Polymers and resins represent approximately 2% of pump applications, but they are among the most technically demanding fluids to pump reliably. They span viscosities from a few hundred to many millions of centistokes, exhibit complex non-Newtonian behaviour, are highly sensitive to shear degradation and often require precise temperature control to remain pumpable. Failure to account for these characteristics leads to pump overloads, product degradation and significant downtime.
Polymer and Resin Types
- Thermoplastic melts: Polyethylene (HDPE, LDPE), polypropylene, nylon — pumped as viscous melts at 180–300 °C; viscosity 1,000–100,000 Pa·s
- Thermoset resins (uncured): Epoxy, polyester, vinyl ester — viscosity 500–50,000 cSt at room temperature; must be pumped before curing is initiated by heat or hardener
- Synthetic rubbers and latex: SBR, NBR, neoprene latex — aqueous dispersions 20–60% solids; shear-sensitive; can coagulate if shear rate is excessive
- Polyurethane systems: Two-component polyol and isocyanate — each component is typically 1,000–5,000 cSt; must be pumped and metered separately and mixed immediately before dispensing
- Silicone polymers: Polydimethylsiloxane (PDMS) and silicone oils — viscosity 1 cSt to 2,500,000 cSt; chemically inert; stable over a very wide temperature range
- Water-soluble polymers: Polyacrylamide, polyethylene oxide — dilute solutions with significant viscosity; used as flocculants in water treatment
Non-Newtonian Behaviour
- Nearly all polymers are strongly pseudoplastic (shear-thinning) — viscosity in the pump may be 10 to 100 times lower than the quiescent value
- Polymer melts exhibit elastic behaviour (die swell, Weissenberg effect) that can destabilise flow in centrifugal pumps
- Thermoset resins begin to cure once activated — pumping must be completed before gel time is reached
- Some rubber latices are thixotropic — viscosity recovers after agitation; provide adequate pre-shearing before pump inlet
Temperature Control
- Steam-jacketed casing: For thermoplastic melts and high-viscosity resins — maintains fluid temperature and prevents solidification in the pump and suction line
- Cooling jackets: For exothermic thermoset resins — prevent premature curing caused by heat generated during mixing or shear in the pump
- Insulation: All piping, pump casing and valve bodies must be insulated to prevent heat loss and viscosity increase in cold-weather installations
- Temperature sensors: Monitor fluid temperature at pump suction and discharge — automatic shutdown if temperature falls below minimum pumpable limit
Pump Type Selection
- Moderate viscosity resins (100–10,000 cSt): Gear pump — constant, accurate flow; self-priming; handles high pressure required for injection moulding feed
- High-viscosity polymer melts (above 10,000 cSt): Twin-screw extruder pump or gear pump — designed for melt pressures up to 400 bar
- Shear-sensitive latex and emulsions: Progressive cavity or peristaltic pump — minimal shear; gentle handling
- Two-component systems (polyurethane, epoxy): Two metering membrane or gear pumps in synchronised operation — precise ratio control
- Flocculant solutions (dilute polyacrylamide): Centrifugal pump at low speed — high shear from centrifugal pumps can degrade long-chain molecules
Applications
- Plastics extrusion and injection moulding — polymer melt feed to die or mould
- Coatings and adhesive manufacturing — resin blending, transfer and dispensing
- Rubber and latex processing — compound transfer, vulcanisation line feed
- Polyurethane foam and RRIM production — component metering and mixing
- Composite manufacturing — resin transfer moulding and pultrusion resin feed
- Water treatment — flocculant and coagulant polymer dosing
- Paint manufacturing — alkyd and acrylic resin blending and filling