Il sale nei detergenti (in progress)

[Lola]

https://www.ulprospector.com/knowledge/ ... -products/

Salt thickens by reducing micelle charge density, helping to promote the conversion of spherical micelles to rod-shaped micelles. Historically, sodium chloride has been used. However, divalent salts like magnesium sulfate are more efficient if compatible in the formulation. Viscosity of salt-thickened formulations decreases with increasing temperature and will not stabilize suspended particles. Using too much salt (>2%) can also impact the clarity and cloud point of the formulation.

Trad: Il sale addensa riducendo la densità di carica micellare, contribuendo a promuovere la conversione delle micelle sferiche in micelle a forma di bastoncino. Storicamente è stato utilizzato il cloruro di sodio. Tuttavia, i sali bivalenti come il solfato di magnesio sono più efficienti se compatibili nella formulazione. La viscosità delle formulazioni addensate con sale diminuisce con l'aumentare della temperatura e non stabilizzerà le particelle sospese. L'uso di una quantità eccessiva di sale (>2%) può anche influire sulla limpidezza e sul punto di intorbidimento della formulazione.


Cavolo! Ho trovato una curva di addensamento del sarcosinato (che come è noto addensa a pH5) e il discrimine tra denso e liquido è sempre dato dalle micelle che diventano a bastoncino e non più tonde:

https://www.sciencedirect.com/science/a ... 5720300169

Abstract
Wormlike micelles in mixed surfactant mixture containing an amino acid-derived anionic surfactant, sodium lauroyl sarcosinate (SLSar), and a zwitterionic surfactant, cocoamidopropyl hydroxysultaine (CAHS) were investigated. The total surfactant concentration was maintained at 15% wt/v, while the ratio of SLSar and CAHS was varied and the pH was lowered from 7.5 to 4.5. Steady-shear rheology, potentiometric titration, cross-polarized microscopy, zeta potential and cryo-TEM were used to obtain zero-shear viscosity and analyze the structure-rheology relationship. As pH dropped, viscosity increased to a maximum followed by a viscosity decrease in four out of five tested systems. The synergistic effect was strongest in the SLSar 6 %:CAHS 9 % composition or an equivalent molar ratio of 1:1 between the two surfactants, for which the viscosity maximum was 9.6 Pa.s at pH 4.8. The viscosity peak of each system occurred in the pH range 4.8–5.0, close to the system’s experimental pKa. The intermolecular forces between the SLSar acid form, SLSar anionic form and CAHS reduced the charge repulsion and contributed to the thickening behavior of these systems.

[Lola]

https://yeserchem.com/the-key-role-of-s ... nsistency/

Not All Surfactants Can Be Effectively Thickened by Salt

While the concept of salt as a viscosity builder holds true for many surfactants, it’s important to note that not all surfactants can be effectively thickened by salt. The salt responsiveness varies among different classes of surfactants. Below are some examples:

Alkyl Sulfates (e.g., Sodium Lauryl Sulfate – SLS): These surfactants exhibit excellent responsiveness to salt for thickening.
Alkyl Ether Sulfates (e.g., Sodium Lauryl Ether Sulfate – SLES): These display good thickening responses when salt is added.
Sulfosuccinates (e.g., Disodium Laureth Sulfosuccinate): Unfortunately, these surfactants do not thicken with the addition of salt.
Fatty Acid Isethionates (e.g., Sodium Cocoyl Isethionate): These display good responsiveness to salt for thickening.
Fatty Acid Taurides (e.g., Sodium Cocoyl Methyl Taurate): These have an excellent response to salt for thickening.
Acyl Glutamates (e.g., Sodium Cocoyl Glutamate): Like Sulfosuccinates, these surfactants don’t thicken with salt.
Acyl Sarcosinates (e.g., Sodium Lauroyl Sarcosinate): They do thicken a little with salt.
Amphoteric Surfactants (e.g., Cocamidopropyl Betaine, Hydroxysultaines) and Non-Ionic Surfactants (e.g., Alkyl Glucosides): These surfactant categories also do not thicken with salt.
The uneven responsiveness of different surfactants to salt underscores the need for understanding individual surfactant properties when formulating a liquid detergent. It shows that formulating effective and consistent liquid detergent goes beyond merely adding salt, but requires an in-depth understanding of the chemistry of surfactants and their interaction with salt.

Practical Guidelines for Adding Salt to Thicken Detergents

It’s important to understand how to correctly add salt in practical manufacturing to effectively modulate the viscosity of liquid detergents. Here’s a step-by-step guideline, integrating the key points shared above and other essential information, to help you master this process.

Adjust the Slurry pH: Before you begin adding salt, ensure that the pH of the slurry is properly balanced. pH can have a significant impact on the viscosity of the detergent. A sudden change in pH can either cause a spike or a drop in viscosity. Normally, the optimal pH for most detergents ranges between 7 and 9. Use a reliable pH meter to monitor this.
Pre-Dissolve the Salt: Rather than adding dry salt directly into the slurry, first, pre-dissolve the salt with a small amount of water. This will ensure that the salt is evenly distributed throughout the detergent mixture, resulting in a more homogeneous product with uniform viscosity.
Add Salt Gradually: Strictly follow the protocol of adding salt in 0.3 – 0.5% w/w increments at a time. After each addition, allow the mixture to properly incorporate before adding more.
Monitor the Viscosity: Closely observe and monitor the changes in viscosity after each salt addition. It’s critical to avoid oversalting, which can cause irreversible thinning of the detergent. Use an appropriate viscosity measurement tool like a viscometer for accurate results.
Be Patient: The process of adding salt and checking viscosity is a gradual one and requires patience. Hurrying it may lead to incorrect viscosity levels, affecting the overall quality of the detergent product.
Consider the Surfactant Type: Always remember that not all surfactants respond to salt in the same way. Keep the nature of the surfactant in your formulation in mind when adding salt.
Implementing these guidelines into the manufacturing process can ensure better control over the product’s viscosity, leading to superior-quality detergent formulations. Remember, understanding is half the battle – when you comprehend the ‘why’, the ‘how’ becomes much easier to master.