| |
Answer:
The main reason for development of shampoo was that “hair became rough
and damaged when soap was used to wash hair”, as you mentioned. Thus,
shampoo is specific for washing hair.
However, both shampoo and soap employ “surfactants” as the main
compound to remove dirt. Let us look at the main kinds of surfactants
in the history of shampoo development.
Types of surfactants and the history of shampoo development
1. Soap
This is made from boiling beef tallow or palm oil with an alkaline
solution to produce the salt of a fatty acid (surfactant), this
process is called “saponification”. The product produced this way can
dissolve oil and remove dirt.
However, the relationship between alkali and hair is not beneficial.
Alkali gradually causes damage to the proteins of hair. It may also
react with other preparations for hair and cause problems. In
addition, soap reacts with metal ions (Ca2+ etc. ) and forms a complex
called “scum”, which is also not good for washing hair. (You are able
to see scum on your bath tub.)
2. Oil (petroleum) detergent
These types of detergents (surfactants), such as alkyl benzene
sulfonates, were originally invented in Germany during the war. At
that time, Germany had to synthesize a detergent independent of fat
because of the economic blockade.
Incidentally, oil detergent, which is still used as dish soap or
laundry soap, is good for removing dirt. However, it also removes the
components that hair needs. This removes oil from hair and damages the
skin. Bluing was invented, and some additives were added to shampoos
in order to solve this problem. However, you may still feel sticky or
dry depending on how thoroughly you rinse the hair after using these
shampoos
 3. Higher alcohol detergents
This
type of detergent (surfactant) was developed to avoid the disadvantage
of soap and oil detergents. “Higher” means the alcohol molecule has
more than 8 carbons. For example, higher alcohol detergents made from
palm oil (picture: hearts of palm) have usually between 12 and 18
carbons.
*
*
*
Thus, we see that new surfactants have been developed to make up for
the disadvantages of the original surfactants. By the way, what kinds
of surfactants do current shampoos contain?
The difference between shampoo and soap
These are properties which shampoo should have:
-
Proper detergency without degreasing
-
Ability to form delicate and rich bubbling
-
Easy rinsing
-
Good finish after washing hair
-
Minimal skin/eye irritation
-
No damage to hair
-
Low toxicity
-
Good biodegradability
Surfactants are chosen based on these factors. In many current
shampoos, the higher alcohol type–anion surfactant provides the proper
detergency and forms rich bubbles, and a non-ion surfactant is added
as coadjuvant. The reason why more than one kind of surfactant is
employed in shampoo is to make better bubbling and to have a more
beautiful finish for the hair.
In addition to surfactants, many other ingredients are added to
shampoo in order to prevent dandruff, to treat the hair, to rinse the
hair and to give him/her a fresh feeling, etc. This is the difference
between shampoo and soap.
What if shampoo is used for washing a body?
As has already been mentioned, shampoo has many functions besides
taking out dirt.
Thus, these functions would not damage skin, but
there would be some disadvantages – for example, many ingredients in
shampoo are not needed for skin (bad efficiency), and you might feel a
bit slimy. In addition, the cost of shampoo is usually more than
the cost of soap.
Acknowledgement
We thank following teachers for their careful teachings and kind
suggestions in this report.
Shirosaka Co.,LTD
This company has a website containing a lot of information about hair
and fashion.
Kao
Corporation, Chemical Business Division
This website introduces industrial chemical products (Fats and Oil
Derivatives, Surfactants, etc.) made by Kao Corporation.
This article is translated by Chemistryquestion.com from the original
article in Chemistryquestion.jp. Please let us know if you find any errors.
|
|
