SynopsisThree commercial disperse dyes and a laboratory-synthesized disperse azo dye were converted to different crystal forms. These were characterized by melting point, x-ray diffractograms, and their dyeing behavior on polyester fibers. The different crystal modifications of the same dye were shown to dye polyester fibers (but not polyamide fibers) a t different rates and to different fiber saturation values. An attempt has been made to explain these differences based on a thermodynamic approach. An attempt is made to apply the concept of crystal modification of disperse dyes to same of the earlier studies done on dyeing and printing of disperse dyes on polyester and secondary cellulose acetate substrates reported in the literature.

SynopsisA series of chemically modified celluloses with different functional groups present in various extents were prepared by separately oxidizing cotton cellulose by potassium metaperiodate, potassium dichromate-sulfuric acid, potassium dichromate-xalic acid and further modifying them by treatment with chlorous acid and sodium borohydride. These were dyed with two purified direct dyes to equilibrium a t 95"C, and their thermodynamic affinities for these substrates were determined, assuming various extents of ionization of carboxyl groups present in them. It has been shown that the affinity decreases with increase in carboxyl value of the oxycelluloses if the carboxyl groups are assumed to be un-ionized and increases with increasing carboxyl value if they are considered to be fully ionized.

Studies of atkytated and esteritit'd wo ols shcvvecl an increased affinity for dyes 1. 2. S I. V'c eskrilied Tussar silk with ntcthanol in the presence of 0.1 A HCI and studied its effect c>n dyeahility with Brilliant Ponn'aux .31t (('I Acid Red 18), So)BBay H)ueBBS(CIAcidB!ue45),and(~roceinScar)et.< .;BS ((_'I I Arid Red 2,S). The (1B-(,s were purili,'d Iw the nwt hod of Roltinwn and Mills ~ ~ I. T'uw;cr silk yarn was (leguninic(i by treatment with textile soap (.i.5 gli.) in the presence of sodium hexametaphosphate (0.$ t:/1.) at thc boil for I hr with a material:liquor ratio of 1:50 131. The v:rmplc wa, rinscc) lir~t with hot and then with cold water and thu c1c-Humming was rcltcatccl. The dt-~umnll'd Tussar silk was hll'arlwd 1.B I with hvclro~cn Iwroxide 1 2 val) in thc pre~l'nce of sodium silicate ( 2 1:/1) and sodium carhonate ( 5.3 gill.) at 80 C for I hr with a material:liquor ratio. of 1:,10. After washing su(,ccssiB-elB-with hot and cald water, the samplc was bteached with sodium hwlrowltitc (5 t:/I.) at 60 C for 10 min and washed. Thc residual alkali was remond 1)B* treatment with 0.01 .1' HCI, followed hy washin~: free of acid. The dl'gumnwd samplc (20 g) was conclitioncd at 30&dquo;C and 657(-RH. Esterilication was carried out at 65&dquo;C for 3 hr with a matl'rial: liquor ratio of I: 50. The simple was washed, dried at 30'C and conditioned.Hsterined and unesterihed 1-g santltlcs of Tussar silk were treated with a solulion containing the purined dye (2j1, owf) and sulfuric acid (O.5j{) at 27, 60, and 98°(' for .<0 min. The initial and final dye concentrations in the dyebath were determined colorimetrically with a Hilgcr Biochem Ahsorptiometer. The amount of the dye taken up by the fiber was calculated from these values. Figure 1 shows that esterified silk takes up more acid dye than the uncstcrificd silk at all temperatures.Esterification affects the extent of dyeing to different del;rees: at 60°C, the effect is more pronounced, but at 98°C (near the boil), the uptake increase drops, presumably due to partial hydrolysis of the ester groups by the sulfuric acid. At each temperature, the relative increases in the dye uptake for Crocein Scarlet 3 BS, Solway Blue B 1S and Brilliant Ponceaux 3 R are in the ratio 2.8:1.8:1.0, respectively.Further work on other varieties of Indian wild silks and with other alcohols is in progress and will be reported later. Ft'. ! 1. Effect of the dyeing temperature on the cfvc uptake of esteritted and unestcrificd Tussar silk: Brilliant Ponn'aux -i R 1 p unesteritied, Vesterifie(i) ; Sotway Blue B BS (6 unesterified, A csterified) ; and Crocein Scarlet .1 RS (0 unesterific(l. 0 esterified).

A. method. for ca~rying out potenttometric~itration of reduced vat dyes in aqueous alkaline solutions usmg a potassium ferricyanide solution as the oxidant is described The standard method is modified on the basis of certain assumptions, and the values of potentials~re~lculated and termed.".01aracteristic redox potentials." An account of the deter':lIn~tlOn of these charac~e\lslc redox potential values for a series of purified vat dyes IS given. The.characteristie redox potential values of vat dyes are compared with the ease of reduction of these dyes and also with their tendering behavior. The effect of substitution on these values is discussed.

synopsisVarious methods suggested for the determination of carboxyl groups in chemically modified celluloses suffer from some drawbacks. Attempts have been made to overcome the drawbacks of some of these methods. The influence of alkali-sensitive reducing groups, enediol groups, and lactones on the carboxyl estimation is discussed and the importance of borohydride treatment of the oxycelluloses before the estimation of carboxyl groups by alkali titration method or by iodometric method is stressed. The usefulness and the limitations of both methods are pointed out.