Polymer compatibility with refrigeration lubricants

Polymer compatibility with refrigeration lubricants

Keywords Lubricants,Lubrizol, Polymers

Problems have been experienced with the extraction of low molecular weight components from some polymers used in refrigerator compressors due to the higher solvency power of the lower viscosity lubricants which are now being used in the interests of higher operating efficiency. A number of in-depth studies have been undertaken by Lubrizol Corporation to better understand the factors involved. Although previous studies had shown that polyethylene terephthalate (PET) motor insulation was most stable in the dry state, Lubrizol's investigations have now shown that dry polyol ester lubricants can extract low molecular weight oligomeric components from both PET and polybutylene terephthalate (PBT). Linear-branched esters were shown to extract more PET trimer from the insulation than ×-branched esters, the degradative trend increasing sharply with lower molecular weight esters. However, it was also noted that trimer level alone does not provide an accurate account of polymer interaction with lubricants, since,although the ×-branched ISO 7 extracted the least amount of trimer, it contained the highest amount of total oligomer. The presence of nucleophilic species such as water, alcohols, etc., was a further complicating factor.