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Strong Polyvinyl Alcohol (PVA)/Bamboo Charcoal (BC) Nanocomposite Films with Particle Size Effect Mohanad Mousa, and Yu Dong ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02750 • Publication Date (Web): 27 Nov 2017 Downloaded from http://pubs.acs.org on November 28, 2017
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Strong Polyvinyl Alcohol (PVA)/Bamboo Charcoal (BC) Nanocomposite Films with Particle Size Effect Mohanad Mousa and Yu Dong* Department of Mechanical Engineering, School of Civil and Mechanical Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
*Corresponding author email address:
[email protected] Institution Mailing Address: Department of Mechanical Engineering, School of Civil and Mechanical Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
ABSTRACT In this paper, bamboo charcoals (BCs) were considered as alternative ecofriendly and sustainable carbon-based nanoparticles since their good affinity with water soluble biopolymer polyvinyl alcohol (PVA) to achieve strong (PVA)/ (BC) nanocomposites. Two different types of
BC particles, namely microdiameter bamboo charcoals (MBCs) and nanodiameter bamboo charcoals (NBCs) were successfully fabricated by solution casting method. Nanofiller reinforcement effect was investigated from BC particle size and dispersion, morphological structures, and interfacial interactions between BCs and PVA matrices. Overall, the addition of NBCs yields increasingly higher mechanical properties of PVA/BC nanocomposites when compared with that of MBCs. The maximum enhancements in tensile moduli of nanocomposites were achieved up to 123% and 100% with the inclusion of 10 wt% NBCs and MBCs, respectively. Whereas corresponding tensile strengths were improved by 110% and 72% with the incorporation of 3 wt% NBCs and MBCs accordingly, as opposed to those of PVA. Such findings obtained may be attributed to more uniform BC particle dispersion in PVA/BC nanocomposites, and better interfacial interactions between BCs and PVA matrices. Tensile moduli of PVA/BC nanocomposites were predicted by Halpin-Tsai model and combined Mori-Tanaka model and laminate theory in both BC well-aligned and randomly
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oriented states, suggesting that the introduction of effective volume fractions of randomly oriented BCs led to the best modulus estimation. This study confirms the necessity of using BCs to replace conventional carbon-based nanofillers for developing more economical and eco-friendly nanocomposites. KEYWORDS: Polyvinyl alcohol (PVA), bamboo charcoals (BCs), nanocomposites, mechanical properties, analytical modelling INTRODUCTION Polyvinyl alcohol (PVA) is a popular water-soluble and eco-friendly biopolymer with favorable mechanical properties, thermal resistance, excellent flexibility,1 recyclability and bio-tribological properties.2 Furthermore, its biotechnological applications comprise tissue engineering, drug delivery, articular cartilage and biosensors.1-3 In recent years, the incorporation of nanofillers such as montmorillonite (MMT) clays,4,5 halloysite nanotubes (HNTs),6-8 carbon nanotubes (CNTs),9,10 graphene sheets,11,12 cellulose nanocrystals,13,14 laponite15 and nanodiamond16 into PVA matrices in nanocomposite systems have drawn great attention to significantly improve mechanical properties of PVA nanocomposites. Among different nanofillers, CNTs are considered as effective reinforcements widely used in polymer nanocomposites. In addition to their high material cost, nanotoxicity is deemed as the major drawback to CNTs due to their accumulation in cytoplasm with the resulting ability to destroy human cells under certain inhalational conditions.17 On the other hand, graphene sheets have also experienced limited use owing to their tendency to form agglomerates.18 Notwithstanding effective reinforcements with unique eco-friendliness and environmental sustainability, bamboo charcoals (BCs), as newly used carbon-based particles, have not been widely employed up to date when compared with above-mentioned popular nanofillers. BC particles are generally produced from carbonized bamboo at a typical temperature of 1000-1500˚C under nitrogen atmosphere,19 which results in the formation of significant amounts of lengthwise and crosswise pores within BC structures.19,20 In a nanocomposite system, BC morphology displays
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a wide range of pore distributions from less than 1 nm to 1 µm.21 As such, polymeric chains tend to easily penetrate into internal BC pores22 to form strong mechanical bonding in addition to the hydrogen bonding of pores, which is believed to improve mechanical properties of resulting nanocomposites.23,24 Nonetheless, the appropriate selection of polymer matrices also plays a leading role in successful preparation of nanocomposites in addition to the incorporation of BCs. Previous work mainly concentrated on the fabrication and characterization of hydrophobic polymer/BC composites such as polylactic acid (PLA)/BC composites,23 ultra-high molecular weight polyethylene (UHMWPE)/BC composites24 and polyaniline (PANI)/BC composites.25 According to Laplace theory,22,26 when hydrophobic polymer is chosen, the surfaces of hydrophobic media can generate negative capillary pressures to hinder the entry of polymeric chains into BC pores, thus leading to typical phase separation in a nanocomposite system. In contrary, when hydrophilic media are selected, applied positive capillary pressures drive polymeric chains into BC pores to form both mechanical and chemical bonding, which is the reason why PVA has been chosen to study in this paper. The material selection of hydrophilic biopolymers such as PVA to interact with BC particles has been rarely studied for the enhancement of mechanical properties in a nanocomposite system, which can narrow the potential use of BC particles as effective nanofillers. The only results reported by Tang et al27 as to mechanical properties of PVA/BC nanocomposite membranes indicated a moderately maximum increase of 38% in tensile strength with the inclusion of 1 wt% BCs. Herein, we holistically investigated the effects of BC nanoparticles on achieving much better mechanical properties and modelling of PVA/BC nanocomposites with the consideration of particle size effect and effective volume fraction to develop new eco-friendly and super strong nanocomposite films, which, to our best knowledge, has not been mentioned systematically in previous research studies at all. Furthermore, directly experimental measurement of Young’s modulus of BC nanoparticles was reported for the first time via atomic force microscopy (AFM) along with the use of effective volume fractions of BCs, which
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presents a more reliable approach to accurate modelling work of PVA/BC nanocomposite films. EXPERIMENTAL SECTION Materials. PVA biopolymer used in this study (material type: MFCD00081922 from Sigma Aldrich Pty. Ltd, Australia) has an average molecular weight Mw=89000-98000 g/mol and a degree of hydrolysis over 99%. MBCs (particle diameter < 500 nm) and highly bioactive NBCs (particle diameter
