Stability Issues in Liquid Coffee Scrub Soap Formulation

Hello,

Thank you for providing details about your liquid coffee scrub soap formulation. Based on the issues you described (separation, oily layer, settling, and thinning after adding Tween 80), here is an explanation of what might be happening and general principles for addressing these issues:

1. Separation and Oily Layer: The oily layer at the bottom likely consists of non-polar components (oils, lipids) originating from your natural ingredients such as coffee grounds, milk, honey, and the plant extracts (Thanaka, Turmeric, Plai). These components are not easily soluble or dispersible in the water-based surfactant system (N 70 / SLES). Without a proper emulsifier system, these oily components will separate over time.
2. Settling of Solids: The coffee grounds and other solid particles from Thanaka, Turmeric, and Plai are settling because the liquid soap base does not have sufficient suspending power. While Sodium Chloride helps thicken the SLES system, this type of thickening (viscosity increase) is generally not enough to effectively suspend dense solid particles long-term.
3. Thinning After Adding Tween 80: Tween 80 is an emulsifier that can help disperse oils. However, adding it to your existing SLES/salt thickened system likely disrupted the micellar structure that was providing viscosity. This can cause the mixture to become thinner, which unfortunately worsened the settling problem.

To create a stable liquid scrub formulation that prevents separation and settling, you typically need:

• An effective Emulsifier System: To keep any oily components from separating. Tween 80 can be part of this, but the required type and amount depend on the specific oils present.
• A Suspending Agent (Rheology Modifier): This is crucial for keeping solid particles dispersed. Ingredients like Carbomer, Xanthan Gum, or Acrylates Copolymer are commonly used in liquid washes to create a gel-like structure or yield stress that holds particles in suspension. Salt thickening alone is usually insufficient.
• Compatibility and Stability: Ensuring all ingredients are compatible and stable together is key, especially with natural ingredients which can vary in composition and introduce microbial or chemical instability risks.

Formulating with a high load of natural ingredients like coffee grounds, milk, honey, and various plant extracts is complex because these ingredients contain a mix of components (shorthand: sugars, proteins, lipids, solids) that can be challenging to keep stable in a single phase.

Unfortunately, it is very difficult to fix a batch that has already separated and thinned, especially without knowing the exact properties and quality of all the natural ingredients used. A stable formulation needs to be designed from the start with appropriate emulsifiers and suspending agents balanced with the surfactant system.

We recommend researching standard formulation principles for exfoliating liquid washes or seeking advice from suppliers who specialize in cosmetic raw materials and can provide guidance on incorporating natural ingredients and selecting suitable suspending agents and emulsifiers for your desired product type.