Preparation Of Dialdehyde Cellulose Nanofibers And Their Application In Fruit Cultivating Bag Paper

Fruit cultivating bag paper is a kind of agricultural technical paper to protect fruits and facilitate their growth and development.It is generally produced by waste paper,so the mechanical properties are usually poor.Adding reinforcing agents is helpful to improve the mechanical strength of paper.Fruit cultivating bags are used in large quantities,in which the presence of petroleum-based reinforcing agents tends to cause greater pressure on the environment.Therefore,the research and development of environmental-friendly and efficient paper reinforcing technology are particularly significant.Nanocellulose fiber generally exhibits the characteristics of light weight,high strength and green environmental protection.Nanocellulose inherently belongs to biomass material,which holds great potential in enhancing the mechanical strength of paper.The dialdehyde modification is able to open the ring at the C₂-C₃ position in the structural unit of cellulose and introduce two aldehyde groups.Dialdehyde nanocellulose can increase the structural strength of paper by forming hemiacetal or acetal crosslinking between aldehyde group and hydroxyl group on fiber surface,which makes them have high application potential in papermaking process.In the present work,DACNF was obtained based on dialdehyde modification of CNF using sodium periodate as highly selective oxidation,and the reaction was accelerated by a metal salt solution.The effects of different metal salts were compared to confirm the promoting effect of metal salts on the reaction.Meanwhile,the influence of Zn Cl₂ concentration,oxidizer concentration,reaction temperature and oxidation time on the oxidation reaction was also explored.It was discovered that within a certain range,increasing the reaction time and the dosage of oxidant led to a higher content of aldehyde groups.Additionally,the aldehyde group content initially increased and then decreased with the increase of Zn Cl₂ concentration and reaction temperature.After comprehensive comparison,the optimal reaction conditions were determined as follows:the concentration of Zn Cl₂was 8 g/L,the oxidation time was 120-150 min,the reaction temperature was 60-75℃,and the dosage ratio of sodium periodate to CNF was 1.5-2.Qualitative detection of aldehyde groups was achieved through the silver mirror reaction.Moreover,characteristics of DACNF were analyzed using SEM,FT-IR,XRD,TG,and Zeta potential analyzer.The absorption peak changed in the FT-IR confirmed successful modification.SEM analysis illustrated that the modification gradually reduced the size of coarse fiber bundles as well as resulted in a more compact arrangement of fibers.Furthermore,fuzzing was observed on the surface of the fibers at a high oxidation level.XRD analysis further revealed that the oxidation reaction was found to have limited effect on the crystal structure,but caused a degree of damage to the crystalline region.Zeta potential analysis indicated that the aldehyde modification weakened the surface electronegativity of CNF.TG results showed that the thermal stability decreased slightly with the deepening of dialdehyde modification,but it remained high.In addition,the antibacterial activity of DACNF against Staphylococcus aureus was confirmed using the bacteriostatic zone method.By controlling the amounts of CNF and DACNF and utilizing DACNF with varying aldehyde group contents,fruit cultivating bag paper was produced from waste paper pulp via wet end formation process.The impact of DACNF on the drainage properties of pulp was analyzed.Furthermore,the various properties of the paper,including surface morphology,dry and wet tensile indexes,air permeability,water absorption,and light transmittance,were evaluated.In addition,based on DACNF,antibacterial agents were applied to the fruit cultivating bag paper,and the efficacy of paper in inhibiting Escherichia coli and Staphylococcus aureus was examined.It was found that CNF had a negative impact on the drainage properties of pulp,which can be improved by dialdehyde modification.CNF was effective in achieving a uniform distribution of fibers in the paper,while DACNF obviously improved the cross-linking density.Within a certain range,the increase of DACNF aldehyde group content made the dry and wet tensile index of fruit cultivating bag paper firstly improve and then decrease.Furthermore,with the increase of DACNF addition,the dry and wet tensile index of fruit cultivating bag paper gradually rose.With the increase of aldehyde group content and addition of DACNF,the air permeability of fruit cultivating bag paper demonstrated a downward trend,and the Cobb value first decreased and then increased.DACNF was proved to have a more significant strengthening effect on the paper compared to CNF.It made the dry and wet tensile index higher,and the Cobb value and air permeability lower.When the aldehyde group content was 1.660 mmol/g and the addition amount reached 1%,the wet tensile index of fruit cultivating bag paper exhibited an increase of 23.58%,while the Cobble values of the front and back sides displayed a decrease of 5.72%and 15.65%respectively.With the addition of 3%,the dry tensile index of fruit cultivating bag paper added with DACNF showed an increase of 36.97%.The increase of aldehyde group content and addition of DACNF had limited effect on the transmittance of fruit cultivating bag paper in ultraviolet light,but slightly improved the transmittance in visible light.Additionally,the paper showed significant antibacterial activity against Escherichia coli and Staphylococcus aureus after the application of DACNF with antimicrobial finishing.