Active matter arithmetic
A surfactant raw material is rarely 100 percent active. Sodium Laureth Sulfate is commonly sold as a 70 percent paste, cocamidopropyl betaine as a 30 percent solution, and many blends at similar strengths. The percent on the formula sheet is the weight of the raw material, while the percent that cleans is the active matter inside it. Confusing the two is the most common reason a shampoo is either harsh or weak. A 70 percent paste for 10 percent active weighs 14.3 g per 100 g of product, because 14.3 multiplied by 0.70 is 10.01. Writing 10.00 g of paste would give only 7.00 g of active and a thinner, weaker foam.
The primary anionic surfactant is often used at about 8 to 12 percent active matter in a shampoo. Below that band the foam is weak and the product feels underpowered; above it the shampoo cleans well but strips the scalp and hair, especially with daily use. The amphoteric, usually cocamidopropyl betaine, is often used at about 2 to 5 percent active matter. It softens the harshness of the anionic, improves foam quality, and helps the viscosity build. A non-ionic such as a glucoside can add mildness, and a cationic polymer can improve wet comb, but neither replaces the primary anionic at the same weight.
Do the arithmetic before you weigh, and write both numbers on the card. The raw material weight goes in the percent column; the active matter goes in a note. When a supplier changes the strength of a paste from 70 to 68 percent, the raw material weight must rise to keep the same active, and the water line must fall to keep the total at 100.00. This is a real change that happens without warning, and a shampoo can change character overnight if nobody checks. Add the active matter calculation to the batch record, not just to the training notes.
Active matter also drives the claims and the cost. A shampoo that says 12 percent active on the front and delivers 8 percent in the bottle is a claim problem as well as a performance problem. The label on a retail cosmetic must declare ingredients in descending order of predominance, so the surfactant system sits high in the list and should correspond to the formula. Keeping the arithmetic honest is therefore not only bench hygiene; it is the basis on which the label can be defended if someone reads it against the batch record. A label that cannot be matched to a batch record is a claim with nothing behind it.
- 1. Read the as-supplied strength on the surfactant data sheet before any calculation.
- 2. Convert grams of raw material to grams of active matter by multiplying by the strength.
- 3. For 10 percent active from a 70 percent paste, weigh 14.3 g per 100 g of product.
- 4. Set the primary anionic target at about 8 to 12 percent active matter for a shampoo.
- 5. Set the betaine at about 2 to 5 percent active matter, and count its own strength separately.
- 6. Add the active matter figures in the notes column, not in the percent column.
- 7. Recalculate the raw material weight if the supplied strength changes, and adjust water to 100.
- 8. Compare the finished foam and feel against the active matter target, not against the raw weight.
Bench example: two pastes, same formula weight
A 100 g shampoo card calls for 14.30 g of a 70 percent Sodium Laureth Sulfate paste, which gives 10.01 g of active. The supplier runs out and sends a 68 percent paste. If the bench weighs 14.30 g of the new paste, the active falls to 9.72 g, a loss of about 0.29 g, or roughly 3 percent of the surfactant system. That is enough to change the foam and the salt curve. To hold the target, divide 10.01 by 0.68, which gives 14.72 g of the new paste. The extra 0.42 g comes out of the water line, which falls from 68.30 to 67.88 g, and the sheet still totals 100.00. Write the paste strength, the calculation and the new water line on the batch record. A shampoo is a system, and a small change in active matter moves the viscosity peak as well. Record the new paste strength in the notes, and tell the person who fills the bottles, because the batch carries the change even when the label declaration does not. Write the calculation in the notes so the next person can follow it.
Caution: Never swap a surfactant paste for another strength at the same weight. Recalculate the active matter, then let water absorb the difference.
Building a shampoo
A shampoo is a surfactant system with water, a thickener, conditioning agents and a preservative. Build it in an order that avoids foam and protects the small lines. Disperse any gum or polymer in water or glycerin first, add the water-soluble ingredients, then the primary anionic with slow stirring. Add the amphoteric and the non-ionic next, then the conditioning polymer. Adjust pH before the salt, because salt thickens differently at different pH values. Add preservative and fragrance under 40 C, then the salt premix in steps to the viscosity peak, and recheck the pH at the end. If the batch foams during mixing, let it stand; trapped air makes every reading unreliable and every fill weight light.
Do not aerate the batch. Foam in the making vessel wastes raw material, traps air in the bottle, and makes the fill weight wrong. Stir with a paddle at a speed that moves the liquid without folding air into it. If foam forms, let the batch stand rather than stirring harder. A shampoo that is full of bubbles at filling can settle in the bottle and leave a headspace that looks like a short fill. The same trapped air makes a viscosity reading unreliable, so measure after the batch has stood and the bubbles have risen. A degassing pause of ten minutes is cheaper than a bottle that looks half empty on the shelf.
Preservation needs care in a shampoo because the pH and the surfactant load both affect the system. Organic acids such as sodium benzoate and potassium sorbate work in the acid form and generally need a product pH under about 5.5. A shampoo at pH 5.0 to 6.5 sits near the edge, and at the top of that range the acids are less effective. A chelator supports the system but is not a preservative. A challenge test on the finished formula, in the finished pack, is the only proof that the system works. Rinse-off products have a shorter contact time, but they still grow microbes in the bottle between uses.
Viscosity, pH and foam are the three readings that tell you the batch is right. Record them at a stated temperature, because a shampoo thick at 20 C can be thin at 35 C and the client may notice. Check the appearance in a clear sample jar against a light: a hazy shampoo may be a fragrance that is not solubilised, a polymer that has not hydrated, or a preservative that has dropped out. Each has a different fix, and none of them is fixed by adding more salt. The batch record should carry the readings, the salt total and the order of addition.
- 1. Disperse the polymer or gum in water or glycerin before the surfactants go in.
- 2. Add the water and water-soluble lines, and warm gently only if a raw material needs it.
- 3. Add the primary anionic slowly, with a paddle, to avoid folding air into the batch.
- 4. Add the betaine and any non-ionic, then the conditioning polymer, one at a time.
- 5. Add the chelator, then set the pH to the target before any salt is weighed.
- 6. Add the preservative at the temperature its supplier sheet allows, then the fragrance under 40 C.
- 7. Add the salt as a premix in steps, checking viscosity after each addition, and stop at the peak.
- 8. Recheck pH, viscosity and appearance, and record all three with the temperature.
Bench example: clear shampoo, 100 g
Formula for 100 g, figures in grams. Sodium Laureth Sulfate 70 percent paste 14.30; Cocamidopropyl Betaine 30 percent 10.00; PEG-7 Glyceryl Cocoate 2.00; Glycerin 2.00; Polyquaternium-7 0.50; Sodium Chloride 1.20; Citric acid 10 percent solution 0.50; Phenoxyethanol at the supplier dose 0.80; Disodium EDTA 0.10; Fragrance 0.30; water to 100 68.30. The lines total 100.00 g. Active primary surfactant is 14.30 times 0.70, which is 10.01 g, about 10 percent. Active betaine is 10.00 times 0.30, which is 3.00 g, inside the 2 to 5 percent band. Dissolve the surfactants in the water, add the rest except salt and fragrance, adjust pH to about 5.5, then add the salt premix to the target viscosity. Cool, add preservative and fragrance, and recheck pH. Confirm every dose with the supplier sheet and run a challenge test before sale. Every weight belongs in the batch record. If the batch is to be sold, keep a retained sample and send the formula for a challenge test before the first bottle leaves the salon. The pH and viscosity readings belong on the same page as the weights.
Caution: Do not add salt before the pH is set. The same salt level can thicken at one pH and thin at another, and the batch cannot be undone.
The salt curve
Salt thickens a sulfate shampoo, but only up to a point. As sodium chloride is added, viscosity rises, reaches a peak, and then falls again as the micelle structure changes. The peak is different for every surfactant blend, every active matter level and every pH. That is why salt is added as a premix in small steps with a viscosity check after each one, and why the total in the formula is a starting charge rather than a fixed law. A formula that lists 1.20 percent salt may need 0.90 or 1.60 in a particular batch, and the record should show what was actually used.
Temperature changes the reading. A shampoo measured warm is thinner than the same shampoo at room temperature, and a batch measured in a cold room is thicker. Fix a temperature for the measurement, usually 25 C, and let the sample stand long enough to reach it. Fix the spindle and speed as well. A reading without those three parameters is a number that cannot be compared with anything, including the next batch of the same formula. Write them beside the result, every time. A reading taken at 30 C and compared with one taken at 20 C will suggest a change that did not happen.
Salt is not the only thickener, and it is not always the right one. A PEG-based thickener, a betaine at a higher level, or a small amount of a gum can build viscosity in systems where salt does not respond. A sulfate-free system often needs a different thickener entirely, because the salt curve may be flat or inverted. Before adding salt to a formula that will not thicken, check the active matter, the pH and the polymer hydration. Salt cannot rescue a system that has too little surfactant or a pH far from the target. Read the supplier sheet for the thickener before you add it, because some thickeners need a pH range of their own.
Too much salt is worse than too little. Past the peak, the shampoo thins, and adding more salt makes it thinner still. The batch is then difficult to correct without diluting, which changes every percentage. The safe habit is to stop a little before the peak, measure, and add the last increment slowly. If the batch overshoots, record it and adjust the formula for the next version rather than pretending the salt line was always right. A shampoo that is slightly thinner than target is a product; one that has passed the peak and lost its structure is a rework.
- 1. Set the pH before the first salt addition, and record the reading.
- 2. Make a 20 percent sodium chloride premix so small increments can be weighed accurately.
- 3. Add the premix in steps of about 0.20 percent of the batch, stirring until uniform.
- 4. Measure viscosity after each step at a fixed temperature, spindle and speed.
- 5. Stop when the viscosity stops rising, and add no more salt after the peak.
- 6. Record the total salt used, including the water that came with the premix.
- 7. Reduce the water line in the next version by the premix weight, so the sheet still totals 100.00.
- 8. If the batch passes the peak, stop adding and note the deviation rather than diluting blindly.
Bench example: finding the peak on a 500 g batch
A 500 g shampoo batch is at pH 5.4 and reads 1800 centipoise at 25 C. A 20 percent salt premix is added in 5.00 g steps, which is 1.00 percent of the batch, and each step carries 1.00 g of salt. After the first step the reading is 2600, after the second 3900, after the third 4800, and after the fourth 4600. The peak sits between the third and fourth steps, so the batch has passed it. The total salt is 4.00 g, or 0.80 percent, plus the water in the premix, which is 16.00 g. The batch now weighs 520.00 g, and the water line must be reduced by 16.00 g in the next version. Record the peak, the salt total and the new batch weight. If the product is too thick to fill, a small dilution is a new formula version, not a correction to the old one. A dilution changes the active matter and the preservative dose, so it needs a new card, a new pH check and a new challenge test if the product is sold. That is a decision for the owner, not a quiet adjustment at the sink.
Caution: Past the salt peak, more salt makes a shampoo thinner. Stop before the peak and record the total, or the next batch will overshoot again.
This is a Nandu Nai textbook. It is a private brand book, not a government licence, and it does not give the right to give medical treatment.