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Development of structured natural dyes for use into plastics
Dyes and Pigments 136 (2017) 248e254
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Development of structured natural dyes for use into plastics rgio R.K. Velho a, *, Luis F.W. Brum f, Carlos O. Petter b, Joa ~o Henrique Z. dos Santos c, Se d e Stefanija Simuni c , Wilfried Helmut Kappa Ministry of Science Technology, Innovations and Communications e MCTIC, Esplanada dos Minist erios, Bloco E 3 andar, 70067-900, Brasília, DF, Brazil Department of Mine Engineering, Engineering College, Technology Center, Federal University of Rio Grande do Sul (UFRGS), Caixa Postal (PO Box) 15021, 91501-970, Porto Alegre, RS, Brazil c Department of Inorganic Chemistry, Chemistry Institute, Federal University of Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, 91501-970, Porto Alegre, RS, Brazil d Independent Chemicals Professional, Chromos-Tar-Kutrilin, Zagreb, Croatia e Dr-Kappa Services Ltd, Nostadstr. 67, D-55411 Bingen, Germany f Food Science and Technology Institute, Federal University of Rio Grande do Sul (UFRGS), Av.Bento Gonçalves, 9.500, 91.501-970, Porto Alegre, Brazil a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 July 2016 Accepted 8 August 2016 Available online 18 August 2016
This study aimed to identify whether natural dyes encapsulated in a silica matrix via the sol-gel process with the use of alkoxides (as described in INPI patent BR 10 2013 0219835) and subsequently injected into a polyvinyl chloride (PVC) matrix would preserve their original color characteristics after being subjected to Xenon-accelerated weathering (using the ASTM D4452-12 standard). A comparison was conducted of the same natural dyes - carmine, turmeric, indigo and annatto e with and without encapsulation, injected into the same PVC matrix. Color change measurements were made before the weathering test and after 126 h, 252 h, 378 h and 504 h in a Xenon weathering chamber using the ASTM D4459-12 standard. A non-encapsulated Tartrazine dye (INS 102, an azo dye) was used for comparison of the behavior of natural dyes vs. that of synthetic ones. The results pointed to a lack of discoloring protection for the encapsulated natural dyes, which lost saturation more severely than the non-encapsulated ones. It thus follows that some care is required during the encapsulation stages of natural dyes, such as careful dispersion of natural colorants and the inclusion of repeat stages for the encapsulation of the xerogel. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Natural dyes Sol-gel process Xenon-accelerated Weathering
1. Introduction Color is a paramount contributor to the beauty of nature. It is a major sensory attribute that deeply influences us and is present in a number of items, like fabrics, food, decorative objects and in countless other ways around our environment. It is crucial, for example, for the attractiveness and global acceptance of products such as food [8]. Dyes and pigments are chemical substances or compounds, natural or synthetic, which change the color of another substance or compound when applied to it. Their use has been an activity of economic importance since ancient times, the same consequently
* Corresponding author. E-mail addresses: [email protected] (S.R.K. Velho), Luisfbrum.engenheiro@ gmail.com (L.F.W. Brum). URL: http://www.ufrgs.br http://dx.doi.org/10.1016/j.dyepig.2016.08.021 0143-7208/© 2016 Elsevier Ltd. All rights reserved.
being true for the search for new ones. The first dyes were natural, obtained from plants, animals and fungi; the first synthetic dyes, i.e. those made by technological synthesis, would only emerge during the nineteenth century with the development of organic chemistry from fossil sources [2]. The main differences between natural and synthetic dyes are of stability and cost: synthetic dyes are generally more stable and less expensive than natural ones [4]. Despite these advantages, the findings of recent toxicological studies [7], coupled with consumer protection regulations and the associated search for sustainable products that do not have fossil sources, has led to renewed interest in natural dyes that can replace synthetic ones. Such replacements, however, must fall within acceptable parameters of resistance to weathering (especially fading, which is the decrease of saturation by light, especially UV) and be competitive in terms of costs if they are to present a competitive advantage to synthetic dyes. Taking these aspects into account, this study aims to verify the applicability of the patent registered at the INPI (Brazilian Institute
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254
SOL
GEL
Xerogel
• Addition of TEOS (10 ml) • Addition of 0.2N HCl solution (8,6 ml) • Addition of Aluminum trichloride (AlCl3) (300 mg)
• Stirring at 200 RPM at room temperature • 24 hours
• Aging and drying at 50°C • Grinding • Natural extract encapsulated
Fig. 1. Flowchart for obtaining natural dyes encapsulated in the silica matrix via the sol-gel process.
of Intellectual Property) under No. BR1020130219835, date of deposit 08/28/2013 under the title: “Structuring Process for Natural Dyes with Hybrid Features Compatible for Application in Polymeric Materials and Cellulosic, Synthetic and Mixed Fibers”. The invention describes a process for developing natural dyes with hybrid characteristics (whose product is compatible for use in thermally and mechanically stable polymers and cellulosic and synthetic fibers) that are capable of reproducing the color characteristics of the original natural pigments and present improved performance regarding light fastness and better resistance to several changes when exposed to the weather. The product of the hybrid materials developed can then be applied through simplified processes (with reduced need for inputs, auxiliary products and mordants) on cellulosic, leather and synthetic polymeric materials such as laminates and plastic packages. This study aims to determine whether the encapsulation proposed for the sol-gel structuring of natural dyes described in the invention in fact minimizes the tint loss-inducing effects of light (i.e. fading or loss of color or saturation). The encapsulation via the sol-gel process uses alkoxides to obtain hybrid (i.e. organicinorganic) materials, which are then subjected to hydrolysis and condensation reactions through a precursor in order to promote the formation of colloidal-size particles (sol) and subsequent formation of a three-dimensional network (gel). The sol-gel process is a method applied to the preparation of materials that is based on the polymerization - at room or low temperatures - of simple inorganic compounds. It opened a new
249
field in materials science, focused on macromolecular chemistry [1]. The natural dyes chosen were selected based on the previous experiments that led to the registration of the patent. In them, the best responses to color migration assays for Polyvinyl Chloride (PVC) (ISO 15701:1998) were obtained from the following dyes: indigo carmine (Indigofera, blue), carmine cochineal (Dactylopius coccus, pink) and turmeric (Curcuma Longa L., yellow). These assays were performed with the dyes encapsulated with alkoxides in silica matrices. These natural dyes, including annatto (Bixa Orellana, red), are also used quite frequently in the market, having prominent commercial value, which in turn also facilitated their use for this study. The natural dyes encapsulated in the three-dimensional network with silicon alkoxides were initially prepared through grinding and sifting and then injected into a Polyvinyl Chloride (PVC) polymer matrix. After the injection of the specimens, the colorimetric spectra of the samples were measured using the ASTM D 2244-14 standard, after which they were subjected to accelerated weathering tests in a Xenon arc chamber (Xenotest) in compliance with the ASTM D4459-12 standard - which is standard practice for Xenon arc exposure in testing plastics intended for indoor use. The effect of sunlight was simulated with Xenochrome 320 lamps featuring filters that simulate solar radiation as specified by the International Commission on Illumination (CIE). Sample hue was measured with a CIELab colorimeter at the following times: 0 h (start), 126 h, 252 h, 378 h and 504 h (end). Sample colors were measured after the weathering test in the Xenotest chamber in order to accurately assess the loss of saturation/hue and/or fading said test caused in the colors of the specimens. This study aimed to identify whether natural dyes encapsulated in a silica matrix by the sol-gel process with the use of alkoxides (as described in INPI patent BR 10 2013 0219835) and subsequently injected into a polyvinyl chloride (PVC) matrix would preserve their original color characteristics after being subjected to accelerated weathering. A comparison was conducted of the same natural dyes with and without encapsulation and injected into the same PVC matrix. A Tartrazine dye (INS 102, an azo dye) without encapsulation was used for comparison of the behavior of natural dyes vs. that of synthetic ones. There is a promising future for the use of natural dyes in the near future, especially due to the reduced environmental impacts (such as carbon footprint) they represent for the plastic products in which they are used. The use of Life Cycle Assessment (LCA) for products is already a reality in some markets, especially European
Table 2 Xenon-Arc Accelerated weathering test parameters. Xenon-Arc Accelerated weathering Equipment used for exposure
Q-Sun Xe-3-HS accelerated weathering chamber, brand Q-Lab, Serial No. 13-0681-47-X3Hs. CR20/340/BSL Radiometer, Serial No. 12-27717-1-340/BSL Equipment used for color variation ASTM D2244-11-compliant Spectrophotometer: BYK Gardner, Spectro-Guide 45/0 Gloss model (Geometry 45 circ./0), Serial No. evaluation 036848; CIE L*a*b* Color System. D65 Illuminant e 10 Observer Lamp type used Xenon lamp Total test time 504 h Start Date 11/21/2015 Standard ASTM D4459-12 CIELab sample measurement times 0 h, 126 h, 252 h, 378 h and 504 h Cycle description 504 h of light exposure Irradiation intensity 0.3 W/m2/nm at 340 nm Black panel temperature 55 ± 2 C Humidity 50 ± 10% Filter used Window BSL Radiometer used CR20/340/BSL Filter usage time at start of test 15,075 h Filter usage time at test end 15,579 h
250
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254 Table 5 Encapsulated turmeric weathering results. Encapsulated turmeric (Curcuma Longa L.)
CIELAB*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
Table 3 Encapsulated carmine cochineal weathering results.
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
(0 h)
(0 h)
(0 h)
(0 h)
CIELAB* L*
a*
b*
5.59 5.60 DL* ¼ 0.01 DE ¼ 5.39 8.33 11.53 DL* ¼ 3.20 DE ¼ 7.56 5.96 9.04 DL* ¼ 3.08 DE ¼ 11.02 6.77 13.42 DL* ¼ 6.65 DE ¼ 10.92
15.56 20.77 Da* ¼ 5.21
2.98 4.36 Db* ¼ 1.38
26.16 31.70 Da* ¼ 5.54
5.94 9.96 Db* ¼ 4.02
18.45 28.23 Da* ¼ 9.78
4.03 8.07 Db* ¼ 4.04
23.26 30.51 Da* ¼ 7.25
5.14 9.89 Db* ¼ 4.75
Non-encapsulated carmine cochineal
CIELAB* L*
a*
b*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
7.00 6.65 DL* ¼ 0.35 DE ¼ 5.60 7.87 9.19 DL* ¼ 1.32 DE ¼ 8.15 12.39 14.19 DL* ¼ 1.80 DE ¼ 6.69 8.18 9.63 DL* ¼ 1.45 DE ¼ 9.14
14.43 19.99 Da* ¼ 5.56
3.26 3.80 Db* ¼ 0.54
12.90 20.67 Da* ¼ 7.77
3.14 5.22 Db* ¼ 2.08
8.11 14.41 Da* ¼ 6.30
1.16 2.53 Db* ¼ 1.37
10.33 19.02 Da* ¼ 8.69
2.32 4.74 Db* ¼ 2.42
(0 h)
(0 h)
(0 h)
(0 h)
(0 h)
b*
51.24 54.08 DL* ¼ 2.84 DE ¼ 36.38 51.07 54.65 DL* ¼ 3.58 DE ¼ 38.95 50.64 66.09 DL* ¼ 15.45 DE ¼ 42.06 43.09 63.04 DL* ¼ 19.95 DE ¼ 37.81
22.56 50.07 2.91 19.58 Da* ¼ 19.65 Db* ¼ 30.49 20.67 45.24 0.86 11.89 Da* ¼ 19.81 Db* ¼ 33.35 20.90 42.84 0.20 9.64 Da* ¼ 20.70 Db* ¼ 33.20 23.23 34.30 0.43 11.67 Da* ¼ 22.80 Db* ¼ 22.63
Non-encapsulated turmeric (Curcuma Longa L.)
CIELAB* L*
a*
b*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
31.06 41.99 DL* ¼ 10.93 DE ¼ 23.20 32.32 55.52 DL* ¼ 23.20 DE ¼ 35.96 34.56 59.94 DL* ¼ 25.38 DE ¼ 45.89 34.65 60.09 DL* ¼ 25.44 DE ¼ 51.53
34.12 22.02 Da* ¼ 12.10
29.78 46.29 Db* ¼ 16.51
36.26 11.68 Da* ¼ 24.58
32.21 44.50 Db* ¼ 12.29
38.23 1.43 Da* ¼ 36.80
34.23 23.85 Db* ¼ 10.38
40.09 0.74 Da* ¼ 39.35
39.71 18.27 Db* ¼ 21.44
(0 h)
(0 h)
(0 h)
(0 h)
Table 7 Encapsulated indigo weathering results. Encapsulated indigo
Table 4 Non-encapsulated carmine cochineal weathering results.
(0 h)
(0 h)
a*
Table 6 Non-encapsulated turmeric weathering results.
Fig. 2. CIELab color space.
Encapsulated carmine cochineal
(0 h)
L*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
CIELAB*
(0 h)
(0 h)
(0 h)
(0 h)
L*
a*
b*
16.81 18.93 DL* ¼ 2.12 DE ¼ 4.96 17.41 21.49 DL* ¼ 4.08 DE ¼ 9.42 21.63 25.79 DL* ¼ 4.16 DE ¼ 10.27 20.65 23.48 DL* ¼ 2.83 DE ¼ 6.58
0.76 1.62 Da* ¼ 0.86
2.46 6.86 Db* ¼ 4.40
1.40 3.79 Da* ¼ 2.39
2.99 11.14 Db* ¼ 8.15
0.39 4.02 Da* ¼ 2.44
2.44 11.63 Db* ¼ 9.07
0.39 1.87 Da* ¼ 1.48
2.44 8.19 Db* ¼ 5.75
ones. Green certification seals have already become a trend in the development of new products, as they allow consumers to make purchasing choices based not only on price, but especially on the sustainability of products (as represented by their carbon and
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254 Table 8 Non-encapsulated indigo weathering results. Non-encapsulated indigo
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
Table 11 Non-encapsulated tartrazine weathering results.
CIELAB*
(0 h)
(0 h)
(0 h)
(0 h)
Non-encapsulated Tartrazine
L*
a*
b*
11.32 12.15 DL* ¼ 0.83 DE ¼ 0.83 10.95 12.49 DL* ¼ 1.54 DE ¼ 1.55 13.61 11.42 DL* ¼ 2.19 DE ¼ 2.26 8.89 12.12 DL* ¼ 3.23 DE ¼ 3.34
2.51 2.45 Da* ¼ 0.06
1.28 1.34 Db* ¼ 0.06
2.43 2.25 Da* ¼ 0.18
1.24 1.13 Db* ¼ 0.11
2.33 2.87 Da* ¼ 0.54
1.05 0.99 Db* ¼ 0.06
3.17 2.61 Da* ¼ 0.56
1.25 0.59 Db* ¼ 0.66
Table 9 Encapsulated annatto weathering results. Encapsulated annatto
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
(0 h)
(0 h)
(0 h)
L*
a*
b*
45.50 59.99 DL* ¼ 14.49 DE ¼ 24.63 41.62 60.24 DL* ¼ 18.62 DE ¼ 28.79 41.61 68.89 DL* ¼ 27.28 DE ¼ 37.02 45.15 70.21 DL* ¼ 25.06 DE ¼ 40.21
23.58 3.85 Da* ¼ 19.73
38.77 36.06 Db* ¼ 2.71
23.33 1.78 Da* ¼ 21.55
32.46 28.25 Db* ¼ 4.21
23.62 0.39 Da* ¼ 23.23
33.10 23.79 Db* ¼ 9.31
24.90 0.07 Da* ¼ 24.97
41.95 22.84 Db* ¼ 19.11
Table 10 Non-encapsulated annatto weathering results. Non-encapsulated annatto
CIELAB* L*
a*
b*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
42.22 42.55 DL* ¼ 0.33 DE ¼ 4.09 43.86 44.35 DL* ¼ 0.49 DE ¼ 4.17 44.90 43.71 DL* ¼ -1.19 DE ¼ 5.85 44.00 43.89 DL* ¼ 0.11 DE ¼ 5.47
26.38 27.82 Da* ¼ 1.44
46.66 50.49 Db* ¼ 3.82
26.56 28.48 Da* ¼ 1.92
45.00 48.68 Db* ¼ 3.68
26.59 28.90 Da* ¼ 2.31
42.80 48.05 Db* ¼ 5.25
28.10 30.69 Da* ¼ 2.59
49.44 54.26 Db* ¼ 4.82
(0 h)
(0 h)
(0 h)
(0 h)
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
(0 h)
(0 h)
(0 h)
(0 h)
CIELAB* L*
a*
b*
34.49 47.09 DL* ¼ 12.60 DE ¼ 21.43 35.49 54.53 DL* ¼ 19.04 DE ¼ 26.09 34.71 55.94 DL* ¼ 21.23 DE ¼ 28.13 36.85 62.23 DL* ¼ 25.38 DE ¼ 32.17
22.59 9.99 Da* ¼ 12.60
20.65 32.55 Db* ¼ 11.90
23.09 6.20 Da* ¼ 16.89
22.38 28.11 Db* ¼ 5.73
22.99 5.91 Da* ¼ 17.08
20.03 27.02 Db* ¼ 6.99
23.36 3.76 Da* ¼ 19.60
24.33 21.76 Db* ¼ 2.57
The study aims to answer the following question: Can natural dyes can be used to color polymers as a replacement of synthetic dyes without substantial loss of characteristics due to weathering?
CIELAB*
(0 h)
251
2. Materials and methods 2.1. Encapsulation of natural dyes The natural dyes - carmine cochineal, turmeric, indigo and annatto - were encapsulated via the sol-gel process at the Physical Chemistry Laboratory of the Federal University of Rio Grande do Sul (UFRGS). Silica gels were prepared from the hydrolysis of monomeric forms of TEOS (tetraethyl orthosilicate) using a 0.2 N hydrochloric acid (HCl) solution as a catalyst and a Lewis acid aluminum trichloride (AlCl3) - at a proportion of 3% of the silica þ natural dye content of the solution. The volumes used for each reagent followed the stoichiometric ratio between the TEOS and hydrochloric acid. The encapsulation reaction in the silica matrix was initiated with the addition of TEOS and subsequent addition of the catalysts (AlCl3 and 0.2 N HCL solution), the result of which was kept stirring on a magnetic stirrer at 200 rpm. The reaction was kept at room temperature for 2 h before the addition of the natural dye solution or dye powder fraction. Reaction time to gelification was of 24 h. Subsequently, the samples were dried at 50 C for 24 h and ground in a porcelain mortar until a fine, homogeneous powder was obtained. The xerogel formed was left to dry naturally for 30 days in a laboratory environment. Fig. 1 below summarizes the whole process (see Fig. 1). ^ All natural dyes were purchased on the market from Baculere ~o Paulo state), with the Corantes Naturais, a company in Olímpia (Sa exception of the indigo dye, which was purchased from Vetec Química Fina, a company in Duque de Caxias (Rio de Janeiro state). Only the carmine was purchased in solution form; all others were purchased in powder. 2.2. Injection into the PVC matrix
water footprints). Offering such choice helps reduce emissions of greenhouse gases and their consequences for global average temperatures. We hope that this work can contribute to such efforts.
PVC (polyvinyl polychloride) was used to inject our samples due to its low injection temperature, which helps prevent degradation of the natural dyes due to heat. The following injection conditions were used (see Table 1: Set samples injection conditions):
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~o Leopoldo (Rio Grande do Sul state, Technological Center in Sa Brazil) between November 21 and December 15, 2015. The results were issued on December 16, 2015 (Report # 2109/15). The following parameters were used during the test (See Table 2): Notes applicable to the test (as defined by the testing laboratory):
Table 1 Set samples injection conditions. Sample injection conditions 190 C 30 s 5% WT
Set Injection Temperature Injection Time Dye Concentration (encapsulated and non-encapsulated) The specimens measured 57 mm 45 mm 2.0 mm.
- Color was measured on the brighter side of the samples. - Since the injected samples had transparency, color was measured with the BYK Gardner equipment against a standard white background. - The injected specimens varied in thicknesses, brightness and color heterogeneity.
The Xenon-accelerated weathering test used the ASTM D445912 reference standard, which is common practice for xenon-arc exposure testing of plastics intended for indoor applications. The test was executed in the laboratories of the SENAI Polymers
∆E x t/hs 12
11.02
10.92
10 9.13
8.15
8
7.55 5.59
6
6.69
5.39 4
--- Encapsulated Carmine − Non-Encapsulated Carmine
2 0 0
100
200
300
HOURS
400
500
600
Fig. 3. DE time (hours)e Natural dye: Carmine cochineal.
Δ E x t/hs
60.00
51.53
50.00 40.00
45.89 42.06
38.95 35.96
36.38
37.81
30.00 23.20
20.00
--- Turmeric Encapsulated − Turmeric Non-encapsulated
10.00 0.00 0
100
200
300
Hours
400
500
600
Fig. 4. DE time (hours) e Natural dye: Turmeric.
Δ E x t/hs
12.00
--- Indigo Encapsulated − Indigo Not Encapsulated
10.00
10.27 9.42
8.00 6.58
6.00 4.96 4.00
3.34 2.26 2.00 1.55
1.19 0.00 0
100
200
300
Hours
400
Fig. 5. DE time (hours) e Natural dye: Indigo.
500
600
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254
253
Δ E x t/h 45.00 40.21
40.00 37.02
35.00 30.00
28.79
25.00 24.63 20.00
--- Annato Encapsulated − Annato Not Encapsulated
15.00 10.00 5.00
5.47
5.86
4.18
4.11 0.00 0
100
200
300
Hours
400
500
600
Fig. 6. DE time (hours) e Natural dye: Annato.
3. Results and discussion Color was objectively assessed by the SENAI Laboratory through reflectance in the CIELab color space, using a BYK Gardner Spectrophotometer (Spectro-Guide 45/0 Gloss model, 45 Geometry, circ./0) of Serial No. 036848, CIELab Color System, D65 Illuminant and observer angle of 10 , following the method described in the ASTM D2244-11 standard. The color parameters indicate lightness (L*), with a maximum value of 100 representing perfect diffuse reflection and minimum value zero representing black. The tone of the samples had no specific numerical limits, but a reference value of 60 color units was chosen (þa* direction towards red, a* direction towards green, þb* direction towards yellow and -b* direction towards blue) (see Fig. 2). Chroma (C*) expresses color saturation or intensity, while hue angle (Hº) indicates the observed color and is defined as starting at the þa* axis, where 0 is þa* (red), 90 is þb* (yellow), 180 is a* (green) and 270 is b* (blue) [5] (see Tables 3e11). A small difference in color can be seen between encapsulated and non-encapsulated samples, with the encapsulated sample showing whiter, greener and bluer according to CIELab* as Fig. 3 above. There is greater saturation in the encapsulated samples (C* ¼ 21.34) vs. the non-encapsulated ones (C* ¼ 10.59). Comparing encapsulated and non-encapsulated samples, it appears that the percentage difference dE is positive up until 252 h (7.88%), from which point more pronounced color loss is observed in the encapsulated samples, reaching a percentage difference of 16.37% at the end. The two samples migrate to the same quadrant (i.e. become whiter, greener and bluer). A considerable difference in color can be seen between the encapsulated and non-encapsulated samples for turmeric: the encapsulated sample is darker (black), redder and bluer according to the CIELab* as Fig. 4 above. There is stronger saturation in the nonencapsulated samples (C* ¼ 50.37) compared with the encapsulated ones (C* ¼ 48.33). The percentage difference in dE is negative between encapsulated and non-encapsulated samples until 252 h (7.68%), from which point a more pronounced loss of color is observed in the non-encapsulated samples, reaching a final percentage difference of þ36.27% at the end. The two samples migrate to the same quadrant (i.e. become whiter, greener and bluer).
A considerable difference in color can be seen between the encapsulated and non-encapsulated samples: the encapsulated sample is darker (black), redder and yellower according to the CIELab* as Fig. 5 above. There is slightly stronger saturation in the non-encapsulated samples (C* ¼ 2.87) compared with the encapsulated ones (C* ¼ 2.81). The percentage difference in dE between encapsulated and non-encapsulated samples is negative and more pronounced in the first hours, reaching a final percentage difference of 49.16% at the end. A considerable difference in color can be seen between the encapsulated and non-encapsulated samples: the encapsulated sample is lighter (black), redder and yellower according to the CIELab* as Fig. 6 above. There is stronger saturation in the nonencapsulated samples (C* ¼ 53.27) compared with the encapsulated ones (C* ¼ 43.66). The percentage difference in dE between encapsulated and non-encapsulated samples is negative and more pronounced throughout the weathering test, reaching a final percentage difference of 86.39% at the end. It became clear that the encapsulated sample suffered markedly from weathering, losing the original colors of Annato. 4. Conclusion Fabjan et al. [3] encapsulated an organic blue dye (b copper phthalocyanine) with silica using alkoxides as precursors. It has been shown that the silica shells obtained can serve as effective protection against the highly reactive products of photocatalysis (i.e. increasing photoreaction speed through a catalyst) [6]. In recent years, photocatalytically active materials have garnered interest for use in various applications, such as paints for the coating of surfaces that feature self-cleaning capabilities. This work has shown that protecting organic dyes (especially natural ones) via the sol-gel process should insulate them from the effects of weathering and allow them to be injected as masterbatches for use in polymers. However, the degree of protection achieved depended not only on the thickness of the silica shell, but also on its porosity. The compact (nonporous) layer of silica shells is intended, in that case, to prevent the penetration of photocatalysts. An analysis of the data obtained from the weathering test conducted in compliance with the ASTM D4459-
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12 standard reveals that encapsulation provided no color loss protection to the silica-encapsulated natural dyes. The encapsulated Turmeric die was the only one that showed better results, mainly after 310 h. The Carmine cochineal die had exhibited protection at the initial stages, but that was reversed after about 260 h. As such, the encapsulation of natural dyes on an alkoxide matrix does not protect them from weathering as they were expected to. We resorted to the work of Fabjan et al. [3] to indicate a few corrections to the synthesis of natural dyes that should be addressed in future works: preparation of stable dye dispersions: one must use cetyltrimethylammonium bromide (CTAB) at the optimum concentration in order to prepare solutions with disperse dyes that can lead to a well-defined inorganic layer around each pigment particle. For that end to be achieved, it is essential that the particles be well dispersed. There is a tendency for nanoparticles of the order of 100 nm or more to appear in agglomerates. Double encapsulation: After the encapsulation step (i.e. aging in oven at 50 C for 48 h), the material should be washed, filtrated and dispersed in a 10% CTAB solution, after which the synthesis step should be repeated at room temperature using TEOS (tetraethyl orthosilicate), hydrochloric acid (HCl) and Lewis acid
(aluminum trichloride) in the same proportions employed for the first synthesis. References xidos como precursores na síntese de novos materiais [1] Airoldi C, Farias RF. Alco s do processo sol-gel. Quím Nova 2004;27(1):84e8. atrave [2] Cardon D. Natural dyes, our global heritage of colours. Textile Society of America; 6e9 de Outubro de 2010 [ONLINE] Available at the website of the University of Nebraska, http://digitalcommons.unl.edu/cgi/viewcontent.cgi? article¼1011&context¼tsaconf [Accessed 15 January 2015]. [3] Fabjan ES, Skapin AS, Skrlep L, Zivec P, Ceh M, Gaberscek M. Protection of organic pigments against photocatalysis by encapsulation. J Sol-Gel Sci Technol 2012:65e74. psulas de bixina em [4] Lobato KB. Produç~ ao e avaliaç~ ao da estabilidade de nanoca ~o e aquecimento. Porto Alegre, RS, Brasil: sistemas modelo de fotossensitizaça UFRGS. ICTA; 2013. [5] Neiro, E.d., Nanni M. R., Romagnoli F., Campos R. M., Cezar E., Chicati M. L., & lise de cor para discriminaça ~o de seis variedades de Oliveira R. B. (2013). Ana pocas de colheita no ano. Anais XVI Simpo sio cana-de-açúcar em quatro e Brasileiro de Sensoriamento Remoto - SBSR, 13 a 18 de abril de 2013, (pp. 274e281). Foz do Iguaçu, PR. ^nea e sua aplicaç~ [6] Nogueira R, Jardim W. A fotocat alise heteroge ao ambiental. Quím Nova 1998;21:69e72. [7] Rodrigues P d. Estudo do uso de corantes artificiais em alimentos e estimativa ~o brasileira. Porto Alegre, RS, Brasil: de ingest~ ao de tartrazina pela populaça UFRGS. ICTA; 2015. ~o e estabilidade de [8] Silva GJ, Constant PB, Figueiredo RW, Moura SM. Formulaça corantes de antocianinas extraídas das cascas de jabuticaba (Myrciaria ssp). Alim Nutr Araraquara 2010;21(3):429e36. jul/set 2010 ISSN 0103e4235.
Contents lists available at ScienceDirect
Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig
Development of structured natural dyes for use into plastics rgio R.K. Velho a, *, Luis F.W. Brum f, Carlos O. Petter b, Joa ~o Henrique Z. dos Santos c, Se d e Stefanija Simuni c , Wilfried Helmut Kappa Ministry of Science Technology, Innovations and Communications e MCTIC, Esplanada dos Minist erios, Bloco E 3 andar, 70067-900, Brasília, DF, Brazil Department of Mine Engineering, Engineering College, Technology Center, Federal University of Rio Grande do Sul (UFRGS), Caixa Postal (PO Box) 15021, 91501-970, Porto Alegre, RS, Brazil c Department of Inorganic Chemistry, Chemistry Institute, Federal University of Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, 91501-970, Porto Alegre, RS, Brazil d Independent Chemicals Professional, Chromos-Tar-Kutrilin, Zagreb, Croatia e Dr-Kappa Services Ltd, Nostadstr. 67, D-55411 Bingen, Germany f Food Science and Technology Institute, Federal University of Rio Grande do Sul (UFRGS), Av.Bento Gonçalves, 9.500, 91.501-970, Porto Alegre, Brazil a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 July 2016 Accepted 8 August 2016 Available online 18 August 2016
This study aimed to identify whether natural dyes encapsulated in a silica matrix via the sol-gel process with the use of alkoxides (as described in INPI patent BR 10 2013 0219835) and subsequently injected into a polyvinyl chloride (PVC) matrix would preserve their original color characteristics after being subjected to Xenon-accelerated weathering (using the ASTM D4452-12 standard). A comparison was conducted of the same natural dyes - carmine, turmeric, indigo and annatto e with and without encapsulation, injected into the same PVC matrix. Color change measurements were made before the weathering test and after 126 h, 252 h, 378 h and 504 h in a Xenon weathering chamber using the ASTM D4459-12 standard. A non-encapsulated Tartrazine dye (INS 102, an azo dye) was used for comparison of the behavior of natural dyes vs. that of synthetic ones. The results pointed to a lack of discoloring protection for the encapsulated natural dyes, which lost saturation more severely than the non-encapsulated ones. It thus follows that some care is required during the encapsulation stages of natural dyes, such as careful dispersion of natural colorants and the inclusion of repeat stages for the encapsulation of the xerogel. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Natural dyes Sol-gel process Xenon-accelerated Weathering
1. Introduction Color is a paramount contributor to the beauty of nature. It is a major sensory attribute that deeply influences us and is present in a number of items, like fabrics, food, decorative objects and in countless other ways around our environment. It is crucial, for example, for the attractiveness and global acceptance of products such as food [8]. Dyes and pigments are chemical substances or compounds, natural or synthetic, which change the color of another substance or compound when applied to it. Their use has been an activity of economic importance since ancient times, the same consequently
* Corresponding author. E-mail addresses: [email protected] (S.R.K. Velho), Luisfbrum.engenheiro@ gmail.com (L.F.W. Brum). URL: http://www.ufrgs.br http://dx.doi.org/10.1016/j.dyepig.2016.08.021 0143-7208/© 2016 Elsevier Ltd. All rights reserved.
being true for the search for new ones. The first dyes were natural, obtained from plants, animals and fungi; the first synthetic dyes, i.e. those made by technological synthesis, would only emerge during the nineteenth century with the development of organic chemistry from fossil sources [2]. The main differences between natural and synthetic dyes are of stability and cost: synthetic dyes are generally more stable and less expensive than natural ones [4]. Despite these advantages, the findings of recent toxicological studies [7], coupled with consumer protection regulations and the associated search for sustainable products that do not have fossil sources, has led to renewed interest in natural dyes that can replace synthetic ones. Such replacements, however, must fall within acceptable parameters of resistance to weathering (especially fading, which is the decrease of saturation by light, especially UV) and be competitive in terms of costs if they are to present a competitive advantage to synthetic dyes. Taking these aspects into account, this study aims to verify the applicability of the patent registered at the INPI (Brazilian Institute
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254
SOL
GEL
Xerogel
• Addition of TEOS (10 ml) • Addition of 0.2N HCl solution (8,6 ml) • Addition of Aluminum trichloride (AlCl3) (300 mg)
• Stirring at 200 RPM at room temperature • 24 hours
• Aging and drying at 50°C • Grinding • Natural extract encapsulated
Fig. 1. Flowchart for obtaining natural dyes encapsulated in the silica matrix via the sol-gel process.
of Intellectual Property) under No. BR1020130219835, date of deposit 08/28/2013 under the title: “Structuring Process for Natural Dyes with Hybrid Features Compatible for Application in Polymeric Materials and Cellulosic, Synthetic and Mixed Fibers”. The invention describes a process for developing natural dyes with hybrid characteristics (whose product is compatible for use in thermally and mechanically stable polymers and cellulosic and synthetic fibers) that are capable of reproducing the color characteristics of the original natural pigments and present improved performance regarding light fastness and better resistance to several changes when exposed to the weather. The product of the hybrid materials developed can then be applied through simplified processes (with reduced need for inputs, auxiliary products and mordants) on cellulosic, leather and synthetic polymeric materials such as laminates and plastic packages. This study aims to determine whether the encapsulation proposed for the sol-gel structuring of natural dyes described in the invention in fact minimizes the tint loss-inducing effects of light (i.e. fading or loss of color or saturation). The encapsulation via the sol-gel process uses alkoxides to obtain hybrid (i.e. organicinorganic) materials, which are then subjected to hydrolysis and condensation reactions through a precursor in order to promote the formation of colloidal-size particles (sol) and subsequent formation of a three-dimensional network (gel). The sol-gel process is a method applied to the preparation of materials that is based on the polymerization - at room or low temperatures - of simple inorganic compounds. It opened a new
249
field in materials science, focused on macromolecular chemistry [1]. The natural dyes chosen were selected based on the previous experiments that led to the registration of the patent. In them, the best responses to color migration assays for Polyvinyl Chloride (PVC) (ISO 15701:1998) were obtained from the following dyes: indigo carmine (Indigofera, blue), carmine cochineal (Dactylopius coccus, pink) and turmeric (Curcuma Longa L., yellow). These assays were performed with the dyes encapsulated with alkoxides in silica matrices. These natural dyes, including annatto (Bixa Orellana, red), are also used quite frequently in the market, having prominent commercial value, which in turn also facilitated their use for this study. The natural dyes encapsulated in the three-dimensional network with silicon alkoxides were initially prepared through grinding and sifting and then injected into a Polyvinyl Chloride (PVC) polymer matrix. After the injection of the specimens, the colorimetric spectra of the samples were measured using the ASTM D 2244-14 standard, after which they were subjected to accelerated weathering tests in a Xenon arc chamber (Xenotest) in compliance with the ASTM D4459-12 standard - which is standard practice for Xenon arc exposure in testing plastics intended for indoor use. The effect of sunlight was simulated with Xenochrome 320 lamps featuring filters that simulate solar radiation as specified by the International Commission on Illumination (CIE). Sample hue was measured with a CIELab colorimeter at the following times: 0 h (start), 126 h, 252 h, 378 h and 504 h (end). Sample colors were measured after the weathering test in the Xenotest chamber in order to accurately assess the loss of saturation/hue and/or fading said test caused in the colors of the specimens. This study aimed to identify whether natural dyes encapsulated in a silica matrix by the sol-gel process with the use of alkoxides (as described in INPI patent BR 10 2013 0219835) and subsequently injected into a polyvinyl chloride (PVC) matrix would preserve their original color characteristics after being subjected to accelerated weathering. A comparison was conducted of the same natural dyes with and without encapsulation and injected into the same PVC matrix. A Tartrazine dye (INS 102, an azo dye) without encapsulation was used for comparison of the behavior of natural dyes vs. that of synthetic ones. There is a promising future for the use of natural dyes in the near future, especially due to the reduced environmental impacts (such as carbon footprint) they represent for the plastic products in which they are used. The use of Life Cycle Assessment (LCA) for products is already a reality in some markets, especially European
Table 2 Xenon-Arc Accelerated weathering test parameters. Xenon-Arc Accelerated weathering Equipment used for exposure
Q-Sun Xe-3-HS accelerated weathering chamber, brand Q-Lab, Serial No. 13-0681-47-X3Hs. CR20/340/BSL Radiometer, Serial No. 12-27717-1-340/BSL Equipment used for color variation ASTM D2244-11-compliant Spectrophotometer: BYK Gardner, Spectro-Guide 45/0 Gloss model (Geometry 45 circ./0), Serial No. evaluation 036848; CIE L*a*b* Color System. D65 Illuminant e 10 Observer Lamp type used Xenon lamp Total test time 504 h Start Date 11/21/2015 Standard ASTM D4459-12 CIELab sample measurement times 0 h, 126 h, 252 h, 378 h and 504 h Cycle description 504 h of light exposure Irradiation intensity 0.3 W/m2/nm at 340 nm Black panel temperature 55 ± 2 C Humidity 50 ± 10% Filter used Window BSL Radiometer used CR20/340/BSL Filter usage time at start of test 15,075 h Filter usage time at test end 15,579 h
250
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254 Table 5 Encapsulated turmeric weathering results. Encapsulated turmeric (Curcuma Longa L.)
CIELAB*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
Table 3 Encapsulated carmine cochineal weathering results.
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
(0 h)
(0 h)
(0 h)
(0 h)
CIELAB* L*
a*
b*
5.59 5.60 DL* ¼ 0.01 DE ¼ 5.39 8.33 11.53 DL* ¼ 3.20 DE ¼ 7.56 5.96 9.04 DL* ¼ 3.08 DE ¼ 11.02 6.77 13.42 DL* ¼ 6.65 DE ¼ 10.92
15.56 20.77 Da* ¼ 5.21
2.98 4.36 Db* ¼ 1.38
26.16 31.70 Da* ¼ 5.54
5.94 9.96 Db* ¼ 4.02
18.45 28.23 Da* ¼ 9.78
4.03 8.07 Db* ¼ 4.04
23.26 30.51 Da* ¼ 7.25
5.14 9.89 Db* ¼ 4.75
Non-encapsulated carmine cochineal
CIELAB* L*
a*
b*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
7.00 6.65 DL* ¼ 0.35 DE ¼ 5.60 7.87 9.19 DL* ¼ 1.32 DE ¼ 8.15 12.39 14.19 DL* ¼ 1.80 DE ¼ 6.69 8.18 9.63 DL* ¼ 1.45 DE ¼ 9.14
14.43 19.99 Da* ¼ 5.56
3.26 3.80 Db* ¼ 0.54
12.90 20.67 Da* ¼ 7.77
3.14 5.22 Db* ¼ 2.08
8.11 14.41 Da* ¼ 6.30
1.16 2.53 Db* ¼ 1.37
10.33 19.02 Da* ¼ 8.69
2.32 4.74 Db* ¼ 2.42
(0 h)
(0 h)
(0 h)
(0 h)
(0 h)
b*
51.24 54.08 DL* ¼ 2.84 DE ¼ 36.38 51.07 54.65 DL* ¼ 3.58 DE ¼ 38.95 50.64 66.09 DL* ¼ 15.45 DE ¼ 42.06 43.09 63.04 DL* ¼ 19.95 DE ¼ 37.81
22.56 50.07 2.91 19.58 Da* ¼ 19.65 Db* ¼ 30.49 20.67 45.24 0.86 11.89 Da* ¼ 19.81 Db* ¼ 33.35 20.90 42.84 0.20 9.64 Da* ¼ 20.70 Db* ¼ 33.20 23.23 34.30 0.43 11.67 Da* ¼ 22.80 Db* ¼ 22.63
Non-encapsulated turmeric (Curcuma Longa L.)
CIELAB* L*
a*
b*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
31.06 41.99 DL* ¼ 10.93 DE ¼ 23.20 32.32 55.52 DL* ¼ 23.20 DE ¼ 35.96 34.56 59.94 DL* ¼ 25.38 DE ¼ 45.89 34.65 60.09 DL* ¼ 25.44 DE ¼ 51.53
34.12 22.02 Da* ¼ 12.10
29.78 46.29 Db* ¼ 16.51
36.26 11.68 Da* ¼ 24.58
32.21 44.50 Db* ¼ 12.29
38.23 1.43 Da* ¼ 36.80
34.23 23.85 Db* ¼ 10.38
40.09 0.74 Da* ¼ 39.35
39.71 18.27 Db* ¼ 21.44
(0 h)
(0 h)
(0 h)
(0 h)
Table 7 Encapsulated indigo weathering results. Encapsulated indigo
Table 4 Non-encapsulated carmine cochineal weathering results.
(0 h)
(0 h)
a*
Table 6 Non-encapsulated turmeric weathering results.
Fig. 2. CIELab color space.
Encapsulated carmine cochineal
(0 h)
L*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
CIELAB*
(0 h)
(0 h)
(0 h)
(0 h)
L*
a*
b*
16.81 18.93 DL* ¼ 2.12 DE ¼ 4.96 17.41 21.49 DL* ¼ 4.08 DE ¼ 9.42 21.63 25.79 DL* ¼ 4.16 DE ¼ 10.27 20.65 23.48 DL* ¼ 2.83 DE ¼ 6.58
0.76 1.62 Da* ¼ 0.86
2.46 6.86 Db* ¼ 4.40
1.40 3.79 Da* ¼ 2.39
2.99 11.14 Db* ¼ 8.15
0.39 4.02 Da* ¼ 2.44
2.44 11.63 Db* ¼ 9.07
0.39 1.87 Da* ¼ 1.48
2.44 8.19 Db* ¼ 5.75
ones. Green certification seals have already become a trend in the development of new products, as they allow consumers to make purchasing choices based not only on price, but especially on the sustainability of products (as represented by their carbon and
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254 Table 8 Non-encapsulated indigo weathering results. Non-encapsulated indigo
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
Table 11 Non-encapsulated tartrazine weathering results.
CIELAB*
(0 h)
(0 h)
(0 h)
(0 h)
Non-encapsulated Tartrazine
L*
a*
b*
11.32 12.15 DL* ¼ 0.83 DE ¼ 0.83 10.95 12.49 DL* ¼ 1.54 DE ¼ 1.55 13.61 11.42 DL* ¼ 2.19 DE ¼ 2.26 8.89 12.12 DL* ¼ 3.23 DE ¼ 3.34
2.51 2.45 Da* ¼ 0.06
1.28 1.34 Db* ¼ 0.06
2.43 2.25 Da* ¼ 0.18
1.24 1.13 Db* ¼ 0.11
2.33 2.87 Da* ¼ 0.54
1.05 0.99 Db* ¼ 0.06
3.17 2.61 Da* ¼ 0.56
1.25 0.59 Db* ¼ 0.66
Table 9 Encapsulated annatto weathering results. Encapsulated annatto
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
(0 h)
(0 h)
(0 h)
L*
a*
b*
45.50 59.99 DL* ¼ 14.49 DE ¼ 24.63 41.62 60.24 DL* ¼ 18.62 DE ¼ 28.79 41.61 68.89 DL* ¼ 27.28 DE ¼ 37.02 45.15 70.21 DL* ¼ 25.06 DE ¼ 40.21
23.58 3.85 Da* ¼ 19.73
38.77 36.06 Db* ¼ 2.71
23.33 1.78 Da* ¼ 21.55
32.46 28.25 Db* ¼ 4.21
23.62 0.39 Da* ¼ 23.23
33.10 23.79 Db* ¼ 9.31
24.90 0.07 Da* ¼ 24.97
41.95 22.84 Db* ¼ 19.11
Table 10 Non-encapsulated annatto weathering results. Non-encapsulated annatto
CIELAB* L*
a*
b*
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
42.22 42.55 DL* ¼ 0.33 DE ¼ 4.09 43.86 44.35 DL* ¼ 0.49 DE ¼ 4.17 44.90 43.71 DL* ¼ -1.19 DE ¼ 5.85 44.00 43.89 DL* ¼ 0.11 DE ¼ 5.47
26.38 27.82 Da* ¼ 1.44
46.66 50.49 Db* ¼ 3.82
26.56 28.48 Da* ¼ 1.92
45.00 48.68 Db* ¼ 3.68
26.59 28.90 Da* ¼ 2.31
42.80 48.05 Db* ¼ 5.25
28.10 30.69 Da* ¼ 2.59
49.44 54.26 Db* ¼ 4.82
(0 h)
(0 h)
(0 h)
(0 h)
Original. before exposure After 126 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 252 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 378 h of exposure Coordinate variation (D) Color variation (DE) Original. before exposure After 504 h of exposure Coordinate variation (D) Color variation (DE)
(0 h)
(0 h)
(0 h)
(0 h)
CIELAB* L*
a*
b*
34.49 47.09 DL* ¼ 12.60 DE ¼ 21.43 35.49 54.53 DL* ¼ 19.04 DE ¼ 26.09 34.71 55.94 DL* ¼ 21.23 DE ¼ 28.13 36.85 62.23 DL* ¼ 25.38 DE ¼ 32.17
22.59 9.99 Da* ¼ 12.60
20.65 32.55 Db* ¼ 11.90
23.09 6.20 Da* ¼ 16.89
22.38 28.11 Db* ¼ 5.73
22.99 5.91 Da* ¼ 17.08
20.03 27.02 Db* ¼ 6.99
23.36 3.76 Da* ¼ 19.60
24.33 21.76 Db* ¼ 2.57
The study aims to answer the following question: Can natural dyes can be used to color polymers as a replacement of synthetic dyes without substantial loss of characteristics due to weathering?
CIELAB*
(0 h)
251
2. Materials and methods 2.1. Encapsulation of natural dyes The natural dyes - carmine cochineal, turmeric, indigo and annatto - were encapsulated via the sol-gel process at the Physical Chemistry Laboratory of the Federal University of Rio Grande do Sul (UFRGS). Silica gels were prepared from the hydrolysis of monomeric forms of TEOS (tetraethyl orthosilicate) using a 0.2 N hydrochloric acid (HCl) solution as a catalyst and a Lewis acid aluminum trichloride (AlCl3) - at a proportion of 3% of the silica þ natural dye content of the solution. The volumes used for each reagent followed the stoichiometric ratio between the TEOS and hydrochloric acid. The encapsulation reaction in the silica matrix was initiated with the addition of TEOS and subsequent addition of the catalysts (AlCl3 and 0.2 N HCL solution), the result of which was kept stirring on a magnetic stirrer at 200 rpm. The reaction was kept at room temperature for 2 h before the addition of the natural dye solution or dye powder fraction. Reaction time to gelification was of 24 h. Subsequently, the samples were dried at 50 C for 24 h and ground in a porcelain mortar until a fine, homogeneous powder was obtained. The xerogel formed was left to dry naturally for 30 days in a laboratory environment. Fig. 1 below summarizes the whole process (see Fig. 1). ^ All natural dyes were purchased on the market from Baculere ~o Paulo state), with the Corantes Naturais, a company in Olímpia (Sa exception of the indigo dye, which was purchased from Vetec Química Fina, a company in Duque de Caxias (Rio de Janeiro state). Only the carmine was purchased in solution form; all others were purchased in powder. 2.2. Injection into the PVC matrix
water footprints). Offering such choice helps reduce emissions of greenhouse gases and their consequences for global average temperatures. We hope that this work can contribute to such efforts.
PVC (polyvinyl polychloride) was used to inject our samples due to its low injection temperature, which helps prevent degradation of the natural dyes due to heat. The following injection conditions were used (see Table 1: Set samples injection conditions):
252
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254
~o Leopoldo (Rio Grande do Sul state, Technological Center in Sa Brazil) between November 21 and December 15, 2015. The results were issued on December 16, 2015 (Report # 2109/15). The following parameters were used during the test (See Table 2): Notes applicable to the test (as defined by the testing laboratory):
Table 1 Set samples injection conditions. Sample injection conditions 190 C 30 s 5% WT
Set Injection Temperature Injection Time Dye Concentration (encapsulated and non-encapsulated) The specimens measured 57 mm 45 mm 2.0 mm.
- Color was measured on the brighter side of the samples. - Since the injected samples had transparency, color was measured with the BYK Gardner equipment against a standard white background. - The injected specimens varied in thicknesses, brightness and color heterogeneity.
The Xenon-accelerated weathering test used the ASTM D445912 reference standard, which is common practice for xenon-arc exposure testing of plastics intended for indoor applications. The test was executed in the laboratories of the SENAI Polymers
∆E x t/hs 12
11.02
10.92
10 9.13
8.15
8
7.55 5.59
6
6.69
5.39 4
--- Encapsulated Carmine − Non-Encapsulated Carmine
2 0 0
100
200
300
HOURS
400
500
600
Fig. 3. DE time (hours)e Natural dye: Carmine cochineal.
Δ E x t/hs
60.00
51.53
50.00 40.00
45.89 42.06
38.95 35.96
36.38
37.81
30.00 23.20
20.00
--- Turmeric Encapsulated − Turmeric Non-encapsulated
10.00 0.00 0
100
200
300
Hours
400
500
600
Fig. 4. DE time (hours) e Natural dye: Turmeric.
Δ E x t/hs
12.00
--- Indigo Encapsulated − Indigo Not Encapsulated
10.00
10.27 9.42
8.00 6.58
6.00 4.96 4.00
3.34 2.26 2.00 1.55
1.19 0.00 0
100
200
300
Hours
400
Fig. 5. DE time (hours) e Natural dye: Indigo.
500
600
S.R.K. Velho et al. / Dyes and Pigments 136 (2017) 248e254
253
Δ E x t/h 45.00 40.21
40.00 37.02
35.00 30.00
28.79
25.00 24.63 20.00
--- Annato Encapsulated − Annato Not Encapsulated
15.00 10.00 5.00
5.47
5.86
4.18
4.11 0.00 0
100
200
300
Hours
400
500
600
Fig. 6. DE time (hours) e Natural dye: Annato.
3. Results and discussion Color was objectively assessed by the SENAI Laboratory through reflectance in the CIELab color space, using a BYK Gardner Spectrophotometer (Spectro-Guide 45/0 Gloss model, 45 Geometry, circ./0) of Serial No. 036848, CIELab Color System, D65 Illuminant and observer angle of 10 , following the method described in the ASTM D2244-11 standard. The color parameters indicate lightness (L*), with a maximum value of 100 representing perfect diffuse reflection and minimum value zero representing black. The tone of the samples had no specific numerical limits, but a reference value of 60 color units was chosen (þa* direction towards red, a* direction towards green, þb* direction towards yellow and -b* direction towards blue) (see Fig. 2). Chroma (C*) expresses color saturation or intensity, while hue angle (Hº) indicates the observed color and is defined as starting at the þa* axis, where 0 is þa* (red), 90 is þb* (yellow), 180 is a* (green) and 270 is b* (blue) [5] (see Tables 3e11). A small difference in color can be seen between encapsulated and non-encapsulated samples, with the encapsulated sample showing whiter, greener and bluer according to CIELab* as Fig. 3 above. There is greater saturation in the encapsulated samples (C* ¼ 21.34) vs. the non-encapsulated ones (C* ¼ 10.59). Comparing encapsulated and non-encapsulated samples, it appears that the percentage difference dE is positive up until 252 h (7.88%), from which point more pronounced color loss is observed in the encapsulated samples, reaching a percentage difference of 16.37% at the end. The two samples migrate to the same quadrant (i.e. become whiter, greener and bluer). A considerable difference in color can be seen between the encapsulated and non-encapsulated samples for turmeric: the encapsulated sample is darker (black), redder and bluer according to the CIELab* as Fig. 4 above. There is stronger saturation in the nonencapsulated samples (C* ¼ 50.37) compared with the encapsulated ones (C* ¼ 48.33). The percentage difference in dE is negative between encapsulated and non-encapsulated samples until 252 h (7.68%), from which point a more pronounced loss of color is observed in the non-encapsulated samples, reaching a final percentage difference of þ36.27% at the end. The two samples migrate to the same quadrant (i.e. become whiter, greener and bluer).
A considerable difference in color can be seen between the encapsulated and non-encapsulated samples: the encapsulated sample is darker (black), redder and yellower according to the CIELab* as Fig. 5 above. There is slightly stronger saturation in the non-encapsulated samples (C* ¼ 2.87) compared with the encapsulated ones (C* ¼ 2.81). The percentage difference in dE between encapsulated and non-encapsulated samples is negative and more pronounced in the first hours, reaching a final percentage difference of 49.16% at the end. A considerable difference in color can be seen between the encapsulated and non-encapsulated samples: the encapsulated sample is lighter (black), redder and yellower according to the CIELab* as Fig. 6 above. There is stronger saturation in the nonencapsulated samples (C* ¼ 53.27) compared with the encapsulated ones (C* ¼ 43.66). The percentage difference in dE between encapsulated and non-encapsulated samples is negative and more pronounced throughout the weathering test, reaching a final percentage difference of 86.39% at the end. It became clear that the encapsulated sample suffered markedly from weathering, losing the original colors of Annato. 4. Conclusion Fabjan et al. [3] encapsulated an organic blue dye (b copper phthalocyanine) with silica using alkoxides as precursors. It has been shown that the silica shells obtained can serve as effective protection against the highly reactive products of photocatalysis (i.e. increasing photoreaction speed through a catalyst) [6]. In recent years, photocatalytically active materials have garnered interest for use in various applications, such as paints for the coating of surfaces that feature self-cleaning capabilities. This work has shown that protecting organic dyes (especially natural ones) via the sol-gel process should insulate them from the effects of weathering and allow them to be injected as masterbatches for use in polymers. However, the degree of protection achieved depended not only on the thickness of the silica shell, but also on its porosity. The compact (nonporous) layer of silica shells is intended, in that case, to prevent the penetration of photocatalysts. An analysis of the data obtained from the weathering test conducted in compliance with the ASTM D4459-
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12 standard reveals that encapsulation provided no color loss protection to the silica-encapsulated natural dyes. The encapsulated Turmeric die was the only one that showed better results, mainly after 310 h. The Carmine cochineal die had exhibited protection at the initial stages, but that was reversed after about 260 h. As such, the encapsulation of natural dyes on an alkoxide matrix does not protect them from weathering as they were expected to. We resorted to the work of Fabjan et al. [3] to indicate a few corrections to the synthesis of natural dyes that should be addressed in future works: preparation of stable dye dispersions: one must use cetyltrimethylammonium bromide (CTAB) at the optimum concentration in order to prepare solutions with disperse dyes that can lead to a well-defined inorganic layer around each pigment particle. For that end to be achieved, it is essential that the particles be well dispersed. There is a tendency for nanoparticles of the order of 100 nm or more to appear in agglomerates. Double encapsulation: After the encapsulation step (i.e. aging in oven at 50 C for 48 h), the material should be washed, filtrated and dispersed in a 10% CTAB solution, after which the synthesis step should be repeated at room temperature using TEOS (tetraethyl orthosilicate), hydrochloric acid (HCl) and Lewis acid
(aluminum trichloride) in the same proportions employed for the first synthesis. References xidos como precursores na síntese de novos materiais [1] Airoldi C, Farias RF. Alco s do processo sol-gel. Quím Nova 2004;27(1):84e8. atrave [2] Cardon D. Natural dyes, our global heritage of colours. Textile Society of America; 6e9 de Outubro de 2010 [ONLINE] Available at the website of the University of Nebraska, http://digitalcommons.unl.edu/cgi/viewcontent.cgi? article¼1011&context¼tsaconf [Accessed 15 January 2015]. [3] Fabjan ES, Skapin AS, Skrlep L, Zivec P, Ceh M, Gaberscek M. Protection of organic pigments against photocatalysis by encapsulation. J Sol-Gel Sci Technol 2012:65e74. psulas de bixina em [4] Lobato KB. Produç~ ao e avaliaç~ ao da estabilidade de nanoca ~o e aquecimento. Porto Alegre, RS, Brasil: sistemas modelo de fotossensitizaça UFRGS. ICTA; 2013. [5] Neiro, E.d., Nanni M. R., Romagnoli F., Campos R. M., Cezar E., Chicati M. L., & lise de cor para discriminaça ~o de seis variedades de Oliveira R. B. (2013). Ana pocas de colheita no ano. Anais XVI Simpo sio cana-de-açúcar em quatro e Brasileiro de Sensoriamento Remoto - SBSR, 13 a 18 de abril de 2013, (pp. 274e281). Foz do Iguaçu, PR. ^nea e sua aplicaç~ [6] Nogueira R, Jardim W. A fotocat alise heteroge ao ambiental. Quím Nova 1998;21:69e72. [7] Rodrigues P d. Estudo do uso de corantes artificiais em alimentos e estimativa ~o brasileira. Porto Alegre, RS, Brasil: de ingest~ ao de tartrazina pela populaça UFRGS. ICTA; 2015. ~o e estabilidade de [8] Silva GJ, Constant PB, Figueiredo RW, Moura SM. Formulaça corantes de antocianinas extraídas das cascas de jabuticaba (Myrciaria ssp). Alim Nutr Araraquara 2010;21(3):429e36. jul/set 2010 ISSN 0103e4235.