Allnex USA Inc. investigated the performance of defoamers in different blends of base oil and additives, with testing being completed at San Antonio-based Southwest Research Institute. Polyacrylate defoamers were added to API Groups I through V base oils, combined with defoamerless commercial additive packages, and tested for foaming tendencies.

ASTM D892 (Standard Test Method for Foaming Characteristics of Lubricating Oils) was followed, with the exception that the same base oil, defoamer and additive package (where appropriate) were used in all three sequences. The first sequence is meant to simulate a cold engine start; the second simulates engine operation, and the third a restart of the engine. The test protocol calls for fresh oil in sequence 1 and sequence 2. Using the same oil sample in all three sequences represented a harsher test than the one normally required.

Four types of polyacrylate defoamers from Allnex were used in the test samples: A standard polyacrylate defoamer (PC-1244), a higher molecular weight polyacrylate defoamer for high temperature and air entrainment (PC-1844), a hybrid generation 1 polyacrylate structure designed for use in synthetic base oils (PC-2544) and the companys newest hybrid polyacrylate structure (PC-3144) designed for use in all base oils.

The defoamers were diluted with solvent naptha to a 1 percent active level before being added to the base oil, which is typical in formulated oils. The base oil and defoamer were mixed for 1 minute in a Waring blender at high speed before starting the test.

Foam Tendency Without Additives

In order to understand the base oil contribution to foaming, the initial testing was done without additive packages. Four base oil blends were developed for the assessment with a similar viscosity profile. One was a blend of a Group I bright stock and a 4 centiStoke Group II, while the second was a blend of 4 cSt and 6 cSt Group III+ oils. The third and fourth blends were made from polyalkylene glycol, polyalphaolefin and ester base stocks.

The blend of Group I/II base oils had a significantly higher foaming tendency than the blend of Group III+ oils tested. The Group IV and V oil blends did not sustain foam during any sequence of the evaluation and were not further tested in this study. The conclusion from the first round of testing was that foam from the mineral oil base stocks was greater than from the synthetic base oils. (Group III oils are considered synthetic for the purposes of this study.)

The question, then, is whether fully formulated synthetic base oils also foam less or require less defoamer to control the foam versus their mineral oil counterparts. The commercial advantage would be less foaming challenge with the synthetic oils, thus making the synthetics a preferred base oil choice. Another series of foam tests was conducted to document the foaming tendencies of some typical formulated base oils.

Foaming Tendency with Additives

Two commercial additive packages were obtained that were formulated without defoamer. Additive package A was a fully formulated package, and additive package B was less formulated for more economical applications. Both packages were designed for gear oils. The detailed composition of the additive packages was not provided nor analyzed during testing, by agreement with the supplier.

The recommended addition rates for these additive packages were 7.5 percent for package A and 4 percent for package B. The variables considered were what impact the dosage of the additive package plays in the foaming tendency of the lube, and if there is a difference in foaming caused by the additional features of package A.

The following tests were done to assess the effect of these additive packages in the different mineral and synthetic base oils:

Constant 4 percent level of package B across the base oils blends.

A comparison of 4 percent and 7.5 percent levels of package A tested across the base oil blends.

The recommended 4 percent and 7.5 percent levels of each additive package across the base oil blends.

As before, the polyacrylate defoamers were diluted with solvent naptha to a 1 percent active level before being added to the base oil. The base oil, additive package and defoamer were mixed for 1 minute in a Waring blender at high speed before starting the test. Table 1 shows the result of adding one additive package across the different base oils. In this case, additive package B was utilized at a 4 percent dosage with the defoamer added at 58 parts per million active defoamer.

All four defoamers proved effective at reducing the foam levels in the Group I and Group III+ base oil blends at the 58 ppm dosage. Foam reduction was greater with the new hybrid defoamer compared to traditional polyacrylate defoamers, indicating a reduction in defoamer content is possible with the hybrid defoamers in these grades. One interesting result from the testing was the dramatically higher foam levels-compared to other base oils with package B or to neat base oil-when additive package B was added to the Group I/II blend. Given the results, a significantly higher level of defoamer would be required to control the foam of this combination.

Once again, the hybrid formulation controlled the foam better and would require less defoamer versus the traditional defoamers; however, the level will still be much higher than 58 ppm.

These results indicate the additive package has a different foaming contribution by base oil type. More testing would be needed to understand why the blend of Group I/II base oils created this level of foam, but it isnt as simple as the difference between mineral oils and synthetic oils.

Defoamer Dosage

This is the first indication of the potential inefficiency and cost impact for formulators that continue using the same defoamer base oil to base oil. It is clear that systems can require defoamers with different designs to control foam across different base oil and additive package combinations. Using the same defoamer may be effective with higher (or lower) dosages. However, there may be a significant usage penalty in favoring that choice.

One theory of effective foam control is that an ideal defoamer droplet size is achieved when added to the oil and must be maintained during the oils service life. The mobility and availability of these droplets to contact and drain the foam bubble lamella-ultimately destabilizing and rupturing the foam bubbles-are critical design parameters for defoamers. The droplet size is governed by at least two factors: the incompatibility of the defoamer with the base oil and formulation, as well as the energy used to shear the defoamer into the oil.

Assuming the energy used to incorporate the defoamer into the oil is constant, defoamer incompatibility is the only design parameter that can be altered to improve the efficiency of the defoamer in any lube system. As the base oil composition changes from Group I to Group V, the additive packages change accordingly. Thus the defoamer requirement changes as the incompatibility differences with the defoamer change, including the need for a different dosage and type of defoamer.

Additive Package Effect

What happens if the concentration of the additive is increased in the same system? The impact on foam from an increased additive package concentration within the same base oil is linear. If the additive package concentration is doubled, the corresponding defoamer demand is also increased two-fold. To the extent that the formulating needs can be achieved by increasing or decreasing the additive package concentration, the defoamer requirement follows in the same degree.

The final series of tests was run to assess the challenge of adding two different additive packages to the same base oils, albeit at the recommended dosage levels of 4 and 7.5 percent. The sample preparation and testing was the same as in the previous two cases. The defoamer dosage again was 58 ppm on an active basis. All three sequences were run, but Sequences 1 and 3 gave the most significant results and are detailed here.

As shown in Table 2, the more fully formulated additive package A usually generates lower foam results with the same defoamer level versus the lesser featured package B. To better understand why would require analyzing the components of the two packages. Clearly, the composition of additive package B has a higher impact on defoaming versus additive package A.

Hybrid Defoamers

One consistent trend through the testing was that the new hybrid defoamer technologies are more effective at controlling foam in all of the base oil types tested. This further supports the need to include these new defoamer types in evaluation for new synthetic lubricants as well as in mineral oil lubrication package designs.

In both the mineral oil and synthetic oil systems, the hybrid defoamers have foam reduction that consistently gives the lowest results after testing. The design of the hybrid defoamer results in controlled incompatibility in each of the systems. While the testing conducted is only a small fraction of the types of lubes being formulated today, it makes a case for having these hybrid defoamers included in any current development being done for new lubricants.

Since it appears that base oils, additive package types and the concentration of the additive packages in the lube all contribute to the foam tendency of the lubricant, the opportunity for a more universal defoamer that can work effectively across lubricant systems and simply require dosage adjustments would have significant advantages for the formulator in both accelerating innovation and reducing complexity and cost.

Morris Bingham is key account manager for polyacrylate defoamers and Americas additives business development manager at Allnex USA. He can be contacted at morris.bingham@allnex.com