Meaning
A fluid property ratio measures the flow time of a polymer solution compared to the flow time of the pure solvent measured at identical temperatures. Quality control laboratories measure relative viscosity according to ISO 307 to assess molecular weight degradation in polyamides and polyesters during melt processing. Thermal hydrolysis from improper resin drying cleaves polymer chains, lowering solution viscosity.
Comparing raw material pellets against molded components identifies process-induced degradation resulting from excessive barrel residence times.
Degradation Assessment
Capillary viscometers calculate solution efflux time by passing dissolved resin through precise glass capillary tubes at controlled temperatures. Reductions in relative viscosity reflect loss of molecular chain length, directly correlating with decreased impact strength and reduced elongation at break. Regrind addition drops solution viscosity values if thermal history has damaged polymer backbone structures.
Receiving inspection protocols use solvent testing to reject degraded virgin resin lots prior to production.
Solvent Testing
Dissolving hygroscopic polymers like nylon 66 in formic or sulfuric acid requires strict temperature control and careful moisture control. Determining relative viscosity via dilute solution testing avoids shear heating errors common in high-shear melt flow index measurements.
Material Verification
Automotive and structural components require strict adherence to minimum molecular weight thresholds. Verifying relative viscosity guarantees that processed components maintain specified structural performance standards under mechanical loading.
