Preparation of Toddalia asiatica (L.) Lam. Extract Microcapsules and Their Effect on Optical, Mechanical and Antibacterial Performance of Waterborne Topcoat Paint Films
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Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Nanjing Forestry University, Nanjing 210037, China
2
College of Furnishings and Industrial Design, Nanjing Forestry University, Nanjing 210037, China
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Author to whom correspondence should be addressed.
Coatings 2024, 14(6), 655; https://doi.org/10.3390/coatings14060655
Submission received: 22 March 2024
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Revised: 6 May 2024
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Accepted: 17 May 2024
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Published: 22 May 2024
(This article belongs to the Special Issue Multilayer and Functional Graded Coatings—2nd Edition)
Abstract
:The antibacterial microcapsules were prepared by encapsulating Toddalia asiatica (L.) Lam. extracts with urea–formaldehyde resin. The orthogonal test was designed to investigate the effects of the mass ratio of core and wall materials (Wcore:Wwall), emulsifier concentration, reaction temperature and reaction time on the yield rate and coverage rate of microcapsules, and to obtain the best preparation technology for microcapsules. The single-factor results indicated that the maximum influence factor was the Wcore:Wwall of the microcapsules; the larger the Wcore:Wwall, the easier the microcapsules were to agglomerate; and when the Wcore:Wwall was 0.8:1, the coverage rate reached the maximum value of 11.0%. The waterborne topcoat paint film was prepared by adding the microcapsules in the same content. The yield rate, coverage rate, and microscopic morphology of Toddalia asiatica (L.) Lam. extract microcapsules were analyzed, as well as the effects of microcapsules on the microscopic morphology, optical properties, cold liquid resistance, mechanical properties and antibacterial properties of a waterborne topcoat paint film. Combining the optical properties, cold liquid resistance, physical properties, and antibacterial properties of the waterborne topcoat paint film, the comprehensive performance of the waterborne topcoat paint film with the Wcore:Wwall of 0.8:1 was superior. The gloss was 8.07 GU, color difference ΔE was 9.21, visible light transmittance was 82.90%, resistance to citric acid, ethanol and detergent were grade 1, 2 and 2, respectively, elongation at break was 15.68%, and roughness was 3.407 µm. The antibacterial activity against Escherichia coli and Staphylococcus aureus were 42.82% and 46.05%, respectively. In this study, a waterborne topcoat paint film with a microcapsule-coated plant-derived antibacterial agent as the core was prepared, expanding the application prospect of plant-derived antibacterial microcapsules.
1. Introduction
With the continuous promotion of carbon neutrality policies, green, low-carbon, environmentally protective, and healthy lifestyles have gradually become hot topics of concern [1,2,3,4]. As an environmentally friendly coating, waterborne paint films use water as a dispersant medium and have advantages such as their use of sustainable raw materials and in terms of green environmental protection [5,6,7,8]. In daily life, furniture surfaces are highly susceptible to the erosion of bacteria and other microorganisms, leading to a decrease in service life [9,10,11]. Therefore, it is particularly important to improve the antibacterial properties of waterborne paint films [12,13].
Microencapsulation is a technology that utilizes natural or synthetic polymer materials to encapsulate solids, liquids, and gases to form microencapsulated particles [14,15,16]. The encapsulation process allows bioactive substances to maintain their original physical state, enhance stability, reduce volatility, and prolong shelf-life. It also has targeting, slow-release, and controlled release functionality. Therefore, it has a wide range of applications and research value in many fields, such as medicine, food, textiles, cosmetics, and coatings [17,18,19]. Huang et al. investigated the effect of urea–formaldehyde resin coated aloe–emodin microcapsules on the antibacterial performance of water-based coatings, demonstrating the practicality of microcapsule technology in antibacterial paint films [20]. Roshan et al. prepared chitosan-based nanoencapsulated Toddalia asiatica essential oil (neTAEO). It was confirmed that neTAEO exhibited stronger antifungal and aflatoxin B1 inhibitory activities than the essential oil of Toddalia asiatica (L.) Lam. and was more promising [21]. However, most research on the application of Toddalia asiatica (L.) Lam. extract is distributed in the field of medicine, while less research has been conducted on waterborne topcoat paint films for the surfaces of furniture [22,23].
Plant-derived antibacterial agents are natural, green, and environmentally friendly materials with advantages relating to their wide availability, renewability, and biodegradability. Toddalia asiatica (L.) Lam. is used in traditional Chinese medicine [24,25,26]. Its roots, bark, leaves, and other parts have high medicinal value, and its chemical composition contains alkaloids, coumarins, triterpenoids, and flavonoids with antibacterial activity, which have good antibacterial properties against Staphylococcus aureus and Escherichia coli [27,28]. Toddalia asiatica (L.) Lam. is a natural plant-derived antibacterial agent, which is a green and environmentally friendly material. It was found that Candida albicans erythrocyanidins isolated from the root of Toddalia asiatica (L.) Lam. showed strong antibacterial activity against Gram-positive bacteria, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and extended-spectrum β-lactamase Staphylococcus aureus. The lowest inhibitory concentration against all three bacteria was 0.156 mg/mL [29]. Raj et al. utilized hexyl hydride, trichloromethane, ethyl acetate, methanol, and water sequentially in the extraction of the active constituents from Toddalia asiatica (L.) Lam. leaves, and the results showed that the extracts exhibited antimicrobial activity against selected bacteria and fungi [30]. The Toddalia asiatica (L.) Lam. extract microcapsules were prepared through the use of microencapsulation technology and they were added to a waterborne topcoat paint film. It maintained the stability of the substrate, improved antimicrobial efficacy, and reduced environmental pollution, as well as other advantages [31,32]. The innovation of this paper is the extended application research of Toddalia asiatica (L.) Lam. extracts in the field of waterborne paint films. The original optical properties, cold liquid resistance, and mechanical properties of the waterborne topcoat paint film were maintained, which improved the antimicrobial properties and broadened the application range of waterborne paint films.
In this paper, microcapsules of urea–formaldehyde resin-coated Toddalia asiatica (L.) Lam. extracts were prepared, and the four-factor, three-level orthogonal test was designed to derive the optimal preparation process of microcapsules [33]. The waterborne topcoat paint film was obtained by adding the microcapsules to the waterborne topcoat at the same content. The microscopic morphology, optical properties, mechanical properties, and antibacterial properties against Staphylococcus aureus and Escherichia coli of the Toddalia asiatica (L.) Lam. extract microcapsules on the properties of the waterborne topcoat paint film were investigated, broadening the prospects of the application of antibacterial microcapsules of plant origin [34].
2. Test Materials and Methods
2.1. Experimental Materials
The leaves of Toddalia asiatica (L.) Lam. were procured from Qinzhou, Guangxi Province, China. The paint film used is the waterborne acrylic topcoat, sourced from Jiangsu Himonia Technology Co., Ltd., Zhenjiang, China. The leaves were dried in an oven at 40 °C until reaching constant weight, pulverized into powder, sieved through a 60-mesh sieve, and stored in sealed opaque glass bottles. The size of the silicone mold for the preparation of the waterborne topcoat paint film was 50 mm × 50 mm × 10 mm, and the size of the glass substrate was 25 mm × 75 mm × 10 mm. The test materials and the apparatus are shown in Table 1 and Table 2.
2.2. Preparation of Microcapsules
2.2.1. Preparation Process of Microcapsules
For the preparation of the wall material prepolymers, 10.00 g of urea and 16.22 g of formaldehyde were weighed in a beaker according to a molar ratio of 1:1.2, and a magnetic stirrer was added. The beaker was placed in a water bath with a speed of 600 rpm and a temperature of 70 °C, and the mixture was mixed well. The appropriate amount of triethanolamine was added to adjust the pH value of the mixed solution to 9, and the reaction was conducted for 1 h to make a urea–formaldehyde prepolymer solution.
For the emulsification of the core material, the leaf powder and anhydrous ethanol were mixed in the glass bottle at a 1:15 ratio by mass into a beaker. The beaker was placed in a thermostatic water bath for 120 min at 60 °C. The extract was centrifuged in a centrifuge at 4000 rpm for 10 min, and the filtrate was filtered with a vacuum pump and a Büchner funnel. The filtrate was rotary evaporated and dried to obtain the solid extracts [35]. The deionized water and sodium dodecylbenzene sulfonate were weighed according to the quantity, and an emulsifier solution with a concentration of 2.0% was prepared. The prepared emulsifier was added dropwise to the extracts of Toddalia asiatica (L.) Lam., the emulsification was carried out at a temperature of 50 °C and a rotational speed of 600 rpm for 45 min to obtain a uniformly dispersed core material solution.
For the preparation of urea–formaldehyde resin-coated Toddalia asiatica (L.) Lam. extracts microcapsules, the temperature of the water bath was set to 60 °C at a speed of 600 rpm. A dropper was used to suck up the prepolymer solution to drop into the core emulsion. A mass fraction of 10% of citric acid monohydrate solution was added to adjust the pH value of the solution to 3. The mixture was microencapsulated in the water bath for 2 h, cooled at room temperature and let stand for 48 h. The product was rinsed by repeated filtration with distilled water and anhydrous ethanol, and the microcapsules were obtained by drying the product in an oven at 60 °C for 24 h.
2.2.2. Orthogonal Test Design of Microcapsules
The main factors affecting the preparation of Toddalia asiatica (L.) Lam. extract microcapsules were the Wcore:Wwall, emulsifier concentration, reaction temperature and reaction time (Table 3). The arrangement of the orthogonal test is shown in Table 4 and Table 5, and the schedule of the single-factor test is shown in Table 6.
2.3. Preparation of the Waterborne Topcoat Paint Film
The microcapsules were added to the waterborne topcoat acrylic paint with a content of about 5.0% and mixed well to obtain 1.0 g of the waterborne topcoat paint film. The waterborne topcoat paint film was evenly coated in a silicone mold, leveled at room temperature for 20 min, then placed in the baking oven at temperature of 55 °C for 30 min, and taken out when the quality of the waterborne topcoat paint film was constant.
2.4. Testing and Characterization
2.4.1. Characterization of Microcapsules
(1) Concerning the coverage rate, the mass of microcapsules was weighed (M1), fully ground and soaked in the ethanol for 24 h, then placed in the water bath at 50 °C for 2 h. The mass of the filter paper was recorded as M2, and then the soaked product was rinsed for filtration to complete the filtration. The filter paper and the wet blank were placed in an oven at 60 °C and dried until the constant weight mass was unchanged. After drying, the overall mass of the filter paper and the wall material was weighed as M3.
C = (M1 + M2 − M3)/M1
(2) Concerning the yield rate, Formula (2) represents the calculation method for microcapsule yield rate, where Y is the yield rate of microcapsules, m2 is the mass of microcapsules, and m1 is the sum of the masses of the core material, wall material, and emulsifier used to prepare the microcapsules of the sample.
Y = m2/m1
(3) Concerning microstructure and chemical composition analysis, the morphology of the microcapsules was observed using a Zeiss optical microscope (OM), and the microcapsules and the waterborne topcoat paint films were analyzed with scanning electron microscope (SEM). The chemical composition of the microcapsules and the prepared the waterborne topcoat paint film were analyzed through the use of Fourier-Transform Infrared Spectroscopy (FTIR).
2.4.2. Color Difference Test
According to GB/T 11186.3-1989 [36], the color difference of the waterborne topcoat paint film was measured and recorded using a SEGT-J colorimeter and the color difference was calculated. The L value is the brightness difference of the waterborne topcoat paint film. The a value is the red–green difference of the waterborne topcoat paint film. The b value is the yellow–blue difference of the waterborne topcoat paint film. Three places on the pure paint film were measured to obtain the average values of L1, a1, and b1. Then, three places on the paint film were measured to obtain another set of data: L2, a2, and b2. The pure paint film was used as a reference sample, and the ΔE of the waterborne topcoat paint film with microcapsules was calculated using the color difference Formula (3).
ΔE = [(ΔL)2 + (Δa)2 + (Δb)2]1/2
2.4.3. Gloss Test
According to GB/T 9754-2007 [37], the gloss value of the waterborne topcoat paint film was tested and recorded at three incidence angles of 20°, 60° and 85° by using the HG268 gloss meter, and the unit of the test is GU.
2.4.4. Transmittance Test
Transmittance is the ability of light to pass through a sample, and the percentage of the luminous flux passing through the sample to incident luminous flux is the transmittance of the waterborne topcoat paint film. A UV spectrophotometer was used to compute the transmittance of the waterborne topcoat paint film in the visible band (350–780 nm).
2.4.5. Roughness and Tensile Test
A J8-4C roughness tester was used to test and record the roughness value. The sample was placed on the test table, and the down button was adjusted to move the test probe. The roughness value unit is µm.
Using silicone molds for curing and demolding of the waterborne topcoat paint film, the two ends of the waterborne topcoat paint film were clamped with the fixture of the universal mechanical testing machine. The waterborne topcoat paint film was elongated at a stretching speed of 0.5 mm/min until it broke, at which time the stretching stopped. The calculation method for the elongation at break of the waterborne topcoat paint film is shown in Formula (4), where e represents the elongation at break of the waterborne topcoat paint film at the point of fracture, L1 is the original length of the sample, and L is the length at fracture.
e = (L − L1)/L1 × 100%
2.4.6. Cold Liquid Resistance Test
Based on the cold liquid resistance determination method specified in GB/T 4893.1-2021 [38], the corrosion resistance of the furniture surface to liquids was evaluated. Citric acid solution (mass fraction of 10%), undenatured ethanol (volume fraction of 96%), and detergent prepared with deionized water were selected as the test liquids. A 26 mm diameter filter paper saturated with the test liquid was put on the surface of the test piece, and a glass Petri dish was used to cover the test piece. After 24 h, the filter paper piece was removed, and the glass Petri dish was removed and placed for another 18 h. The test surface was dried, and the damage was examined under the specified light conditions, and the results of the test were evaluated by the grades indicated using numbers.
2.4.7. Antibacterial Properties Test
The test operation was carried out according to the method of determining the antibacterial properties of waterborne topcoat paint films specified in GB/T 21866-2008 [39]. Firstly, live Escherichia coli (ATCC25922) and Staphylococcus aureus (ACTT6538) bacteria were used. The plate agar medium was prepared by weighing 24 g of agar medium with 1000 mL of distilled water, which was then sterilized. The slant-preserved strains were inoculated onto the plate agar medium and placed in a box with constant temperature and humidity, with a relative temperature of 38 °C for 18–20 h.
Next, the desired bacterial suspension was prepared. For this, 9.0 g of nutrient broth and 500 mL of distilled water were weighed and sterilized. Then, 1–2 rings of fresh bacteria were scraped off from the live bacterial agar medium using an inoculation ring added to the nutrient broth. Then, the bacterial suspension was diluted with sterilized nutrient broth to a concentration of 106 Cfu/mL and set aside.
Finally, the sample test was carried out. For this, 0.5 mL of the test bacterial suspension was added to the surface of the waterborne topcoat paint film and control group, respectively. The surface of the test piece was covered with sterilized plastic film using sterilized tweezers, ensuring that the bacterial suspension was dispersed on the surface of the test piece and without air bubbles. The sample was placed in a sterilized Petri dish and transferred to the box with constant temperature and humidity for 24 h; the constant temperature and humidity box was 38 °C, and the relative humidity was RH > 90%. After 24 h, the cultured samples were taken out and rinsed repeatedly with 20 mL eluent. The rinsing solution was taken and inoculated into nutrient agar medium, which was placed in the box with constant temperature and humidity with a relative temperature of 38 °C for 48 h, and the resulting agar medium was recovered. Based on GB/T 4789.2-2022 [40], the number of colonies in the medium was determined and recorded using a colony counter, and the number of colonies was multiplied by 1000 as the actual value of colonies recovered after 48 h of incubation for each sample. The formula used for the antibacterial rate is shown in Formula (5), where R denotes the antibacterial rate in %, B denotes the average number of colonies recovered after 48 h of the pure paint film samples in CFU/piece, and C denotes the average number of bacteria recovered after 48 h of the waterborne topcoat paint film samples in CFU/piece.
R = (B − C)/B × 100%
3. Results and Discussion
3.1. Analysis of Microencapsulation Preparation
3.1.1. Analysis of Microencapsulation Yield Rate and Coverage Rate
Table 7 shows the results of the yield rate obtained through orthogonal tests. The microcapsule yield rate is an important influencing factor when evaluating the microcapsule preparation process. Among the nine sets of microcapsule samples in the orthogonal test, sample 2# had the highest yield rate of 61.75%, followed by sample 4# with a 60.94% yield rate and sample 6# with a 60.60% yield. From the polar results shown in Table 7, the effect of reaction temperature on microcapsule yield rate was the most significant. For the yield rate of microcapsules, the main level of the factors affecting the preparation process was C > A > D > B, and the best preparation process was A2 B2 C2 D2. Table 8 shows the analysis table of the variance results of the yield; the variance results of the four factors were the same as the extreme variance results, and the four influencing factors were not significant.
The coverage rate is the mass ratio of the core material to microcapsules, which is used to evaluate the core material content and is an important factor affecting the antibacterial influence of microcapsules. Table 9 shows the results of the orthogonal test results of the microcapsule coverage rate analysis. From the extremely different results, it can be concluded that the four factors were A > B > C = D, and the greatest impact on the coverage rate was factor A (Wcore:Wwall). From the variance results shown in Table 10, it can be concluded that the optimal preparation process was A1 B2 C3 D1, and the better preparation process parameters of microcapsules were as follows: Wcore:Wwall was 0.6:1, the concentration of the emulsifier was 2.0%, the temperature was 70 °C, and the time was 1 h.
The single-factor test was designed to combine the better preparation process parameters of yield rate and coverage rate from the orthogonal test. Wcore:Wwall, which had a large influence on the synthesis, was set as the variable, and the three factors of emulsifier concentration, reaction temperature, and reaction time were set as fixed factors for the single-factor test. Table 11 shows the yield rate and coverage rate in the single-factor test. The highest yield rate of 62.67% was obtained for sample 10#, and the highest coverage rate of 11.0% was obtained for 12#. As the Wcore:Wwall of the microcapsules gradually increased, the yield rate gradually decreased, and the coverage rate showed a tendency of first improving and then reducing. The reason for analyzing such a change in the coverage rate was that as the mass of the core material increased, the concentration of the emulsifier was constant. There will be a situation in which part of the core material is not fully emulsified, and thus, the uncoated core material will be washed out in the process of pumping and filtration.
3.1.2. Analysis of Microscopic Morphology
In the microscopic diagrams of the microcapsules from the orthogonal tests shown in Figure 1, A–I corresponds to microcapsule samples 1#–9#. The nine groups of microcapsule samples were successfully prepared, and there were differences in their morphology. According to the principle of light diffraction, due to the different absorption and reflection effects of light by the core and wall materials, an obvious microcapsule shell–core structure can be seen, with the inner white layer as the core material and the ring-shaped dark material as the wall material. Among them, 1#, 3#, 5#, and 7# microcapsules had a small amount of agglomeration, while 2#, 4#, 6#, 8#, and 9# microcapsules were more dispersed and homogeneous with less agglomeration. The morphology was similar to a round shape and had a clear shell–core structure.
Figure 2 shows the microscope diagram of the microcapsules in the single-factor test. The 10#–14# microcapsule samples were dispersed more uniformly with better morphology. With increasing Wcore:Wwall, microcapsule agglomeration gradually increased. There was greater agglomeration seen in the 14# sample microcapsules, and Wcore:Wwall was 1.2:1; therefore, it can be concluded that the microcapsule core is not conducive to the dispersal of microcapsules in excessive amounts.
Figure 3 shows the scanning electron microscope images of microcapsules in the case of the single-factor test. Figure 3A–E show the morphology of the microcapsule samples of samples 10#–14# under a 3000× microscope, and Figure 3F–J show the morphology of the microcapsules under a 5000× microscope. It can be seen that the microcapsules with a Wcore:Wwall of 0.4:1 have fewer spheres and larger gaps in particle size. The microcapsules with a Wcore:Wwall of 0.6:1 had more spheres and were more rounded, with a smaller gap in particle size, and the microcapsules with a Wcore:Wwall of 0.8:1 had spheres that were rounded and had a full volume and had a more uniform distribution of particle sizes, but with more serious agglomerations; and the microcapsules with a Wcore:Wwall of 1:1 had varying particle sizes and a small amount of irregularly shaped aggregated substances. The microcapsules with a Wcore:Wwall of 1.2:1 had different particle sizes, and a few irregularly shaped aggregated substances were present. The microcapsules prepared with a Wcore:Wwall of 1.2:1 had large pieces of adherent and irregularly shaped substances, and the particle size of the microcapsules was relatively small. From Figure 3, it can be seen that with the increasing Wcore:Wwall of microcapsules, the agglomeration phenomenon of microcapsules is continuously strengthened.
3.1.3. Analysis of Chemical Composition of Microcapsules
The infrared spectra of the core, wall, and microcapsules is shown in Figure 4. The chemical constituents in the Toddalia asiatica (L.) Lam. are mainly coumarin-like compounds and alkaloids. The absorption peaks appearing at 3350 cm−1 were the C-O of the core material as well as the telescopic vibration peaks of -NH and -OH of the wall material [41]. The 1639 cm−1 and 1550 cm−1 were the characteristic peaks of C=O and C=N in the urea–formaldehyde resin, respectively. The absorption peak at 1247 cm−1 was the characteristic peak of C=O and C=N in the urea–formaldehyde resin. The absorption peaks were caused by the stretching vibration of C-N and N-H in the urea–formaldehyde resin, indicating the presence of urea–formaldehyde resin chemistry in the microcapsules [42]. The characteristic peaks of C=N and C-O in coumarin analogs in the core material were at 1600 cm−1 and 1110 cm−1 [43], which exist in the absorption curves of the microcapsules, but the absorption peaks were weak, proving the presence of core material Toddalia asiatica (L.) Lam. extracts in microcapsules. This was due to the lower content of the core material and lower coverage rate, thus the characteristic peaks of the core extract were weaker. The above indicates that the microcapsules contain the characteristic peaks of core material and wall material, which proves that the microcapsules had been successfully encapsulated.
3.2. Analysis of the Waterborne Topcoat Paint Film Properties
3.2.1. Analysis of the Waterborne Topcoat Paint Film on Microscopic Morphology and Chemical Composition
The microscopic morphology of the waterborne topcoat paint film prepared with different core–wall ratios of the microcapsules under the content of 5.0% in Figure 5. The surface of the waterborne topcoat paint film without added microcapsules is flat and smooth, and the waterborne topcoat paint film prepared by adding microcapsules with the Wcore:Wwall of 0.4:1 and 0.6:1 had a small number of bumps and folds, which was due to the fact that the microcapsules of the samples 10# and 11# have fewer agglomerates, and thus can be dispersed uniformly in the waterborne topcoat paint film. The waterborne topcoat paint film containing microcapsules with the Wcore:Wwall of 0.8:1, 1:1, 1.2:1, respectively, had poor flatness and a large number of agglomerated bumps. This was due to the fact that the microcapsules of samples 12#, 13# and 14# were more agglomerated, leading to uneven dispersion of microcapsules during the addition of waterborne topcoat paint film.
Figure 6 shows the infrared spectra of the waterborne topcoat paint film with added microcapsules and a pure paint film. The absorption peak at 1729 cm−1 shown in the figure is the absorption peak of C=O in the waterborne topcoat paint film [44]. The 1639 cm−1, 2924 cm−1, and 1144 cm−1 peaks were the telescopic vibration peaks of C=O, -CH3, and C-O-C, respectively, in the urea–formaldehyde resin of the microcapsule wall material. The absorption peak of C-O in the core material of the microcapsule was 1114 cm−1 [45]. It was proven that after the microcapsules were added to the waterborne topcoat paint film, the microcapsule wall and core components still existed without chemical reaction.
3.2.2. Microcapsules on the Optical Properties of the Waterborne Topcoat Paint Film
The waterborne topcoat paint film had glossy optical characteristics on the surface of the paint film, which was expressed in terms of the specular reflection ability of the surface of the waterborne topcoat paint film to light [46]. The effect of Wcore:Wwall on the gloss of the waterborne topcoat paint film is shown in Table 12. From the surface gloss measured at three incidence angles of 20°, 60°, and 85°, as shown in Figure 7, it can be seen that the addition of microcapsules will greatly reduce the gloss itself. Under the same addition content of 5.0%, with the increasing Wcore:Wwall of the microcapsules, the gloss showed an overall trend of improving and then declining. When the Wcore:Wwall of the microcapsules was 0.8:1, the gloss of the waterborne topcoat paint film reached maximum values at three incidence angles of 2.47 GU, 8.07 GU, and 2.10 GU, respectively. This is because the unevenness of the waterborne topcoat paint film with microcapsules increases the surface microscopic roughness, increasing the scattering of light and thereby reducing the gloss of the film.
The chromaticity and color difference of the waterborne topcoat paint film are shown in Table 13. The color difference is an important index when characterizing the decorative properties of the paint film. Figure 8 shows that in the same added content, with an increasing addition of Wcore:Wwall, the L value of the waterborne topcoat paint film showed a downward trend, the a value of the waterborne topcoat paint film first rose and then fell, the b value of the waterborne topcoat paint film showed a rising trend, and the overall color difference of the waterborne topcoat paint film showed a fluctuating trend. In the case of sample 12#, the color difference reached a minimum value of 9.21; at this time, the Wcore:Wwall was 0.8:1. In the case of sample 13#, the color difference reached a maximum value of 13.07 when the Wcore:Wwall was 1:1. The core material content of samples 10#, 11#, and 12# was less; therefore, the color of the microcapsule was lighter than that of samples 13# and 14#. The microcapsules of samples 13# and 14# were more dispersed, and the L value of the waterborne topcoat paint film was higher; the a value and b value were relatively low, and the color difference value was smaller. After the preparation of samples 13# and 14#, waterborne topcoat paint film flatness was poor, the core material content was high, and the microcapsules were light yellow in color. The brightness value of the waterborne topcoat paint film was lower, and the yellow–blue value and the red–green value were relatively high; therefore, the obtained color difference value was larger.
Figure 9 shows the effect of the microcapsules on the light transmittance of the waterborne topcoat paint film [47]. The light transmittance without microcapsules was much higher than that of the waterborne topcoat paint film with microcapsules. The waterborne topcoat paint film with microcapsules was less flat and rougher, which makes the incident light neither transmit nor reflect; instead, it dissipates in the form of scattering, decreasing the transmittance of the waterborne topcoat paint film. The increased core–wall ratio showed a descending trend in terms of the light transmittance of the waterborne topcoat paint film with microcapsules. This is because that with the increasing Wcore:Wwall, the microcapsule agglomeration phenomenon continues to increase, resulting in the unevenness of the waterborne topcoat paint film surface, which reduces the transmission and reflection of the incident light and reduces light transmittance.
3.2.3. Effect of Microcapsules on the Cold Liquid Resistance of the Waterborne Topcoat Paint Film
The cold liquid resistance of the waterborne topcoat paint film is an important expression of the surface properties of a paint film [48]. Table 14 shows the cold liquid resistance grades of the waterborne topcoat paint film with core-to-wall microcapsule ratios. With the increasing Wcore:Wwall ratios of microcapsules in the waterborne topcoat paint film, the cold liquid resistance of the waterborne topcoat paint film gradually improved, and the increase in the detergent-resistant grade was particularly significant. Compared with the waterborne topcoat paint film without microcapsules, the liquid resistance of the waterborne topcoat paint film with microcapsules to citric acid was 1; it had good acid resistance. The ethanol resistance level of the waterborne topcoat paint film with microcapsules was 2, and changes can be observed when the light source was irradiated on the surface of the waterborne topcoat paint film, and the ethanol resistance level was improved compared with that of the waterborne topcoat paint film. When the microcapsules of samples 10#, 11#, and 12# were added, the detergent resistance of the waterborne topcoat paint film was grade 2. When the microcapsules of samples 13# and 14# were added, the detergent resistance of the waterborne topcoat paint film was grade 1, and the area under test was basically unchanged from the area before the test. This is because that the added microcapsules protect the waterborne topcoat paint film from the erosion of detergents. Therefore, in combination with the data shown in Table 14, when the Wcore:Wwall of the microcapsules added in the waterborne topcoat paint film were 1:1 and 1.2:1, the prepared waterborne topcoat paint film had the optimal cold liquid resistance.
3.2.4. Effect of Microcapsules on the Mechanical Properties of the Waterborne Topcoat Paint Film
The elongation at break of the waterborne topcoat paint film is used to judge whether the paint film has good ductility and toughness. From Table 15, it can be observed that the elongation at break of the waterborne topcoat paint film without added microcapsules was higher, while the waterborne topcoat paint film with microcapsules reduced the tensile properties and elongation at break. As the Wcore:Wwall of the microcapsules increased, the elongation at break of the waterborne topcoat paint film tended to increase and then decrease. When the microcapsules of sample 12# were added, the elongation at break of the waterborne topcoat paint film reached a maximum value of 15.68%; at this time, the Wcore:Wwall was 0.8:1. This is because the microcapsules added to the waterborne topcoat paint film reduced the ductility, and the hardness and brittleness of the waterborne topcoat paint film were enhanced; therefore, the tensile properties of the waterborne topcoat paint film and the ability to resist rupture were reduced [49], and the service life of the waterborne topcoat paint film was shortened to a certain extent.
The roughness had a certain influence on the decorative and aesthetic properties of the waterborne topcoat paint film. Table 15 shows the roughness of the waterborne topcoat paint film with different Wcore:Wwall microcapsule ratios. It can be seen that the Wcore:Wwall and the roughness value of the waterborne topcoat paint film were positively correlated. This is because as the Wcore:Wwall of the microcapsules increases, the agglomeration phenomenon becomes more and more serious, leading to the uneven dispersion of the microcapsules in the waterborne topcoat paint film; therefore, the roughness value of the waterborne topcoat paint film continues to increase.
3.2.5. Effect of Microcapsules on the Antibacterial Performance of the Waterborne Topcoat Paint Films
Table 16 shows the antibacterial rate of the waterborne topcoat paint film with different Wcore:Wwall ratios on the surface of glass substrates. Compared with the pure paint film without added microcapsules, the average number of viable bacteria recovered from the surface of the waterborne topcoat paint film with added microcapsules was significantly reduced, proving that the prepared waterborne topcoat paint film had an inhibitory effect on the growth of both bacteria. Figure 10 shows the trends of the antibacterial rate of the waterborne topcoat paint film with added microcapsules against Escherichia coli and Staphylococcus aureus. It can be seen that the antibacterial rate of the waterborne topcoat paint film with Wcore:Wwall increases, and the antibacterial rate of the waterborne topcoat paint film against Escherichia coli first decreased, then increased and then decreased. With a Wcore:Wwall ratio of 0.8:1, the antibacterial rate of Escherichia coli reached a maximum value of 42.82%, with a minimum value of 37.07%, and the Wcore:Wwall at this time was 1.2:1. This is because when the Wcore:Wwall ratio was 1.2:1, the microcapsule agglomerates are significantly unevenly dispersed in the waterborne topcoat paint film, thus reducing the slow-release effect of the core antibacterial agent. The antibacterial rate of the waterborne topcoat paint film against Staphylococcus aureus showed a tendency to increase and then decrease with an increasing Wcore:Wwall ratio. A maximum value was obtained 46.05% when the Wcore:Wwall ratio was 0.8:1. The minimum value of 34.10% when the Wcore:Wwall was 0.4:1. This is due to the fact that the microcapsule core with a Wcore:Wwall ratio of 0.4:1 has less content, and less antibacterial agent can be slow-released; therefore, the antibacterial rate of the waterborne topcoat paint film is lower. As can be seen in Figure 10, on the whole, the antibacterial rate of the waterborne topcoat paint film against Staphylococcus aureus was higher than that against Escherichia coli. This is due to the effective antibacterial component, coumarin analogs, in the Toddalia asiatica (L.) Lam. extracts of the core material, which has a higher antibacterial effect on Staphylococcus aureus than on Escherichia coli [50,51]. Therefore, the prepared antibacterial varnish achieved the maximum antibacterial rate against both Escherichia coli and Staphylococcus aureus when the Wcore:Wwall ratio was 0.8:1 (Sample 12#). The volatility of the standard deviations of the antimicrobial rates of the two bacteria was low, and the data were informative.
4. Conclusions
Using urea–formaldehyde resin as the wall material and Toddalia asiatica (L.) Lam. extracts as the core material, microcapsules were prepared and subsequently optimized through the use of four-factor three-level orthogonal tests. The largest factor affecting the coverage rate of microcapsules was the Wcore:Wwall ratio. Under the premise of the same additive content, with increasing Wcore:Wwall ratio in the waterborne topcoat paint film, the gloss of the surface of the prepared waterborne topcoat paint film showed an overall trend of increasing and then decreasing, and the gloss of the surface of the waterborne topcoat paint film reached a maximum value of 8.07 GU when the Wcore:Wwall ratio was 0.8:1. With increasing Wcore:Wwall, the color difference of the waterborne topcoat paint film fluctuated, and reached a minimum value of 9.21 when the Wcore:Wwall ratio of the microcapsules was 0.8:1. The light transmittance of the waterborne topcoat paint film was negatively correlated with the Wcore:Wwall ratio, and the light transmittance of the waterborne topcoat paint film was the highest when the Wcore:Wwall ratio of the added microcapsules was 0.4:1, which was 84.1%. The cold liquid resistance of the waterborne topcoat paint film was gradually improved with the increase in the Wcore:Wwall ratio of the added microcapsule, and the liquid resistance level was increased from level 4 to level 1. The elongation at break of the waterborne topcoat paint film reached a maximum value of 15.68% when the Wcore:Wwall ratio of the added microcapsules was 0.8:1. The roughness value of the waterborne topcoat paint film and the Wcore:Wwall ratio were positively correlated. When the Wcore:Wwall ratio was 0.8:1, the antibacterial rate of the prepared waterborne topcoat paint film against Escherichia coli and Staphylococcus aureus reached their maximum values: 42.82% and 46.05%, respectively. The waterborne paint film containing microcapsules had preliminary antibacterial properties, and the mechanical properties and cold liquid resistance of the waterborne topcoat paint film improved; the optical properties compared with the expected results were poor. However, the comprehensive performance of the waterborne topcoat paint film was excellent, laying the foundation for the subsequent application of waterborne topcoat paint films on wood. Due to the complex composition of the extract, it is also necessary to isolate and purify the main antibacterial components and prepare antibacterial microcapsules with excellent performance so as to improve the antibacterial performance of waterborne topcoat paint films.
Author Contributions
Conceptualization, methodology, validation, resources, data management, writing—review and editing and supervision, Y.W.; formal analysis, investigation, X.Y. All authors have read and agreed to the published version of the manuscript.
Funding
This project was partly supported by the Postgraduate Research and Practice Innovation Program of Jiangsu Province (SJCX23_0324) and the Natural Science Foundation of Jiangsu Province (BK20201386).
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Data are contained within the article.
Conflicts of Interest
The authors declare that there is no conflicts of interest.
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Figure 1.
Microscopic images of microcapsules under the orthogonal test: (A) 1#, (B) 2#, (C) 3#, (D) 4#, (E) 5#, (F) 6#, (G) 7#, (H) 8#, and (I) 9#.
Figure 1.
Microscopic images of microcapsules under the orthogonal test: (A) 1#, (B) 2#, (C) 3#, (D) 4#, (E) 5#, (F) 6#, (G) 7#, (H) 8#, and (I) 9#.
Figure 2.
Microscopic images of microcapsules under the single-factor test: (A) 10#, (B) 11#, (C) 12#, (D) 13#, and (E) 14#.
Figure 2.
Microscopic images of microcapsules under the single-factor test: (A) 10#, (B) 11#, (C) 12#, (D) 13#, and (E) 14#.
Figure 3.
SEM images of microcapsules prepared with different ratios of core to wall: (A) 10# under 3000×, (B) 11# under 3000×, (C) 12# under 3000×, (D) 13# under 3000×, (E) 14# under 3000×, (F) 10# under 5000×, (G) 11# under 5000×, (H) 12# under 5000×, (I) 13# under 5000×, and (J) 14# under 5000×.
Figure 3.
SEM images of microcapsules prepared with different ratios of core to wall: (A) 10# under 3000×, (B) 11# under 3000×, (C) 12# under 3000×, (D) 13# under 3000×, (E) 14# under 3000×, (F) 10# under 5000×, (G) 11# under 5000×, (H) 12# under 5000×, (I) 13# under 5000×, and (J) 14# under 5000×.
Figure 4.
Infrared spectra of microcapsules.
Figure 5.
SEM images of the waterborne topcoat paint films prepared by microcapsules with different core-to-wall ratios and 5.0% added content: (A) the waterborne topcoat paint film without added microcapsules, (B) 10 #, (C) 11#, (D) 12#, (E) 13#. (F) 14#.
Figure 5.
SEM images of the waterborne topcoat paint films prepared by microcapsules with different core-to-wall ratios and 5.0% added content: (A) the waterborne topcoat paint film without added microcapsules, (B) 10 #, (C) 11#, (D) 12#, (E) 13#. (F) 14#.
Figure 6.
Infrared spectrum of the waterborne topcoat paint film.
Figure 7.
The effect of microcapsule on the gloss of the waterborne topcoat paint film.
Figure 8.
The chromaticity and color difference of the waterborne topcoat paint film: (A) L value, (B) a value, (C) b value, and (D) ΔE value.
Figure 8.
The chromaticity and color difference of the waterborne topcoat paint film: (A) L value, (B) a value, (C) b value, and (D) ΔE value.
Figure 9.
The microcapsule on the transmittance of the waterborne topcoat paint film.
Figure 10.
The antibacterial rate of the waterborne topcoat paint film of microcapsules with different Wcore:Wwall.
Figure 10.
The antibacterial rate of the waterborne topcoat paint film of microcapsules with different Wcore:Wwall.
Table 1.
Details of the test materials.
| Material | Specification | Manufacturer |
|---|---|---|
| Urea | AR | Sinopharm Chemical Reagent Co., Ltd., Shanghai, China |
| 37% Formaldehyde | AR | Xilong Science Co., Ltd., Shantou, China |
| Triethanolamine | AR | Tianjin Zhiyuan Chemical Reagent Co., Ltd., Tianjin, China |
| Citric acid monohydrate | AR | Sinopharm Chemical Reagent Co., Ltd., Shanghai, China |
| Sodium dodecylbenzene sulfonate | AR | Tianjin Juhengda Chemical Co., Ltd., Tianjin, China |
| Anhydrous ethanol | AR | Wuxi Jingke Chemical Co., Ltd., Wuxi, China |
| Nutrient agar medium | - | GuangDong Zhongshan Baike Microbiotechnology Co., Ltd., ZhongShan, China |
| Nutrient broth medium | - | Hangzhou Microbiology Reagent Co., Ltd., Hangzhou, China |
| Sodium chloride | AR | Sinopharm Chemical Reagent Co., Ltd., Shanghai, China |
| Staphylococcus aureus | - | Beijing Bio-Care Biotechnology Co., Ltd., Beijing, China |
| Escherichia coli | - | Beijing Bio-Care Biotechnology Co., Ltd., Beijing, China |
| Detergent | Guangzhou Liby Enterprise Group Co., Ltd., Guangzhou, China |
Table 2.
Details of the test instruments.
| Device | Specification | Manufacturer |
|---|---|---|
| Thermostatic heating magnetic stirrer | DF-101S | Shanghai Qiuzuo Scientific Instrument Co., Ltd., Shanghai, China |
| Suction filter | SHZ-D (Ⅲ) | Shanghai Qiuzuo Scientific Instrument Co., Ltd., Shanghai, China |
| Drying box | DHG-9240A | Shanghai Aozhen Instrument Manufacturing Co., Ltd., Shanghai, China |
| Scanning electron microscope | Quanta-200 | Thermo Fisher Scientific, Massachusetts, United States |
| Zeiss optical microscope | AX10 | Carl Zeiss AG, Oberkochen, Germany |
| Infrared spectrometer | VERTEX 80V | Brucker AG, Karlsruhe, Germany |
| Glossmeter | HG268 | Shenzhen San’enshi Technology Co., Ltd., Shenzhen, China |
| Colorimeter | SEGT-J | Zhuhai Tianchuang Instrument Co., Ltd., Zhuhai, China |
| Ultraviolet spectrophotometer | U-3900/3900H | Hitachi Instruments (Suzhou) Co., Ltd., Suzhou, China |
| Roughness meter | J8-4C | Shanghai Taiming Optical Instrument Co., Ltd., Shanghai, China |
| Universal mechanical testing machine | AG-IC10OKN | Kyoto Shimadzu Production Institute, Kyoto, Japan |
| Constant temperature and humidity incubator | HWS-80 | Zhejiang Lichen Instrument Technology Co., Ltd., Zhejiang, China |
| High speed centrifuge | LC-LX-HR185C | Zhejiang Lichen Instrument Technology Co., Ltd., Zhejiang, China |
| Colony counter | XK97-A | MingGuang GuangJulong Experimental Equipment Business Department, MingGuang, China |
Table 3.
The orthogonal test factors and levels.
| Level | Wcore:Wwall | Emulsifier Concentration (%) | Temperature (°C) | Time (h) |
|---|---|---|---|---|
| 1 | 0.6:1 | 1 | 50 | 1.0 |
| 2 | 0.8:1 | 2 | 60 | 1.5 |
| 3 | 1:1 | 3 | 70 | 2.0 |
Table 4.
The orthogonal test schedule.
| Sample (#) | Wcore:Wwall | Emulsifier Concentration (%) | Temperature (°C) | Time (h) |
|---|---|---|---|---|
| 1 | 0.6:1 | 1 | 50 | 1.0 |
| 2 | 0.6:1 | 2 | 60 | 1.5 |
| 3 | 0.6:1 | 3 | 70 | 2.0 |
| 4 | 0.8:1 | 1 | 60 | 2.0 |
| 5 | 0.8:1 | 2 | 70 | 1.0 |
| 6 | 0.8:1 | 3 | 50 | 1.5 |
| 7 | 1:1 | 1 | 70 | 1.5 |
| 8 | 1:1 | 2 | 50 | 2.0 |
| 9 | 1:1 | 3 | 60 | 1.0 |
Table 5.
Material table for orthogonal tests.
| Sample (#) | Urea (g) | 37% Formaldehyde (g) | Ethanol (g) | Extracts of Toddalia asiatica (L.) Lam. (g) | Emulsifier (g) | Deionized Water (g) |
|---|---|---|---|---|---|---|
| 1 | 10.00 | 16.22 | 9.41 | 0.19 | 1.04 | 102.96 |
| 2 | 10.00 | 16.22 | 9.41 | 0.19 | 1.04 | 50.96 |
| 3 | 10.00 | 16.22 | 9.41 | 0.19 | 1.04 | 33.63 |
| 4 | 10.00 | 16.22 | 12.54 | 0.26 | 1.43 | 141.57 |
| 5 | 10.00 | 16.22 | 12.54 | 0.26 | 1.43 | 70.07 |
| 6 | 10.00 | 16.22 | 12.54 | 0.26 | 1.43 | 46.24 |
| 7 | 10.00 | 16.22 | 15.68 | 0.32 | 1.76 | 174.24 |
| 8 | 10.00 | 16.22 | 15.68 | 0.32 | 1.76 | 86.24 |
| 9 | 10.00 | 16.22 | 15.68 | 0.32 | 1.76 | 56.91 |
Table 6.
Material table for single-factor test.
| Sample (#) | Urea (g) | 37% Formaldehyde (g) | Ethanol (g) | Extracts of Toddalia asiatica (L.) Lam. (g) | Emulsifier (g) | Deionized Water (g) |
|---|---|---|---|---|---|---|
| 10 | 10.00 | 16.22 | 0.13 | 6.27 | 0.72 | 35.28 |
| 11 | 10.00 | 16.22 | 0.19 | 9.41 | 1.04 | 50.96 |
| 12 | 10.00 | 16.22 | 0.26 | 12.54 | 1.43 | 70.07 |
| 13 | 10.00 | 16.22 | 0.32 | 15.68 | 1.76 | 86.24 |
| 14 | 10.00 | 16.22 | 0.38 | 18.82 | 2.09 | 102.41 |
Table 7.
Analysis of orthogonal test microcapsule yield rates.
| Sample (#) | Factor A Wcore:Wwall | Factor B Emulsifier Concentration (%) | Factor C Temperature (°C) | Factor D Time (h) | Yield Rate (%) | Standard Deviation |
|---|---|---|---|---|---|---|
| 1 | 0.6:1 | 1 | 50 | 1.0 | 56.53 | 0.7 |
| 2 | 0.6:1 | 2 | 60 | 1.5 | 61.75 | 0.5 |
| 3 | 0.6:1 | 3 | 70 | 2.0 | 52.18 | 1.5 |
| 4 | 0.8:1 | 1 | 60 | 2.0 | 60.94 | 1.3 |
| 5 | 0.8:1 | 2 | 70 | 1.0 | 58.85 | 1.2 |
| 6 | 0.8:1 | 3 | 50 | 1.5 | 60.60 | 1.5 |
| 7 | 1:1 | 1 | 70 | 1.5 | 56.03 | 1.3 |
| 8 | 1:1 | 2 | 50 | 2.0 | 57.69 | 1.4 |
| 9 | 1:1 | 3 | 60 | 1.0 | 58.52 | 1.9 |
| Mean 1 | 56.820 | 57.833 | 58.273 | 57.967 | ||
| Mean 2 | 60.130 | 59.430 | 60.403 | 59.460 | ||
| Mean 3 | 57.413 | 57.100 | 55.687 | 56.937 | ||
| Range | 3.310 | 2.330 | 4.716 | 2.523 | ||
| Factor primary and secondary levels | C > A > D > B | |||||
| Optimal decision | A2 B2 C2 D2 | |||||
Table 8.
Analysis of variance for yield rate results.
| Factors | Sum of Squared Deviations | Degrees of Freedom | Fratio | Fcritical Value | Significance |
|---|---|---|---|---|---|
| A | 18.688 | 2 | 1.063 | 4.460 | |
| B | 8.516 | 2 | 0.484 | 4.460 | |
| C | 33.475 | 2 | 1.904 | 4.460 | |
| D | 9.658 | 2 | 0.549 | 4.460 | |
| Error | 70.34 | 8 |
Table 9.
Analysis of orthogonal test coverage rate.
| Sample (#) | Factor A Wcore:Wwall | Factor B Emulsifier Concentration (%) | Factor C Temperature (°C) | Factor D Time (h) | Coverage Rate (%) | Standard Deviation |
|---|---|---|---|---|---|---|
| 1 | 0.6:1 | 1 | 50 | 1.0 | 11.0 | 0.8 |
| 2 | 0.6:1 | 2 | 60 | 1.5 | 14.0 | 1.2 |
| 3 | 0.6:1 | 3 | 70 | 2.0 | 10.0 | 0.8 |
| 4 | 0.8:1 | 1 | 60 | 2.0 | 6.0 | 1.3 |
| 5 | 0.8:1 | 2 | 70 | 1.0 | 10.0 | 0.9 |
| 6 | 0.8:1 | 3 | 50 | 1.5 | 5.0 | 0.8 |
| 7 | 1:1 | 1 | 70 | 1.5 | 7.0 | 0.7 |
| 8 | 1:1 | 2 | 50 | 2.0 | 8.0 | 0.3 |
| 9 | 1:1 | 3 | 60 | 1.0 | 6.0 | 1.1 |
| Mean 1 | 11.667 | 8.000 | 8.000 | 9.000 | ||
| Mean 2 | 7.000 | 10.667 | 8.667 | 8.667 | ||
| Mean 3 | 7.000 | 7.000 | 9.000 | 8.000 | ||
| Range | 4.667 | 3.667 | 1.000 | 1.000 | ||
| Factor primary and secondary levels | A > B > C = D | |||||
| Optimal decision | A1 B2 C3 D1 | |||||
Table 10.
Analysis of variance for coverage rate results.
| Factors | Sum of Squared Deviations | Degrees of Freedom | Fratio | Fcritical Value | Significance |
|---|---|---|---|---|---|
| A | 43.556 | 2 | 2.554 | 4.460 | |
| B | 21.556 | 2 | 1.264 | 4.460 | |
| C | 1.556 | 2 | 0.091 | 4.460 | |
| D | 1.556 | 2 | 0.091 | 4.460 | |
| Error | 68.22 | 8 |
Table 11.
The yield rate and coverage rate in single-factor test.
| Sample (#) | Wcore:Wwall | Yield Rate (%) | Standard Deviation for Yield Rate | Coverage Rate (%) | Standard Deviation for Coverage Rate |
|---|---|---|---|---|---|
| 10 | 0.4:1 | 62.67 | 2.2 | 8.0 | 1.0 |
| 11 | 0.6:1 | 60.88 | 2.4 | 10.0 | 1.0 |
| 12 | 0.8:1 | 58.85 | 2.0 | 11.0 | 1.3 |
| 13 | 1:1 | 51.88 | 2.3 | 7.0 | 1.0 |
| 14 | 1.2:1 | 50.24 | 2.2 | 9.0 | 0.9 |
Table 12.
The effect of microcapsule on the gloss of the waterborne topcoat paint film.
| Sample (#) | Gloss (GU) | ||
|---|---|---|---|
| 20° | 60° | 85° | |
| 0 | 5.97 | 18.53 | 39.57 |
| 10 | 1.67 | 5.83 | 1.02 |
| 11 | 2.03 | 7.07 | 1.50 |
| 12 | 2.47 | 8.07 | 2.10 |
| 13 | 1.43 | 5.23 | 1.07 |
| 14 | 1.60 | 6.33 | 0.80 |
Table 13.
Effect of microcapsules on the chromaticity and color difference values of the waterborne topcoat paint film.
Table 13.
Effect of microcapsules on the chromaticity and color difference values of the waterborne topcoat paint film.
| Sample (#) | L1 | a1 | b1 | L2 | a2 | b2 | ΔE |
|---|---|---|---|---|---|---|---|
| 0 | 84.30 | 1.35 | 5.41 | 84.65 | 1.25 | 5.70 | - |
| 10 | 75.15 | 1.95 | 8.55 | 75.45 | 1.95 | 8.25 | 9.63 |
| 11 | 75.50 | 2.41 | 10.20 | 75.30 | 2.40 | 10.3 | 10.28 |
| 12 | 76.50 | 3.65 | 9.75 | 76.75 | 3.50 | 9.85 | 9.21 |
| 13 | 73.75 | 3.55 | 12.51 | 73.65 | 3.55 | 12.70 | 13.07 |
| 14 | 75.25 | 3.35 | 11.95 | 75.25 | 3.35 | 11.65 | 11.33 |
Table 14.
Effect of microcapsules on the cold liquid resistance level of the waterborne topcoat paint film.
Table 14.
Effect of microcapsules on the cold liquid resistance level of the waterborne topcoat paint film.
| Sample (#) | Liquid Cooling Resistance Level (Grade) | ||
|---|---|---|---|
| 10% Citric Acid Solution | Ethanol | Detergent | |
| 0 | 2 | 3 | 4 |
| 10 | 1 | 2 | 2 |
| 11 | 1 | 2 | 2 |
| 12 | 1 | 2 | 2 |
| 13 | 1 | 2 | 1 |
| 14 | 1 | 2 | 1 |
Table 15.
The effect of microcapsule on the elongation at break and roughness of the waterborne topcoat paint film.
Table 15.
The effect of microcapsule on the elongation at break and roughness of the waterborne topcoat paint film.
| Sample (#) | Elongation at Break (%) | Roughness (μm) |
|---|---|---|
| 0 | 23.85 | 0.201 |
| 10 | 9.98 | 2.511 |
| 11 | 11.61 | 2.107 |
| 12 | 15.68 | 3.407 |
| 13 | 10.88 | 4.269 |
| 14 | 9.17 | 4.726 |
Table 16.
The actual recovery rate of live bacteria and antibacterial activity of the waterborne topcoat paint film.
Table 16.
The actual recovery rate of live bacteria and antibacterial activity of the waterborne topcoat paint film.
| Sample (#) | Average Recovered Colony Count (CFU/piece) | Antibacterial Rate (%) | Standard Deviation | |||
|---|---|---|---|---|---|---|
| Escherichia coli | Staphylococcus aureus | Escherichia coli | Staphylococcus aureus | Escherichia coli | Staphylococcus aureus | |
| 0 | 383 | 367 | - | - | - | - |
| 10 | 224 | 242 | 41.51 | 34.10 | 2.3 | 1.6 |
| 11 | 231 | 231 | 39.69 | 37.06 | 1.1 | 1.3 |
| 12 | 219 | 198 | 42.82 | 46.05 | 1.8 | 1.5 |
| 13 | 238 | 204 | 37.86 | 44.41 | 1.5 | 1.5 |
| 14 | 241 | 223 | 37.07 | 39.24 | 1.9 | 1.1 |
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MDPI and ACS Style
Wang, Y.; Yan, X. Preparation of Toddalia asiatica (L.) Lam. Extract Microcapsules and Their Effect on Optical, Mechanical and Antibacterial Performance of Waterborne Topcoat Paint Films. Coatings 2024, 14, 655. https://doi.org/10.3390/coatings14060655
AMA Style
Wang Y, Yan X. Preparation of Toddalia asiatica (L.) Lam. Extract Microcapsules and Their Effect on Optical, Mechanical and Antibacterial Performance of Waterborne Topcoat Paint Films. Coatings. 2024; 14(6):655. https://doi.org/10.3390/coatings14060655
Chicago/Turabian StyleWang, Ying, and Xiaoxing Yan. 2024. "Preparation of Toddalia asiatica (L.) Lam. Extract Microcapsules and Their Effect on Optical, Mechanical and Antibacterial Performance of Waterborne Topcoat Paint Films" Coatings 14, no. 6: 655. https://doi.org/10.3390/coatings14060655
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