22
increase in the use of fibers from renewable resources and the use of non-toxic
chemical agents are being investigated for textile applications (Blackburn 2009). An
additional area of focus is the emerging area of ‘smart’ textiles, i.e. imparting
apparel and clothing the ability to record data from external stimuli, and possibly
provide a response. Outside the apparel and clothing sector, textile science and technology are used in various applications, from composites for automobiles and construction, scaffolds for tissue engineering, to supports for catalysts in industrial
chemical processes (Horrocks and Anand 2016a, b).
The research in the areas described above encompasses both chemical processes
for modifying the fibers, and changes to the design of fiber assemblies and the
modes of their construction. The chemical processing of fibrous substrates is a
broad subject. For this reason, the recent chemical processing strategies selected to
modify the fiber bulk and its surface will be described in this chapter.
3.2 Fiber Modifications
3.2.1 Alkali Treatments
The most researched polymer regarding the effects of alkali treatments on structure
and reactivity is perhaps cellulose (Klemm et al. 2004a, b; Budtova and Navard
2016; Gutiérrez and Alvarez 2017). Alkali treatments are a common part of the
processing sequence of cellulosic textiles, and are used anywhere from the cleaning
of raw (or ‘greige’) materials, to modifications of the structure. The modifications
of the structure occur in treatments with sodium hydroxide (NaOH) solutions of
concentrations greater than ca. 12–15% (w/w), which is often called ‘mercerization’
(Klemm et al. 2004a). This causes a change in the crystalline structure of the celluloses, thus improving their sorption properties and as a consequence also their
reactivity changes. Zahid et al. (2017) reported recently that mercerization pretreatments can mitigate the potential for acid hydrolysis in application of the conductive
poly(3,4-ethylenedioxythiophene) (PEDT):poly(styrene sulfonate) mixture for the
creation of smart textiles. Another recent report found that hot alkali treatments on
jute remove lignin and hemicellulose and break larger fiber bundles into smaller
sizes, which helps improve their adhesion in epoxy resin composites (Wang et al.
2019), while a treatment of cellulose acetate fibers with ethanol/NaOH solutions,
progressively deacetylates them from the outside inwards and creates a shell of cellulose surrounding a hydrophobic core (Tulos et al. 2019).
Alkali treatments have also been used for hydrolytic treatments of textile substrates to improve the effectiveness of subsequent coating and functionalization
treatments. Alkali hydrolysis of polyester, if limited to the surface, does not significantly affect the strength and increases the surface density of the hydroxyl and carboxyl groups and the surface roughness, (Mazrouei-Sebdani and Khoddami 2011;
Hashemizad et al. 2012; Han et al. 2016 Hashemizad et al. 2017; Nourbakhsh et al.
A. P. Manian et al.
increase in the use of fibers from renewable resources and the use of non-toxic
chemical agents are being investigated for textile applications (Blackburn 2009). An
additional area of focus is the emerging area of ‘smart’ textiles, i.e. imparting
apparel and clothing the ability to record data from external stimuli, and possibly
provide a response. Outside the apparel and clothing sector, textile science and technology are used in various applications, from composites for automobiles and construction, scaffolds for tissue engineering, to supports for catalysts in industrial
chemical processes (Horrocks and Anand 2016a, b).
The research in the areas described above encompasses both chemical processes
for modifying the fibers, and changes to the design of fiber assemblies and the
modes of their construction. The chemical processing of fibrous substrates is a
broad subject. For this reason, the recent chemical processing strategies selected to
modify the fiber bulk and its surface will be described in this chapter.
3.2 Fiber Modifications
3.2.1 Alkali Treatments
The most researched polymer regarding the effects of alkali treatments on structure
and reactivity is perhaps cellulose (Klemm et al. 2004a, b; Budtova and Navard
2016; Gutiérrez and Alvarez 2017). Alkali treatments are a common part of the
processing sequence of cellulosic textiles, and are used anywhere from the cleaning
of raw (or ‘greige’) materials, to modifications of the structure. The modifications
of the structure occur in treatments with sodium hydroxide (NaOH) solutions of
concentrations greater than ca. 12–15% (w/w), which is often called ‘mercerization’
(Klemm et al. 2004a). This causes a change in the crystalline structure of the celluloses, thus improving their sorption properties and as a consequence also their
reactivity changes. Zahid et al. (2017) reported recently that mercerization pretreatments can mitigate the potential for acid hydrolysis in application of the conductive
poly(3,4-ethylenedioxythiophene) (PEDT):poly(styrene sulfonate) mixture for the
creation of smart textiles. Another recent report found that hot alkali treatments on
jute remove lignin and hemicellulose and break larger fiber bundles into smaller
sizes, which helps improve their adhesion in epoxy resin composites (Wang et al.
2019), while a treatment of cellulose acetate fibers with ethanol/NaOH solutions,
progressively deacetylates them from the outside inwards and creates a shell of cellulose surrounding a hydrophobic core (Tulos et al. 2019).
Alkali treatments have also been used for hydrolytic treatments of textile substrates to improve the effectiveness of subsequent coating and functionalization
treatments. Alkali hydrolysis of polyester, if limited to the surface, does not significantly affect the strength and increases the surface density of the hydroxyl and carboxyl groups and the surface roughness, (Mazrouei-Sebdani and Khoddami 2011;
Hashemizad et al. 2012; Han et al. 2016 Hashemizad et al. 2017; Nourbakhsh et al.
A. P. Manian et al.