Doctoral Dissertations

Date of Award

5-2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Marion Hansen

Abstract

The purpose of this project is the further development of in-line spectroscopic measurements for molten polymer systems. There are two main focuses: development of an online technique for the determination of concentration of ultraviolet stabilizers and antioxidant additives in polypropylene at orders of magnitude higher than those previously studied, and the development of a practical on-line color measurement technique. The additive project is an extension of the work completed by Dr. Marion Hansen and graduate students at the Measurement and Control Engineering Center located at the University of Tennessee, Knoxville. The color measurement technique is novel in its approach. Quality control is one of the most important factors in plastics compounding. Compounding companies engage in the production of additive and color concentrates to be further diluted (or "let-down") by their customers. The end products are usually plastic pellets to be used in molding, film manufacturing, or fiber production. The end concentrations of additives and pigments in these end products are usually less than 1 % and more often in the 100-200 ppm region. These low concentrations mandate the knowledge of the actual concentrations of pigments and additives contained in the concentrate. Current quality control methods are predominantly off-line techniques. Most companies employ a method where a small sample is obtained from the production area and taken to a quality control analytic laboratory, where it is tested for additive concentration and/or color. Depending on the size and capacity of the facility, a large quantity of off specification material can be produced. Off-line techniques also have a given lag period before changes to the operating conditions can be made. The development of on-line measurement techniques not only provides a real time indication of the operating conditions, but is the fundamental element missing in the development of a real time, feed-back control system of the manufacturing process. The development of fiber optic cable allowed for traditional laboratory techniques to be applied in the production area of chemical processing facilities. The use of this type of cable has allowed the development of online techniques using near infrared (NIR), Fourier transform infrared (FTIR), ultraviolet (UV), and Raman spectroscopy. The additives objective of this project is to look at several of the most commonly used UVstabilizer and antioxidant additives in the polyolefin fiber industry. The objective is to determine a spectroscopic technique or combination of techniques to determine the amount of these additives contained in the sample. Research will also be conducted to investigate the effect of additive loading on the rheological properties of the polymer. These results are correlated back to the spectroscopic data to develop an on-line measurement of the viscosity or melt index of the material. The sample additives are compounded with an unmodified polypropylene resin. Research is focused at determining the best spectroscopic technique utilizing NIR or W methods as well as the optimal mathematical regression to provide the most accurate measurement of the additive concentration . The color objectives of this project are to look at several commonly used pigments in the plastics industry and also develop a spectroscopic technique to determine the pigment concentration. The actual measurement of color is impossible. It is the final customer that determines whether the material is the correct color for their product. There are several methods to determine color numbers currently that aid color matching. These numbers, however, are determined using a flat plaque and the final pigment loading, not the actual concentrated material. If the pigment is treated like another additive, it is possible to correlate the specification material to the color standard. Once the correct pigment loading is established, online measurement will indicate off specification material. This project will also investigate the different spectroscopic techniques currently available to determine the optimum method for measuring concentration, as well as the proper mathematical regression technique for the most accurate concentration measurements.

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