Sustainable oxidation protection for technical lubricants

Accord­ing to the cur­rent state of the art, lubri­cants are main­ly pro­duced on the basis of min­er­al oils. Although veg­etable oils are already being used for biol­u­bri­cants, the pro­por­tion is still very small. Both have one thing in com­mon: oil-based lubri­cants are par­tic­u­lar­ly sus­cep­ti­ble to oxi­da­tion. To increase sta­bil­i­ty, they are there­fore mixed with addi­tives that serve as antiox­i­dants. To make new prod­ucts avail­able in the spir­it of the bioe­con­o­my, the Fraun­hofer Insti­tute for Process Engi­neer­ing and Pack­ag­ing IVV has devel­oped a sus­tain­able and envi­ron­men­tal­ly friend­ly alter­na­tive to con­ven­tion­al, min­er­al oil-based antiox­i­dants. They con­sist of bio-based extracts obtained from resid­ual mate­ri­als from the agri­cul­tur­al and food indus­tries. With the high antiox­i­dant poten­tial of these sec­ondary plant sub­stances, it has been pos­si­ble to real­ize pure­ly plant-based antiox­i­dant addi­tives for tech­ni­cal applications.

In the bio-based lubri­cant sys­tems already avail­able, devel­op­ment for more sus­tain­able prod­ucts has so far focused main­ly on the base media rather than the added addi­tives. Addi­tives for lubri­cants are active ingre­di­ents that are mixed into the base media. They impart phys­i­cal and/or chem­i­cal prop­er­ties to the prod­ucts that are required for lubri­ca­tion but are not present in the base media. Fre­quent­ly used addi­tives are main­ly oxi­da­tion, cor­ro­sion and wear pro­tec­tion addi­tives as well as deter­gents, emul­si­fiers, defoamers and vis­cos­i­ty index improvers. Lubri­cat­ing oils tend to oxi­dize under the influ­ence of heat and oxy­gen. This decom­po­si­tion process is accel­er­at­ed by acid reac­tion prod­ucts and traces of met­als. This leads to an aging process in which acids as well as varnish‑, resin- and sludge-like deposits are formed, most of which are insol­u­ble in oil. An increase in vis­cos­i­ty and gum­ming of the lubri­cant are the result, which short­ens the life­time of the lubri­cant. Antiox­i­dants there­fore rep­re­sent an essen­tial addi­tive group used in almost all lubri­cant systems.

Biobased extracts with high technofunctionality and increased active potential

For this large addi­tive group, which plays a cru­cial role in increas­ing the sta­bil­i­ty of oil-based lubri­cants, the Fraun­hofer IVV has devel­oped a sus­tain­able and envi­ron­men­tal­ly friend­ly alter­na­tive to con­ven­tion­al min­er­al oil-based antiox­i­dants. Bio-based extracts were obtained as part of a research project. They have an increased effi­ca­cy poten­tial for a com­plete­ly new gen­er­a­tion of addi­tives. For the pro­duc­tion of the addi­tive alter­na­tives, resid­ual mate­ri­als from the food and agri­cul­tur­al indus­tries are used that could not be put to any use until now. Some of these residues con­tain valu­able sub­stances whose prop­er­ties make them suit­able for tech­ni­cal applications.

Due to their extreme­ly high func­tion­al­i­ty, the sec­ondary plant sub­stances they con­tain can replace syn­thet­ic addi­tives in tech­ni­cal prod­ucts and thus increase recy­cla­bil­i­ty and biodegrad­abil­i­ty. Plant antiox­i­dants, for exam­ple, exhib­it high oxi­da­tion pro­tec­tion, but it is not suf­fi­cient in all cas­es. The chal­lenge was to achieve an antiox­i­dant sys­tem through the tar­get­ed com­bi­na­tion of dif­fer­ent plant mol­e­c­u­lar com­po­nents that is char­ac­ter­ized by the mutu­al, sup­port­ive inter­ac­tion of indi­vid­ual molecules.

The way to industrial production is paved

“With our work, we were able to show that by vary­ing the extrac­tion para­me­ters and adjust­ing them, the antiox­i­dant poten­tial of the plant extracts obtained can be influ­enced in a very tar­get­ed man­ner. This knowl­edge is of cru­cial impor­tance for the func­tion­al­i­ty of plant extracts. In addi­tion, we have devel­oped a process for extract­ing plant raw mate­ri­als that is tai­lored to obtain­ing antiox­i­dant extracts for the tech­ni­cal indus­try. This lays the foun­da­tion for the indus­tri­al pro­duc­tion of the extracts.”

- Dr. San­dra Kiese, Project Manager

In the research project, the insti­tute also iden­ti­fied very effec­tive extract com­bi­na­tions that can also be used sta­bly in lipophilic lubri­cant sys­tems and endowed with tech­no­func­tion­al prop­er­ties. In lipophilic prod­uct for­mu­la­tions, very high antiox­i­dant effects could be achieved in this way, which are often not attained in this form even with con­ven­tion­al antiox­i­dants. The sci­en­tif­ic and tech­ni­cal find­ings form the basis for the devel­op­ment of fur­ther bio-based lubri­cants and additives.