This first in a series of articles characterized the different varieties of Indian silk for their macrostructural parameters, such as filament length, degumming loss, denier, cross section, moisture regain, and intrinsic viscosity, for example. The results of amino acid analysis using a reverse-phase technique were also reported. Five Indian silk varieties-two mulberry (bivoltine and crossbreed) and three nonmulberry (tasar, muga, and eri)-were investigated. The differences existing between the different varieties and the extent of lengthwise variations within a cocoon in the dimensional and macrostructural parameters were discussed. It was observed that denier of the filament decreases considerably from the outer to the inner layers, whereas density showed an increasing trend in all the varieties. Both the mulberry silks demonstrated lower moisture regain. Electron micrographs of all the nonmulberry varieties showed microvoids in their cross section. Fraction studies showed the development of mushroom structure on the tips. In both types of mulberry silk, glycine, alanine, and serine constitute about 82% of the amino acids present. On the other hand, in nonmulberry silks, these constitute about 73% with a high proportion of alanine. The nonmulberry varieties showed a substantial proportion of amino acids with bulky side groups. Similarly, the higher hydrophilic to hydrophobic amino acid ratio (9.06 -9.85) for nonmulberry silks, compared against that of the mulberry varieties (5.29 -6.22), was shown to be responsible for the higher moisture content of nonmulberry silks. Cystine and methionine were present in all the varieties. The higher intrinsic viscosity of nonmulberry varieties suggested their higher molecular weight. Through amino acid analysis, it was shown that there is no difference in chemical architecture between the outer and the inner layers of cocoons.

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SYNOPSISSolution copolymerization of acrylonitrile (AN) with various vinyl acids, i.e., acrylic acid (AA), methacrylic acid (MAA), and itaconic acid (IA), was carried out in DMF at 70°C using a,a'-azobisisobutyronitrile (AIBN) as an initiator with an acidic monomer of 0.012-0.092 mol %. Copolymers were characterized by FTIR, CHN analysis, 'H-and 13C-NMR, and viscometry. The reactivity ratios were calculated using Fineman-Ross and Kelen-Tudos methods. In all three systems, the value of rl (AN) is much less than the value of r2. However, the rz (MAA) is higher than r2 of (AA) and (IA). The reactivity ratios were calculated using Q and e schemes also. The results are in good agreement with experimentally calculated data. The tacticity and sequence length distribution of these copolymers were calculated using 13C-NMR from C=N and CH signals. It was observed that the isotacticity of acrylonitrile-itaconic acid copolymer P(AN-IA) with 8.2 mol % of a comonomer is lower than that of P(AN-MAA) with 10.3 mol % and P(AN-AA) with 7.61 mol %. 0

Dry-jet-wet spinning of three copolymers, poly(acrylonitrile/methyl acrylate), poly(acrylonitrile/ methacrylic acid), and poly(acrylonitrile/itaconic acid), was performed with a dimethylformamide/water (60:40 v/v) coagulation bath at different temperatures (10 -40°C). The fibers were stretched to different levels (1.1-6ϫ) in boiling water, collapsed, and annealed over a heater plate at 130°C.

Polyacrylonitrile (PAN) and copolymer of acrylonitrile-vinyl acids prepared by solution polymerization technique have been characterized by Differential Scanning Calorimetry (DSC) (under dynamic as well as isothermal conditions), themograviemetric analysis (TGA), and online DSC-FTIR spectroscopy. The DSC of copolymers was carried out at 5°C/min in nitrogen and air. In nitrogen atmosphere the DSC exotherm show a very sharp peak, whereas, in air atmosphere DSC exotherm is broad, and starts at a much lower temperature compared to what is observed in nitrogen atmosphere. The initiation temperature of PAN homopolymer is higher than that for the copolymers. For instance, the initiation temperature of PAN in air is 244°C, whereas, the onset of exothermic reaction is in the range of 172 to 218°C for acrylonitrile-vinyl acid copolymers. As the vinyl acid content increases the ⌬H value reduces. The ⌬H value of PAN in air was 7025 J/g, whereas, for P(AN-AA) with 5.51 mol % of acid it was 3798 J/g. As the content of acrylic acid comonomer is increased to 17.51 mol % the value of ⌬H decreases further to 1636 J/g. The same trend was observed with MAA and IA as well. DSC-FTIR studies depict various chemical changes taking place during heat treatment of these copolymers.