INVESTIGATIONS OF USED HYDRAULIC OILS DER IVED FROM RAPESEED OIL FROMA LONG-TERM PRACTICE TEST

Because of their excellent biodegradation and their low water pollutio n potential hydraulic oils derived from plant oils are suitable to rep lace the dominantly used hydraulic oils derived from mineral oil. In a long-term practice test a rapeseed based hydraulic oil (Plantohyd 40 N, Fuchs Mineralolwerke GmbH) was tested for a period of 30 months in a sheet steel press. During the operating lime (> 7000 h) samples were taken in non-regular intervals. As a measure for oil aging, the acid value and the viscosity at 40 degrees C were determined. Polymerisatio n has led to an increase of viscosity; the portion of the resulting di meric and oligomeric triglycerides was determined by GPC. A determinat ion of the oxidative stability by means of Rancimat apparatus only mak es sense when applied for samples with short operating times (< 1000 h ) because of the short induction period. GPC also showed an increase o f free fatty acids and other low molecular weight compounds. The polar compounds (including the non-polar dimeric triglycerides) were isolat ed. The structure determination of the resulting dimeric fatty acids a nd low molecular weight products remains to be done.