Modelling the properties of one-step pigment-dyed and finished polyester/cotton fabrics using response surface methodology Muhammad Awais Imran a, * and Tanveer Hussain b a Department of Textile Science, Faculty of Engineering, Science, and Technology, Indus University, Karachi, 75300, Pakistan Email: awais.imran89@gmail.com b Dean Faculty of Engineering and Technology, National Textile University, Faisalabad, 37610, Pakistan Received: 25 December 2014; Accepted: 23 May 2016 Dyeing of polyester/cotton blended fabrics with two different classes of dyes for polyester and cotton is a lengthy and expensive procedure owing to different fibre contents that need different auxiliaries, pH, and temperature conditions. The aim of this study was to investigate and model the properties of a combined pigment dyeing and hand-building finishing system for polyester/cotton blended fabrics. The one-step process was investigated using response surface methodology, taking concentrations of pigment, softener, and hand-building finish as experimental variables. It was found that increase in hand-building finish helps to improve colour fastness at higher pigment concentrations but results in deterioration in fabric tear strength. However, the decrease in tear strength can be minimised by increasing the softener concentration. For a 15 g l 1 pigment concentration, optimum fabric tear strength, crease recovery angle, bending length, and dry and wet rubbing fastness properties were obtained using 60 g l 1 of softener and 65 g l 1 of hand- building finish. The prediction equations developed in this study can be used to determine the required amounts of softener and hand-building finish to achieve commercially acceptable results at different pigment concentrations. Coloration Technology Society of Dyers and Colourists Introduction Polyester/cotton (P/C) blended fabrics are very popular in apparel and home textiles, with a worldwide share of around 58.45% [1,2]. The blending of cotton with polyester is governed by economy, durability, physical properties, colour, and physical appearance factors. A P/C blend has the advantage of polyester’s tensile strength, abrasion resistance, and dimensional stability and cotton’s ability to absorb water, and provides wearing comfort [3]. The processing of P/C fabric is a lengthy and expensive proce- dure owing to the combination of the two different fibre chemistries. Polyester is commonly based on polyethylene terephthalate (PET), whereas cotton is primarily composed of cellulose. Generally, P/C fabrics are dyed using a two- bath two-step method, where chemical cost and process time are major concerns [4]. Several developments have been reported by researchers to shorten the dyeing process [5–11]. These developments have not been fully commer- cialised owing to the high cost of the suitable dyes and critical technical factors in the appropriate application methods. In contrast to dyeing with dyes, pigment dyeing is an alternative approach of one-step dyeing of P/C fabrics because of ease in application and no washing-off require- ment after the dyeing process [12]. The fastness properties of pigment-dyed fabrics are comparable with those of fabric dyed with disperse/reactive dyes [13]. The control of migration, good rubbing fastness, and stable dispersion are some of the major problems faced by the textile industry in pigment dyeing. Pigment dyeing with an exhaust system is unpopular because of the nagging unevenness problem [14]. In many textile processing industries, it is more popular for pastel and dye-for-print fabrics, because very light shades are possible by the pad-dry-cure method on a stenter machine without using an infrared (IR) predryer. However, some industries use IR predryers for medium shades to avoid migration problems. Hand-building finishing involves the application of stiff- ening agents (mainly starch, polyvinyl acetate, or acrylic copolymers) on fabrics to get the desired stiff handle and to increase the weight of the fabrics [15]. The combination of dyeing and finishing processes in one step is a more economical and ecological approach that has been explored by many researchers [16–23]. In the present work, the one-step pigment dyeing and hand-building finishing process on P/C fabric was investi- gated using the pad-dry-cure method. The aim of this study was to model the properties of the one-step pigment dyeing and hand-building finishing process using response surface methodology (RSM), which has not been reported earlier to the best of our knowledge. RSM comprises a collection of mathematical and statistical techniques for modelling the relationship between different factors/parameters of a pro- cess and its response variables. Quadratic models of the form Y ¼ b 0 þ b 1 x 1 þ b 2 x 2 þ b 11 x 2 1 þ b 22 x 2 2 þ b 12 x 1 x 2 þ e represent the relationship between response variable and process parameters, where Y is the response variable, x 1 and x 2 are the process parameters, b is the regression coefficient, and e is the estimated error. The central composition design of experiment (CCD) is not only efficient and economical because of the smaller number of experiments (e.g. 20 414 © 2016 The Authors. Coloration Technology © 2016 Society of Dyers and Colourists, Color. Technol., 132, 414–420 doi: 10.1111/cote.12230