Preparation And Properties Of Food Grade Complex Sulfonate Calcium Grease

In recent years,the leakage of lubricants causes product contamination and seriously affect consumer health and safety.The use of food-grade lubricants in food,medicine and other manufacturing equipment can ensure the reliability of equipment operation and product safety.Therefore,the preparation and properties of food-grade complex sulfonate calcium grease（CSCG-FG）were studied in this article.CSCG-FG was prepared by using non-toxic raw materials such as food-grade white oil,calcium sulfonate of high basic value petroleum,and acetic acid.Food-grade stearate and carbon nano onions（CNOs）were selected as additives to improve the tribological properties of the CSCG-FG.These results will provide reference for the research and development of food manufacturing equipment grease and the selection of related additives.Firstly,CSCG-FG was prepared by using food-grade white oil as base oil,acetic acid as conversion agent and 12-hydroxystearic acid,calcium hydroxide,boric acid as thickener.The better mass ratio of acetic acid to petroleum calcium sulfonate with high alkali value was investigated by the drop point,coning degree and appearance of the prepared samples.Thermogravimetric analyzer（TGA）,differential scanning calorimeter（DSC）and rotary rheometer were used to characterize the thermal stability and rheological properties of CSCG-FG.Cell viability test was used to characterize the safety performance of CSCG-FG.Compared with similar greases in the market,the results show that the prepared CSCG-FG has good thermal stability,shear resistance and safety performance.Secondly,food grade calcium stearate and magnesium stearate were selected as additives to ensure the safety of grease while improving its comprehensive performance.The friction testing machine and white light interferometer were used to investigate the effect of stearate on the tribological properties of CSCG-FG.X-ray photoelectron spectroscopy（XPS）was adopted for elemental analysis of wear trace surface to explore the synergistic mechanism of CSCG-FG and additives.TGA,DSC and rotary rheometer were used to investigate the effect of stearate on the thermal stability and rheological properties of CSCG-FG.The effect of stearate on the safety performance of CSCG-FG was characterized by cell viability test.The results showed that calcium stearate and magnesium stearate can effectively improve the tribology performance of CSCG-FG at lower temperatures.At 25oC,when calcium stearate content was4%,the corresponding average coefficient of friction（a Co F）and wear volume reached the lowest,which were reduced by 29.4%and 72.9%compared with pure CSCG-FG,respectively.When magnesium stearate content was 5%and 6%,respectively,the corresponding a Co F and wear volume reached the lowest,which decreased by 27.5%and 73.3%compared with pure CSCG-FG,respectively.This may be due to that the CSCG-FG forms a lubricating film containing Ca CO₃ and metal oxide on the surface of the friction pairs,while the lamellar stearate reduces friction and anti-wear through sliding between the friction pairs.In addition,the cell survival rate test showed that the CSCG-FG with stearate had better safety performance.Finally,CNOs with good biocompatibility and high temperature resistance was selected as additive to improve the tribological properties of CSCG-FG.The friction testing machine and white light interferometer were used to investigate effects of CNOs on the tribological properties of CSCG-FG,and the wear surface was analyzed by XPS and Raman spectroscopy to explore the synergistic mechanism of grease and CNOs.The results show that the a Co F and wear volume of reached the lowest when the addition amount of CNOs was 0.10%,which were31.4%and 70.0%lower than those of pure CSCG-FG at 25oC,respectively.The main reason is that CNOs plays the role of“ball bearing”between friction pairs,and the exfoliated graphite layer adheres to the friction surface and plays the role of friction reduction,anti-wear and micro-polishing.In addition,the cell viability test showed that CSCG-FG containing CNOs had good safety performance.These results provide some reference value for the selection of food-grade grease and additives.