Effect of Natural Nanostructured Rods and Platelets on Mechanical and Water Resistance Properties of Alginate-Based Nanocomposites

ORIGINAL RESEARCH published: 19 December 2018 doi: 10.3389/fchem.2018.00635 Effect of Natural Nanostructured Rods and Platelets on Mechanical and Water Resistance Properties of Alginate-Based Nanocomposites Dajian Huang*, Zhuo Zhang, Zonghong Ma and Qiling Quan School of Materials Science and Engineering, Lanzhou Jiaotong University, Lanzhou, China Edited by: Wenbo Wang, Lanzhou Institute of Chemical Physics (CAS), China Reviewed by: Yushan Liu, Zhengzhou University, China Yuqi Li, Guilin University of Technology, China *Correspondence: Dajian Huang Specialty section: This article was submitted to Green and Sustainable Chemistry, a section of the journal Frontiers in Chemistry Received: 29 June 2018 Accepted: 07 December 2018 Published: 19 December 2018 Citation: Huang D, Zhang Z, Ma Z and Quan Q (2018) Effect of Natural Nanostructured Rods and Platelets on Mechanical and Water Resistance Properties of Alginate-Based Nanocomposites. Front. Chem. 6:635. doi: 10.3389/fchem.2018.00635 Frontiers in Chemistry | www.frontiersin.org A series of biopolymer-based nanocomposite films were prepared by incorporating natural one-dimensional (1D) palygorskite (PAL) nanorods, and two-dimensional (2D) montmorillonite (MMT) nanoplatelets into sodium alginate (SA) film by a simple solution casting method. The effect of different dimensions of nanoclays on the mechanical, water resistance, and light transmission properties of the SA/PAL or MMT nanocomposite films were studied. The field-emission scanning electron microscopy (FE-SEM) result showed that PAL can disperse better than MMT in the SA matrix in the case of the same addition amount. The incorporation of both PAL and MMT into the SA film can enhance the tensile strength (TS) and water resistance capability of the film. At a high content of nanoclays, the SA/PAL nanocomposite film shows relatively higher TS, and better water resistance than the SA/MMT nanocomposite film. The SA/MMT nanocomposite films have better light transmission than SA/PAL nanocomposite film at the same loading amount of nanoclays. These results demonstrated that 1D PAL nanorods are more suitable candidate of inorganic filler to improve the mechanical and water resistance properties of biopolymers/nanoclays nanocomposites. Keywords: palygorskite, montmorillonite, bionanocomposite films, sodium alginate, mechanical strength, water resistance INTRODUCTION Over the past decades, the commodity plastics (i.e., polyethylene, polypropylene, and polyethylene terephthalate) as commonly used food packaging materials have plaid very important roles in human daily production. However, these plastic packaging materials are totally non-biodegradable, so their widespread use caused serious environmental pollution problems (Souza et al., 2017; Costa et al., 2018; Salama et al., 2018). Therefore, the development of biodegradable films using natural, non-toxic, and environment benign polymers such as polysaccharides, proteins, and lipids has drawn much more attention in both of academic and industrial areas (Mushi and Berglund, 2014; Wang and Jing, 2017; Youssef and El-Sayed, 2018). Among numerous biodegradable natural polymers, sodium alginate (SA) was especially concerned owing to its excellent biocompatibility, film-forming ability, and active functional groups (Shankar et al., 2016; Fabra et al., 2018). SA is an anionic natural biomacromolecule, which is composed of poly-b-1, 4-D-mannuronic acid (M units), and a 1, 4-L-glucuronic acid (G units) in different proportions by 1–4 linkages. It is extracted from marine algae or produced by bacteria, and so it has the advantages including abundance, 1 December 2018 | Volume 6 | Article 635 Huang et al. Sodium Alginate/Clay Nanocomposites transmission properties of the films. The potential of 1D PAL nanorods and 2D MMT for fabricating SA-based nanocomposite film was also assessed by a systematic comparative study. renewability, non-toxicity, water-solubility, biodegradability, and biocompatibility (Wang and Wang, 2010). However, the inherent hydrophilicity and brittleness of neat SA films limited their applications in film materials (Rhim, 2004; Zhang et al., 2017). In order to overcome the drawbacks of neat SA films, a variety of nanoscale particles such as montmorillonite (MMT) (Tunç and Duman, 2010; Zlopasa et al., 2015), graphene oxide (Liu et al., 2017), and cellulose nanocrystals (Sirvio et al., 2014) have been incorporated into the SA matrix to fabricate a nanocomposite. Abdollahi et al. (2013) developed an alginate/MMT nanocomposite by a solvent casting method, and found that the mechanical properties of the alginate/MMT composites were enhanced significantly after the addition of MMT. However, MMT forms an agglomeration in the polymer matrix when its addition amount exceeds a certain value, which leads to the decrease of the mechanical properties of the film. It has been shown that MMT is a 2:1-type layered clay mineral with a sandwiched structure composed of two 2D platelets and interlayer cations (i.e., Na+ , Ca2+ , Mg2+ ). The strong hydrogenbinding and electrostatic interaction, and van der Waals forces between two platelets make MMT difficult to be exfoliated and tend to be present in a form of agglomeration (Zhang et al., 2014; Block et al., 2015; Liu et al., 2016). In comparison, natural 1D rod-like nanoclays are easy to be dispersed as nanoscale size, and showed great potential to be used to develop polymer/nanoclays composites (Nikolic et al., 2017; Ajmal et al., 2018; Shankar et al., 2018; Zhang P. et al., 2018). It has been demonstrated that the dispersion of nanoclays in polymer matrix, and the comprehensive performance of the resultant polymer composites exhibited interesting dependence on the shape of fillers. Usually, rod-like nanoclays have a relatively smaller contact surface and weaker interaction amount rods, so that they could probably be dispersed in the polymer matrix well with less aggregation (Bilotti et al., 2009). Palygorskite (PAL) is a naturally available 1D nanorod-like silicate clay mineral (Deng et al., 2012; Zhang et al., 2018b). It consists of two double chains of the pyroxenetype (SiO3 )2− like amphibole (Si4 O11 )6− running parallel to the fiber axis (Gard and Follett, 1968; Zhu et al., 2016; Zhang et al., 2018a). PAL is a potential filler to fabricate polymer composite due to its unique advantages, such as high aspect ratio, large specific surface area, good thermal stability, and high modulus (Huang et al., 2012; Ruiz-Hitzky et al., 2013; Ding et al., 2019). It has been confirmed that the incorporation of silylated PAL into the polyurethane matrix improved significantly the thermal stability and mechanical properties of polyurethane (Peng et al., 2011). In addition, 1D fibrous nanoclay has relatively higher density of silanol groups on its surface than 2D layered silicates, making it able to form more hydrogen bonds with hydrophilic biopolymers (Alcantara et al., 2014). So (...truncated)