Friction of High Density Polyethylene Filled by Vegetable Oils

摘要

The aim of the present work is to introduce new selflubricating polymeric materials for bearing applications. The proposed polymeric composites are consisting of high density polyethylene (HDPE) filled by different types of vegetables oils such as almond oil, camphor oil, castor oil, cress oil, flax seed oil, black seed oil, lettuce oil, olive oil, sesame oil and sun flower oil in content up to 10 wt.%. The friction coefficient and wear resistance displayed by the proposed composites are investigated at different values of applied load when sliding against steel. Experiments showed drastic friction decrease for HDPE filled by oil up to 1 wt.% followed by slight decrease with further increase of oil content. The oils that displayed the lowest values of friction coefficient are ranked as follows: lettuce, olive, sun flower, flax seed, sesame, black seed, cress, camphor, almond, and castor oils. The friction decrease was attributed to the presence of pores inside the HDPE matrix filled by oil which during friction leaked out to the sliding surface forming oil film. The ranking of the tested oils depended on their lubricating properties which were influenced by the adhesion of their molecules to the sliding surfaces, where their adhesion depends on their polarity. Polar molecules will form multilayers, which strengthen the adhesion of oil into the contact surfaces. Polarity of oil molecules influenced the thickness of oil film. Besides, friction coefficient decreased with increasing normal load.