Mitsubishi Chemical Advanced Materials UHMW-PE 88 is an unfilled ultra-high-molecular-weight polyethylene stock-shape grade within the producer’s Polystone® M portfolio. The suffix 88 functions as an internal product code rather than an ISO or ASTM material designation. Where grade-specific certifications are not separately issued, the nearest published engineering baseline is the unfilled Polystone M UHMW-PE family. Representative density is 0.93–0.94 g/cm³ (ISO 1183-1); water absorption is below 0.01% (ISO 62). The resin belongs to the UHMW-PE class with a weight-average molecular weight typically above 3.1 × 10⁶ g/mol, whereas conventional HDPE grades are commonly supplied in the 2 × 10⁵ to 5 × 10⁵ g/mol range. This molecular-weight difference eliminates practical melt-flow measurement under ISO 1133-1 and governs the product’s abrasion resistance and impact response.

The tensile yield stress of approximately 22 MPa (ISO 527-2/1B/50) is relatively low compared with acetal and polyamide; selection on the basis of short-term strength alone will therefore misrepresent the grade’s function. The relevant properties in abrasive handling are the Charpy notched impact response reported as no break at 23 °C (ISO 179-1/1eA), the dry dynamic coefficient of friction against polished steel of 0.07–0.11, and the low moisture absorption that maintains dimensional stability in wet environments. The linear thermal expansion coefficient of 15–20 × 10⁻⁵ K⁻¹ (ISO 11359-2) is approximately one order of magnitude higher than steel, and thermal movement must be considered in any rigid mounting detail.

The molecular weight threshold above which UHMW-PE cannot be processed by conventional melt extrusion is commonly associated with a zero-shear viscosity exceeding 10⁸ Pa·s at 190 °C; the measured value for UHMW-PE 88 is not published by the producer, but the class behaviour is well established. In such entangled systems, the terminal relaxation time is several orders of magnitude longer than for HDPE, and the melt exhibits elastic slip at the die wall rather than homogeneous shear flow. Ram extrusion therefore operates at lower shear rates than screw extrusion and relies on frictional heating and pressure-driven sintering of the powder compact. For compression molding, the powder is consolidated above the crystalline melting point under high pressure and then cooled slowly to increase crystallinity and reduce internal stresses. Cooling rate affects the degree of crystallinity and therefore the final density and wear response; a slower cooling cycle generally produces higher lamellar thickness and better toughness, but excessive cycle times are commercially impractical. These process conditions explain why the property range for a given UHMW-PE grade is specified as a band rather than a single value.

How does UHMW-PE 88 compare with HDPE and PE1000 under sliding wear and impact?

Against HDPE, the principal difference is molecular weight and its effect on chain entanglement. UHMW-PE 88 is not melt-flow processable by screw extrusion or injection molding, while HDPE is. In notched impact testing, UHMW-PE stock shapes typically show no break at 23 °C under ISO 179-1/1eA, whereas HDPE commonly returns finite values of 5–15 kJ/m². In dry-sand rubber-wheel abrasion (ASTM G65) and sand-slurry wear tests, unfilled UHMW-PE stock shapes generally exhibit lower volume loss than HDPE and PE1000, although the exact ratio depends on particle size, water content, and test temperature. Published data for this specific configuration is limited; comparative purchasing should use producer test reports for the exact lot. The coefficient of friction against polished steel is similar across the polyethylene family, but UHMW-PE retains that value at higher bearing pressures because of higher entanglement density and lower creep under short-duration sliding.

Compared with PE1000, the distinction is narrower. PE1000 is a higher-density high-molecular-weight polyethylene with better rigidity and lower cost, but UHMW-PE 88 is generally specified where impact loading and abrasive wear are more severe. In hopper-liner service subject to high-velocity particle impingement, field observations on production-scale material-handling lines indicate that UHMW-PE liners sustain less edge cracking than PE1000, particularly at temperatures below 0 °C. The difference is not large in slow-moving, low-impact chutes; in such cases the lower cost of PE1000 may make it the preferred material. The specification writer should therefore link the material choice to impingement angle, particle velocity, and temperature cycling rather than to wear rate alone.

Stock-shape production for UHMW-PE 88 is typically performed by compression molding at melt temperatures of 200–220 °C and molding pressures above 5 MPa, followed by controlled cooling to reduce internal voids and orientation. Ram extrusion is used for rod and profile. The polymer is not processed on twin-screw extruders or injection molding machines because the zero-shear melt viscosity at 190 °C remains extremely high; conventional screw plastication is not applicable. Machining practice for UHMW-PE stock shapes requires carbide-tipped or polycrystalline diamond tooling with high clearance angles and low cutting forces. Saw speeds in the range of 1000–3000 m/min are common for circular saws, while band-saw speeds are reduced for thick sections. The material does not require pre-drying because water absorption is below 0.01%. However, frictional heat at the tool/workpiece interface can cause local melting; chip clearance and positive rake geometry are therefore more critical than cutting speed alone. Production machining shops report that surface smearing and burr formation increase when tooling is dull or when feed rates are too low, producing dimensional drift of more than 0.1 mm on long wear strips. These are general UHMW-PE fabrication boundaries, not grade-specific process settings for UHMW-PE 88.

Machined tolerances for UHMW-PE 88 should account for thermal equalization and stress relief. A rough-machined blank may release internal stress after a first pass, altering flatness; multiple passes with intermediate cooling are common for thick plates above 30 mm. The recommended procedure is to rough-cut, allow dimensional relaxation at 20 ± 2 °C, then finish-machine to final dimensions. Tolerances tighter than ±0.05 mm are difficult to maintain on large flat parts because of thermal expansion and the polymer’s compliance under clamping pressure. This is a general limitation of UHMW-PE stock shapes and applies to UHMW-PE 88 as an unfilled grade.

Thermal and chemical service boundaries for machined UHMW-PE 88 components

The crystalline melting point is 130–136 °C (ISO 11357-3). Continuous service is limited to 80 °C in lightly loaded or unloaded conditions; under sustained compressive load the practical ceiling is lower because creep accumulates above 40 °C. At cryogenic temperatures down to −200 °C, the unfilled grade retains high impact toughness, but thermal contraction and fitting clearance changes must be designed using the actual expansion curve from ISO 11359-2. The product is resistant to most dilute acids, alkalis, salt solutions, and polar solvents below 60 °C; it is incompatible with strong oxidizing acids, hot aromatic hydrocarbons, and chlorinated solvents at elevated temperature. Concentrated nitric acid above 40 % is not recommended. Environmental stress cracking may occur in certain surfactant and detergent packages. Outdoor exposure of natural UHMW-PE leads to UV embrittlement; black or UV-stabilised variants are required for long-term solar exposure.

Under continuous load, UHMW-PE 88 exhibits time-dependent creep. The short-term tensile modulus of 680 MPa (ISO 527-2) should not be used for bearing design; creep-modulus curves under ISO 899 show a rapid apparent modulus reduction at loads above 5 MPa. At 23 °C, a sustained compressive stress of 10 MPa may produce several percent strain within hours and continues over the service life. For bearing blocks, static bearing pressure should therefore be kept below about 3–5 MPa, while intermittent service can tolerate higher pressures. In bolted connections, torque relaxation occurs because the polymer creeps away from the clamped zone; spring washers or load-distributing plates are preferable. No intrinsic PV limit is published for UHMW-PE 88 specifically; the class is generally limited to 0.07–0.11 m/s sliding speed at low pressures unless external lubrication and heat removal are provided.

For food-contact use, natural unfilled UHMW-PE grades may comply with FDA 21 CFR 177.1520 and EU 10/2011 when the final article satisfies migration limits. Black or colored subgrades are generally not certified for direct food contact unless the producer’s certification explicitly includes them. Electrical and chemical compliance should be verified against the batch certificate; the unfilled natural grade typically contains no intentionally added RoHS-restricted substances. A compliance snapshot is shown below.

Incoming stock-shape quality is usually verified against density, tensile yield, elongation at break, and Shore D hardness. For critical wear applications, a hardness check alone is insufficient because Shore D is insensitive to molecular weight differences within the UHMW-PE class. The producer’s certificate of analysis should be supplemented by ASTM G65 dry-sand rubber-wheel testing or a slurry wear panel test for each new lot if the component operates near the wear limits. Batch-to-batch molecular-weight variations can shift wear performance without significantly changing density or hardness, so procurement contracts for chute liners and bearing strips often specify a maximum volume loss under defined abrasion conditions rather than resin properties alone. In the absence of a certified property set for UHMW-PE 88, the ASTM D4020 material classification provides the minimum tensile strength, elongation, and molecular-weight requirements for UHMW-PE shapes, and the producer’s technical datasheet for the Polystone M family supplies the baseline property envelope.

When UHMW-PE 88 replaces acetal or cast nylon in dry-running conveyor components

UHMW-PE 88 is specified in place of acetal homopolymer or cast polyamide 6 when moisture absorption, impact toughness, and low friction under wet or particulate-laden sliding are more important than compressive strength and upper service temperature. POM-H typically shows a yield stress of 60–70 MPa (ISO 527-2), and moisture-conditioned cast PA6 commonly falls between 70 and 80 MPa. UHMW-PE 88 yields at approximately 22 MPa; it is therefore not a direct substitute for highly loaded structural gears or large bushings. In low-pressure dry-running applications, the difference narrows because wear rate and stick-slip behaviour often control service life rather than short-term tensile yield. The unfilled grade also has a lower density of 0.93–0.94 g/cm³ compared with POM-H at 1.41 g/cm³ and cast nylon at 1.15 g/cm³, reducing inertial loads on high-speed conveyor components. In food-processing environments, UHMW-PE 88 is often preferred over acetal because it is not subject to hot-water hydrolysis and can be machined without moisture-related dimensional shifts.

Against PTFE, UHMW-PE 88 exhibits lower creep under load, higher abrasion resistance in particulate sliding, and lower material cost. PTFE retains a lower coefficient of friction and a much higher continuous use temperature, above 260 °C. Against cross-linked UHMW-PE, the unfilled grade has lower wear resistance in artificial joint simulators, but cross-linked grades are not standard industrial stock shapes for liners and are outside this product specification.

Typical installations include chain guide rails and wear strips in bottling and packaging lines, star wheels and screw flights in food transport, bearing blocks in agricultural equipment, and chute or hopper liners in dry-bulk material handling. In mass-flow hopper design, UHMW-PE 88 liners are installed with slotted holes or expansion gaps because thermal movement of 1.5–2.0 mm/m per 10 K temperature rise is typical. For hopper liners exceeding 2 m in length, butt joints should include expansion clearance. In slurry handling, the grade is used for scraper blades and return idler covers, but it is not recommended for direct contact with sharp angular particles at velocities above 6 m/s unless the producer’s wear test data supports the specific impact angle. In marine fender pad service, the Charpy no-break response at 23 °C and the low friction against water-lubricated steel control installation. The main field failure modes reported for UHMW-PE wear components are not catastrophic fracture but creep, thermal expansion buckling, and edge debonding from rigid backing plates. These are managed by mechanical fastening rather than adhesive bonding, because the low surface energy of UHMW-PE inhibits reliable adhesion without flame, plasma, or corona treatment.

Published wear-rate data for UHMW-PE 88 under high-velocity slurry impingement are limited; the designer should request ASTM G65 or slurry-loop results for the specific lot when the installation operates near the 6 m/s boundary. The grade is available as compression-molded sheet, ram-extruded rod, and machined profiles in standard stock-shape dimensions; custom fabricated parts are produced to the user’s drawings. Because the suffix 88 is an internal product code, procurement specifications should reference the producer’s full material code and the applicable ASTM D4020 classification to avoid substitution with lower-molecular-weight PE grades.