Preparation And Properties Of Cellulose-based Biocomposites

Materials manufactured from renewable lignocellulosic biomass through environmental-friendly processes have received great attentions owing to their advantages including low cost,biocompatibility,and biodegradability.Cellulose is one of the main components of cell walls in lignocellulosic biomass,as well as the most aboundant polysaccharide in the nature.The composites based on cellulose have been widely used in many fields,such as papermaking,fabric,biomedical materials,and water treatment,etc.In this dissertation,special attention has been paid to the preparation,properties,and applications of cellulose-based biocomposites.Herein,we report a series of cellulose-based biocomposites that are prepared through microwave-assisted hydrothermal method,conventional hydrothermal method and sonochemical method.The physicochemical properties of the as-prepared cellulose-based biocomposites were characterized,and the cytocompatibility as well as their applications in drug delivery,protein adsorption,and antibacterial fields were investigated.The results were summarized as follows:(1)The cellulose/hydroxyapatite(HA)nanocomposites have been prepared by the sonochemical method in NaOH/urea aqueous solution.The as-prepared cellulose/HA nanocomposites exhibited a high ability to induce the formation of apatite when immersed in simulated body fluid(SBF),and maximum mass of the nanocomposites was reached 1.82 times of initial mass after 28 days of soaking.Moreover,the as-prepared cellulose/HA nanocomposites have good cytocompatibility,and show a relatively high protein adsorption ability(321.5 mg g-1)using hemoglobin as a model protein,thus they can be used as a transport carrier for the delivery of protein drugs.(2)In order to investigate the influences of phosphorus sources on the preparation of cellulose/HA nanocomposites,the cellulose/HA nanocomposites have been synthesized using inorganic phosphorus source(NaH2PO4�2H2O),or organic phosphorus sources(adenosine 5'-triphosphate disodium salt(ATP),creatine phosphate disodium salt tetrahydrate(CP),or D-fructose 1,6-bisphosphate trisodium salt octahydrate(FBP))through the microwave-assisted hydrothermal method.Experimental results revealed that the phase,size,and morphology of the minerals in the nanocomposites can be monitored by varying the phosphorus sources or adjusting the microwave heating time and temperature.For example,the HA nanorods were obtained at 150 ? for 10 min by using NaH2PO4�2H2O or FBP as phosphorus source,while HA with pseudo-cubic structure(accompanied by calcite as byproduct)was obtained when using ATP as phosphorus under the same condition,and HA with pseudo-spherical structure was obtained when prolong reaction time to 60 min.(3)In order to simplify the preparation process,and utilize all the components of lignocelulose(including cellulose,lignin,and hemicellulose),the lignocellulose/HA nanocomposites have been prepared by the microwave heating method in NaOH/urea aqueous solution.Experimental results revealed that both the microwave heating time and the concentration of inorganic substances have influence on the size and morphology of the nanocomposites.For example,when the heating time was 10 min,the HA nanoparticles were densely dispersed on the lignocellulsoe substrate,while the nanocomposites with porous structure can be obtained when prolong the heating to 60 min.The higher concentration(20%)of inorganic substances favored for the preparation of HA nanoparticles with uniformly sizes.(4)The cellulose/vaterite nanocomposites have been synthesized by the sonochemical method in ethylene glycol.Experimental results showed that the crystallization process of CaCO3 can be controlled by adjusting the cellulose concentrations,and the porous vaterite nanospheres were formed by self-assembly of rice-shaped vaterite nanoparticles.The as-prepared cellulose/vaterite nanocomposites are efficient for docetaxel loading(425.9 mg g-1)and exhibit a high ability to kill cancer cells(cholangiocarcinoma cell line RBE)after loading docetaxel.The as-prepared cellulose/vaterite nanocomposites also show a relatively high protein adsorption ability(247.5 mg g-1)using hemoglobin as model protein.(5)The lignocellulose/CaCO3 nanocomposites have been prepared by a rapid and green microwave-ionic liquid method,in which the ionic liquid([Bmim]Cl)simultaneously served as the microwave adsorbent and the solvent for lignocelluloses.The influence of CaCO3 concentrations on the microstructure,morphology and thermostability of the nanocomposites have been investigated in detail,and the formation mechanism of lignocelluloses/CaCO3 nanocomposites has been proposed.(6)The silver nanoparticles(AgNPs)have been synthesized by a facile one-pot hydrothermal method using holocellulose(HC)as substrate and reducing agent for silver ions.The as-prepared HC/Ag nanocomposites exhibited good cytocompatibility to the cells and highly toxic to microorganisms.The inhibition zones against Gram-positive Staphylococcus aureus(S.aureus)and Gram-negative Escherichia coli(E.coli)were up to 12.0-16.0 mm and 7.5-13.0 mm,respectively,the minimal inhibitory concentrations(MICs)against S.aureus was 2.5 mg mL-1.Thus they are promising for applications in biomedical fields such as bandage or wood dressings.(7)In order to investigate the influences of cellulose types on the cellulose/Ag nanocomposites,the cellulose/Ag nanocomposites have been fabricated by using four types of cellulose(cellulose nanocrystals(CNC),microcrystalline cellulose(MCC),HC,and cellulose fibers(CF))through a microwave-assisted hydrothermal method.Experimental results revealed that cellulose types played a vital role in the microstructure,morphology,and thermostability of AgNPs.For example,the silver with low crystallinity and flocculent morphology can be obtained using CNC as matrix at 160? for 10 min,while the AgNPs with high crystallinity and cubic structure were obtained by using HC or CF as matrice,and the samples prepared using different cellulose types had different thermal stabilities.(8)In order to explore the important role of hemicellulose played in the preparation of cellulose/Ag nanocomposites,the cellulose/Ag nanocomposites have been synthesized through the microwave-hydrothermal method using cellulose extract from cotton stalk as substrate,and hemicellulose as reductant.Experimental results indicated that the hemicellulose was an effective reductant for Ag+ions,and all of the facters including the hemicellulose concentration,the microwave-hydrothermal heating time and temperature have influences on the size,content,and dispersion of the AgNPs.Moreover,the antimicrobial properties of the as-prepared cellulose/Ag nanocomposites are explored using S.aureus and E.coli by both disc diffusion method and agar dilution method,and the nanocomposites showed excellent antibacterial activity.The inhibition zones against S.aureus and E.coli were 7.5?7.6 mm and 1.2?2.0 mm,respectively,the MICs against S.aureus was 1?2 mg mL-1.