Doctoral Dissertations

Dong Zhang

Date of Award

12-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Human Ecology

Major Professor

Gajanan Rhat, Larry C. Wadsworth

Committee Members

Kermit E. Duckett, Roberto S. Benson

Abstract

The spunbonding process involves extrusion, followed by non-isothermal extensional flow of the melt, and crystallization, accompanied by molecular orientation. The kinematics and development of morphology in the filaments are governed to a large extent by a combination of elongational deformation and stress-induced crystallization. Understanding the influence of the spinline dynamics on the structure of the filament can help in manipulating the process conditions to achieve the desired properties in the filaments. The inherent properties of the filaments are of utmost importance in spunbonded webs. A good understanding of the structure of individual filaments will be helpful in comprehending the whole process better. Two kinds of polymers, a polypropylene homopolymer and a copolymer of polypropylene containing less than 5 percent polyethylene, were processed using the Reicofil spunbonding line at the Textiles and Nonwovens Development Center, The University of Tennessee, Knoxville. The filament samples were collected before thermal-bonding. The important filament properties were determined through a variety of experimental techniques, such as molecular orientation in filaments through birefringence, filament and web crystallinity through differential scanning calorimetry and density measurement, x-ray diffraction, scanning electron microscopy, and single filament mechanical properties. In addition, thermo-rheological properties, such as Thermal Mechanical Analysis (TMA), and Thermal Deformation Analysis (TDA) of the collected filament, and the nonwoven samples were evaluated under different temperature and stress. The filaments were annealed at both constant and free length conditions. The effect of annealing time and temperature was also studied. The structure and properties such as crystalline orientation by x-ray diffraction, crystallinity by DSC, mechanical properties, filament diameter and birefringence of the fibers, before and after annealing, were investigated. In order to understand the effects of various process variables on the final web properties, the related nonwovens were taken after thermal-bonding and characterized for strength (tensile, burst, and tear), tensile elongation, isotropy, air permeability, stiffness, fiber diameter, and bond appearance through microscopy. The results were analyzed through a statistical design. The effect of temperature, throughput, and their interaction were evaluated through statistical means. A mathematical model was developed to evaluate the quality of nonwovens objectively and comprehensively and to optimize the processing conditions.

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