Surface Hydrophilization of Polyester Hafiz Affan Abid, M.Sc. SUMMARY OF THE THESIS Title of the thesis: Hydrophilization of Polyester Author: Hafiz Affan Abid, M.Sc. Field of study: Textile Technics and Materials Engineering Mode of study: Full Time Department: Department of Material Engineering Supervisor: Ing. Jana Šašková, Ph.D. Committee for defence of the dissertation: Chairman: prof. RNDr. David Lukáš, CSc. FT TUL, Department of Nonwovens and Nanofibrous Materials Vice-chairman: doc. Ing. Eva Kuželová Košťáková, Ph.D. FT TUL, Department of Nonwovens and Nanofibrous Materials Members of the committee: prof. Dr. Ing. Mir. Černík, CSc. (opponent) The Institute for Nanomaterials, Advanced Technology and Innovation TUL prof. Ing. Ivan Stibor, CSc. FP TUL, Department of Chemistry doc. Ing. Ladislav Burgert, CSc. (opponent) Univerzity of Pardubice, Faculty of Chemical Technology doc. Ing. Antonín Kuta, CSc. UCT Prague, Department of Polymers doc. Rajesh Mishra, Ph.D., B. Tech. FT TUL, Department of Material Engineering Ing. Michal Černý, Ph.D. Univerzity of Pardubice, Faculty of Chemical Technology Ing. Petr Janák, CSc. INOTEX spol. s r.o., Dvůr Králové n. L. 1 Abstract Polyester is the most widely used material for both textile and non-fibrous applications. The major potential applications are high mechanical strength, good stretchability, heat stability, rapid drying, wrinkle resistance and resistance to usual organic solvents. The inherent hydrophobic nature of the polyester products are lacking water and moisture wicking, poor adhesion properties and ability to develop static charge. The modification of surface of the polyester by low concentration alkaline hydrolysis with NaOH in aqueous finishing bath under hot drying conditions is explored in this study. Moreover the surface of polyester film is modified by synergistic effect of sulphuric acid and sodium hydroxide in order to achieve hydrophilic surface with improved adhesion. The use of chemicals allows the surface hydrophilization of polyester at conventional pad-dry stenters without use of any sophisticated equipment that is required by most of the physical modifications (like plasma, corona, ozone etc). The surface hydrophilization of polyester fabric is done by low concentration of sodium hydroxide. The time of treatment, curing temperature and concentration of sodium hydroxide played very important role in getting better wicking rate and stability of the treatment. The weight loss of the fabric is minimized through the low liquor ratio pad-dry method of application. The use of hygroscopic agents like glycerin and urea at elevated temperatures has contributed to retain humidity during hot dry reaction conditions. The weight loss is far less than the high liquor ratio alkali treatment of polyester fabric. In this work optimization of parameters for getting higher vertical wicking rate and less surface scission through weight loss has been achieved by varying concentration of sodium hydroxide (20, 35 and 50 g/l), time of treatment (2,4, and 6 minutes) and drying temperature (130, 150 and 170 ˚C). Later the stability of the surface hydrophilization is evaluated at different temperatures by placing for longer times. The hydrophilized polyester fabric surface shows good stability at different temperatures and in comparison with plasma and ozone surface hydrophilic treatment. The activated polyester fabric shows good fastness against number of washing cycles. The surface morphology and chemical characterization of the hydrophilized polyester fabric is measured by Scanning Electron Microscope (SEM), X-ray Photoelectron spectroscopy (XPS) and Brunauer Emmett Teller (BET). The polyester film is hydrophilized with strong sulphuric acid solution and followed by low concentration alkali solution to evaluate the surface wettability and adhesion properties. The super hydrophilic surface is obtained at 80 % sulphuric acid and 50 g/l sodium hydroxide aqueous solution treatment. These treatment conditions give the polyester film surface with lowest water contact angle and high SFE values with good adhesion properties. The presence of hydroxyl groups on the surface with significant decrease in the surface energy has been confirmed through contact angle measurements. The SEM, BET analysis and T-peel data obtained by the polyurethane resin has indicated the increase in adhesion strength after chemical treatment and improvement of adhesion by thermoset resin can be attributed to the increase in surface wettability and roughness due to the surface modification. Key words: Polyester, hydrophilized surface, optimization, stability, vertical wicking, wettability, roughness 2 Anotace Polyester je nejrozšířenějším materiálem jak pro textilní, tak pro nevlákenné aplikace. Hlavní potenciální aplikace předurčuje vysoká mechanická pevnost, dobrá tažnost, tepelná stabilita, rychlé sušení, nemačkavost a odolnost vůči obvyklým organickým rozpouštědlům. Vlastní hydrofobní povaha polyesterových výrobků bez přítomnosti vody a vlhkosti zapříčiňuje špatné adhezní vlastnosti a schopnost vytvářet statický náboj. Modifikace povrchu polyesteru alkalickou hydrolýzou s nízkou koncentrací NaOH ve vodné dokončovací lázni za podmínek sušení za tepla se zkoumá v této studii. Navíc je povrch polyesterové fólie modifikován synergickým účinkem kyseliny sírové a hydroxidu sodného, aby se dosáhlo hydrofilního povrchu se zlepšenou přilnavostí. Použití chemikálií umožňuje povrchovou hydrofilizaci polyesteru na konvenčních zařízeních bez použití sofistikovaného vybavení, které vyžaduje většina fyzikálních modifikací (jako je např. plazma, korona, ozón apod.) Povrchová hydrofilizace polyesterové tkaniny se provádí nízkou koncentrací hydroxidu sodného. Doba úpravy, teplota sušení a koncentrace hydroxidu sodného hrály velmi důležitou roli při získávání vyšší vzlínací rychlosti a stability úpravy. Úbytek hmotnosti tkaniny je minimalizován aplikací suchého způsobu nanášení na suchý podklad. Použití hygroskopických činidel, jako je glycerin a močovina, při zvýšených teplotách přispělo k udržení vlhkosti při reakčních podmínkách sušení za zvýšených teplot. Ztráta hmotnosti je mnohem nižší, než je poměr vysokého obsahu alkoholu při alkalickém zpracování polyesterové tkaniny. V této práci byly optimalizovány procesní parametry pro dosažení vyšší vertikální rychlosti nasákavosti a nižšího narušení povrchu sledovaného prostřednictvím úbytku hmotnosti, a to pomocí změny koncentrace hydroxidu sodného (20, 35 a 50 g/l), doby zpracování (2, 4 a 6 minut) a teploty sušení (130, 150 a 170 °C). Stabilita povrchové hydrofilizace se sleduje po delší dobu, při různých teplotách. Hydrofilizovaný povrch polyesterové tkaniny vykazuje dobrou stabilitu při různých teplotách a ve srovnání s hydrofilním zpracováním povrchu plazmy a ozonu. Aktivovaná polyesterová tkanina vykazuje dobrou stálost vůči počtu pracích cyklů. Morfologie povrchu a chemická charakterizace hydrofilizované polyesterové tkaniny se měří pomocí skenovacího elektronového mikroskopu (SEM), rentgenové fotoelektronové spektroskopie (XPS) a Brunauer Emmett Teller (BET). Polyesterová fólie se hydrofilizuje silným roztokem kyseliny sírové a následně působením alkalického roztoku o nízké koncentraci za účelem průzkumu povrchové smáčivosti a adhezních vlastností. Superhydrofilní povrch se získá při použití 80% roztoku kyseliny sírové a 50 g/l vodného roztoku hydroxidu sodného. Tyto podmínky zpracování poskytují polyesterovému povrchu fólie nejnižší kontaktní úhel smáčení vodou a vysoké hodnoty SFE s dobrými adhezními vlastnostmi. Přítomnost hydroxylových skupin na povrchu s výrazným poklesem povrchové energie byla potvrzena měřením kontaktního úhlu. SEM, BET analýza a T-Peel data získaná s využitím polyuretanové pryskyřice naznačila zvýšení adhezní síly po chemickém zpracování a zlepšení adheze termosetovou pryskyřicí lze přičítat nárůstu smáčivosti povrchu a zvýšení drsnosti díky povrchové modifikaci. Klíčová slova: polyester, hydrofilizovaný povrch, optimalizace, stabilita, vertikální vznícení, smáčivost, drsnost 3 Table of Contents 1 Introduction ....................................................................................................................... 5 2 Purpose and aim of the thesis .......................................................................................... 5 3 Overview of the current state of problem ....................................................................... 6 4 Used Methods, study materials ........................................................................................ 7 4.1 Alkali surface hydrophilization of polyester fabric ..................................................... 7 4.2 Optimization of treatment parameters for alkali Hydrophilized polyester .................. 8 4.3 Characterization of hydrophilized polyester ................................................................ 8 4.4 Surface treatment of polyester film .............................................................................. 9 4.5 Characterization of polyester film ................................................................................ 9 5 Summary of the results achieved ................................................................................... 12 5.1 Alkaline hydrolysis (Polyester fabric sodium hydroxide and urea Treatment) ......... 12 5.2 Optimization of Alkali treatment parameters ............................................................. 15 5.3 Durability of surface hydrophilization against washing cycles ................................. 18 5.4 Surface hydrophilization of polyester film ................................................................ 19 5.5 Surface free energy .................................................................................................... 20 5.6 Scanning electron microscope (SEM) evaluation ...................................................... 22 5.7 T-PEEL test of adhesion ............................................................................................ 23 6 Evaluation of results and new findings ......................................................................... 23 6.1 Surface hydrophilization by Pad-dry method ............................................................ 23 6.2 Optimization of hydrophilized parameters ................................................................ 24 6.3 Durability against different temperature conditions of hydrophilized polyester fabric ........................................................................................................... 24 6.4 Washing fastness properties of hydrophilized polyester fabric ................................. 24 6.5 Development of hydrophilic polyester film surface by synergistic effect of sulphuric acid and sodium hydroxide .................................................................... 24 6.6 Proposed applications and limitations ........................................................................ 25 6.7 Future work ................................................................................................................ 25 7 References ........................................................................................................................ 26 8 List of published papers by the author ......................................................................... 28 8.1 List of publications in Impact factor Journals ............................................................ 28 8.2 List of related publications in international conferences ........................................... 28 8.3 Research Projects ....................................................................................................... 28 9 Curriculum Vitae ............................................................................................................ 30 4 1 Introduction Polyethylene terephthalate (PET) is one of the most important and widely used material in both textile industry for its apparel applications and in nonfibrous applications. They have properties like easy care, high strength, suitability for blending with other hydrophilic fibers, dimensional stability, thermal and chemical resistance, these properties make polyester fibers useful for versatile applications in the textile industry. Polyester fibers have taken the major position in textiles all over the world but they have some drawbacks like low moisture regain, static electricity accumulation, poor soil release properties, formation of pills on the garment. Research work is done in order to minimize the abovementioned deficiencies in the polyester by the controlled alkali treatment of the polyester fibers and fabrics through exhaust method [1-3] and hydrolysis of PET by strong acid or alkali [4], amine treatment [5], alcholysis [6] and treatment by various radiations including plasma [7, 8]. The modification of polyester surface is field to achieve hydrophilicity and surface that has specific characteristics to be used to provide better suitability for the use of adhesives [9], biomaterials [10] and protective coatings [11]. The strong acid causes micro scale roughness on the surface of PET that can then be used for further treatment of the polyester. In this study the acid treatment of polyester is done and then followed by alkaline hydrolysis and its effect on contact angle and surface energy is studied. Polyester is hydrolyzed by aqueous sodium hydroxide and undergoes nucleophilic substitution reaction as hydroxyl ion attacks carboxyl carbon of polyester following the chain scission results in production of hydroxyl and carboxylate end groups. This attack occurs at surface of fiber and loss in weight of fiber occurs [12]. The weight reduction of polyester fabric is usually done by the exhaust method under high liquor ratio [13, 14]. This leads to the longer cycle time and more weight loss of the polyester fabric. The padding technology is a well-known process in the field of polyester and cotton fabric processing. The padding and drying technology involve the use of less liquor and higher production rate at high temperature. The padding technology in dyeing and finishing of polyester is widely used in order to save the liquor and achieving more smooth fabric properties with high reproducibility [15]. The alkaline treatment of polyester fabric is carried out by padding method with the objective to study the effect of different treatment conditions on the wetting and physical characteristics of polyester fabric. 2 Purpose and aim of the thesis The non-availability of surface polar groups in polyester leads to the high hydrophobicity, low moisture regain, static charge accumulation, low wettability and poor adhesion properties. The alkaline hydrolysis of polyester by sodium hydroxide is a well-known method in order to create some polar groups on the surface of polyester that leads to the improvement in the wettability of polyester fabric. This alkali treatment is usually done by exhaust method that leads to the longer time of treatment, high liquor ratio, more weight loss and low reproducibility. The control of conditions such as time, temperature and concentration of alkali is necessary for non-destructive modification of polyester. Padding and drying technology is used to for fabric alkaline hydrolysis and its effect on wetting properties is 5 studied. The combined effect on wetting properties by strong acid followed by alkali treatment on polyester film is also studied. The main aims of the study are as follows:  To study the effect of different hygroscopic agents on alkali treatment of polyester fabric by Pad-dry method  To optimize parameters for surface hydrophilization of polyester fabric by dry heat fixation method  Performance and durability of optimized pad-dry heat sodium hydroxide treated polyester fabric at different temperature conditions  Development of super hydrophilic surface of polyester film by combined acid and alkali treatment 3 Overview of the current state of problem The alkali treatment of the polyester fibers and fabrics by the use of caustic soda imparts hydrophilicity to the treated substrate but in the process the polyester losses weight due to the hydrolysis by caustic soda [16]. The caustic soda treatment of polyester fibers and yarns is usually done by exhaust method that involves treatment of polyester at boil and longer time of treatment. The hydrophilic properties are achieved by the controlling the conditions of treatment and concentration of the caustic soda. This treatment method contributes to the loss in weight and strength of the treated polyester substrates [17, 18]. The caustic treatment also contributes to the functionalization of the polyester fabric for in cooperation of the particles for improving properties like UV blocking etc [14]. H. Tavanai has thoroughly investigated the weight reduction phenomena of polyester fabric and its effects on the fabric handle properties [16]. Structural modification of polyester fiber can influence the hydrophilic properties due to efficient moisture transport and release mechanism. Moisture can remain in the cross-section of the fiber, in the void space within a yarn, and void space created by the yarn crossover in the woven and knitted fabrics. Moisture regain of fabric depends on the air permeability, independent of fiber type. However, capillary wicking of water largely depend on the degree of hydrophilicity of individual polyester fiber [19-21]. When the liquid wets the fibres, it reaches the spaces between the fibres and produces a capillary pressure. The liquid is forced by this pressure and is dragged along the capillary due to the curvature of the meniscus in the narrow confines of the pores [22]. The kinetics of wicking and liquid diffusivity in the porous textiles is determined by different models [23-27]. In addition to the chemical processing route, the hydrophilicity of polyester can also be increased by improved fiber or yarn design. Use of microfibers instead of regular fibers can significantly improve the moisture management of polyester. The improved design of polyester filament with a hollow structure, which significantly improved the breathability, water absorption, and release rate [28, 29]. The adhesive bonding of solids has been associated with their surface energies and an improvement of adhesion usually involves ways to increase surface energy, one of the most effective ways being to chemically change the functional groups at the polymer surface. The most common are surface grafting [30], UV irradiation [31] and wet chemical reaction. 6 Alkaline hydrolysis is one of the most rapid methods to modify the chemical and physical characteristics of a polyester. 4 Used Methods, study materials The fabric used in this study was lab grade 100 % polyester with GSM 165 with equal warp and weft density of 20 threads per cm. The fabric was treated with hot water in order to remove any wax and dirt. Laboratory grade caustic soda flakes were used for caustic treatment of the samples and laboratory grade acetic acid was used to neutralize the fabric after the caustic treatment. Lab grade Glycerin and urea is obtained from Sigma Aldrich. Commercial polyester film of 30 µm in thickness is selected. The film is MylarTM, supplied by DUPONT. The selected material has good properties high melting temperature (> 250 ˚C), good mechanical strength, plasticity and intrinsic low surface energy makes it a potential material for chemical surface modification. Caustic soda flakes, ethyl alcohol, acetic acid and sulphuric acid of highest purity are obtained from Sigma Aldrich and used as received. 4.1 Alkali surface hydrophilization of polyester fabric Polyester samples were impregnated in caustic soda solution at concentrations (20 g/l and 50 g/l) and then padded at the pickup of 80%. The experiments are conducted, one to see the effect of concentration, time and temperature of treatment. The schematic diagram of the method for conduction of experiments is shown in figure 1. Second set of experiments are conducted with the addition of 50 g/l urea with 50 g/l NaOH at 150 °C for different times. Standard treatment (NaOH 50 g/l, time 30 minutes and temperature at 90 °C) is also done for comparison. The glycerin treatment is also carried out by pad dry method in the similar way as the sodium hydroxide treatment is done. The technique used for alkali treatment is the impregnation of polyester fabric in padding bath and then drying under tension state at fixed width. The purpose of fixing the width of fabric is to minimize the effect of shrinkage that can occur during high temperature hot drying. After padding and drying the fabric samples were rinsed and neutralized with acetic acid until all the caustic soda is removed from the samples. All the treated samples were dried in ambient air followed by conditioning and testing. Washing Analysis Padding Heat Treatment Conditioning Drying (Neutralization) (Testing) Figure 1. Scheme of treatment for polyester fabric 7 4.2 Optimization of treatment parameters for alkali Hydrophilized polyester The polyester fabric is first treated with non-ionic detergent followed by hot water in order to remove any dirt, dust and wax. The fabric was then dried, stabilized and conditioned. The sodium hydroxide treatment effect is studied under three variables.  Sodium Hydroxide Concentration (SHC)  Time of Treatment (TIME)  Temperature for treatment (TEMP) Three levels of sodium hydroxide concentration are selected that are 20 g/l, 35 g/l and 50 g/l. Three different levels of treatment time (2, 4 and 6 minutes) and three different levels of treatment temperature (130 ˚C, 150 ˚C and 170 ˚C). The optimization was performed using Box-Behnken design and response surface modeling under three levels and three factors as mentioned in table 1. The mathematical relationship between the three independent variables and the response is approximated by the second order polynomial as given in equation (1) and equation (2). Table 1. Selected factors and levels for sodium hydroxide treatment of polyester fabric Number of Factors Levels [-] [0] [+] SHC (g/l) 20 35 50 TIME (min) 2 4 6 TEMP (˚C) 130 150 170 (1) (2) Where and are model constant; X , X , X and , , are linear coefficients; , , 1 2 3 and , , are cross product coefficients and , , and , , are the quadratic coefficients. The coefficients of main effect and two factor interaction effect are estimated from the experimental results using the mathematical software package MINITAB. 4.3 Characterization of hydrophilized polyester Capillary rise measurements (Wicking) The rise of liquid in the fabric is measured according to the AATCC 197 method. The samples were placed vertically with the lower end dipped in a thin layer of a 1 % solution of methylene blue dye that has no affinity towards synthetic fibers as shown in Figure 10. The apparatus was set in a closed chamber in order to keep a saturated vapor atmosphere. The blue 8 coloration of dye solution on white fabric clearly indicated the height of capillary rise, and a ruler marked off in millimeters assembled along the fabric can make the height measurement easier. Height readings were recorded 20 minutes after the fabric was dipped in the liquid. Each measurement was carried out 5 times and the average height values were regarded as the final results. Percentage weight loss The weight of the fabric samples that were treated with the alkali were measured before and after the treatments using an electronic balance with an accuracy level of ± 0.001 g and the percentage weight loss was calculated using the following formula: (3) Where W and W are weights of the fabric samples before and after the alkali treatment 1 2 respectively. X-Ray photoelectron spectroscopy (XPS) analysis XPS measurement is performed on machine by Omicron Technology. Monochromatic primary radiation is used. The measurement is done in CAE mode with constant pass energy for surveillance of 50 [eV] and 20 [eV] spectrum. It is done for detail measurement of individual line spectra. 4.4 Surface treatment of polyester film The polyester film is immersed in alcohol water solution (1/1, v/v) for 2 hours in order to remove any dirt or oil for clean surface, rinsed with distilled water and then dried at room temperature for 24 hours. For hydrolysis reaction by acid the film is immersed in solution of sulphuric acid for specific time of treatment at room temperature. Two concentrations of sulphuric acid, 75 % and 80 %, are used for the treatment of film. The time of treatment for 80 % concentration of sulphuric acid is 3 sec and for 75 % concentration of sulphuric acid is 2 min. After this treatment the samples are rinsed and dried at room temperature for 12 hours. The acid treatment is followed by alkali treatment of samples for time of treatment (30 sec, 1, 2, 4, 6… 16min) at temperature of 90 ˚C. Alkali treatment is followed by neutralization of samples by 5 % solution of acetic acid followed by rinsing and drying at room temperature overnight. All the samples are conditioned and then measurements are carried out. The schematic diagram of treatment of samples is shown in figure 2. 4.5 Characterization of polyester film Contact angle measurements The surface wettability is evaluated using the sessile drop method and measurements are carried out on Advex instrument (figure 3) using 5 µl for liquid drop contact angle measurements. This measurement is used both to assess the wettability of the polymer film and critical surface energy measurements. Each sample is measured 10 times for liquid at room temperature and the contact angle (CA) values are averaged. 9