Preparation and characterization of bio-based hybrid film containing chitosan and silver nanowires
Graphical abstract
Introduction
To develop sustainable alternatives for present-day functional materials based on increasingly depleted primary fossil resources, innovative development of high performance bio-based materials with advanced functionalities is highly desirable. Among these chitosan is one of the most important polymer due to their different reactivity of the amino group at C2 position and the primary and secondary hydroxyl groups at C6 and C3 positions. The nontoxicity, biocompatibility and polyatomic nature (Xu, Kim, Hanna, & Nag, 2005) of chitosan (CS) films have made them widely applicable for the synthesis of biomaterials, for example, as wound dressing, skin grafting template, hemostatic agent, and drug delivery vehicle (Cardenas et al., 2010).
Although such bio-based materials have been developed and used extensively but the resulting mechanical properties of such materials mostly fall drastically due to disruption of higher order of the hierarchical natural structures. Organic/inorganic nanocomposites are promising materials that are designed to improve the mechanical properties. Metals and ceramic reinforcements offer striking routes to certain unique, mechanical properties coming from inorganic nanoparticles, which add to the polymer properties such as processibility and film forming capability (Fernandez & Ingber, 2012, Bonderer et al., 2008; Sun et al., 2011, Sun et al., 2014). For instance, inorganic tablets including clay (Giannakas et al., 2014), Al2O3 (Bonderer et al., 2008), montmorillonit (MMT) (Yao et al., 2010), and other metal oxides or salts Fe3O4, α-Zr (HPO4)2·H2O, (Marroquin et al., 2013, Pan et al., 2011, Wu et al., 2010) have been employed to fabricate the bio-based nanocomposite. Using this approach, the mechanical properties of polymers can be improved while keeping their lightweight and ductile nature (Meghri et al., 2010). Importantly, some inorganic nanofiller not only can improve the mechanical properties of the polymer, but also can provide some special advantaged functions for these nanocomposites due to the unique character of the inorganic fillers.
Silver (Ag) possesses excellent malleability, mechanical robustness, the highest electrical conductivity (1.6 × 10−6 Ω cm) among metals, and is highly resistant to corrosion. In particular highly anisotropic silver nanowires (AgNWs) have extra advantages in forming a percolated network when applied to rough surfaces (e.g., paper) or fabricated a film (Yang et al., 2011). Moreover, AgNWs are known to be safe for humans compared to other non-metallic conductive materials (e.g., carbon nanotubes) due to its antimicrobial and electronic properties (Yoksan & Chirachanchai, 2010). Recently, with the boom of flexible electronics, mechanical flexibility has become an important measure of the performance of electronic materials. AgNWs have been paid more attention to fabricate such related composites due to its unique structure and nature (Gaynor et al., 2011, Zeng et al., 2010, Miller et al., 2013). Some new polymer matrices such as polyvinyl alcohol, polyacrylates and resins have been used as substrates or protection layers for the AgNWs in order to achieve a conductive sheet with flexibility, high thermal and chemical stabilities (Im et al., 2014, Gaynor et al., 2011). However, continuous and excessive use of these polymers will generate serious environmental concerns. Therefore, there is a need for developing some new sustainable substrates or protective films with the AgNWs to get multifunctional performance for practical application.
In this work, a simple and efficacious solution-based method is demonstrated to achieve a flexible chitosan AgNWs bio-based film. To the best of our knowledge, this is the first time to prepare the chitosan-AgNWs using such method. This hybrid nanocomposite showed excellent mechanical performance, good conductivity and antibacterial properties due to the unique character of the nanocomposites, which may show a promising application in the fields of flexible electron, package or medicine.
Section snippets
Materials
CS with viscosity-average molecular weight of 185,000 g/mol and 90% degree of acetylation was purchased from Jifa Company of China. Acetic acid (99.2%) used to dissolve the CS and polyvinylpyrolidone (PVP) with molecular weight 55000, AgNO3 (99.5%) and NaCl (98.5%), glycerol (98%) for AgNWs synthesis obtained from Sino Pharm Company. NaBH4 (98%) was also purchased from Sino pharm company of China for synthesis of AgNPs.
Preparation of AgNWs
Complete process for the preparation of the AgNWs by polyol method presented
Result and discussion
AgNWs were prepared by modified polyol reduction method according to the method proposed by Yang et al. (2011). The Possible mechanism for the synthesis of AgNWs may be AgNO3 in the presence of NaCl and glycerol converts in to AgCl and NaNO3 and after nucleation AgNWs are produced. Reduction at high temperature changed the color of solution from brown to grayish green indicating presence of silver nanowires. Fig. 3(a) is showing the vial containing the AgNWs that were introduced in CS film by
Conclusion
In conclusion, a bio-based hybrid film containing CS and AgNWs has been successfully prepared by a simple and efficacious solution-based method. EDS spectrum of CS-AgNWs film confirmed the presence of nanocrystalline elemental silver. X-ray diffraction and FTIR spectroscopy were used to evaluate the interaction of Silver with CS matrix. Only 15% AgNWs could increase the tensile strength of hybrid film from (41.66 ± 2.16 MPa) to (67.68 ± 4.26 MPa). This increment was 62% and 36.7% more when compared
Acknowledgements
This work was supported by K.C. Wong Education Foundation, Youth Innovation Promotion Association of CAS; the Qingdao Institute of Bioenergy and Bioprocess Technology Director Technology Foundation; Shandong Provincial Natural Science Foundation for Distinguished Young Scholar, China (No. JQ201305), China and CAS-TWAS President's PhD Fellowship programme of K.S (2013A8017908241).
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