In wet-process lithium-ion battery separator production, SUNFINE UH981 powder is used as a melt-strength modifier in a high-density polyethylene/paraffin oil compound. The compound is prepared on a co-rotating twin-screw extruder with L/D not less than 48 and a vacuum devolatilisation stage before slot-die casting. Because UHMWPE does not exhibit measurable melt flow under ISO 1133-1:2022, the blend is processed at barrel set points between 180°C and 240°C, with melt temperature measured at the die lip by an infrared pyrometer. At addition levels below 10 wt%, UH981 raises low-shear elongational viscosity and suppresses film neck-in during cast-film orientation. Above 15 wt%, undissolved gel particles can cause streaking and thickness variation, so the practical boundary is set by post-extraction film inspection under transmitted light. The die lip gap is typically set between 0.8 mm and 1.5 mm before orientation, and cast roll temperature is adjusted so that the oil-rich phase separates without premature pore collapse.

Post-extraction pore structure is fixed by biaxial stretching after solvent removal. The presence of UH981 creates elongated tie chains that transmit stress during transverse-direction drawing. Puncture strength is measured according to ASTM F1306-19; a separator containing a UHMWPE-modified layer typically shows a puncture force shift that depends on basis weight and draw ratio. The upper processing temperature for UH981 is bounded by thermo-oxidative degradation onset, which appears as an increase in carbonyl index at 1715 cm⁻¹ in FTIR after prolonged residence. If the line stops for more than 15 min, the compound in the extruder must be purged with lower-viscosity polyethylene to avoid gel build-up. Precompounding of UH981 is performed under nitrogen blanketing where prolonged exposure to oxygen above 120°C is possible. Condensation on cold powder can introduce surface water; therefore, indoor storage below 60% relative humidity is recommended before hopper loading.

Why Does UH981 Suppress Melt Fracture in High-Draw Gel Fibre Extrusion?

In gel spinning of ultra-high-molecular-weight polyethylene filament, SUNFINE UH981 is dispersed in decalin or in a paraffin oil system at solids loadings between 2 wt% and 10 wt%. The suspension is converted to a homogenous solution in a jacketed vessel under nitrogen, using a high-torque agitator that maintains 50–150 rpm. The spin solution is extruded through a multi-hole spinneret, quenched in water, and drawn to total draw ratios exceeding 60:1. The final fibre reaches breaking tenacity above 2.5 GPa when tested according to ISO 2062 or ASTM D885. The role of UH981 is to supply a high entanglement molecular weight so that the gel network can survive extension without fracture. If the solution is under-extended, residual solvent causes fusion during subsequent hot drawing; if over-extended, surface fibrillation appears at the spinneret exit. Spin packs are typically fitted with sintered metal filters of 10–20 µm absolute rating to trap undissolved gels.

Chain entanglement in UHMWPE is governed by the number of entanglements per chain. UH981’s high molar mass increases this value, but the gel-spinning process reduces the entanglement density through solvent dilution. Too high entanglement density results in melt-like elastic stress during spinning, leading to die-face gel build-up and draw resonance. Too low entanglement density, caused by over-dilution, reduces maximum achievable draw ratio because chain extension cannot be transmitted across the crystallising gel. The practical optimum is determined by measuring solution Deborah number in a capillary rheometer. Batch-to-batch differences in particle size distribution can shift the dissolution temperature by several kelvin; therefore, the dissolution vessel temperature is held within ±2°C after initial swelling. Residual solvent is removed in heated draw zones, and recovered solvent moisture must stay below 100 ppm. Published data for UH981-specific draw ratio ceilings in a given spinneret geometry is limited; validation must be performed on the target line.

Ram extrusion of UH981 solid round rod and profile for wear pads uses a reciprocating hydraulic ram with a heated die land rather than a rotating screw. The powder is compacted in a feed hopper, transported by a barrel piston, and sintered at wall temperatures between 200°C and 230°C. During sintering, the compacted powder forms a continuous body through interparticle neck growth. Density after die-land fusion is measured by ISO 1183-1 and should exceed 0.930 g/cm³ for mechanically stable stock. Die-land back pressure in ram extrusion often ranges from 8 MPa to 25 MPa, depending on profile cross-section and die temperature. Because no melt mixing occurs, inconsistencies in powder bulk density can cause axial density bands in the extrudate. Bulk density of the incoming UH981 powder is therefore checked by ASTM D1895 Method A or an equivalent Scott volumeter. The production line must avoid sudden die temperature changes greater than 5°C per 10 min because the rod can develop internal shrinkage voids.

Ram-extruded UHMWPE is used for chain guides, wear strips, and liner blocks in conveyor and bottling plants. The key mechanical requirement is resistance of the machined part to abrasive sliding under low-speed, high-load contact. This property is evaluated under ISO 15527, which covers compression-moulded and extruded UHMWPE plates and defines wear-rate classes. When UH981 is ram-extruded, the absence of screw-induced shear preserves the ultra-high molar mass, so sand-slurry wear rates track with the inverse of molecular weight. The limitation is that profile tolerance is controlled by downstream machining, not by die swell. Machining requires carbide-tipped tools with positive rake angles and low cutting speeds; high cutting temperatures can generate surface smear and local melting. Cutting without coolant permits the swarf to wrap around the tool, so water-cooled or air-blast setups are used. Oxidative degradation during ram extrusion is checked by measuring yellowness index on the rod surface; a value above 5 on a 100 mm thick section indicates improper temperature control.

Compression-Moulded Sheet for Medical-Grade Bearing and Industrial Liner Stock

Compression moulding of SUNFINE UH981 for orthopaedic sheet and industrial liner plates is performed on hydraulic presses with daylight platen parallelism below 0.1 mm/m. The powder is filled into a female mould at a predetermined weight to control final thickness after sintering. The press applies 5–10 MPa while the mould is heated to 200–220°C; holding time depends on part thickness, with a common rule of 10 min per centimetre of thickness. Cooling is then performed under pressure to reduce void formation and warpage. The moulded sheet is tested for tensile yield strength per ISO 527-3 or ASTM D638-14, and for double-notched impact strength per ISO 21304-2. For implantable grades, the material must meet the oxidation index and residual free radical requirements described in ISO 5834-2. If UH981 is intended for medical use, the processor must verify traceability, packaging, and biological evaluation under ISO 10993-1 before component release. Industrial UHMWPE liners do not require that pathway but typically require a certificate of conformity to ISO 11542-1.

Compression-moulded UHMWPE sheet is machined into acetabular cup liners or into chute and hopper liners for bulk solids. In orthopaedic bearing applications, oxidative stability is critical because gamma sterilisation can generate free radicals. If the grade is not stabilized with vitamin E or thermal annealing, oxidation can reduce toughness over time; the relevant methods are described in ISO 5834-3, which specifies accelerated ageing and oxidation index measurement. For industrial liners, the operational boundary is tied to the pressure–velocity limit. UHMWPE does not suit high-speed dry sliding above 1 m/s because frictional heating lowers hardness. In such cases, the bearing must be lubricated or the mating surface must be changed. Avoid contact with strong oxidising acids at elevated temperature because chain scission can reduce molecular weight at the wear surface. The mould must be purged with nitrogen if temperatures above 240°C are used for any reason to suppress oxidative gel formation.

Sintered UHMWPE filter tubes and porous sheets made from UH981 begin as a powder bed compacted in a male-female tool set to achieve interconnected porosity. The particle size distribution of the raw powder controls pore size after sintering. Sintering temperature in a convection or infrared oven is maintained within ±5°C because the difference between particle surface fusion and powder collapse is narrow. Porosity is measured by mercury intrusion porosimetry or by the water absorption method in ASTM D570. Porous UHMWPE is installed in wastewater aeration diffusers, laboratory filter plates, and suction box covers in paper machines. The selected pore size range determines air-permeability and dust retention. A sintered body with 30–40 vol% porosity can pass air while excluding particles above the mean pore diameter. During operation, the material resists hydrolysis and biological fouling, but the continuous service temperature should remain below 80°C under wet load to avoid creep.

Fabrication of sintered UHMWPE components requires a pressing schedule that avoids premature densification. The powder is first compressed at low pressure to set the pore network, then heated without additional mechanical load so that interparticle necks form. This is different from compression moulding, where full densification is the target. If the same tool is used for both processes, the clearance gap must be reset because porous parts require a final thickness that is not governed by hot-flow densification. Pore size distribution is validated by the bubble point method using ASTM F316. The raw powder must be protected from airborne fines and high relative humidity; moisture from hygroscopic additives can create steam pockets during sintering, which enlarge pores and reduce bubble point. The oven exhaust must remove trace volatiles to prevent surface skinning; a nitrogen purge of 2–5 m³/h per cubic metre of oven volume is typical for closed ovens.

When Dry Sliding Contact in Food-Processing Conveyors Eliminates External Lubrication

In dry food-processing conveyor tracks, SUNFINE UH981 is specified where the bearing surface cannot be lubricated. The polymer is machined into guide rails that contact stainless steel chains under intermittent loads. The relevant material requirement is not tensile strength but the combination of low friction coefficient and abrasion resistance under particulate contamination. Dynamic coefficient of friction against polished stainless steel is measured by ASTM D1894, with typical values for UHMWPE below 0.25 at low speed. The material’s food-contact status is covered by FDA 21 CFR 177.1520 for olefin polymers, provided the final component meets the extractables limits for the intended food type and temperature. In the EU, compliance must be verified under Regulation (EU) 10/2011 and its amendments, including overall migration limits. Repeated washdown with alkaline detergents at 60°C is acceptable, but strong oxidising sanitisers above 80°C can increase surface oxidation rate.

Machining of UH981 into food-contact profiles uses water-cooled carbide tools. Thermal expansion during machining must be considered; UHMWPE has a linear coefficient of thermal expansion near 1.5×10⁻⁴ K⁻¹. If the part is machined at room temperature but installed at a washdown temperature of 60°C, a 1 m length can increase by several millimetres. Mounting slots must be elongated to accommodate expansion. Steam washing above 80°C is not recommended because it can distort thin cross-sections. Creep modulus under load is evaluated by ISO 899-2, and design stress should stay below 3 MPa for continuous service to avoid excessive deformation. The processing record should include the lot number, machining date, and the measured density of the incoming plate because density variations above 0.005 g/cm³ can affect cut finish and dimensional stability.