Stearic Acid 硬脂酸

photo from: https://draxe.com/nutrition/what-is-stearic-acid/

 

以下文章擷取自：SOAP QUEEN 之【How to Make Soap Last Longer in the Shower】

Use More Hard Oils
In general, firmer bars of soap last longer in the shower. Using more hard oils helps create a firmer bar of soap. Hard oils refer to oils that are solid at room temperature such as palm oil, coconut oil, beeswax and palm kernel flakes. In general, soap with about 60% hard oils would be considered a firm bar of soap. That looks something like 30% coconut oil, 30% palm oil, 30% olive oil and 10% “something extra.” If your soap contains large percentage of soft oils, allowing it to cure for longer can help it last longer in the shower. For example, soap made with 100% olive oil (known as Castile soap) benefits from curing for six months to a full year.

Use Stearic Acid
Stearic acid is a great addition to soap recipes if you’d like to create an extra firm bar of soap. It’s usually used as a thickening agent in lotion. It’s a vegetable derived waxy substance that can be used at a 0.5% of your oils in cold process soap. That sounds like a very small amount, but a little goes a long way when it comes to stearic acid! Keep in mind if you use stearic acid in your recipe, it will trace faster and needs a hotter soaping temperature (at least 160 ° F) to make sure it stays melted.

Use Sodium Lactate/Salt
Sodium lactate is the liquid salt of lactic acid. It’s generally added to cooled lye water at a rate of 1 teaspoon per pound of oils. It does wonders for hardening up your bar, and really helps extend the life in the shower. I use it in just about every one of my batches! Learn more about sodium lactate here. If you don’t have sodium lactate on hand, you can also add table salt to your lye solution. In the Palm Free Vertical Twist recipe, we used about 1 tsp. of table salt per pound of oils in the recipe…just like using sodium lactate! Sodium lactate or table salt is especially great when the recipe tends to be a little softer (like a palm free recipe).