Study of Microencapsulation in Dyeing Presented By Arka Das Entry No- 2012TTF2404
IntroductionMicro-encapsulation is a process in which tiny particlesor droplets are surrounded by a coating to give smallcapsules many useful properties. In a relatively simplisticform, a microcapsule is a small sphere with a uniform wallaround it. The material inside the microcapsule is referred toas the core, internal phase, or fill, whereas the wall issometimes called a shell, coating, or membrane.The potential size range of the microcapsules produced isenormous, with typical diameters being between 2 and 2000µm.Capsule walls are typically 0.5-150 µm thick, althoughwalls measuring less than 0.5 µm can be achieved.
Cont…………..The proportion of core material in the capsule is usuallybetween 20 and 95% by mass.There are over 50 different known wall materials; bothnatural and synthetic polymers can be used to form themicrocapsules. These include the natural polymersgelatin, gum arabic, carrageenan and alginate, and syntheticpolymers such as ethylcellulose.In recent years microencapsulation techniques have beenused in the pharmaceutical, agricultural, bulk chemical, foodprocessing, and cosmetic and toiletry industries.The textile industry, although initially slow to exploit thetechnology, is now generating innovative ideas and inventionswithin the field.
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 methodsThis spray technique coats finerparticle while they are suspended in anupwards moving air steam. The processsimultaneously applies and hardensthe wall materials onto the particles.Heated air flows into the chamberthrough small holes in the base plateand the particle rise within thechamber.Small amounts of coating solutionfrom a spray nozzle at the centre of thechamber are deposited on the particles.
Wall deposition from solutionMicrocapsules produced can range in size between 2 and50 µm.Coacervation can be divided into two distinctcategories, simple and complex, the former involving onlywith a single colloidal solute and the latter more than onecolloid.
Interfacial reactionThis process is based on interfacial polycondensationpolymerisation.The capsule shell will be formed at the surface of thedroplet or particle by polymerization of the reactivemonomers.The substances used are multifunctional monomers.Generally used shell forming material include diaminesand diacid chlorides.it will be dispersed in aqueous phase containing dispersingagent.
Physical ProcessesA dual fluid stream of liquid core and shellmaterials is pumped through concentric tubesand forms droplets under the influence ofvibration.A membrane of wall material is formed across acircular orifice at the end of the nozzle and thecore material flows into the membrane, causingthe extrusion of a rod of material.Droplets break away from the rod and The shellis then hardened by chemical crosslinking, cooling, or solvent evaporation.Solid capsules are removed by filtration or othermechanical means and the immiscible carrierfluid, after passing through the filter, is reheatedand recycled.This process is capable of producing capsulesranging from 400- 2000µm in diameter.
Matrix SolidificationMicroencapsulation is achieved usingspray drying or chilling techniques byatomising a combined solution of core andwall material.The process of spray drying consists of fourstages.The first of these involves atomisation ofthe core/wall material solution, whichgoverns the size of the capsules (generally10-200 µm)The solution may be heated to keep theingredients in solution and to ensure thatpremature hardening or drying does nottake place.The small droplets formed on atomisationquickly assume their equilibrium sphericalshape and, on contact with the airstream, drying of the product begins.
Naturally ocurring microcapsulesFilamentous fungi,protozoa and yeast havebeen mentioned as apossible sources of capsules;however, most of theexamples given and claimspresented have involvedyeast.These micro-organismsappear to lend themselves tothe microencapsulationprocess and thereforefurther work hasconcentrated on utilisingwaste yeast (Saccharomycescerevisiae) from the brewingand baking industries.
Textile Applications of Microencapsulation Microencapsulation of Disperse dye Microencapsulation of Acid dyes These will be discussed briefly.
Dyeing of polyester using microencapsulateddisperse 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 UsedCI Disperse Blue 56 (1) and CI Disperse Red 60 (2)
Preparation of microcapsulesPolyurea microcapsules (PMs) were prepared usingan interfacial polymerisation reaction in emulsion formas described earlier.PMs contained Diphenylmethane-4,4′diisocyanate(MDI)(wall material) and disperse dye(core material) and were prepared at an adequate ratiowith 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 wereseperated by decantation.After washing with 10% w/w ethanol to removeunreacted isocyanate, the microencapsulated materialwas dried in a vacuum oven at 25 °C for 24 h.
Results and DiscussionThermal properties of the PMsIn the DSC analysis, thermal changewas not apparent below 280 °C, withan absorption peak around thattemperature (Figure a). Between 160and 230 °C the curve was moreuniform, and endothermic transitionof the dyes was not detected.TG showed that the microcapsuleweight decreased with increasingtemperature by as much as 40%(Figure b). A small initial weight lossoccurred between 160 and 230 °C dueto progressive release of core materialfrom the microcapsule.
Particle Size and distributionThe mean size of all the resulting particles afteremulsification stirring at 10 000 rpm was about 23μm, and the size distribution was narrow (ca. 6–60 μm).
Dyeing behaviorThe dyeing behavior of the dyes in PM form was compared withfabric dyed traditionally.The results show that the levelness and fastness to soaping andrubbing of PET samples dyed with 1 in PM form, withoutauxiliaries or reduction clearing, were at least as good as thoseobtained by traditional disperse dyeing after washing andreduction clearing.The excellent wash-off properties of the PET fabric dyed withthe PM disperse dyes may be attributed to reduced staining of thesurface of the fibre, making the need for washing much lessimportant.
Reuse of recovered wastewaterPET fabric samples were dyedunder similar conditions usingdyes 1 and 2 in PM form infiltered wastewater.The dyeing rate curves areshown in Figure 3. In each casethe dyeing rate curves aresimilar, which means thatresidual dye 1 remaining in thewastewater had little influence onthe dyeing behaviour of this dyein PM form.
Effect of Microencapsulation on Dyeing Behaviors of Disperse Dyes Without Auxiliary SolubilizationMicroencapsulated disperse dye can be used to dyehydrophobic fabric in the absence of auxiliaries and withoutreduction clearing. However, little available information fordyeing practice is provided with respect to the effect ofmicroencapsulation on the dyeing behaviors of disperse dyes.In this research, disperse dyes were microencapsulated underdifferent conditions. The dyeing behaviors and dyeing kineticparameters of microencapsulated disperse dye on PET fiber,e.g. dyeing curves, build up properties, equilibriumadsorption capacity C1, dyeing rate constant K, half dyeingtime t1/2, and diffusion coefficient D were investigatedwithout auxiliary solubilization and compared with those ofcommercial disperse dyes with auxiliary solubilization. Theresults show that the dyeing behaviors of disperse dye areinfluenced greatly by microencapsulation.
Preparation of microencapsulated disperse dyes with different shell materials and mass ratios of core to shellDisperse dye microcapsules were prepared by in situpolymerization.Disperse dyes (C.I. disperse red 73 or C.I. disperse blue 56, noany 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, 4g, trimethylolmelamine or hexamethylolmelamine) was added atambient temperature.After being stirred uniformly, the reaction system was heated to65C (heating rate 1C/min) and maintained for 120 min to formmicroencapsulated disperse dyes with different mass ratios ofcore 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 DISCUSSIONCharacterization of microencapsulated disperse dyesThe microcapsules shownin Figure 4 are nearlyspheric with rough surfaceand irregular pores on thesurface.The surface ofmicrocapsules prepared byhexamethylolmelamine ismuch looser than thesurface of microcapsulesproduced bytrimethylolmelamine.The more loosermicrocapsule shell is, thefaster dye release rate it willbe.
Thermogravimetric analysisresults of microcapsule shellsprepared with different materialsare given in Figure.Melamine resin as athermosetting polymer exhibitsgood thermal stability below250˚C.Due to possessing morehydroxylgroups, hexamethylolmelamineshows more severe weight loss TGA curves of microcapsule shellsthan trimethylolmelamine above prepared with different materials (a)250C. trimethylolmelamine; (b) hexamethylolmelamine.
The particle size distribution ofmicroencapsulated disperse dyesare shown in figure.The mean size of C.I. dispersered 73 microcapsules prepared bytrimethylolmelamine is 8.9 μm.While the mean size of C.I.disperse blue 56 microcapsulesprepared byhexamethylolmelamine is 11.5μm.Two microcapsule samples Size distribution curves ofreveal relatively concentrated microencapsulated disperse dyes: (a)particle size distribution. 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 conditions on diffusibility
Effect of microencapsulation conditions on diffusibilityDyeing curves of commercial and microencapsulated disperse dyes: (a) Commercial disperse dyes; (b) microencapsulateddisperse 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 on build-up properties
Microencapsulation of Disperse Dye Particles with Nano Film Coating Through Layer by Layer TechniqueIn this study, weak polycation poly(allylamine hydrochloride)and strong polyanion poly(sodium styrene sulfonate) were usedfor fabrication of nano film through layer by layer technique onthe surface of disperse dye particles. Then micron-sizedparticles were surrounded by poly(urea formaldehyde) using in-situ polymerization. Chemical structure, surfacemorphology, and size distribution of these novel microcapsuleswere characterized by Fourier transform infraredspectrometry, differential scanning calorimetry, opticalmicroscopy, 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 ofurea.As it can be seen, polycondensation reaction between urea and formaldehyde wereproved by the absence of absorption band owing to urea at 2806 and 2640 cm -1and manifestation of absorption peak of poly(urea formaldehyde), which isassigned at 3707–3050 (NH and OH), 1649 ( ), 1544 ( ) and 1027 ( ) cm -1. On theother hand, the absorption peaks of 1556, 1035, and 630 cm -1 are appeared inboth microcapsules and dyes spectra.
Microencapsulation of Acid Dyes in MixedLecithin/Surfactant Liposomic StructuresNon-uniformity occurring in polyamide dyeing, caused by therapid uptake of dye by the fibers, can be reduced by retardingand leveling agents.Liposomes release the microencapsulated dye slowly,promoting a retarding effect, comparable with the oneobtained with retarding agents, making them a good alternativeto commercial levelling products.The objective of this work is to study microencapsulation ofthe dye in liposomes with lecithin from soy, as an alternative toretarding and leveling agents.The effect on the dyeing rate of the microencapsulated dyes iscompared with that from common retarding and levelingagents.The influence of surfactants on the stability of the liposomesand hence on the exhaustion curves of the dyeing is evaluated
Results and Discussion Dyeing with lecithin liposomesThe best lecithinconcentration to obtain adyeing rate close to thatwith the commercialretarding and levelingagents was l g/L Figure. Exhaustion curves of microencapsulated c.I. Acid blue 113 using different lecithin concentrations
ConclusionMicroencapsulation of disperse dyes provides theopportunity to carry out dyeing in absence of auxiliariesand without dyeing without affecting other properties.Thus this techniques results in reduced BOD and COD ofdye baths from dyeing.Different disperse dyes having different dyeing behaviorcan be make to behave similarly by microencapsulation.So this technique is a very useful tool in compound shadedyeing.Microencapsulation of acid dyes can be used forimproving leveling. This can also be used improve barredyeing. As this technique retard the rate of dyeing it canbe used successfully.