Studies On Preparation Of CNW Hybrids And Their Influence On Polyvinyl Alcohol Composites

With the advancement of society and science and technology,environmental protection has been widely concerned,and energy consumption has become increasingly serious.Using biomass materials as fillers to modify polymer composites can help alleviate energy problems.Chitin is a renewable biomass material widely found in nature,mainly in crustaceans,with an annual biosynthesis of up to 10 billion tons.Nano chitinwhisker（CNW）was prepared by hydrolysis of chitin with acid,and a variety of hybrid materials were prepared with silicon dioxide,boron nitride and antibacterial metal particles.The hybrid materials were compounded with polyvinyl alcohol（PVA）to prepare high-performance functional PVA composites,which expands the application of CNW in various fields and is in line with the sustainable development strategy.Firstly,the chitin was hydrolyzed by hydrochloric acid to remove the amorphous area and retain the crystalline area to prepare CNW with rod-shaped fibers.Scanning electron microscope（SEM）and atomic force microscope（AFM）analysis showed that it was about 100nm-1μm long and about 30 nm-70 nm in diameter.Fourier transform infrared spectroscopy（FTIR）and X-ray diffraction（XRD）analysis showed that it wasα-Chitin crystal form and its chemical structure did not change.Thermal stability analysis showed that its thermal stability was slightly lower than that of Chitin.Silica modified CNW hybrid particles Si O₂-CNW were synthesized in situ by hydrolysis condensation of tetraethyl orthosilicate（TEOS）.The thermal stability of Si O₂-CNW hybrid particles was higher than that of CNW,but the particle size was larger.Using CNW and Si O₂-CNW modified PVA.The results show that with the increase of CNW content,the thermal stability of the PVA/CNW composites are slightly improved,and the mechanical properties are improved.The tensile strength gradually increases,while the elongation at break first increases and then decreases.When the CNW content is 6 phr,the tensile strength and elongation at break of the PVA/CNW composite are increased by 18.4%and 28.3%respectively compared with pure PVA.As the addition of Si O₂-CNW increases,the thermal stability of PVA/Si O₂-CNW composites gradually increases.The the elongation at break gradually increased and tensile strength gradually decreased.When 8 phr Si O₂-CNW was added,the elongation at break increased by 16.9%,and the tensile strength of the composites decreased by 35.0%.The addition of CNW and Si O₂-CNW will not reduce the transparency of PVA composites.Two kinds of m-BN（BNSi and BNPVP）were prepared by surface treatment of boron nitride（BN）with silane coupling agent APTES and polyvinylpyrrolidone（PVP）.And two m-BN@CNW hybrid materials（BNSi@CNW and BNPVP@CNW）were prepared by compounding m-BN and CNW.FTIR,XRD and SEM analysis show that CNW and m-BN have a compact structure,which greatly increases the number of active groups on the surface of the BN sheet and improves the compatibility of BN and PVA matrix.Using unmodified BN,two m-BN and two m-BN@CNW hybrid materials as fillers,PVA composites were prepared.The results show that all five fillers can enhance the thermal conductivity of PVA composites.Among them,the two m-BN@CNW hybrid materials have the best enhancement effect.And the thermal conductivity of PVA composites increases as the filler content increases.When 35phr hybrid material is added,the thermal conductivity of PVA/BNSi@CNW and PVA/BNPVP@CNW composites reach 1.034 W/（m·K）and 1.049 W/（m·K）,respectively,which are 192.9%and 197.2%higher than pure PVA,and 29.3%and 31.1%higher than PVA/BN composites.Furthermore,on the basis of PVA/BNPVP@CNW composites,one-dimensional thermal conductive material CNT is added to form a space-planar thermal conductive network,which further enhances the thermal conductivity of PVA composites.When 2 phr CNT is added,the thermal conductivity of the PVA composites reaches 1.241W/（m·K）,which is 18.3%higher than that of the PVA composites without CNT.The insulation performance of the PVA composites remained stable without significant decline.Using L-ascorbic acid（Vc）as the reducing agent,CNW@Ag and CNW@Cu hybrid materials were prepared by reducing Ag NO₃ and Cu SO₄on the surface of CNW.The MIC test showed that they have certain antibacterial activity.The Minimum inhibitory concentration（MIC）of CNW@Ag against S.aureus and E.coli are 0.15 mg/m L and 0.10 mg/m L,and the MIC of CNW@Cu against S.aureus and E.coli are 0.25 mg/m L and 0.15 mg/m L.With CNW@Ag and CNW@Cu as fillers,PVA composite film and PVA composite gel were prepared by casting method and cyclic freezing-thawing method,respectively,and their antibacterial properties were evaluated by the bacteriostatic rate and the size of the bacteriostatic zone.With the increase of filler content,the antibacterial performance of PVA composite film and gel gradually improved.When the addition amount is 30 phr,the bacteriostatic rate of PVA/CNW@Ag composite film against S.aureus and E.coli are respectively 56%and 61%,the size of the bacteriostatic zone of PVA/CNW@Ag composite gel against S.aureus and E.coli are 4.03 mm and 3.83 mm,respectively.The bacteriostatic rates of the PVA/CNW@Cu-30 composite film against S.aureus and E.coli are 46%and 41%,respectively.And the size of the bacteriostatic zone of PVA/CNW@Cu-30 composite gel against S.aureus and E.coli were 4.56 mm and 2.61 mm,respectively.