Research on Nano-ZnO/fluorine Polyacrylate Linen Fabric Finishing Agent

ABSTRACT

With nano-ZnO, methyl methacrylate (MMA), ethyl acrylate (EA), and dodecafluoroheptyl methacrylate (DFMA) as reaction monomers, potassium persulfate as initiator, nano-ZnO/fluorine polyacrylate linen fabric finishing agent was prepared by semi-continuous seed emulsion polymerization to improve the hydrophobicity and anti-fouling performance of linen fabric. The structure and properties of the film and the finished fabric were characterized and analyzed by¹HNMR, FT-IR, and TG. The results showed that the nano-ZnO/fluorine emulsion was successfully prepared with a particle size of about 46 nm, which was combined with linen. The contact angle of the finished linen fabric to water was 130.33°, which indicated that the finished linen fabric had good hydrophobicity. Meanwhile, the anti-fouling performance of the finished linen fabric was also improved. The introduction of nano-ZnO and organic fluorine in turn made linen fabric had the properties of the heat-resistant stability, UV resistance, antibacterial properties, and yellowing resistance.

摘要

以纳米氧化锌、甲基丙烯酸甲酯（MMA）、丙烯酸乙酯（EA）和甲基丙烯酸十二氟庚酯（DFMA）为反应单体，过硫酸钾为引发剂，采用半连续种子乳液聚合法制备了纳米氧化锌/氟聚丙烯酸酯亚麻织物整理剂，以提高亚麻织物的疏水性和防污性能. 通过1HNMR、FT-IR和TG对薄膜和成品织物的结构和性能进行了表征和分析. 结果表明，成功制备了粒径约为46 nm的纳米ZnO/氟离子乳液，并与亚麻布相结合. 亚麻织物与水的接触角为130.33°，表明亚麻织物具有良好的疏水性. 同时，成品亚麻织物的防污性能也得到了提高. 纳米氧化锌和有机氟的引入使亚麻织物具有耐热稳定性、抗紫外线、抗菌性和抗黄变性.

KEYWORDS:

• Nano-ZnO
• organic fluorine
• polyacrylate
• UV resistance
• hydrophobicity
• linen

关键词:

• 纳米ZnO
• 有机氟
• 聚丙烯酸酯
• 抗紫外线
• 疏水性
• 亚麻布

Introduction

With the intensification of environmental pollution, the ozone layer is destroyed, resulting in aggravation of the harmful ultraviolet rays. As the ozone layer is depleted by 1%, 2% of UV through the earth, which is likely to endanger human health (Abd El-Hady, Farouk, and Sharaf 2013; Diffey 1991; Ren et al. 2018). Generally, natural fabric can be used as an effective barrier against UV for the human body, but it tends to breed bacteria in a humid environment. Therefore, the finishing of fabric has become very important. The finishing can give textiles unique properties such as anti-ultraviolet, hydrophobic and antibacterial properties, among others (Norouzi, Gharehaghaji, and Montazer 2018; Xiong, Ren, and Liu 2020; Zhu et al. 2012). Polyacrylate has good film formation, gloss adhesion, and low price, and is often used as a finishing agent. However, polyacrylate has some disadvantages such as heat-adhesive and cold brittleness, poor water resistance, and thermal stability, which limits wide application in the textile field (Bao et al. 2015). Organic fluorine has excellent characteristics such as high surface activity, high heat stability, high chemical stability, water and oil repellency, etc. The modification of the physical properties of polyacrylate via the addition of organic fluorine to improve its application value (Huang, Meng, and Qing 2007; Tang, Huang, and Qing 2011; Yang et al. 2014; Zhang et al. 2017; Zhong et al. 2019).

Inorganic-organic composites have been widely studied for their good chemical and physical properties (Hsu et al. 2013; Shaban, Mohamed, and Abdallah 2018). Zhou et al. (2018) synthesized the core-shell nano-TiO₂/fluorinated polyacrylate emulsion by soap-free emulsion polymerization. The results show that the latex film has better thermal stability, mechanical properties, or UV shielding performance. The cotton fabric treated by composite emulsion has outstanding antibacterial and water-repellent properties because of the coarse surface of the film. Li et al. (2018) prepared fluorine-containing polyacrylate/silica composite coatings by in-situ polymerization. The results show that the prepared composite film has good hydrophobic properties and thermal stability, and still has high transparency in the visible light range.

Nano-ZnO is nontoxic, tasteless, remarkable thermal stability and ultraviolet shielding effect, as well as the effect of inhibiting bacterial reproduction and deodorizing (Shahidi et al. 2018). In addition, the characteristics of poor dispersion and easy agglomeration of nano-ZnO restrict its use.

In this paper, 3-(methacryloyloxy) propyltrimethoxysilane was employed to modify nano-ZnO to solve the agglomeration phenomenon of nano-ZnO. Double-bond surfaces of nano-ZnO that could participate in the polymerization reaction and be uniformly dispersed in the copolymer emulsion, thereby improving the stability of the emulsion. In this paper we propose a simple, green, and low-cost method for the preparation of multifunctional linen textiles. The inorganic nano-ZnO and fluorine-containing monomer (DFMA) were selected as functional raw materials to prepare a functional linen fabric finishing agent that was harmless to humans, and the linen fabric was finished. The influence of nano-ZnO and organic fluorine on the application performance of the linen fabric was discussed.

Experiment

Material

The sample is linen with a linear density of 45tex × 45tex. (warp and weft density is 228 pieces/10 cm × 161 pieces/10 cm).

Nano-ZnO (30 nm) and 3-(methacryloyloxy) propyltrimethoxysilane (KH-570) were supplied by Shanghai Aladdin Biochemical Technology Co., Ltd. Dodecafluoroheptyl methacrylate (DFMA) was purchased from Harbin Xuejia Fluorosilicone Chemical Co., Ltd. Ethyl acrylate (EA) and methyl methacrylate (MMA) were obtained from Tianjin Bodi Chemical Co., Ltd. Emulsifier OP-10 was offered by Tianjin Guangfu Fine Chemical Research Institute. Sodium dodecyl sulfate and potassium persulfate were produced from Tianjin Kaitong Chemical Reagent Co., Ltd. All the chemicals were used without further purification.

Preparation method and application

Modification of nano-ZnO

0.5 g of fully dried nano-ZnO was put into a beaker containing 80 g of water-anhydrous ethanol (m (water): m (anhydrous ethanol) = 1:3), and dispersed by step ultrasonic for 30 min. The dispersed suspension was transferred to a three-necked flask at 80°C, and then .1 g of KH-570 was added, followed by stirring and reacting for 2 h. After cooling to 40°C, modified nano-ZnO was washed with anhydrous ethanol and centrifuged for 3–5 times, and dried and preserved in the end.

Preparation of nano-ZnO/fluorine polyacrylate emulsion

The preemulsion was prepared by adding 2.88 g DFMA, 5.4 g EA, and 1.8 g MMA into a mixture of 0.138 g OP-10, .092 g SDS, and 10 g deionized water and dispersing ultrasonic for 30 min.

0.276 g OP-10, .184 g SDS, 40 g deionized water, 1.44 g modified nano-ZnO, 3.6 g EA, 3.6 g MMA were added to a four-necked flask with a thermometer, agitator, and reflux device, a small amount of sodium bicarbonate was ultrasonically dispersed for 30 min. Then, the K₂S₂O₈ solution (composed of .058 g of K₂S₂O₈ and 5 g of deionized water) was slowly added at 80°C for 30 min. The preemulsion and K₂S₂O₈ solution (composed of .115 g of K₂S₂O₈ and 10 g of deionized water) were added within 2–3 h, and the reaction was continued for 60 min. Finally, the mixture was cooled to 40°C and filtered by a 200-mesh sieve to obtain nano-ZnO/fluorine polyacrylate emulsion.

Linen fabric finishing process

The prepared nano-ZnO/fluorine polyacrylate emulsion (solid content of 25.59%) was used to treat the samples. After soaking the linen emulsion for 20–30 min, the excess solution was removed by the rolling mill. This operation was repeated 2 times so that the liquid was 75% of the fabric weight. Then, the samples were dried at 70°C for 5 min and cured at 120°C for 5 min.

Characterization and test

¹HNMR test analysis

The naturally dried latex film was taken and dissolved by CDCl₃. After the film was completely dissolved, ¹HNMR (BRUKER, USA) spectra were measured by the Avance superconducting nuclear magnetic resonance instrument.

Infrared spectrum analysis

The structure of the linen fabric before and after finishing was characterized by the Spectrum Fourier Infrared Spectrometer (Perkin Elmer, USA).

TEM and particle size analysis of composite emulsion

A right amount of composite emulsion was diluted 100 times with deionized water, and then the diluted liquid was dropped on the copper mesh and stained with phosphotungstic acid solution. After drying, the morphology of emulsion particles was observed under H-7650 transmission electron microscope (Hitachi, Japan). The particle size of the emulsion was measured by Zetasizer Nano ZS90 Nano particle size analyzer (Malvern Instruments Co., Ltd., UK).

EDS analysis of latex film

The distribution and content of elements on the film surface were measured by S-3400 scanning electron microscope (Hitachi, Japan).

Thermogravimetric (TG-DTG) analysis of fabrics

Linen fabric samples treated with polyacrylate emulsion, fluorine-containing polyacrylate emulsion and nano-ZnO/fluorine polyacrylate emulsion were investigated by TG/DTA-6000 thermogravimetric analyzer (PE, USA), respectively.

Water contact angle and stain resistance of fabrics

The linen fabric was finished with different fluorine content composite emulsions, and the contact angle of fabric was measured by JY-82B video contact angle tester (Chengde Dingsheng Testing Equipment Co., Ltd., China). After that, the linen fabric was fixed in the test tube containing solid dirt, and the test tube was turned over to make the fabric fully contact with the dirt. Simultaneously, the stained part of the fabric was observed, and the stain resistance grade of the fabric was assessed. Severe contamination of the fabric surface is level 1, large area pollution on the fabric surface is level 2, slight pollution on the fabric surface is level 3, small pollution area on the fabric surface is level 4, and the non-pollution on the fabric surface is level 5.

UV absorption performance test of fabrics

The linen fabric was finished by composite emulsion with different nano-ZnO contents, and conducted by YG (B) 912E textile anti-ultraviolet performance tester.

Antibacterial performance test

The nano-ZnO/fluorine polyacrylate emulsion was dripped on the filter paper and the finished fabric, and its antibacterial performance was tested after drying (Escherichia coli).

Results and discussion

¹HNMR analysis of latex film

Figure 1 shows the¹HNMR spectrum of nano-ZnO/fluorine polyacrylate latex film。

Figure 1. ¹HNMR spectrum of the latex film.

As can be seen from Figure 1, the absorption peaks at δ: 1.52 (-CH₂-), δ: 4.5 (-OCH₂CF₂-), and δ: 5.5 (-CHF₂) were produced by hydrogen atoms in DFMA. δ: 1.2 (-CH₃), δ: 3.6 (-OCH₃), δ: 1.8 (-CH₂-CH₂-CO-), δ: 2.2 (-CH₂-CH₂-CO-), δ: 4.0 (-O-CH₂-CH₂-CH₃), δ: 1.3 (-O-CH₂-CH₂-CH₃), δ: .9 (-CH₂-CH₂-CH₃) were generated from hydrogen in acrylate monomers. The peak at δ:.0 was generated by Si-CH₂- and unhydrolyzed Si-OCH₃ in KH-570. Thus, it can be confirmed that both organic fluorine and KH-570 modified nano-ZnO have polymerized with other acrylic monomers to form nano-ZnO/fluorine polyacrylate emulsion.

FT-IR analysis

FT-IR curves of the linen fabric before and after the nano-ZnO/fluorine polyacrylate emulsion finishes are shown in Figure 2, where a is the linen fabric, and b is the finished linen fabric.

Figure 2. FT-IR curve of linen (a) and treated linen (b).

As can be seen from Figure 2, the O-H stretching vibration peak in the linen fabric was at 3337.63 cm⁻¹. Compared to curve a, the characteristic peaks at 2959.94 cm⁻¹ and 2876 cm⁻¹ in curve b are the C-H stretching vibration absorption peaks in -CH₃ and -CH₂-, respectively. Similarly, the peak at 1451.03 cm⁻¹ is the absorption peak of C-H in -OCH₃ of MMA, and the peak at 1160.67 cm⁻¹ is the characteristic peak of C-O in EA. Notably, there was a peak at 1730.23 cm⁻¹ due to the stretching vibration absorption peak of C=O. While the absorption peak at 1239.73 cm⁻¹ and 743.02 cm⁻¹ attribute to stretching vibrations of C-F and -CF₂CF₃. The curve b had a weak peak for Si-O at 1112.01 cm⁻¹. The stretching vibration peak of at C=C (1638 cm⁻¹) disappeared in spectra. In summary, nano-ZnO/fluorine polyacrylate emulsion had been finished on flax fabric, in agreement with¹HNMR analysis.

TEM analysis of emulsion

Figure 3 displays the TEM picture of the prepared composite emulsion diluted 100 times (×200000 times).

Figure 3. TEM images of composite emulsion particle (×200000 times).

The particles of nano-ZnO/fluorine polyacrylate emulsion prepared had obvious core-shell structure, and the core-shell region had obvious color difference is shown in Figure 3. Specifically, the brighter center area of the particle was a nano-ZnO-polyacrylate core, and the surrounding darker area was a fluorine-containing polyacrylate shell. Furthermore, it can be seen that the surface of emulsion particles was smooth and spherical, and the distribution was relatively uniform without cluster. This phenomenon showed that the reaction process was stable and the modified nano-ZnO overcame the agglomeration. The particle size of the emulsion measured by a nanoparticle size analyzer was nanoscale, and its average particle size was 46 nm. To some extent, the high gloss of the film depended on the small particle size. The emulsion with small particle size has good fluidity, which is beneficial to penetrate into the fiber gap of the fabric and improve the surface properties of flax fiber. In conclusion, the prepared nano-ZnO/fluorinated polyacrylate emulsion was a good fabric finishing agent with good dilution stability and excellent film-forming performance.

EDS analysis on both surfaces of latex film

Energy dispersive spectrometer (EDS) can qualitatively and quantitatively analyze the types and contents of elements in the micro-zone of the material. It is usually used in conjunction with a scanning electron microscope to analyze the point, line, and surface distribution of the elements on the surface of the material. The surface distribution (EDS-Mapping) analysis was performed on the two interfaces of the latex film dried at room temperature. As presented in Figure 4(a, b), the distribution of F, Si, and Zn elements is distributed at the two interfaces of nano-ZnO/fluorinated polyacrylate latex film. Meanwhile, Figure 4(c, d) presents the distribution curve of each element content at the two interfaces of nano-ZnO/fluorinated polyacrylate latex film. Among them, (a) is the latex film–air interface, and (b) is the latex film–glass interface. In addition, the migration of F and Si chain segments in the film formation process of nano-ZnO/fluorinated polyacrylate emulsion is shown in Figure 5.

Figure 4. Distribution of F, Si and Zn elements of latex film–air interface (a) and latex film–glass interface (b), element content of of latex film–air interface (c) and latex film–glass interface (d).

Figure 5. Film formation process of emlusion.

Figure 4(a, b) showed the F, Si elements and Zn dots all appeared in the plane. These elements were uniformly distributed on the two interfaces of the latex film, which means that F, Si and Zn elements were enriched on the surface of the film. At the same time, the F and Si elements at the latex film–air interface were 2.321% and .557% times higher than those at the latex film–glass interface (Figure 4(c, d)). During the formation of the film, more F and Si elements migrated to the air surface, reducing the surface energy of the latex film and endowing the surface with better self-cleaning properties, as shown in Figure 5. The synergistic migration of F and Si side segments under the influence of polarity occurs due to the accumulation and solidification of the main segment during the film formation. Thus, the latex film has excellent hydrophobic properties because most of the silicone-chain segments are oriented to the latex membrane–air interface migration arrangement, leading to a large number of fluorine and silicon elements enriched on the outer surface.

Thermogravimetric analysis of fabrics

Figure 6 is respectively the TG and DTG curves of linen fabric. Table 1 is the comparison table of thermal decomposition temperature of linen fabric, where a is the linen fabric finished with polyacrylate emulsion, b is the linen fabric finished with fluorine-containing polyacrylate emulsion and c is the linen fabric finished with nano-ZnO/fluorine polyacrylate emulsion.

Figure 6. TG-DTG curve of polyacrylate linen (a), F-polyacrylate linen (b) and nano-ZnO/F-polyacrylate linen (c).

Table 1. Comparison of thermal decomposition temperature of linen fabric.

Flax type	Initial decomposition temperature (℃)	Maximum decomposition temperature (℃)	End temperature (℃)
a	308.68	384.04	429.68
b	319.58	39.58	434.58
c	328.08	398.06	436.18

From Figure 6 and Table 1, the linen fabric finished with nano-ZnO/fluorinated polyacrylate emulsion had good thermal stability. Compared with the linen fabric finished with polyacrylate emulsion, the initial decomposition temperature, and maximum thermal decomposition temperature were increased by 19.4°C and 14.02°C, respectively. The reason is that during the curing process of emulsion on the surface of linen fabric, the fluorine-containing chain segment migrates and enriches to the surface of the film. Likewise, the bond energy of the C-F bond is very large, up to 485 kJ/mol, which can play a significant protective role in the main chain. Apart from that, inorganic nano-ZnO has high surface energy and good thermal stability. Here, the crosslinking density of the copolymer is increased, and the thermal stability of the linen fabric is further improved.

Water contact angle and stain resistance of fabrics

Figure 7 individually shows the test results of the contact angle to water after finishing linen fabrics with composite emulsions of different fluorine content.

Figure 7. The contact angle to water of finished linen fabrics.

The results of the evaluation of the stain resistance of the fabric showed that the better the stain resistance result of the fabric was the presence of high fluorine content. The highest evaluation results (Grade 4) were obtained when the fluorine content was 20% or 25%. According to Figure 7, the water contact angle of the finished fabric was gradually increased with increasing fluorine. Since the composite emulsion forms a film on the surface of the linen fabric, the fluorine-containing segment with low surface energy weakens the critical surface tension of the fabric surface, improving hydrophobicity and stain resistance When the organic fluorine content in the composite emulsion was 20% and 25%, the contact angle of the linen fabric to water after finishing was 130.33°and 133.12°, respectively, the stain resistance grade was the same. It seemed that the 20% fluorine content on the surface of the fabric was saturated, and further addition of fluorine had no effect on the improvement of contact angle and stain resistance. In other words, the fluorine-containing fabric had better hydrophobic properties compared with non-fluorine fabric. This was ascribed to the excellent hydrophobic properties imparted to the fabric by the fluorine finish.

Anti-ultraviolet performance test of fabrics

The ultraviolet part of sunlight is harmful to human body, especially the far ultraviolet UVB (280–315 nm) is more dangerous than the near ultraviolet UVA (315–400 nm) (De Gruijl 2002; Jones et al. 1987; Kappes et al. 2006). Long-term exposure can cause allergic and chronic reactions in the human body, causing skin melanization and cancer. Figure 8 demonstrates the results of anti-ultraviolet performance of linen fabrics finished by nano-ZnO composite emulsions with different contents.

Figure 8. Ultraviolet resistance of linen fabric.

As shown in Figure 8, by increasing the content of nano-ZnO from 0% to 1%, the UV resistance of fabrics increased gradually with the decrease of fabric transmittance through increased content of nano-ZnO. The UV transmittance of the finished fabric decreased by about 11%. Due to the surface effect and quantum size effect of nano-ZnO, and the selected nano-ZnO particle size is less than 50 nm. The wide band gap has good UV shielding efficiency for far ultraviolet UVB and near ultraviolet UVA, which can give linen fabric good UV protection performance. As expected, the UV resistance is the best when the nano-ZnO content is 1.0%. Compared to the linen fabric, the linen fabric after the nano-ZnO/fluorine polyacrylate emulsion finishing had good UV resistance. The finishing agent of UV resistance may be attributed to that nano-ZnO is wrapped in the emulsion, thereby improving the UV resistance of linen fabric.

Antibacterial performance test

The results of the antibacterial experiment against Escherichia coli, in which (a) is a filter paper, (b) is a linen fabric, (c) is a filter paper containing a finishing agent, and (d) is a finished linen fabric in Figure 9.

Figure 9. Antibacterial test results.

It can be seen from Figure 9(a, b) that none of the samples had obvious antibacterial effect with covered Escherichia coli. However, when Escherichia coli was disappeared, an inhibition zone was formed around the sample with obvious antibacterial effect in (c) and (d). It is a peculiar surface effect in the emulsion on account of the unique structure of nano-ZnO. Nano-ZnO can decompose free-moving electrons on the surface while absorbing external energy. Then, a positively charged hole is left, the hydroxyl electron in the environment is taken over to generate a hydroxyl radical after the electron transitions. Chemically active hydroxyl radicals can react with a variety of organic compounds, including Escherichia coli. Hence, the bacteria were killed, forming the inhibition zone that gave the filter paper and fabric bacteriostatic properties. In summary, due to the existence of nano-ZnO, the finishing agent was endowed with antibacterial properties, and the growth of Escherichia coli was inhibited by the finished linen fabric.

Conclusion

In this work, the core-shell nano-ZnO/fluorine polyacrylate emulsion was prepared by semi-continuous seed emulsion polymerization. Evidenced by¹HNMR and FT-IR results, the modified nano-ZnO, organic fluorine, and acrylic monomers all participated in the polymerization reaction. TEM confirmed that the average particle size of the prepared composite emulsion was about 46 nm, and the emulsion good stability was good. XPS showed that the chains containing fluorine and silicon would migrate to the air interface, which reduced the critical surface tension of the fabric surface and improved the hydrophobic and anti-fouling properties of the fabric during the film forming process. When the fluorine content was 20%, the contact angle of the finished fabric to water was 130.33°, and the anti-fouling performance was grade 4. TG showed that the introduction of nano-ZnO and organic fluorine effectively contributed to the thermal stability of the fabric, and the maximum thermal decomposition temperature increased by about 14.02°C. The anti-ultraviolet performance and antibacterial performance results illustrated that the linen fabric good UV shielding effect and excellent antibacterial properties by nano-ZnO. More interestingly, the wearability and added value of the fabrics were improved.

Highlights

• Multifunctional linen fabric finishing agent was prepared by semicontinuous seed emulsion method.

• The maximum hydrophobic angle of finished linen fabric is 130.33°.

• After the addition of nano-ZnO linen fabric has excellent UV resistance, and also has good antibacterial properties for Escherichia coli.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The research is financially supported by “Fundamental Research Business Expenses of Universities in Heilongjiang Province” under grant 145209509.