Preparation of a liquefied banana pseudo-stem based PVAc-nanosilica hybrid membrane and its modification by octadecyltrichlorosilane

Abstract

A novel addition cured liquefied banana pseudo-stem based PVAc (LBP–PVAc) composite membrane with a nano-silica sol was successfully prepared in this study. Surface hydrophobic modification has been carried out using a octadecyltrichlorosilane (OTS) reagent. Scanning electron microscopy (SEM) results showed that nano-silica particles distribute well in the LBP–PVAc system and the structural homogeneity of the hybrid membrane is enhanced. Fourier transform infrared spectroscopy (FTIR) confirmed the self-assembled monolayers of octadecyltrichlorosilane (OTS SAMs) formed on the surface of membranes. Anti-moisture absorption is highly enhanced as water contact angle (CA) on the modified membrane is about 134.88° and relatively stable. The optimal mechanical tensile strength and break elongation of the hybrid membrane were increased by 425.79% and 250.81%, when the concentration of nano-silica is 0.5 wt%. Thermogravimetric (TG) analysis suggested that the thermal stability of the cured hybrid membranes is also improved.

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Introduction

Presently, most polymers are petrochemicals, including PE, PP, PVC, PET, PS, and EVA.^1,2 The accumulation of polymer waste will inevitably bring about environmental problems due to its resistance to natural degradation.³ To alleviate the problems of fossil fuel consumption and environmental pollution, lignocellulosic biomass, acting as an alternative source of clean energy, has drawn considerable attention due to its prominent advantages of renewable, abundance and biodegradable. Numerous techniques have been developed to exploit lignocellulosic biomass, namely, liquefaction, pyrolysis and gasification.⁴ Among which, direct liquefaction has been shown to be the most prevalent process for converting solid biomass to liquid products with high reactivity. The liquefaction process is usually conducted under a relatively mild reaction conditions using polyhydric alcohols as liquefaction solvents.^5,6 Combining the multifunctional groups from both biomass and organic solvents applied in liquefaction, the liquid products produced, which are rich in hydroxyl groups, can be utilized directly to obtain all types of polymeric chemicals such as resins and polyurethane material.^5,7 The liquid products could also act as a modifying agent. Li et al.⁸ published a research on the blending of liquefied banana pseudo-stem (LBP) with polyvinyl acetate emulsion (PVAc) to prepare polymer membranes. The elongation and water resistance of PVAc membrane are enhanced after treating with LBP.

Nowadays, the use of three-, two-, and one-dimensional (e.g., 3D-, 2D-, and 1D-) nano-size fillers, such as silica and rubber nanoparticles, carbon nanotubes (CNTs), clay and graphene nanoplatelets, to modify polymers has attracted extensive interest because of their promise to provide special and enhanced physicochemical properties of plastics.^9,10 It is shown that silica nanoparticles and rubber particles have an equal effect on enhancing the fracture toughness/energy; however, the effect of clay platelets or CNTs on delaying crack growth in epoxy matrices is not obvious.⁹ Moreover, surface treatment of fumed silica, clays, CNTs and graphene is usually essential to help improve their compatibility in the polymer matrix. In contrast, silica sol has exclusive attributes, such as large specific surface area, presence of hydroxyl groups on its surface, low viscosity, and high dispersion.¹¹ Mixing silica sol could also improve the transmittance of polymer composites.^12,13 However, silica sol is mostly limited to waterborne polymer systems in the preparation of organic–inorganic composites because they contain hydrophilic groups on the surface.^13,14

It was reported that introducing siloxane unit could not only improve the mechanical properties of resins, but also change the surface roughness, which influences the contact angle and hydrophobic properties.^15–18 Mori¹⁹ prepared a biodegradable polyurethane resin by adding tetraethoxysilane into liquefied wood-derived polyurethane. The introduction of the inorganic Si network improved the mechanical strength and thermal stability of the material. Kumar et al.²⁰ found that bio-based PU coatings prepared from liquefied black poplar wood and modified with orthotrichlorosilane presented increased scratching resistance, improved cold liquids resistance and better thermal properties. Silicon-containing composites can be synthesized via in situ polymerization,¹¹ sol–gel approach^9,12,20 or physical blending.¹³

Accordingly, in this study, the renewable LBP–PVAc membrane was reinforced by a nano-silica sol via simple physical blending and end-capped by octadecyltrichlorosilane (OTS) via sol–gel process. Originally, the liquefied product was obtained from banana pseudo-stem, and homogeneous mixtures containing various amounts of silica and LBP were prepared by ultrasonic dispersion. The hybrid membranes were then synthesized by blending the mixture with PVAc under room temperature. After curing, the obtained LBP–PVAc membrane was further modified by OTS. The mechanical, morphological, hygroscopic, structural, and thermal properties of the nanocomposite membranes were characterized.

Experimental

Materials

Banana pseudo-stem (BP) from Hainan province in Southern China was dried at 105 °C for 24 h, milled and sieved to a particle size of 0.3 mm prior to liquefaction. Chemical composition of BP contains 23.82% of cellulose, 25.69% of hemicellulose and 8.56% of acid-insoluble lignin. Polyethylene glycol 400 (PEG 400), glycerol and n-hexane were purchased from Xilong Chemical Co., Ltd (China). Commercial polyvinyl emulsion (PVAc) was purchased from the Zhejiang Haiyan Emulsion Coating Factory (China). Silica sol was synthesized by Stöber method.²¹ OTS (C₁₈H₃₇SiCl₃) was purchased from J&K Scientific Ltd (China). All chemicals and reagents were of analytical grade or purer.

Synthesis of LBP–PVAc composite membranes

Banana pseudo-stem was liquefied in polyethylene glycol–glycerol co-solvent with sulfuric acid (H₂SO₄) as a catalyst, as described in our previous publication.⁸ The values of the acid number and hydroxyl number for LBP were 24.16 and 246.52, respectively, measured according to the literature.^22,23 Inorganic–organic hybrid membranes were produced as follows: the LBP-to-PVAc mass ratio was fixed to 1 : 3 and the nano-SiO₂ to total of LBP and PVAc at mass ratio of 0%, 0.5%, 1%, and 1.5%. Silica sol and LBP were uniformly mixed with each other by ultrasonication. The obtained homogeneous mixtures were blended with PVAc via ball milling (Fritsch, Germany). After casting into glass sheets and drying at 100 °C for 1.5 h, the hybrid membrane was formed. All samples were characterized after keeping 7 days at a relative humidity of 50% ± 5% at room temperature and approximately 0.3 mm thick membrane was formed.

Surface hydrophobic modification of hybrid membrane with OTS

LBP–PVAc membranes were cleaned by ethanol and oven-dried before deposition. Silane solution was obtained by dissolving OTS into n-hexane at a ratio of 1% (v/v). The samples were then immersed into the solution for 2 h, followed by washing with n-hexane and drying at 50 °C for 2 h. The as-prepared samples are named as LBP–PVAc–OTS, LBP–PVAc–0.5Si–OTS, LBP–PVAc–1Si–OTS and LBP–PVAc–1.5Si–OTS.

Characterizations

Infrared spectra were obtained using a Perkin Elmer spectrometer in attenuated total reflection mode (ATR-FTIR). An average of 32 scans of each sample ranging from 4000 cm⁻¹ to 650 cm⁻¹ at 25 °C was obtained. The morphology of cured polymer membranes was studied by scanning electron microscopy (SEM, Hitachi S4800, Japan) operating at an accelerating voltage of 10 kV. All the samples were cleaned with alcohol and coated with a thin gold layer using the sputtering technique. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) (NETZSCH5 209F3) were carried out over a temperature range from 40 to 800 °C with a heating rate of 10 °C min⁻¹ under N₂ atmosphere.

Mechanical performance evaluation

The tensile properties of the samples were measured by a Universal Testing Machine (WDW-1, JiNan; China) by following the specification of ASTM D882-02 at a temperature of 25 ± 2 °C and relative humidity of 50% ± 5%. The membranes were cut into dumbbell shapes with 75 mm long and 4 mm wide and loaded to failure at a rate of 50 mm min⁻¹ across head speed. Tensile strength and elongation at break were obtained from the stress–strain curves, 5 specimens were tested for each sample and the average value was adopted.

Contact angles (CA) measurements

The water CA was measured by the sessile drop method using telescoping goniometers at room temperature. 15–20 μL of distilled water was pumped from a micro-syringe onto the surface of membranes, and an image was captured by a telescope fitted with a video camera. All results were expressed as the average of at least five independent measurements.

Immersion test

The immersion test was conduct as follows: pre-weighed dry membranes were cut into 10 mm × 10 mm pieces and immersed in distilled water at room temperature for 7 days. After wiping off the surface water with a piece of filter paper, they were weighed to calculate the water absorption ratio and weight loss ratio by the formulas (eqn (1) and (2)):

Water absorption ratio (%) = [(W_s − W)/W] × 100% (1)

Weight loss ratio (%) = [(W − W_d)/W] × 100% (2)

W: weight of the pre-weighed dry membranes, W_s: weight of the swollen membranes, W_d: weight of the complete dried membranes after immersion.

Results and discussion

Mechanical properties of the LBP–PVAc composite polymer membranes

Fig. 1 shows that the mechanical properties of LBP–PVAc/silica nanocomposite membranes exhibit a rapid increase over pure LBP–PVAc with the addition of silica sol. When the concentration of silica is 0.5 wt%, the break elongation reaches the maximum, i.e. 899.29%. However, when the content is higher than 1 wt%, the mechanical properties of the hybrid membrane become poor. Nevertheless, the membrane containing 1.5 wt% nanoparticles still have the higher mechanical performance compared with that of the neat membrane. This probably accounts for the condensation reaction between the silica functional group and hydroxymethyl groups of the LBP–PVAc, which increased the cross-linking density of the polymer. With excessive nanoparticle incorporation, disproportionate cross-linking points in the system are consumed, resulting in a deterioration of the curing process and the formation of some defects. Typically, these defects are prone to cause stress concentrations and become the weakness of materials, thereby turn to severely reduce the tensile strength and break elongation of polymer.²⁴

Fig. 1 Effect of the silica concentration and OTS treatment on the mechanical properties of the hybrid membranes.

The tensile strength of the membranes was enhanced further after the OTS treatment, but the break elongation of the hybrid membranes shows a slight decrease. This phenomenon may be attributed to OTS being chemically connected to the hybrid LBP–PVAc chains, and the incorporation of siloxane not only works as a reinforcement filler, but also increases the hardness of membranes.^18,20 Optimal performance was observed for LBP–PVAc–0.5Si–OTS, of which the tensile strength and the break at elongation were increased significantly by 425.79% and 250.81%, respectively, compared to the pristine LBP–PVAc membrane. The enhanced membrane can be used as commodity packaging materials.

Wettability and swelling properties

Water contact angle measurements were used as a determination of wettability of the cured membranes. Table 1 demonstrates that the control LBP–PVAc membrane shows a water CA of about 10.26° (LBP–PVAc–0.5% Si, 10.46°; LBP–PVAc–1% Si, 6.61°), measured 1 s after the sessile drop from the micro-syringe onto the surface of the membranes. Interestingly, the water CA values of the membrane surfaces increase greatly up to 134.88° (LBP–PVAc–0.5% Si–OTS, 127.65°; LBP–PVAc–1% Si–OTS, 112.31°) after treated by OTS. It can be supposed that OTS SAMs formed on the membranes. In addition, water CA on the surface of membranes without OTS modified tended to decrease with time in 60 s, whereas it remained stable and unchanged after treatment of OTS, preventing water penetrating into the membranes.²⁰

Table 1 Water CA on the surface of the hybrid membranes measured at different times after water drop deposition

Codes	1 s (°)	30 s (°)	60 s (°)
LBP–PVAc	10.26	10.4	5.56
LBP–PVAc–0.5Si	10.46	8.74	4.82
LBP–PVAc–1Si	6.61	6.35	4.58
LBP–PVAc–OTS	134.88	134.88	134.88
LBP–PVAc–0.5Si–OTS	127.65	127.65	127.65
LBP–PVAc–1Si–OTS	112.31	112.31	112.31

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Immersion tests were conducted as supplemental measurements of water resistance for hybrid membranes. The PVAc membrane treated with LBP is more stable in water, as reported in previous work.⁸ It was understood that the cross-linking reaction was triggered between the hydroxyl groups in the LBP and the hydroxyl groups in the PVAc, which generated an ether bond or an ester bond. In contrast, LBP–PVAc membranes mixed with silica sol exhibit significant swelling after immersing in water for 1 h, as shown in Fig. S1.† Owing to many hydrophilic groups introduced into the system and a part of organic–inorganic hybrid materials that did not cure a cross-link with too much nano-SiO₂ incorporation, LBP–PVAc–1Si is dissolved in water after dipping in it for 24 h. Based on the overall immersion test for 72 h, LBP–PVAc–0.5Si kept swelling and the size is approximately expanded to nine times larger than the original sample without degradation, which is likely associated with the strong hydrogen bonding interaction between the membrane matrix system and water. Importantly, it shows that the water resistance of the OTS treated membranes is enhanced dramatically and only some slight swelling phenomenon occurs. This observation further verified that OTS has an excellent effect on mitigating water penetration.

The results of the water absorption ratio and weight loss ratio of the nanocomposite membranes are depicted in Table 2 after immersion in water for 7 days. The measurements of membranes that modified with silica merely failed because they swelled or dissolved. It was found that the water-absorption ratio increased after the OTS treatment for LBP–PVAc membrane. The two most likely reasons are (a) the dissolution rate of pure LBP–PVAc membrane is higher than its swelling rate and (b) the hydrolysis of less-well-ordered OTS on the modified membrane and amphiphilic species (hydrophilic head in OTS molecules) were produced.^25,26 Although the water-absorption ratio increased with increasing silica content because of the increase in hydrophilic group or hydrogen bonding with water, no structural failure occurs, as shown in Fig. S1.† On the contrary, the weight loss ratio is found to decrease after incorporating silica and modified by OTS in the curing membranes in comparison to the control (Table 2), which is likely due to the increase in cross-link density and end-capped by siloxane, thus slowing down the dissolution rate of samples in water.^15,16 Such phenomena support the hypothesis that dissolution and swelling of a sample coexist in water. This suggests that the hybrid membrane would be degraded naturally after a longer period of time.

Table 2 Water absorption and weight loss ratio of the LBP–PVAc nanocomposite membranes after immersing in water for 7 days^a

Codes	Water absorption^1 (%)	Weight loss ratio^2 (%)
a 1, 2: no data because the membranes is excessively swelling or dissolved.
LBP–PVAc	92.87	66.67
LBP–PVAc–OTS	129.74	64.87
LBP–PVAc–0.5Si	—	—
LBP–PVAc–0.5Si–OTS	177.78	47.67
LBP–PVAc–1Si	—	—
LBP–PVAc–1Si–OTS	271.24	54.90

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Morphology of the hybrid membranes

Fig. 2 presents the SEM images and Si mapping of cured LBP–PVAc membranes. It shows that the surface with micro- and sub-micro structures of hybrid LBP–PVAc membranes is formed. For native LBP–PVAc (Fig. 2(a)), a relatively flat and smooth surface with some harmful air bubbles is observed. A homogeneous and dense micro wrinkles structure is formed after introducing 0.5 wt% silica (Fig. 2(d)), which is somewhat similar to the surface morphologies of fluorinated polymethacrylate/waterborne polyurethane blend induced by the tension shrinkage of the interface and micro-phase separation.¹⁴ In Fig. 2(g), the reduced micro wrinkled structures and increased sub-micro particles are shown, which is presumably related to the main interaction between the silica–silica interactions being stronger than the LBP–PVAc–silica interactions, in other words, formation of agglomerates occurred as the silica content increases. According to the Si mapping for the silica mixed membranes (Fig. 2(j) and (k)), the red dots display the silicon atoms, showing that particles are dispersed uniformly throughout the polymer matrix. Uniform distribution of nano-silica as fillers in the matrix played an important role in the mechanical properties and thermo-tolerant performance of polymers.^27,28

Fig. 2 SEM morphologies of the hybrid membranes. (a) LBP–PVAc; (b and c) LBP–PVAc–OTS; (d) LBP–PVAc–0.5Si; (e and f) LBP–PVAc–0.5Si–OTS; (g) LBP–PVAc–1Si; (h and i) LBP–PVAc–1Si–OTS; (j and k) Si mapping of LBP–PVAc–0.5Si and LBP–PVAc–1Si; the insets in (a, d, g) and (c, f, i) are the images of water drops.

As shown in Fig. 2(b), (e) and (h), there are distinct changes in the surface morphology of the hybrid membranes modified by OTS. The special surface structure with micro-scale sags and crests contributes to the much-increased surface roughness, which is related to the self-organization of OTS. Fig. S2† shows that the OTS layer formed on the surfaces of the membrane has a relatively high density and a certain thickness (LBP–PVAc–OTS, 19 μm; LBP–PVAc–0.5Si–OTS, 50 μm; LBP–PVAc–1Si–OTS, 78 μm). Based on existing research, it is worth pointing out that the surface morphology of the OTS modified samples varies from the substrate that OTS grow on.^20,29,30 The CA of water highly increased (Table 1 and inset in Fig. 2) and the waterproof layer was largely enhanced, as discussed above. It has been reported that roughness and surface energy are the factors that determine the wettability.^31,32 Wenzel developed a model to describe the contact angle Ψ at rough surface with the following formula:

cos Ψ = r cos θ (3)

where θ is the contact angle on the smooth surface of the same material and r is the roughness factor, which is defined as the ratio of the actual area of a rough surface to the geometric projected area. For OTS treated samples, r > 1, the roughness and hydrophobicity of membrane are improved. Jiang³³ and Wu¹⁴ obtained a similar result. Liu et al.^29,30 conducted studies on OTS modified poly(vinyl alcohol) (PVA)/SiO₂ coatings and epoxy/silica coatings on wood surfaces, respectively, both of which exhibited stable superhydrophobic property. The hydrophobic membrane has a promising prospect of application in agricultural areas, such as for ground film and shed films, which have good antifogging properties and can prevent the adhesion of rain or snow.

FTIR studies

The spectra of the LBP–PVAc/silica hybrids are displayed in Fig. 3. The absorption regions of C=O (1716 cm⁻¹, 1736 cm⁻¹ and 1248 cm⁻¹) initially present in PVAc, and C–O (1085 cm⁻¹) in LBP–PVAc results from the reaction between the hydroxyl groups in the LBP and the hydroxyl groups in the PVAc.⁸ The bands at 2916 cm⁻¹ correspond to the stretching vibration of –CH₂. The absorption peak at 3365–3410 cm⁻¹ ascribed to the hydroxyl groups in the membranes and unreacted silanol groups. In addition, the absorption bands at 1022 cm⁻¹ and 796 cm⁻¹ are observed, which were attributed to the Si–O–Si asymmetrical stretching and symmetrical stretching, respectively. Earlier studies indicated the formation of hydrogen bonding or covalent bonding between the inorganic and organic components.^11,34–36 The characteristic absorption band of Si–O–C is not obvious, which is likely to be covered by C–O absorption regions (1100 cm⁻¹–1000 cm⁻¹);¹⁹ therefore, it is indistinguishable on the LBP–PVAc/silica hybrid membranes.

Fig. 3 FTIR spectra of LBP–PVAc and hybrid membranes. (a) LBP–PVAc; (b) LBP–PVAc–0.5Si; (c) LBP–PVAc–1Si; (d) LBP–PVAc–OTS; (e) LBP–PVAc–0.5Si–OTS; (f) LBP–PVAc–1Si–OTS.

After OTS modification, new absorbing regions appear, such as CH stretching (2848 cm⁻¹, 2977 cm⁻¹), CH₂ scissoring deformation (1467 cm⁻¹). However, the absorption peaks including 3365–3410 cm⁻¹ tend to be weaker or broader for membranes with OTS end-capped. The results can be attributed to the incorporation/reaction of hybrid membranes with silanol of hydrolysed OTS, resulting in the consumption of hydroxyl groups. Some free hydroxyl groups still remained due to the unreacted parts caused by steric hindrance existing in the liquefied products and partly less-well-ordered silane layers.^20,37 In addition, Si mapping of the membrane cross-section confirmed that the OTS layer is successfully formed (Fig. S2(c), (f) and (i)†). OTS SAMs formed on the surfaces of membrane may not easy fall off by chemical bonding with membrane substrate, which will increase the service life of the hydrophobic membrane.

Enhancement mechanism

Based on the SEM and FTIR results, a mechanism of enhancement for LBP–PVAc/silica nanocomposites has been proposed, as shown in Scheme 1. First, the crosslinked network structures are generated using silica nanoparticles, acting as cross-linked or bridge precursors to connect the LBP–PVAc with LBP–PVAc.^8,11 The OTS was involved in the formation of self-assembled monolayers (SAMs) on the surface of membranes by hydrolysis and condensation.^25,26 A three dimensional structure in LBP–PVAc/silica nanocomposites was produced ultimately, contributing to reinforcing their mechanical or hydrophobic properties.

Scheme 1 Reaction mechanisms of preparing LBP–PVAc nanocomposite membrane.

Thermal behavior of LBP–PVAc and hybrid membranes systems

TG and DTG analysis were utilized to evaluate the thermal stability of the membranes. As shown in Fig. 4(a), there are mainly three stages of the thermal decomposition in the range of 50–600 °C. The first stage in the 50–120 °C range is mainly the decomposition of the residual solvents, water and short oligomers. The second stage in the 120–350 °C range is probably the breaking of the hard segment, which involves decarboxylation reactions and the decomposition of α- and β-aryl-alkyl-ether linkages and aliphatic chains.²⁰ The third stage may be the decomposition of the soft segment, which involves the polyester, polyether and silica bond.

Fig. 4 TG (a) curves and DTG, (b) curves of LBP–PVAc hybrid membranes.

Fig. 4(b) and Table 3 show that the maximum weight-loss rate of the hard segment for LBP–PVAc occurred at 184.4 °C and that of LBP–PVAc–0.5Si and LBP–PVAc–1Si occurred at around 216.1 °C and 218.6 °C, respectively. Compared to pure LBP–PVAc, the 10%, 25% and 50% mass loss temperature of LBP–PVAc/silica are higher. Another DTA peak at ∼486 °C appears after the OTS treatment (Fig. 4(b)). This may be due to the formation of stable covalent bonds Si–O–Si between nanosilica and siliane present in the OTS layers.³⁸ The residue weight percentages at 800 °C increased with the nanosilica content and the deposition of OTS SAMs. The results obtained provide additional evidence of successful covalent coupling generated from the interaction between the inorganic phase and organic phase. The improved thermal stability make it possible for the service temperature of the products made by the hybrid membrane to be up to 110–120 °C.

Table 3 Detailed DTG data of LBP–PVAc membranes as obtained from TGA measurements under N₂

Codes	T10% (°C)	T25% (°C)	T50% (°C)	TDTAmax (°C)	R800 (°C)
LBP–PVAc	139.6	203.7	330.9	184.4/393.5	9.76
LBP–PVAc–OTS	161.9	218.2	356.8	181.3/402.3	11.54
LBP–PVAc–0.5Si	178.1	224.6	332.4	216.1/394.4	12.54
LBP–PVAc–0.5Si–OTS	191.5	232.8	341.0	210.9/392.3	12.59
LBP–PVAc–1Si	189.1	229.8	340.5	218.6/393.6	13.15
LBP–PVAc–1Si–OTS	190.3	231.1	340.8	218.8/401.2	13.79

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Conclusions

A renewable and environmental friendly organic–inorganic hybrid liquefied banana pseudo-stem-based PVAc membrane was successfully prepared in this study. Introducing a silica sol into the membrane plays a crucial rule in increasing its crosslinking density and expanding its tensile properties. FTIR spectroscopy confirmed that OTS SAMs were chemically bonded to the surfaces of hybrid membranes. The formed hydrophobic layers increased the surface toughness of the membranes and significantly enhanced its water resistance. The thermal stability of the nanocomposites membrane was also improved. The renewable and degradable hybrid membranes have potential to replace fossil fuel-based plastics to be applied in the field of packaging materials.

Acknowledgements

The authors are thankful for the financial supports from the National Natural Science Foundation of China (No. 51263006), the Ministry of PhD Education, Advisor Class Special Fund (20134601110004), the Hainan Province of Key Project (ZDXM20130086), the Hainan International Science and Technology Cooperation Specific (KJHZ2014-02), and the Hainan Natural Science Foundation (314074). The authors would like to express their gratitude to the Analytical and Testing Center of Hainan University.

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Footnote

† Electronic supplementary information (ESI) available: Fig. S1 photograph images of LBP–PVAc nanocomposite membranes immersing in water for 0 h, 1 h, 24 h, 48 h and 72 h, respectively. Fig. S2 shows SEM images of the cross sections of the membranes and Si mappings for selected membranes. See DOI: 10.1039/c6ra20154g

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