Advanced Fiber Spinning Technology by T. Nakajima


Advanced Fiber Spinning Technology
by T. Nakajima

Advanced fiber spinning

Table of Contents
Fundamentals of spinning, Melt spinning; Solution spinning; Spinning for nonwovens; The spinning of highly aesthetic fibres; Fibre spinning of anisotropic polymers; Spinning of thermotropic liquid-crystal polymers; Gel spinning processes; Spinning of ultra-fine fibres; Spinning of optical fibres.

This book covers the new developments of fiber spinning science and technology. Much of the success of Shingosen, the newly specified synthetic fiber which has been developed in Japan, depends upon a skilful application of the spinning technology. This book gives a comprehensive presentation of the techniques with the theoretical background for an understanding of them. I hope that this volume will be found useful for readers in many countries and will contribute to a better understanding of the science and technology of the field of spinning.

Some of the most interesting developments of the last few decades in the field of fiber manufacture have been the result of intensive study in Japanese industry and research institutes. Features of such research are a determination to push the technology towards its limits and a willingness to embark rapidly on commercial exploitation of the results. An unusual combination of intensive competition and co-operation between the many substantial companies involved results in a rapidly evolving technology. Consequently the rate of introduction of new processes and products is considerably higher in Japan than in other countries.

This book was originally published in Japanese by the Society of Fiber Science and Technology, Japan, in order to present a thorough scientific and technological review of advances in fiber production, and is now published in English to mark the 50th anniversary of the foundation of the Society. The emphasis is upon developments either originated or adopted in Japan. With the exception of a chapter about aramid fibers contributed from Du Pont, the authors are leading Japanese academic and industrial research workers.

In editing the translation we have tried to make it as friendly to English-speaking readers as possible. We have, however, retained many references to journals and patents written in Japanese, since it has seldom been possible to identify clearly equivalent material in other languages.

Fundamentals of spinning

There are a great many subjects covered by the heading ‘Fundamentals of spinning’. In this chapter, however, we confine ourselves to a description of the fundamentals of mathematical simulation for spinning and of new findings on structural formation during spinning and fiber structure. This description should be undertaken for each of the three types of spinning: melt spinning, dry spinning and wet spinning. However, we are concerned here mainly with melt spinning because it is the easiest for us to formulate and accordingly its theory is the most sophisticated of the three. The others are described only briefly with literature references to the details. Nevertheless, the authors hope that this short treatise will help the readers to understand other parts of this book.

1.1 Introduction
The viscose rayon method was developed towards the end of the last century and the melt spinning method for synthetic fibers was established in the early part of the 1930s. In the beginning of the history of spinning, progress in spinning technique was mainly made by accumulating empirical facts; that is to say, by repeating a set of procedures such as setting a spinning condition and measuring the resultant properties and structures of the spun fibers. There were few studies on physiochemical changes and on structural formation in the spun fibers between the spinneret and the take-up device. With the rapid advance of the synthetic fiber industry in the 1940s, a strong need arose to understand the basics of the spinning process in order to improve the productivity and quality control of the fibers. Consequently, towards the end of the 1950s, Ziabicki published a series of papers concerning melt spinning in which the spinning process was analyzed mathematically as an engineering problem: the papers served as a powerful incentive to researchers in this field of study. About the middle of the 1960s, Kase and Matsuol ,2 established a method for the quantitative description of the melt spinning conduction. Subsequently, Katayama et aP studied structural formation and crystallization during a melt spinning process by using a special model spinning apparatus. From then on, studies in this field have been extensively carried out in Japan and elsewhere and most of the results are to be found in several references.4-9

In melt spinning, we can predict the diameter and temperature and the tension in a running filament if the spinning conditions and the rheological properties of a polymer used in the spinning process are given; the predicted values are, of course, in good agreement with the experimental results. Such a prediction, however, can be made only when no significant crystallization occurs during the spinning process. If crystallization must be taken into consideration, it becomes increasingly difficult for us to carry out mathematical simulation of the quantities mentioned above.

In this case, full quantitative knowledge of the following four points is needed for performing a mathematical simulation of melt spinning:

  1. Molecular orientation caused by elongational melt flow.
  2. Influence of molecular orientation on crystallization kinetics.
  3. Changes in the rheological properties of the polymer caused by molecular orientation and crystallization.
  4. Kinetics of non-isothermal crystallization.

The correlation between the above points is shown in Fig. 1.1. In this figure, an arrow indicates that an item from which the arrow starts influences another item to which the arrow is pointing.

In the theory of Kase and Matsuo, mean values of temperature and of stress over the whole area of a transverse section of the filament were used. In the process of high speed spinning, however, the variables such as temperature, stress, orientation and crystallinity must be expressed as functions of the radial distance from the central axis of the filament as well as the distance from the spinneret. For example, consideration of the radial distribution of these variables is inevitable in discussing inhomogenous structures such as skin-core structure. In order to understand the spinning process, it is indispensable for us to know how structure will be formed during the process as well as to carry out the detailed technological analysis of the process. In the following part of this chapter, the fundamental equations describing the melt spinning process accompanied by crystallization will be developed. After this the oriented crystallization, which is closely related to the structure formation during the spinning process, will be discussed and the differences between oriented and unoriented crystallization will be highlighted. Then the importance of gelation in the process of solution spinning and of phase separation will be mentioned. Finally, examples of mathematical simulation of high speed melt spinning will be demonstrated.

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