Celanese UHMW-PE 5113, also designated GUR 5113 in Celanese technical documentation, is a virgin ultra-high-molecular-weight polyethylene powder supplied for ram extrusion and compression moulding of stock shapes and machined wear components. The material falls within the PE-UHMW classification described in ISO 11542-1 because its viscosity number in decalin at 135 °C exceeds 2000 mL/g and because it does not produce a measurable melt flow index under ISO 1133-1:2022. Published datasheet values for the grade include an average molecular weight of approximately 3.9 × 10⁶ g/mol by viscosity correlation to ISO 1628-3 or ASTM D4020, a density of 0.93 g/cm³ under ISO 1183-1, and a crystalline melting peak between 133 °C and 136 °C under ISO 11357-3. These values are used for incoming inspection because the resin has no conventional melt-processing fingerprint such as a stable MFR value.

The powder is not a drop-in replacement for HDPE pipe or film grades. The molecular architecture creates a sinterable compact that fuses above the crystalline melting range without forming a low-viscosity melt. This distinction is central to the product specification. The table below summarizes characteristic values reported for GUR 5113 and the standards used to determine them. The values are typical engineering references and are not lot-release guarantees; the supplier certificate of analysis remains the controlling document for a specific lot.

Specimen preparation influences the reported mechanical values. Tensile bars machined from a fully fused compression-moulded sheet may show yield stress near 21 MPa under ISO 527-2, while under-sintered or porous sections can fail at lower values. For this reason, incoming-material testing on powder samples is supplemented by destructive testing on sintered plaques or extruded sections to confirm fusion quality rather than relying on resin viscosity alone.

Powder morphology is part of the specification because PE-UHMW cannot be melt-pelletized without degrading its high molecular weight. The resin is therefore delivered as a reactor powder with a controlled particle-size distribution. Bulk density under ISO 60 or ASTM D1895 is used to size hopper and mould cavities. Sieve fractions are typically reported under ASTM D1921; the acceptable band is supplier-specific. Excess fines can reduce cold-compaction density and create dust-handling issues, while coarse particles can increase fusion time and lower the density of sintered cores.

The molecular weight of 3.9 × 10⁶ g/mol implies reptation times that are many orders of magnitude longer than those of conventional high-density polyethylene. This is why sintering relies on intimate particle contact and temperatures above the crystalline melting point. Under the low-shear conditions of compression moulding, melt viscosity can exceed 10⁸ Pa·s, although capillary measurement is not well defined. The practical outcome is that the resin does not flow to fill a mould; it must be compacted into final geometry before heating.

Oxidative stability is evaluated by oxidation induction temperature or time using ISO 11357-6 or ASTM D3895. The natural grade’s stabilizer package is designed for processing rather than long-term high-temperature oxidative service. Prolonged exposure at 120 °C in air degrades the polymer; actual lifetime is affected by thickness, antioxidant concentration, and fluid media. Oxidation induction tests are run on sintered sheet rather than powder to capture the thermal history introduced by moulding.

What Limits the Processing Window of This PE-UHMW Grade?

The processing window is defined by two competing boundaries: the crystalline melting point of the powder and the onset of thermo-oxidative degradation. Ram extrusion and compression moulding equipment must hold the stock above 133 °C long enough for inter-particle diffusion, but heating above 250 °C for prolonged periods causes chain scission, discoloration, and surface oxidation. Published data for this specific configuration is limited, but industrial practice for PE-UHMW positions the heated section between 200 °C and 230 °C. The exact setpoint is adjusted by profile cross-section and ram cycle time. A heating deviation of more than ±5 °C across the die face can create central porosity or uneven skin formation in thick sections because the outer layer may fuse before the core reaches the sintering temperature.

Moisture is not a primary plasticization issue as in polyamides, but surface moisture trapped in the powder can produce voids and steam marks. When storage humidity exceeds 60 % RH, pre-drying at 80 °C for 2 hours in an air-circulating drier is a common preventive measure. The powder should not be dried at temperatures approaching the melting range because particle agglomeration can occur.

Conveying air and hopper feeder settings must be controlled to avoid fines segregation. Volumetric and gravimetric feeders used for powder feeding can display apparent density drift when powder particle-size distribution is not consistent; this is a known batch-to-batch variance factor on production lines. Sieve analysis under ASTM D1921 or equivalent particle-size methods may be specified between supplier and processor to control the fines fraction.

Thermal and Rheological Parameters for Sintering-Grade Powder

Because GUR 5113 has no measurable steady-shear melt flow under standard capillary rheometry conditions, process behaviour is evaluated through sintering and compaction parameters rather than MFR. The powder is charged into a mould or ram extruder, compacted cold, and then passed through a heated die or heated press cycle. The compaction phase is typically conducted at 5–10 MPa to remove void volume; the sintering phase uses 10–20 MPa on compression presses and a die wall temperature of 200–230 °C in ram extruders. The molten surface of each particle must undergo reptation across the grain boundary; molecular weight and viscosity number are direct predictors of the time required for this fusion.

The rate-limiting step is not pellet melting but inter-particle chain diffusion. Thick sections require a heat-soak time that increases with wall thickness. Operators commonly ramp the cooling under pressure at 5–15 K/min until the part is below 70 °C to reduce shrinkage voids and warpage. If cooling is too rapid, residual internal stresses can be released during machining, causing dimensional drift in finished components.

On a production-scale ram extruder with a barrel diameter between 60 mm and 200 mm, the reciprocating ram compacts powder into the heated die block in discrete strokes. A 90 mm ram can require a pressing force in excess of 60 kN at compaction pressures near 10 MPa depending on the die section. The die land length is selected to provide residence time at the sintering temperature; profiles with wall thickness above 25 mm may require multiple heating zones or lower haul-off speeds. A common failure mode is stroke-boundary lamination when the die temperature is too low or the stroke frequency is too high, resulting in incomplete fusion at the interface between successive powder charges. The condition is detected by sectioning the extruded profile and observing faint horizontal laminar lines near the centre. Adjustments to die temperature and stroke dwell time are required rather than increases in ram pressure alone.

Compression moulding of thick sheets follows a similar logic. Platen temperatures are held at 200–220 °C, and pressure is maintained during cooling. The part geometry and mould mass determine cycle time; published data for this specific configuration is limited, and each mould requires thermal mapping to verify that the core has exceeded 133 °C for an adequate time. Thermocouple placement at the core of a tool during commissioning is standard practice. Defects include centre-plane porosity, shrinkage voids at thickness changes, and vacuum voids from entrapped air. Vacuum-assisted moulds may be used to remove air before full compaction. Press pressure is held during cooling to maintain contact between the mould surface and the polymer; if pressure is released too early, the part can delaminate internally even though the outer surface appears fused.

Machining of GUR 5113 stock shapes requires sharp tools with high clearance angles because the material is ductile and can deflect away from the cutting edge. Conventional milling, sawing, and planing are used. Stress-relieving anneal after rough machining is sometimes performed at 70–80 °C for 2–4 hours to reduce dimensional change during final finishing. Actual cycles depend on part size and residual stress from the extruded or moulded stock.

When GUR 5113 Is Evaluated Against Alternative PE-UHMW Grades

Within the Celanese GUR UHMW-PE portfolio, grade differences are expressed primarily in molecular weight, particle-size distribution, and additive packages. GUR 5113 is positioned as a sinterable powder for ram extrusion and thick-section compression moulding where uniform fusion and machinability are required. Higher-molecular-weight grades such as GUR 4120 and GUR 4150, when compared under the same sintering conditions, tend to require longer heat history and may exhibit higher resistance to abrasive wear in some slurry tests, but they can be more difficult to compact in high-output ram extrusion lines. The exact comparative ranking in a specific test depends on molecular weight distribution, specimen preparation, and test geometry; published data for the specific comparative set is limited, and end-use qualification is required.

Compared with conventional HDPE, the difference is not merely incremental. HDPE grades intended for pipe or sheet extrusion exhibit measurable melt flow under ISO 1133-1:2022, typically in the range of 0.1–1.2 g/10 min at 190 °C and 2.16 kg depending on the grade. GUR 5113 does not flow under these conditions. The practical consequence is that injection moulding and conventional single-screw plastication are outside the normal processing envelope for GUR 5113. Components are produced as extruded profiles or compression-moulded sheets and then machined into finished parts.

Different product grades may include processing stabilizers, calcium stearate as an acid scavenger, or other surface treatments. The presence of these additives changes the oxidation induction time and the friction response during solid-state ram extrusion. Processors should not substitute GUR 5113 with another PE-UHMW grade solely on the basis of molecular weight because particle size distribution and additive package also influence the sintering cycle and lot-to-lot fusion.

Friction and wear data are generated with pin-on-disc or block-on-ring configurations. The dynamic coefficient of friction for PE-UHMW on polished steel under dry conditions is commonly reported in the range 0.10–0.20 using ASTM D1894; the value rises with surface roughness, temperature, and contamination. Abrasion resistance is often tested by sand-slurry circulation in accordance with ISO 15527 or by rotating drum methods; the results are comparative rather than absolute. Published data for the specific abrasive ranking of GUR 5113 against filled grades are limited; qualification on the actual conveyor or chute geometry is required.

End-use applications for GUR 5113 include chain guides, wear strips, star wheels, guide rails, chute liners, suction box covers, and other machined components in packaging, food-processing, and material-handling machinery. In these applications, the material is selected because the sintered stock shape can be machined to close tolerances and because the surface provides low sliding resistance without external lubrication. Designers should not infer suitability from hardness or tensile data alone; wear tests such as the sand-slurry method in ISO 15527 or field trials are used to confirm performance under real particle-laden or cyclic load conditions.

Chemical resistance follows the general behaviour of semicrystalline polyethylene. The material resists many aqueous salt solutions, alkalis, and dilute acids at ambient temperature, but aromatic hydrocarbons, chlorinated solvents, and strongly oxidizing acids can cause swelling or stress cracking, particularly under load. Chemical exposure should be evaluated under ISO 175 using the actual service fluid and temperature, not inferred from a general resistance table. Continuous service under mechanical load in air is typically limited to 80 °C because of oxidative ageing and creep; intermittent excursions to 100 °C may be tolerated for short periods but are not a design basis without creep and oxidative-induction-time testing under ISO 11357-6.

The natural material has limited UV resistance; outdoor applications require a UV-stabilized variant or a carbon-black masterbatch suitably dispersed during the sintering stage. Attempts to incorporate high levels of inorganic fillers into the fine powder can reduce inter-particle fusion and create machinability problems. If wear-resistant fillers or colourants are required, the suitability of the additive package for PE-UHMW sintering must be verified on the production line, because laboratory melt-blending does not replicate the powder sintering process.

Regulatory Assessments Depend on Supplier-Lot Documentation

When the machined parts are intended for incidental food contact, the resin may be evaluated under FDA 21 CFR 177.1520 and EU Regulation 10/2011 by the supplier. Compliance is lot- and formulation-specific and should be confirmed from the current supplier statement rather than assumed from generic PE-UHMW literature. The natural grade does not contain intentionally added heavy-metal heat stabilizers or plasticizers; therefore RoHS 2011/65/EU restrictions for lead, cadmium, mercury, and hexavalent chromium are not typically relevant to the base resin, but supplied documentation must be checked for packaging and processing aids.

Under REACH 1907/2006, the supplier is required to communicate SVHC content above 0.1 % w/w in the article as supplied. Processors should maintain the safety data sheet and the technical data sheet revision history because changes in additive stabilisation or powder surface treatment can alter sintered colour and ageing resistance without changing the base density or molecular weight.

Batch-to-batch consistency is documented by the supplier through viscosity number, density, particle-size distribution, and residual moisture. Processors that cannot access full blend data may encounter variable fusion times and machined-part warpage. A practical incoming-inspection plan therefore combines the supplier certificate of analysis with periodic compression-moulding trials and profilometer or density checks on sintered sheet cores.