Effect of Fully Biobased Coatings Constructed via Layer-by-Layer

Research Article pubs.acs.org/journal/ascecg

Effect of Fully Biobased Coatings Constructed via Layer-by-Layer Assembly of Chitosan and Lignosulfonate on the Thermal, Flame Retardant, and Mechanical Properties of Flexible Polyurethane Foam Ying Pan,† Jing Zhan,†,‡ Haifeng Pan,† Wei Wang,† Gang Tang,§ Lei Song,*,† and Yuan Hu*,† †

State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, PR China School of Civil Engineering and Environmental Engineering, Anhui Xinhua University, Hefei, Anhui 230088, PR China § School of Architecture and Civil Engineering, Anhui University of Technology, 59 Hudong Road, Ma’anshan, Anhui 243002, PR China ‡

ABSTRACT: A fully biobased coating containing chitosan (CS) and lignosulfonate (LS) was facilely fabricated on the surface of flexible polyurethane foam (FPUF) using layer-by-layer assembly method. The CS/LS based coatings were successfully deposited on the substrate, as demonstrated by UV−vis absorption spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, and scanning electron microscopy. Subsequently, the different bilayers of the coatings were applied to enhance the thermal stability, fire resistance, and mechanical properties of FPUFs. It was found that the thermal degradation of coated FPUF under nitrogen atmosphere was obviously retarded compared with the pure FPUF. Furthermore, an eight-bilayer CS/LS based coating significantly improved the fire resistance of FPUF, as evidenced by the remarkable reduction (42%) of peak heat release rate. Meanwhile, the mechanical property of coated FPUF was improved. After the FPUF was covered with the eight-bilayer coating, the tensile strength was increased from 0.17 to 0.19 MPa compared with pure FPUF. KEYWORDS: Chitosan, Lignosulfonate, Layer-by-layer assembly, Coating, Flexible polyurethane foam

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INTRODUCTION During past decades, scientists have paid much attention and interest to renewable and biodegradable resources due to environment concerns and the realization of the gradual depletion of fossil resources. As a natural nontoxic polyaromatic polyol, lignin is one of the most abundant and relatively inexpensive sustainable polymers.1 Every year about 50 million tons of industrial lignin is produced.2 However, less than 2% is recovered for utilization as a chemical product and the vast majority is primarily burned for recovering energy.3 Therefore, the comprehensive utilization of industrial lignin remains a big challenge. Until now, many researchers have explored its application. Among these applications, it has been found that it can be used as a filler in polymers to improve the thermal stability and flame retardancy of the matrix.4−7 Lignin has been filled alone or mixed with other compounds such monoammonium phosphate and melamine in polypropylene (PP).8 The additives improved the thermal degradation temperature of PP, increased the formation of char residue in a nitrogen atmosphere, and reduced the heat release rate (HRR) of PP during the cone tests. Fu et al. studied the effects of alkali lignin on the thermal stability and fire resistance of styreneacrylonitrile-butadiene copolymer (ABS).3 The incorporation of lignin improved the char residue of ABS in thermal degradation and 20 wt % lignin caused a 32% reduction in peak © XXXX American Chemical Society

heat release rate (PHRR). Since lignin is able to generate a high amount of char residue upon heating at elevated temperature in an inert atmosphere, the char formation can reduce the combustion heat and HRR of polymeric materials. Since Grunlan et al.9 first used a layer-by-layer (LbL) assembly method to produce a flame retardant coating on fabric in 2009, the LbL assembly technique has been an important method of flame retardant finishing to fabrics and flexible polyurethane foams (FPUF). Lots of materials, such as polyelectrolytes, nanoparticles, and micelles can be used to fabricate the multilayers on the substrates and endow them with multifunctional properties.10 The poly(acrylic acid)/ branched polyethylenimine/montmorillonite (MMT) nanobrick walls on the FPUF were prepared by Li et al. through the LbL assembly method.11 PHRR of the coated FPUF decreased 33% compared with that of pure foam. It can be known that LbL self-assembly is an efficient mean to reduce the flammability of FPUF. Among these works, some biobased polyelectrolytes was used independently or cooperated with some nanoparticles. Grunlan et al.12 prepared an effective flame retardant coating comprised of positively charged chitosan and anionic poly(vinyl sulfonic acid sodium salt) on FPUF using Received: November 4, 2015

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DOI: 10.1021/acssuschemeng.5b01423 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. Schematic of construction of chitosan/lignosulfonate nanocoatings on the FPUF. The process was alternating submersion in chitosan solution and sodium lignosulfonate solution with washing (rinse and wring) between each submersion.

LbL assembly. Moreover, this group also deposited thin films comprised of chitosan and MMT on the surface of polyurethane foam.13 These coatings can significantly reduce the HRR of the substrates and the coatings contained biomass materials (chitosan). From these results, it can be concluded that the biobased polyelectrolytes will be a promising choice to prepare environmentally friendly, renewable, and flame retardant coatings on polymeric substrates. As one of the most available commercial lignins, lignosulfonate (LS) is produced as byproducts of sulfite pulping.14 The LS macromolecule contains a hydrophobic backbone (C6−C3 structure monomers linked together by ether and carbon bonds) and hydrophilic branches (sulfonic, carboxyl, and phenolic hydroxyl groups) and, thus, possesses a certain degree of surface activity.15,16 Due to the ionization of functional groups, LS has negative charges and exhibits polyelectrolyte behavior in aqueous solution.17,18 Therefore, it is possible to construct LbL multilayers of LS and some cationic polyelectrolytes. Due to LS being and inexpensive industrial byproduct, available in large quantities, LbL assembly of LS for FPUF modification has technical as well as economical significance. As a kind of polymer material, FPUFs have a wide range of application, including the furniture, construction, and automotive fields.19−21 However, the high flammability of FPUF brings potential fire hazards to its applications. The phenomena of collapse and melt-dripping during the combustion of FPUF accelerate flame propigation.22 It is essential to do some flame retardant treatment on FPUF to reduce the threat to life and property. In this work, chitosan (CS) was chose to cooperate with LS for fabricating a LbL coating on the surface of FPUF. It is anticipated that this polyelectrolyte coating could be successfully deposited on FPUF, thus resulting in significantly enhanced thermal stability and improved flame retardation of the substrate. This work attempts to provide a promising strategy for constructing a novel coating on FPUF so as to expand the application of these biobased materials.

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(used for UV−vis absorption spectrometry test) was treated in a bath of H2SO4/H2O2 (3/1 by v/v) and, then, thoroughly rinsed with deionized and dried under nitrogen flow. The surface of the quartz slide was hydroxylated by this procedue.24 Then, the treated FPUF or quartz slides were successively immersed in the solutions of CS and LS for 2 min. Each time before soaking in the solutions, the FPUF or the quartz slides were washed in the deionized water for 2 min (quartz slide: dried with N2 after washed). One bilayer was built up by a CS layer and a LS layer. The process of LbL assembly is presented in Figure 1. When the bilayers reached to the desired number, the samples were dried at 70 °C overnight and then stored in a desiccator for 24 h. The FPUFs coated with four and eight bilayers were named as FPUF-4BL and FPUF-8BL, respectively. The samples with different numbers of bilayers and concentrations of solutions are listed in Table 1.

Table 1. Concentration of Dipping Solution and Weight Gain of the Coated FPUF with Different Bilayers sample

CCS (wt %)

CLS (wt %)

bilayer

weight gain (wt %)

FPUF FPUF-4BL FPUF-8BL

0 0.5 0.5

0 0.5 0.5

0 4 8

0 3.4 7.2

Measurements. UV−vis absorption spectra were detected using a Solid3700 (SHIMADZU) spectrometer. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra were recorded by a Nicolet 6700 spectrophotometer using 32 scans in the frequency region of 4000−400 cm−1. Scanning electron microscopy (SEM) was performed on the surface of the foam using a FEI Sirion200 scanning electron microscope. The specimens were previously coated with a conductive layer of gold. The thermogravimetric analysis (TGA) of sample under nitrogen atmosphere was examined on a TGA-Q5000 apparatus (TA Instruments Inc., USA) from 50 to 700 °C at a heating rate of 20 °C/min. Thermogravimetric analysis−Fourier transform infrared spectrometry (TG-FTIR) of the samples was performed using a TGA Q5000 IR thermogravimetric analyzer that was interfaced to the Nicolet 6700 FTIR spectrophotometer through a Thermo-Nicolet TGA special connector. Limit oxygen index (LOI) tests were performed according to ISO 4589-2 using a HC-2C oxygen index instrument, and the size of the specimen was 150 mm × 10 mm × 10 mm (length × width × thickness). The horizontal burning tests of the FPUF samples were measured according to ISO 9772-2001. Each specimen with dimensions of 150 mm × 50 mm × 13 mm was exposed to direct flame from a methane Bunsen burner in a burning chamber. The combustion test was performed on the cone calorimeter (Fire Testing Technology, UK) according to ISO 5660 standard procedures, with 100 mm × 100 mm × 25 mm specimens. Aluminum foil was wrapped around the sample except on the irradiated, heavy metal container. Each specimen was exposed horizontally to 50 kW/m2 external heat flux.

EXPERIMENTAL SECTION

Materials. Flexible polyurethane foam (DW30, density: 0.03 g/ cm3) was obtained from Jiangsu Lvyuan New Material Co., Ltd. CS (viscosity: 50−800 mPa·s, degree of deacetylation 80−95%), sodium hydroxide, and hydrochloric acid (HCl 36−38%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Polyacrylic acid (PAA, Mw ∼ 3000) and sodium LS (purity: 96%) were received from Aladdin Industry Co., Ltd. LbL Deposition. CS and sodium LS solutions were dissolved in pH = 5 and 3 deionized water with mechanical stirring for 24 h to prepare 0.5 and 0.5 wt % homogeneous solutions, respectively. FPUF was first immersed in 0.1 wt % poly(acrylic acid) solution for 5 min to obtain negatively charged sample.23 Quartz slide (10 mm × 20 mm) B


Research Article

ACS Sustainable Chemistry & Engineering Raman spectroscopy measurements were carried out at room temperature with a SPEX-1403 laser Raman spectrometer (SPEX Co, USA) with excitation provided in backscattering geometry by a 514.5 nm argon laser line. Tensile measurements were performed with a universal testing CMT6104 (Shenzhen SANS Material Detection Co. Ltd., China) testing machine according to ISO 1798:2008 at a crosshead speed at 500 mm/min. Sample were cut to a dumbbell shape with the size of 40 mm × 10 mm × 10 mm. The compression set was determined according to ISO1856-2000 standard. The dimensions of the samples were 50 mm × 50 mm × 20 mm. The thickness of the foams was measured, and the foams were then compressed between two metallic plates to 50% of their original thickness and left at 70 ± 1 °C for 22 h. The residual thickness was measured after 30 min when the pressure was released. Compression set is defined as the percentage of thickness loss.

intensity of peaks at 267 nm and number of bilayers is displayed at the inset plot, which demonstrates that the LS increase with the addition of deposited bilayers. In general, the LS and CS can deposit successfully on the substrate and the deposited amount can be controlled by changing the number of bilayers. In order to evaluate the growth of the biobased coating on the FPUF, ATR-FTIR spectroscopy was chose to detect the characteristic groups on the surface of FPUF. The ATR-FTIR spectra of the pure FPUF and coated FPUF and are shown in Figure 3a. It can been found that a new peak at 1043 cm−1 appears on the spectra of coated foam, which corresponds to the absorption of C−O bond of LS and CS. The peak at 1101 cm−1 is ascribed to C−O−C stretching vibration of polyurethane foam. Figure 3b shows the plot of the relative absorbance intensities (A1043 cm−1/A1101 cm−1) as functions of the sample. The ratio of A1043 cm−1/A1101 cm−1 increases with the addition of bilayers, which illustrates that more LS are absorbed on the surface of FPUF. Figure 4 shows the SEM images of the pure FPUF and coated FPUF with different magnification. From the SEM images of the uncoated FPUF in Figure 4a and d, its exhibits a smooth surface. In Figure 4b, c, e, and f, the surfaces of the coated foams become much rougher than those of the pure foams, which demonstrates that the coated surfaces have been fully covered with CS/LS coatings. In the SEM images at high magnification (Figure 4e and f), it is evident that these multilayer coatings deposit uniformly on the substrate. However, there are more cracks on coating FPUF-4BL compared to FPUF-8BL. This can be explained as follows: the thinner coating on FPUF-4BL will produce more cracks during the drying procedure relative to FPUF-8BL. Moreover in order to characterize the roughness of the coating, the views of the FPUF fractures are shown in Figure 4g, h, and i. From a side view, it is obvious that the surface becomes rougher and thicker with the increasing number of bilayers deposited on the surface of FPUF. Thermal Stability of Pure and Coated FPUF. TGA as an efficient method to assess the thermal behavior of materials has been used to investigate the thermal property of pure and coated FPUF. Figure 5a and b shows the TG and DTG curves of CS, LS, and FPUFs. The representative parameters obtained from TG and DTG curves are summarized in Table 2. It is obvious that CS and LS can get high char residue, which are 47.6 and 36.2 wt % respectively. And the initial decomposition temperature of LS is as high as 279 °C. The degradation of the

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RESULT AND DISCUSSION Characterization of the CS/LS Coatings. In order to characterize the process of LbL assembly, UV−vis absorption spectrometry was used to monitor the CS/LS multilayer growth. Figure 2 shows the UV−vis absorption curves of

Figure 2. UV−vis absorption spectra of the multilayer assembly of (CS/LS)n coatings deposited on the quartz slides. (inset) Absorption intensity at 267 nm relative to the bilayer number.

coatings with different number of bilayers that deposited on the quartz slides. The apparent peak at 267 nm corresponds to the absorption of LS.25 This peak is obvious when the bilayer number is more than 5. Moreover, the relationship between

Figure 3. (a) ATR-FTIR spectra of the pure FPUF, FPUF-4BL, and FPUF-8BL. (b) Plot of the different samples corresponds to groups’ relative absorbance intensities. C


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Figure 4. SEM images of pure FPUF(a, d, g), FPUF-4BL (b, e, h), and FPUF-8BL (c, f, i).

Figure 5. TG (a) and DTG (b) curves of the CS, LS, pure FPUF, FPUF-4BL, and FPUF-8BL under a nitrogen atmosphere.

about 40 °C relative to pure FPUF. The CS/LS covered on the surface of FPUF can retard the thermal decomposition of the substrate owing to the high thermal stability of LS and charforming ability of CS and LS. As a result, the thermal stability of FPUF is enhanced due to the protective effect of coating. TG-FTIR was used to analyze the gas products during the thermal degradation process of the materials. Some of the volatilized pyrolysis products of FPUF can be detected by FTIR signals. In Figure 6a−d, total and some specific volatilized products were selected to investigate, including hydrocarbons (2975 cm−1), carbonyl compounds (1741 cm−1), and amide (1462 cm−1). The peak at 3100−2800 cm−1 appears after 815 s indicating the appearance of −C−H groups for various hydrocarbons. The appearance of these compounds is mainly attributed to the decomposition of the FPUF. When the time increases to 995 s, the strongest absorptions of all the pyrolysis products suggest the maximum decomposition rate at this time. As shown in Figure 6a, the strongest absorptions of all the pyrolysis products for FPUF-8BL appear at 1070 s, whereas those for pure FPUF have the maximum release at 955 s. It can be interpreted that the CS/LS based coating can retard the decomposition of FPUF. However, the absorbance intensity of

Table 2. TGA Data of the CS, LS, Pure FPUF, FPUF-4BL, and FPUF-8BL under Nitrogen Atmosphere

a

sample

T−5% (°C)

Tmax1 (°C)

Tmax2 (°C)

char residuea (wt %)

CS LS pure FPUF FPUF-4BL FPUF-8BL

141 279 250 257 255

/ / 279 284 285

/ / 353 393 391

47.6 36.2 2.7 4.1 5.4

At 700 °C.

FPUFs under nitrogen atmosphere is divided into two stages. The first stage of mass loss occurs at about 200−310 °C, which corresponds to the decomposition caused by the cleavage of urethane and substituted urea bond. At 320 °C, the polyether oligomer begins to decompose to volatile fragments.26 The 5% weight loss temperature (T−5%) is defined as the initial decomposition temperature, and Tmax refers to the temperature of the maximum decomposition rate. From Table 2, it can be observed that the T−5% and Tmax1 of coated foams were improved 5−7 °C compared with those of pure FPUF. Notably, the Tmax2 of FPUF-4BL and FPUF-8BL was increased D


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Figure 6. Absorbance of pyrolysis products for pure FPUF and FPUF-8BL vs time: (a) total; (b) hydrocarbons; (c) carbonyl; and (d) amide.

real fire.27 The HRR, THR, SPR, and TSP curves of the samples are plotted in Figure 7, and the related data are listed in Table 3. The combustion of FPUF is accompanied by significant change in volume, due to the collapse of the foam to low viscosity liquid. The two peaks on the HRR curve are correlated to the two combustion stages of the foam. The first stage is ascribed to the collapse of the foam and the second stage corresponds to pool fire.28 As shown in Figure 7, the HRR curves still contain two peaks after covered with the coating. This can be explained with the photographs of uncoated and coated FPUF after cone test in Figure 8. The coated foams collapse into thin char residue so that the first peak on the HRR curves can be observed obviously. In Figure 7 and Table 3, it is evident that PHRR values of the coated FPUFs were reduced significantly. Pure FPUF burns quickly after ignition with sharp PHRR of 736 kW/m2. The PHRR of FPUF-4BL is 503 kW/m2, with a reduction of 32% compared with that of pure FPUF. When BL number grows to 8, the peak in the HRR curve of FPUF-8BL was reduced 43%. This significant reduction can be ascribed to the carbonization of the coating efficiently hinder the transmission of heat and flammable gases. This carbonization effect is reflected on the char residue in Figure 8. Under the strong thermal radiation, the coated foams leave more char residue than the pure foam. Moreover, the PHRR of FPUF-8BL is lower than that of FPUF-4BL. From SEM images in Figure 4, the coating on surface of FPUF-8BL has less cracks than the FPUF-4BL. Thus, the eight-bilayer coating on the surface has a better barrier effect to hinder heat and flammable gas transmission. However, the THR value of pure FPUF is 19.2 MJ/m2. After being coated with CS/LS, the THR values of FPUF-4BL and FPUF-8BL achieved to 19.6 and 20.3 MJ/m2, respectively. The THR values of coated foams increase slightly. This is due to the biobased coating also releasing heat during the combustion. Similarly to the HRR curves, the time to the peak of smoke production was retarded. In Figure 7c and d, the SPR and TSP of coated FPUF

pyrolysis products for FPUF-8BL is lower than that for pure FPUF. Consequently, the coating can reduce the release of combustible gas. Flammability of Pure and Coated FPUF. The results of LOI and horizontal flame tests are listed in Table 3. The LOI Table 3. LOI Values, Horizontal Burning Test Results, and Cone Results for the Pure FPUF, FPUF-4BL, and FPUF8BLa

a

sample

FPUF

FPUF-4BL

FPUF-8BL

LOI burning rate (mm/s) TTI (s) PHRR (kW/m2) THR (MJ/m2) SPR (m2/s) TSP (m2)

17.5 1.4 ± 0.1 5±1 736 ± 44 19.2 ± 1.1 0.10 ± 0.01 4.5 ± 0.1

18.0 1.7 ± 0.1 6±1 503 ± 17 19.6 ± 0.7 0.09 ± 0.02 4.2 ± 0.1

18.0 1.8 ± 0.2 5±2 420 ± 37 20.3 ± 0.5 0.08 ± 0.01 4.2 ± 0.2

TTI: time to ignition.

value was slightly changed which means that this biobased coating has little effect on LOI value. As previous researches mentioned, the melt-dripping of the FPUF during the combustion is serious.22 For the horizontal burning test, the melt-dripping phenomenon disappeared after the FPUFs were covered with the CS/LS based coating. However, the burning rate was improved. This is due to the melt-dripping of pure sample take the flame away so that the spread of the flame on the sample become slow. Thus, the coating can effectively prevent the melt-dripping during the combustion while accelerate the burning rate on the sample. On the basis of the oxygen consumption principle, cone calorimeter has been widely used to investigate the combustion behavior of materials. HRR, total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) are recorded to evaluate the combustion behavior of material in E


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Figure 7. Heat release rate, total heat release, smoke production rate, and total smoke production curves of pure FPUF, FPUF-4BL, and FPUF-8BL during the cone test.

Figure 8. Photographs of pure FPUF (a), FPUF-4BL (b), and FPUF-8BL (c) after the cone test. SEM images of FPUF-4BL (d) and FPUF-8BL (e) after the cone test.

were reduced slightly compared to the pure FPUF. This result demonstrates that the biobased coating has a limited effect on reducing the smoke production of FPUF. As shown in Figure 8 the morphology char residues after cone test are characterized by SEM. In Figure 8b and c, it seems that there is no much difference between FPUF-4BL and FPUF-8BL. When the char residue is magnified, the skeleton structures of foam can be seen in Figure 8e. Moreover, these skeleton structures on the char residue of FPUF-8BL are more than those of FPUF-4BL, which demonstrates that the more

deposited CS/LS based coating can keep the foams from melt together during combustion. Raman spectroscopy is an effective tool to characterize the graphitic structure and measure the graphitization degree of carbon materials. Similar to other carbon materials, two marked peaks appear in the Raman spectra of the char residues after cone tests (Figure 9). The D-band (approximately 1360 cm−1) is associated with the vibration of carbon atoms with dangling bonds in the plane termination and it represents the disordered graphite or glass carbons. G-band (approximately 1585 cm−1) F


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Figure 9. Raman spectra of char residue of pure FPUF, FPUF-4BL, and FPUF-8BL after the cone test.

corresponds to the stretching vibration mode with E 2g symmetry in the aromatic layers of the crystalline graphite.29 The graphitization degree of char residue is estimated by the area ratio of the D and G bands (AD/AG), where AD and AG are the integrated area of the D and G bands, respectively. Basically the lower the ratio of AD/AG, the better the structure of the char. The AD/AG ratio of samples follows the sequence: pure FPUF > FPUF-4BL > FPUF-8BL. Therefore, the char residues of all coated FPUFs have a higher graphitization degree than that of pure FPUF. The char residue with high graphitization degree can act as an effective barrier to retard the evolution of flammable volatilized products, the oxygen and heat ingress to the condensed phase and mass transfer into the combustion zone. Mechanical Properties of Pure and Coated FPUF. It is interesting to note that the thermal stability and flame retardant properties of CS/LS coated FPUFs were not the only aspect of the foams influenced. The typical stress−strain behaviors for pure and coated are presented in Figure 10. The tensile

Table 4. Compression Set of Pure FPUF, FPUF-4BL, and FPUF-8BL sample

pure FPUF

FPUF-4BL

FPUF-8BL

compression set (%)

7±1

8±1

8±1

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CONCLUSION Herein, we have reported a water-based route to prepare CS/ LS coating on FPUF by LbL assembly method. Results from UV−vis absorption spectroscopy, ATR-FTIR spectroscopy, and SEM showed that the coating was successfully and uniformly covered on the surface of substrate. Incorporating this coating on FPUF gave rise to a 40 °C increase in the maximum decomposition temperature. Furthermore, the presence of CS/ LS coating endowed FPUF with 42% reduction of PHRR compared to pure FPUF. Meanwhile, the SPR and TSP of coated FPUF were reduced slightly compared to the pure FPUF. Such a great enhancement in thermal stability and fire resistance was mainly attributed to the high decomposition temperature of LS and the char forming of LS and CS. Moreover, the continuous distributed coating improves the tensile strength of FPUF.

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AUTHOR INFORMATION

Corresponding Authors

*Tel./Fax: +86 551 63601664. E-mail address: yuanhu@ustc. edu.cn (Y.H.). *Tel./Fax: +86 551 63600081. E-mail address: leisong@ustc. edu.cn (L.S.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work was financially supported by the National Basic Research Program of China (973 Program) (2012CB719701) and National Natural Science Foundation of China (No.51036007 and 51303167).

Figure 10. Typical stress−strain behaviors for pure FPUF, FPUF-4BL, and FPUF-8BL.

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strength (σ) and elongation at break (ε) of the pure FPUF approximately reached to 0.17 MPa and 82%, respectively. Owing to CS/LS based coatings, the coated FPUFs exhibit improvement in tensile strength. Specifically, the FPUF-8BL possesses strength of 0.19 MPa. The reason for the enhancement in tensile strength is that the coating itself has ability to resist the deformation and interfacial interaction is formed on the surface of FPUF. The data of the compression set test are shown in Table 4. The compression set of coated foams increases from 7% to 8% compared with the pure one. This slight change demonstrates that the biopolymer based coating has a little influence on the resilience of the FPUF.

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Effect of Fully Biobased Coatings Constructed via Layer-by-Layer

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