Celanese UHMW-PE 4523, supplied as GUR 4523, is a virgin ultra-high-molecular-weight polyethylene powder intended for compression moulding, ram extrusion, and sintered porous-part production. The grade has a viscosimetric average molar mass of 9.2 × 10⁶ g/mol when evaluated under ISO 1628-3; a fully consolidated plaque density of 0.930 g/cm³ under ISO 1183; and a powder bulk density of approximately 0.43 g/cm³ under ISO 60. Melt mass-flow rate is not applicable as a useful release parameter because the high entanglement density suppresses measurable flow under ISO 1133-1:2022. The product is used for wear strips, chain guides, food-contact conveyor components, pump wear plates, filtration support plates, and sintered porous bodies requiring low friction, impact tolerance, and abrasive-wear resistance. The grade differs from lower-molar-mass UHMW-PE products primarily through slower chain diffusion during fusion, longer pressure-holding requirements, and higher resistance to abrasive loss in fully consolidated stock. In stock-shape production, the absence of measurable melt flow means that processing equipment must be designed for pressure-driven consolidation rather than conventional screw transport.

How Does GUR 4523 Compare with Lower-Molar-Mass UHMW-PE Grades in the Same Portfolio?

Relative to GUR 4022 and GUR 4120, GUR 4523 has a higher molar mass. The practical difference is not a large shift in static density or Shore D hardness; it is expressed in the temperature-time integral required for particle fusion, in the lower self-diffusion coefficient of the polymer chains, and in the greater resistance to sand-slurry abrasive loss after full consolidation. In compression moulding of 20 mm sheet, GUR 4523 typically requires a moulding temperature of 200 °C to 240 °C and a controlled cooling rate below 10 K/min through the crystallisation range. Lower-molar-mass grades may tolerate faster cooling because the shorter chains can reorganise more readily before the bulk solidifies. Failure to maintain this cooling profile in GUR 4523 produces density gradients that are not visible on the surface but can reduce double-notched Charpy impact values under ISO 11542-2. Published data comparing the exact output loss of GUR 4523 with GUR 4120 on a specific ram-extruder barrel diameter is limited; the output reduction is equipment-dependent and must be established through start-up trials on the target line. The selection boundary is therefore not a universal molecular-weight number, but a balance between end-use wear life and the fabricator’s ability to hold the required fusion and cooling conditions.

On production-scale ram-extrusion lines processing GUR 4523, the absence of screw-generated mixing places the entire thermal burden on barrel wall conduction and frictional work at the die entry. Barrel temperatures are normally maintained between 200 °C and 240 °C, with the die temperature set near the upper limit to reduce wall friction. Charge weight, axial pressure, pulse frequency, and cooling water temperature are controlled to generate a continuous fused body across successive powder charges. A recurring failure mode on line is the appearance of transverse knit lines at the charge interface when the barrel temperature drops below the fusion range or when bulk powder moisture exceeds approximately 0.1 wt%. In high-humidity production environments above 60% relative humidity, pre-drying at 80 °C for 4 h in a dry-air hopper is required; residual moisture converts to steam during the pressure pulse, leaving longitudinal microvoids that lower notched impact strength and accelerate abrasive wear. Because the grade has no measurable shear-thinning melt plateau, conventional extrusion with a rotating screw is not applicable. The material must be consolidated by axial compression, not by viscous drag. Cold axial compression of the powder preform to approximately 90% of fully consolidated density is commonly employed before final thermal consolidation, with cold compaction pressures in the 20 MPa to 50 MPa range to improve heat transfer into the core.

The high molar mass of GUR 4523 also reduces the critical shear rate for melt fracture; in conventional extrusion, this would appear as gross melt fracture at very low output. Because the product is not processed by screw extrusion, the practical constraint appears instead as a maximum axial pressure at the ram face. Above the pressure limit, the powder can undergo shear-induced heating at the die wall and localised oxidation, creating brownish flow marks in the extrudate. The maximum pressure is machine-specific and depends on barrel diameter, die land length, and temperature set-point; published data for this specific configuration is limited, and the limit must be established on the target production line.

During compression moulding of GUR 4523, powder is loaded into a multi-zone heated platen press and consolidated under pressure before the core reaches the crystallite melting range. Platen temperatures of 220 °C with soak times of 20 min to 30 min per 20 mm of cavity depth are used in some conversion operations, but the required soak time increases with cavity depth and powder charge size. Consolidation pressure is typically held between 5 MPa and 15 MPa on the projected part area. Insufficient pressure during the first 10 min of heating produces surface porosity and edge defects. The part is then cooled in the press under pressure until the core temperature falls below 100 °C; early demoulding can introduce warpage because the long entangled chains have slow stress relaxation kinetics. Mould release lines, venting grooves, and powder preheating must be accounted for in tooling design because the material does not flow into thin sections. For sections thicker than about 100 mm, published data for GUR 4523-specific core cooling profiles is limited; process development should include thermocouple-instrumented plaques to verify the core temperature before demoulding.

The rate-limiting step in particle fusion for GUR 4523 is not the melting of crystallites but the interdiffusion of partially disentangled chains across the original powder particle boundaries. Because self-diffusion scales inversely with molar mass, the diffusion distance achieved during a given holding time is lower than in GUR 4022 or GUR 4120. In practice, this means that the same nominal melt temperature produces a lower degree of interfacial healing in GUR 4523 unless the holding time is extended. Equipment with high platen temperature overshoot should be avoided because oxidative surface degradation begins at the uppermost temperature boundary before the core achieves complete healing.

Wear, Impact, and Sliding-Friction Data Under Standardised UHMW-PE Test Protocols

The following table records typical physical property values for GUR 4523 as reported in current Celanese technical literature. These values are not guaranteed minimums and should be confirmed against the certificate of analysis for a specific lot. The property combination is dominated by the high molar mass: double-notched Charpy impact testing according to ISO 11542-2 frequently reports a no-break result under the standard impact energy, while tensile yield stress remains near 20 MPa under ISO 527-2. Sliding-friction performance is strongly dependent on counterface roughness, normal pressure, sliding velocity, and surface transfer-film formation. On polished steel counterfaces with arithmetic mean roughness below 0.1 µm, the dry coefficient of friction can fall below 0.2, but the value must be verified by the end user under the actual load-speed matrix. Abrasion resistance in sand-slurry testing is higher than for lower-molar-mass virgin UHMW-PE grades, but the magnitude varies with sand type, impingement angle, and particle sharpness. No single abrasion value is therefore specified without the exact test apparatus description.

The tensile modulus of approximately 680 MPa under ISO 527-2 and the Shore D hardness value in the table indicate that GUR 4523 remains a ductile, low-modulus polymer. The mechanical response is time-dependent; creep tests under ISO 899-1 should be included for structural design where sustained static loads exceed approximately 5 MPa. The design stress for continuously loaded guide rails and wear strips should be derived from creep-rupture data at the service temperature, not from short-term tensile yield. The low hardness relative to steel means that third-body debris can embed into the polymer surface if the counterface is not maintained; embedded grit then accelerates abrasive wear of both the polymer and the metal track.

Regulatory status for GUR 4523 follows the UHMW-PE product family. The grade is typically supported for compliance with FDA 21 CFR 177.1520 for olefin polymers in food-contact applications and with European Commission Regulation EU 10/2011 under defined migration-testing conditions. REACH registration under EC 1907/2006 and RoHS Directive 2011/65/EU are normally documented in the manufacturer’s regulatory data sheet. These clearances are use-specific and do not automatically cover finished food-contact articles; the fabricator must verify that processing aids, colourants, welding rods, and secondary machining operations do not alter the migration profile. Chemical resistance is generally high in dilute acids, alkalis, and polar solvents, but the grade is not recommended for service with strong oxidising acids at elevated temperature, aromatic hydrocarbons under stress, or chlorinated solvents in deep-section parts where environmental stress cracking may develop. Continuous service temperature is limited by oxidative degradation; short-term excursions above 80 °C are possible, but long-term exposure above this boundary requires ageing validation under the specific chemical and mechanical load. Ultraviolet exposure can embrittle natural UHMW-PE unless carbon black or a suitable UV stabiliser is incorporated at the compounding stage.

For purchase specifications, GUR 4523 can be described under the classification systems of ASTM D4020 for PE-UHMW moulding and extrusion materials or ISO 21304-1. These standards define cell classifications for density, viscosity-related properties, tensile strength, and elongation, allowing the grade to be specified without relying on trade-name ambiguity. Procurement documents should demand a certificate of analysis that includes lot-specific molar mass, powder particle-size distribution, and moisture content, because these variables affect fusion behaviour more than a single nominal density value.

When Thin Cross-Sections and Higher Output Rates Become the Controlling Variables

GUR 4523 is not the default choice when wall thickness falls below approximately 5 mm or when annual stock-shape output per line must exceed the capability of a single ram extruder. In thin sections, frictional heat dissipates too rapidly, and charge interfaces may freeze before molecular interdiffusion is complete. The resulting weld lines are not always visible in translucent thin sheet until the part is subjected to flexural fatigue or double-notched impact loading. For such applications, lower-molar-mass grades with faster fusion kinetics are usually specified. Similarly, sintered porous parts made from GUR 4523 require a longer furnace dwell than lower-molar-mass grades because the larger molecules resist viscous coalescence at the sintering plateau. The bottleneck is not the melting point, which remains near 133 °C by differential scanning calorimetry, but the time required for interface elimination at the sintering temperature. Published data for the specific pore-size distribution of GUR 4523 sintered plaques is limited, so bench-scale sintering trials are necessary to confirm bubble-point pressure and porosity targets.

Suitable stock-shape applications for GUR 4523 include pump wear plates and impellers handling abrasive slurries, chain-rail profiles on bottling and packaging conveyors, guide rails for food-processing machinery, marine fender pads, and components in bulk solids handling where metallic contact surfaces cause unacceptable noise or wear. The grade is also used in compressed-skive filter sheets and porous distributor plates. In these applications, replacement of lower-molar-mass UHMW-PE with GUR 4523 is justified only when the service-life extension offsets the lower processing throughput and longer thermal history. The user should compare the total cost per installed part, not the powder price per kilogram. Selection is therefore dominated by the end-use specific load, sliding speed, food-contact requirement, and the fabricator’s ability to hold fusion temperature and cooling rate within the required limits.