Preparation And Properties Of Cellulose-Based Antibacterial Materials

Food safety is a major issue generally concerned about.Food-borne pathogens such as Staphylococcus aureus and Escherichia coli have caused the most serious harm.To ensure food safety,it's very important and necessary to control food-borne pathogens.At the same time,Alicyclobacillus acidoterrestris and other food spoilage bacteria also pose a huge threat to food production and storage.Traditional sterilization methods mainly include physical methods such as ultraviolet irradiation and ultra-high pressure sterilization,chemical preservatives,and antibiotics.Physical methods require special equipment or high cost,which limits their application in food production,while conventional chemical preservatives may have certain toxicity and be easy to remain in the human body and cause potential harm.Therefore,the development of safe,efficient and environment-friendly antibacterial materials is particularly important.In recent years,cellulose has received wide attention due to its biosafety,biodegradability,chemical stability and low cost.However,the lack of antibacterial and other activities of cellulose has limited the application of cellulose.Chemical modification of cellulose will endow cellulose with good antibacterial activity.Based on the above research background,this thesis uses cotton linter cellulose as raw material to carry out the preparation and performance research of new cellulose-based antibacterial materials.The main content and results are as follows:?1?Preparation,characterization and antibacterial activity test of nisin grafted magnetic cellulose beads.Aldehyde groups were introduced into cellulose molecules via oxidation of sodium periodate,and nisin was anchored on the cellulose beads through spontaneous Schiff base reaction.The composite beads were characterized by Fourier transform infrared spectroscopy?FTIR?,field emission scanning electron microscopy?FESEM?,energy dispersive X-ray spectroscopy?EDS?and X-ray diffraction?XRD?,which confirmed the amino group of nisin reacts with cellulose aldehyde groups.The thermogravimetric analysis?TGA?results show that the thermal degradation temperature of the beads was above 200°C.The hysteresis loops of the beads were studied by a vibrating magnetometer?VSM?,and the results showed that the beads were superparamagnetic.The composite beads inhibited the growth of A.acidoterrestris DSM 3922,S.aureus ATCC 29213 and E.coli ATCC 25922within 12 hours,which was verified by growth curve method.?2?Preparation,characterization and antibacterial activity test of chitosan quaternary ammonium salt grafted magnetic cellulose beads.According to the results of previous studies,3-chloro-2-hydroxypropyl trimethyl ammonium chloride chitosan?HTCC?was prepared.Based on the research method in the previous chapter,aldehyde groups were introduced into cellulose by sodium periodate and HTCC was grafted onto the beads by spontaneous Schiff base reaction.The composite beads were characterized by FTIR,FESEM,EDS,XRD,TGA,and VSM,which confirmed the oxidation and the Schiff base reaction.The results showed the composite beads were superparamagnetic and the degradation temperature was 200-300°C.The HTCC grafted beads inhibited the growth of A.acidoterrestris and S.aureus within 12hours,and only exhibited weak antibacterial activity against E.coli under high grafting quantity.?3?Preparation,characterization and antibacterial activity test of?-polylysine grafted cellulose beads.The beads were prepared by a sol-gel conversion method,and carboxyl groups were introduced by a two-step oxidation method.EDC/NHS method was used to graft?-polylysine onto the beads.The composite beads were characterized by FTIR,FESEM,XRD,and TGA,which confirmed oxidation and amidation reactions.The results showed degradation temperature of the beads was 200-300°C.Using BET and BJH models,the specific surface area of the beads was 0.4-1 m² g^-1,and the average pore diameter was about 19-33 nm.The?-polylysine grafted beads inhibited the growth of S.aureus,E.coli and A.acidoterrestris within12 hours.?4?Preparation,characterization and antibacterial activity test of?-polylysine cross-linked cellulose composite films.The cellulose was dissolved in an alkali/urea system and then casted to form cellulose hydrogel.Epichlorohydrin was used as crosslinking agent to anchor?-polylysine on the surface of the films.The films were characterized by FTIR,FESEM,XRD,TGA,etc.The results showed surface morphology of the films was dense and smooth,and the hydrophobicity increased with the increase of the amount of EPL.The transmittance of all films in visible light spectrum were above 80%.After crosslinking,the tensile strength of the film decreased while the elongation at break increased.The antibacterial activities of the films were investigated by shake-flask method and the films inhibited the growth of S.aureus,E.coli and A.acidoterrestris within 12 hours.In this thesis,based on the selective oxidation and cross-linking reaction of cellulose,nisin grafted magnetic beads,chitosan quaternary ammonium salt grafted magnetic beads,?-polylysine grafted beads and?-polylysine cross-linked composite films were prepared,respectively.The growth of S.aureus,E.coli and A.acidoterrestris was inhibited within 12 h.The beads and films are expected to become new green antibacterial materials.