# Lactic Acid Modified Natural Rubber-Bacterial Cellulose Composites
## Materials and Methods
### Characterization of Composite Films  
The cross-section morphology of composite films was examined by scanning electron microscopy (SEM). The images were immediately viewed at an accelerating voltage of 15 kV under SEM using a JEOL JSM-5410 LV microscope (Tokyo, Japan) [4]. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectra of the films were measured at wavenumbers ranging from 4000 to 600 cm\({}^{-1}\) at a resolution of 4 cm\({}^{-1}\) with a Nicolet SX-170 FTIR spectrometer (Thermo Scientific, Waltham, MA, USA). The static water contact angles (1 \(\mu\)L drop size) were measured by using the sessile drop method. The images of the drop were captured and evaluated by using a Kruss Drop Shape Analyzer (DSA 10 Mk2). Crystallinities of films were characterized by an X-ray diffractometer (model D8 Discover, Bruker AXS, Karlsruhe, Germany). X-ray diffraction patterns were recorded with CuKa radiation (k = 1.54 A). The operating voltage and current were 40 kV and 40 mA, respectively. Samples were scanned from 10 to 40\({}^{\circ}\) 2\(\uptheta\) at a scan speed of 3\({}^{\circ}\) min\({}^{-1}\). Profile fitting and crystallinity (%) calculations were performed with Topas version 3.0 (Bruker, AXS) software. Thermogravimetric analysis (TGA) was performed on a TGA Q50 V6.7 Build 203, Universal V4.5A (TA Instruments, New Castle, DE, USA) equipped with a platinum cell. The scanning range was 30-600 \({}^{\circ}\)C using a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\). The temperature at maximum weight loss rate (T\({}_{\rm max}\)) was measured from the DTG curves. The melting temperature (T\({}_{\rm m}\)) and glass transition temperature (T\({}_{\rm g}\)) were measured by differential scanning calorimetry (DSC). Samples about 3-5 mg were sealed in an aluminum pan. Samples were measured under a nitrogen atmosphere. Nonisothermal DSC analysis of samples was performed using a NETZSCH DSC 204 F1 Phoenix (Selb, Germany). The samples were heated from -100 to 300 \({}^{\circ}\)C at a rate of 10 \({}^{\circ}\)C min\({}^{-1}\) using a cool-heat mode. Mechanical properties were measured in terms of Young's modulus, tensile strength, and elongation at break. Films were cut into strips 1 cm wide and 10 cm long. The mechanical properties of films were determined with a Lloyd 2000R (Southampton, UK) universal testing machine. The test conditions followed ASTM D882. The Young's modulus, tensile strength, and elongation at break were the average values determined from five specimens. Films were determined for toluene and water uptake at room temperature according to ASTM D471. Each test specimens were in the form of 2 \(\times\) 2 cm\({}^{2}\). The weight of each samples were measured before immersion into toluene and water for 1, 2, 3, and 4 weeks. The degree of swelling was calculated as  
\[\text{Degree of swelling}(\%)=\frac{W_{w}-W_{d}}{W_{d}}\times 100 \tag{1}\]  
where \(W_{w}\) and \(W_{d}\) represent the weight of wet and dry films, respectively. The average values were determined from three specimens. Water vapor transmission rates (WVTRs) of the NRBC and ANRBC dry films were determined with a water vapor permeation tester (Labthink Model W3/031). The test conditions followed ASTM E 96-00 water vapor transmission of material. WVTR testing was analyzed under 38 \({}^{\circ}\)C and 90% relative \begin{table}
\begin{tabular}{c c c} \hline
**Samples** & **Area (cm\({}^{2}\))** & **Thickness (mm)** \\ \hline NR & 400 & 0.27 \(\pm\) 0.02 \\ NRBC20 & 400 & 0.17 \(\pm\) 0.02 \\ ANRBC20 & 400 & 0.18 \(\pm\) 0.02 \\ NRBC50 & 400 & 0.06 \(\pm\) 0.01 \\ ANRBC50 & 400 & 0.06 \(\pm\) 0.01 \\ NRBC80 & 400 & 0.03 \(\pm\) 0.01 \\ ANRBC80 & 400 & 0.03 \(\pm\) 0.01 \\ BC & 400 & 0.04 \(\pm\) 0.00 \\ \hline \end{tabular}
\end{table} 
Table 1: Area and thickness of films. humidity. The principle of this measurement was similar to that of the conventional method in that one side of the film was exposed to water vapor.