Application of Functionalized SWCNTs for Increase of Degradation Resistance of Acrylic Paint for Cars

Physical properties of automotive acrylic paint are improved by incorporation of three different types of carbon nanotubes: singlewall carbon nanotubes (SWCNTs), OH-functionalized single-wall carbon nanotubes (OH-SWCNTs), and aniline-functionalized single-wall carbon nanotubes (aniline-SWCNTs).e formed composites are studied by electronmiscroscopymethods and Raman spectrometry. It is found that the acrylic paints with addition of OH-SWCNTs and aniline-SWCNTs show better quality for their applications. In particular, the resistance against degradation by electron beam increased in ∼500%.


Introduction
Due to a wide variety of mechanical, thermal, and electric properties of the carbon nanotubes (CNTs), there are a host of their applications in the nanotechnology �elds, described in special technical reports [1], books [2][3][4][5], reviews [6][7][8], and original reports [9][10][11][12].Frequently, an addition of small quantities of CNTs into matrices of various materials frequently improve their properties [13,14].In this work, we studied the changes in the automotive acrylic paint caused by the incorporation of CNTs, in particular improvement of mechanical resistance and degradation.

CNTs Functionalization with
Anilines.e functionalized carbon nanotubes were prepared as follows.Carboxyl groups formation was reached by addition of commercial SWCNTs (0.05 g) to oleum (30 mL) in a Shlenk tube for 12 h at permanent stirring at r.t.under nitrogen atmosphere [15,16].en, the corresponding aniline (4-aminopyridine 1.1 g, 5-aminoisophthalic acid 2.43 g, p-anisidine 1.65 g) (Figure 1) was added, stirring the mixture for 30 min under nitrogen at r.t.sodium sul�te (0.92 g) and t-butyl peroxide (1.2 mL) were added to generate aryl-diazonium salt.
In order to achieve an interchange of formed -COOH groups by diazonium groups (−+ ≡ ) (Figure 2), the temperature was increased to 80 ○ C using an oil bath and maintained for 3 h at permanent stirring under nitrogen �ow.en, the reaction path was interrupted by cooling in ice.
In order to get a solid product, the �ltration equipment, shown in Figure 3, was used.e �lter was a polycarbonate      membrane of 0.45 m thickness.As a result, a black thin �lm of functionalized carbon nanotubes was obtained (Figure 4).A series of 15-min.washing procedures with distilled water, N,N-dimethylformamide and acetone was applied in the sonication e�uipment and further �ltration each time.e �nal product was dried in an oven at 200 ○ C for 5 h.e functionalized SWCNTs, obtained by this route, were used for incorporation into the matrix of the automotive acrylic paint.

Incorporation of CNT's into the Acrylic Paint.
Diverse paint-SWCNTs composites were prepared varying the percentage of incorporated SWCNTs via direct aggregation of nanotubes.e used nomenclature is shown in Table 1.
Applying the experiment design ANOVA (Varianza Analysis) of 3 factors, the experimental scheme indicated in Table 2 was  were carried out at r.t. and ambient pressure containing the following steps.
(1) Corresponding quantities of SWCNTs were weighed using recipients de 2 mL.
(3) 1 mL of the paint was added and sonicated for 5 min.
(4) Using a pistol connected to the air compressor, the formed composite was applied on the metallic surface (aluminium and steel).
(5) 20 min aer the application, the piece was subjected to a thermal treatment for drying at 200 ○ C for 5 h in the oven SL SHELLAB, M: 1400E.

Analysis of Carbon Nanotubes, Functionalized with
Organic Molecules (Aniline-SWCNT's).Figure 5 shows electron microscopy images of 4-aminopyridine-SWCNTs.As a result of functionalization, the unions are formed, which can be used for construction of cross-linkers due to supramolecular interactions of the SWCNTs aer being modi�ed with organic molecules.
In case of the SWCNTs, functionalized with aminoisophthalic acid, Figure 6(a) shows the sites, where the carbon nanotube can be connected with another one.is can be used for creation of a larger structural net, which serves as an enforcement for a polymer matrix.e arrows in Figure 6(b) show these sites, appreciated as small protuberances.Evidently, the nanotube reaches to be connected with another   one via action of organic molecules added during the functionalization process.Figure 7(a) shows a TEM image of the simple of panisidine-SWCNTs and an interaction of two nanotubes, whose result is the formation of a ring.e arrow shows the nanotube surface, where the functionalization takes place.e increase of tension of carbon "lines" on the nanotube surface causes the effect, that the p-anisidine-SWCNTs are transformed in ringes and arcs (Figure 7(b)).is tension could be attributed to the methoxy group (-O-CH 3 ) in the benzene ring.

Raman Spectroscopy Analysis of Functionalized Nanotubes.
Figure 8 shows Raman spectroscopy data of the functionalized SWCNTs and the G-band (peak at ∼1600 cm −1 ).For all functionalized samples, considerable changes, in comparison with nonfunctionalized SWCNTs, are observed in the ranges of ∼200-300 cm −1 and 1250-1370 cm −1 .

Analysis and Study of Composite Paints aer Incorporation of Carbon
Nanotubes.e main observations of composite paints, obtained by aggregation of SWCNTs to the conventional paint, are as follows.
(1) Via a visual inspection, it was determined that the SWCNTs presented a low level of homogenization in the acrylic paint.e color change, attributed to the SWCNTs presence, was practically absent.(2) e paint composite aer incorporation of OH-SWCNTs showed very high particle homogenization level due to the presence of OH-groups.e composite color was changed from white (original color of the paint) to obscure grey.
(3) High distribution of in the paint matrix increases the capacity of covering material surface of the paint up to 30%.Maintaining the quality of the paint layer, the best results were obtained with incorporation of OH-functionalized carbon nanotubes at 0.38 wt.%.
(4) In case of incorporation of anisidine-SWCNTs, a high homogenization level was reached, leading to increase of the capacity of covering material surface by the paint up to 30%.
(5) In case of drying process at 200 ○ C, it was determined that, in case of OH-SWCNTs and anisidine-SWCNTs, the composite paints possess a higher hardness and a rapid dissipation of temperature, compared with the original paint or the paint with incorporated nonfunctionalized nanotubes.
(6) e process of degradation of the paint using the electron �ow of 30 �� and evaluation of SEM and AFM images offer a criterion to determine possible changes of the structural morphology, expecting to �nd better matrix covering �17, 18].

ickness of the Final
Layer.e thic�ness of the �nal layer of the formed paint layer using additives of SWCNTs, OH-SWCNTs, and anisidine-SWCNTs are shown in Table 3. e medium magnitudes of 5 experimental data for each sample were calculated.

Fastness of ermal Dissipation
. e fastness of thermal dissipation was calculated in a temperature range 25 ÷ 180 ○ C per minute, approximately (Table 4 and Figure 9).e fastest dissipation was found in the paints, whose samples correspond to P1SWOH, for example, the major fastness 51.66 ○ C/min was observed for the sample P1SWOH4.
According to these results, it is recommended for industrial applications to use OH-SWCNTs due to the quality of thickness of the layer and the capacity of thermal dissipation.

AFM Analysis of the Automotive Paint with SWCNTs
Additives (for the Sample of P1SWFC5).e presence of nanocraters can inhibit the process of solar degradation, as well as the size of the protuberances caused by the OH-SWCNTs.e evaluated sample of P1SWFC5 is shown in Figure 10, where the effect of the CNTs on the modi�cation of relief of the paint aer its application to a material surface can be appreciated.It is expected that the protuberances impact development of the paint, increasing its life circle.

SEM Analysis of the Automotive Paint with SWCNTs
Additives (for the Sample of P1SWFC4).e aniline group -NH 2 , incorporated to the SWCNTs surface, possess high polarity and, together with OH groups, are most common functional groups in the automotive paint [19].For the samples, treated in the process 1 (heating of the paint, applied to the surface, at 200 ○ C, dried at 200 ○ C, the crystal formation was observed, maybe due to the presence of metal oxides.It is known that the automotive paints contain additives of metal oxides in order to improve some paint properties, for instance adherence.e composite of the anisidine-SWCNTs, incorporated to the matrix of the paint, was studied by SEM microscopy; the resulting image for the sample P1SWFC4 is shown in Figure 11.It is important to note that, aer the degradation via electron �ow, the formed crystals and the added anisidine-SWCNTs remain in the sample (the matrix is considerably degraded).

Relative Degradation via Electron Flow.
To evaluate matrix degradation and incorporation of SWCNTs to the paint, the samples were subjected to a related degradation via the electron �ow in the SEM microscopy, applying electrons of 30 kV. e results are presented in Table 5.
By incorporation of SWCNTs, the resistance of the resulting composite paint against degradation increases.e effect of the SWCNTs on the resistance of paints against degradation up to ∼500%, as it is shown in Figure 12.
It is important to comment that relative degradation of the composite was carried out in the similar conditions for all samples.As a result of degradation treatments, the SWCNTs are not destroyed by electron �ow, in a difference with the polymeric matrix of the paint.

Conclusions
It was established that via the functionalization of carbon nanotubes with aryl diazonium salts, the molecules with para (4-aminopiridine, p-anisidine) and meta (5aminoisophthalic acid) can be used.e presence of methoxy group in the benzene ring in p-position leads to the ring morphology of the functionalized SWCNTs.ese nanostructures can be applied for improvement of automotive paints.
On the basis of dispersion of SWCNTs in an organic solvent, it is possible the incorporation of SWCNTs, OH-SWCNTs, and anisidine-SWCNTs in automotive paint matrices.From the industrial point of view, the best properties of the paint are achieved by incorporation of OH-SWCNTs and anisidine-SWCNTs, in comparison with nonfunctionalized SWCNTs or functionalized with other molecules.
e effect of the OH-SWCNTs and anisidine-SWCNTs, being incorporated in a automotive paints, corresponds to the ∼500% higher resistance against degradation by electron �ow of 30 kV in comparison with the paint without incorporation of SWCNTs.
e incorporation of SWCNT�s modi�es the resulting paint color.In case of the OH-SWCNTs, the nanotubes are predominantly accommodated vertically in the paint applied in the surface (Figures 10 and 11).
It has been proved that physical properties of the composite paint can be considerably improved, leading to high capacity of the applied paint (ability to cover surfaces), fastness of thermal dissipation, high homogeneity in the paint matrix and, possibly, high probability of inhibition of solar degradation.e incorporation of OH-SWCNTs in the automotive paint was chosen as the best additive to improve its physical properties.

( 6 )
en, the paint on metallic sheets is subjected to degradation treatment.e characterization of SWCNTs samples was carried out in electron microscopy equipments TEM and SEM, as well as by Raman spectroscopy.e generated paint-SWCNTs NCT-A3-102910-022 Print mag: 3270000x @ 7 in 5 nm HV = 200 kV Direct mag: 500000x AMT camera system (a) (b) F 7: (a) TEM image of p-anisidine-SWCNTs, (b) SEM image of the sample, showing the formation of spiral-type rings and arcs.composites were studied by proofs of thermal dissipation (TRITEC sensor of external temperature Pt1000), thickness, surface morphology (AFM), and by relative degradation by electron �ow in SEM (model: FEI Nova NanoSEM 200).

F 9 :
Relation between the fastness of thermal dissipation and thickness of the �nal layer.

F 10 :F 11 :
AFM image of the P1SWFC5: (a) phase mode, (b) the protuberance width is 300 nm, height is 42.96 nm.SEM image of the sample P1SWOH4: (a) distribution of nanotubes in the matrix, (b) OH-SWCNTs aer degradation of the matrix via electron �ow (sample P1SWOH4).

F 12 :
�egradation of samples using the electron �ow of 30 kV.
T 1: Nomenclature of SWCNTs-acrylic paint composites, used in the present research.