Influence of monomer concentration on the morphology , contact angle , water uptake , and antibacterial activity of grafted cellulose obtained from peel durian

The objective of the current study is to evaluate and determine the effect of monomer concentration of 2-[acryloyloxyl] ethyltrimethylammonium chloride (CIAETA) on the grafting copolymerization of oxidized cellulose which isolated from peel durian. Four concentrations of ClAETA were used in this study, e.g., 40, 50, 60, and 70%. Several analyses were performed to determine the material characteristic, e.g., degree of grafting, Fourier Transform Infrared (FTIR) Spectroscopy, surface morphology, contact angle, degree of swelling, and antibacterial activity. The result showed, monomer concentration plays a significant role to the physical and surface morphology of DAC-ClAETA. The degree of grafting of ClAETA was found in the range of 15-31%, and at the concentration of 50% the grafted oxidized cellulose has 30.4% of degree of grafting. SEM images showed the pore volume has linear correlation to the monomer concentration, it increased the surface roughness. Also, the contact angle confirmed the hydrophilicity and degree of swelling of grafted oxidized cellulose was increase that linear to ClAETA concentration. DAC-gClAETA was found antibacterial active against Staphylococcus aureus, Staphylococcus epidermis, and Candida alibcans than DAC


INTRODUCTION
Grafting polymerization between cellulose and monomer is one technique to modify natural properties of cellulose for the wide application. This technique had been utilized since 1960s for preparing modified cellulose' surface[1], prepare new derivate of grafted cellulose [2], grafting cellulose and poly(vinyl alcohol), PVA [2] [3], copolymerization between in the presence of Mn 3+ as initiator [4] [5]. Other modifications have also been done by researcher to develop new cellulosic materials. [6][7] [8] Technically, the grafting copolymerization is affected by several factor, e.g., reaction temperature, contact time, solvent, initiator, and monomer concentration. [9][3] [10]. In the previous study, [11] we already done the grafting of quaternary ammonium salt, called as ClAETA or [2-(acryloyloxyl) ethyl] trimethylammonium chloride, on the surface of oxidized cellulose (DAC, dialdehyde cellulose) under a specific condition, e.g., 2-[acryloyloxyl] ethyltrimethylammonium chloride (CIAETA) 50%, temperature 80 o C, contact time 180 min in the presence of potassium persulfate as initiator [11], which produced a material which has 30.4% of degree of grafting. Another study revealed, a material which has 61.3% of degree of grafting could be obtained by modifying cellulose using methyl acrylate monomer under this following condition: monomer concentration 0.68 mol/L, temperature 50 o C, contact time 115 minute in the presence of initiator, potassium persulfate.
Those mentioned previous study [11] indicated that the reaction parameter have important role for obtaining an optimized reaction. Different reaction condition will produce a different result. Based on this literature review, the objective of this current study is to determine the effect of one parameter, in this case *Corresponding Author: roslianalubis@staff.uma.ac.id monomer concentration of ClAETA, in the grafting copolymerization of oxidized durian peel' cellulose. Several characterizations have been performed to evaluate the properties of the obtained material, e.g., degree of grafting, FTIR, surface morphology analysis, contactangle, degree of swelling, and antibacterial activity.

Methods
Grafting of ClAETA onto cellulose 5 g of oxidized cellulose with sodium metaperiodate (NaIO4: cellulose by ratio 0.6) [11] was dispersed in distilled water for 4 h into three-neck round flask heated up to 50 o C, after 30 min heating, potassium persulfate (5% of monomer weight) and 25 mL ClAETA with variant concentration 40,50, 60, and 70% were added into the solution to initiate the reaction. Grafting reaction was carried out at 80 o C under nitrogen atmosphere for 3 h, then the dispersion was cooled and methanol/acetone mixed solution was added to separate the entreated monomer and the grafted cellulose. The obtained of grafted cellulose fiber was dried in vacuum oven.

Determination of grafting yield
The grafted cellulose fiber was dried in vacuum oven at 60 °C until a constant weight was reached. The grafting yield (GY) was determined gravimetrically and calculated as follows according to previous report [10]: Where W1 is the weight of cellulose before and W2 is the weight of cellulose after grafting.

Experimental Analysis FTIR Analysis
The spectra of the practical gathering of unblemished and united oxidized cellulose were used by an FTIR spectrophotometer utilizing Cary 630 FTIR Agilent. All acquired range was recorded in the accompanying condition: the goal of 4 cm -1 and wavenumber scope of 4000-650 cm -1 and checked multiple times.

Surface morphological characterization
The surface morphology characterization of cellulose and altered cellulose were resolved to utilize an examining electron magnifying lens (SEM) JEOL/EO JSM-6510 LA version 1.0.

Contact angle analysis
The wetting surface capability of the modified cellulose was determining by measuring the contact angle using sessile drop method using Ganiometer, CCD camera resolution 50 fps (1980 x 1080 pixel).
Water Uptake Capability DAC-g-CIAETA were first gauged and (m0) absorbed refined water for various time points at 1, 2, 3, 4, 5, 6, and 7 h. After taking out the example pieces from the arrangement, the perfect tissue paper was utilized to eliminate unnecessary water on the outside of the test and the subsequent weight was recorded (m1). The growing proportion of each example was determined by the Eq.(2).

Swelling ratio (%) = [[m1-mo]/mo] x 100% (2)
Antimicrobial activity Gram-positive bacterial, S. aureus and S. epidermis, and C. albicans were utilized to decide the antimicrobial of united oxidized cellulose fiber disconnected from durian skin. The estimation was performed utilizing plate dispersion Kirby-Baauer (KB). The detach of microscopic organisms was refined on supplement agar (NA) medium, and parasites were refined on a potato dextrose agar (PDA) medium. Each segregate with a thickness of 108 was immunized into a physiological arrangement of NaCl 0.85%. The thickness of microbes and growths was resolved utilizing a standard arrangement of Mc. Farland. The grouping of adjusted cellulose was changed, for example 25, 50, 75, and 100%. Brooding was performed at 30 o C for 48 h [11].

Degree of grafting of DRC-g-CIAETA
The grafting of ClAETA onto the oxidized cellulose surface was performed using free radical polymerization technique, as the initiator is sulfate radical obtaining from the thermal heterolysis of potassium persulfate. Mechanism of grafting of CIAETA onto Cellulose using KSP as the initiator in Figure  1. The effect of monomer concentration to the degree of grafting of the obtained material is shown in Table 1.  [10]. Another reason, when the ClAETA concentration was increase to 60-70%, the number of homopolymer that produced during the grafting reaction is also increase the competing reaction between the grafting and homopolymer formation is happened in the uncontrolled free radical polymerization. The homopolymer formed is separated by purification using acetone.
In the free radical copolymerization, monomer concentration is an important factor that influence the threshold value equivalent (TVE) of the optimum degree of grafting. Above TVE, the degree of grafting will decrease, and vice versa. The decrease of degree of grafting is caused by homopolymer formation and monomer decomposition as the thermal effect [18][19] [20].

FTIR
The monomer concentration effect on the obtained product was also evaluated using FTIR, as in Fig. 2. The FT-IR spectrum shows that there is no significant change on the wavenumber shift and the band shape. The band was observed at 1729 cm -1 associated with the C=O ester group molecular structure [12]. Another characteristic of CIAETA modification at 1476 and 1217 cm -1 corresponds for the vibration of trimethyl group of quaternary ammonium salt [13] and C-C-N asymmetric [14]. These further confirmed that CIAETA molecules were chemically anchored onto oxidized DRC surface and may significantly enhance the density of positive surface charges (R-N(CH 3) + ).

Morphology analysis of DAC-g-ClAETA
Figure-3 shows the micrograph image obtaining from SEM analysis before and after grafting process. A change on the topology surface of DAC was confirmed. The neat DAC has long band fiber with smooth surface. However, DAC-g-ClAETA has roughness surface than the previous one (750x magnification). The increase of ClAETA concentration significantly affected the morphology of material molecule. Table 2 shows the contact angle of DAC and DAC-g-ClAETA. The measurement was performed using sessile drop method, and the droplet contact angle was observed during this time: 0, 60, 120, and 180 s. Table 2 confirms monomer concentration significantly affected the contact angle of modified material. The increase of ClAETA concentration affected on the decrease of contact angle. This result indicating the hydrophilicity of material is also increase. When the material has contact angle between 0 and 90 o , the material can be said as hydrophilic material, above those value the material is hydrophobic [21] distortion phenomenon as explained in the previous section. The presence of pore volume can facilitate the water molecule to diffusion into the fiber segments. The higherthe pore volume, the lower contact angle that will be observed. Table 2. Contact angle of DAC and DAC-g-CIAETA

Degree of swelling
The capability of material to adsorb water is known as degree of swelling, which influence by its hydrophilicity [22]. ClAETA as monomer has higher density that water, i.e., 1.132 g/mL, and known as cationic monomer with high hydrophilic character. The grafting of ClAETA onto DAC surface will enhance the hydrophilic character of DAC, and it will affect the degree of swelling of DAC. Figure 4 shows the correlation of degree of swelling and ClAETA concentration.
The increase of ClAETA that used during grafting process improve the degree of swelling of modified DAC.

Antibacterial activity
Several concentrations of DAC-g-ClAETA were tested to determine its potential as antibacterial agent against Staphylococcus aurous, Staphylococcus epidermis, and Candida albicans. As control, chloramphenicol was used to determine the capability of DAC-ClAETA. The inhibition zone diameter that produced by DAC-g-ClAETA is shown in Table 3. The DAC-g-ClAETA which prepared with high ClAETA concentration shows the high antibacterial activity. As reported, ClAETA is a quaternary ammonium and classified as cationic surfactant which has antibacterial and antifungal activities. It able to interact through electrostatic interaction between cationic group from ClAETA and negative charge molecule which present in cell membranes. This interaction then form a complex of surfactant-microbe, and able to disrupt the function of cell membranes and biological activities, indirect impact is it will lower the capability of microbe to perform selfmultiplication [24] [25].

CONCLUSION
Grafting copolymerization of oxidized cellulose in the presence of various concentration of ClAETA monomer shows it able to control the surface roughness, hydrophilicity, and biological activity of material. Degree of grafting is this study is in the range of 15-31%, with the highest percentage is found at the ClAETA concentration of 50%. The increase on ClAETA concentration the contact angle is found increase, as the impact its hydrophilicity of material also increases. The presence of ClAETA on the DAC surface improves the antibacterial activity of DAC.

ACKNOWLEDGMENT
Author thanks to Laboratory of Graduate School of Chemistry, Universitas Sumatera Utara, and Laboratory of Chemistry, Universitas Medan Area for all facilities and support that provided during this study.