56 RHEOLOGY MODIFIERS
applications such as skin care, sun care, makeup, hair care, and skin cleansing. It is also biodegradable, approximately 72-74% of the components in the formulation have demonstrated to be readily biodegradable according to OECD 301F.
Materials and methods Gel preparations steps with oil-soluble rheology modifier Gels can be processed using 1% polymer up to 15% polymer. Use levels at or above 15% are generally used for rigid stick formulations. The polymer is dissolved into the oil of choice using a dispersion blade with an overhead mixer (Caframo) at 90°C for 30 minutes. Processing temperatures may be reduced to
80-85°C with higher shear such as homogenization. Mixing speeds can be kept at a high enough rate to ensure good turnover of sample batch with no splashing of material outside the mixing vessel. It is important to note that the polymer functions
via hydrogen bonding to build its network, so it is recommended to minimize mixing below process temperature. In addition, it is advisable to let the gel rest in a room temperature chamber (25°C) for 24 hours before any physical testing.
Physical testing methods of gel samples After 24 hours, gel samples may be screened for viscosity and syneresis. Other test parameters may be evaluated at this time, depending on the formulator’s objectives. Viscosity is measured using a viscometer (Brookfield DV2T extra, AMETEK) with a Heliopath attachment. Utilizing the Heliopath is important due to the
shear thinning nature of the polymer’s structure. Viscosity is determined after one minute at 10 rpm (revolutions per minute). Spindle size is predicated on polymer use levels. Syneresis is a form of instability and is simply defined as the expulsion of a liquid from a gelled structure. The presence of syneresis will give some understanding of how well the polymer structure stabilizes the oil component in the formula. Quantifying syneresis is suggested after
samples have been at rest for 24 hours at 25°C. Syneresis samples are tested in a six-dram vial (approximately 15 grams). After 24 hours of conditioning, a sample vial is placed on a 45° angle for five minutes. While the sample is at rest at a 45° angle, a weigh boat is tared on a scale. After five minutes, the vial (without the cap) is
Figure 1: Polymer’s general structure
900000 800000 700000 600000 500000 400000 300000 200000 100000 0
Figure 2: Polymer’s granules
■ Caprylic/Capric Triglyceride (CCT) ■ Sunflower Oil (SFO)
■ Mineral Oil -80%: Caprylic/Capric Triglyceride -20% (MO:CCT)
■ Caprylyl Methicone -50%: C12-15 Alkyl Benzoate -50% (CM:AB)
Rigid solid
0
3
6 Polymer, wt% Figure 3: Viscosity response of the polymer in various oil types
inverted on the tared weigh boat for five minutes. This will allow any surface oil to be collected in the weigh boat and measured. The resulting weight from the collected oil residue is calculated as a percentage of the initial weight (15 grams). A percentage result below 1% is favourable, and
any specification will be established internally. At this point, additional sample vials can be entered into a stability protocol where the impact of elevated temperatures on syneresis can be studied.
Skin care Oil compatibility As stated earlier, oil compatibility is a critical
attribute for oil rheology modifiers. Evaluation for oil compatibility was conducted on various oil types: Caprylic/Capric Triglyceride, Mineral Oil, Sunflower Oil, Caprylyl Methicone and C12-15 Alkyl Benzoate. These oils can be classified as polar and
non-polar. Due to the mechanism of action, the polymer demonstrates the best performance in natural and polar oils. To obtain optimal results in the presence of non-polar oils, blending with polar oils is a solution, while varying the ratio of polar to non-polar allows the generation of a wide range of viscosities. The ratio of oil blends will have an impact on clarity as well. The oil rheology modifier was screened at
9
12
Figure 4: Clarity pictures of the polymer in various oil types. From left to right: Caprylic/capric triglyceride, sunflower oil, 80% mineral oil with 20% caprylic/ capric triglyceride and 50% caprylyl methicone with 50% C12-15 alkyl benzoate
PERSONAL CARE MAGAZINE May 2026
Figure 5: Suspension test with high-density beads. The three samples on the left are initial room temperature. Three samples on the right are aged one month at 50°C. From left to right: Caprylic/Capric Triglyceride, Sunflower Oil, Silicone/ester blend
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Viscosity*, (cPs)
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