Ecofriendly pretreatment of grey cotton fabric with enzymes in supercritical carbon dioxide fluid

Highlights

• A novel method for grey cotton pretreatment was developed with enzymes in SCF-CO₂.

• High efficiency of impurity removal for grey cotton was achieved in SCF-CO₂ media.

• A significant improvement in wettability of treated substrate was obtained.

• An optimized bio-pretreatment process for cotton in SCF-CO₂ was recommended.

Abstract

A novel and Ecofriendly process was developed at the first time for the pretreatment of grey cotton fabric by employing enzymes with microemulsion in supercritical carbon dioxide fluid (SCF-CO₂). The results show that high efficiency of impurity removal and significant improvement in wettability of treated substrate were achieved with the supposed bioprocess. The fabric weight loss and capillary rise height of substrate were notably influenced by system temperature and pressure, the dosages of enzymes and sodium bis (2-ethylhexyl) sulfosuccinate (AOT), the presence of water and initial pH value, as well as treatment time. An optimized enzymatic and Ecofriendly pretreatment process for desizing and scouring of grey cotton was recommended in supercritical carbon dioxide media with a system temperature at 50.0 °C and a pressure at 13.0 MPa for 60.0 min in the presence of small amounts of ethanol, water, several enzymes and AOT in the reactor at an initial pH value of 7.0–8.0. Moreover, the feasibility and the efficiency of the supposed supercritical bio-pretreatment process were further validated by scanning electronic microscopy (SEM) analysis.

Introduction

As a natural cellulose fibre, cotton is one of the most employed materials in textile industry with a world annual production about 25 million tonnes (International Cotton Advisory Committee, 2014) and world consumption share of 34% in recent years (Wang et al., 2013), and their based products are widely favourable by customers due to its excellent services properties, such as high moisture and water absorbency, good gas permeability and heat preservation, soft handle, skin-friendly, wholesomeness and comfortable to wear. However, raw cotton fibres and their based products involve natural and human-induced impurities at approximately 4–10% on weight of fibres. Depending on its species, origin, culture conditions, weather and fibre maturity, etc., raw cotton fibres usually contain various natural non-cellulosic impurities (Kalantzi et al., 2008, Shafie et al., 2009), such as pectins, waxes, lignins, proteins, natural oils, fats, aches, organic acids, sugars and some yellowish or brown colourants (Wang et al., 2013). Moreover, some human-induced impurities are also always presented on the substrate during manufacturing and/or transformation environment, such as the purposefully added sizing materials on warp yarns, processing lubricants from harvesting, ginning, spinning and weaving (Abdel-Halim and Al-Deyab, 2011, Kan and Yuen, 2012, Phatthalung et al., 2012). Furthermore, the non-cellulosic impurities form various hydrophobic layers or inhibiting covers around the cellulosic components and/or warp yarns, impeding the wetting and swelling behaviours of native cotton, as well as the mass transfer between an aqueous treatment bath and the cellulose substrate. Thus, the non-cellulosic impurities significantly inhibit the further processes for product manufacturing, such as the efficient and uniform dyeing, printing and finishing (Kalantzi et al., 2008, Dhiman et al., 2008).

Therefore, various pretreatment processes for removal of those impurities are indispensible and carried out as the first procedure during the manufacturing of cotton based products to prepare qualified semi-products for subsequent processes in textile industry (Wang et al., 2013). Up to date, various conventional wet-chemical pretreatment processes play a crucial role in eliminating such non-cellulosic impurities from raw cotton substrate, which usually includes traditional desizing, scouring, bleaching and even mercerizing processes, etc. (Wang et al., 2013). However, these conventional wet-chemical pretreatment processes generally involve harsh chemicals and severe conditions (Kalantzi et al., 2008, Benli and Bahtiyari, 2015). For example, concentrated alkalis, like sodium hydroxide, and so on, are commonly utilized in industry practice either for desizing, scouring, bleaching, or mercerizing treatments. Moreover, strong oxidants, such as hydrogen peroxide, sodium hypochlorite, are also employed for cotton desizing, bleaching in aqueous alkaline solutions. In addition, a high temperature and long treatment duration, as well as various surfactants, are usually involved in most of the pretreatment processes, to accelerate the hydrolysis and removal of sizing materials, hydrophobically natural non-cellulosic impurities such as pectins, waxes, lignins and fats, on the cotton substrate (Dhiman et al., 2008, Shafie et al., 2009). Consequently, conventional wet-chemical pretreatment processes consume enormous amounts of harsh chemicals, water and energy, resulting in high costs and a serious environmental pollution due to toxic and non-biodegradable effluents with high chemical oxygen demand (COD), biologic oxygen demand (BOD) and high pH values, as well as high salt content (Kalantzi et al., 2008, Benli and Bahtiyari, 2015, Mukhopadhyay et al., 2013). Moreover, the harsh chemicals and severe treatment conditions readily lead to damage cotton fibres, resulting in deterioration in physico-mechanical properties of the substrate such as the degradation of tensile strength, fabric shrinkage, as well as other appearances and handle of cotton substrate (Kalantzi et al., 2008, Shafie et al., 2009).

Therefore, various methods and processes have been developed as alternatives to the conventional wet-chemical pretreatment processes for the preparation of cotton or cotton based substrates with more environmentally friendly and more cost efficient, such as the low-temperature pretreatments for bleaching of cotton (Abdel-Halim and Al-Deyab, 2011), low-temperature plasma applications in grey cotton pretreatments (Kan et al., 2014, Wang et al., 2013), ultrasonic technology or combined with other methods for pretreatment of cotton fabrics (Li and Qiu, 2012, Benli and Bahtiyari, 2015, Shen et al., 2015), and enzymatic desizing, scouring and bleaching processes for cotton substrate (Oner and Sahinbaskan, 2011, Ahlawat et al., 2009, Chand et al., 2012), etc. It is most important that the bio-pretreatment processes for grey cotton substrate by employing various enzymes are gaining a critical demand in textile industry in the last decades, due to their numerous advantages. These bioprocesses with enzymes not only provide feasibilities in commercially acceptable quality of products and cost efficiency to replace conventional wet-chemical pretreatment processes, but also are more environmentally friendly. Generally, unlike chemicals, enzymes are very specific and selective with their substrates and actions, thus each pretreatment enzyme can only catalyze one kind of reactions to degrade the specific non-cellulosic impurity on cotton substrate, and cannot affect the backbone of cellulose polymers which readily avoids the destruction damage to the cotton fibre itself. Moreover, the bioprocesses with enzymes are carried out under mild and normal conditions in a high cost-efficiency manner, with minimum side reactions, water and energy conservation, as well as environmentally safe and healthy (Vankar and Shanker, 2008, Gremos et al., 2012, Ali et al., 2014).

Up to date, there are many reports are available in literature about the applications of various enzymes in the pretreatment processes for cotton substrates, and different enzymes are screened and evaluated for the pretreatments of grey cotton according to the composition of non-cellulosic impurities (Chand et al., 2012, Hao et al., 2013, Tian et al., 2012). In addition, some integrated or combination processes for pretreatment of cotton substrate are also available by employing different suitable enzymes (Shafie et al., 2009, Ali et al., 2014). In brief, it is really true that the textile industry is becoming one of the main fields of industrial applications of enzymes in the last decades.

Furthermore, novel investigations and applications of enzymes in non-aqueous media of supercritical carbon dioxide fluid or in which water is not the predominant content, are gaining momentum in recent years due to the numerous advantages of the medium, such as non-toxic, higher diffusion rates for solutes than those of in conventional liquids, less side reactions, being readily removed from products by simple depressurization, low risk of microbial contamination, expressing adequate activities of various enzymes and relatively high enzyme stability compared with aqueous solution, etc. (Melgosa et al., 2015, Leitgeb et al., 2013, Ciftci and Saldana, 2012). For example, Gremos et al. (2012) developed a novel and green methodology for the enzymatic acylation of fibrous cellulose with long fatty chain in supercritical carbon dioxide, and found that fibrous cellulose was acylated by a long chain aliphatic group in one step by employing immobilized lipase, esterase and cutinase. In early time, Matsuda et al. (2004) reviewed enzymatic reactions such as carboxylation, asymmetric reduction and esterification by corresponding enzymes in supercritical CO₂ medium, and demonstrated that this medium displayed new possibilities for synthesis by various kinds of enzymes. Recently, he also reviewed the last advances and progress of biocatalysis in the supercritical medium (Matsuda, 2013). Moreover, Ciftci and Temelli (2013) employed immobilized lipase as biocatalyst in a batch supercritical carbon dioxide bioreactor for synthesis of biodiesel from corn oil, and highest product content about 81.3% was achieved at the optimized conditions with more advanced than conventional biodiesel process. Dutta and Bhattacharjee (2015) used α-amylase from Bacillus licheniformis for enhanced yield of piperine-rich extract by supercritical carbon dioxide, and the results showed that both batch and continuous modes significantly increased the yields and phytochemical properties of piperine-rich extracts. Blattner et al. (2006) examined the esterification of lauric acid and 1-propanol catalyzed by using lipase encapsulated in microemulsion-based organogels in supercritical carbon dioxide, and turned out that the initial rates of the reaction in the supercritical medium were higher than those observed in the reference system.

As described above, most of the available investigations of different enzymes in supercritical carbon dioxide medium were mainly about their activities and stabilities, and their applications in biocatalysis synthesis, carboxylation, asymmetric reduction, enantioselective esterification, enzymatic acylation and extraction of natural products, etc. However, up to date, very few researches have been reported about the pretreatment of grey cotton fabric by employing enzymes in supercritical carbon dioxide fluid, especially for degradation and/or removal of additional and natural impurities on grey cotton fabric in supercritical carbon dioxide medium, although it is very desirable and promising process for the cleaner production of cotton textile due to waterless or very less water involved.

The objective of this work is to develop a novel and Ecofriendly pretreatment process for grey cotton fabric by employing mixed enzymes in supercritical carbon dioxide medium for biodegradation and/or removal of various impurities on the substrate with one-bath method. The effects of system temperatures, pressures, the dosage of mixed enzymes, AOT concentration, water contents, initial pH values of added solutions and treatment times on different pretreatment efficiency indexes such as weight loss and fabric capillary rise height, were investigated and optimized with a commercial grey cotton fabric in supercritical carbon dioxide fluid. Moreover, the feasibility and the efficiency of the supposed supercritical bio-pretreatment process for raw cotton substrate were also proved by scanning electronic microscopy (SEM) analysis.