Preparation Of Bamboo-based Micro-nano Cellulose And Its Strengthening Effect On Polyurethane Foam

The biomass utilization and green development of bamboo resources can alleviate the predicament of the shortage of wood resources,so focusing on the structure and properties of bamboo-based cellulose and its nanomaterials is a necessary prerequisite for high-energy utilization and bio-controllability,as well as an important way to develop new high-performance and high-value-added nanocomposite materials.The purpose of this research is to prepare bamboo-based micro-nano cellulose II with stable properties as a reinforcing component to strengthen and toughen traditional polyurethane foam materials through a greener method.In this study,bamboo was used as raw material,and using spectroscopy as the analysis method to explore the hydrogen bonding of bamboo-based cellulose crystal variants;bamboo-based micro-nano cellulose II was prepared by mechanochemical reaction method—planetary high-energy ball milling,combined with water or NaOH-urea mixed solution as solvent,and the green preparation process of micro-nano cellulose and the influence of two solvents on the properties of bamboo-based micro-nano cellulose were discussed;in addition,the mechanism and effect of the prepared bamboo-based micro-nano cellulose on the strengthening and toughening of polyurethane foam materials were investigated.The results showed as follows:(1)NIRS shows that the hydrogen bond in the crystalline region of bamboo cellulose I and cellulose II has a high wave number shift from 6292 cm^-1 to 6354 cm^-1 in the near infrared characteristic band,and the front wave number reflects the strong hydrogen bonding of the intramolecular hydrogen bonds O2-H2…O6 of cellulose I,the back wave number corresponds to the strong hydrogen bonding of the intermolecular hydrogen bonds O2-H2…O2 of cellulose II;bamboo-based cellulose II formed a double peak in the semi-crystalline region.There was a good correlation between the quantitative analysis results of cellulose crystallinity by NIRS and the XRD analysis results,the r² reached 0.99.(2)With a certain amount of water as the solvent,the crystalline structure of cellulose can be transformed from type I to type II by ball milling,and the degree of transformation becomes more extensive with the increase of water content,when the water content is 30%and the ball milling time is120 min,the most uniform type II bamboo-based micro-nano cellulose particles BC₁₂³⁰ ₀ with a size of100?500 nm are obtained;with the increase of water content,the sample's crystallinity also increases during the ball milling process,but decreases with the increase of ball milling time;meanwhile,the HBI and LOI obtained by FTIR were used to quantitatively analyze the crystallinity of cellulose,and the results were consistent with XRD,which demonstrated the feasibility of this method.(3)With different concentration ratios of NaOH-urea mixed system as the solvent,the bamboo-based micro-nano cellulose II with good dispersibility was obtained by ball milling.When the NaOH is 7wt%,the sample changes from cellulose I to cellulose II;when the NaOH is 20wt%,the type II characteristic peak of sample BC₀²⁰ is the most obvious,indicating that the appropriate concentration of NaOH is 20wt%;it also explains the interaction between NaOH and cellulose,and the auxiliary isolation effect of urea.(4)Bamboo-based micro-nano cellulose are used as a reinforcing component in the foaming process,and a chemical cross-linking reaction occurs with the PU foam matrix,the particles can be evenly distributed in the foam cell wall of foaming material to withstand a certain external force,which strengthens the foam wall,significantly improves the structure of the foam hole,so that the mechanical properties,thermal stability and the apparent density of the composite foam materials are ameliorated significantly;and the optimal addition amount of the reinforcing component bamboo-based micro-nano cellulose is 2%.In a word,this research provides a green and feasible method for the acquisition of micro-nano cellulose II,and innovatively broadens the application of bamboo-based micro-nano cellulose in the field of composite foam materials,provides a feasible and reliable way for the high-value-added utilization and sustainable development of bamboo resources and composite foam materials.