Preparation and Research of Fiber Coatings with Self-cleaning and Self-healing Properties

Fiber is a common fabric in life, but it is easy to get stains during use

Since the fiber coating will wear or crack during long-term use, which will affect the appearance and performance, if the fiber coating can be repaired in time after damage, the service life can be extended

In order to obtain a fiber coating with both self-cleaning and self-repairing properties, a composite coating material with silicon-modified epoxy resin as matrix, modified nano-TiO2 as functional filler, and DA reaction as repair mechanism was proposed in this paper

1Experimental part

1.

1,3-bis(3-aminopropyl)tetramethyldisiloxane (APDS, purity>95%), glycidyl furfuryl ether (FGE, purity>96%): Shanghai Aladdin Biochemical Technology Co.

SYDC-100 dipping and pulling coating machine: Shanghai Sanyan Experimental Instrument Co.

1.

Weigh 4.

1.
3 Preparation of modified nano-TiO2

Preparation of amino-modified TiO2: take 5g of TiO2 in 100mL of ethanol, and sonicate for 30min, then take 0.
1g of KH550 and dissolve it in 30mL of water, mix it and place it at 70 °C for 6h reaction, centrifuge to obtain a precipitate, and wash with deionized water and ethanol each 3 times, and finally dried at 50 °C, and finally ground and pulverized to obtain modified nano-TiO2
.

Preparation of furan ring-modified TiO2: Take 1 g of the amino-modified powder into a conical flask, add 0.
28 g of FGE, and then add 10 g of DMF to help it disperse and dissolve, and place it in an oil bath at 90 °C for 6 h.
The mixture was taken out and centrifuged to obtain a precipitate and dried in an oven at 60°C
.

1.
4 Preparation of fiber coating

Quantities of silane-modified prepolymer/DMF solution (10 g), modified TiO (20.
377 g) and BMI (3.
415 g) were mixed in a beaker
.
The furan group and the maleimide group are measured according to the amount of the same substance
.
Coatings were prepared on the surfaces of different fibers (filter paper, cotton cloth, chemical fiber cloth) using a dip-pulling coating machine.
The pulling speed was 100 μm/s, and the curing conditions were 60 °C for 12 h
.

1.
5 Performance Test

Fourier transform infrared spectroscopy was used to test the chemical structures of silane-modified prepolymers and modified TiO2, and the reversibility of DA reaction; nuclear magnetic resonance spectroscopy was used to test the chemical structures of silane-modified prepolymers
.
Before the test, the silane-modified prepolymer should be dried in an oven at 60 °C until the solvent is completely evaporated
.

The relative molecular mass of the silane-modified prepolymer was tested by gel chromatography, and the prepolymer was completely dissolved in the solvent N-methylpyrrolidone
.

Thermogravimetric analyzer was used to characterize the thermal decomposition behavior of TiO2 samples before and after modification by FGE and KH550.
The test temperature was from room temperature to 800 °C, the heating rate was 10 °C/min, and the air atmosphere was used.
Scanning electron microscopy was used to observe the decomposition of different fiber coating samples.
Surface morphologies at the initial stage, after damage and after heating repair; the water contact angle of the fiber coating before and after physical wear, chemical damage and self-healing was measured by a contact angle meter; transmission electron microscopy was used to characterize FGE and KH550 modification.
The morphology and structure of TiO2 before and after denaturation were measured; the reflectance spectra of the fiber coating before and after pollution and before and after xenon lamp irradiation were measured by UV-Vis spectrophotometer
.

2  Results and Discussion

2.
1 Mechanism of coating preparation

The schematic diagram of coating preparation is shown in Figure 1
.

Fig.
1 Preparation method of coating for self-cleaning and self-healing fibers

As can be seen from Figure 1, firstly, a silane-modified prepolymer with a furan group at the end was synthesized by combining APDS and FGE
.
And use KH550 to carry out amino group grafting on the surface of nano-TiO2, and finally use FGE to carry out furan grafting on its end
.
The thermally induced self-healing fiber coating material was prepared by DA reaction between silane-modified prepolymer, modified TiO2 and maleimide group of BMI
.
The introduction of silane can reduce the surface tension of the coating, realize the hydrophobicity and improve the self-levelling behavior during heating; the modified TiO2 can promote the dispersion and realize the photodegradation of the fiber coating after pollution
.

2.
2 Characterization of prepolymer structure

Figure 2(a) is the infrared spectrum of the reaction of FGE and APDS for 0~12h, and Figure 2(b) is the H NMR spectrum of the silane-modified prepolymer
.

Fig.
2 Characterization of the reaction process of FGE and APDS

It can be seen from Figure 2(a) that the peak at 916cm-1 belongs to the characteristic peak of epoxy group, and the peak intensity gradually weakens, indicating that with the progress of the reaction, the number of epoxy on FGE gradually decreases, and it is grafted with APDS to form silane modification.
Sexual prepolymers
.
It can be seen from Figure 2(b) that δ=2.
48 belongs to the characteristic peak of methylene group, δ=3.
6 belongs to the -OH characteristic peak after the reaction between epoxy group and amino group, and δ=6.
37 and 7.
58 belong to furan group.
The characteristic peak, in which the peak area ratio of hydroxyl and furan groups is 0.
8334, gives the conversion of epoxy groups
.
From the above results, it can be seen that this method successfully prepared the silane-modified prepolymer
.

2.
3 Morphology and structure characterization of modified TiO2

The morphology, structure characterization and performance test results of modified TiO2 are shown in Figure 3
.

Fig.
3 Morphology, structure characterization and performance test results of modified TiO2

It can be seen from Figure 3(a) and (b) that the size of the modified TiO2 is 20~30nm, the dispersion is uniform, and there is no agglomeration
.
It can be seen from Figure 3(c) that the infrared spectra of TiO2 before and after modification have characteristic peaks at 500-700 cm-1, which are attributed to TiO2, and 1640 and 3430 cm-1, which are attributed to the —OH groups on the surface of TiO2
.
Compared with FGE-modified TiO2, after KH550 modification, the peak intensities of TiO2 and -OH were weakened, indicating that the hydroxyl groups on the surface of TiO2 reacted with KH550, and the -OH peak intensity was slightly enhanced after FGE modification, which may be due to The epoxy groups in FGE react with amino groups to form hydroxyl groups
.
It can be seen from the above results that KH550 and FGE were successfully grafted to the surface of TiO2
.
It can be seen from Figure 3(d) that the mass loss of TiO2 before modification below 500 °C is about 1.
1%, which is due to the evaporation of water
.
After modification by KH550, the mass loss was about 2% before 500 °C.
Compared with TiO2, the mass loss of KH550 changed, indicating that KH550 was successfully grafted to the surface of TiO2
.
After FGE modification, the mass loss was about 3.
4%, and the change in mass loss was caused by grafting FGE
.
It can be seen from the above results that KH550 and FGE were successfully grafted on the surface of TiO2
.

2.
4 Characterization of DA reversible behavior

Under low temperature conditions, the coating is cross-linked and cured, and reversible covalent bonds are formed, while under high temperature conditions, the covalent bonds will be broken.
In order to study the reversible changes, 60 °C curing and 150 °C heat treatment are adopted
.
Figure 4 shows the state of the mixture of silane-modified prepolymer and BMI, the mixture of modified TiO2 and BMI, and the mixture of silane-modified prepolymer, modified TiO2 and BMI heated at 150 °C for 10 min and cured at 60 °C for 1 h and corresponding infrared spectrum
.
Among them, the photos are the photos of the three samples before (left) and after (right) curing
.

Fig.
4 State and infrared spectra of different mixtures heated at 150℃ for 10min and cured at 60℃ for 1h

It can be seen from Figure 4 that the characteristic peak at 1774 cm-1 is attributed to the reversible covalent bond of DA.
After heating at 150 °C for 10 min, the peak intensity is weakened, indicating that the covalent bond is broken and a reverse DA reaction occurs
.
The characteristic peak at 1146cm-1 was attributed to the maleimide group, indicating that BMI was released after heating
.
Compared with the initial sample, after heating at 60 °C for 1 h, the characteristic peaks of DA reversible covalent bonds were significantly enhanced, and the characteristic peaks of maleimide were gradually weakened, indicating that DA reversible covalent bonds were regenerated to form a network structure
.
At the same time, the three samples showed good fluidity at 150 °C, but solidified at 60 °C and could not flow, which also proved the existence of DA reversible reaction
.

2.
5 Self-healing behavior of fiber coating

The filter paper, cotton cloth and chemical fiber cloth were immersed in the mixed solution of silane-modified prepolymer/DMF, modified TiO2 and BMI, respectively, and the coatings were covered on the surfaces of the three fibers by dipping and pulling method, and cured at 60 °C for 12 h.
The surface of the fiber was rubbed with 800-mesh sandpaper.
The SEM results of the three kinds of fiber cloths before and after rubbing and the heating repair with an electric iron are shown in Figure 5
.

Fig.
5 SEM images of filter paper, cotton cloth and fiber cloth with functional coating before and after grinding and repairing

It can be seen from Figure 5 that the three kinds of fiber cloths were seriously damaged after friction, and the water contact angle before and after friction decreased from about 120° to about 80°
.
Then, heating repaired with an electric iron.
Due to the reverse DA reaction, the silane-modified prepolymer that regained its exercise ability wetted the surface of the fiber and the fractured surface, and the water contact angle increased, indicating that the surface of the fiber still had hydrophobic properties after repair
.

The generation of hydrophilic groups on the surface of the coating was simulated by O2 plasma treatment, and then heated and repaired with an electric iron.
The change of the water contact angle of the cotton cloth coating is shown in Figure 6
.

Fig.
6 Changes of water contact angle of cotton cloth coating after multiple plasma treatments and electric iron heating repair

It can be seen from Figure 6 that the water contact angle drops to about 50°, indicating that the low surface energy structure produces hydrophilic properties after chemical etching, and then heated and repaired with an electric iron, the silane-modified prepolymer moves to the free surface again, making the fibers Again with hydrophobic properties
.
In order to study the washing resistance of the fiber coating, the cotton cloth coating was placed in the washing powder water and stirred for 7 days.
The results of the water contact angle change are shown in Figure 7
.

Fig.
7 Change of water contact angle of cotton cloth coating in washing powder water for 7 days

It can be seen from the results in Figure 7 that the water contact angle of the coating shows a decreasing trend, but the decrease is not large, and the hydrophobicity is always maintained, indicating that the cotton cloth coating has excellent water-washing resistance
.

2.
6 Self-cleaning behavior of fiber coating photodegradation

Figure 8 is the UV-Vis spectrum of the photodegradation of the fiber coating after being polluted by rhodamine B, methyl violet and fruit juice.
From left to right in the figure are the original coating, the coating after pollution, and irradiated by xenon lamp for 10min, 20min and 30min.
Photo of post coating
.

Fig.
8 UV-Vis spectra of fiber coatings after contamination with different pollutants and before and after photodegradation

It can be seen from Figure 8 that the contaminated surface was irradiated with a xenon lamp to simulate sunlight.
The results showed that after 30 minutes of irradiation with the xenon lamp, the pollutants disappeared, and the coating surface was not much different from that before the pollution
.
This is because the nano-TiO2 contained in the coating causes the pollutants to undergo photodegradation reaction under light conditions and decompose into small molecules, indicating that the coating can achieve self-cleaning by adding photocatalytic pollutants in addition to its hydrophobic properties
.
The photodegradation behavior of the coating after wear and heating repair was further studied.
The results are shown in Figure 9.
From left to right in the figure, the repaired coating and the methyl violet-contaminated coating after the repair were illuminated for 10min and 20min respectively.
, The photo of the coating after 30min
.

The results in Figure 9 show that the repaired coating still exhibits excellent photodegradation effect
.
This indicates that the coating also has the ability to repair its photocatalytic self-cleaning behavior
.

Fig.
9 UV-Vis spectrum of fiber coating after repair

3  Conclusion

In this study, a functional coating for fibers with hydrophobic-photocatalytic dual self-cleaning properties and self-healing ability under physical abrasion-chemical erosion was prepared
.
The coating is composed of silane-modified prepolymer, BMI and modified nano-TiO2, and can be coated on various fabrics such as filter paper, cotton cloth, and chemical fiber cloth
.
The introduction of silane in the silane-modified prepolymer enables the coating surface to have low surface energy and hydrophobic properties that can be recovered under chemical attack; the introduction of modified TiO2 endows the coating with a strong ability to photodegrade pollutants; and based on the DA reaction A reversible covalent bond is established between the silane-modified prepolymer and the modified TiO2, which can realize the self-repair of the coating's hydrophobicity and self-cleaning ability under physical wear
.
The coating helps to expand the application field of multifunctional smart fiber coatings
.

Source of this article: Issue 2 of "Coatings Industry" in 2022

Authors: Li Ling, Ma Yue, Fang Liang, Lu Chunhua, Xu Zhongzi