Abstract:

Objective: This study aims to explore the enhancement mechanism of the interface modified by biomimetic mineralization of nano-SiO₂ and dopamine/polyethylenimine, so as to provide a basis for the modification of bamboo fiber by biomimetic mineralization of nano-SiO₂ and improve the interface compatibility of bamboo plastic composites. Method: Using polylactic acid resin as matrix and bamboo fiber as reinforcement material, functional coating was constructed on the surface of bamboo fiber by dopamine-polyethylenimine hybrid polymerization, and nano SiO₂ was prepared by“sol-gel”. Through electrostatic interaction, nano SiO₂ was induced to accumulate and grow on the surface of bamboo fiber, and then to improve the interface properties. Fourier infrared spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction were used to analyze the changes of fiber surface elements and fiber crystal structure after modification. The mechanism of bionic mineralization modification of nano-SiO₂ to improve the interface compatibility of bamboo plastic composite was comprehensively discussed through mechanical property testing and analysis, thermogravimetric analysis, scanning electron microscopy and dynamic thermomechanical property analysis. Result: The nano-SiO₂ was attached to the fiber surface, and the content of Si element on the surface of bamboo fiber was significantly increased, and the modification did not cause the change of fiber crystal structure. The test of mechanical properties showed that the bending strength, tensile strength and impact strength of the composite modified by nano-SiO₂ bionic mineralization are increased by 18.99%, 15.91% and 34.34%, respectively. SEM analysis showed that the fiber pulling out at the interface of the modified composite was reduced, the fiber surface was coarser, and the interface bond between the fiber and the matrix was closer. The thermogravimetric analysis showed that the introduction of nano-SiO₂ improved the thermal stability of the composite, and the thermal degradation temperature of the fiber moved to the high temperature region, and the initial degradation temperature and maximum thermal degradation rate temperature of the composite increased by 22.81 ℃ and 11.54 ℃, respectively. The results of differential scanning calorimetry showed that the interaction between the modified fiber and the matrix increases the molecular movement resistance of polylactic acid, decreased the crystallinity of the composite and increased the melting temperature of the composite. The dynamic thermal mechanical properties analysis shows that the energy storage modulus of the modified composite increased and the loss modulus decreased, which indicated that the internal defects of the composite are reduced and the interface properties of the composite are improved. Conclusion: The biomimetic mineralization modification of nano-SiO₂ formed an organic-inorganic hybrid modified network of SiO₂ on the surface of bamboo fiber, which enhanced the mechanical anchoring and chemical bonding cooperation between fiber and matrix, improved the interface bonding force between fiber and matrix, improves the interface performance of the composites, and thus enhanced the interface compatibility.

Key words: bamboo fiber, nano-SiO₂, interfacial properties, enhancement mechanism, composites