Elsevier

Carbohydrate Polymers

Volume 134, 10 December 2015, Pages 390-397
Carbohydrate Polymers

Carboxymethyl chitosan/clay nanocomposites and their copper complexes: Fabrication and property

https://doi.org/10.1016/j.carbpol.2015.07.089Get rights and content

Highlights

  • A new type of environmentally friendly antifouling agent were prepared.

  • The thermostability and antibacterial advantages of CMC, OMMT and Cu+ was combined.

  • CMC/OMMT–Cu nanocomposites showed high thermal stability.

  • CMC/OMMT–Cu nanocomposites exhibited excellent antimicrobial activity.

  • The lowest MIC of CMC/OMMT–Cu nanocomposite against E. coli was only 0.0003125%.

Abstract

To obtain environmentally friendly antifouling agent, an effort was made to intercalate carboxymethyl chitosan into the interlayer of organic montmorillonite to prepare carboxymethyl chitosan/organic montmorillonite nanocomposites and their copper complexes. In comparison, carboxymethyl chitosan–copper complexes were also obtained. Their structures were characterized by X-ray diffaraction, transmittance electron microscopy and Fourier transform infrared, and their thermal behavior and antimicrobial activity were discussed. The results revealed that the interlayer distance of carboxymethyl chitosan/organic montmorillonite nanocomposites enlarged with the increasing mass ratio of carboxymethyl chitosan to organic montmorillonite, when the mass ratio was at 20:1, the layer spacing of carboxymethyl chitosan/organic montmorillonite nanocomposites reached the maximum of 3.68 nm. As compared to other samples, carboxymethyl chitosan/organic montmorillonite–copper nanocomposites showed much higher thermal stability and inhibitory activity against Escherichia coli, the lowest minimum inhibition concentration was only 0.0003125% (w/v). The study provides a new method to find novel antifouling agent.

Introduction

In the process of the development of marine antifouling paints, the self-polishing antifouling paint with the function group of organotin (TBT) acrylic resin was praised as special weapons of marine antifouling. However, TBT caused serious damage to marine ecological environment (Antizar-Ladislao, 2008), therefore it is urgent to find a non-toxicity antifouling paint.

Chitosan is natural, biocompatible, biodegradable, non-toxic and multifunctional resource, which is regarded as environmentally friendly antifoulant by chemists (He, Davis, & Illum, 1999; Khan, Badshah, & Airoldi, 2015; Kurmaev et al., 2002; Rhazi et al., 2002). Chitosan is the only kind of alkaline natural amino polysaccharide which is composed of β-(1,4)-2-acetamino-2-deoxy-d-glucose binary linear copolymer (Ling, Li, Zhou, Wang, & Sun, 2015; Li, Liu, Ye, Wang & Sun, 2015). Carboxymethyl chitosan (CMC) is water-soluble chitosan derivative with remaining excellent antibacterial properties (Liu, Wang, Li et al., 2012, Liu, Wang et al., 2012; Sun, Du, Fan, Chen, & Yang, 2006), which can chelate effectively with metal salts (Paradossi, Chiessi, Venanzi, Pispisa, & Palleschi, 1992), and the self-polishing antifouling paint can be simulated by chelating CMC with metal ion such as copper ion that is widely considered as a broad antibacterial material and used to kill algae (Heuser, Rivera, Nunez, & Cardenas, 2009; Muzzarelli & Tubertini, 1970). But the thermal stability and the antimicrobial activity of CMC–Cu complex are still not satisfactory.

From this point, it is noted that chitosan-based layered silicate nanocomposites have drawn people's attention for coupling of numerous merits of chitosan and layered silicate (Deng et al., 2012, Liu, Wang, Yang, Sun, 2011; Liu, Wang, Yang, Wang & Sun, 2011; Wang et al., 2009, Wang et al., 2006). Montmorillonite (MMT) is a 2:1 typed layered silicate with high thermal stability, and more interestingly, the previous study demonstrated that MMT had no antibacterial activity itself, but it showed dual performance of adsorbing bacteria and killing bacteria when the cationic material with antibacterial activity was intercalated into the interlayer of MMT (Guo, Ma, Guo, & Xu, 2005; Yao-Zong, Shi-Rong, & Delvaux, 2004). OMMT is modified MMT with surfactant, compared with pure MMT, OMMT owns a higher interlayer spacing and a larger specific surface area, and it even shows stronger antimicrobial activity. So the addition of OMMT may improve the possibility for CMC–Cu complex as the antifouling agent. However, there is still no report about preparing the composite of CMC, MMT and copper ions in order to combine their thermostability and antibacterial advantages.

In this work, CMC and CMC–Cu complexes were firstly obtained, and organic montmorillonite (OMMT) was prepared to make the insertion of CMC into the interlayer of MMT easier. Afterwards, CMC/OMMT and CMC/OMMT–Cu nanocomposites were prepared. Their structures were characterized by XRD, TEM and FT-IR, and TGA was used to investigate the thermal stability. Furthermore, the inhibition ability against Escherichia coli was evaluated.

Section snippets

Materials

Chitosan (CS) was purchased from Haidebei Ocean Biochemical Co., Ltd. (Jinan, China). Its degree of deacetylation was 85%, and its weight average molecular weight (Mw) was 2.0 × 105. Chloroacetic acid was purchased from Kelong Chemical Reagent Factory (Chengdu, China). Sodium based montmorillonite (Na–MMT) was purchased from Josiah reagent factory, its cation exchange capacity was 87 mmol/100 g, Cetyltrimethyl Ammonium Bromide (CTAB) was purchased by Henan Titaning Chemical Technology Co., Ltd.

Mw and DS of CMC

Table 1 presents the weight average molecular weight (Mw) and degree of substitution (DS) of CMC. The DS of CMC increased as the mass ratios of chloroacetic acid to chitosan increased. It could be explained that the increase of chloroacetic acid would largely destroy the internal structure and crystalline region of chitosan, which ensured the further infiltration and proliferation of carboxymethyle groups.

FT-IR analysis

Fig. 1a shows FT-IR spectra of chitosan, CMC and CMC–Cu. Compared to chitosan, CMC

Conclusions

Based on the inherent environmentally friendly characteristics and biological activity of chitosan compounds, CMC/OMMT–Cu nanocomposites were prepared. There were strong hydrogen bonding and covalent bonding interaction in CMC/OMMT–Cu nanocomposites. And the nanocomposites showed high thermal stability and excellent antibacterial activity because of the combinative advantages of CMC, OMMT and copper ions, which were related to the interlayer distance and content of OMMT.

Acknowledgement

This work was financially supported by Natural Science Foundation of Guangdong Province (No. 2014A030313142).

References (38)

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