Sunscreen Gel Formulation Questions

Based on your formula and the previous discussion, here are the answers to your remaining questions:

1. Mixing Procedure

Your proposed mixing procedure is generally correct for this type of formula structure:

• Phase A: Combine water, MatteSilica™, and Pro Polymer. Mix until the gel is fully formed and smooth. Allow sufficient time for the Pro Polymer to hydrate completely to avoid lumps.
• Phase B: Combine Titanium Dioxide Nano EasyDisperse™ and Dimethicone. Mix thoroughly until the powder is fully dispersed in the Dimethicone, forming a smooth paste or cream.
• Combining Phases: Slowly add Phase B to Phase A while continuously stirring or blending. It is best to use a blender or high-shear mixer during this step to ensure the sunscreen particles are evenly dispersed in the gel base and prevent clumping.
• Phase C: Add Phenoxyethanol to the combined mixture and mix until fully incorporated.

This method ensures that the water-soluble gel maker (Pro Polymer) is properly hydrated and the oil-dispersible sunscreen (Titanium Dioxide in Dimethicone) is well dispersed before combining the phases.

2. SPF Calculation

Calculating the exact SPF of a sunscreen formula based solely on the percentage of active ingredients is not precise, especially for physical sunscreens like Titanium Dioxide and Zinc Oxide. The actual SPF value depends on various factors, including the specific grade and particle size of the sunscreens, how well they are dispersed in the formula, and the final film formed on the skin.

While 7.5% Titanium Dioxide contributes to SPF, achieving SPF 15 typically requires a combination of UV filters and often higher concentrations or specific treated grades optimized for UV protection. The staff's suggestion to include Zinc Oxide and/or DHHB indicates that your original formula with only 7.5% Titanium Dioxide Nano EasyDisperse™ might not provide sufficient broad-spectrum protection or reach SPF 15 effectively, and adding Zinc Oxide is a common way to boost UVA protection and SPF while potentially reducing the white cast when used in combination.

To know the precise SPF and PA values, the final product must undergo laboratory testing.

3. Nano vs. Regular Titanium Dioxide for Sun Protection

Using regular (non-nano) Titanium Dioxide instead of a nano grade like Titanium Dioxide Nano EasyDisperse™ at the same percentage will likely not provide the same level of sun protection, even if you disregard the white cast.

Here's why:

• Particle Size: Nano-sized particles (typically below 100nm) are more effective at scattering and absorbing UV radiation per unit weight compared to larger, non-nano particles. They also tend to be more transparent on the skin, reducing the white cast.
• Treatment: Sunscreen-grade Titanium Dioxide (both nano and sometimes non-nano) is often specially treated (e.g., coated with silicones or other materials) to improve dispersion, stability, and UV absorption/scattering efficiency in formulations. Regular pigment-grade Titanium Dioxide is primarily intended for color opacity and may not have these treatments or the optimal particle size distribution for UV filtering.

While non-nano Titanium Dioxide does offer UV protection (primarily UVB and some UVA), a sunscreen formulated with a treated nano-grade at a specific concentration is designed and expected to perform differently in terms of SPF and PA compared to one using a non-treated, larger particle pigment grade at the same concentration.

4. MatteSilica™ Clumping

You experienced clumping with MatteSilica™ XL at 5% in a previous gel. MatteSilica™ (5 Micron) is also a fine powder. Incorporating powders, especially oil-absorbing ones like silica, into a pre-formed gel can sometimes lead to clumping if not done carefully.

The clumping issue is often related to the powder's tendency to agglomerate and how easily it disperses in the chosen base. MatteSilica™ is designed to absorb oil, and while your formula is water-based, the powder still needs to be fully wetted and dispersed into the gel matrix.

To minimize clumping when using 5% MatteSilica™ in your gel formula:

• Ensure the Pro Polymer gel is completely smooth before adding the silica.
• Add the MatteSilica™ very slowly to the gel while stirring continuously.
• Using a high-shear mixer or blender during the incorporation step will significantly help to break up any clumps and ensure even dispersion.
• Alternatively, as suggested for the modified formula's Phase B, you could try dispersing the MatteSilica™ along with the Titanium Dioxide and Dimethicone in Phase B before adding it to the gel phase.

5. Silicone to Sunscreen Ratio

As the staff reply indicated, you can use a silicone (like Dimethicone) to sunscreen powder ratio less than 1:1 when preparing the dispersion phase (Phase B in your formula). However, using a lower ratio makes it more challenging to achieve a complete and even dispersion of the powder. It will likely require the use of a high-speed mixer or blender to ensure the sunscreen particles are fully wetted and separated, preventing aggregation and ensuring optimal performance and stability of the formula.

6. Dimethicone and Pro Polymer Emulsification

Yes, Pro Polymer can help stabilize Dimethicone in a water-based gel formula. While Dimethicone is an oil-soluble silicone that does not dissolve in water, Pro Polymer is a gel maker that can also function as an emulsifier or suspending agent in water + oil systems. It creates a polymeric network in the water phase that can trap or disperse oil/silicone droplets, preventing them from separating and creating a stable, creamy gel texture.

In your formula, Pro Polymer helps to create the gel structure and also assists in incorporating and stabilizing the Dimethicone and the Titanium Dioxide dispersed in it within the water phase, effectively creating an emulsified gel or a stable dispersion.