THE EFFECTS OF VANILLIN AS CARRIER IN THE DYEING OF POLYESTER FABRIC
CHAPTER ONE
1.0 INTRODUCTION
In 2009, global production of polyester fibres reached 31.9million tonnes; about 45% ofworldwide fibre production (Oerlikon,2010). Polyester (polyethylene terephthalate (PET)) fibres havea growing importance, and are mainly used in clothing, geotextileand automotive industries. PET has excellent tensile strength andchemical resistance. However as PET is hydrophobic and has nochemically active groups, its dyeing in aqueous conditions is quitedifficult. Dyeing is achieved with disperse dyes having good diffusivityand solubility in PET fibre. Moreover, the highly crystallinestructure of PET fibre slows down the rate of dye diffusion into thefibre(Trotman, 1970).Dyeing of polyester fabrics can be achieved using three differentmethods depending on the quantity of fabrics to be dyed (Dupont,2002).
Thermosol process used for continuous dyeing of thousands of metres of polyester fabrics, is carried out by impregnation of the PET fabric in the dye bathfollowed by squeezing of excess dye bath and then subsequent dried(100-140°C) before dye fixation (at 200-225°C during 12-25sec.). This technique is however restricted to disperse dyes thatcan sublimate and penetrate inside the PET fibre in gaseous state.Thus, only a limited amount of colour shades can be obtained.When special shades are needed, dyeing of polyester fabricswith disperse dyes is achieved usingexhaustion method (deepdyeing)(Dupont,2002). The fabric to be dyed is immersed in the dye bath forlonger period (about 1hr.) under high temperature and pressure,under agitation, with or without addition of a carrier to allow dyediffusion inside the polyester fibre.
Exhaustion method is used fordyeing of smaller quantities of polyester fabrics or for dyeing ofpolyester textiles in the form of fibres, yarns or knitted fabrics. Twoexhaust dyeing methods are used: Dyeing under atmosphericconditions (below 100°C) with the aid of carriers and dyeingunder high-temperature and pressure conditions (125-135°C) without carrier. Thelast method is the most commonly applied but it requires highenergy consumption because of high temperature conditions.Carriers are used for dyeing of PET fibres in order to improveadsorption and accelerate diffusion of disperse dyes into the fibre atlow temperature and pressure conditions. Nevertheless, most carriers are toxic e.g. phenol, naphthalene, dicloro benzene, etc., to humans and aquatic organisms (Murray andMortimer,1971).
During dyeingand rinsing, a large amount of carriers is released into wastewater,but part remains entrapped in the fibre(Vigo,1994) andis likely to be emitted into air during drying, thermofixation andlater use (e.g. ironing).Chemical carriers include: phenolics, chlorinated aromatics,aromatic hydrocarbons and ether(Vigo, 1994). Some carriers aresaid to be “hydrophobic” and some are “hydrophilic”, and their mode ofaction differ accordingly. Hydrophobic carriers are more effectivethan hydrophilic ones (Burkinshaw,1995). In textile industry, hydrophobiccarriers such as dichloro and trichloro-benzene arealready substituted by hydrophilic carriers such as benzoic acid (Vigo,1994).
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THE EFFECTS OF VANILLIN AS CARRIER IN THE DYEING OF POLYESTER FABRIC
