**2. Coloration of PP fiber**

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 pigmented PP fibers.

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

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 between dye and fiber.

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 length for good fastness and levelness properties.

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 dyeing techniques.

Reactive modification involves treatment of PP fiber with certain chemicals in controlledconditions [9]. This type of modification increases costs in excess drying, handling, recovery of materials and operational steps. The treated fibers also showed ring dyeing and inferior physical properties. Reactive modification is thus not a commercially viable option.

Incorporating dye receptive groups in a polymer chain is known as copolymerization, whereas attaching a segment of a dye receptive group as a side chain is termed graft copolymerization [9]. Several disadvantages are associated with the copolymerization of PP:


Graft copolymerization was more technically appealing in the case of PP, but the expensive technology was considered as a barrier to the commercial adaptation [9].
