Accepted Manuscript Title: Enhancing antibacterium and strength of cellulosic paper by coating triclosan-loaded nanofibrillated cellulose (NFC) Author: Kai Liu Lihui Chen Liulian Huang Yonghao Ni Bo Sun PII: DOI: Reference:
S0144-8617(14)01019-4 http://dx.doi.org/doi:10.1016/j.carbpol.2014.10.014 CARP 9367
To appear in: Received date: Revised date: Accepted date:
29-7-2014 7-10-2014 9-10-2014
Please cite this article as: Liu, K., Chen, L., Huang, L., Ni, Y., and Sun, B.,Enhancing antibacterium and strength of cellulosic paper by coating triclosan-loaded nanofibrillated cellulose (NFC), Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.10.014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Enhancing antibacterium and strength of cellulosic paper by coating
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triclosan-loaded nanofibrillated cellulose (NFC)
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Kai Liu a,b,*, Lihui Chen a, Liulian Huang a, Yonghao Ni b,*, Bo Sun c
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350002, China
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of New Brunswick, Fredericton, NB, E3B 5A3, Canada
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c
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Technology, Tianjin 300457, China
Limerick Pulp and Paper Centre and Department of Chemical Engineering, University
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Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science and
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* Corresponding Author: Dr. Kai Liu, Dr. Yonghao Ni
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E-mail: [email protected] (K. Liu), [email protected] (Y. Ni).
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College of Material Engineering, Fujian Agriculture and Forestry University, Fuzhou
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Abstract: The nanofibrillated cellulose (NFC) was used as substrates to carry triclosan
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(TCS), which was then applied as a coating agent for impacting antibacterial property to
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paper while also improving its strength. The TCS-loaded NFC material was further
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characterized. UV-vis spectra results showed that a characteristic absorption band at 282
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nm was observed, which was attributed to triclosan, confirming its successful loading
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onto NFC. The antibacterial activity tests indicated that the coated paper exhibited
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excellent antibacterial activity against E. coli, and the growth inhibition of bacteria (GIB)
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increased as the loading amount of triclosan coated on paper increased. The GIB can
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reach 98.7% when the 0.023g TCS-loaded NFC was coated on paper. Meanwhile, the
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tensile and tear index of the coated paper increased by 18.0% and 26.4%, respectively
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compared to the blank paper. Therefore, the triclosan-loaded paper could be potentially
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used in the medical field.
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Keywords: Nanofibrillated Cellulose, Triclosan, Antibacterium, Strength, Paper
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Introduction Nanofibrillated cellulose (NFC), disintegrated from wood pulp, have great potential for a wide variety of applications due to its renewable nature, biocompatibility,
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biodegradability and high specific strength (Liu et al., 2014; Dash, Cateto, & Ragauskas,
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2014; Liu et al., 2013; Fernandes et al., 2010; Trovatti et al., 2012; Zhu et al., 2014a; Zhu
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et al., 2014b). Among these application, NFC as a carrier for nanoparticles has attracted
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more attention in recent years because of its nano-dimensional network structure (Arola
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et al., 2012; Valo et al., 2013). For example, Li et al. prepared a uniform, flexible,
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magnetic nanopaper by the immobilization of Fe3O4 nanoparticles in an NFC network in
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an aqueous medium, and found the resulting transparent magnetic nanopaper possesses
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excellent transparency and magnetic properties combined with outstanding mechanical
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performance and flexibility (Li et al., 2013). Moreover, NFC can be used as reinforcing
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agent for a variety of composite materials because of its high stiffness and network
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structures (Huq et al., 2012; Martins et al., 2012; Srithep, Turng, Sabo, & Clemons, 2012;
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Besbes , Vilar, & Boufi, 2011; Lee et al., 2012; Zimmermann, Bordeanu, & Strub, 2010).
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For example, Alcalá et al. used the NFC as reinforcement in the preparation of
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biocomposites in the form of paper handsheets. They found that the presence of NFC
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induced an increase in the density of biocomposites and significant enhancement of the
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mechanical properties (Alcalá et al., 2013).
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In the previous work of our group, we studied nanocrystalline cellulose (CNC) as carriers for hydrophobic spirooxazine (SO)-based dye and alkenyl succinic anhydride 3 Page 3 of 26
(ASA), it was found that the use of CNC could improve the stability of SO-based dye and
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ASA, thus resulting in a significant improvement in the SO coloration efficiency and
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ASA sizing efficiency (Sun et al., 2014a; Sun et al., 2014b). This indicated that
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nanocrystalline cellulose would be a promising carrier for chemicals that have specific
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end-user application.
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Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol), a synthetic and broad-spectrum
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antimicrobial compound, is commonly used in a variety of personal care products (Anger
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et al., 2013). Triclosan possesses antibacterial properties as well as some antifungal and
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antiviral properties, so it can be used in papermaking process for enhancing the
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antimicrobial property of paper. For example, Soares et al. produced reinforced
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antibacterial paper packaging using the antimicrobial triclosan and organically modified
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montmorillonite via coating process. They found that the presence of 1% triclosan in the
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coated papers exhibited inhibitory effects against Staphylococcus aureus and Escherichia
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coli (Soares, Moreira, Fialho, & Melo, 2012). Obviously, triclosan is an effective
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antimicrobial agent for paper. However, triclosan can not be easily retained in paper
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because of its hydrophobic property under the paper making conditions of slightly acidic
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or near neutral pH.
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In the present study, NFC was used as a carrier for loading triclosan so that triclosan
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can be dispersed and used in an aqueous system at a mild pH without the aid of an
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organic solvent, the triclosan-loaded NFC was then coated on paper to induce the
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antibacterial property to paper while enhancing its mechanical strength. The antibacterial 4 Page 4 of 26
property was tested against Escherichia coli (E. coli, ATCC 11229). Such paper products
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may have the potential in the household/health/medical field.
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Materials and Methods
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Materials
Nanofibrillated cellulose (NFC) (2%, w/w) was from Tianjin Haojia Cellulose Co.,
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Ltd (China). Triclosan (99%) was purchased from Alfa Aesar reagent Co., Ltd. Phosphate
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buffered saline and LB Broth with agar were purchased from Sigma-Aldrich reagent Co.,
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Ltd. All other chemicals were of analytical grade and used without further purification.
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Methods
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Preparation of triclosan-loaded NFC
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Triclosan solution was prepared by dissolving 0.001, 0.003, 0.005, 0.007, 0.01, 0.05,
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and 0.1 g of triclosan in 5 ml of 1% NaOH solution at room temperature, respectively.
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Then 15 g of 2% (w/w) NFC was added and stirred at a stirring rate of 8000 rpm. After 5
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min, 1.8 mL of 3.7% HCl solution was added into the above suspensions and stirred for
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10 min at a stirring rate of 15000 rpm. The amount of triclosan loaded on the NFC was
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0.0033, 0.01, 0.017, 0.023, 0.033, 0.17, and 0.33 g/g NFC.
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Coating of paper
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The NFC loaded with different amount of triclosan was coated on a filter paper (dia.
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18.5 cm, 100 g/m2) using a laboratory coater machine (K303 Multicoater, RK Print coat
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Instruments Ltd., U.K.), the coated paper was then kept in a drying oven at 105 °C for 20
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min. The other side of the paper was also coated with the triclosan-loaded NFC and kept 5 Page 5 of 26
in a drying over at 105 °C for another 20 min. The total coating amount of
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triclosan-loaded NFC on paper was 300±20 mg/g paper.
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Characterization of the triclosan-loaded NFC and coated paper
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The triclosan solution (0.04 g/L in 1% NaOH solution) and the NFC loaded with different amount of triclosan were analyzed using an Ultraviolet- visible (UV-vis)
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Spectrometer (Genesys 10-S, Thermo Electron Corporation, USA). UV-vis spectra were
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recorded between 200 and 500 nm at room temperature. Thermogravimetric analysis
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(TGA) of the blank paper, triclosan, and coated paper were performed on a DSC-TGA
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instrument (SDT Q600, TA Instruments, USA). Approximately 5 mg of sample was
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weighed and heated from room temperature to 600 °C at a heating rate of 10 °C/min
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under nitrogen flow rate of 100 mL/min.
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SEM analysis
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The surface morphology of the blank paper and coated paper was investigated using
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a Scanning Electron Microscope (SEM) (JSM-6400, JEOL, Japan). The surface of the
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sample was carbon coated and then gold coated for conductivity, and the accelerating
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voltage of SEM was 15kV.
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Antibacterial activity of the paper coated with triclosan-loaded NFC
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The shaking flask method was used to detect the antimicrobial activity of the coated
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paper, and the Gram-negative bacteria Escherichia coli (E. coli, ATCC 11229) was
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chosen as the test microorganism. The test method was conducted as follows (Zhang, &
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Xiao, 2013): about 4.5 ml of 0.01 M phosphate buffered saline solution was mixed with 6 Page 6 of 26
0.5 ml E. coli (105 CFU/ml) in a sample tube, and 0.1 g blank paper or coated paper was
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added into the above solution. The sample tube was then immersed in a water bath shaker
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and shaken at 37 °C for 1 h. About 0.1 ml of each culture was transferred and seeded on
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an agar plate, the plate was then kept in an incubator at 37 °C for 24 h. The number of the
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colonies was counted, and the inhibition of the bacteria growth was calculated using Eq.
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1:
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Growth Inhibition of Bacteria (GIB) (%)
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where A0 and A1 are the number of the colonies detected from the blank paper and coated
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paper, respectively.
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Strength properties
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The tensile properties of the paper and coated paper were tested using a tensile
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strength tester (L&W, Sweden). Tensile strength and stretch were measured in
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accordance with TAPPI Test Method T 494. The tear strength of the paper and coated
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paper was tested using a tearing tester (L&W, Sweden) according to the ASTM D 689
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test method.
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Results and Discussion
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Preparation of triclosan-loaded NFC
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A simple method was used to load triclosan using NFC as a carrier. In the method,
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the triclosan was firstly soluble in the alkaline aqueous solution and dispersed in NFC
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suspension, a certain amount of hydrochloric acid solution was then added to precipitate 7 Page 7 of 26
triclosan particles on the surface of NFC. The formation of triclosan particles loaded on
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the NFC was confirmed by UV–vis spectral analysis. From the UV–vis spectra of the
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triclosan solution and triclosan-loaded NFC (Fig. 1), a characteristic absorption was
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observed at 282 nm for triclosan-loaded NFC, and its intensity increased as the amount of
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triclosan loaded increased. Lavecchia et al. reported that the absorption spectrum of
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triclosan in aqueous ethanol had a sharp peak at 282 nm (Lavecchia, & Zuorro, 2009).
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This indicated that triclosan has been loaded on the NFC successfully. However, at an
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alkaline condition, the characteristic absorption of triclosan occurs at 292 nm, instead of
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282 nm, due to the ionization of phenolic hydroxyl group of triclosan (Vukovic, Jurišic
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Grubešic, Kremer, & Spaic, 2013). This explains the red shift of the characteristic
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absorption of triclosan from 282 to 292 nm.
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Thermal property of the coated paper
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Thermal stability of the triclosan-loaded NFC is very important to the coated paper
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during drying process. The thermogravimetric (TG) and derivative thermogravimetric
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(DTG) curves of the blank paper, triclosan, and coated paper were shown in Fig. 2. It can
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be seen from Fig. 2a that the TG curve of triclosan exhibited only one step, and the
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degradation during this step was about 95.3 wt% due to the degradation of triclosan.
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However, the TG curves of the blank paper and coated paper exhibited three main steps.
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The blank paper degradation during the first, second, and third steps was 3.5, 79.6, and
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2.5 wt%, respectively. The coated paper degradation during the first, second, and third
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steps was 5.6, 61.5, and 8.8 wt%, respectively. The mass loss of the blank paper and 8 Page 8 of 26
coated paper during the first step can be attributed to evaporation of the free water came
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from paper. The second mass loss of the blank paper and coated paper was ascribed to the
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thermal decomposition of cellulose and triclosan.
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In addition, the degradation temperature of the blank paper and triclosan were found to be 244 and 352 °C, respectively (Fig. 2b). The lower degradation temperature of
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triclosan than blank paper indicated that triclosan possessed worse thermostability than
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did the cellulose of paper. However, the degradation temperature of the coated paper was
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337 °C, which was between that of triclosan and blank paper. This may be the reason that
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the triclosan with poor thermastability had a lower decomposition temperature, resulting
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in a lower peak decomposition temperature for paper coated with triclosan-loaded NFC.
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Many studies for thermal stability of composites indicated the similar results. For
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example, Salam et al. studied the thermal stability of modified starch nanoparticles,
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chitosan, and their composites. They also found that the maximum degradation
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temperature of the modified starch nanoparticles/chitosan composites was between that of
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them (Salam, Lucia, & Jameel, 2013).
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SEM studies
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SEM was used to confirm the coating of triclosan-loaded NFC on paper, and the
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SEM images of blank paper and coated paper were shown in Fig. 3. It was found that lots
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of pores between fibers existed on the surface of the blank paper (Fig. 3 a-1), and there
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were not any particles loaded on fibers (Fig. 3 a-2). However, some pores between fibers
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were covered after the triclosan-loaded NFC was coated on the blank paper (Fig. 3 b-1). 9 Page 9 of 26
Meanwhile, a lot of particles can also be observed on the fiber of the coated paper (Fig. 3
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b-2). This indicated that the triclosan-loaded NFC was coated on the surface of the paper
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and the triclosan particles were kept on the paper.
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Antibacterial activity studies
The shaking flask method was used to test the antibacterial property of the paper
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coated with triclosan-loaded NFC, and the Escherichia coli (E. coli), a common bacteria
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harm to human health, was chosen as the test object (Zhang, & Xiao, 2013). The test
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results were shown in Fig. 4 and Table 1. It was found that a lot of colonies have grown
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on the plate for the blank paper (Fig. 4a). This indicated that the cellulose of blank paper
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has no antibacterial property. However, the number of colonies on the plate decreased
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greatly for the paper coated with 0.023g triclosan-loaded NFC (Fig. 4b), and there were
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no colonies on the plate for the paper coated with 0.33g triclosan-loaded NFC (Fig. 4c).
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According to the calculation of GIB, it was found that the GIB of the coated paper
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increased as the loading amount of triclosan coated on paper increased (Table 1), and the
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GIB reached 100% when the 0.33g TCS-loaded NFC was coated on paper. This indicated
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that the coated paper had excellent antibacterial activity against E. coli when sufficient
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level of triclosan was coated on the paper. It was mainly due to the strong antibacterial
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property of triclosan. Soares et al. evaluated the antibacterial property of the paper coated
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with triclosan and modified montmorillonite composites and found the presence of 1%
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triclosan in the coated papers exhibited inhibitory effects against E. coli and S. aureus
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(Soares, Moreira, Fialho, & Melo, 2012). The different between his results and the results
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in this study was the experimental method and conditions used to test the antibacterial
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activities. The antibacterial activity tests in this study clearly demonstrated that the
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triclosan was successfully loaded on NFC and coated on the paper.
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Strength Property Studies
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The strength property of the blank paper and coated paper were studied by testing
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the tensile and tear strength, and the results were shown in Table 2. It was found that the
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tensile index of blank paper was only 24.93 N.m/g. However, the tensile index can reach
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29.41 N.m/g after the triclosan-loaded NFC was coated on paper. Furthermore, the tear
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index also increased from 7 to 8.85 mN.m2/g. The increase of the tensile and tear strength
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of the coated paper was attributed to the NFC coated on the surface of the paper. The
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NFC had smaller size than did the fibers of paper and could form a network structure
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with a lot of hydrogen bonds between fibers, thus enhancing the strength property for
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paper. Littunen et al. prepared the composites of poly(methyl methacrylate) and
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nanofibrillated cellulose (NFC) by solution blending, injection and compression molding,
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and found the formation of a percolating nanofibril network between 1 and 5 wt% of
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NFC by dynamic rotational rheometry in molten state (Littunen, Hippi, Saarinen, &
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Seppälä, 2013). Our previous studies also pointed out that NFC had great reinforcement
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effect for a variety of biomaterials because of its nano- to submicron-wide size and the
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formation of strong interactions between adjacent whiskers by hydrogen bonding (Liu et
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al., 2014; Liu et al., 2013). In addition, the blank and coated paper had similar stretch,
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suggesting that the coating of triclosan-loaded NFC had little effect on the stretch of
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paper. Due to the fact that cellulosic papers are user friendly, biodegradable, cost-effective,
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among other associated advantages, they are more and more used in our daily lives, for
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example, tissue products in personal hygiene. One example of the present concept would
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be the paper/non-woven mat used in the hospital.
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Conclusions
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The trichlosan (TCS) was loaded on NFC using a simple method, and then the
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TCS-loaded NFC was applied as surface coating onto paper surface for impacting
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antibacterial properties to paper and enhancing its strength property. The resultant
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paper-based novel composite was very effective in inducing the antibacterial activity
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while enhancing its strength properties. The results showed that the coated paper
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exhibited excellent antibacterial property against E. coli, and the growth inhibition
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reached 98.7% when the 0.023g TCS-loaded NFC was coated on paper. Meanwhile, the
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tensile and tear index of the coated paper increased by 18.0% and 26.4%, respectively
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compared to the blank paper. These results suggest that the triclosan-loaded paper could
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be a potential bio-material based product that may have applications in the medical field.
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Acknowledgments
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This project was funded by an NSERC CRD grant, an Atlantic Innovation Fund,
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Canada Research Chairs programs of the Government of Canada. The authors
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acknowledge
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(2014H0001), Natural Science Foundation of Fujian Province (2014J01070), the Forestry
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Industrial
Technology
Key
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Fujian
Province
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Science and Technology Promotion Project of Fujian Province ([2013]14-2), the
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Technology Project of Fujian provincial education department (JB13031), the Science
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and Technology Cooperation Project of Fuzhou Government and University (2013-G-81),
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and the Research Fund for Distinguished Young Talents of Fujian Agriculture and
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Forestry University (XJQ201213) for financial support.
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Valo, H., Arola, S., Laaksonen, P., Torkkeli, M., Peltonen, L., Linder, M.B., Serimaa, R., Kuga, S., Hirvonen, J., & Laaksonen, T. (2013). Drug release from nanoparticles
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embedded in four different nanofibrillar cellulose aerogels. European Journal of
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Pharmaceutical Sciences, 50, 69-77.
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Vukovic, J., Jurišic Grubešic, R., Kremer, D., & Spaic, A. (2013). One step solid phase
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UV spectrophotometric method for phenol determination in vaccines: development
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and quality assessment. Journal of Analytical Chemistry, 68(12), 1033-1043.
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Zhang, D., & Xiao, H.N. (2013). Dual-functional beeswaxes on enhancing antimicrobial
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activity and water vapor barrier property of paper. ACS Applied Materials &
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Interfaces, 5, 3464-3468.
Zimmermann, T., Bordeanu, N., & Strub, E. (2010). Properties of nanofibrillated
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cellulose from different raw materials and its reinforcement potential. Carbohydrate
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Polymers, 79, 1086-1093.
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Zhu, H., Li, Y., Fang, Z., Xu, J., Cao, F., Wan, J., Preston, C., Yang, B., & Hu, L. (2014a). Highly thermally conductive papers with percolative layered boron nitride 17 Page 17 of 26
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nanosheets. ACS Nano, 8, 3606-3613. Zhu, H., Fang, Z., Preston, C., Li, Y., & Hu, L. (2014b). Transparent paper: fabrications, properties, and device applications. Energy & Environmental Science, 7, 269-287.
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Figure captions
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Figure 1. UV–vis absorption spectra of TCS and TCS-loaded NFC
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Figure 2. (a) TG and (b) DTG curves of the blank paper, triclosan, and paper coated with
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0.33g TCS-loaded NFC
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Figure 3. SEM images of (a-1, a-2) blank paper and (b-1, b-2) paper coated with 0.023g
385
TCS-loaded NFC. a-1 and b-1 were photographed at low magnifications; a-2 and b-2
386
were photographed at high magnifications.
387
Figure 4. Photographs of bacterial colonies formed by Escherichia coli: (a) blank paper,
388
(b) paper coated with 0.023g TCS-loaded NFC, (c) paper coated with 0.33g TCS-loaded
389
NFC
390
Table 1. Antibacterial property of paper coated with TCS-loaded NFC
391
Table 2. The comparison of tensile strength, tear strength, and stretch of blank and coated
392
samples (The amount of triclosan loaded on NFC was 0.023 g/g NFC)
394 395 396
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401
Figure 1
1.2
0.8 0.6 0.4
282nm
300
350
407 408 409 410
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450
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Wavelength (nm)
403
405
400
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0.0 250
404
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0.0033g TCS-loaded NFC 0.017g TCS-loaded NFC 0.033g TCS-loaded NFC TCS
0.2
402
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292nm
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Absorbance
1.0
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415
Figure 2
(a)
Paper Triclosan Coated paper
First step
100
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Second step
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Third step 20 0 100
200
300
400
500
Temperature (oC)
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600
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Paper Triclosan Coated paper
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(b)
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First step
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Weight (percent)
80
0.2 0.0
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-0.2
-0.6
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DTG
-0.4
337oC
-0.8
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-1.0 -1.2
244oC
-1.4 -1.6
417 418 419
0
100
200
300
352oC 400
500
600
Temperature (oC)
420 421 422 423
21 Page 21 of 26
Figure 3
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Figure 4
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Table 1 Loading amount of triclosan (g/g NFC)
0
0.0033
0.01
0.017
0.023
0.033
0.17
0.33
GIB (%)
0
12.5
79.2
87.5
98.7
99.8
99.9
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Table 2 Tensile index (N.m/g)
Tear index (mN.m2/g)
Stretch/Elongation (%)
Blank paper (control)
24.93±0.60
7.00±0.081
2.68±0.35
Triclosan-loaded
29.41±1.97
8.85±0.26
2.77±0.41
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NFC coated paper
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Highlights
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Nanofibrillated cellulose (NFC) was used as substrates to carry triclosan (TCS).
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The triclosan-loaded NFC was coated on paper.
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The coating of TCS-loaded NFC on paper resulted in improvement of paper strength.
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The paper coated with TCS-loaded NFC exhibited excellent antimicrobial activity.
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S0144-8617(14)01019-4 http://dx.doi.org/doi:10.1016/j.carbpol.2014.10.014 CARP 9367
To appear in: Received date: Revised date: Accepted date:
29-7-2014 7-10-2014 9-10-2014
Please cite this article as: Liu, K., Chen, L., Huang, L., Ni, Y., and Sun, B.,Enhancing antibacterium and strength of cellulosic paper by coating triclosan-loaded nanofibrillated cellulose (NFC), Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.10.014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Enhancing antibacterium and strength of cellulosic paper by coating
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triclosan-loaded nanofibrillated cellulose (NFC)
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Kai Liu a,b,*, Lihui Chen a, Liulian Huang a, Yonghao Ni b,*, Bo Sun c
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a
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350002, China
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b
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of New Brunswick, Fredericton, NB, E3B 5A3, Canada
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c
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Technology, Tianjin 300457, China
Limerick Pulp and Paper Centre and Department of Chemical Engineering, University
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Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science and
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* Corresponding Author: Dr. Kai Liu, Dr. Yonghao Ni
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E-mail: [email protected] (K. Liu), [email protected] (Y. Ni).
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College of Material Engineering, Fujian Agriculture and Forestry University, Fuzhou
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Abstract: The nanofibrillated cellulose (NFC) was used as substrates to carry triclosan
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(TCS), which was then applied as a coating agent for impacting antibacterial property to
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paper while also improving its strength. The TCS-loaded NFC material was further
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characterized. UV-vis spectra results showed that a characteristic absorption band at 282
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nm was observed, which was attributed to triclosan, confirming its successful loading
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onto NFC. The antibacterial activity tests indicated that the coated paper exhibited
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excellent antibacterial activity against E. coli, and the growth inhibition of bacteria (GIB)
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increased as the loading amount of triclosan coated on paper increased. The GIB can
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reach 98.7% when the 0.023g TCS-loaded NFC was coated on paper. Meanwhile, the
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tensile and tear index of the coated paper increased by 18.0% and 26.4%, respectively
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compared to the blank paper. Therefore, the triclosan-loaded paper could be potentially
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used in the medical field.
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Keywords: Nanofibrillated Cellulose, Triclosan, Antibacterium, Strength, Paper
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2 Page 2 of 26
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Introduction Nanofibrillated cellulose (NFC), disintegrated from wood pulp, have great potential for a wide variety of applications due to its renewable nature, biocompatibility,
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biodegradability and high specific strength (Liu et al., 2014; Dash, Cateto, & Ragauskas,
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2014; Liu et al., 2013; Fernandes et al., 2010; Trovatti et al., 2012; Zhu et al., 2014a; Zhu
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et al., 2014b). Among these application, NFC as a carrier for nanoparticles has attracted
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more attention in recent years because of its nano-dimensional network structure (Arola
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et al., 2012; Valo et al., 2013). For example, Li et al. prepared a uniform, flexible,
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magnetic nanopaper by the immobilization of Fe3O4 nanoparticles in an NFC network in
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an aqueous medium, and found the resulting transparent magnetic nanopaper possesses
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excellent transparency and magnetic properties combined with outstanding mechanical
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performance and flexibility (Li et al., 2013). Moreover, NFC can be used as reinforcing
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agent for a variety of composite materials because of its high stiffness and network
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structures (Huq et al., 2012; Martins et al., 2012; Srithep, Turng, Sabo, & Clemons, 2012;
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Besbes , Vilar, & Boufi, 2011; Lee et al., 2012; Zimmermann, Bordeanu, & Strub, 2010).
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For example, Alcalá et al. used the NFC as reinforcement in the preparation of
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biocomposites in the form of paper handsheets. They found that the presence of NFC
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induced an increase in the density of biocomposites and significant enhancement of the
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mechanical properties (Alcalá et al., 2013).
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In the previous work of our group, we studied nanocrystalline cellulose (CNC) as carriers for hydrophobic spirooxazine (SO)-based dye and alkenyl succinic anhydride 3 Page 3 of 26
(ASA), it was found that the use of CNC could improve the stability of SO-based dye and
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ASA, thus resulting in a significant improvement in the SO coloration efficiency and
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ASA sizing efficiency (Sun et al., 2014a; Sun et al., 2014b). This indicated that
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nanocrystalline cellulose would be a promising carrier for chemicals that have specific
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end-user application.
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Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol), a synthetic and broad-spectrum
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antimicrobial compound, is commonly used in a variety of personal care products (Anger
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et al., 2013). Triclosan possesses antibacterial properties as well as some antifungal and
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antiviral properties, so it can be used in papermaking process for enhancing the
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antimicrobial property of paper. For example, Soares et al. produced reinforced
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antibacterial paper packaging using the antimicrobial triclosan and organically modified
77
montmorillonite via coating process. They found that the presence of 1% triclosan in the
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coated papers exhibited inhibitory effects against Staphylococcus aureus and Escherichia
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coli (Soares, Moreira, Fialho, & Melo, 2012). Obviously, triclosan is an effective
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antimicrobial agent for paper. However, triclosan can not be easily retained in paper
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because of its hydrophobic property under the paper making conditions of slightly acidic
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or near neutral pH.
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In the present study, NFC was used as a carrier for loading triclosan so that triclosan
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can be dispersed and used in an aqueous system at a mild pH without the aid of an
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organic solvent, the triclosan-loaded NFC was then coated on paper to induce the
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antibacterial property to paper while enhancing its mechanical strength. The antibacterial 4 Page 4 of 26
property was tested against Escherichia coli (E. coli, ATCC 11229). Such paper products
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may have the potential in the household/health/medical field.
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Materials and Methods
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Materials
Nanofibrillated cellulose (NFC) (2%, w/w) was from Tianjin Haojia Cellulose Co.,
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Ltd (China). Triclosan (99%) was purchased from Alfa Aesar reagent Co., Ltd. Phosphate
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buffered saline and LB Broth with agar were purchased from Sigma-Aldrich reagent Co.,
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Ltd. All other chemicals were of analytical grade and used without further purification.
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Methods
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Preparation of triclosan-loaded NFC
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Triclosan solution was prepared by dissolving 0.001, 0.003, 0.005, 0.007, 0.01, 0.05,
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and 0.1 g of triclosan in 5 ml of 1% NaOH solution at room temperature, respectively.
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Then 15 g of 2% (w/w) NFC was added and stirred at a stirring rate of 8000 rpm. After 5
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min, 1.8 mL of 3.7% HCl solution was added into the above suspensions and stirred for
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10 min at a stirring rate of 15000 rpm. The amount of triclosan loaded on the NFC was
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0.0033, 0.01, 0.017, 0.023, 0.033, 0.17, and 0.33 g/g NFC.
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Coating of paper
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The NFC loaded with different amount of triclosan was coated on a filter paper (dia.
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18.5 cm, 100 g/m2) using a laboratory coater machine (K303 Multicoater, RK Print coat
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Instruments Ltd., U.K.), the coated paper was then kept in a drying oven at 105 °C for 20
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min. The other side of the paper was also coated with the triclosan-loaded NFC and kept 5 Page 5 of 26
in a drying over at 105 °C for another 20 min. The total coating amount of
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triclosan-loaded NFC on paper was 300±20 mg/g paper.
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Characterization of the triclosan-loaded NFC and coated paper
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The triclosan solution (0.04 g/L in 1% NaOH solution) and the NFC loaded with different amount of triclosan were analyzed using an Ultraviolet- visible (UV-vis)
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Spectrometer (Genesys 10-S, Thermo Electron Corporation, USA). UV-vis spectra were
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recorded between 200 and 500 nm at room temperature. Thermogravimetric analysis
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(TGA) of the blank paper, triclosan, and coated paper were performed on a DSC-TGA
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instrument (SDT Q600, TA Instruments, USA). Approximately 5 mg of sample was
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weighed and heated from room temperature to 600 °C at a heating rate of 10 °C/min
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under nitrogen flow rate of 100 mL/min.
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SEM analysis
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The surface morphology of the blank paper and coated paper was investigated using
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a Scanning Electron Microscope (SEM) (JSM-6400, JEOL, Japan). The surface of the
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sample was carbon coated and then gold coated for conductivity, and the accelerating
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voltage of SEM was 15kV.
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Antibacterial activity of the paper coated with triclosan-loaded NFC
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The shaking flask method was used to detect the antimicrobial activity of the coated
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paper, and the Gram-negative bacteria Escherichia coli (E. coli, ATCC 11229) was
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chosen as the test microorganism. The test method was conducted as follows (Zhang, &
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Xiao, 2013): about 4.5 ml of 0.01 M phosphate buffered saline solution was mixed with 6 Page 6 of 26
0.5 ml E. coli (105 CFU/ml) in a sample tube, and 0.1 g blank paper or coated paper was
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added into the above solution. The sample tube was then immersed in a water bath shaker
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and shaken at 37 °C for 1 h. About 0.1 ml of each culture was transferred and seeded on
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an agar plate, the plate was then kept in an incubator at 37 °C for 24 h. The number of the
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colonies was counted, and the inhibition of the bacteria growth was calculated using Eq.
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1:
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Growth Inhibition of Bacteria (GIB) (%)
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where A0 and A1 are the number of the colonies detected from the blank paper and coated
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paper, respectively.
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Strength properties
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The tensile properties of the paper and coated paper were tested using a tensile
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strength tester (L&W, Sweden). Tensile strength and stretch were measured in
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accordance with TAPPI Test Method T 494. The tear strength of the paper and coated
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paper was tested using a tearing tester (L&W, Sweden) according to the ASTM D 689
143
test method.
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Results and Discussion
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Preparation of triclosan-loaded NFC
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A simple method was used to load triclosan using NFC as a carrier. In the method,
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the triclosan was firstly soluble in the alkaline aqueous solution and dispersed in NFC
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suspension, a certain amount of hydrochloric acid solution was then added to precipitate 7 Page 7 of 26
triclosan particles on the surface of NFC. The formation of triclosan particles loaded on
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the NFC was confirmed by UV–vis spectral analysis. From the UV–vis spectra of the
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triclosan solution and triclosan-loaded NFC (Fig. 1), a characteristic absorption was
152
observed at 282 nm for triclosan-loaded NFC, and its intensity increased as the amount of
153
triclosan loaded increased. Lavecchia et al. reported that the absorption spectrum of
154
triclosan in aqueous ethanol had a sharp peak at 282 nm (Lavecchia, & Zuorro, 2009).
155
This indicated that triclosan has been loaded on the NFC successfully. However, at an
156
alkaline condition, the characteristic absorption of triclosan occurs at 292 nm, instead of
157
282 nm, due to the ionization of phenolic hydroxyl group of triclosan (Vukovic, Jurišic
158
Grubešic, Kremer, & Spaic, 2013). This explains the red shift of the characteristic
159
absorption of triclosan from 282 to 292 nm.
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Thermal property of the coated paper
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Thermal stability of the triclosan-loaded NFC is very important to the coated paper
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during drying process. The thermogravimetric (TG) and derivative thermogravimetric
163
(DTG) curves of the blank paper, triclosan, and coated paper were shown in Fig. 2. It can
164
be seen from Fig. 2a that the TG curve of triclosan exhibited only one step, and the
165
degradation during this step was about 95.3 wt% due to the degradation of triclosan.
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However, the TG curves of the blank paper and coated paper exhibited three main steps.
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The blank paper degradation during the first, second, and third steps was 3.5, 79.6, and
168
2.5 wt%, respectively. The coated paper degradation during the first, second, and third
169
steps was 5.6, 61.5, and 8.8 wt%, respectively. The mass loss of the blank paper and 8 Page 8 of 26
coated paper during the first step can be attributed to evaporation of the free water came
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from paper. The second mass loss of the blank paper and coated paper was ascribed to the
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thermal decomposition of cellulose and triclosan.
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In addition, the degradation temperature of the blank paper and triclosan were found to be 244 and 352 °C, respectively (Fig. 2b). The lower degradation temperature of
175
triclosan than blank paper indicated that triclosan possessed worse thermostability than
176
did the cellulose of paper. However, the degradation temperature of the coated paper was
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337 °C, which was between that of triclosan and blank paper. This may be the reason that
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the triclosan with poor thermastability had a lower decomposition temperature, resulting
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in a lower peak decomposition temperature for paper coated with triclosan-loaded NFC.
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Many studies for thermal stability of composites indicated the similar results. For
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example, Salam et al. studied the thermal stability of modified starch nanoparticles,
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chitosan, and their composites. They also found that the maximum degradation
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temperature of the modified starch nanoparticles/chitosan composites was between that of
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them (Salam, Lucia, & Jameel, 2013).
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SEM studies
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SEM was used to confirm the coating of triclosan-loaded NFC on paper, and the
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SEM images of blank paper and coated paper were shown in Fig. 3. It was found that lots
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of pores between fibers existed on the surface of the blank paper (Fig. 3 a-1), and there
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were not any particles loaded on fibers (Fig. 3 a-2). However, some pores between fibers
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were covered after the triclosan-loaded NFC was coated on the blank paper (Fig. 3 b-1). 9 Page 9 of 26
Meanwhile, a lot of particles can also be observed on the fiber of the coated paper (Fig. 3
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b-2). This indicated that the triclosan-loaded NFC was coated on the surface of the paper
193
and the triclosan particles were kept on the paper.
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Antibacterial activity studies
The shaking flask method was used to test the antibacterial property of the paper
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coated with triclosan-loaded NFC, and the Escherichia coli (E. coli), a common bacteria
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harm to human health, was chosen as the test object (Zhang, & Xiao, 2013). The test
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results were shown in Fig. 4 and Table 1. It was found that a lot of colonies have grown
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on the plate for the blank paper (Fig. 4a). This indicated that the cellulose of blank paper
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has no antibacterial property. However, the number of colonies on the plate decreased
201
greatly for the paper coated with 0.023g triclosan-loaded NFC (Fig. 4b), and there were
202
no colonies on the plate for the paper coated with 0.33g triclosan-loaded NFC (Fig. 4c).
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According to the calculation of GIB, it was found that the GIB of the coated paper
204
increased as the loading amount of triclosan coated on paper increased (Table 1), and the
205
GIB reached 100% when the 0.33g TCS-loaded NFC was coated on paper. This indicated
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that the coated paper had excellent antibacterial activity against E. coli when sufficient
207
level of triclosan was coated on the paper. It was mainly due to the strong antibacterial
208
property of triclosan. Soares et al. evaluated the antibacterial property of the paper coated
209
with triclosan and modified montmorillonite composites and found the presence of 1%
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triclosan in the coated papers exhibited inhibitory effects against E. coli and S. aureus
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(Soares, Moreira, Fialho, & Melo, 2012). The different between his results and the results
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in this study was the experimental method and conditions used to test the antibacterial
213
activities. The antibacterial activity tests in this study clearly demonstrated that the
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triclosan was successfully loaded on NFC and coated on the paper.
215
Strength Property Studies
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The strength property of the blank paper and coated paper were studied by testing
217
the tensile and tear strength, and the results were shown in Table 2. It was found that the
218
tensile index of blank paper was only 24.93 N.m/g. However, the tensile index can reach
219
29.41 N.m/g after the triclosan-loaded NFC was coated on paper. Furthermore, the tear
220
index also increased from 7 to 8.85 mN.m2/g. The increase of the tensile and tear strength
221
of the coated paper was attributed to the NFC coated on the surface of the paper. The
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NFC had smaller size than did the fibers of paper and could form a network structure
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with a lot of hydrogen bonds between fibers, thus enhancing the strength property for
224
paper. Littunen et al. prepared the composites of poly(methyl methacrylate) and
225
nanofibrillated cellulose (NFC) by solution blending, injection and compression molding,
226
and found the formation of a percolating nanofibril network between 1 and 5 wt% of
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NFC by dynamic rotational rheometry in molten state (Littunen, Hippi, Saarinen, &
228
Seppälä, 2013). Our previous studies also pointed out that NFC had great reinforcement
229
effect for a variety of biomaterials because of its nano- to submicron-wide size and the
230
formation of strong interactions between adjacent whiskers by hydrogen bonding (Liu et
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al., 2014; Liu et al., 2013). In addition, the blank and coated paper had similar stretch,
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suggesting that the coating of triclosan-loaded NFC had little effect on the stretch of
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paper. Due to the fact that cellulosic papers are user friendly, biodegradable, cost-effective,
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among other associated advantages, they are more and more used in our daily lives, for
236
example, tissue products in personal hygiene. One example of the present concept would
237
be the paper/non-woven mat used in the hospital.
238
Conclusions
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The trichlosan (TCS) was loaded on NFC using a simple method, and then the
240
TCS-loaded NFC was applied as surface coating onto paper surface for impacting
241
antibacterial properties to paper and enhancing its strength property. The resultant
242
paper-based novel composite was very effective in inducing the antibacterial activity
243
while enhancing its strength properties. The results showed that the coated paper
244
exhibited excellent antibacterial property against E. coli, and the growth inhibition
245
reached 98.7% when the 0.023g TCS-loaded NFC was coated on paper. Meanwhile, the
246
tensile and tear index of the coated paper increased by 18.0% and 26.4%, respectively
247
compared to the blank paper. These results suggest that the triclosan-loaded paper could
248
be a potential bio-material based product that may have applications in the medical field.
249
Acknowledgments
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This project was funded by an NSERC CRD grant, an Atlantic Innovation Fund,
251
Canada Research Chairs programs of the Government of Canada. The authors
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acknowledge
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(2014H0001), Natural Science Foundation of Fujian Province (2014J01070), the Forestry
the
Industrial
Technology
Key
Project
of
Fujian
Province
12 Page 12 of 26
Science and Technology Promotion Project of Fujian Province ([2013]14-2), the
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Technology Project of Fujian provincial education department (JB13031), the Science
256
and Technology Cooperation Project of Fuzhou Government and University (2013-G-81),
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and the Research Fund for Distinguished Young Talents of Fujian Agriculture and
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Forestry University (XJQ201213) for financial support.
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References
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Alcalá, M., González, I., Boufi, S., Vilaseca, F., & Mutjé, P. (2013). All-cellulose
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composites from unbleached hardwood kraft pulp reinforced with nanofibrillated
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cellulose. Cellulose, 20, 2909-2921.
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365 366
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Figure captions
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Figure 1. UV–vis absorption spectra of TCS and TCS-loaded NFC
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Figure 2. (a) TG and (b) DTG curves of the blank paper, triclosan, and paper coated with
383
0.33g TCS-loaded NFC
384
Figure 3. SEM images of (a-1, a-2) blank paper and (b-1, b-2) paper coated with 0.023g
385
TCS-loaded NFC. a-1 and b-1 were photographed at low magnifications; a-2 and b-2
386
were photographed at high magnifications.
387
Figure 4. Photographs of bacterial colonies formed by Escherichia coli: (a) blank paper,
388
(b) paper coated with 0.023g TCS-loaded NFC, (c) paper coated with 0.33g TCS-loaded
389
NFC
390
Table 1. Antibacterial property of paper coated with TCS-loaded NFC
391
Table 2. The comparison of tensile strength, tear strength, and stretch of blank and coated
392
samples (The amount of triclosan loaded on NFC was 0.023 g/g NFC)
394 395 396
cr
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M d
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Ac ce p
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ip t
380
397 398 399 400
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401
Figure 1
1.2
0.8 0.6 0.4
282nm
300
350
407 408 409 410
d te Ac ce p
406
450
M
Wavelength (nm)
403
405
400
an
0.0 250
404
cr
0.0033g TCS-loaded NFC 0.017g TCS-loaded NFC 0.033g TCS-loaded NFC TCS
0.2
402
ip t
292nm
us
Absorbance
1.0
411 412 413 414
20 Page 20 of 26
415
Figure 2
(a)
Paper Triclosan Coated paper
First step
100
ip t
Second step
60 40
Third step 20 0 100
200
300
400
500
Temperature (oC)
416
600
an
0
Paper Triclosan Coated paper
0.4
M
(b)
cr
First step
us
Weight (percent)
80
0.2 0.0
d
-0.2
-0.6
te
DTG
-0.4
337oC
-0.8
Ac ce p
-1.0 -1.2
244oC
-1.4 -1.6
417 418 419
0
100
200
300
352oC 400
500
600
Temperature (oC)
420 421 422 423
21 Page 21 of 26
Figure 3
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cr
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424
425
427 428 429 430 431
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432 433 434 435
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Figure 4
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436
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an
437
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23 Page 23 of 26
Table 1 Loading amount of triclosan (g/g NFC)
0
0.0033
0.01
0.017
0.023
0.033
0.17
0.33
GIB (%)
0
12.5
79.2
87.5
98.7
99.8
99.9
100
ip t
442
443
cr
444
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445
an
446 447
M
448
452 453 454 455 456
te
451
Ac ce p
450
d
449
457 458 459
24 Page 24 of 26
Table 2 Tensile index (N.m/g)
Tear index (mN.m2/g)
Stretch/Elongation (%)
Blank paper (control)
24.93±0.60
7.00±0.081
2.68±0.35
Triclosan-loaded
29.41±1.97
8.85±0.26
2.77±0.41
cr
NFC coated paper
ip t
460
us
461
Ac ce p
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an
462
25 Page 25 of 26
Highlights
462
Nanofibrillated cellulose (NFC) was used as substrates to carry triclosan (TCS).
464
The triclosan-loaded NFC was coated on paper.
465
The coating of TCS-loaded NFC on paper resulted in improvement of paper strength.
466
The paper coated with TCS-loaded NFC exhibited excellent antimicrobial activity.
ip t
463
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cr
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26 Page 26 of 26
