Polyacrylic Acid

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Introduction



Poly(acrylic acid) or PAA (CAS number 9003-1-04) is a type of polymer. The monomer of poly(acrylic acid) is Acrylic Acid. In a water solution at neutral pH, many of the side chains of PAA will lose their protons and acquire a negative charge.

Dry PAA is a white solid. It is capable of absorbing many times its weight in water, and hence is used in disposable diapers. In diapers it is a fine powder - see picture of material form a diaper.


Chemical Properties


Polyacrylic acid is a large-molecular-weight compound called a polymer, which consists of small repeating units called monomers. The polyacrylate polymer used in diapers is constructed from the acrylic acid and sodium acrylate monomers. The length of the polymer chain and the properties of the polymer may be changed by varying the reaction conditions. The reaction conditions can affect the the length of the chains and can change the characteristics of the polymer. The polyacrylate is dried and formed into microparticles of irregular shape that are stable for extended periods. The particles quickly swell and absorb water, urine, or other aqueous solutions.


History


A super-absorbent (SAP) or polyacrylic acid was patented in 1966 by Gene Harper of Dow Chemical and Carlyle Harmon of Johnson & Johnson. It was first used in diapers in 1982 in Japan.


Uses


Polyacrylic acid is found in a wide variety of household and personal care products:

  • Diapers
  • Hand sanitizer
  • Mascara
  • Aftershave
  • Toothpaste
  • Hair-styling products (gels, dyes, sprays)
  • Moisturizer
  • Pet shampoo
  • Metal polish


Toxicity


Human Health Effects

Products containing polyacrylic acid warn of a mild irritation if eye or skin exposure occurs. Not meant for skin contact.


Material Safety Data Sheets (MSDSs) for Polyacrylic Acid


A common statement on MSDSs is "To the best of our knowledge the chemical, physical & toxicological properties have not been thoroughly investigated."


Manufacture


Note that the polyacrylic acid contains some of the monomer acrylic acid.

Information from Chemquat and their website on Polyacrylic acid
Polyacrylic Acid
IUPAC Name: acrylic acid
CAS Number: 9003-01-4
Chemical Formula: C3H4O2

Appearance: colorless to pale yellow transparent solution
Solid content, % 25-42
Free monomers as acrylate: 0.5% max
Molecular weight 1200-100000
pH of 1% solution: 3.0 max
Specific gravity; g/cm3:1.15 min
Packing 200l plastic drum
Gross weight 260kg
Net weight 250kg


Regulation


References


  • U.S. Department of of Health and Human Services Household Products Database: Polyacrylic acid
  • Cool Science website: Diapers - Short introduction to SAP and diapers
  • University of Southern Mississippi Polymer Science Learning Center: Acrylates - Explains the chemistry of different configurations
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