Experimental results

Silicone deposition on hair: the total amount of silicone deposited on hair was measured on hair that was treated five times with the prototype formulation listed in Table 1.

The hair was rinsed and dried between each treatment. Two types of virgin hair, European brown hair and Asian hair, and one type of damaged hair, commercial bleached hair (all are sourced from International Hair Importers and Products Inc.), were used for this study.

The silicone was extracted from the hair by a 50/50 (v/v) methyl butyl ketone / toluene solution, and then measured using atomic absorption spectrophotometry. The results using both surfactants “A” and “B” showed that the structure of the cationic HEC, especially the molecular weight, the particle size of silicone, and the types of hair, all have a very strong influence on silicone deposition. In Figure 1, the formulation containing small silicone particle size (0.5µm) without cationic HEC, such as Formula E-I gave very poor silicone deposition on all types of hair. However, formulation containing cationic HEC enhances the deposition of small particle size silicone. For instances, cationic HEC with high molecular weight (HL in Formula E-V), delivered more small particle size silicone than that with low molecular weight polymer (LH in Formula E-III). The hydrophobically modified cationic HEC, PQ-67, deposited even more silicone on the hair, especially on damaged, commercial bleached hair. This trend was reversed with all formulations containing large particle size silicone.

In Figures 2 and 3 the formulations containing large silicone particle size (20µm) without cationic HEC (Formulas E-II and A-II) yield very high silicone deposition on undamaged hair, such as European brown hair and Asian hair. This phenomenon can be explained by the fact that the attractive Van der Waals forces between particles increase with particle size and, eventually, the large particles tend to adhere better when they collide with another surface.6

However, the silicone deposition measurement shows a big variation of silicone deposition on different hair tresses.

This indicates the deposition is uncontrollable and can lead to inconsistent conditioning and eventual silicone build-up. Conversely, the formulation containing cationic HEC yields a more consistent and controlled deposition.

The data also suggests that when large particle size silicone is used, low molecular weight cationic HEC should be used to maximise deposition onto undamaged hair yet controlling possible buildup of silicone in the absence of cationic polymer in formulation.

This difference in deposition profile may be due to the ability of high molecular weight polymers stabilising the large silicone droplets, thus preventing them from colliding onto the hair surface.

The large particle size silicone, however, is relatively easier to deposit onto undamaged, European brown hair than damaged, commercial bleached hair regardless of which polymer is used. The bleaching process has significantly modified the hair surface of the commercial bleached hair to a highly negatively charged surface which potentially affects the silicone deposition process.

Silicone deposition from the formulation with Surfactant “B” containing large silicone particles shows a similar trend as the formulation with Surfactant “A” (Figs. 2 & 3). However, the relative amount of silicone deposited onto European brown hair from surfactant “B” is much lower than from surfactant “A”. This demonstrates that different surfactant system can significantly change the silicone deposition process.

Data suggests that deposition of silicone from silicone-containing shampoos onto the hair is a very complex process. Many factors, such as silicone droplet size, types of cationic polymer, surfactant system and hair type can greatly affect the deposition process. The general trend of silicone deposition with different silicone particle sizes and different molecular weight of cationic HEC polymer is summarised in Figure 4.

In general, deposition of larger particle size silicone is greatly enhanced by lower molecular weight HEC, whereas deposition of smaller particle size silicone is greatly enhanced by higher molecular weight HEC. One of the major roles of cationic HEC in a conditioning shampoo is to control the amount of silicone deposition in order to maintain a desired overall conditioning performance. Thus, formulators are able to maximise the performance of their shampoo formulation with the careful selection of the appropriate silicone particle size and cationic polymer structure combination.

Conclusion

This study demonstrates the importance of matching the optimum silicone particle size and cationic polymers structure in order to deliver the desired amount of silicone onto a specific type of hair in a predictable way resulting in the maximisation of conditioning performance of the shampoo without causing an issue in silicone buildup after multiple washes.


Source from https://www.personalcaremagazine.com