Polymer-Encapsulated Colorful Al Pigments with High NIR and UV

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Polymer-encapsulated colorful Al pigment with high NIR and UV reflectance and their application in textiles BENJAMIN TAWIAH, Christopher Narh, Min Li, Liping Zhang, and shaohai fu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b03555 • Publication Date (Web): 11 Nov 2015 Downloaded from http://pubs.acs.org on November 17, 2015

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Industrial & Engineering Chemistry Research

Polymer-encapsulated colorful Al pigment with high NIR and UV reflectance and their application in textiles Benjamin Tawiah ‡, †, Christopher Narh ‡, †, Min Li ‡, Liping Zhang ‡, Shaohai Fu⃰⃰ ‡

‡

Key Laboratory of Eco-Textile, Jiangnan University, Ministry of Education, Wuxi, Jiangsu 214122, China †

Kwame Nkrumah University of Science and Technology, Private Mail Bag - Kumasi, Ghana

Abstract: A polymer-encapsulated colorful Al pigment (PCAP) for fabric coatings was successfully prepared by combined sol-gel spray drying assisted in-situ polymerization method, and the near-infrared (NIR) reflectance and ultra-violet protection factor (UPF) of the coated fabrics were investigated. TGDSC, SEM and anti-solvent test results proved that the reactive dyes was chemically attached to KH-550 modified Al pigment via covalent bond. The PCAP was stable in strong alkaline (pH 12) or acidic (pH 1) conditions. The NIR reflectance and ultra-violet protection factor (UPF) of PCAP coated cotton fabrics were 80.05% and 290.76 respectively when the mass ratio of monomer to colorful Al pigment was 1:10 with the coating thickness of 50 µm. PCAP coated fabrics showed excellent color strength, good washing and rubbing fastness with relatively good handle.

Keywords: Polymer-encapsulated colorful Al pigment; sol-gel/in-situ polymerization method; coating; NIR; UPF.

Shaohai Fu: TEL: +86051085912007, Email: [email protected]

ACS Paragon Plus Environment


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1 Introduction The solar radiation consists of 5 % ultra-violet radiation, 46 % visible radiation and 49 % nearinfrared radiation (750–2500 nm) 1, 2. Obviously, the near-infrared rays (NIR) in the solar spectrum is mainly responsible for heat build-up in the environment, especially in the regions of the world that experience extremely high temperatures 3, 4. Also, the ultraviolet rays (UVA 400-320 nm, UVB 320290 nm) cause erythema and skin burns, which inhibits skin tanning ordinarily responsible for skin cancer and aging 2, 5. Taking into account the deleterious effect of the solar radiation to human health and well-being, it has become very crucial to develop multi-functional materials that can inhibit or minimize the effect of NIR and ultraviolet (UV) rays in order to maintain the body’s health. Some kinds of colorants, such as perylene-based pigments 6, lanthanum-strontium copper silicate intense blue 7, YIn0.9Mn0.1O3-ZnO 8, copper phthalocyanine and metallic pigments

3, 9, 10

have been

identified to possess excellent NIR and UV reflectance properties, which can effectively minimize the transfer of heat in buildings and clothing to achieve significant cooling effect, and thus conserve energy required for cooling and ensuring comfort

3, 9, 11, 12

. Among these pigments, Al pigment is widely used

due to its excellent styling effects, reflective properties, metallic luster and electrical conductivity and above all cheaper 4, 9, 13, 14. However, Al pigments easily corrode in alkaline or acidic solution, making it unfavorable for formulating waterborne formulations 15, 16 especially for textile applications where water is mainly used during the processing and the subsequent final usage of the product. The unfortunate reaction between water and Al pigment leads to the formation of aluminum oxide and other metal complexes

15, 17

, which destroys the color performance, NIR and UV reflective properties of the

pigment. Additionally, hydrogen gas is generated when aluminum pigments are formulated into waterborne paste for storage making it unattractive for textile printing hence the need to prepare colorful


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Al pigment that is highly stable in waterborne formulations for textile printing without compromising its NIR and UV reflectance properties. Several techniques for preparation of colored Al pigment such as deposition of colorful pigment onto Al pigment with the aid of polymer coatings, adhesion of colorful pigment onto Al pigment through flax capping, sol-gel process, metal organic chemical vapor deposition, physical vapor deposition, laser cladding, and thermal spraying have been proposed. These proposed methods have achieved significant progress in the coloration of aluminum pigments but drawbacks such as lack of vivid color tones 18 and corrosion after long exposure

19

have remained. In order to improve the amount of colorful pigment

deposition and ensure good corrosion resistance, methods involving the use of interference layer where iron oxide is deposited on Al pigment first, then coated with TiO2, SiO2, and PMMA was designed. In this method, large volume of colorful pigment was deposited but other problems, such as exfoliation, defect in chroma due to corrosion, color fading and complicated preparation processes have still remained. Presently, many encapsulation techniques such as phase seperation, miniemulsion polymerization, insitu polymerization method and sol-gel 15, 20, 21 have been used to enhance the preparation and corrosion protection of colored aluminum pigments. Among these methods, sol-gel technology, which involves the growth of inorganic networks through the formation of sols and gel and has been researched extensively for its flexibility in different solution chemistries, especially in the inhibition of the corrosion for various metallic pigments

21, 22

. In-situ polymerization has the advantage of forming

interfacial coatings on the surface of materials in the continuous phase, which makes it very suitable for forming interference layer for Al pigment. Besides, spray drying offers the flexibility of manipulating particle sizes of encapsulated materials by controlling the atomization of the liquid feed and the hot gas inlet, making it very appropriate for production of colorful Al pigment. In summary, although many



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researches for the preparation of colored Al pigment has been done over the years, the fixation of reactive dyes onto Al pigment surface using combined sol-gel/spray drying assisted in-situ polymerization technique for waterborne formulations and its application in textiles has rarely been reported. In this paper, the polymer-encapsulated colorful NIR Al pigment was prepared via combined solgel/spray drying assisted in-situ polymerization technique and applied on fabrics. The color performance, NIR reflectance and ultra-violet protection factor (UPF) of the coated fabrics were investigated.

2. Experimental Section 2.1 Materials Al pigment (particle size 50 µm, 9-10 µm, and 1-2 µm) was supplied by Tianjiu Metal Materials Co., Ltd. Changsha, China. 3-aminopropyltriethoxysilane (KH-550, Chart 1) was provided by Jiangsu Chenguang Co., Ltd., Changzhou, China. Glycidyl methacrylate (GMA, AR grade) and 1, 6-hexanediol diacrylate (AR grade), and Surfynol 440 were purchased from Aladdin Industrial Corporation, Shanghai, China. Binder (DM-5218), thickener (DM-5268) and crosslinker (FWO-B) were purchased from Demei Chemical Company Ltd., Guangzhou, China. Methyl methacrylate (MMA), 2, 2 azobis-iso-butyronitrile (AIBN), n-hexane, tetraethyl orthosilicate (TEOS), acetone, ethanol, aqueous ammonia (NH3.H2O), hydrochloric acid, sodium hydroxide, glycerol, tetrachloroethylene (TCE), dimethyl sulfoxide (DMSO) and urea were all of analytic grade, and purchased from Sinopharm Chemical Reagent Co. Ltd., Shanghai, China. C.I. Reactive blue 4 (X-BR) was purchased from Jiangsu World Chemical Co. Ltd., China. Distilled water was used for the entire experiments.


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Chart 1. Chemical structure of 3-aminopropyltriethoxysilane (KH-550)

2.2. Preparation of colorful aluminum pigment (CAP)

12 g Al pigment was dispersed in 100 ml ethanol by Ultrasonic JY98-3D homogenizer (NingBo Scientz Biotechnology Co., Ltd, China) for 20 min to get Al pigment dispersion. 2 ml hydrochloric acid, 20 ml water/diethyl ether (volume ratio 3:1) and 70 ml TEOS/ethanol (volume ratio 6:1) was mixed and stirred 1h at 40 ºC to get the sol solution. 14ml NH3.H2O was dropwisely added into the Al pigment dispersion under stirring. The temperature was maintained at 40 º C with continuous stirring for 3 h to prepare SiO2 encapsulated Al pigment (Al/SiO2). 25ml KH-550 and 10ml ethanol was added to the Al/SiO2 dispersion and kept 40 ºC with continuous stirring for 2 h to prepare the KH-550 modified Al/SiO2 (Al/SiO2/ KH-550, abbreviated as MAP). 2 g X-BR was added to the MAP dispersion, pH was adjusted to 8.5 and the reaction was kept at 40 ºC with continuous stirring for 2 h. The dispersion was centrifuged to get the cake and then washed in dimethylformamide (DMF), rinsed in water/ethanol solution and dried at 60 ºC in a vacuum oven to obtain colored Al pigment (Al/SiO2/KH-550/dye, abbreviated as CAP). 2.2.2 Encapsulation of CAP via in-situ polymerization 10 g CAP dispersed in 50g n-hexane with the help of ultrasonic bath for 30 min. A certain amount of methyl methacrylate, 1, 6-hexanediol diacrylate styrene, and glycidyl methacrylate were added into the CAP dispersion. The mixture was heated to 80°C and then added corresponding amount of AIBN while stirring in an atmosphere of nitrogen gas for 18 h. The mixture was cooled to room temperature and then fed into a spray dryer (Lab Ultima Spray Drier Model: LU 222). The atomizing air and temperature feed rate were kept constant at 1.15 kg/cm3 and 30 °C respectively. The airflow was set at 60 m3/h for the entire experiment. The liquid feeding pump flow-rate was set at 2 ml/min, while inlet and outlet



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temperature were set at 160 °C and 85 °C respectively. The atomization process was performed using a single standard nozzle (0.7 mm). Glass cyclone used in this process as drying chambers have a size of ID, OD and length 12 cm 14 cm 41 cm respectively. The precipitate was washed twice with alcohol and dried in a vacuum oven to obtain polymer encapsulated-colored aluminum pigment (Al/SiO2/KH550/dye/polymer, abbreviated as PCAP). 2.2.3 Preparation of PCAP dispersion 15 g PCAP and 2 g surfynol 440 was added in 40 ml distilled water, and then homogenized with a magnetic stirrer for 20minutes.

2.3 Fabric coating The coating paste formulation (based on weight): PCAP dispersion 10%, glycerol 5%, DM-5268 1%, urea 5%, FWO-B 4%, DM-5218 20% and distilled water 55%. These components were mixed until a homogenous paste was obtained. Cotton, polyester, and silk fabrics obtained from Shandong Weiqiao Pioneering Group Co., Ltd, China were coated using rapid auto coat machine (Xiamen Rapid Company Ltd., china). The coated fabrics were dried in an oven at 60 °C for 1h and then baked at 150 °C for 3 min.

2.4 Characterization 2.4.1 Thermal properties Differential scanning calorimetry was performed under atmospheric condition using DSC (Q200, TA Instruments, United States) with a ramp between 25-300°C. Thermo-gravimetric (TGA) analyses was performed under atmospheric conditions using TG apparatus (TGA/SDTA851e, Mettler Toledo instrument co., LTD, Switzerland) with 10 ºC/min ramp between 25-700°C. 2.4.2 Anti-corrosion performance Chemical stability of the aluminum pigment was measured using the method described by Zhang et al., 2011 23. 1 g of Al samples were immersed in 100 mL water with pH value 1 and 12 respectively at


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25 ± 2°C for 336 h. The amount of evolved gas was measured during the exposure time. The less the volume of gas evolved, and the better the anti-corrosion performance. 2.4.3 SEM Surface morphology of samples were observed using Scanning Electron Microscope (Hitachi Model S-3200H), designed for surface observation at high resolution equipped with an STS X-Stream Imaging System. Mean particle size of samples was determined by a Zetasizer 3000 HSA analyzer (MALVERN). 2.4.4 NIR reflectance NIR reflective properties of samples were measured using Lambda 950 UV-vis NIR spectrophotometer (with integrating sphere). Polytetrafluoroethylene (PTFE) was used as the comparison standard. The scanning range of 540– 2500 nm and the sampling interval of 2 nm was used. The spectral reflectance data were used to calculate the solar reflectance of each sample. The NIR solar reflectance (R*) in the wavelength range from380 nm to 2500 nm was calculated according to ASTM standard number G159-98 (ASTM G159-98, 1998). The R* was calculated according to equation (1). ∗

=

(1)

where r (λ) is the experimentally obtained spectral reflectance (W m-2) and i (λ) is the solar special irradiance (W m-2 nm-1) obtained according to ASTM standard G159-98. 2.4.5 UPF Ultraviolet protection factor (UPF) was measured using Cary 50 UV/Vis spectrophotometer (Varian made in Australia). UV protection properties of the samples were evaluated according to the Australian/New Zealand Standard AS/NZS 4399:1996. The UPF was calculated by using equation (2). =

(2)

where Sλ is erythema action spectrum, Eλ is solar irradiance, dλ is wavelength interval in nm, and Tλ is spectral transmittance of the specimen.



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2.4.6 Color performance The colorimetric values of the samples in the CIE lab color space were measured on a Color-Eye automatic differential colorimeter (Xrite- 8400, X-Rite Color Management Co., Ltd. USA) under illuminant D65 with the CIE 1964 Standard Observers and the color strength (K/S) of the coated fabrics were determined using Kubelka–Munk equation (3). / =

(3)

Where R defines the relationship between the spectral reflectance of the sample and its absorbance coefficient (K) and scattering coefficient (S). The CIE 1976 L*a*b* colorimetric method was used to evaluate the color indices where L* is the color lightness (L* = 0 for black and L* = 100 for white), a* is the green (-)/red (+) axis, and b* is the blue (-)/yellow (+) axis. The parameter C* (chroma) represents saturation of the color and is defined as C* = ∗ + " ∗ . The hue angle, ho is expressed in degrees and ranges from 0 to 360 and is calculated by using the formula ho = tan-1(b*/a*). For each sample, three measurements were made and the average value was taken. The rubbing and washing fastness of the coated fabrics were evaluated according to the standard method GB/T 3921-2008 and GB 3920-1983, respectively. Coating thickness was measured with Paramount thickness tester precision gauge according to the standard method ASTM D1777 - 96(2011). The softness of coated fabric was evaluated according to the Kawabata Evaluation System for Fabrics (KES-FB,) on a handle instrument (KESFB-2, Kato Giken Co., Ltd. Japan). The contact angle of CAP before and after in-situ polymerization process was measured using Krüss DSA 100.


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3. Results and discussion 3.1 Preparation of PCAP

Scheme 1. The mechanism for the preparation of colorful Al pigment The preparation of colorful Al pigment (CAP) proceeded in three steps as shown in Scheme 1. Firstly, the Al pigment was encapsulated by SiO2 through sol-gel process, and then modified with KH-550 to introduce some amount of -NH2 groups onto the surface of SiO2 encapsulated Al pigment. The -NH2 groups on the surface of modified Al/SiO2 then reacted with the purified reactive dyes via nucleophilic substitution to obtain the colorful Al pigment. The prepared samples were soaked in different solvent for



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5h to ascertain the quality of bond formed between the dyes and the K-550 modified Al/SiO2 and the results are shown in table 1 Table 1. Color retention of Al/SiO2/dye and KH-550 modified Al/SiO2 colored pigment (CAP) after washing in different solvents

Samples

Color retention (%) Water

TCE

Acetone

DMF

DMSO

Al/SiO2/dye

2.01

1.03

0.00

0.00

0.00

CAP

99.14

98.05

98.75

96.67

96.46

Table 1 shows that more than 96% color was retained for CAP after washing in different solvents unlike Al/SiO2/dye, which just about 2% retained. The small amount of reactive dyes washed by water, TCE, acetone, DMF, DMSO could be as a result of hydrolyzed dyes still existing on the surface of CAP. The results suggests that covalent bond was possibly formed between the -NH2 groups and reactive dyes. To enhance the chemical stability of CAP, it was further encapsulated by a dense film of colorless polymer via spray drying assisted in-situ polymerization technique, which formed a thin film of protective layer on the surface of CAP as can be seen from the SEM micrograph. During the in-situ polymerization modification process, the monomer droplets undergo a polycondensation reaction where molecules join together; losing small molecules such as water and methanol as the polymerization initiator (AIBN) is introduced. During this process, the monomers tend to form dimers and trimers first and then grow into a complex chain of polymer over the entire surface of CAP with constant supply of heat over time. After this process, PCAP was characterized to attest the presence of polymer on CAP as hypothesized. As a result, color coordinates of CAP and PCAP were measured and the results are shown in table 2. It is obvious that K/S value of CAP was higher than PCAP, and the more amount of monomer used, the lower the K/S value. This suggests that the polymer on the surface of CAP can reduce the color strength of the pigment. Moreover, the L* (lightness) of PCAP decreased from 20.78 to 16.28 when the


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percentage of monomer for PCAP increased from 5% to 10%, indicating that higher monomer content could ensure better covering layer but at the same time have a detrimental effect on the K/S value. Table 2. Color coordinate of PCAP Sample CAP PCAP 1 PCAP 2 PCAP 3 PCAP 4

Monomer content (%) -5 10 15 20

K/S value 5.73 5.45 5.44 3.95 3.48

L* 20.78 17.36 16.28 15.23 13.85

Color coordinates a* b* C* -0.65 -32.89 42.67 -0.61 -33.12 41.45 -0.59 -34.23 39.02 -0.42 -34.44 38.96 -0.39 -35.02 37.62

ho 267 252 246 241 235

Figure 1 shows the contact angle to deionized water of CAP and PCAP. It can be seen that the contact angle of PCAP to deionized water was 64.3⁰, larger than CAP. The smaller contact angle of CAP (figure 1b) to deionized water could be attributed to the presence of –SO3- groups in X-BR on the surface of modified Al/SiO2. The larger contact angle of PCAP to deionized water could be attributed to the polymer layer covering the –SO3- groups on CAP, thereby reducing the contact angle to deionized water. These results shows that CAP was encapsulated by a layer.

Figure 1. Contact angle of (a) PCAP, (b) CAP to deionized water.



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3.2. Surface morphology and particle size distribution Figure 2 shows the surface morphology of Al pigment, CAP and PCAP. Comparing with Al pigment, a large amount of nanoscale particulate can be seen on the surface of CAP, suggesting that some SiO2 was coated on Al pigment. In addition, Figure 2e and f showed that PCAP surface was relatively smoother than CAP, which is probably due to the polymer layer coated on CAP via in-situ polymerization and subsequent spray drying, which ensured the excellent anti-corrosion performance for the CAP. The mean particle size of CAP and PCAP were also measured and the result is shown in figure 3. It can be seen that the particle size distributions of the two samples were quite different with an average particle size of 1690nm and 1728nm respectively. The mean particle size of the latter was bigger (38nm) than the former, which may be due to the encapsulated polymer layer.

Figure 2. SEM micrograph of (a, b) Al pigment (c, d) CAP and (e, f) PCAP


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Figure 3. Particle size distribution of CAP and PCAP dispersion

3. 3. Thermal properties Polymeric materials undergoes physical changes when subjected differential calorimetric examination 24

as can be seen figure 4a. The DSC curve of Al pigment, KH-550 modified SiO2 encapsulated Al

pigment (MAP), CAP, and PCAP all underwent some level of phase transition with Al pigment showing minor glass transition at 95-100⁰C due to the less impurities on its surface. MAP and CAP recorded well-defined endothermic peaks at approximately 113⁰C due to the glass transition of the silicon polymer on the surface of Al pigment. There was however no significant change in enthalpy of PCAP except the minor endothermic peaks around 160⁰C and glass transition between 169-173⁰C caused by the encapsulated polymer layer, as the temperature increases further, PCAP continued to experience endodermal loss whiles MAP and PCAP experienced a gradual phase transition till 300⁰C. 3 (a) Al pigment (b) MAP (c) CAP (d) PCAP

2 1

100

95

0

90

-1

Weight (%)

DSC(mw/mg) Exotherm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-2 -3 -4 -5

85

80

(e) Al pigment (f) MAP (g) CAP (h) PCAP

75

-6

70

-7

Tg

-8 40

60

80

65 100

120

140

160 0

180

200

220

240

260

100

200

Temperature ( C)

300

400

500 0

Temperature ( C)


600

700


Figure 4. DSC curves of (a) aluminum pigment (b) modified aluminum pigment (MAP) (c) CAP and (d) PCAP, TG curve of (e) Al pigment (f) MAP, (g) CAP (h) PCAP A similar phenomenon was observed in TG curves (figure 4e-h) with a gentle weight loss of 0.90 % between 250°C and 650°C for Al pigment due to the decomposition of impurities on its surface. MAP however experienced a constant dehydroxylation from approximately 150°C to 700°C. Nonetheless, CAP gained weight slightly between 100°C to 275°C followed by a sharp decomposition till 620°C due to the presence of organic-inorganic products (SiO2 and reactive dyes) on the surface of Al pigment. PCAP however recorded much faster and higher rate of decomposition due to the poor thermal stability of the encapsulated polymer at high temperature.

3. 4. Anti-corrosion performance 4.0

(a)

(b)

MAP CAP PCAP

3.5

6.0 5.5

M AP CAP PCAP

5.0

3.0

H2 gas volume (mL)

4.5

2.5 2.0 1.5 1.0

4.0 3.5 3.0 2.5 2.0 1.5 1.0

0.5

0.5

0.0

0.0

0

24

48

72

96 120 144 168 192 216 240 264 288 312 336 360

0

24

48

72

96

120 144 168 192 216 240 264 288 312 336 360

Tim e (hrs)

Time (hrs)

5.0

(c) 4.5

MA P CAP PCAP

4.0

H2 gas volume (mL)

H2 gas volume (mL)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 0

10

20

30

40

50

60

Tim e (h)


70

80

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o

Figure 5. Anti-corrosion to acid and alkali of MAP, CAP and PCAP powder, (a) 25 ± 2 C, pH 12 (b) 25 o

o

± 2 C, pH 1, Paste (c) 50 C ± 1, pH 10 Figure 5 shows the anti-corrosion properties of MAP, CAP and PCAP to acid and alkali at different temperature over time. It can be seen that H2 began to evolve after 72h and 120h for MAP and CAP in the alkali conditions respectively while no H2 was produced for PCAP. Similar phenomenon was observed in the acidic medium except the early inception of H2 gas in the as shown in figure 5b. These results indicate that PCAP was stable under extreme acidic and basic conditions due to the polymer on the surface of PCAP. The gassing phenomenon observed in MAP and CAP was as a result of gradual percolation of acid and alkali solutions through the modified silica layer onto the metallic core after long exposure forming AlCl3 and NaAlO2 according to the following reaction 14. 2Al + 6HCl →2AlCl3 +3H2 ↑ 2Al +2NaOH+ 2H2O → 2NaAlO2 + 3H2↑ Accelerated aging test also shows that PCAP was stable with no H2 gas generated after storage at 50 ⁰C ± 1 for 72h (figure 5c). This illustrates that the polymer on CAP surface was effective against the penetration of solvent onto the metallic core even under harsh conditions.

3. 4 Properties of PCAP coated fabrics 3. 4.1 NIR reflectance 90

90

Flake-shaped Al Ball-shaped Al

(a)80

(b)80 70

Reflectance (%)

70

Reflectance (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60 50

Flake-shaped

40 30

60 50 40 30

50um 9-10um 1-2um

20

Ball-shaped

20

10

10

0 750

1000

1250

1500

1750

W avelength (nm )

2000

2250

2500

750

1000

1250

1500

1750

W avelength (nm)


2000

2250

2500


80

80

(c)

(d)

70

70

60

Reflectance (%)

Reflectance (%)

50 40 30

10% 15% 20%

20

60

50

40

30

50 um 40 um 30 um

20

10 750

1000

1250

1500

1750

2000

2250

750

2500

1000

1250

W avelength (nm)

1500

1750

2000

2250

2500

W avelength (nm)

80

(e) 70

Reflectance (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

50

40

C o tto n P o lye ste r S ilk

30

20 750

1000

1250

1500

1750

2000

2250

2500

W av e le n g th (n m )

Figure 6. Effect of (a) morphology of Al pigment, (cotton fabric, monomer ratio 10%, coating thickness 50 µm) (b) particle size of Al pigment, (cotton fabric, monomer ratio 10%, coating thickness 50 µm) (c) monomer content, (cotton fabric, coating thickness 50 µm) (d) coating thickness, (cotton fabric, monomer ratio 10%) and (e) fabric type, (monomer ratio 10%, coating thickness 50 µm), on NIR reflectance at wavelength 540-2500nm The solar heat energy generated in the NIR region (700-1100nm) create “heat waves” which results in abnormal rise in body temperature, making people feel uncomfortable. Therefore, the development of functional textiles material that can stay cool under the sun is necessary to improve people’s lives. In order to functionalize textile with maximum NIR reflectance performance, the relationship between morphology of Al pigment, monomer content, particle size of Al pigment, coating thickness, fabric type on NIR reflectance performance were investigated.


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Figure 6a shows that within the spectrum range 750–1300 nm, NIR reflectance of PCAP coated cotton fabrics prepared from flake and ball-shaped were 80.13% and 67.84% respectively, indicating that the flake-shaped Al pigment is more suitable for preparing of NIR reflectance materials. Obviously, the flake-shaped Al pigment has larger surface area compared to ball-shaped Al pigment at the same weight, which might have accounted for the high reflectance of the incident rays in the NIR region. Figure 6b shows the effect of particle size of flake-shaped Al pigment on NIR reflectance. It can be seen that the larger the particle size of the Al pigment, the higher the NIR reflectance of PCAP. This phenomenon can be attributed to higher rate of diffuse reflectance on smaller size PCAP due to small surface area. Also, it can be observed from figure 6c that the more the amount of monomer used in the in-situ polymerization process, the poorer the NIR reflectance performance of PCAP coated cotton fabric. This may be due to the increasing amount of polymer weight on the surface of PCAP, which unfortunately enhanced the absorption ability of incident rays in the NIR region instead of reflecting it. Similarly, Figure 6d showed that the NIR reflectance increased from 71.08% to 80.03% when the coating thickness increased from 30um to 50m probably due to increased weight of metallic content in PCAP on the surface of coated fabric and the high covering factor 25. Figure 6e illustrates NIR reflectance values, 79.99%, 71.67%, and 61.94% were recorded for cotton, polyester, and silk respectively. The marginally poor NIR reflectance of PCAP coated polyester and silk due to the poor affinity of PCAP to these fabrics. Based on the NIR reflectance values obtained from the VIS-vis-NIR examination, we concluded that the PCAP coated fabrics can be regarded as “cool” material

11

.

3.4.2 UV protection Frequent and prolonged exposure to UV radiation may damage the immune system and cause skin diseases, therefore, it is important to prepare a materials with excellent UV protection ability to prevent



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humans from harmful UV radiations. According to the Australia/New Zealand standards AS/NZS 4399:1996, fabrics can be regarded as possessing UV protection ability when UPF of the fabric exceed 50+, and the higher the UPF, the better the UV protection. Table 3. UPF of PCAP coated cotton fabrics Coating thickness (µm)

UPF

UPF protection class

0

8.66

No class

30

95.53

Excellent

40

125.52

Excellent

50

290.76

Excellent

*Note: Cotton fabric was used. Table 3 shows that as the coating thickness increased from 0 to 50µm, the UPF value increased from 8.66 to 290.76, which indicates that UPF of PCAP coated fabrics had excellent UV protection, meanwhile, UPF can be adjusted by controlling the coating thickness, but care must be taken not to compromise the handle of PCAP coated fabrics. 3 . 4 . 3 Color performance Table 4. Effect of PCAP coating thickness on color performance Coating thickness (µm )

K/S value

Rubbing fastness

Washing fastness

Dry

Changing

Wet

Staining

Handle

0

0.00

---

---

---

---

Softest

30

5.12

4

4

3

3-4

softer

40

6.87

4

4

4

3-4

soft

50

7.54

3

3

4

4-5

Poor

Table 4 shows the effect of coating thickness on color performance of PCAP coated fabrics. It can be seen that the K/S improved marginally, while rubbing and washing fastness changed little as the coating thickness increased. Obviously, increasing the coating thickness help the fabrics absorb more visible


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light, resulting in the high K/S values recorded. In addition, it should be noted that the washing and rubbing fastness of PCAP coated fabrics are mainly dependent upon the amount of binder in the coating paste. From table 5, it can be seen that the washing and rubbing fastness improved greatly when the content of binder increased, but unfortunately, the handle of the fabric was adversely affected, and therefore a compromise ought to be made depending on the end use of the fabric. Table 5. Effect of binder content on rubbing and washing fastness1

Binder content (%) 0 10 20 30 40

Rubbing fastness (grade) Dry Wet

3 4 4 4-5 1 Note: coating thickness 30µm

2-3 4 4-5 4-5

Washing fastness (grade) Staining Changing

Handle

3 3 5 5

softest softer softer soft stiff

2-3 3-4 5 5

4 Conclusion Polymer-encapsulated colorful Al pigment (PCAP) with high NIR and UV reflectance was prepared via sol-gel/in-situ polymerization technique. PCAP had excellent anti-corrosion stability in extremely alkaline (pH12) and acidic (pH10) conditions. Flaky PCAP coated fabrics demonstrated the higher NIR reflectance of 80.05% than ball-shaped PCAP. Similarly, bigger size flake shaped PCAP had higher NIR reflectance whereas high monomer ratio to CAP content tend to affect the NIR reflectivity of coated cotton fabrics and also affect the color performance of PCAP. PCAP coated cotton fabrics showed excellent UPF irrespective of the coating thickness even though fabric handle could be compromised with high coating thickness. The coated fabric had good rubbing and washing fastness.



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Supporting Information Further information on optimization of baking temperature and its effect on K/S value of PCAP coated fabric is available free of charge via http://pubs.acs.org

AUTHOR INFORMATION Corresponding Author Shaohai Fu. TEL: +86051085912007, Email: [email protected]

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Competing Financial Interest. The authors declare no competing financial interest for this research work. Acknowledgement The authors are grateful to the National Natural Science Foundation of China (Grant No. 21346009), the Universities and Enterprises Prospective Joint Research Project of Jiangsu Province (BY2012050), Natural Science Foundation of Jiangsu Province (BK2012212) and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. We also thank Jiangnan University for supporting this research.


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Reference

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Homogenized Al pig. in ethanol

TEOS + HCl + H2O

+ + +++ + ++++ + + + ++++ + + + + ++ + ++ KH-550 +Ethnol + ++ + + ++++ + + + + + ++ + + ++++ + + + + ++ + surface modiﬁcation + ++ + + ++ ++ +++ ++ + + ++ + + + + ++ + + + + + ++++ + ++ + + ++ + + ++ +

NH3.H2O + H2O

Hydrolyisis/condensation

Gelation

+ ++++ CAP GMA, ST, MMA, HDA

Disperse CAP in N-hexane

Centrifuge, wash and dry

Reactive dye + H2O

AIBN

Spray drying

Polymerization

Drying chamber

Atomization gas

PCAP

PCAP in soln. Drying gas

Washing, drying

Cyclone

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Powdered PCAP


Polymer-Encapsulated Colorful Al Pigments with High NIR and UV

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