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illustrates a comparison between three Ethylene Oxide (EO) Polyethylene Oxide (PO) long chain alcohol surfactants claimed by the market to have the same performances and the same HLB value (10.5).
In a second Design of Experiment, 22 tests are carried out and for each one the stability index, maximum foam volume generated and the time taken for the foam to halve, are collected. Minimising both ‘maximum foam volume’ and ‘time of foam halving’, while maximising ‘stability index’, can help to identify the balance point (fig. 4).
The balance point represents the best solution of fluid in term of concentrate stability and foaming properties. Comparing optimised formulations with a standard one obtained following research & development technical know-how with no selection of surfactants, a significant difference was witnessed in terms of foaming properties.
While non-optimised stabilisation shows 250 ml foam generated and more than 300 seconds to halve it, the optimised fluid generated 150 ml foam and 18.5 seconds to halve it (fig. 7).
Figure 3: Foaming properties of three different surfactants EO/PO long chain alcohol
Surfactant number 3 exhibits strong low foaming characteristics compared to other two surfactants, while it exhibits the same stabilising performances in emulsifiable concentrates and emulsions. The screening resulted in a selection of the best surfactant for each class.
Keeping the base formulation fixed, a Design of Experiment (DoE) technique is used to create a consistent approach to the test method for the product with a fixed amount of three high-performance emulsifiers and stabilisers (fig. 4). The output of the data from the test method allowed us to develop a long-term concentrate stability index, with the intention that the higher the concentrate stability, the more favourable the outcome.
Analysis of the data output contour plot allowed for the definition of a ‘safe area’, an area in which all the points represent stable formulations and which can be investigated more deeply with a second DoE to analyse foaming properties of the fluids.
22 LUBE MAGAZINE NO.169 JUNE 2022
Figure 4: Ternary DoE of concentrate stability contour plot. Red dots represent tested formulations from a total of 21 tests.
Defoamer study
Once the formulation is optimised, focus can be turned to the use of anti-foaming agents. Anti-foaming agents are typically a dispersion of insoluble liquids or solids in a continuous medium, and so they are subjected to all the characteristics of instability such as aggregation, coalescence and sedimentation.
Thermodynamics of the system cannot be changed in any way; the instability depends on the kinetics – the rate at which the process occurs. Kinetics has a strong correlation with temperature, the Arrhenius equation, and the concentration of defoamer.
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