Printer Friendly

Preparations of microencapsulated PCMs-coated nylon fabrics by wet and dry coating process and comparison of their properties.


Recently, in the field of functional outer sports/leisure wear, winter clothing increasingly requires additional protective properties, to provide protection from severe outdoor conditions, while maintaining the conventional water vapor permeability (WVP) and water repellent properties. For this high performance clothing, previous investigators studied the incorporation of additives into the fabrics such as aluminum, ceramics, PCMs (phase change materials) (1-3), and so on (4), (5). However, although the incorporation of a dispersion of aluminum in polyurethane (PU) in the form of a coating reflected some radiation heat, it did not come up to its expectations owing to its high heat conductivity and low radiation efficiency. Also, ceramics were found to have remarkable thermal heat insulation properties and low heat conductivity, but had hardly any thermal storage effect. In addition, PCMs, which can store or release a large quantity of latent heat at a fairly constant temperature during the phase transition, allow the solid-liquid phase change problem to be solved, but their cost is high and, thus, they are not convenient to use. Accordingly, various materials have been studied for phase change thermal heat storage in textiles (6-10), but no international standards for the use of PCMs in fabrics and the evaluation of their thermal properties have yet been defined. In this respect, it is expected that microencapsulated PCMs (PCMMcs) will provide the best solution, as they provide a large heat transfer area. Royon et al. (11) developed a new material for low temperature storage, which contained water as PCMs within a polyacrylamide, which keeps its shape, requires no coating, and so can be used directly. Nevertheless, the potential use of microencapsulated PCMs in control applications is limited to some extent by their cost. Similarly, in textiles, the major problem is not only the modification of the PCMs, but its incorporation into the fabrics. Also, PCMMcs can be occasionally embedded into the spinning dope and the structure of polymer forms, or coated onto fabrics. Consequently, in the case where PCMMcs are incorporated into fabrics, even if the PCMMcs is very effective and convenient to use, low embedding into fabrics may decrease their heat storage capacity and degrade their original functionalities such as their vapor or moisture permeability, soft touch, and wearing comfort. Moreover, practical difficulties may sometimes cause the fabrics to have low thermal conductivity and stability problems, due to extended cycling and the phase separation of the PCMs.

In this study, in case of application of the PCMs to textiles, in order to overcome these problems, waterproof and breathable finished nylon fabrics were prepared directly using two different coating methods without a binder, namely, wet coating using a wettable and micro-porous PU resin with the incorporation of PCMMcs into the fabrics, and dry coating using a hydrophilic and non-porous PU resin. In addition, the improvement of the thermal insulation properties of the waterproof finished nylon fabrics with PCMMcs was discussed, and a comparison was made of the thermal insulating effect of the PCMMcs according to the coating conditions and contents.



Four different types of PCMMcs (5-30 [micro]m) with similar melting point ranging from 25[degrees]C to 28[degrees]C were examined, in which the difference in their phase changing temperature. [T.sub.m], is due to the difference in the preparation conditions. The characteristics of the PCMMcs tested in this study are detailed in Table 1. The used PCMMcs were chosen by considering their compatibility with the wet porous type of PU (MP-840K. Kangnam hwasung, Korea) solution and the ease of the coating process. After trying out different PCMMcs to laminate the fabrics, the most suitable PCMMcs was found to be that obtained from J&S Tech (Korea). The fabrics of nylon used in this work were pretreated with breathable and waterproof finish, and textured warp and weft composition with 70D FD 155 and 160D FD ATY 70, respectively. All other commercially available solvents and additives used in this study, such as the dulling agent (OK-412, Acement, Germany) and DMF (N, N-dimethylformamide, Hanwon), dispersion agent (DC-200, Bugang), surfactant (SD-8I, Daemung Inchem), wet-crosslinking agent (DC-W, Daemung Inchem), and accelerant (Daechon chemical engineering) supplied from local manufacturers of Korea, were of general purpose grade and used as received without further purification.
TABLE 1. Characteristics of tested PCMMcs.

Substance Manufacturer [T.sub.m] ([degrees]C) Appearance

PMCD-28 M1KILIKHN 28 Liquid, white
PMCD-25 MIKILIKEN 25 Liquid, powder
KL-83 J&S TECH 28 Liquid, powder
A-83 HUMANTECHPLUS 25 Liquid, powder

Substance Size ([mu]m) Compatibility (a)

PMCD-28 -- No good
PMCD-25 20-50 Good
KL-83 5-30 Good
A-83 3-5 Good

(a) Dispersion ability between PCMMcs and PU resin.

Preparation of PCMMcs-Coated Fabrics by Wet and Dry Coating Procedure

In the preparation of PCMMcs fabrics at wet coating process, to prepare the coating solution, PCMMcs was dispersed in PU solution with an aqueous 10, 20, and 30% by weight of PU resin at a room temperature, in which the mixing ratio of PU resin:color toner:DMF: additives:PCMMcs have controlled of 100:10:35:5:0, 10, 20, and 30, respectively. After mixing the coating solution, bubbles were completely removed by means of a defoamer. The wet coating was performed by rolling the fabrics without the loading using a 0.15-0.2 mm gapped pole and then coagulated by dipping them in a sufficient amount of water for about 5-10 min. The prepared nylon fabrics different amounts of PCMMcs were washed, the water squeezed from them with a mangle, and dried in an oven at 160[degrees]C for 90 s. Next, the dry coating of the PCMMcs-encapsulated nylon fabrics was performed in two-steps, by first applying the base coating and then the top coating. The first step of the overall dry coating process was performed with a defoamed base coating solution which was prepared by mixing the PU resin, cross-linking agent, accelerator, DMF, and toluene, and then spreading this solution on the fabrics and rolling it using a knife with the pressure two times. Once the base coating layer was formed, the treated fabrics were dried in an oven at 160[degrees]C while maintaining them under tension. The second step was the hardening of the PCMMcs through the top coating procedure. This process was followed by controlling the concentration of the PCMMcs so that an appropriate microencapsulated mixture was formed. This mixed PU resin with catalyst and DMF as solvent was controlled by PCMMcs with 10, 20, and 30 wt% (w/w) against PU resin, and then the solution was removed from bubble by defoam machine. At this point, the mixing ratio of PU resin:color toner:DMF:toluene:additives:PCMMcs was 100:30:10:30:10:0, 10, 20, and 30, respectively. Subsequently, the top coating was processed using the same method as that used for the base coating. Consequently, this well dried coating layer was remarkably thin (about 2-3 mm) when compared with that of the wet coated layer, due to its application using a knife, even though the process involved two steps.


The morphologies of the plane surface and cross-section of the PCMMcs-coated Nylon fabrics were observed using SEM. This measurement was carried out on a HITACHI, S-4200 (Japan) instrument operating at an acceleration voltage of 15 kV. Before conducting the SEM analysis, the samples were ion sputter-coated (VPS 020, ULVAC VACUUM, Japan) with a layer of white gold (400 [Angstrom]) for 120 s. All images were taken at a magnification of 500X.

Measurement of Water Vapor Permeability (WVP) and Water Penetration Resistance (WPR)

The WVP values of the untreated and PCMMcs-encapsulated nylon fabrics were measured according to the ASTM E 96 desiccant method using an LH20-11vp (Nagono). The WVP values of the coated and uncoated fabrics were calculated as follows: WVP (g/[m.sup.2] 24 h) = {([a.sub.1] - [a.sub.2])/S} X 24, where [a.sub.1] - [a.sub.2] is the weight change of the permeation cup with the sample (g) and S is the area of permeation ([m.sup.2]). In addition, the WPR was measured according to the KS K 0591 low range hydrostatic pressure method by means of an FX3000 (TEXTEST).

Thermal Evaluation by DSC and Thermal Vision Camera

The thermo-physical characteristics and phase transition temperatures were determined using a differential scanning calorimeter (DSC, Dupont 2010 TA Instrument) cooled with liquid nitrogen circulation. The sample (accurately 5 mg) was prepared by conditioning and sealing it in an aluminum pan. The pan was placed in a stage and heated from 0 to 50[degrees]C with a heating rate of 10[degrees]C/min using a nitrogen gas flow rate of 50 ml/min. Furthermore, the temperature distribution determined from the thermal insulation change of the sample was displayed by a thermal vision camera (NEC, TH41-464) having a thermal sensitivity of 0.06-0.03[degrees]C at 30[degrees]C, a wavelength of 8-14 [micro]m, a measurement range of -40-2000[degrees]C, and a frame rate of 1/60 s. The imager has a resolution of 320 X 256 pixels. The observers viewed the screen from a distance of approximately 40 cm at 23[degrees]C, 50% RH.

Peel Strength

The peel strengths of the PCMMcs-coated nylon fabrics were measured using a universal testing machine, model Z-005 (Zwick, Germany), to assess the adhesion ability between the coated layer and nylon fabrics at 25[degrees]C and 60% RH.


Characteristics of PCMMcs

Microcapsules used for textile coating should be stable against physicochemical conditions such as the pressure of the coating, heating, the solution environment, etc. The powdery PCMMcs used for this study was chosen on the basis of its providing good compatibility with the PU resin and having easy handling properties during the coating process. The DSC thermogram of the tested PCMMcs (data not shown), which allows its use as a heat storage material to be evaluated, shows that the maximum [T.sub.m] and [T.sub.c] values were 28.22[degrees]C and 16.3[degrees]C, respectively. Moreover, the heat capacity of thermal storage and release was 92.55 J/g at melting and 117.6 J/g at crystallization.

Morphology Observed by SEM

The microencapsulated PCMs were successfully coated on the porous waterproof and breathable nylon fabrics by the wet and dry laminating methods. Figure 1 shows the SEM photographs of the cross section of the wet-coated fabrics with and without PCMMcs. It can be seen that the nylon fabrics without PCMMcs formed large numbers of micropores. As the amount of PCMMcs was increased, the pores of the PU resin became closely compacted with the PCMMcs particles. As shown in Fig. 1d, in the coated fabrics with a PCMMcs content of 30%, the PCMMcs formed well shaped globular type particles inside the coating layer as well as on their surface, whereas micropores could not be observed in the dry-coated fabrics without PCMMcs due to the use of hydrophilic, nonporous type PU resin. Although the hydrophilic, nonporous PU resin can be useful, increasing the water entry pressure when compared with the dry coating process where of the coating layer is remarkably thin. However, after the PCMMcs was coated on the nylon fabrics, as shown in Fig. 2, the pore size of the coating layer gradually increased. It would seem that the growing pores in the PU might result from the breaking of the PCMMcs particles during the coating process, or the phase separation of PCMMcs.



WVP and Water Penetration Resistance

It is well known that waterproof and breathable textiles commonly have a pore size of 1-10 [micro]m. The diameters of the PCMMcs received in this study were about 5-30 [micro]m. Figure 3 shows the WVP and WPR values of the wet- and dry-coated nylon fabrics as a function of the PCMMcs content. As shown in Fig. 3a, the WVP value gradually decreased with increasing PCMMcs content in the wet coating process. It is supposed that the decrease of the WVP in the wet-coated fabrics was due to the clogging of the microporous PU by the coating of microcapsules into the PU pores. Similarly, the WVP of the fabrics coated under dry conditions changed from 8500 at 10% of PCMMcs to 8300 at 30% of PCMMcs, except for incredibly increasing up to 10% of PCMMcs which is considered to be the strong interaction between the coating solution and fiber structure during the coating process. Typically, the WVP in a functional textile is a very important value for the evaluation of the comfort properties. Even though the values of the WVP shift to a lower value with increasing PCMMcs content, except for the initial PCMMcs content of 10%, this does not pose a problem, because the values are not less than 4000 g/[m.sup.2]/day, which is the commercially desired WVP value for waterproof and breathable textiles. These results showed that the WVP values of the PCMMcs coating on the waterproof and breathable nylon were still sufficiently high after the application of the coating with either the wet or dry method. Moreover, from the data in Fig. 3b, it can be seen that, in the case of the wet coating, the WPR value declined rapidly from 3700 for the control to 800 mm [H.sub.2]O for a PCMMcs content of 30% and, in the case of the dry coating, slightly decreased from 2200 for the control to 1400 mm [H.sub.2]O for a PCMMcs content of 30%. In the case of the wet coating, the decrease in the WPR value is correlated with the improvement of the durable property which sustains the PCMMcs in the coating membranes between the microencapsulated layer and PET fabrics. These similarly decreased WVP and WPR values can be attributed to the structural differences of the fabrics, which are based on the SEM observation. Though the PU resin in the dry coating is nonporous, it allows the perspiration to penetrate from inside of the waterproof and breathable fabrics to the outside. Therefore, the water vapor can penetrate through the PU resin, thus contributing to the body comfort.


Thermophysical Characteristics Analyzed by DSC

In our previous report (12), the melting thermograms of PCMMcs show that the melting point and the highest melting point of PCMMcs was revealed at 24.6[degrees]C and 28.2[degrees]C, respectively. Also, during the crystallization, the PCMMcs was observed with broader and weak peak from 23.0[degrees]C and showed the highest peak at centered 16.3[degrees]C. The thermal insulation capability of the PCMMcs-coated fabrics depends on the surrounding temperature and time. The thermal insulation capability is only observed during the temperature range of the phase change and ends when the phase change is complete. The thermal properties, such as the phase change enthalpy and phase change transition temperature, as a function of the weight ratio of PCMMcs to that of the coating fabrics were determined from the heating and cooling curves which were obtained using DSC analysis. Figures 4 and 5 show the DSC curves of the nylon fabrics according to the PCMMcs content in the case of the wet and dry coatings, respectively. As seen in the DSC thermograms, the patterns in Figs. 4 and 5 demonstrate that the samples show quite different phase transition temperatures from each other. The curves have sharp peaks corresponding to the solid-liquid phase change of melting or the liquid-solid phase change of crystallization, whereas only small endothermic monotonous peaks correspond to the solid-solid phase transition. In comparison with the phase change temperature of Fig. 4, it was found that the melting transition points in the coated fabrics 10, 20, and 30% of PCMMcs made by wet coating were changed by 0.02, 0.58, and 0.1[degrees]C, as the freezing transition points changed by 4.4, 4.0, and 4.0[degrees]C, respectively. Similarly, increases in the thermal release capacities of 5.37, 7.922, 11.27, and 18.99 J/g and those in the storage capacity of 5.364, 9.861, 14.05, and 22.22 J/g, corresponding to the wet treatment of the fabrics 0, 10, 20, 30% of PCMMcs, respectively, are found in the DSC curves. On the other hand, in Fig. 4, the thermal release capacities of the dry-coated fabrics were increased by merely 0.34 and 1.08 and the thermal storage capacity by 0.8 and 1.393 for the fabrics 20 and 30% of PCMMcs, respectively. As mentioned above in the discussion of the SEM analysis, it can be seen that the change in the DSC curve is greater for the wet-coated fabrics than for the dry-coated fabrics. In our cases, this may be related to the fact that the prepared PU for the wet and dry coating on the fabrics was a wet porous type and a hydrophilic nonporous type, respectively. On the basis of the results obtained during this study, we can conclude that it is important to perform the coating process under the same conditions as in the case where the processing is performed on a large scale.



Temperature Distribution by Thermal Vision Camera

A thermal vision camera can be used to analyze the surface temperature distribution of a particular object and evaluate the warmth property of clothing through a digital thermal display. The change in the surface temperature of the PCMMcs-coated fabrics according to time was measured using an infrared thermal vision camera and the thermal images of the nylon surfaces of the fabrics with and without PCMMcs are shown in Fig. 6. The rates of temperature decrease for both the wet and dry-coated fabrics with a PCMMcs content of 30% were higher than that of the fabric without PCMMcs during the phase change process. It is therefore clearly guessed that the wet-coated fabrics were far superior to the uncoated fabrics with regard to their thermal insulating properties. Accordingly, it is easy to understand that the proper control of the PCMMcs content and coating method of the nylon fabrics is necessary for the preparation of functional materials with a high thermal storage capacity.


The Peeling Strength between PCMMcs/PU Layer and Nylon Fabrics

The peel test is a very common method of investigating the bonding strength between a coating layer and textile material. The bonding strength corresponds to the force that is necessary to pull off the coating. These test methods cover procedures used for characterizing the delamination, strength of the bonding, appearance, and shrinkage propensity of bonded, fused, and coated fabrics after dry cleaning and laundering. The results of the peel tests of the nylon fabrics PCMMcs are shown in Table 2. The coatings with and without PCMMcs treatment were both investigated. The coating without PCMMcs treatment had sufficient bonding strength. The bonding strengths of the wet coatings on the nylon fabrics with PCMMcs treatment were about 300 g/[cm.sup.2]. This low bonding strength is caused by the coating method and the different pressures of rolling and different thicknesses of the coatings. It was found that the decrease of the peeling strength according to the PCMMcs content is not caused by the presence of DMF as a diluting agent, but by the coating method. Accordingly, the value measured for the dry coating was higher than that for the wet coating. There was a considerable decrease in the peeling strength; however, the values of the peeling strength were nevertheless over 300 g/[cm.sup.2], which is sufficient for clothing textiles.
TABLE 2. Peeling strength of PCMMcs-coated nylon fabrics under wet and
dry coating conditions.

Substances Wet (g/[cm.sup.2]) Dry (g/[cm.sup.2])

Control 525.30 709.92
PCMMcs 10% 363.12 665.04
PCMMcs 20% 347.82 556.92
PCMMcs 30% 308.04 593.64


Four different types of microcapsules were evaluated for use as PCMMcs in commercial nylon coatings for thermal functionality. The advantages of the microencapsulated PCMs lie in its compatibility with the PU, thus allowing for permanent PCMMcs effects. The microcapsules and microencapsulated nylon fabrics were examined by thermal analysis in nitrogen gas. The DSC curves for the selected microcapsules in this study show evidence of interactions between the PCMMcs and PU resin, and the microcapsules exhibit significant compatibility with the PU that can be attributed to the development of a thermal effect. Also, in the SEM images of the wet-coated fabrics, PCMs microcapsule particles were certainly observed, whereas it was impossible to confirm their presence in the case of the dry coating process. The thermal properties of nylon fabrics with PCMMcs-treated and untreated were also studied by DSC thermogram and thermal temperature distribution analyses. The coatings with 30% PCMMcs sample showed decreases in their WPR and WVP propensity. Both tendency of decrease value of WPR and WVP was very similar in all cases, except for the WVP of the dry coating with 10% of PCMMcs. However, in the comparison of the coatings with different PCMMcs contents, the DSC curves present a smaller total heat capacity at dry coating and, thus, as expected above, a smaller enhancement in their thermal insulating effect. The microencapsulated PCMs does not develop a strong enough thermal storage effect to resist cold conditions and wearing stresses. Future work will be needed to evaluate whether the thermal properties of the PCMMcs-encapsulated textiles are permanent. Also, the microcapsules application of the fabrics should be studied to evaluate their potential use as functional comfort materials in different fabrics.


The authors are grateful for the materials provided by Mi Kwang Dyetech Co., LTD.


(1.) N. Sarier and E. Onder, Thermochim. Acta, 452, 149 (2007).

(2.) B. Ying, Y.L. Kwok, Y. Li, C.Y. Yeung, and C. Yeung, Polym. Test., 23, 541 (2004).

(3.) G. Burdett, Ann. Occup. Hyg., 42, 21 (1998).

(4.) G.L. Zou. X.Z. Lan, Z.C. Tan, L.X. Sun, and T. Zhang, Acta Phys. Chim. Sin., 20, 90 (2004).

(5.) M.N.A. Hawlader, M.S. Uddin, and M.M. Khin, Appl. Energy, 74, 195 (2003).

(6.) K. Junghye and C. Gilsoo, Text. Res. J., 72(12), 1093 (2002).

(7.) J.C.H. Chen, and J.L. Eichelberger, U.S. Patent 4,505,953 (1985).

(8.) M.H. Hartmann, U.S. Patent 6,689,466 (2004).

(9.) G. Nelson, Int. J. Pharm., 242, 55 (2002).

(10.) H. Shim, E.A. McCullough, and B.W. Jones, Text. Res. J., 71(6), 495 (2001).

(11.) L. Royon, G. Guiffant, and P. Flaud, Energy Conversion Manage, 38, 517 (1997).

(12.) K. Koo, J.D. Choe, J.S. Choi, E.A. Kim, and Y.M. Park, J. Korean Soc. Dyers Finishers, 19, 24 (2007).

K. Koo, (1) Y.M. Park, (2) J.D. Choe, (1) E.A. Kim (2)

(1) School of Textiles, Yeungnam University, 214-1 Dae-dong, Gyeongsan, Gyeongbuk, 712-749 Korea

(2) Clothing and Textiles, Yonsei University, 314 Sinchon-dong, Seodaemungu, Seoul, 120-749 Korea

Correspondence to: Youngmi Park; e-mail:

Contract grant sponsor: The regional industrial technology development program (the Ministry of Commerce, Industry and Energy); contract grant number: 10024464; contract grant sponsor: The Brain Korea 21 program (Korea Research Foundation of South Korea); contract grant number: 2006-8-0724. DOI 10.1002/pen.21350

Published online in Wiley InterScience ( [C]2009 Society of Plastics Engineers
COPYRIGHT 2009 Society of Plastics Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2009 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:phase change materials
Author:Koo, K.; Park, Y.M.; Choe, J.D.; Kim, E.A.
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:9SOUT
Date:Jun 1, 2009
Previous Article:The influence of the stress relaxation and creep recovery times on the Viscoelastic properties of open cell foams.
Next Article:Start-up of slot die coating.

Terms of use | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters