Triacetate fibres

An important property of triacetate fibres is the ability to undergo structural changes under the influence of heat. Triacetate is not effected by dry heat up to 150 C. The fibre becomes increasingly plastic between 150 to 190 C and at still higher temperatures up to 220 C molecular reorientation occurs to an increasing extent accompanied by increase in crystallinity so that imbibation of the fibre falls from 16 to 10% and there is corresponding reduction in absorption and desorption 

Approximate Heat-setting Conditions of Different Polyesters 

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Secondary cellulose acetate has also been used for fibres and lacquers whilst cellulose triacetate fibre has been extensively marketed in Great Britain under the trade name Tricel. 

Polyamide and polyester fibres are generally scoured using an alkyl poly(oxyethylene) sulphate and sodium carbonate. Some polyester qualities are subjected to a causticisation treatment with sodium hydroxide in the presence of a cationic surfactant to give a lighter fabric with a silkier handle [154,156]. This treatment involves etching (localised saponification) of the polyester surface and is broadly analogous to the S-finish used on triacetate fibres. The process has attracted considerable interest in recent years but its... 

Atmospheric ozone has also been reported as causing fading of certain dyes in some countries [425,426] diallyl phthalate (10.182) used as a carrier in the dyeing of cellulose triacetate fibres, is said to be an effective ozone inhibitor [427]. Nylon, especially when dyed with certain amino-substituted anthraquinone blue acid dyes, can also be susceptible to ozone fading [428,429]. Selection of ozone-resistant dyes is obviously the best counteractive measure, although hindered phenols (10.161) and hindered amines (10.162) are said to provide some protection. 

Cellulose acetate and triacetate fibres are brightened with disperse-type FBAs, including derivatives of 1,3-diphenylpyrazoline (11.19). These form a commercially important group of FBAs. If suitably substituted they can be applied to substrates other than acetate and triacetate. The commercially more important products of this type are used to brighten nylon and acrylic fibres. Their preparation and other aspects of pyrazoline chemistry are discussed in section 11.8. Examples of pyrazolines used to brighten acetate and triacetate... 

Diacetate fibres can be dissolved out by two treatments with acetone and triacetate fibres by three treatments with dichloromethane, in each case for 10 min at room temperature. In this way they can be separated from cellulose, wool, silk, polyester or acrylic fibres, which then remain as a residue. 

Cellulose di- and triacetate fibres (CA, CT) as well as acrylic fibres (polyacrylonitrile, PAN) are all soluble in the zinc chloride-iodine reagent. An initial differentiation is made using the acetone test on a watchglass only CA and CT fibres dissolve (evidenced by a cloudy evaporation residue). Differentiation between CA and CT fibres CA dissolves in Frott6 II reagent (see Table 8.1), CT only swells. Results are similar in zinc chloride/formic acid, but with a less distinct difference (CT swells more markedly). PAN fibres dissolve in cold concentrated nitric acid and in dimethylformamide at 100 °C. They swell in boiling 85 % formic acid and decompose at about 280 °C without melting. 

Reference has already been made to the fact that the normal product of acetylation of cellulose is the triacetate which does not dissolve in acetone. Early attempts to spin were abandoned partly because of the difficulty in finding an economically satisfactory and safe solvent. Methylene dichloride has since become available on a commercial scale and has reopened the possibility of making triacetate fibres. 

The actual experimental conditions employed range from the use of cultured broths of common microorganisms, through the use of cell-free extracts, to the use of columns of fully immobilized enzymes embedded on cellulose triacetate fibres, and reactions are rapid at 30°. 

The property profile of cellulose-based plastics and cellulose products used in typical plastics applications covers a broad range where the intrinsic cellulose properties can be recognized to different degrees. So, hydrophilicity is a prominent feature for pure cellulose products, which is reduced as the number of ester substituents and their chain length is increased. Equilibrium moisture content of cellulose fibres, for example, is around 12% while the moisture regain of diacetate fibres is 6.5% and of triacetate fibres 3.2% [43]. In this respect, propionic and butyric esters are superior when fully substituted, but even mixed esters of the CAP and CAB types... 

As indicated previously the degree of esterification of the various types of cellulose acetate has a significant influence on solubility. This effect is illustrated in Table 11.7 wherein solubilities of various types of cellulose acetate are compared. The most important solvent for materials with lower degrees of esterification is acetone about 56% acetic acid yield generally represents the upper limit of acetone solubility for commercial products. In the manufacture of fibre, a solution of cellulose acetate in acetone is extruded through a spinneret into a heated chamber, wherein the acetone is evaporated to leave the fibre. In the production of packaging film, a solution of cellulose acetate in acetone is cast on to a band and the solvent is evaporated, leaving the film. A methylene chloride/methanol mixture is the most common solvent used for the preparation of cellulose triacetate fibre and film. 

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