| The effect of heat treatment on three polyester (PET) fabrics and the effect of heat and solvent modification on Dacron 54 PET fibers was studied. The solvents used were N,N-dimethylformamide, methyl benzoate and bromobenzene. Internal morphology was characterized using critical dissolution time, density and birefringence measurements, differential thermal analysis (DTA), Wide Angle X-ray Scattering (WAXS) and dyeing methods.; Results from the characterization of thermally modified fabrics were found to be dependent on the initial morphology of the PET fabric.; Enthalpies of melting were found to be orientation-sensitive. At treatment temperatures above 160 degrees celsius, polymer orientation decreases and enthalpy values begin to decline. The polyester with the highest initial orientation exhibited the sharpest drop in heat of melting for heat treatment temperatures above 160 degrees celsius.; While heat treatments lead primarily to the formation of new crystallites, solvent modification allows for the reorganization of existing crystallites into fewer, larger crystalline regions, as well as the emergence of new crystals.; Solvent treatment tended to increase dye adsorption values. Treated fibers did not however reach equilibrium dye adsorption faster than untreated fibers.; Sorption of rod-shaped dyes was found to be increased markedly in DMF-treated fibers. The higher affinity of DMF-modified fibers for the long, flat dyes supports evidence from WAXS and DTA data which indicates that DMF treatment leads to the formation of crystallites which are longer in the direction of the polymer chain than are found after exposure to the other solvents used.; The shape of dyeing rate curves was observed to change after solvent treatment in some cases. Initial diffusion into fibers usually is proportional to the square root of time. Diffusion into solvent treated fibers dyed with large dyes approached the linear dependence on time characteristic of relaxation-controlled processes.; The extent of structural modification is dependent on the structure of the solvent used. The solvent best able to disrupt the strong dipole interactions of polyesters carbonyl groups, DMF, produced the most drastic structural changes. Methyl benzoate, with an aromatic ring in addition to a portion capable of dipole interaction effected less modification and the almost wholly aromatic solvent bromobenzene, the least. |
