**2.1.1 Addition of dye receptors**

Addition of dye receptor additives prior to fiber extrusion has been explored by many researchers [9]. Three different classes of these additives are:

a. Metallic compounds

156 Textile Dyeing

impetus for manufacturing from PP fiber a variety of materials such as towels, floor coverings, sportswear and select technical products. Due to its nonpolar and hydrophobic nature, most of the production of PP fiber is colored by means of mass pigmentation. This route of coloration gives excellent fastness properties during end use; however, it restricts the producer in fulfilling the changing fashion demands of the market. An alternative way of coloring PP fiber exists in which the fiber can be made dyeable by means of post modification, creating active sites for dye association or adding hydrophilic comonomers, but this route has adverse effects on the mechanical properties and costs of the fiber. The development of a truly aqueous process for dyeing PP in its generic, unmodified form is of significant importance vis-à-vis the rising demand for this relatively inexpensive fiber. The developed batch exhaust dyeing methods for PP fiber by us were reported earlier [4-6] and the continuous pad steam and pad/dry heat methods are reported in our recent paper [7]. This chapter covers the state of the art in PP dyeing as well as our adopted approach to develop a commercially viable coloration process for unmodified PP fiber in conventional

The major portion of colored PP fibers is currently manufactured by melt pigmentation (called spun dyed fibers) [8]. Melt pigmentation involves the addition of pigment particles in the polymer melt prior to extrusion and fiber spinning. Melt pigmentation can be performed in various ways. Pigments can be added to the pre-melted fiber polymer, or it can be mixed with the chips (also known as chip pigmentation) in order to produce melt

Three general approaches to aqueous color PP fiber are reported in the literature [9]:

The influence of dyestuff constitution and auxiliaries in the dyeing of unmodified PP has been studied by Herlinger et al.[10] The authors determined that the use of toluene and pxylene as carriers, together with some anthraquinone disperse dyes having longer alkyl groups, improved the fixation of dyes into PP fiber by increasing the intermolecular forces

Oppermann et al. [11] reported the synthesis of disperse dyes with alkyl substituents of varying lengths and dyed unmodified PP with them at a high temperature (125oC) for 150 min. Wash fastness of the dyed samples increased on increasing the chain length of the alkyl substituent; however, the levelness also decreased. An octyl substituent proved an optimum

Stright et al. [12] reviewed different ways to dye PP including the development of new dyes which were fixed in the fiber by formation of dye-metal complexes on the metalcontaining PP fiber, resulting in adequate dyeings in a variety of shades. Dye-metal complex forming dyes could be applied to a wide variety of materials utilizing standard

Reactive modification involves treatment of PP fiber with certain chemicals in controlledconditions [9]. This type of modification increases costs in excess drying, handling, recovery

a. Attempts to color unmodified PP fiber with modified dyeing methods.

b. Modification of the fiber surface to create dye receptive sites.

aqueous systems.

pigmented PP fibers.

between dye and fiber.

dyeing techniques.

**2. Coloration of PP fiber** 

**2.1 Different methods to aqueous dye PP fiber** 

c. Copolymerization and graft copolymerization.

length for good fastness and levelness properties.


The additive approach can be divided into four major areas of research involving the development of:


Brown et al. [13] reported disperse and acid dyeable olefin fibers. The dyeable olefin fiber was prepared in two ways: (a) formed a blend of alpha-monoolefin polymer and 1-5% by weight of a pyridine type polymer dye receptor which led to disperse dyeable PP fiber; (b) formed a blend of less than 97% by weight of alpha-monoolefin polymer, 0.5-5% by weight of pyridine type polymer dye receptor and 0.5-5% of hydrophilic compound containing ethylene oxide units. The resultant fibers were dyeable by both anionic and disperse dyes. The approach was to dye the uniformly-dispersed additives so that the whole fiber appeared colored. This approach was found much easier and efficient than fiber pretreatments, copolymerization or grafting, and also less harmful to the fiber's physical properties.
