Masters Theses

Yiqun Lin

Date of Award

5-1991

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

Joseph E. Spruiell

Committee Members

Donald C. Bogue, Edward S. Clark

Abstract

The effects of pigment additions on the development of structure and properties of melt spun polypropylene filaments were studied. Two polypropylene resins with melt flow rates (MFR) of 45 and 12 were evaluated and the main portion of the study was carried out on a set of samples containing four different pigments and have three different pigment concentrations. The investigation included the evaluation of the influence of pigments on spinline dynamics and crystallization kinetics during processing by the on-line experimental techniques, the characterization of the as-spun fibers with regard to orientation, crystallinity, birefringence and mechanical properties, the determination of the relative amount of smectic and crystalline monoclinic phases by x-ray diffraction, the observation of morphology of spherulites in polypropylene samples and the study of pigmented samples' thermal behavior by DSC technique.

Several different sets of melt spinning processing conditions were chosen in order to examine the effects of spinning conditions such as take-up velocity, mass throughput on final structure and properties of as-spun pigmented polypropylene filaments.

The results from this research indicated that the pigment additions act as nucleating agents and cause crystallization to occur at higher temperatures and at shorter distances from the spinneret during melt spinning. By nucleating the crystallization at higher temperatures the pigments 1) encourage the formation of monoclinic rather than smectic phase, 2) allow greater opportunity for crystals to grow during subsequent cooling, 3) result in higher levels of crystallinity for a given set of spinning conditions, and 4) reduce the as-spun molecular orientation due to lower molecular orientation in the melt at the point at which crystal nuclei are formed. However, the ability of pigments to act as nucleating agents varies among the pigments. The white and black pigments studied (inorganic pigments) have less effect on nucleating crystallization than the blue and red pigments (organic pigments).

Pigments that produce a marked effect on crystallization kinetics also affect the mechanical properties of the melt spun filaments. Increased nucleating power causes crystallization at higher temperatures in the spinline and causes the as-spun filaments to have lower tenacity and higher elongation to break. The change in mechanical properties increases as the concentration of pigment increases for each pigment.

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