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Comparatively Speaking: Formulating by Numbers

Contact Author Anthony J. O'Lenick, Jr., IFSCC and Siltech LLC
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Throughout the many (40) years I have been in the personal care industry—and more specifically, working with silicone polymers (30 years)—an article written in 1984 is, I believe, one of the best articles I've ever read written about PEG/PPG dimethicone compounds; even being 34 years old and written in the early silicone era days.

The article was written by Steven Vick, Ph.D., of what then was Union Carbide. What makes the article so great is that it provides real, timely (despite being 34 years old) and useful information that can help the formulator immediately. 

A very "busy" table from the referenced paper (see Table 1) reveals the entire structure, molecular weight, surface tension of a 1% solution, foam and wetting data of PEG/PPG dimethicone. In short, at a glance, it shows all the data a chemist really wants to know. These materials, all water-soluble, are described in a way that takes the guess work out of selecting them for a particular function in a formulation.

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Table 1. PEG/PPG Dimethicone Properties
(click to enlarge)

OLenick_Table1
 
Figure 1 depicts the structure for the polymers described:
OLenick_Figure1b1
Table 1 can easily be divided into useful sections based upon properties; firstly, based on the number of moles of EO and PO, and secondly, based on surface tension. The ability of a polymer to lower surface tension of water from 72 dynes/cm to below 25 dynes/cm is a terrific trick that affects aesthetics, spreadability and uniformity on the hair or skin. Such an approach allows for splitting the table into Tables 2, 3 and 4 as follows.
 
Table 2. Water-soluble PEG/PPG Dimethicone with Surface Tension below 25 dynes/cm (7.5 moles of EO)
OLenick_Table2_FormulateByNumbers
 
We can now use the data to select those materials that reduce surface tension better than others, those with high or low foam, and those that are good or poor wetting agents. From these properties, we can select a good foaming polymer that also lowers surface tension to use in a shampoo that improves spread and wet-combing properties.
 
Alternatively, we can choose a low foam version to better control the foam in filling bottles. Again, these products are potential additives to shampoos to improve wetting and mild conditioning. We can now link properties of the polymer to desired properties in specific formulations.
 
Table 3. Water-soluble PEG/PPG Dimethicone with Surface Tension above 25 dynes/cm (17.5 moles of EO)
OLenick_Table3FormulatingByNumbers
 
Table 3 shows the effect of adding a higher number of moles of PEG to the silicone. Generally, these polymers have a higher percentage of PEG than those in Table 2. The surface tension is higher and closer to that of fatty surfactants. Foam levels are higher than 100 for all but two of the polymers, and wetting takes longer than those in Table 2 (except for sample 17).
 
Table 4. Water-soluble PEG/PPG Dimethicone with Surface Tension above 25 dynes/cm (24 moles EO and 27 moles of PO)
OLenick_Table4_Formulatingbynumbers
 
Table 4 shows polymers that are principally of interest as emulsifiers, processing aids and emulsion stabilizers.
 
A paper like Vick's allows formulators to understand how to approach formulations. Clearly, we choose silicone polymers for the properties they confer on formulations and not the chemistry used to make them. However, structure dictates function and providing a full disclosure as this article does makes the formulation much easier using Minimally Disruptive Formulation, since a low concentration of additive is needed to modify the formulation to give very different aesthetics in many personal care applications.
 

References

1. S Vick, Structure/function relationship for silicone polyalkyleneoxide copolymers and their effects on performance in cosmetics, Soap Cosmetics and Chemical Specialties (May 1984) pp 38

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Table 1. PEG/PPG Dimethicone Properties (enlarged)

OLenick_Figure1_larger

A very "busy" table from the referenced paper reveals the entire structure, molecular weight, surface tension of a 1% solution, foam and wetting data of PEG/PPG dimethicone.

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