Full definition
The standard laboratory instrument for measuring the viscosity of raw rubber and compounded rubber using a rotating disc (rotor) embedded in a heated rubber sample. Per ASTM D1646 and ISO 289. Operation: a rubber sample fills a sealed, heated die cavity; a serrated rotor (large or small) rotates at 2 RPM; the torque resistance to rotation is measured in Mooney Units (MU, 0-200 scale). Test conditions: reported as ML(1+4)@100°C for raw rubber or ML(1+4)@100°C for compounds — meaning large rotor, 1-minute preheat, 4-minute test at 100°C. Typical values: raw NR (SMR 20) 60-80 MU, raw SBR 1502 45-55 MU, mixed compound 30-80 MU depending on formulation. Lower Mooney = easier processing (extrusion, calendering, injection). Higher Mooney = stiffer, harder to process but often better physical properties. Also measures: Mooney scorch (MS) — time to a defined viscosity rise at elevated temperature (121 or 127°C), indicating processing safety/scorch risk. The Mooney viscometer is the rubber industry's primary incoming QC instrument for raw polymers. Manufacturers: Alpha Technologies, MonTech, Prescott Instruments.