# Lactic Acid Modified Natural Rubber-Bacterial Cellulose Composites
## 4 Discussion  
Films of NRBC were prepared via a latex aqueous microdispersion process and were modified by lactic acid treatment. Significant changes and improvements in some properties were achieved from the acid modification. The acid modification affected the polarity of films. The polarity could be enhanced with the increase of hydroxyl, carbonyl, and carboxyl groups on the surface of the composite films. In addition, the surface morphology change might also have affected the value of the contact angle. The water contact angle could be decreased because of increasing surface roughness [15]. According to lactic acid modification, ANRBC20 shows a slight increase in hydrophilicity when compared to NRBC20 film due to a more hydrophilic polymer surface generated by acid treatment. According to the FTIR results, it has been suggested that OH groups on the cellulose chain could form a hydrogen bond interaction with lactic acid. The interaction between lactic acid and BC via acid modification could promote the inter- and intra-molecular interaction of OH groups on BC fibers [16]. However, at high BC loadings \(\geq\)50 wt.%, there are no significant changes in hydrophilicity between ANRBC and NRBC. The acid modification showed some effects on the crystallinity of films. Generally, the XRD pattern of BC demonstrated peaks observed at 14.1\({}^{\circ}\), 16.1\({}^{\circ}\), and 22.4\({}^{\circ}\)[17; 18]. The XRD patterns of the composite films showed three peaks at similar degrees to those of BC. The crystallinity of the composite  
Figure 11: Cell viabilities (%) of HEK 293 (\(\square\)) and HaCaT (\(\blacksquare\)) cultured in extract medium of the NR, BC, and ANRBC films for 24 h as compared to the control. the values were expressed as mean \(\pm\) SD (n = 3). films increased with the increase of BC loading content. Significant improvement in crystallinity after lactic modification was observed in ANRBC with 80% BC loading. As compared with NRBC50, the crystallinity of NRBC80 was only slightly increased, which is probably due to the aggregation and disorder distribution of BC fibers when a very high amount of BC was loaded in the NR matrix. However, with lactic acid modification, the presence of the hydrogen bond interaction between the lactic acid and OH groups on the composite surface promoted a uniform distribution of BC fibers in the NR matrix, resulting in higher crystallinity of ANRBC80 as compared with NRBC80. The change in crystallinity of the composite films could imply the reorganization of the film structure. The acid modification also showed some effects on the thermal properties of the composite films. The temperature for degradation of BC was around 301 \({}^{\circ}\)C, which was close to the temperature at which the thermal depolymerization of hemicelluloses and the breakdown of glycosidic linkages of cellulose occurred, as was previously reported for plant celluloses [19; 20]. The degradation of the NR film occurred from 220 \({}^{\circ}\)C to 450 \({}^{\circ}\)C [21]. The T\({}_{\text{max}}\) of the NRBC composites decreased as BC loading increased, owing to the higher thermal stability of the C=C bonds of NR than the glycosidic linkages of BC. Compared to NRBC, ANRBC showed a slight decrease in T\({}_{\text{max}}\), which was possibly due to the inter- and intra-molecular interactions with lactic acid. The improved interfacial interaction between NR and BC and the higher composite homogeneity after the acid modification could promote the heat transfer of the composite films. The disorder or disarrangement of NR crystalline units as the BC fibers integrated into the NR matrix reduced T\({}_{\text{m}}\)[22; 23; 24]. ANRBC composites showed a relatively higher T\({}_{\text{m}}\) when compared with the NRBC composites. The results supported that the lactic acid modification promoted the homogeneousness between NR and BC, and it may have improved the interfacial interaction between the BC fibers and NR chains, and the intra- and inter-molecular interaction of the BC fibers.