Microencapsulation in dyeing

Study of Microencapsulation in Dyeing

Presented ByArka Das

Entry No- 2012TTF2404

Introduction

Micro-encapsulation is a process in which tiny particles or droplets are surrounded by a coating to give small capsules many useful properties. In a relatively simplistic form, a microcapsule is a small sphere with a uniform wall around it. The material inside the microcapsule is referred to as the core, internal phase, or fill, whereas the wall is sometimes called a shell, coating, or membrane.

The potential size range of the microcapsules produced is enormous, with typical diameters being between 2 and 2000 µm.

Capsule walls are typically 0.5-150 µm thick, although walls measuring less than 0.5 µm can be achieved.

The proportion of core material in the capsule is usually between 20 and 95% by mass.

There are over 50 different known wall materials; both natural and synthetic polymers can be used to form the microcapsules. These include the natural polymers gelatin, gum arabic, carrageenan and alginate, and synthetic polymers such as ethylcellulose.

In recent years microencapsulation techniques have been used in the pharmaceutical, agricultural, bulk chemical, food processing, and cosmetic and toiletry industries.

The textile industry, although initially slow to exploit the technology, is now generating innovative ideas and inventions within the field.

Cont…………..

Shapes of Microencapsulation

Microencapsulation Process

(a) Spray coating methods, e.g Wurster air suspensionCoating

(b) Wall deposition from solution, e.g. coacervation orphase separation

(c) Interfacial reaction

(d) Physical processes, e.g. annular jet encapsulation

(e) Matrix solidification, e.g. spray drying or chilling

(f)Naturally occuring microcapsules

Spray Coating methods

This spray technique coats finer particle while they are suspended in an upwards moving air steam. The process simultaneously applies and hardens the wall materials onto the particles.Heated air flows into the chamber through small holes in the base plate and the particle rise within the chamber.Small amounts of coating solution from a spray nozzle at the centre of the chamber are deposited on the particles.

Wall deposition from solution

Microcapsules produced can range in size between 2 and 50 µm.

Coacervation can be divided into two distinct categories, simple and complex, the former involving only with a single colloidal solute and the latter more than one colloid.

Interfacial reactionThis process is based on interfacial polycondensation polymerisation.

The capsule shell will be formed at the surface of the droplet or particle by polymerization of the reactive monomers.

The substances used are multifunctional monomers.

Generally used shell forming material include diamines and diacid chlorides.

it will be dispersed in aqueous phase containing dispersing agent.

Physical ProcessesA dual fluid stream of liquid core and shell materials is pumped through concentric tubes and forms droplets under the influence of vibration. A membrane of wall material is formed across a circular orifice at the end of the nozzle and the core material flows into the membrane, causing the extrusion of a rod of material.Droplets break away from the rod and The shell is then hardened by chemical cross linking, cooling, or solvent evaporation.Solid capsules are removed by filtration or other mechanical means and the immiscible carrier fluid, after passing through the filter, is reheated and recycled.This process is capable of producing capsules ranging from 400- 2000µm in diameter.

Matrix SolidificationMicroencapsulation is achieved using spray drying or chilling techniques by atomising a combined solution of core and wall material.The process of spray drying consists of four stages.The first of these involves atomisation of the core/wall material solution, which governs the size of the capsules (generally 10-200 µm)The solution may be heated to keep the ingredients in solution and to ensure that premature hardening or drying does not take place.The small droplets formed on atomisation quickly assume their equilibrium spherical shape and, on contact with the air stream, drying of the product begins.

Naturally ocurring microcapsules

Filamentous fungi, protozoa and yeast have been mentioned as a possible sources of capsules; however, most of the examples given and claims presented have involved yeast.These micro-organisms appear to lend themselves to the microencapsulation process and therefore further work has concentrated on utilising waste yeast (Saccharomyces cerevisiae) from the brewing and baking industries.

Textile Applications of Microencapsulation

Microencapsulation of Disperse dyeMicroencapsulation of Acid dyesThese will be discussed briefly.

Dyeing of polyester using microencapsulated disperse dyes in the absence of auxiliaries

Dyeing of polyester requires water and certain chemical auxiliaries such as dispersing agents, penetrating agents and levelling agents, in the dyebath. Unfortunately, residual auxiliaries and dyestuff may be present in the effluent and may cause pollution.

Polyester fabric was dyed with microencapsulated CI Disperse Blue 56 using a high temperature dyeing process without dispersing agents, penetrating agents, levelling agents or other auxiliaries. The quality of the polyester fabric dyed in this manner without reduction clearing was at least as good as that dyed traditionally after washing and reduction clearing. After separating off the polyurea microcapsules, the dyebath was virtually colourless and was shown to be suitable for reuse.

Dye Used

CI Disperse Blue 56 (1) and CI Disperse Red 60 (2)

Preparation of microcapsulesPolyurea microcapsules (PMs) were prepared using an interfacial polymerisation reaction in emulsion form as described earlier.PMs contained Diphenylmethane-4,4′diisocyanate(MDI)(wall material) and disperse dye (core material) and were prepared at an adequate ratio with GPE2040 (2% w/w) as the emulsifier and PVA (1% w/w) as the stabiliser.The reaction being carried out at 50°C for 180 min.After reaching room temperature microcapsules were seperated by decantation.After washing with 10% w/w ethanol to remove unreacted isocyanate, the microencapsulated material was dried in a vacuum oven at 25 °C for 24 h.

Results and Discussion

In the DSC analysis, thermal change was not apparent below 280 °C, with an absorption peak around that temperature (Figure a). Between 160 and 230 °C the curve was more uniform, and endothermic transition of the dyes was not detected.TG showed that the microcapsule weight decreased with increasing temperature by as much as 40% (Figure b). A small initial weight loss occurred between 160 and 230 °C due to progressive release of core material from the microcapsule.

Thermal properties of the PMs

Particle Size and distribution

The mean size of all the resulting particles after emulsification stirring at 10 000 rpm was about 23 μm, and the size distribution was narrow (ca. 6–60 μm).

Morphological structure of microcapsules

Dyeing behavior

The dyeing behavior of the dyes in PM form was compared with fabric dyed traditionally.The results show that the levelness and fastness to soaping and rubbing of PET samples dyed with 1 in PM form, without auxiliaries or reduction clearing, were at least as good as those obtained by traditional disperse dyeing after washing and reduction clearing.The excellent wash-off properties of the PET fabric dyed with the PM disperse dyes may be attributed to reduced staining of the surface of the fibre, making the need for washing much less important.

Dyebath wastewater

Reuse of recovered wastewater

PET fabric samples were dyed under similar conditions using dyes 1 and 2 in PM form in filtered wastewater.

The dyeing rate curves are shown in Figure 3. In each case the dyeing rate curves are similar, which means that residual dye 1 remaining in the wastewater had little influence on the dyeing behaviour of this dye in PM form.

Reuse of recovered wastewater

Reuse of recovered wastewater

Effect of Microencapsulation on Dyeing Behaviors of

Disperse Dyes Without Auxiliary Solubilization

Microencapsulated disperse dye can be used to dye hydrophobic fabric in the absence of auxiliaries and without reduction clearing. However, little available information for dyeing practice is provided with respect to the effect of microencapsulation on the dyeing behaviors of disperse dyes. In this research, disperse dyes were microencapsulated under different conditions. The dyeing behaviors and dyeing kinetic parameters of microencapsulated disperse dye on PET fiber, e.g. dyeing curves, build up properties, equilibrium adsorption capacity C1, dyeing rate constant K, half dyeing time t1/2, and diffusion coefficient D were investigated without auxiliary solubilization and compared with those of commercial disperse dyes with auxiliary solubilization. The results show that the dyeing behaviors of disperse dye are influenced greatly by microencapsulation.

Dyes Used

Preparation of microencapsulated disperse dyes

with different shell materials and mass ratios

of core to shell

Disperse dye microcapsules were prepared by in situ polymerization.Disperse dyes (C.I. disperse red 73 or C.I. disperse blue 56, no any additives, 1 g) and MS aqueous solution (1% w/w, 100 mL) were mixed by high-speed emulsifier (10,000 rpm) for 5 min.The pH of the mixture was adjusted to 4–5The mixture was then put immediately into a flask with stirring.Designated amount of shell material (1 g, 2 g, 3 g, 4 g, trimethylolmelamine or hexamethylolmelamine) was added at ambient temperature.After being stirred uniformly, the reaction system was heated to 65C (heating rate 1C/min) and maintained for 120 min to form microencapsulated disperse dyes with different mass ratios of core to shell (1 : 1, 1 : 2, 1 : 3, 1 : 4 w/w).Reaction system was cooled down and its ph was adjusted to 7–8 using ammonia.

RESULTS AND DISCUSSION

The microcapsules shown in Figure 4 are nearly spheric with rough surface and irregular pores on the surface.The surface of microcapsules prepared by hexamethylolmelamine is much looser than the surface of microcapsules produced by trimethylolmelamine.The more looser microcapsule shell is, the faster dye release rate it will be.

Characterization of microencapsulated disperse dyes

Thermogravimetric analysis results of microcapsule shells prepared with different materials are given in Figure.

Melamine resin as a thermosetting polymer exhibits good thermal stability below 250˚C. Due to possessing more hydroxyl groups, hexamethylolmelamine shows more severe weight loss than trimethylolmelamine above 250C.

TGA curves of microcapsule shells prepared with different materials (a) trimethylolmelamine; (b)hexamethylolmelamine.

The particle size distribution of microencapsulated disperse dyes are shown in figure.The mean size of C.I. disperse red 73 microcapsules prepared by trimethylolmelamine is 8.9 μm.While the mean size of C.I. disperse blue 56 microcapsules prepared by hexamethylolmelamine is 11.5 μm.Two microcapsule samples reveal relatively concentrated particle size distribution.

Size distribution curves of microencapsulated disperse dyes: (a) core material, C.I. disperse red 73; shell material, trimethylolmelamine; mass ratio of core to shell, 1 : 2; (b) core material, C.I. disperse blue 56; Shell material, hexamethylolmelamine; mass ratio of core to shell, 1 : 2.

Effect of microencapsulation conditionson diffusibility

Effect of microencapsulation conditionson diffusibility

Dyeing curves of commercial and microencapsulated disperse dyes: (a) Commercial disperse dyes; (b) microencapsulated disperse dyes (microencapsulated C.I. disperse red 73: trimethylolmelamine as shell material, mass ratio of core to shell 1 : 2; microencapsulated C.I. disperse blue 56: hexamethylolmelamine as shell material,mass ratio of core to shell 1 : 2).

Effect of microencapsulation onbuild-up properties

Microencapsulation of Disperse Dye Particles with Nano Film Coating Through Layer by

Layer Technique

In this study, weak polycation poly(allylamine hydrochloride) and strong polyanion poly(sodium styrene sulfonate) were used for fabrication of nano film through layer by layer technique on the surface of disperse dye particles. Then micron-sized particles were surrounded by poly(urea formaldehyde) using in-situ polymerization. Chemical structure, surface morphology, and size distribution of these novel microcapsules were characterized by Fourier transform infrared spectrometry, differential scanning calorimetry, optical microscopy, and scanning electronic microscopy.

Chemical structure of microcapsules containing disperse dye:

Doublet bands at 3445 and 3355 cm-1 are presented by the FTIR spectrum of urea. As it can be seen, polycondensation reaction between urea and formaldehyde were proved by the absence of absorption band owing to urea at 2806 and 2640 cm -1 and manifestation of absorption peak of poly(urea formaldehyde), which is assigned at 3707–3050 (NH and OH), 1649 ( ), 1544 ( ) and 1027 ( ) cm -1. On the other hand, the absorption peaks of 1556, 1035, and 630 cm -1 are appeared in both microcapsules and dyes spectra.

Microencapsulation of Acid Dyes in Mixed Lecithin/Surfactant Liposomic Structures

Non-uniformity occurring in polyamide dyeing, caused by the rapid uptake of dye by the fibers, can be reduced by retarding and leveling agents.Liposomes release the microencapsulated dye slowly, promoting a retarding effect, comparable with the one obtained with retarding agents, making them a good alternative to commercial levelling products.The objective of this work is to study microencapsulation of the dye in liposomes with lecithin from soy, as an alternative to retarding and leveling agents.The effect on the dyeing rate of the microencapsulated dyes is compared with that from common retarding and leveling agents.The influence of surfactants on the stability of the liposomes and hence on the exhaustion curves of the dyeing is evaluated

Results and Discussion

The best lecithin concentration to obtain a dyeing rate close to that with the commercial retarding and leveling agents was l g/L

Dyeing with lecithin liposomes

Figure. Exhaustion curves of microencapsulated c.I. Acid blue113 using different lecithin concentrations

Influence of surfactants in the liposolles

Influence of surfactants in the liposolles

ConclusionMicroencapsulation of disperse dyes provides the opportunity to carry out dyeing in absence of auxiliaries and without dyeing without affecting other properties. Thus this techniques results in reduced BOD and COD of dye baths from dyeing.

Different disperse dyes having different dyeing behavior can be make to behave similarly by microencapsulation. So this technique is a very useful tool in compound shade dyeing.

Microencapsulation of acid dyes can be used for improving leveling. This can also be used improve barre dyeing. As this technique retard the rate of dyeing it can be used successfully.

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