1.1. Mechanical properties of CP/CNF and CP/CNF/ZIF-67
1.1.1. Stress–strain curves
The stress–strain curves and the effects of CNF dosage on the tensile strength, elastic modulus, and elongation at break of CP/CNF and CP/CNF/ZIF-67 are shown in Fig. 3 and Tables S1–S4. As shown in Fig. 3(A) and Table S1, the tensile strength, elastic modulus, and elongation at break of neat CP is 7.37 MPa, 996 MPa, and 3.07%, respectively. After coating and crosslinking with CNFs, the mechanical properties of CP/CNF significantly improved. In particular, the tensile strength and elastic modulus of the CP/CNF composites with 2.5 wt% of CNFs reached 17.20 and 1489 MPa, respectively, which were approximately 1.3 and 0.5 times higher compared to those of the neat …show more content…
After the in situ growth of ZIF-67, as shown in Fig. 3(B) and Table S2, the tensile strength and elastic modulus of CP/CNF/ZIF-67 surprisingly improved to a certain degree compared to that of the CP/CNF, probably attributing to the presence of ZIF-67 nanoparticles, acting as the crosslinkers, enhancing the interactions between the cellulosic molecular chains. The determination of mechanical properties under wet condition is of great significance to the paper-based materials. As shown in Fig. 3(C) and Table S3, the CP under wet condition had poor mechanical properties with tensile strength and elastic modulus of 0.15 and 22 MPa , respectively. In contrast, the CP/CNF showed favorable mechanical performance under wet conditions. Especially when the CNF concentration was 2.5 wt%, the tensile strength and elastic modulus values reached 1.90 and 149 MPa, respectively. These values were about 11 and 5.5 times higher compared to those of CP. In addition, the existence of ZIF-67 also improved the tensile strength and elastic modulus of CP/CNF/ZIF-67 composites, as shown in Fig. …show more content…
Therefore, the antibacterial activity and cytotoxicity of neat ZIF-67 should be investigated with priority. The antibacterial activities of ZIF-67 were analyzed via the spread plate method as shown in Figs. 5(a)–(g), , and their bacteriostasis rate is shown in Fig. 5(h). It is clear that the presence of ZIF-67 can significantly inhibit bacterial proliferation. Even when the ZIF-67 concentration was only 10 μg mL-1, the antibacterial rate reached 80%, and further increase in its concentration only gradually improved the antibacterial activity. According to the previous reports [ ][ ], the bacteriostatic effect on E. coli is because of the leaching of active antibacterial species metal ions from MOF nanoparticles, thus changing the surrounding environment of bacterial cell leading to the ion balance being broken and the ion channels being destroyed. In addition, the functional groups of organic ligands in MOF can bond with cations such as Ca2+ and Mg2+ in the cells [ ]. Eventually, this behavior will rupture the cell membrane, and the outflow of cytoplasm will lead to the death of bacteria [
1.1.1. Stress–strain curves
The stress–strain curves and the effects of CNF dosage on the tensile strength, elastic modulus, and elongation at break of CP/CNF and CP/CNF/ZIF-67 are shown in Fig. 3 and Tables S1–S4. As shown in Fig. 3(A) and Table S1, the tensile strength, elastic modulus, and elongation at break of neat CP is 7.37 MPa, 996 MPa, and 3.07%, respectively. After coating and crosslinking with CNFs, the mechanical properties of CP/CNF significantly improved. In particular, the tensile strength and elastic modulus of the CP/CNF composites with 2.5 wt% of CNFs reached 17.20 and 1489 MPa, respectively, which were approximately 1.3 and 0.5 times higher compared to those of the neat …show more content…
After the in situ growth of ZIF-67, as shown in Fig. 3(B) and Table S2, the tensile strength and elastic modulus of CP/CNF/ZIF-67 surprisingly improved to a certain degree compared to that of the CP/CNF, probably attributing to the presence of ZIF-67 nanoparticles, acting as the crosslinkers, enhancing the interactions between the cellulosic molecular chains. The determination of mechanical properties under wet condition is of great significance to the paper-based materials. As shown in Fig. 3(C) and Table S3, the CP under wet condition had poor mechanical properties with tensile strength and elastic modulus of 0.15 and 22 MPa , respectively. In contrast, the CP/CNF showed favorable mechanical performance under wet conditions. Especially when the CNF concentration was 2.5 wt%, the tensile strength and elastic modulus values reached 1.90 and 149 MPa, respectively. These values were about 11 and 5.5 times higher compared to those of CP. In addition, the existence of ZIF-67 also improved the tensile strength and elastic modulus of CP/CNF/ZIF-67 composites, as shown in Fig. …show more content…
Therefore, the antibacterial activity and cytotoxicity of neat ZIF-67 should be investigated with priority. The antibacterial activities of ZIF-67 were analyzed via the spread plate method as shown in Figs. 5(a)–(g), , and their bacteriostasis rate is shown in Fig. 5(h). It is clear that the presence of ZIF-67 can significantly inhibit bacterial proliferation. Even when the ZIF-67 concentration was only 10 μg mL-1, the antibacterial rate reached 80%, and further increase in its concentration only gradually improved the antibacterial activity. According to the previous reports [ ][ ], the bacteriostatic effect on E. coli is because of the leaching of active antibacterial species metal ions from MOF nanoparticles, thus changing the surrounding environment of bacterial cell leading to the ion balance being broken and the ion channels being destroyed. In addition, the functional groups of organic ligands in MOF can bond with cations such as Ca2+ and Mg2+ in the cells [ ]. Eventually, this behavior will rupture the cell membrane, and the outflow of cytoplasm will lead to the death of bacteria [