The Effect of Shampoo on the Tensile Strength of Hair Barbara McHugh 9th Grade Academy of Notre Dame de Namur

Problem What effect does shampoo have on the tensile strength of hair?

Research Hair is mostly made up of the protein keratin. It is also made up of natural oils, produced from the sebaceous gland, and water. The sebaceous gland adds a layer of protection, and keeps hair shiny and healthy. A hair strand has three different layers to it; the cuticle, outside layer, the cortex, middle layer, and the medulla, the soft core. The hair root from which the hair grows is called the follicle, and tiny blood vessels in the follicle nourish the hair root to keep it growing. Once the hair grows and reaches the skin’s surface, the cells that compose the strand die.

Research Hair is composed of amino acid chains which are found in the cortex of the hair. These amino acids contain carbon, hydrogen, oxygen, nitrogen, and sulfur, and are held together by peptide bonds which can turn into polypeptide chains. These polypeptide chains have side bonds. There are salt bonds, hydrogen bonds, and disulfide bonds. Salt and hydrogen bonds are more common, but heat and moisture break them. Disulfide bonds are less common, but are stronger. Each side bond makes up one-third of each hair’s strength.

Common Shampoo Ingredients Shampoo is about 80% water. Cocamide or cocamidopropyl give the bubbles and suds to shampoo. Ingredients such as sodium citrate or citric acid control the pH level of shampoo. They help to keep hair smooth. Dimethicone and other silicones give hair a coating and add smoothness. Polyquaternium keeps hair under control and easy to handle. Ingredients like panthenol add moisture and give hydration.

Hypothesis If someone uses a shampoo that contains certain ingredients, then it may make their hair stronger or weaker.

Materials 1 cotton towel 5 hair weaves 20mL of 3 different brands of shampoos A force meter and weights 7 400mL of 38.89°C water 2 plastic containers

Procedure Four plastic containers were set out. Gloves were used when handling the weaves. A container was filled with 400 mL of 38.89°C. A weave was washed for 2 minutes with 20 mL of shampoo. After washing for 2 minutes, the weave soaked for 2 minutes on the side of the container of water. 6. The weave was then put in a new container of 400 mL of water at 38.89°C and rinsed clean for 2 minutes. 7. Then the weave was laid flat down on a white cotton towel to air dry for 24 hours. 8. This same procedure was repeated for 2 other weaves. 9. For a fourth weave, it was just washed in water for 2 minutes in 400 mL of 38.89°C and then put on the towel to dry for 24 hours. 10. For the fifth weave, nothing was done to it; it was just placed on the towel with the other four weaves for 24 hours. 11. After 24 hours, the five weaves were tested using the force meter and weights in order to determine how much strength it takes to break a strand of a weave.

Procedure 3 Tests were done for each weave. The independent variable was the shampoo. The dependent variable was the tensile strength of the hair. The control was the hair that was just washed in water and the hair with nothing done to it. The constants included the same amount of pull on the hair, same environment where the hair was stored, and the same amount of water and shampoo to wash the hair. The same type of hair was also used for each test.

The weave with Brand B shampoo was stringy, hard, and not smooth. Weaves After 24 hours of drying, the weave with Brand A shampoo was smooth, silky, and not stringy or hard. The weave with Brand B shampoo was stringy, hard, and not smooth. The weave with Brand C shampoo was crunchy, stringy, and the hairs were stuck together in groups. The weave with just water was smooth, and similar to the weave with Brand A shampoo. The weave with nothing in it was also smooth, but not as silky as the weave with Brand A shampoo. The hair had static.

These are the weaves after 24 hours of drying Brand A Weave Brand B Weave Brand C Weave Weave w/ just water Weave w/ Nothing These are the weaves after 24 hours of drying

Tests The room temperature for every day of testing was the same at 21.11°C. For every test, a strand of hair from each weave was tied in a double knot around the force meter, and then pulled until it broke. All the tests had similar points of breaking, but different physical appearances after 24 hours of drying.

Chart of Test Results Brand A Brand B Brand C Hair w/ water   Brand A Brand B Brand C Hair w/ water Hair w/ nothing Test 1 3.03 3.35 3.13 3.06 2.92 Test 2 1.2 1 Test 3 1.4 Mean 1.876667 1.983333 1.91 1.753333333 1.773333333 SD 1.003809 1.187785 1.061273 1.136016432 0.993042463 CI 1.135896 1.344081 1.200921 1.285499988 1.123712684

Brand A Shampoo Brand B Shampoo Brand C Shampoo Water   Water Ammonium Lauryl Sulfate Sodium Laureth Sulfate Ammonium Laureth Sulfate Cocamidopropyl Betaine Dimethicone Sodium Chloride Cocamide Mea Fragrance Distearyl Ether Glycol Distearate Glycol Distearat Cocamide Mipa Dimethiconol Ammonium Xylenesulfonate Glycerin Behenyl Alcohol Citric Acid Carbomer Laureth-2 Guar Hydroxypropyltrimonium Chloride Pyrus Malus Extract/Apple Fruit Extract Panthenyl Ethyl Ether TEA-Dodecylbenzenesulfonate PPG-5-Ceteth-20 Panthenol PPG-9 Polyquaternium-10 Tetrasodium EDTA Sodium Methylparaben Sodium Citrate TEA-Sulfate Sodium Benzoate DMDM Hydantoin Disodium Edta Niacinamide Peg-7M PEG-45M Pyridoxine HCI Cetyl Alcohol Methylchloroisothiazolinone Methylisothiazolinone Mica Saccharum Officinarum/Sugar Cane Extract Titanium Dioxide Methyl Cocoate Yellow 5 Linalool Yellow 6 Sodium Cocoate Butylphenylmethylpropional Citrus Medica Limonum Peel Extract/Lemon Peel Extract Camellia Sinensis/Camellia Sinensis Leaf Extract

Results After testing, it seemed that Brand B shampoo worked the best because, on average, the weave that used Brand B shampoo needed the most force to break. On test 2 and 3 especially, all the weaves had very similar results. However, all the results ended up being extremely close.

Conclusion If someone uses a shampoo that contains certain ingredients, then it may make their hair stronger or weaker. The hypothesis was not supported because the results were all very similar, and there was not a huge difference. To improve the experiment, the shampoo should have soaked in the hair for a longer period of time, it should be dabbed to remove excess water, and the hair should have been hung to dry rather than laying it flat.

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