Acetic acid has the chemical formula CH3COOH:
When cellulose reacts with acetic acid, it creates cellulose acetate. It can be used as a fiber or as a thermoplastic. In labs, cellulose undergoes acetylation by acetic anhydride. More useful and important, highly acetylated cellulose transforms to cellulose acetate under hydrolysis. The physical properties make it ideal to use in many areas. Its density is 1.3 g cm-3, just a little more than water, making it strong, but not too heavy. It burns, but does not ignite. It resistes ultraviolet light well. Over time, it absorbs little water. Its transparency makes it perfect for safety glass and protective goggles. Acetate sheeting can be easily die cut, beaded, punched, stitched, embossed, laminated and cemented. It will not warp or crack under extreme temperatures. For more details on electrical, thermal, mechanical, and chemical resistance properties, please see tables on page 3.
It is shaped by molding and, most commonly, injection molding. Other forms of cellulose did not mold well, but the combination with acetate works very well. Its greatest advantage over its predecessor, cellulose nitrate, is its flame resistance. Cellulose nitrate was used frequently, but it was very very flammable. Cellulose acetate replaced it in photographic film, movie reels, and safety glass. During wartime, cellulose acetate was used to coat early airplanes' fabric wings, since it will burn, but is hard to ignite. It is often used to cover electrical wire. In cars, it is used because it has high mechanical strength, toughness, wear resisitance, transparency, and moldability. It has a high impact resistance, which makes it suitable for goggles, tool handles, and oil gauges. Newer polymers are taking over, but it is still used, especially in film and for injection molding small items, like eyeglass frames and toothbrushes. As a fiber, it is used in yarns, as it is attractive, strong, and holds colors well. A list of common applications of cellulose acetate can be found below. As a senior, I find it uncommon and unique that cellulose acetate is wrinkle resistant and has low moisture absorption, and so it is used to make graduation gowns! For several samples, come to BLAIR 2000's GRADUATION ON JUNE 5th, 2000!
List of Applications
Physical Properties
Density 1.3 g cm-3
Flammability Combustible
Limiting Oxygen Index 19 %
Refractive Index 1.49
Resistance to Ultra-violet Good
Water Absorption - over 24 hours 1.9-7.0 %
Electrical Properties
Dielectric Constant @1MHz ~5
Dielectric Strength 11 kV.mm-1
Dissipation factor @ 1kHz 0.06
Volume Resistivity 5 x 1012 Ohmcm
Thermal Properties
Heat-Deflection Temperature - 0.45MPa 52-105 ¡C
Heat-Deflection Temperature - 1.8MPa 48-86 ¡C
Lower Working Temperature -20 ¡C
Specific Heat 1.2-1.9 kJ.kg-1.K-1
Thermal Conductivity @23¡C 0.16-0.36 W m-1 K-1
Thermal Expansivity 80-180 x10-6 K-1
Upper Working Temperature 55-95 ¡C
Mechanical Properties
Abrasive Resistance - ASTM D1044 65 mg/1000 cycles
Hardness - Rockwell 34-125
Izod Impact Strength 100-450 J m-1
Tensile Modulus 1.0-4.0 GPa
Tensile Strength 12-110 MPa
Chemical Resistance
Acids - concentrated Poor
Acids - dilute Fair
Alcohols Fair
Alkalis Poor
Aromatic Hydrocarbons Good
Greases and Oils Good
Halogens Good
Ketones Poor
BIBLIOGRAPHY
"Early Synthetic Polymers"
http://www.psrc.usm.edu/macrog/early.htm
"Cellulose"
http://www.psrc.usm.edu/macrog/cell.htm
"Cellulose acetate" Encyclopedia Britannica
"Major Industrial Polymers" Encyclopedia Britannica