Elsevier

Applied Clay Science

Volume 168, February 2019, Pages 428-435
Applied Clay Science

Research Paper
Inorganic-organic bio-nanocomposite films based on Laponite and Cellulose Nanofibers (CNF)

https://doi.org/10.1016/j.clay.2018.12.003Get rights and content

Highlights

  • New nanocomposites based on Laponite and Cellulose Nanofibers have been prepared.

  • In nanocomposites, thermal stability and water vapor permeability were increased.

  • Nanocomposites can be used as scaffold in tissue engineering or drug delivery system.

Abstract

Nowadays there is a demand for ecologically efficient sustainable materials. The combination of cellulose and clay can provide materials with improved mechanical, thermal, and optical properties, besides better water and gas barrier, and flame resistance than pristine polymers. In the present work, composites were produced using cellulose nanofibers (CNF) and Laponite. The presence of clay modified the properties of the composite films compared to the pristine cellulose nanofibers film, such as lower CNF aggregation, better thermal stability (45 °C for CNF/Lap 3.5:1 by mass) and higher water vapor permeability (157% for CNF/Lap 1:1). In addition, XRD data suggested isolation of different types of CNF/Laponite composites when the mass ratio is modified, pointing out applications for these materials as for instance scaffold in tissue engineering, in regenerative medicine or as drug delivery systems.

Introduction

Currently, there is a great search for sustainable and ecologically efficient materials that can be used as a substitute for materials from non-renewable sources (Potulski et al., 2014; Jawaid and Abdul Khalil, 2011; Nechyporchuk et al., 2015). Cellulose has exciting potential for technological development since it is a renewable, abundant and low-cost material that present ecologically friendly properties such as biodegradability and non-toxicity. In addition, cellulose in nanometric scale, called nanocellulose, can be used in the production of materials with well-defined structures from nano to micro dimensions, as well for nanocomposites preparation (Nechyporchuk et al., 2015; Potulski et al., 2014).

Nanocelluloses can be defined as cellulose structures on a nanometer scale (1–100 nm) and, according to their properties, composition and mode of production, are classified into three types: Cellulose Nanocrystals (CNC) or Cellulose Whiskers (CNW), Nanofibers or Cellulose Nanofibrils (CNF) and Bacterial Cellulose (BC) (Nechyporchuk et al., 2015; Abitbol et al., 2016).

Cellulose nanofibers have been exploited in the production of bio-nanocomposites by the modification of non-biodegradable petroleum-derived polymers (such as polypropylene or polyethylene) (John and Thomas, 2008; Zhang et al., 2013), as well in the reinforcement of biodegradable polymers (for instance polylactic acid or polyhydroxyalkanoate) (Potulski et al., 2014). Consequently, the engendered materials show lower production cost, ecological compatibility, higher rigidity and better mechanical resistance (Potulski et al., 2014; Zhang et al., 2013; Mautner et al., 2017; Jonoobi et al., 2010; Saba et al., 2017). CNF has also been investigated in the production of aerogels (Nunes, 2014; Bendahou et al., 2015; Nechyporchuk et al., 2015), drug delivery systems (Zhang et al., 2013; Valo et al., 2011; Abitbol et al., 2016), optical devices of high transparency (Nunes, 2014), and flame retardant materials (Carosio et al., 2015, Carosio et al., 2016; Liu et al., 2011).

Commonly, inorganic-particles-reinforced polymers display enhanced physical and chemical properties or even reduced production cost. The incorporation of layered silicate into polymers has been known for >50 years but gained more visibility after a patent from the Toyota company about a polymer based on nylon-6/montmorillonite, which presented superior features than the pristine nylon-6 (Okada et al., 1990).

In the medical field, layered silicates as Laponite have been exploited in the production of composites for controlled-release of drugs, as for example the doxorubicin delivery in a pH-sensitive system (Xiao et al., 2016), or in the production of scaffolds for tissue engineering and regenerative medicine (Tomás et al., 2017).

Some studies reported the production of composites comprising Laponite and cellulosic materials. Perotti et al. (2011) obtained nanocomposites based on Laponite and Bacterial Cellulose (CB) whose mechanical properties were affected by the presence of clay: the values of the Young modulus and the tensile strength increased from 164 MPa and 11.6 GPa (pristine CB) to 227 MPa and 21.0 GPa (CB/Lap 30% by mass), respectively. Besides it was also observed an increase in the composite decomposition temperature (268 °C) compared to pristine CB (228 °C). Laponite and carboxymethylcellulose (CMC) composites reported by de Oliveira et al. (2015) showed better mechanical properties, higher water vapor barrier function (reduction of about 42%) and increased decomposition temperature (about 65 °C) compared to the pristine CMC.

Native cellulose can be found as a constituent of the cell wall of plants, along with lignin and hemicellulose, in the form of fibrils exhibiting 2–100 nm in diameter, commonly referred as cellulose nanofibres (CNF) (Damasio, 2015; Jonoobi et al., 2015; Herrick et al., 1983; Nechyporchuk et al., 2015).

The main treatments for the production of vegetable source of cellulose nanofibers are mechanical procedures such as high-pressure homogenization, grinders, and ultrasonification. However, it is very common to use additional treatments that facilitate the isolation of CNFs, such as purification, mechanical pre-treatments, and biological/chemical pre-treatments. The combination of pre or post treatments coupled to the mechanical method can produce CNFs with different nanofiber sizes, amounts of residual microscopic fibers or even particular hydrophilic/hydrophobic properties to attend specified applications (Jonoobi et al., 2015; Nechyporchuk et al., 2015).

The objective of this work is to prepare bio-nanocomposites using Laponite and Cellulose Nanofibers (CNF) in several proportions to evaluate possible modifications in the structural properties of CNF, as well to improve properties such as water permeability and thermal resistance.

Section snippets

Materials

Cellulose Nanofibers (CNF) sample was supplied by Suzano Paper and Cellulose Industry (Limeira-SP, Brazil). Laponite RD (abbreviated Lap), coding S/12796/11, was provided by Buntech (Brazil). This synthetic hectorite has particles of 25 nm of diameter, BET specific surface area equal to 370 m2/g, negative charge of 50–55 mmol/100 g, and the following chemical composition (dry basis): SiO2: 59.5%, MgO: 27.5%, Li2O: 0.8%, Na2O: 2.8%, loss on ignition: 8.2% (Technical Information B-R1 21 LAPONITE

Results and discussion

The thickness of semi-transparent and macroscopically homogeneous self-supported composite films was 40.0, 40.3, 37.0, 40.3 and 41.7 mm for materials CNF, CNF/Lap X where X = 10:1, 3.5:1, 2:1, 1.5:1 and 1:1 w/w, respectively. These films were flexible (not brittle) and easily detachable from Petri dishes. Fig. 2 shows pictures of the pristine CNF and CNF/Lap 1.5:1 films after drying while Fig. 3 presents the transmittance spectra of the films in the UV–Vis region.

CNF and CNF/Lap X films have

Conclusion

Semi-transparent and flexible nanocomposites based on cellulose nanofibers and Laponite were obtained, in which the presence of clay modified some properties of the materials compared to the pristine CNF film, such as the aggregation of the cellulose fibers, the increase of the thermal resistance, and the increase in water vapor permeability. Considering the WVP behaviour of CNF/Lap samples, if water can be transported through the films and access the active adsorption sites of clay, other

Acknowledgments

Suzano cellulose and paper for the supply of CNF. Brazilian funding agencies CNPq, CAPES and FAPESP.

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