Textiles printing using microencapsulated pigments in biodegradable thickeners

6122 | P a g e M a r c h 2 0 1 8 h t t p s : / / c i r w o r l d . c o m / Textiles printing using microencapsulated pigments in biodegradable thickeners Meram S. Abdelrahman, Sahar H. Nassar*, Hamada Mashaly, Safia Mahmoud, Dalia Maamoun 1 Dyeing, Printing and Auxiliaries Department, Textile Research Division, National Research Centre, Cairo 12622, Egypt 2 Faculty of Applied Arts, Helwan University, Cairo, Egypt *Corresponding author: sh.wahab@nrc.sci.eg Abstract


Introduction
Pigments are a significant set of colorants that have been widely used in the coloration technology processes such as inks, paints and textile printing pastes. Such variety of applications for pigments results from their excellent properties such as photosensitivity, color strength, brilliance and transparency. However, the poor dispersion capability, poor colorfastness, and low weather durability are major problems for organic pigments in various applications. Organic pigments possess very poor solubility in aqueous environment. Therefore, they are generally employed in a dispersion form in presence of dispersing agent. However, traditional pigment dispersion generally has large particles, broad particle size distribution and low stability because particles aggregate easily, and consequently limiting their application in textile printing [1][2][3][4][5][6].
Micro-encapsulation is an extensively used technique wherein an active interior substance is microencapsulated in an exterior substance, usually polymer, with low permeability. The inner substance in the microcapsule is usually known as a core, while the outer substance is called a shell [7][8][9][10][11]. Microencapsulation technology has been applied in several fields such as pharmaceutical industry, fertilizers, cosmetics, and dyeing of textile fabrics. Many studies have been performed on the preparation, stabilization, and characterization of aqueous well-dispersed nano/micro-scale materials. Encapsulation is a promising method to enhance materials processing, environmental protection such as UV and pH, and prevent agglomeration. Microcapsules introduce the advantages that they are adjustable; the active core materials can be liberated at a controlled rate a transporter shell. Micro-encapsulated colorants have been paid attention in a variety of textiles applications. Pigments are ideal for micro-encapsulation [12][13][14][15][16][17][18].
The current study has employed micro-encapsulation of pigment that has led to a new environmentally safe technique for textile printing in the absence of auxiliaries using disperse dyes microencapsulated with polyurea. In this study, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were used to gain information about the quality of the micro-encapsulated pigments, as well as their printing performance on polyester/cotton blend fabric.

Materials and substrates
Scoured polyester/cotton textile blend fabrics were supplied from Misr El-Mahallah for Spinning and Weaving Company, Mahalla El-Kobra, Egypt. The fabrics were further treated with a solution containing 2 g/L nonionic detergent (Hostapal® CV-Clariant), at 60ºC for 30 minutes, then the fabrics were thoroughly rinsed with tap water and air-dried at room temperature.

Preparation of pigment printing paste
The printing paste of pigment was prepared according to the following recipe:

Synthesis of triglyceride polylactic acid (TGPLA) polymer
Triglyceride polylactic acid polymers with various molar ratios of glycerol and lactic acid were synthesized via one-step polycondensation procedure as shown in Scheme 1. The typical synthesis is proceeded as follows (for ratio: 50% LA to 50% GL): A mixture of lactic acid (18 g, 20 mmol) and glycerol (17.2 g, 20 mmol) was stirred in a 500 mL conical flask, while raising the temperature to 90˚C. 2-3 drops of concentrated sulfuric acid were added. The reaction was then heated at 100˚C for additional 20-30 minutes. After cooling, concentrated solution of sodium hydroxide was gradually added to neutralize the reaction mixture. The mixture was then subjected to water evaporation using rotary evaporator to obtain the pure solid content. The polymer composite can also be separated by addition of ethanol to afford a wet gel that can be filtered, dried and milled.

Synthesis of Carboxy Lactic Methacrylate (CLMA) polymer
P (LA-MAA) polymers of various monomers molar ratios were synthesized from MAA and various molar ratios of LA by a two-step one-pot polymerization procedure shown in Scheme 1. The typical synthesis were proceeded as follows (for the ratio: 50% LA to 50% MAA): A mixture of lactic acid (18 g, 20 mmol) and methacrylic acid (17.2 g, 20 mmol) was stirred in a 500 mL conical flask, while raising the temperature to 90˚C. 2-3 drops of concentrated sulfuric acid were added and the temperature was then raised to 105˚C. The mixture was stirred for 20-30 minutes followed by addition of N,N-methylene diacrylamide crosslinker (2 g). After the crosslinker is completely soluble, potassium persulfate (270 mg, 1 mmol) was added. The reaction was then heated at 105˚C for additional 10-15 minutes. Hydroquinone (110 mg, 1 mmol) was then added to the reaction mixture. After cooling, concentrated solution of sodium hydroxide was gradually added to neutralize the reaction mixture. The mixture was then subjected to water evaporation under vacuum using rotary evaporator to obtain the pure solid content. The polymer composite can also be separated by addition of ethanol followed by filtration of the produced solid [19].

Preparation of microcapsules
An encapsulator BUCHI B-390 (Inotech, Switzerland) equipped with a 500 μm / 750 μm concentric nozzle, a 50 ml syringe and an air pressure solution delivery system was used to prepare microcapsules of thickener with a pigment core. Water solution of CLMA and TGPLA was used as the shell forming phase. Systems saturated with solid 6 M CaCl2 solution were used as the shell/core forming phase. Microcapsules were produced at a shell flow rate of 44.6 mg/s and core flow rates of 7.3 mg/s or 40.1 mg/s. The amplitude of the membrane was constant throughout all experiments and its frequency was set to 3000 Hz. Microcapsules were then filtered using cotton fabric.

Color strength
The colorimetric analysis of the dyed samples was performed using a Hunter Lab ultra Scan® PRO spectrophotometer. The corresponding colour strength value (K/S) was assessed by applying the Kubelka Munk equation as follows.
Where, R is the decimal fraction of the reflection of the dyed fabric, K is the absorption coefficient, and S is the scattering coefficient.

Results and Discussion
It is clear from the data that the higher K/S value was achieved upon using encapsulated pigment. It is obviously seen also that even at lower pigment concentration at 0.5 % wof, the K/S was increased from 6.26 to 14.38, i.e. by almost 26.04%. The printing paste samples prepared via encapsulated thickener/pigment system and printed was found to acquire the highest K/S was chosen and subjected to overall color fastness measurements. The printed untreated cotton/polyester blend fabric was also measured under the same conditions for the sake of comparison. Tables 1 and 2     In the current work, we study the effects of encapsulation of pigment during printing process of cotton/polyester blend fabric, whereas the pigment is the core and the thickener is the shell. Such encapsulation helps to better disperse the pigment leading to color properties in the pigment properties technology. This study aims to enhance the printing properties of cotton/polyester blend fabric to improve color strecgth and decrease the employed amount of pigment. We utilized triglyceride / polylactic acid (TGPLA) and Carboxy Lactic / Methacrylate (CLMA) in the paste composited thickeners. To achieve this goal, the morphology and size of the prepared thickener/pigment capsules was monitored using scanning electron microscopy (SEM) as shown in Figures 3. The elemental compositions were also investigated by the energy dispersive X-ray spectroscopy (EDX) Figure 3 and Table 3. A close examination of the SEM micrographs signifies an average of 350 nm of capsules. Samples of cotton/polyester blend fabric was treated with the prepared thickener/pigment formula in both conventional and encapsulation forms. The K/S as well as the color fastness properties of the treated and printed samples, in addition to the quantity of used pigment on fabrics was investigated.

Conclusions
Nano/microscale organic pigments were encapsulated in a synthetic thickener were successfully prepared by using encapsulator. The prepared thickener showed better color stregcth and colorfastness properties. Furthermore, lower amounts of pigments were used. The effective encapsulation was con-firmed by SEM and EDX. Using the encapsulated pigment in a biodegradable synthetic thickener for textile printing is a much simpler, cheaper and environment friendly method. The printed fabrics displayed soft handle and very good colorfastness properties.