Dyeability of Polymer Nanocomposite Fibers

The dyeability and mechanism of dyeing of synthetic fibers change significantly on incorporation of any nanomaterial in the fibrous structure. Different nanomaterials, such as nanoclay, polyhedral oligomeric silsesquioxane (POSS), and silica (Si02), have a strong potential to improve the dyeability of polymer nanocomposite fibers in comparison to pure synthetic fibers. This chapter deals with the dyeability of different polymer nanocomposite fibers. Incorporation of various nanomaterials and their ability to change the structure and morphology of different polymer nanocomposites that affect their dyeability and fastness properties have been discussed in the present composition.

Introduction

Nowadays, different synthetic fibers, such as polyester or poly (ethylene terephthalate) (PET); polypropylene (PP); polyamide

Nanotechnology in Textiles: Advances and Developments in Polymer Nanocomposites Edited by Mangala Joshi

Copyright © 2020 Jenny Stanford Publishing Pte. Ltd.

ISBN 978-981-4800-81-5 (Hardcover), 978-1-003-05581-5 (eBook) www.jennystanford.com

  • (nylon 6 and nylon 6,6); and polyurethane (PU), like Spandex® and Lycra®, are extensively used in textile and apparel industries. Most commonly these fibers are blended with other cellulosic fibers, such as cotton and viscose, or even used as neat material for some applications. The fibers are dyed to enhance their appearance and esthetic look in clothes and garments. However, most of the neat synthetic fibers are difficult to dye for various reasons. For example:
  • • Dyeing of pure PP filaments is very difficult due to its high crystallinity and lack of any dye site for the reaction or fixation of dyes [1].
  • • Because of the compact and highly crystalline structure as well as hydrophobic nature, PET fibers are also difficult to dye. PET fibers are generally dyed with a disperse dye at a very high temperature (thermosol process) or by using a high temperature/high pressure (HT/HP) process [2].
  • • Thermoplastic polyurethane (TPU)-based Spandex® or Lycra® also shows lower dye absorption, poor color values, and poor fastness properties [3].

Researchers have taken a keen interest and followed different approaches for improving the dyeability of synthetic fibers, such as modification of the physical/chemical structure of fibers [4-6] and dyeing processes [7-9]. More recently, nanotechnology is getting more importance for improving the dyeability of synthetic fibers.

The mechanism of dyeing and dyeability of a fiber/filament depends on both its physical as well as chemical structure. In addition to this, incorporation of various nanomaterials in a polymer also has a significant effect on altering the dyeability property of synthetic fibers, which will be discussed in detail in this chapter.

Nanomaterials and Polymer Nanocomposites

Potential of Nanomaterials for Improving Dyeability of Synthetic Fibers

Polymer nanocomposites consist of nanomaterials/nanofillers (reinforced phase) dispersed in a polymeric matrix, where at least one dimension of the nanofillers must be in the range of 1-100 nm [10]. Due to the large surface area-to-volume ratio of nanomaterials, better interaction is possible between matrix and reinforcement, which results in their having much better properties compared to microcomposites, even at a very low content of nanofillers [10, 11]. Therefore, nowadays, polymer nanocomposites are attracting the attention of material scientists for various applications. There are many possibilities that can enhance the dyeability of polymer nanocomposite fibers, compared to pure synthetic fibers [3, 4, 12, 13], as discussed below.

  • • The accessible chemical groups of raw or functionalized nanomaterials dispersed in a polymeric matrix of a nanocomposite are capable of forming physical and/or chemical linkages with particular dyestuffs. However, surface potential and type of chemical groups may affect the dyeing mechanism as well as the dye uptake percentage [3].
  • • In many cases, with the incorporation of nanomaterials in a polymer matrix, reduction in the crystal size and/or the crystalline fraction is observed, which may cause an increase in the dye uptake [12,14].
  • Tg of nanocomposite fibers may shift to a slightly lower value compared to that of pure synthetic fibers, which causes easy movement of polymeric chains, leading to better dye diffusion [13,14].

Nanomaterials Used for Improving the Dyeability of Fibers

Before highlighting the dyeability of polymer nanocomposites, it is important to discuss different potential nanomaterials that can be effectively used to improve the dyeability of synthetic fibers.

Nanoclay

Layered silicates, or nanoclay-reinforced polymer nanocomposites, have been studied extensively for improving different properties of polymeric substrates, such as mechanical, thermal, flame retardancy,

Structure of 2:1 layered silicates. Reprinted from Ref. [16], Copyright (2003), with permission from Elsevier

Figure 5.1 Structure of 2:1 layered silicates. Reprinted from Ref. [16], Copyright (2003), with permission from Elsevier.

and gas barrier since the successful development of nylon/clay nanocomposites by Toyota in 1990 [15].

The most commonly used nanoclay for the preparation of polymer nanocomposites belongs to the class of 2:1 phyllosilicates, or layer silicates. The crystallographic structure of 2:1 phyllosilicates involves multiple layers stacked one on top of the other, where an individual layer (thickness about 1 nm) contains one octahedral sheet of either aluminum or magnesium hydroxide fused between two tetrahedral sheets of silicon atoms (Fig. 5.1). The stacked silicate layers are bound by weak van der Waals force, and the interlayer galleries are occupied by different alkali and alkaline cations (like Na+, K+, Ca2+, etc.), which are exchangeable [16].

Montmorillonite (MMT), bentonite, saponite, and hectorite are the most commonly used nanoclays. Being hydrophilic in nature, pristine clays are not miscible with most of the hydrophobic polymers [17]. Therefore, they are modified by cation exchange reactions with different cationic surfactants, such as primary, secondary, tertiary, and quaternaiy alkylammonium or alkylphosphonium cations [16]. Generally, after modification of clay, its intergallery spacing (d-spacing) increases compared to that of pristine clay, which helps in better intercalation/exfoliation of clay platelets in polymer matrices. Due to abundant availability and low cost, clay minerals are extensively used as absorbents for the removal of different dyes, like reactive, acid, basic, and disperse dyes [18, 19]. This phenomenon of nanoclay has been utilized by many researchers for improving the dyeability of various polymers, such as PP [12, 20-23], PET [14, 24], PLA [25], and PU [3, 26], which will be discussed in detail. Table 5.1 provides details of a few MMT-based clays that have been generally used for improving the dyeability of synthetic fibers.

POSS

Polyhedral oligomeric silsesquioxane (POSS) (Fig. 5.2) is one of the most promising nanomaterials that have been used for the preparation of emerging polymer nanocomposites. It is a nanos- tructured hybrid material containing both organic and inorganic components, having a general structure [RSiOs^Jn, (where R = H, aryl, alkyl, or alkoxyl). POSS has a nanosized cage-like or polyhedral structure that consists of an inorganic silicate core and an organic group in the sheath. The silica core provides rigidity and thermal stability. On the other hand, the organic part may be fully reactive, nonreactive, or a mixture of these two [28, 30]. POSS reinforced polymer nanocomposites show improvement in many properties of polymer, such as flame retardancy, thermal stability, and mechanical properties [31]. A few researchers [32, 33] have also emphasized on the improvement of the dyeability of synthetic fibers with the incorporation of POSS. The dyeability and dyeing mechanism of polymer/POSS nanocomposite filaments may be controlled by changing the functionality of the organic parts in the structure of POSS.

Other nanomaterials

Besides nanoclay and POSS, various other nanomaterials have been used for the improvement of the dyeability of polymers; these are mainly:

Clay name

Class

Clay modifier

Modifier concentration (meq/100 g)

Density

(g/cm:t)

d-spacing

(A)

Cloisite Na+ (pristine clay)

MMT (2:1 phyllosilicates)

2.86

11.7

Cloisite 10A

MMT (2:1 phyllosilicates)

Dimethyl, benzyl, hydrogenated tallow, quaternary ammonium

125

1.9

19.2

Cloisite 15A

MMT (2:1 phyllosilicates)

Dimethyl, dihydrogenated tallow, quaternary ammonium (2M2HT)

125

1.66

31.5

Cloisite 20A

MMT (2:1 phyllosilicates)

Dimethyl, dihydrogenated tallow, quaternary ammonium (2M2HT)

95

1.77

24.2

Cloisite ЗОВ

MMT (2:1 phyllosilicates)

Methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium (МТ2ЕЮТ)

90

1.98

18.5

Sovrce: [26, 27)

Note: Here, T represents an alkyl group of composition as ~65% Cie, ~30% Cl(„ and ~5% C14.

Molecular structure of POSS. "R" represents the organic part. Reprinted from Ref. [30], Copyright (2018), with permission from Elsevier

Figure 5.2 Molecular structure of POSS. "R" represents the organic part. Reprinted from Ref. [30], Copyright (2018), with permission from Elsevier.

  • (i) Silica (Si02) [34]
  • (ii) Nanosilver [35]
  • (iii) Nano-titanium oxide (Ti02)/nano-zinc oxide (ZnO) [36]
  • (iv) Phosphor strontium aluminate [SrAl204: Eu2+, Dy3+) nanoparticles (SAOED) [37]

The effect of these nanomaterials on the dyeability of polymer nanocomposites will be discussed later in detail.

Evaluation of Dyeing Behavior of Polymer Nanocomposite Fibers

The dyeing behavior of pure polymeric fibers as well as polymer nanocomposite fibers is generally evaluated on the basis of the following parameters: [1]

values can be analyzed for evaluation of the dyeing behavior of fibers.

• Color strength

The color strength value of any dyed material can be calculated by a spectral reflectance measurement in a spectrophotometer using a D65 illuminant and a 10 standard observer with specular and UV components. Color strength is generally represented by K/S value and calculated using the Kubelka- Munk equation

where, К is the absorption coefficient, S is the scattering coefficient, and R is reflectance at the wavelength of maximum absorption (/Imax) [24, 38]. An increase in the K/S value represents a deeper shade.

• Reflectance and transmittance

The dye uptake by fibers can be determined by measuring the change in reflectance or transmittance of the colored solution using a UV-VIS transmittance spectrophotometer [39].

L*a*b* color coordinates

In the CIELAB system color is expressed by three different parameters: L* (lightness), a* (redness-greenness), and b* (yellowness-blueness). These parameters are measured by a color spectrophotometer [38]. A higher L* represents a lighter or brighter shade, and a lower value represents a darker shade. A positive a* value means a redder tone, and a negative value represents a greener tone. Similarly, a positive b* value means a yellower tone, and a negative value represents a bluer tone.

• Washing fastness

For measuring washing fastness of dyed fibers, they are washed following a standard condition (such as ISO 105-B02), maintaining particular time, temperature, soap concentration, etc. After drying washed samples, any change in color and cross staining on other fibers are evaluated on the basis of numerical values. Generally, wash fastness varies from 1 to 5, where 5 represents the best wash fastness property, showing no change in color after washing [38].

• Light fastness

For light fastness assessment, generally the dyed samples and standard dyed wool samples are exposed to a xenon arc following a particular standard (such as BS: 1006 B02-1078). After exposure, a rating is given on a scale of 1-8 with respect to the color contrast in standard samples [38].

• Rubbing fastness

It is measured by using a Crockmeter following a standard method (such as BS 1006 X12: 1978), while the samples are rubbed for some particular number of cycles. It may cause color fading of dyed samples. A rating is given on a scale of 1-5 on the basis of the change in color. A rubbing fastness rating of 5 means there was no fading of color after rubbing [38].

  • [1] Evaluation of dyeing kinetics There are many numerical equations that can be used formeasuring the rate of dyeing, half-time for dyeing, equilibriumdying time, percentage exhaustion, etc. [21]. These numerical
 
Source
< Prev   CONTENTS   Source   Next >