The Effects Of Vanillin As Carrier In The Dyeing Of Polyester Fabric
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CHAPTER ONE
1.0 INTRODUCTION
In 2009, global production of polyester fibres reached 31.9million tonnes; about 45% of worldwide fibre production (Oerlikon,2010). Polyester (polyethylene terephthalate (PET)) fibres have a growing importance, and are mainly used in clothing, geotextile and automotive industries. PET has excellent tensile strength and chemical resistance. However as PET is hydrophobic and has no chemically active groups, its dyeing in aqueous conditions is quite difficult. Dyeing is achieved with disperse dyes having good diffusivity and solubility in PET fibre. Moreover, the highly crystalline structure of PET fibre slows down the rate of dye diffusion into the fibre(Trotman, 1970).Dyeing of polyester fabrics can be achieved using three different methods 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 bath followed 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 that can 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 fabrics with disperse dyes is achieved using exhaustion method (deep dyeing)(Dupont,2002). The fabric to be dyed is immersed in the dye bath for longer period (about 1hr.) under high temperature and pressure,under agitation, with or without addition of a carrier to allow dye diffusion inside the polyester fibre.
Exhaustion method is used for dyeing of smaller quantities of polyester fabrics or for dyeing of polyester textiles in the form of fibres, yarns or knitted fabrics. Two exhaust dyeing methods are used: Dyeing under atmospheric conditions (below 100°C) with the aid of carriers and dyeing under high-temperature and pressure conditions (125-135°C) without carrier. The last method is the most commonly applied but it requires high energy consumption because of high temperature conditions.Carriers are used for dyeing of PET fibres in order to improve adsorption and accelerate diffusion of disperse dyes into the fibre at low 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 dyeing and 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 and later use (e.g. ironing).Chemical carriers include: phenolics, chlorinated aromatics,aromatic hydrocarbons and ether(Vigo, 1994). Some carriers are said to be “hydrophobic” and some are “hydrophilic”, and their mode of action differ accordingly. Hydrophobic carriers are more effective than hydrophilic ones (Burkinshaw,1995). In textile industry, hydrophobic carriers such as dichloro and trichloro-benzene are already substituted by hydrophilic carriers such as benzoic acid (Vigo,1994).
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