Date of Award

8-2004

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Larry C. Wadsworth

Committee Members

Randy Bresee, Gajanan Bhat, Roberto Benson, Donald W. Dareing

Abstract

The primary goal of this research was to determine optimum processing conditions to produce commercially acceptable melt blown (MB) thermoplastic polyurethane (TPU) webs. The rheological/thermal properties of TPU pellets and the morphological/mechanical properties of MB TPU fibers and webs were characterized by Advanced Rheometric Expansion System (ARES), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR) and etc.

The 6-inch MB line and the 20-inch wide Accurate Products MB pilot line at the Textiles and Nonwovens Development Center (TANDEC), The University of Tennessee, Knoxville, were utilized for this study. Preliminary MB studies were performed with Noveon ESTANE® 58277 on the 6-inch MB line to identify some of the process-properties relationships that needed to be addressed in this dissertation.

The MB TPU trials were performed in four different phases: Phase 1 focused on the envelope of the MB operating conditions for different TPU polymers; Phase 2 focused on the production of commercially acceptable MB TPU webs; Phase 3 focused on the optimization of the processing conditions of MB TPU webs, and the determination of the significant relationships between processing parameters and web properties utilizing statistical analyses; Based on the first three phases, a more extensive study of fiber and web formation in the MB TPU process was made and a multi liner regression model for the MB TPU process versus properties was also developed in Phase 4.

The first phase (Phase 1) of the MB studies in this dissertation was performed with one polyester-based TPU polymer: ESTANE® 58238 (TPU238) and three different polyether-based TPU polymers: ESTANE® 58237 (TPU237), ESTANE® 58245 (TPU245) and ESTANE® 58280 (TPU280) on the 6-inch MB line. Based on the results of 6-inch MB line trials, TPU245 and TPU280 were melt blown on the 20-inch line in the first phase of this research. However, both webs were coarse with large fiber diameters and the webs were spotty in appearance.

Based on the knowledge of MB TPU processing in Phase 1, MB TPU webs, which had improved uniformity and better mechanical properties than Phase 1, were achieved in the next phase of the 20-inch MB line trials (Phase 2) with TPU245 and TPU280.

In Phase 3, uniform webs of MB TPUs were produced having good mechanical properties in the 20-inch MB line trials with TPU245 and TPU280. The MB TPU fibers and webs from the spinneret were characterized by DSC, FTIR, SEM (scanning electron microscope), optical microscopy and etc.

In Phase 4, the fiber and web formation study of the MB TPU process was expanded to include fiber diameter, fiber orientation and fiber entanglement of MB TPUs depending on DCD. Furthermore, the velocity of MB TPU fiber in the spin-line was estimated based on the air velocity and air temperature. In addition, multi liner regression models were introduced to optimize the MB TPU process for predicting and evaluating MB TPU fiber and web properties.

In conclusion, the basic MB process was fundamentally valid for the MB TPU process; however, the MB process was more complicated for TPU than PP, because web structures and properties of MB TPUs are very sensitive to MB process conditions: Furthermore, different TPU grades responded very differently to MB processing and exhibited different web structure and properties.

In Phase 3 and Phase 4, small fiber diameters of less than 5µm were produced from TPU237, TPU245 and TPU280 pellets, and the mechanical strengths of MB TPU webs including the tensile strength, tear strength, abrasion resistance and tensile elongation were notably good. In addition, the statistical model showed useful interaction regarding trends for processing parameters versus properties of MB TPU webs. Die and air temperature showed multicollinearity (a case of multiple regression in which the predictor variables are themselves highly correlated) problems and fiber diameter was notably affected by air flow rate, throughput and die/air temperature. It was also shown that most of the MB TPU web properties including mechanical strength, air permeability and fiber diameters were affected by air velocity and die temperature.

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