Celanese UHMW-PE 4022-6 is an ultra-high-molecular-weight polyethylene powder grade supplied for conversion by compression molding, ram extrusion, and specialty densification. The material is identified in supplier documentation as part of the GUR 4022 series, with a reported viscosity-average molar mass of approximately 4.4 × 10⁶ g/mol derived from dilute-solution viscometry in decalin at 135 °C under ISO 1628-3:2010. Density is typically 0.930–0.940 g/cm³ under ISO 1183-1:2019, and apparent bulk density measured by ISO 60:1977 generally falls between 0.40 g/cm³ and 0.50 g/cm³. The grade does not exhibit a conventional melt flow rate at 190 °C/2.16 kg because the chain length suppresses viscous flow; processing therefore differs fundamentally from lower-molecular-weight polyethylenes.

At the molecular level, polyethylene has an entanglement molar mass of approximately 1.2 × 10³ g/mol. For a chain of 4.4 × 10⁶ g/mol, this corresponds to roughly 3.7 × 10³ entanglement strands per molecule. The resulting zero-shear viscosity exceeds practical melt-processing limits, and the longest relaxation times are orders of magnitude above those of standard injection-molding grades. These properties are the source of both high toughness and the need for quasi-static consolidation processes.

Why Does 4022-6 Avoid Conventional Melt-Flow Rate Measurements?

The standard ISO 1133-1:2022 procedure conditions polymer at 190 °C under a 2.16 kg piston load. For a linear polyethylene with molar mass in the 10⁶ g/mol range, zero-shear viscosity exceeds 10⁸ Pa·s, and the specimen does not leave the capillary within the specified interval. High-load testing at 21.6 kg may force flow through shear-induced disentanglement, but the result is not a reliable processability index because it can coincide with thermo-oxidative changes at the test temperature. Consequently, 4022-6 is not processed by conventional single-screw extrusion, injection molding, or blow molding. It is limited to operations in which powder is heated and consolidated under pressure in a closed cavity or a heated ram barrel. This constraint separates UHMW-PE from standard HDPE, which is routinely processed at melt flow rates of 0.2–10 g/10 min under the same standard.

Powder morphology further influences process selection. Sieve analysis under ASTM D1921 typically places the median particle size (d50) of UHMW-PE powders in the 120–180 µm range. Narrow particle size distribution improves bed uniformity during compression molding, while broad or segregated fractions can produce density gradients and internal voids. The powder is not free-flowing in the same manner as spherical pelletized resins; hopper design for ram extrusion must account for bridging tendencies and inconsistent mass flow at low bulk density.

Compression molding of 4022-6 is carried out in hydraulic presses with platen parallelism controlled to 0.1 mm/m or better. The mold is charged, leveled without shear, and heated under contact pressure to 190–210 °C at the mold wall. Once the cavity reaches uniform temperature, the press is closed to 8–15 MPa and held long enough to eliminate powder particle boundaries; cooling is then conducted under pressure at a rate below 20 K/min. Inadequate peak-temperature dwell produces knit lines and particle boundaries that act as crack initiation sites. Excessive hold above 210 °C accelerates hydroperoxide formation and reduces elongation at break, so mold-wall thermocouples are used to control the heating cycle rather than relying on timer-based recipes alone.

Ram extrusion of rod, sheet, and profile stock uses a heated barrel and die with zone temperatures generally maintained in the 200–230 °C range and ram pressures of 20–40 MPa depending on cross-section and throughput. Published data for grade-specific ram extrusion settings are limited; converters typically establish the acceptable pressure-speed window by trial on a given machine. Pre-drying is not required at relative humidity below 60%. Powder stored in damp conditions is dried at 80 °C before mold charging to avoid steam-induced porosity.

UHMW-PE exhibits a thermal conductivity of approximately 0.4 W/(m·K) under ISO 22007-2:2008, higher than unfilled polyolefins but far below tool steels. For slab thicknesses above 50 mm, heating and cooling time is controlled by conductive heat transfer rather than press pressure or mold temperature setpoint. Cycle time in thick sections scales approximately with the square of wall thickness; doubling the part thickness can increase cycle time by a factor of approximately 4 under identical boundary conditions. This limits the practical thickness of compression-molded 4022-6 plates when cycle time is a production constraint.

Comparative Molecular Weight and Abrasion Performance Boundaries

Relative to standard high-density polyethylene (HDPE) with molar mass typically between 10⁵ g/mol and 5 × 10⁵ g/mol, 4022-6 has a much higher entanglement density. Under ISO 179-1:2010 Charpy impact testing at 23 °C, UHMW-PE specimens of this class commonly show no break, whereas notched HDPE values are typically reported in the 5–20 kJ/m² range. Tensile yield stress is not the decisive differentiator; the practical differences are elongation at break, impact response, and abrasive wear resistance. In three-body abrasive wear evaluated under ASTM G65-16 dry-sand rubber-wheel conditions, UHMW-PE grades show substantially lower volume loss than HDPE, but exact wear rates depend on sand type, wheel hardness, and normal load. Sliding wear against stainless steel evaluated by ASTM G99-17 pin-on-disc protocols commonly places the coefficient of friction of UHMW-PE in the 0.10–0.25 range, with increases at low speed, high roughness, or boundary-lubrication breakdown.

Within the Celanese GUR UHMW-PE range, 4022-6 is positioned at the lower-to-intermediate molecular weight segment relative to grades such as GUR 4150 and GUR 4170. Higher molecular weight grades develop greater abrasion resistance and toughness but demand longer molding cycles, higher consolidation pressures, and stricter thermal control. Lower molecular weight grades may process faster in thin sections or high-output ram extrusion at the expense of wear life. The selection of 4022-6 therefore represents a processability-wear balance rather than a maximum in any single property.

When 4022-6 Is Specified in Sliding-Wear and Impact Service

Component uses for 4022-6 include chain guides, wear strips, chute liners, star wheels, guide rails, and impact pads in materials-handling and food-processing equipment. These applications subject the polymer to sliding contact with metal or plastic countersurfaces, low-speed abrasive contact, and frequent mechanical shock. Moisture absorption under ISO 62:2008 is below 0.01%, which prevents the dimensional shift and friction variation observed in hygroscopic engineering thermoplastics such as polyamide PA66. Compared with polytetrafluoroethylene (PTFE), UHMW-PE is generally less chemically inert and has a lower continuous-use temperature limit near 80–100 °C, but it offers higher resistance to abrasive wear in many dry and slurry-type applications. The operational upper temperature is not governed by melting alone; creep under load increases rapidly above 60 °C, and load-bearing designs require time-dependent modulus data rather than short-term tensile values.

Under dry sliding, frictional heat input is the product of normal load, sliding speed, and coefficient of friction. For UHMW-PE, the pressure-velocity limit is lower than for filled engineering thermoplastics; localized surface temperature can exceed the bulk continuous-use limit even at moderate ambient temperature. Design calculations must therefore use measured or calculated contact temperature rather than bulk service temperature. At elevated sliding speed, lubrication or reduced contact pressure is required to avoid surface melting and transfer film breakdown. This constraint is relevant in high-speed conveyor guides and rotating wear pads, where short-duration frictional heating controls service life more than ambient thermal conditions.

In impact service, Charpy specimens of UHMW-PE do not break at 23 °C under ISO 179-1:2010. Ductility persists at cryogenic temperatures; standard published data report useful impact resistance at -196 °C, but grade-specific certification should be requested for cryogenic service. When the material is machined into components, carbide-tipped tools with positive rake angles and low cutting speeds prevent surface melting. Dimensional stability is limited by thermal expansion and stress relaxation; the coefficient of linear thermal expansion is typically 1.5 × 10⁻⁴ K⁻¹ to 2.0 × 10⁻⁴ K⁻¹ under ISO 11359-2:1999, approximately 10 times that of steel. Long wear strips therefore require slotted holes, expansion gaps, or preloaded spring systems.

In food-contact and packaging machinery, the polymer is often selected for low water absorption and resistance to impact rather than high continuous-use temperature. Wear plates in silos and hoppers operate under low sliding speeds and moderate loads; here the limiting failure mode is often not surface wear but slow creep at bolt holes and support points. Published data for 4022-6 in these specific large-part configurations is limited, so qualification should include creep testing under ISO 899-1:2017 at the intended service temperature and stress.

Compliance status for 4022-6 must be confirmed from the lot-specific certificate of analysis and the current supplier declaration. Typical virgin UHMW-PE grades in this molecular weight class are evaluated under FDA 21 CFR 177.1520 for olefin polymers in food-contact applications and under EU Regulation No 10/2011 for plastic materials intended for contact with food. Migration testing is performed according to EN 1186-1:2002 or equivalent national standards. The grade is not inherently flame-retardant, and continuous exposure to strong oxidizing acids, chlorinated hydrocarbons, or aromatic solvents at elevated temperature is outside the recommended service envelope. Ultraviolet exposure degrades unstabilized UHMW-PE; outdoor use requires carbon black or hindered-amine stabilization. Processing above 230 °C accelerates oxidative chain scission and should be avoided. Regrind addition in compression molding is generally limited to 20 wt% to preserve impact resistance, but the exact level must be validated against the part specification. Thermo-oxidative stability can also be screened by oxidation induction time under ISO 11357-6:2021; unstabilized UHMW-PE powders exhibit shorter induction times than stabilized molding grades, and the stabilization package should be matched to the service temperature.

Because published data for grade-specific chemical compatibility in mixed solvents is limited, qualification trials under ASTM D543-21 are required before use in aggressive media. The same reservation applies to hot-water or steam contact above 60 °C, where oxidation kinetics and mechanical load-bearing capacity must be evaluated together.