Effects of Decalin on Some Properties of Polypropylene Continuous Filaments

This work has setup to determine the effects of a solvent on the structure and properties of polypropylene fibres with different physical structures. Samples of continuous filament yarns with different physical structures (partially oriented (POY) and drawn yarns) are treated with decahydronaphthalene (decalin) at 28, 55, 75 and 95oC. At 95oC, the samples are dissolved completely in decalin and after cooling to room temperature (28oC), only 94% of the polypropylene precipitated. The results of the treating yarn samples with decalin at 28, 55 and 75oC, show a small reduction in the weight of the samples. Breaking strength and elongation remained unchanged and stress-strain curve of the POY samples in the yield region did not change. Fourier transform infrared spectra of the samples are compared with those of the published literature and the changes in the spectrum as the results of the treatment with decalin are verified. X-ray diffraction studies show the changes in the structure of POY samples. Differential scanning calorimeter shows no changes in the melting point of the samples, but confirms the results of X-ray diffraction regarding the changes in the structure of POY samples. For the drawn samples X-Ray diffraction diagrams did not show considerable changes. Measurement of birefringence of the samples shows considerable changes in the molecular orientation of the samples due to solvent treatment. The changes in the structure of the samples treated at low temperature with decalin are explained with reference to the pertinent structural models of polypropylene fibers.