Handbook of Fiber Science and Technology Volume 2

High Technology Fibers: Part B

Menachem Lewin, Jack Preston

• Publisher: CRC Press
• Year: 2017
• Print ISBN:
  9780824780661
• eBook ISBN:
  9781351442664
• Topic: Technology & Engineering
• Subtopic: Chemistry
• Index: Chemistry

Maintaining the high standards set in Part A, this important reference brings you the mostcomprehensive, up-to-date coverage of both recently developed and potentially available fibersfor applications outside the textile industry.Emphasizing practical industrial applications and future research directions for high technologyfibers , Handbook of Fiber Science and Technology: Volume III, Part B sharesresearch developments in high-modulus fibers from organic polymers or inorganic materials... discusses how to predict applications for aramid fibers based upon structure/propertyrelationships .. . sets forth fundamental principles for spinning polymers to fibers . ..reviews the underlying science and technology of fibers derived from thennotropic copolyesters... and more.

1

ARAMID COPOLYMER FIBERS

SHUJI OZAWA* / Teijin Limited, Hino, Tokyo, Japan

KICHIRO MATSUDA / Teijin Limited, Iwakuni, Yamaguchi, Japan

1. Introduction

2. Search for Aramid Copolymer

2.1 Fibers of poly(p-phenylene terephthalamide) (PPTA)

2.2 Introduction of the meta configuration

2.3 Copolymers of isomorphism

2.4 Copolymers with large diamines

3. Copolyterephthalamides of p-Phenylenediamine and 3,4’-ODA

3.1 The effect of the diamine composition

3.2 Discussion of the drawing mechanism of the copolymer fibers

4. Technora^® Fiber

4.1 Manufacturing process

4.2 Mechanical properties

4.3 Chemical properties

4.4 Structural considerations

4.5 Applications

Acknowledgment

References

1. INTRODUCTION

Fiber scientists in pursuit of an ideal synthetic fiber like to try out new crystalline polymers with a regular sequence of a recurring molecular unit. This is because they like to have a crystal structure with a melting point well above the service temperature of the fiber, and yet they have to fabricate the polymer into a fiber by means of a solution or melt process.

Of the three major synthetic fibers, polyester and nylon fibers are manufactured by the melt process at ca. 250 °C, which is well above temperatures to which fibers are often exposed and low enough to fabricate the polymers without too much difficulty. Poly(ethylene terephthalate), poly(hexamethylene adipamide) and poly(ɛ-caprolactam) are representative polymers for the fibers, and are usually homo-polymers except for special types such as those with enhanced dyeability, high moisture uptake, etc. In the case of acrylic fibers, however, copolymers are more common, since poly(acrylonitrile) is not meltable nor soluble enough in a common solvent for making good fibers. Usually, introduction of a nonrecurring monomer unit imparts some new properties to the fiber, but often with a certain loss in important basic properties such as the thermal and/or mechanical properties.

There are groups of polymers in which use of copolymer is rather common in the fiber making. Aromatic polyimides and polyarylates are the typical examples. They are mostly infusible and insoluble when in homopolymer, and need to incorporate a third constituent to render the polymer tractable. Since the thermal properties of the homopolymers are usually quite high, those of copolymers are still high enough for most of the applications in which the high temperature fibers are expected to be utilized.

Generally speaking, the thermo-mechanical properties of copolymer materials can be estimated to be somewhere between those of the two constituent homopolymers. When the properties of a copolymer deviate significantly above or below the proportionally calculated values, the gap is referred as the copolymer effect. Typical patterns are shown in Fig. 1: The crystallinity and the softening point of copolymer materials are lower, and the solubility is higher than the proportional average of the corresponding values of the two constituent homopolymers. This may be understood in terms of disorder in the molecular structure caused by the presence of the comonomer unit.

We can look at the properties of fabricated materials of copolymers in the same fashion, however, with special considerations from a different viewpoint. Here we deal with two different concepts in a single term: for example, under tenacity of a fiber we include the tenacity of real fibers as well as those calculated for a hypothetical fiber in which both the molecular structure and the molecular alignment are idealized. We would refer the latter to the theoretical value. Figure 2 is an exemplary presentation of fiber tenacity versus copolymer composition, in which S is the tenacity observable with sample fibers and T is the tenacity calculated from the bond dissociation energy at the weakest linkage along a single polymer molecule in its most extended form. It is reasonable that the S’s of each homopolymer fall below the corresponding T’s, but this does not necessarily mean that S’s are relative to T’s. In the case of fabricated material, the spatial arrangement of molecular chains is usually very much different from the idealized one, and is not determined simply by the chemical composition of the polymer chains. It is given, rather, as a result of a compound effect of the properties of the substance itself and the conditions of the fabrication process.

Figure 1.1 Thermodynamics versus copolymer composition. (p: e.g., solubility, tractability, q: e.g., crystallinity, softening point.)

Now let us focus on the aramid fibers of the high modulus and high tenacity class in a modern sense. Kevlar (developmental names: Fiber B, PRD 49) was introduced as the first industrial product of this class by E. I. du Pont, and recently Twaron (developmental name: Arenka) by AKZO, and Technora (developmental name: HM-50) by Teijin. All three fibers are based largely on the para-oriented phenylene unit in their molecular structure, typically the p-phenylene terephthalamide linkage. As an example, the S’s and the T’s are compared for poly(p-phenylene terephthalamide) [1, 3]:

Figure 1.2 Mechanical properties of materials versus copolymer composition. ----: theoretical, ––: sample.

	Tenacity (g/d)	Tensile modulus (g/d)
S (observed)	22 [1]	1050 [1]
T (calculated)	230-300 [2]	1500 [3]

As is well known, Kevlar is the result of du Pont’s success in increasing the level of the S in Fig. 2 by adoption of the liquid crystalline state in its spinning process [4, 5, 6]. Yet the S remains as a fraction of the T, suggesting that the molecular arrangement in the fiber is still far from what the scientist wished to achieve. Since the ratio S/T is quite low in tenacity at present, one cannot rule out the possibility of realizing a higher S value at an intermediate copolymer composition than those S values so far attained with each homopolymer, if better molecular arrangement is eventually provided by the copolymer effect.

2. SEARCH FOR ARAMID COPOLYMER

2.1 Fibers of Poly(p-phenylene terephthala...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• About the Series
• Introduction to the Handbook
• Preface
• Contributors
• Contents of Other Handbooks
• 1. Aramid Copolymer Fibers
• 2. Aramid Structure/Property Relationships and Their Role in Applications Development
• 3. Fibers from Naphthalene-Based Thermotropic Liquid Crystalline Copolyesters
• 4. Polymer Single Crystal Fibers
• 5. Aluminum Oxide Fibers
• 6. Lead Fibers
• 7. Polystyrene-Based Functional Fibers
• 8. Bioabsorbable Fibers for Medical Use
• 9. Spinning Thermotropic Polymers
• Index