Secondary cellulose acetate Stabilizers

It has already been implied that cellulose triacetate will not produce a thermoplastic, as its softening point cannot be reduced appreciably by plasticizers. It is used in solution processes, however, to produce films and libers. Triacetate films absorb less water than films of secondary cellulose acetate, and they arc therefore more dimensionally stable in environments where the humidity is not controlled. Triacetate fibers, with a similar resistance to water, impart to fabrics wrinkle resistance, dimensional stability, and the ability to dry rapidly. Under United Slates federal regulations, a filler must tic made from a cellulose acetate having... 

Secondary cellulose acetate (D.S. 2.4) is prepared by interrupting the acetylation reaction leading to CTA by adding water in the form of aqueous acetic acid of 50-75% concentration (as noted above). This also decreases the level of combined sulfuric acid which improves the stabihty of the cellulose acetate. Magnesium ions are added to produce insoluble sulfeles further improving the stability of the product. The hydrolysis rate is controlled by temperature, catalyst concentration and to a smaller extent by the water content. The amount of water influences the ratio of primary to secondary hydror l groups in the hydrolyzed cellulose acetate. 

Cellulose acetate films of the same thickness (8 mil) containing five different stabilizers at three concentrations were evaluated for their effectiveness in protecting the blue wool fabrics (Table II). Unprotected wool fabric and wool fabric covered with film containing no stabilizers exposed to the xenon-arc source under comparable conditions served as primary and secondary controls. Film without any stabilizer offered little protection throughout the exposure period after 550 kj/m2 exposure, fabric protected by such a film had a AE value of 2.38 and unprotected fabric had a value of 2.70. 

The other commercial stabilizer (UV-3), a hindered-amine type, is presumed to afford photochemical protection by functioning primarily as a free radical and/or oxygen scavenger (13). Thus protection should only occur in the primary substrate, the cellulose acetate film, and not in a secondary substrate such as the blue wool fabric. The results shown in Table II verified this assumption the AE values obtained, irrespective of the concentration of UV-3 used in the film, were within experimental error of those observed with the unprotected fabric. 

In systems 5 and 6, this phenomenon is a result of hydrogen-bond formation between the polymer and solvent, which enhances the solubility. As hydrogen bonds are thermally labile, a rise in T reduces the number of bonds and causes eventual phase separation. In solutions, which are stabilized in this way by secondary bonding, the LCST usually appears below the boiling temperature of the solvent, but it has been found experimentally that an LCST can be detected in nonpolar systems when these are examined at temperatures approaching the critical temperature of the solvent. Polyisobutylene in a series of n-alkanes, polystyrene in methyl acetate and cyclohexane, and cellulose acetate in acetone all exhibit LCSTs. 

The most commonly used EWAs in laundry products today are shown in Table 28.2 and represent three chemistries—distyrylbiphenyl, coumarin, and stilbene. The selection of the EWA to be used in a specific type of laundry product will depend on several factors such as compatibility with the formulation, fabrics, product claims, laundry conditions, application, and manufacturing limitations. For example, compounds 60 and 62-65 are substantive to cellulosics and compound 61 is substantive to sUk, wool, nylon, secondary acetate, and triacetate fibers. Eor bleach-based products (e.g., hydrogen peroxide) compound 60 is used as distyrylbiphenyl chemistry exhibits the required stability. 

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