Design and Fabrication of a Renewable and Highly Transparent

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Materials and Interfaces

Design and Fabrication of a Renewable and Highly Transparent Multilayer Coating on Poly(lactic acid) Film Capable of UV-Shielding and Antifogging Tao Zhang, Qiuyan Yu, Jiajun Wang, and Tao Wu Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 21 Mar 2018 Downloaded from http://pubs.acs.org on March 21, 2018

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Industrial & Engineering Chemistry Research

Design and Fabrication of a Renewable and Highly Transparent Multilayer Coating on Poly(lactic acid) Film Capable of UV-Shielding and Antifogging Tao Zhang,†,∗ Qiuyan Yu,‡ Jiajun Wang,†,‡ and Tao Wu† †

Department of Packaging Engineering, School of Art & Design, Zhejiang Sci-Tech University, Hangzhou 310018, People’s Republic of China

‡

College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou 310018, People’s Republic of China

AUTHOR INFORMATION Corresponding Author ∗

E-mail: [email protected]. Tel.: +86 571 86843692. Fax: +86 571 86843291 (T.

Zhang).

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT A new and highly transparent multilayer coating on poly(lactic acid) (PLA) film has been designed and constructed based on the layer-by-layer assembly of green and renewable hydroxypropyl methylcellulose (HPMC) and tannic acid (TA). The surface chemical structure, thickness and morphology analyses of the multilayer coating confirm that HPMC and TA are successfully incorporated based on the hydrogen-bonding interaction. The resultant coated PLA film presents excellent UV-shielding and antifogging properties, which shows strong dependency on the the number of assembly cycles. Although the tensile mechanical property of coated PLA film shows a decrease, the thermal property of the PLA substrate are remained. This work provides a simple but effective pathway to design and fabricate highly transparent and environmentally friendly coating for the UV-shielding and antifogging applications.


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1. INTRODUCTION In our daily life, the UV light damage has always drawn people’s much attention. Overexposure to the UV radiation may cause damage to the human health and material property.1 Therefore, how to reduce the UV light damage has always been one of the main focuses of many endeavors. Up to now, various materials have been introduced to this topic, and the most popular metal oxide nanoparticles such as ZnO1 and TiO22 have been proved to be effective to shield the UV light. However, there are concerns about the side-effect of their photocatalytic activities, which may induce the photodegradation of materials.3 On the other hand, the fog can cause some inconveniences and potential dangers. Before the fog, it is very difficult to see the characters and patterns clearly, which is mostly due to the light scattering.4,5 In order to solve this question, extensive research has been devoted. One of the most studied and effective strategies is to construct hydrophilic or superhydrophilic coating or film, such as pullulan coating,6 poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) multilayer film7 and polyethylene glycol (PEG)-added TiO2 film,8 which can rapidly absorb and spread the condensed water droplets and reduce the light scattering.9 As for the dual-functionality for UV-shielding

and

antifogging,

there

are many literature examples

such

as

poly(ethylene imine)/TiO2@carboxymethyl cellulose coated polypropylene film10 and ZnO nanorod film11. However, their transparencies are often low. Hence, it is still necessary to design and fabricate UV-shielding and antifogging coatings or films with high

transparency.

Furthermore,

from

the point of environmental protection,



exploiting the green and renewable resources is more meaningful. Hydroxypropyl methylcellulose (HPMC) is a semi-synthetic polymer derived from cellulose, which is easily available, very cheap and widely used in the food and drug industries.12-14 Tannic acid (TA) is a kind of natural polyphenol and food-grade material, which is widely found in many plants.15-17 Both HPMC and TA are hydrophilic, which is mostly due to their abundant -OH groups, as shown in Figure 1 for the chemical structures.14,15 Furthermore, HPMC shows excellent film-forming property,13 and TA possess amphiphatic nature and potential UV light absorbing capacity.17,18 Therefore, this work attempts to combine the HPMC and TA to explore their cooperation behaviors for reducing the UV light and fog damage. Figure 1. Herein, we report the design and preparation of HPMC/TA multilayer coating on the surface of representative poly(lactic acid) (PLA) film via hydrogen-bonded layer-by-layer assembly. PLA is a kind of biobased and biodegradable thermoplastic polymer material, which has always attracted much attention for commodity applications.19 However, the PLA shows drawbacks inherent in high permeability to UV light and tendency to fog.20 The hydrogen-bonding interaction driven layer-by-layer assembly is a powerful technique suitable for the -OH group-riched building blocks in constructing multilayer materials.21 The objective of this study was to illustrate the possibility of making highly transparent coating capable of UV-shielding and antifogging based on the renewable and non-photocatalytic materials. The results will be helpful in the future design and preparation of


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dual-functional and even multi-functional environmentally friendly coating. 2. EXPERIMENTAL SECTION 2.1. Materials. Poly(lactic acid) (PLA) film was bought from Shenzhen Esun Industrial Co., Ltd. Hydroxypropyl methylcellulose (HPMC, type I, viscosity 400mPa.s) and tannic acid (TA, AR) were purchased from Aladdin Chemistry Co., Ltd. Ethanol was used as received from Sinopharm Chemical Reagent Co., Ltd. Deionized water with a resistance of 18 MΩ was used for the experiments. The starting reagents were used without further purification. 2.2. Layer-by-layer assembly. For the hydrogen-bonded layer-by-layer assembly, the HPMC and TA solutions were prepared as 1.0 wt % concentration using deionized water at room temperature, respectively. The obtained solutions were used without adjusting the pH values. Prior to assembly, the pristine PLA film was washed with ethanol and water successively for several times and dried under vacuum at 40 oC. As shown in Figure 1, the substrate was first immersed into the HPMC solution for 2 min, washed with deionized water twice each for 1 min, dried; immersed into the TA solution for 2 min, washed with deionized water twice each for 1 min, dried. This process describes an assembly cycle for one bilayer, and it was repeated until the required number (n) of bilayers was achieved. Finally, the coated PLA films were dried under vacuum at 40 o

C. In this work, we denote briefly the coated PLA films that was assembled for 20

bilayers as (HPMC/TA)20.



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2.3. Characterization. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra were recorded on a Nicolet 5700 spectrometer (Thermo-Nicolet, USA) over a region of 4000-400 cm-1. Thickness of the multilayer coatings were measured with a CHY-C2A thickness tester (Labthink, China) with a test pressure of 17.5 ± 1 KPa and a contact area of 50 mm2. Field-emission scanning electron microscopy (FE-SEM) measurements were performed by using a Vltra55 microscopy (Carl Zeiss, Germany) operated at 3 kV. Prior to analysis, the specimens were gold-sputtered for 90 s under a high vacuum. Atomic force microscopy (AFM) experiments in tapping mode of operation were performed by using a XE-100E station (PSIA, Korea), and the root mean square (RMS) roughness (Rq) values were calculated automatically from the instrument software. Ultraviolet-visible (UV-vis) measurements were performed by using a Lambda 900 UV-vis spectrophotometer (Perkin-Elmer, USA) in the range of 200-800 nm. Antifogging properties of the uncoated and coated PLA films were qualitatively analyzed according to the reference9,22 by a COOLPIX S9600 digital camera

(Nikon, Japan) and quantitatively measured

by a

WGT-S light

transmission/haze tester (Shenguang, China) under a CIE standard Illuminant C (daylight with a correlated color temperature of 6774K). Before this analysis, the samples were stored in a refrigerator at about -20 oC for 1h, then held about 5 cm over the boiling water immediately. The water contact angles (WCA) were measured with an OCA 20 contact angle system (Dataphysics) at room temperature. The water droplets (about 3.0 µL) were dropped carefully onto the surface of films, and the


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average values of WCA were obtained by measuring more than five different positions of the same sample. Differential scanning calorimetric (DSC) was carried out by using a DSC Q2000 (TA instruments, USA) under nitrogen atmosphere. The samples were first heated up from 0 oC to 180 oC at 10 oC min-1 and held isothermally for 5 min, then cooled to room temperature at 10 oC min-1, and finally reheated to 180 o

C at 10 oC min-1. Thermogravimetric analysis (TGA) was conducted on a Pyris 1

thermogravimetric analyzer (Perkin-Elmer, USA) under nitrogen atmosphere. The samples were heated from room temperature to 500 oC at a heating rate of 10 oC min-1. Tensile mechanical properties were determined using an Instron 5943 universal testing machine (100 N load cell, Instron, USA) at 25 oC and 50 % relative humidity. The specimens (3 × 30 mm, at least in quintuplicate) were conditioned at 25 oC and 50 % relative humidity for 24 h and then measured at 10 mm min-1 with a gauge length of 10 mm. 3. RESULTS AND DISCUSSION 3.1. Characterization of coated PLA films. The coating growth was firstly monitored by ATR-FTIR spectroscopy, as shown in Figure 2. At around 1750 cm-1, the pristine PLA film shows an absorption peak, which is ascribed to the characteristic stretching vibration of C=O.23,24 The coated PLA film also shows characteristic absorption peak at around 1750 cm-1. However, compared to the pristine sample, the coated PLA film shows obvious and gradual enhanced absorption at around 1610 cm-1 (stretching vibration of C=C for benzene ring), confirming the successive incorporation of TA.17 In the range of 3030-3670 cm-1, the



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pristine PLA film shows no obvious absorption peak. However, in the case of (HPMC/TA)5, a weak and broad peak appears, indicating the presence of –OH group ascribed to the HPMC and TA .14,25,26 Furthermore, as the n increases to 10 and 20, the integrated absorption intensities increase significantly, demonstrating the increased alternate adsorption of HPMC and TA. Figure 2. In order to further monitor the layer-by-layer growth, the thicknesses of multilayer coating were measured and then plotted as functions of the n. Figure 3 shows the representative data of 0, 5, 10, 15 and 20 bilayers for a quantitatively comparison. Clearly, the thickness grows in an accelerated fashion, which shows a similar exponential dependence on the n. After 20 bilayers, the multilayer coating reaches thickness of 1950 ± 109 nm. Similar growth behavior was also observed in many electrostatic

interactions

driven

poly[2-(dimethylamino)ethyl

assembly

of

multilayers,

methacrylate]/poly(acrylic

acid)

such

as stars

(PDMAEMA/PAA)n,27 poly(ethyleneimine)/SiO2 nanoparticles (PEI/SiO2)n28 and poly(diallyldimethylammonium chloride) (PDDA)/PDDA and sodium carboxymethyl cellulose complex (PDDA/PEC-)n29. Generally, hydrogen-bonded layer-by-layer assembly is more difficult than that of electrostatic.21 In this work, both HPMC and TA possess abundant hydroxyl groups. Especially, the polyphenolic TA contains a central carbohydrate core esterified by phenol acids and shows about 25 hydroxyl groups.17,25 As shown in Figure 2, the TA shows absorption of –OH group at around 3381 cm-1. However, the absorption peak of –OH groups for the coated PLA film is


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shifted to high frequency, indicating the hydrogen-bonding interactions between HPMC and TA.26,30,31 Therefore, the accelerated growth of (HPMC/TA)n is mostly due to the strong hydrogen-bonding interactions between the pairs of HPMC and TA. Figure 3. The representative cross sections of the pristine PLA film and (HPMC/TA)20 were imaged by using FE-SEM for direct comparison. Clearly, there is an apparent coating with thickness of about 1000 nm covering one side of the substrate compared with the pristine sample (see the insert of Figure 3), which is consistent with the above measured thickness data. The corresponding surface morphologies were further imaged by using AFM for direct comparison as shown in Figure 4. Compared to the pristine PLA film, the surface of (HPMC/TA)20 presents big and continuous rise and fall domains, which is mostly caused by the hydrogen-bonding complexation between HPMC and TA.32 Accordingly, the Rq value at the 2 × 2 µm scale is increased from 1.024 nm for the PLA film to 4.443 nm for the (HPMC/TA)20. Hence, the accelerated growth of (HPMC/TA)n is also mostly due to its special surface morphology. During the layer-by-layer growth, the rough structure provides more specific surface area so as to produce high capacity for absorbing the next layer, which is similar to the polyethylenimine/ammonium

polyphosphate

(PEI/APP)n33

and

chitosan/poly(γ-glutamic acid) (Ch/γ-PGA)n34 systems. Therefore, the above results demonstrate the effectiveness of the use of HPMC and TA as hydrogen-bonded building blocks. Figure 4.



3.2. Transparency and UV-shielding property. The pristine PLA film and representative (HPMC/TA)20 were firstly photographed with a digital camera as shown in Figure 5. Using our naked eyes, it can be seen that the pristine PLA film shows high visible light transparency (see Figure 5 (a)). Interestingly, with the 20 bilayers of coating, it is still able to completely see the background under the film without any visible shelter or obscure area (see Figure 5 (b)). In addition, the UV-vis measurement was also utilized to quantitatively analyze the specimens. The spectra of PLA, (HPMC/TA)5, (HPMC/TA)10 and (HPMC/TA)20 in the visible region (400-800 nm) are shown in Figure 5 (c). The transparency was determined according to the ASTM D1746-03 and reference35, as shown in Figure 5 (d). As can be seen, the pristine PLA film shows average transmittance of 93.6 % at 550 nm. A slight reduction in the transmittance value is observed for the (HPMC/TA)20, but which still retain the average transmittance of 90.1 %. Figure 5. The UV-vis spectra in the UV region (250-400 nm) of the pristine and coated PLA films are presented in Figure 6 (a) for comparison. Clearly, throughout the UV region, the pristine PLA film maintains transmittance of about 93.4 %, demonstrating almost no UV-shielding capacity. In contrast, the reductions of transmittance values at 250 and 300 nm, especially at 280 nm, are obviously observed for all the coated PLA films. For instance, the transmittance values at 250, 280 and 300 nm of (HPMC/TA)5 are 75.4, 63.8 and 68.5 %, respectively, which are all significantly lower than those of the pristine PLA film. More interestingly, as the n increases, the transmittance values


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decrease progressively, indicating gradually enhanced UV-shielding capacity. Finally, the transmittance values at 250, 280 and 300 nm of (HPMC/TA)20 are 31.7, 5.4 and 12.4 %, respectively. Notably, at 280 nm, the (HPMC/TA)20 performs about 94.6 % UV-shielding capacity. Figure 6. In general, the UV light can be further divided into three sections: short wave UV light (UVC, 200-280 nm), medium-wave UV light (UVB, 280-320 nm) and long wave UV light (UVA, 320-400 nm).36 Compared to the pristine PLA film, all the coated PLA films perform well in UV-shielding at UVB and UVC, especially at the transition region of UVB and UVC. Generally, the workers using the germicidal lamps in the hospital and food factory are most likely to be exposed to the UV radiation in this region, which is known to be harmful to the living cells.37 Since the pristine HPMC film presents stable transmittance of about 92.3 % in the UV region (see Figure 6 (a)), we can conclude that the UV-shielding capacity of the multilayer coating is solely ascribed to the embedded TA layer, which is due to the absorption of its abundant phenyl groups,18 as shown in Figure 6 (c). Figure 6. 3.3. Antifogging property. To assess the antifogging property, the pristine and coated PLA films were firstly stored in a refrigerator at about -20 oC for 1h, then held about 5 cm over the boiling water immediately and photographed with a digital camera as shown in Figure 7. As can be clearly seen, a heavy fog forms on the surface of pristine PLA film



immediately, and the background plant is almost invisible. However, there is a notable improvement for the coated PLA film. For example, the (HPMC/TA)5 shows enhanced light transmittance and clarity. Furthermore, as the n increases, the background plant can be saw more clearly. Finally, there is almost no fog formation anymore for the (HPMC/TA)20, and the green leaves present before our eyes clearly. Furthermore, as shown in the Supporting Information, Movie S1 and S2, the antifogging property for the (HPMC/TA)20 can be repeated 10 times. As the time of repetition increases, the antifogging property for the (HPMC/TA)20 is almost unaffected. Hence, it seems that this repeatable antifogging property can be kept unchanged. Figure 7. Then, the light transmission/haze tester was further utilized to evaluate the antifogging property quantitatively according to the ASTM D1003-07, as shown in Table 1. Over the boiling water, the pristine PLA film exhibits average light transmittance and haze of 66.5 and 26.5 %, respectively, further reflecting the presence of heavy fog. Under the same condition, the coated PLA film shows higher light transmittance and lower haze, demonstrating improved antifogging property. Moreover, as the n increases, the light transmittance increases and the haze decreases significantly. For example, as for the (HPMC/TA)20, the average light transmittance is almost as high as that of without boiling water, and the average haze is as low as only 0.3 %. Table 1.


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As discussed earlier in Figure 2, more and more –OH groups are constructed on the surface of the PLA film as the n increases. In order to get more insight, the water contact angles (WCA) of the representative pristine PLA film and (HPMC/TA)20 were measured and analyzed as shown in Figure 8. Interestingly, the WCA value is decreased from 70 ± 1o for the pristine PLA film to 55 ± 1o for the (HPMC/TA)20. Obviously, with the multilayer coating, the hydrophilic property of the PLA films are improved. This result also demonstrates the possibility of using hydrophilic instead of superhydrophilic surface to antifog, which is similar to the semi-interpenetrating polymer network coating.38 Figure 8. According to the previous literature reports,9,22 the observed fog over the boiling water is caused by the condensed water droplets, which evolves from the frost formed in the extremely cold atmosphere. Therefore, during the fog formation process, the antifogging property of the treated PLA films is mostly ascribed to the hydrophilic multilayer coating, which can absorb and disperse the water molecules rapidly upon water condensation, as shown in Figure 8 (c, d). The above results also highlight the importance and effectiveness of the number of assembly cycles in hindering the fog formation, which is ascribed to the enhanced thickness and the corresponding capacity

for

the

condensed

water.

There

are many literature examples

of

dual-functional coating with excellent UV-shielding and antifogging properties. However, they often show low transparency. For example, the poly(ethylene imine)/TiO2@carboxymethyl cellulose coated polypropylene film shows transparency



of around 45 %.10 The ZnO nanorod film show high transparency,11 but the side-effect of photocatalytic degradation activity should be concerned. In addition, the representative pristine PLA and (HPMC/TA)20 were selected to analyze the effect of multilayer coating on the thermal and mechanical properties. The glass transition temperature (Tg) and melting temperature (Tm) of (HPMC/TA)20 are almost the same as those of the pristine PLA (see Figure S1 and Table S1). A reduction of the melting enthalpy (∆Hm) can be found for the (HPMC/TA)20, which is mostly due to the unnoticeable endothermic or exothermic peaks for the pristine HPMC and TA.39 The 5 wt % weight loss temperature (T5%) and maximum weight loss temperature (Tmax) of (HPMC/TA)20 are almost the same as those of the pristine PLA (see Figure S2, S3 and Table S2). Reductions in the Young’s modulus, yield strength, tensile strength and strain at break are observed for the (HPMC/TA)20 (see Figure S4 and Table S3), which is mostly due to the small molecular TA and the lower tensile mechanical property of the pristine HPMC. In this case, the hydrogen-bonding interactions between HPMC and TA may play an role in preventing a sharp reduction in the tensile mechanical property. A more detailed effect of the multilayer coating on the thermal and mechanical properties and the mechanism needs to be further studied in the future. 4. CONCLUSIONS This work provides a simple but effective method for the construction of highly transparent, UV-shielding and antifogging multilayer coating based on renewable resources. Driven by the hydrogen-bonding interaction, the HPMC and TA are


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successively incorporated onto the surface of PLA film. The UV-vis results highlight the importance of TA for the UV-shielding capacity, which is mostly ascribed to the abundant phenyl groups. Furthermore, the coated PLA film possesses excellent antifogging capacity, which is mostly due to the hydrophilic character of the multilayer coating. The multilayer coating shows negative effect on the tensile mechanical property of the PLA substrate, but almost no effect on the thermal property. Therefore, the improved UV-shielding and antifogging properties of the PLA film indicates the great potentials of the HPMC/TA multilayer coating constructed by hydrogen-bonding interaction driven Layer-by-layer assembly method. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: DSC thermograms of PLA, (HPMC/TA)20, HPMC and TA; parameters obtained from DSC curves of PLA, (HPMC/TA)20, HPMC and TA in the temperature region of 0-180 oC; TGA curves of PLA and (HPMC/TA)20; DTG curves of PLA and (HPMC/TA)20; thermal properties of PLA and (HPMC/TA)20; stress-strain curves of PLA, (HPMC/TA)20 and HPMC; and tensile properties of PLA, (HPMC/TA)20 and HPMC A movie about the antifogging property for the pristine PLA and (HPMC/TA)20 (AVI); and a movie about the antifogging property for the pristine PLA and (HPMC/TA)20 after 9 times of repetition (AVI)



AUTHOR INFORMATION

Corresponding Author ∗

E-mail: [email protected]. Tel.: +86 571 86843692. Fax: +86 571 86843291 (T.

Zhang).

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by the Zhejiang Provincial Natural Science Foundation of China (No. LY18E030007), the Project Grants for 521 Talents Cultivation of Zhejiang Sci-Tech University and the Innovation Research Foundation for the Graduate Student of Zhejiang Sci-Tech University (No. YCX16011). REFERENCES (1) Zhang, Y.; Wang, X.; Liu, Y.; Song, S.; Liu, D. Highly Transparent Bulk PMMA/ZnO Nanocomposites with Bright Visible Luminescence and Efficient UV-Shielding Capability. J. Mater. Chem. 2012, 22 (24), 11971-11977. (2) Oleyaei, S. A.; Almasi, H.; Ghanbarzadeh, B.; Moayedi, A. A. Synergistic Reinforcing Effect of TiO2 and Montmorillonite on Potato Starch Nanocomposite Films: Thermal, Mechanical and Barrier Properties. Carbohyd. Polym. 2016, 152, 253-262. (3) de Moraes, A. C. M.; Andrade, P. F.; de Faria, A. F.; Simões, M. B.; Salomão, F. C. C. S.; Barros, E. B.; Gonçalves, M. d. C.; Alves, O. L. Fabrication of Transparent and


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Cellulose Coatings Capable of Shielding UV, Antifog and Delaying Support Aging. Carbohyd. Polym. 2017, 169, 398-405. (11) Kwak, G.; Jung, S.; Yong, K. Multifunctional Transparent ZnO Nanorod Films. Nanotechnology 2011, 22 (11), 115705-115712. (12) Larsson, M.; Johnsson, A.; Gårdebjer, S.; Bordes, R.; Larsson, A. Swelling and Mass Transport Properties of Nanocellulose-HPMC Composite Films. Mater. Des. 2017, 122, 414-421. (13) Klangmuang, P.; Sothornvit, R. Combination of Beeswax and Nanoclay on Barriers,

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Captions of Figures and Tables Figure 1. Illustration of the layer-by-layer assembly process for construction of HPMC/TA multilayer coating on the PLA film (first row), chemical structures of the HPMC and TA (second row). Figure 2. ATR-FTIR spectra of the HPMC, TA, PLA, (HPMC/TA)5, (HPMC/TA)10 and (HPMC/TA)20 in the frequency region of 3800-2500 cm-1 (a) and 2000-680 cm-1 (b). Figure 3. Thicknesses of (HPMC/TA)n as functions of the n (insert is the cross section SEM image of (HPMC/TA)20). Figure 4. AFM images (2 × 2 µm) of the PLA film (a) and (HPMC/TA)20 (b). Figure 5. The digital images of PLA (a) and (HPMC/TA)20 (b) with a plant as the background in the natural condition. The region surrounded by the dash lines refers to the samples. The UV-vis transmittance spectra in the region of 400-800 nm (c) and the transmittance at 550 nm of PLA, (HPMC/TA)5, (HPMC/TA)10 and (HPMC/TA)20 (d). Figure 6. The UV-vis transmittance spectra of PLA, (HPMC/TA)5, (HPMC/TA)10, (HPMC/TA)20 and HPMC in the region of 250-400 nm (a) and the proposed UV-shielding mechanism (b, c). Figure 7. The digital images of PLA (a), (HPMC/TA)5 (b), (HPMC/TA)10 (c) and (HPMC/TA)20 (d) with a plant as the background. The samples were firstly stored in a refrigerator at about -20 oC for 1h and then held about 5 cm over the boiling water immediately. Figure 8. The photographs of a water droplet on the PLA (a) and (HPMC/TA)20 (b).



The proposed antifogging mechanism of the HPMC/TA multilayer coating on the PLA film (c, d). Table 1. The Light Transmittance and Haze of PLA, (HPMC/TA)5, (HPMC/TA)10 and (HPMC/TA)20 Determined by Using the Light Transmission/Haze Tester


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Figure 1.



Figure 2.


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Figure 3.



Figure 4.


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Figure 5.



Figure 6.


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Figure 7.



Figure 8.


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Table 1 Sample

Light transmittance (%)

Haze (%)

PLA (HPMC/TA)5 (HPMC/TA)10 (HPMC/TA)20

66.5 ± 0.6 79.2 ± 0.5 88.7 ± 0.9 92.5 ± 0.8

26.5 ± 0.3 12.9 ± 0.2 3.8 ± 0.3 0.3 ± 0.1



Table of Contents


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Design and Fabrication of a Renewable and Highly Transparent

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