Study On The Antibacterial Properties Of Cellulose Sponge Modified With Mulberry Leaf Active Substances And Its Application

There are many kinds of active components in mulberry leaves.Among them,mulberry leaf polyphenols have great potential for application in antibacterial materials due to their excellent antibacterial properties,high biological safety,and environmentally friendly synthesis process.Antibacterial materials are often used as fruit preservation packaging and water purification materials and film materials being widely used.However,the film cannot provide sufficient cushioning protection for fruits during transportation.The film also hard to generate high water flux to achieve rapid water purification.Obviously,antibacterial porous materials with flexibility,elasticity,and fatigue resistance are more suitable for these two fields.Cellulose is highly flexible,easy to obtain,and has good biocompatibility,commonly used in the construction of porous materials.Therefore,this study first utilized a structural design strategy to construct major and minor pores using two types of cellulose fibers with significantly different scales as long and short chain fibers,respectively,to prepare cellulose sponges with hierarchical cellular structure.The mechanical properties of the sponges were determined,and chlorogenic acid,quercetin,and mulberry leaf polyphenols crude extract were modified on the sponges through covalent bonding.The components and contents in the crude extract of mulberry leaf polyphenols were determined,and the feasibility of modification was verified by various analytical chemistry methods.Secondly,the protective performance of hierarchical cellular sponges modified with chlorogenic acid was tested by using strawberries as a model fruit.Finally,the antibacterial and antifungal ability of sponge modified with quercetin was tested.Then water containing E.coli was used to simulate sewage,and the sponge modified with quercetin and crude extract of mulberry leaf polyphenols was used as water purification material to test its water purification ability and recycling ability.Detailed results are as follows:（1）A hierarchical cellular cellulose sponge was constructed,and the modification of the sponge by active ingredients in mulberry leaves was achieved.In specific research,two types of cellulose with significant differences in scale were used as long and short chain fibers respectively to construct hierarchical cellular sponge.A covalent modification strategy was used to modify the sponge with chlorogenic acid,quercetin,and mulberry leaves polyphenols crude extract.The SEM results indicated that the synergistic effect of the two types of cellulose endowed the sponge with a layered porous structure.FTIR results showed that after modifying mulberry leaf polyphenols,cellulose exhibited a characteristic peak of hydroxyl groups on the benzene ring.XPS results showed that after modification with chlorogenic acid and quercetin,the C-C and C=O content of cellulose significantly increased.¹³C NMR results showed that after modification,signal peaks corresponding to carbon of chlorogenic acid and quercetin appeared on the cellulose.The above multiple characterization methods have confirmed that mulberry leaf polyphenols have been successfully modified on cellulose sponges.（2）The mechanical properties of hierarchical cellular sponge and the antibacterial properties of sponge modified with chlorogenic acid,and the preservation of berries represented by strawberries were studied.The sponge was determined by quasi-static compression and the result showed that the compression modulus of the sponge was only31.44 k Pa.After 4000 cycles of compression,only 18.04%plastic deformation occurred.This proved that the sponge has softness,elasticity,and fatigue resistance under cyclic compression,so the sponge could offer long lasting cushioning protection for berries.The antibacterial test results suggested that after modification with chlorogenic acid,the sponge exhibits excellent antibacterial ability and the ability to inhibit fungal spore germination.The storage experiment of strawberries using the sponge showed that after 18 days of storage,the strawberries are not moldy,and their physical and chemical properties did not show significant changes.Therefore,this material effectively extends the shelf life of strawberries and provides good conditions for their storage.（3）The ability of hierarchical cellular sponge modified with mulberry leaf polyphenol crude extract to remove microorganisms from water was studied.The mechanical properties of sponges were tested by quasi-static compression experiments,the results showed that the sponge was not broken under high strain compression and cyclic compression,demonstrating its ability to withstand water flow without damage.Water flux and dynamic water contact angle test proved that the porous nature of sponges results in a water flux of up to 4.29×10⁵-4.54×10⁵L·m^-2·h^-1·bar^-1,and the dynamic water contact angle test proved its excellent hydrophilicity,which helps water diffusion in the sponge.The antibacterial experiment showed that the modification of polyphenols endowed sponges with excellent antibacterial ability and the ability to inhibit fungal spore germination.The results of the circulating sterilization water purification experiment show that the sponge had excellent water purification ability,and could remove 98%of bacteria from the water within 0.5 h.After 10 cycles of using,there is still a high and good antibacterial effect.This study successfully modified two active ingredients,chlorogenic acid and quercetin,from mulberry leaves on the surface of cellulose,and used two sizes of cellulose to construct a sponge that combines flexibility,elasticity,and fatigue resistance under cyclic compression without damage.When the sponges were used as berry packaging and water purification materials,they could effectively protect berries from mechanical damage,extend their shelf life,and quickly and effectively remove bacteria from the water.This study provides a new solution for the application of active ingredients in mulberry leaves,a traditional livestock resource,and also provides new design ideas for the development of cellulose elastic porous sponges.