Assessment of Key Issues in the Coloration of Polyester Material

Renzo Shamey, Woo Sub Shim

• Publisher: CRC Press
• Year: 2019
• Print ISBN:
  9780415693271
• eBook ISBN:
  9781000674439
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

This book addresses the problems in the dyeing of polyester textile materials in various forms and provides an overview of various textile operations for polyester. It presents various key steps and critical factors involved in the production of dyed polyester textile materials.

Assessment of key issues in the coloration of polyester material

Renzo Shamey* and Woo Sub Shim

Textile Engineering Chemistry and Science Department, North Carolina State
University, Raleigh, NC 27695-8301, USA

(Received 13 February 2011; revised 16 February 2011)

In a previous publication we reviewed some of the most critical issues that affect the coloration and properties of cotton-based textiles [R. Shamey and T. Hussain, Textile Progress 37(1/2) (2005) pp. 1–84]. Today, polyester is still widely regarded as an inexpensive and uncomfortable fiber, but this image is slowly beginning to fade with the emergence of polyester luxury fibers. Polyester fibers currently comprise a commanding 77% share of the total worldwide production of the major synthetic fibers [F. Ayfi, 2003–2004 Handbook of Statistics on Man-Made/Synthetic Fibre/Yarn Industry. Part One, Fibre for Better Living, Association of Synthetic Fibre Industry, Mumbai, India, 2004, p. 177]. More than 95% of all polyester fibers manufactured today is based on polyethylene terephthalate. The dyeing properties of polyester fibers are strongly influenced by many of the processing conditions to which each fiber may be subjected during its manufacturing or in subsequent handling. Significant differences in properties of fibers can therefore arise due to their different processing history. Often, the root cause(s) of a problem in the dyed synthetic material can be traced as far back as the manufacturing process. In order to resolve many of the outstanding issues that commonly occur in the dyeing of this important fiber, a comprehensive review of the issues dealing with the manufacturing history as well as fiber processing conditions, including preparation, dyeing, and finishing is warranted. Although some of the underlying problems are related to common causes such as water quality and imperfections in machinery employed, others are specific to the treatment conditions of the fiber. Such conditions include preparation of ingredients, polymerization, fiber and filament processing conditions, as well as heat setting that can cause problems in the coloration of fiber. This summary analysis complements the rich pool of knowledge in this domain and addresses problems in the dyeing of polyester textile materials in various forms. An overview of various textile operations for polyester is given in the beginning. Then, various key steps and critical factors involved in the production of dyed polyester textile materials are described in detail and problems originating at each stage are summarized.

Keywords: polyester dyeing; dyes; colorants; troubleshooting dyeing; polyester pretreatment; polyester polymerization; polyester processing

1. Introduction

Polyester fibers are often regarded as cheap and uncomfortable, but this image is slowly beginning to fade with the emergence of luxury polyester products. Figure 1 shows that polyester fibers currently comprise a commanding 77% share of the total worldwide production of major synthetic fibers [1]. More than 95% of all polyester fibers manufactured today is based on polyethylene terephthalate (PET) [2,3], see http://inventors.about.com/library/inventors/blpolyester.htm. The dyeing properties of polyester are strongly influenced by many of the processing conditions to which each fiber may be subjected during manufacturing or in subsequent handling. Significant differences in properties of fibers can therefore arise due to their different processing history [4]. Common problems that occur in the coloration of polyester in various forms are discussed in the following sections.

Figure 1. World production of major synthetic fibres in 2006.

2. Overview of polyester

British chemists, John Rex Whinfield and James Tennant Dickson, employees of the Calico Printers Association of Manchester, patented ‘polyethylene terephthalate’ (also called PET or PETE) in 1941, after advancing the early research of Carothers [5,6]. They indicated that Carothers’s research did not include the formation of polyester from ethylene glycol and terephthalic acid. PET is the base polymer used in the manufacturing of synthetic fibers such as polyester, dacron, and terylene. Polyester is commonly manufactured from petroleum-based chemical compounds to form fibers, films, and plastics. The starting compounds [7, 8, 9] used in the formation of PET are shown in Figure 2.

Polyester fibers are highly crystalline, mechanically tough, and hydrophobic [4]. Polyethylene terephthalate) is generally made from either purified terephthalic acid (PTA) or dimethyl terephthalate (DMT) together with ethylene glycol. Early polyester production was based solely on the ester, but with the advent of PTA on a commercial scale in 1964, it became possible to implement processes based on the acid [10]. In general, there are two routes to form polymers: (1) batchwise, and (2) continuous. Early production was entirely batchwise, but the advantages of continuous production, particularly when integrated with the spinning processes, are such that most large-scale production is now continuous. Batchwise productions are now confined mostly to fine filament yarns, variants, and non-fiber end uses.

Figure 2. Starting compounds for the manufacture of polyethylene terephthalate (PET) fiber. Left: Ethylene glycol (an alcohol); right: terephthalic acid (a carboxylic acid).

Figure 3. Batch wise production of poly (ethylene terephthalate) from dimethyl terephthalate (DMT).

Batchwise systems usually comprise two reaction vessels: (1) an ester interchange vessel or esterfier, and (2) a polymerization vessel. An ester interchange vessel is equipped with heating facilities (external, internal, or both), an agitator, ancillary vessels for metering in ethylene glycol and molten DMT and for introducing a catalyst, and a fractionating column from which the distillate, mainly methanol, is collected in a further vessel and sent for purification. Esterfiers are also heated vessels, and contain a mechanism for the agitation of the contents. Terephthalic acid may be charged as a solid, or more probably as dispersion in the glycol, along with any additives, from a mixing vessel. The water produced is removed by way of a column to return glycol to the batch and a pressure control valve. A simplified arrangement [7] for the manufacture of the polymer is shown in Figure 3.

Continuous polymerization units usually consist of at least three vessels: (1) an ester interchange or a direct esterification unit, (2) a unit for reducing the excess glycol content and producing a pre-polyester, and (3) a unit for completing the polymerization process. The first stage consists of a stirred vessel or vessels where excess glycol is removed and the molecular weight of the product from the first stage is raised to an intermediate value under slightly reduced pressure. The third stage consists of a reactor or reactors that give a high-surface-to-volume ratio and frequent renewal of surface. The product is extracted from a final reactor by a screw that conveys it either directly to melt-spinning or to a polymer extrusion and chipping unit. A simplified schematic arrangement [8, 9, 10, 11] of a continuous polymer production technique is shown in Figure 4 [7].

2.1. Overview of manufacturing offiber; yarn, and fabric

Typical steps in the production of polyester in the fiber, yarn, and fabric forms are summarized in Figure 5 [12,13]. In the case of direct-spun polymer from a continuous polymerization line, the polymer is supplied in molten form and the polymerization process is controlled in such a way to produce a uniform feedstock. When the polymer is in solid form, particularly if it is manufactured batchwise, additional processes of blending, drying, and melting are necessary before processing as textile fiber. Polymer characterization and blending may also be needed to ensure uniform feed to spinning, particularly for filament yarn production. Polymer designed for staple fiber does not require such tight control because of the fiber blending processes at a later stage.

Figure 4. Continuous production of polyethylene terephthalate) from terephthalic acid.

Melt spinning requires no chemical reactions and no solvent recovery system. Polymer melt spinning processes fall into the following four classes: (1) relatively low spinning speed, (2) medium spinning speed, (3) high spinning speed, and (4) ultra high spinning speed systems [13, 14, 15, 16]. The poly...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• 1. Introduction