dispersion is checked at the line using ASTM D5596, and thickness variation across a 2.4 m die width is held within ±5% by profile bolts. Cooling is set through chrome chill rolls at 75 °C to 95 °C, with a roll gap 1.35 mm to 1.45 mm for the required density and surface finish. A drop in die temperature below 210 °C shifts the ethylene-hexene copolymer toward melt fracture and can produce linear die lines that later propagate as folds during hot-wedge seaming. Laboratory release testing on the extruded sheet follows GRI GM13 thresholds: tensile yield stress measured under ASTM D638-14 Type IV at 50 mm/min must not fall below 19 MPa, break elongation must exceed 600%, tear resistance under ASTM D1004 must remain above 125 N, puncture resistance under ASTM D4833 must remain above 400 N, oxidative induction time under ASTM D3895 must exceed 100 min, and high-pressure OIT under ASTM D5885 must exceed 400 min. At 2.0 wt% carbon black, compounded HHM5502 sheet typically shows yield stress near 28 MPa and break elongation above 800%, but these values drop if the regrind fraction exceeds 20 wt% or if carbon black dispersion is poor. Seaming on the installed liner is performed by hot-wedge welding at 350 °C to 400 °C, and seam peel and shear are evaluated per ASTM D6392. Welds fail cohesively when sheet surface oxidation from excessive extrusion temperature has increased the carbonyl index, although published limit data for HHM5502-specific sheet is limited and most converters use FTIR carbonyl index only as an internal control. A process limitation is the narrow melt-temperature window before oxidative degradation: at melt temperatures above 230 °C, the low-torque screw map loses melt stability and antioxidants are consumed, reducing OIT below the GRI GM13 limit even if post-extrusion tensile properties appear unchanged. For outdoor service, UV stabilization from the carbon black package is required. Pellet storage at ambient relative humidity above 80% requires pre-drying at 80 °C for 2 h to avoid condensation-induced pinholing during sheet extrusion.

Table 1. Geomembrane release-test matrix for HHM5502 sheet.

What Limits Accumulator-Head Blow Molding of HHM5502 for 200 L Closed-Head Drums?

Accumulator-head extrusion of HHM5502 for 200 L closed-head drums begins on an 80 mm to 120 mm grooved-feed single-screw machine with 30:1 L/D and a 10 L accumulator head, with barrel temperatures from 175 °C to 210 °C and head zones at 200 °C to 215 °C. Pressure at the head during parison drop is maintained between 18 MPa and 25 MPa to preserve melt-stream continuity. A drop below 15 MPa at the end of the shot produces sharkskin on the inner parison surface and weakens the pinch weld at the bottom chime. The programmed parison mass for a 200 L UN 1H1 drum is usually between 9 kg and 10 kg, and the die gap program is altered from 2.5 mm at the neck to 5.0 mm at the base to compensate for parison sag. Because HHM5502 is a high-molecular-weight ethylene-hexene copolymer, its shear-thinning behavior and high melt strength resist lengthwise draw during extrusion. Nevertheless, head temperatures above 220 °C reduce die swell and can cause parison rupture when shot weight exceeds 11 kg. Blow molds are maintained at 12 °C to 20 °C, and clamp force for the drum mold on a typical shuttle press is between 700 kN and 900 kN. Finished closed-head drums are checked for minimum wall thickness by ultrasonic gauges, with 2.2 mm as the lower limit at the sidewall and 2.5 mm at the chime, and are subjected to UN 6.1.5.3 drop impact after conditioning at -18 °C. Environmental stress crack resistance of the grade under ASTM D1693-15 Condition B, 100% Igepal, is reported above 600 h, which is the decisive property for detergent and surfactant-containing liquid packaging. Aromatic solvents and hydrocarbon emulsions with more than 10% free aromatic content remain an incompatibility boundary: HDPE of this density can environment-stress-crack when tested under constant strain in the presence of xylene or toluene, and converters should prequalify each formulation by ASTM D1693 or notched constant tensile load. Regrind from pinch flash is returned at up to 25 wt% if it is clean, pelletized, and dried at 80 °C for 2 h. Higher regrind loadings introduce black speck contamination and reduce the ESCR below drum-application requirements. Food-contact containers produced from HHM5502 must be verified by the fabricator under FDA 21 CFR 177.1520(c) for the finished article, as the pellet alone does not confer compliance with extraction limits.

When 10 mm HHM5502 Sheet Is Thermoformed Into Freezer-Service Pallet Decking

Thick-sheet thermoforming of HHM5502 at 10 mm section thickness is constrained by the semicrystalline melting range of the ethylene-hexene copolymer. Differential scanning calorimetry under ASTM D3418 gives a peak melting endotherm between 128 °C and 132 °C, and the sheet surface must reach 160 °C to 175 °C under quartz infrared heaters before forming. Core temperature in a 10 mm sheet should remain at 145 °C to 155 °C. If the core drops below 140 °C, frozen-in stress accumulates in the formed part, leading to corner warpage after trimming and reduced drop impact under ASTM D5276. The forming line uses a plug-assisted vacuum system with aluminum tooling held at 65 °C to 80 °C, and clamp frame pressure is set at 0.6 MPa to 0.8 MPa. HHM5502 is converted into heavy-duty pallet decking, freezer separators, and dunnage trays that require low-temperature brittleness resistance under ASTM D746, reported below -75 °C, and flexural modulus under ASTM D790-17 near 1,200 MPa. The sheet extrusion upstream of thermoforming uses a 120 mm 34:1 single-screw machine with a melt pump and a die width of 2.0 m. Die temperature is kept at 210 °C to 225 °C, and roll-stack temperatures are 80 °C to 95 °C to slow crystallization and permit stress relaxation before cutting. A processing conflict occurs when the line operator increases output above 900 kg/h: core cooling lags in the roll stack and the sheet exits at 95 °C or more, causing blocking and surface markings during stacking. Published sag-rate data for HHM5502 under infrared heating is limited, so line validation requires grid-marker measurement of sheet draw and pyrometer confirmation of surface temperature across the forming window. Although HDPE is not hygroscopic, pellet and regrind exposed to relative humidity above 80% should be dried at 80 °C for 2 h before sheet extrusion to prevent moisture-induced pinholing at the die lip. Regrind inclusion in the sheet is kept below 30 wt%. Above this threshold, ASTM D638-14 break elongation and ASTM D1004 tear strength decrease enough to reduce pallet corner integrity under repeated forklift impact.

Secondary containment and electroplating-line liner fabrications use 3.0 mm HHM5502 sheet cut to sump geometry and hot-gas welded at 220 °C to 240 °C with 3 mm or 4 mm round welding rod extruded from the same resin. The upper processing temperature limit for welding is about 240 °C; above that, oxidized surfaces produce weak interface layers. Chemical compatibility is verified under ASTM D543-21 immersion in 30% sulfuric acid, 10% sodium hydroxide, and 5% sodium chloride at 23 °C and 60 °C for 30 d. HDPE of this density generally shows weight change below 1.0% in these inorganic media, but published data for HHM5502 in mixed acid-organic streams is limited and site-specific immersion coupons are required. The liner is continuously supported by a steel or concrete substrate. Unsupported spans are avoided because flexural creep under ASTM D2990 can produce stress whitening and eventual environmental stress cracking when aggressive wetting agents are present. Secondary containment structures are installed to meet EPA 40 CFR 264.193 capacity and chemical compatibility requirements, and seam integrity is checked using ASTM D6392 peel and shear tests plus ASTM D5820 vacuum-box leak testing. Incompatibilities include chlorinated solvents, 98% sulfuric acid, and aromatic hydrocarbons. Exposure to nonylphenol ethoxylate surfactants above trace concentrations can reduce ESCR in stressed HDPE, and such surfactants are excluded from liner cleaning protocols. The extrusion welding rod should not be reground more than one pass, because repeated thermal history narrows molecular weight distribution and melt viscosity, lowering weld toe ductility.

Corrugated Drainage Board Cores Under Heavy Vehicle Loads

In corrugated drainage board and geocomposite drain cores, HHM5502 is extruded on a 90 mm 33:1 single-screw corrugator with vacuum calibration at 0.06 MPa to 0.08 MPa and cooling water at 15 °C to 20 °C. The melt temperature at the die is held between 200 °C and 210 °C. Below 195 °C, the high-molecular-weight resin fails to fill the corrugator profile and produces fold-line cracks along the corrugation valleys. The finished board is used as a drainage core for landfill leak-detection layers, plaza deck drainage, and heavy vehicle load distribution under paved surfaces. Compressive strength is evaluated by ASTM D6364 short-term compression, but published compressive-creep data for HHM5502 in corrugated drainage board under sustained heavy vehicle load is limited, so long-term deflection is confirmed on a project basis using ASTM D2990. The high environmental stress crack resistance of HHM5502 under ASTM D1693-15 Condition B is the main selection criterion for buried drainage board exposed to wetting agents and leachate. The resin density of 0.955 g/cm³ and flexural modulus near 1,200 MPa provide crush resistance, but the product is not a replacement for a structural pavement layer. At corrugator speeds above 6 m/min, residual heat from the 20 mm profile can cause postforming distortion. Cooling water temperature must be raised no higher than 25 °C or the profile may stick to the corrugator blocks. Regrind from edge trim is reused at up to 15 wt% in the core layer. Higher levels are not advised because carbon black dispersion and compressive stiffness degrade.

Table 2. Comparative downstream processing parameters for HHM5502.