Investigation Of The Preparation Process And Performance Of Food-grade Grease

In order to avoid food safety problems caused by the leakage of lubricating materials in food machinery and equipment,it is particularly important to carry out investigation of food-grade lubricating materials and their related properties.As one of the components of food-grade lubricating materials,food-grade grease is widely used in key transmission parts of food processing equipment such as bearings and chains.Therefore,this investigation optimized the preparation process of food-grade grease,carried out the safety evaluation of food-grade grease and investigation of the influence factors of new additives on the tribological properties of food-grade grease,which will provide valuable insights for the development and engineering application of food-grade grease.First,based on food-grade white mineral oil and composite aluminum soap thickener,the process optimization of food-grade composite aluminum-based grease was carried out,that is,the effects of fatty acid type,base oil content,water addition in saponification process,aluminum isopropoxide content and high-temperature refining time on the physical properties of composite aluminum-based grease were investigated.Moreover,the safety of the grease was evaluated by Listeria method and cell viability test.The results indicated that when the fatty acid type was stearic acid,the base oil content was 80%,the molar ratio of aluminum isopropoxide to water was 1.0:2.0,the molar ratio of benzoic acid,stearic acid and aluminum isopropoxide was 1.0:2.0:1.7 and high temperature refining time was 20 mins,the composite aluminum-based grease has good physical properties.In addition,the prepared composite aluminum-based grease has excellent anti-bacterial properties and cell safety.Second,based on the composite aluminum-based grease,food-grade talc（F-Talc）,food-grade calcium silicate（F-Ca Si O₃）and medical-grade montmorillonite（M-MMT）were selected as additives.The effects of additives on the thermal stability and tribological properties of composite aluminum based-grease were investigated by thermogravimetric analyzer,ball-disc wear tester and white light interferometer.The wear scar surface was characterized by electrochemical workstation and X-ray photoelectron spectroscopy.The results indicated that all three silicate additives can improve the thermal stability and tribological properties of the composite aluminum-based grease.Compared with the base grease,when the mass fractions of F-Talc,F-Ca Si O₃ and M-MMT were 1.0%,1.0%and 1.5%,respectively,the average coefficient of friction（a Co F）of the grease was reduced by about 25%,32%and 46%.The wear volume per unit time was also reduced by about 47%,46%,and 74%.The main reason was that the three kinds of layered silicates were easy to form a lubricating film on the surface of the rubbing pair,and some of them can play the role of“sliding”,repairing and micro-polishing to improve the friction-reducing and anti-wear performance of the grease.In addition,the grease containing three silicate additives has good safety performance,and Tal-1 aluminum-based food-grade grease has also passed the US NSF H1 certification,and can be used in occasions where it comes into contact with food accidentally.Finally,based on the composite aluminum-based grease,nano polytetrafluoroethylene（nano-PTFE）and nano calcium carbonate（nano-CaCO₃）were selected as additives and the adsorption properties were investigated.The effects of additives on extreme pressure（EP）performance and tribological properties of composite aluminum-based grease were mainly investigated by four-ball wear tester,ball-disc wear tester and white light interferometer.The wear scar surface was characterized by electrochemical workstation and X-ray photoelectron spectroscopy.The results indicated that nano-PTFE can be better adsorbed on the surface of the friction pair than nano-CaCO₃,and the two nano additives had a good synergistic effect in composite aluminum-based grease.Compared with single additive,the maximal non-seizer load（P_B）,weld point load（P_D）,test stability,a Co F and wear volume of composite aluminum-based grease were significantly improved by compound additive.In addition,the grease containing nano-additives has good anti-bacterial properties.These results provide valuable insights into the development of novel food-grade lubricants.