Rayon reduces in its gloss when acetylated in acetic anhydride-kerosene mixture with potassium acetate catalyst and washed with water. This phenomenon was studied in detail with cellophane. It is very difficult to measure the gloss of staple fibers, while the measurement of opacity for a given film is not only easy but reliable.
Cellophane, treated in the same procedure as written above, also reduces in clearness, looking opaque. In general, opacity of films is shown by 'Degree of Haze [
H]'.
It was found that increase in [
H] does not come from acetylation itself but from swelling of the acetylated cellophane in the acetylating liquid as well as deswelling of the swollen acetylated cellophane brought about by washing with water. When the acetylated cellophane swollen with hydrophobic acetic anhydride is steeped in water, acetic anhydride in the film as swelling agent forms lots of small particles in the film. These particles are gradually substituted by water, leaving their own traces in the film. Observation of the cross section of the opaque acetylated cellophane through a phase-contrast microscope shows a lot of small voids, which are thought to be the traces of particles mentioned above and scatter light beam. The higher the degree of acetylation of cellophane is, the higher [
H] becomes.
Treatment with hydrophilic swelling agents, such as acetic acid and acetone, followed by washing with water, improves [
H] of the acetylated cellophane to a great extent.
Cellophane, acetylated in acetic anhydride vapor, swells a little during its acetylating process with the result that this acetylated cellophane has a low [
H], as compared with the former.
Alon, acetylated in acetic anhydride vapor, looks dull as if it contained TiO
2. High tenacity rayon, starting rayon of Alon, contains many small voids. These voids increase in number and size, when the rayon passes through the acetylating process. Treatment of Alon with acetic acid also gives rise to bright Alon.
抄録全体を表示