26
application of this compound as a means to fix organophosphonate flame retardants
on fabrics. Lewis (2011) using the same crosslinker on cellulose fibers, and then
reacted with polyamines, found a significant increase in the sorption and fixation of
reactive dyes on the substrates, and also discovered that similar treatments are effective on wool and nylon fibers. This approach has thus been proposed as a means to
reduce the load of salt and dye in wastewater, as well as to reduce the amounts of
water required to remove unbound dyes. An alternative approach has been proposed
by Lewis and Yao (2000) by treating the fibers with 2,4-dichloro-6-(ρ-[(2′sulphatoethyl)sulphonyl]phenylamino)-1,3,5-triazine followed by nicotinic acid for
the purpose of increasing the affinity of the reactive dyes hydrolyzed by cellulose.
3.2.3 Grafting
The grafting reactions can be classified into two categories: (1) ‘conventional’ reactions, where there is minimal or no control over polymer chain lengths and chain
length distributions, and (2) ‘controlled/living’ reactions, where mechanisms
are used to control the aforementioned aspects. According to Hubbe et al. (2015),
grafting can be defined as ‘the attachment or unit-by-unit polymerization of an
oligomeric or polymeric chain onto a fiber surface’. As the definition states, grafting
reactions can be classified into two types: ‘grafting-to’ or ‘grafting-from’. In the
first, the pre-formed polymer chains are attached onto fiber surfaces via physisorption (e.g. electrostatic interactions, forced solvent removal) or chemisorption, where
the polymer chains are end-group functionalized with reactive groups such as thiols
and silanols, and then are reacted covalently to fiber surfaces (Tsukruk 1997; Zhao
and Brittain 2000; Barbey et al. 2009; Carlmark 2013), while in the second, the
monomers are directly polymerized ‘from’ the fiber surfaces. The grafting-from
approaches are generally more difficult than grafting-to approaches, but offer the
significant advantage of greater graft densities, since it is difficult to achieve close
packing of pre-formed polymer chains due to steric hindrances. In grafting-from
approaches, the substrate pretreatments are usually required to activate or introduce
grafting sites onto polymers, which in some cases involve the use of organic solvents, thus presenting challenges in scaling-up of laboratory results to industrial
scale processes (Carlmark 2013). In principle, the same polymerization mechanisms can be used for both grafting-to and grafting-from approaches. In the following section, we describe some common controlled/living polymerization techniques
for fiber grafting.
3.2.3.1 Anionic and Cationic Polymerization
These are essentially addition polymerizations where the chain propagation is
through ionic species: carbanions and carbocations (Advincula 2006). Polar solvents are required for chain propagation, and the solvent can exert a strong influence
A. P. Manian et al.
application of this compound as a means to fix organophosphonate flame retardants
on fabrics. Lewis (2011) using the same crosslinker on cellulose fibers, and then
reacted with polyamines, found a significant increase in the sorption and fixation of
reactive dyes on the substrates, and also discovered that similar treatments are effective on wool and nylon fibers. This approach has thus been proposed as a means to
reduce the load of salt and dye in wastewater, as well as to reduce the amounts of
water required to remove unbound dyes. An alternative approach has been proposed
by Lewis and Yao (2000) by treating the fibers with 2,4-dichloro-6-(ρ-[(2′sulphatoethyl)sulphonyl]phenylamino)-1,3,5-triazine followed by nicotinic acid for
the purpose of increasing the affinity of the reactive dyes hydrolyzed by cellulose.
3.2.3 Grafting
The grafting reactions can be classified into two categories: (1) ‘conventional’ reactions, where there is minimal or no control over polymer chain lengths and chain
length distributions, and (2) ‘controlled/living’ reactions, where mechanisms
are used to control the aforementioned aspects. According to Hubbe et al. (2015),
grafting can be defined as ‘the attachment or unit-by-unit polymerization of an
oligomeric or polymeric chain onto a fiber surface’. As the definition states, grafting
reactions can be classified into two types: ‘grafting-to’ or ‘grafting-from’. In the
first, the pre-formed polymer chains are attached onto fiber surfaces via physisorption (e.g. electrostatic interactions, forced solvent removal) or chemisorption, where
the polymer chains are end-group functionalized with reactive groups such as thiols
and silanols, and then are reacted covalently to fiber surfaces (Tsukruk 1997; Zhao
and Brittain 2000; Barbey et al. 2009; Carlmark 2013), while in the second, the
monomers are directly polymerized ‘from’ the fiber surfaces. The grafting-from
approaches are generally more difficult than grafting-to approaches, but offer the
significant advantage of greater graft densities, since it is difficult to achieve close
packing of pre-formed polymer chains due to steric hindrances. In grafting-from
approaches, the substrate pretreatments are usually required to activate or introduce
grafting sites onto polymers, which in some cases involve the use of organic solvents, thus presenting challenges in scaling-up of laboratory results to industrial
scale processes (Carlmark 2013). In principle, the same polymerization mechanisms can be used for both grafting-to and grafting-from approaches. In the following section, we describe some common controlled/living polymerization techniques
for fiber grafting.
3.2.3.1 Anionic and Cationic Polymerization
These are essentially addition polymerizations where the chain propagation is
through ionic species: carbanions and carbocations (Advincula 2006). Polar solvents are required for chain propagation, and the solvent can exert a strong influence
A. P. Manian et al.