Biodegradable polyesters are a relevant candidate in the field of biomedical applications such as drug delivery,wound dressings,tissue engineering owing to their suitable properties to support cellular growth and proliferation.However,the applications of biodegradable polyesters in the biomedical are limited due to their low degradation rate,uncontrollable degradation for many clinical applications,poor mechanical and thermal properties.Therefore by understanding the combined effects of inorganic Zn O nanoparticles and biomass cellulose nanocrystals(CNCs)from most abundant natural cellulose resources as UV absorber and antibacterial agents into biopolyester especially(poly(3-hydroxybutyrate-co-3-hydroxy valerate,PHBV)matrix with or without the addition of polyethylene glycol(PEG)as organic phase change materials could provide new prospects to the sustainable use of nanotechnology and nanocomposites with improvement in the thermal and mechanical properties for potential applications in antibacterial wound dressings,UV shielding materials,drug delivery,and thermal energy storages fields.In this dissertation,a series of ultra-high performance biopolyester nanocomposites were successfully fabricated by well dispersed of CNC-Zn O nanohybrids with modulated contents as nanofillers into bio-polyester(poly(3-hydroxybutyrate-co-3-hydroxy valerate,PHBV)matrix.The impact of nanofillers content and fabrication techniques on their structures designs and properties were discussed in details.This research can provide a theoretical basis and technical guidance for the preparation and fabrication of these novel biopolyester nanocomposites with multi-functional properties for potential uses as biomedical biomaterials.The main results are summarized as follows:1)Green synthesis of sheet-like cellulose nanocrystal-zinc oxide nanohybrids withmultifunctional performance through one-step hydrothermal method.In this study,wereport novel sheet-like cellulose nanocrystal-zinc oxide nanohybrids(CNC-Zn O)by using aone-step hydrothermal method.Various concentrations of Zn2+ ions were functionalized inCNC surface and a possible mechanism for the formation of CNC-Zn O nanohybrids with hexagonal sheet-like structure converted to the flower-like structure was also presented.Additionally,the sheet-like CNC-Zn O5.0 showed good antimicrobial activity,excellent thermal stability and high photocatalytic activity of 95.21% of MB dye was decomposed after 200 min under UV light irradiation.More significantly,the CNC-Zn O5.0 nanohybrid can be recycled three times with good Turnover frequency values(TOF).Compared to pure CNC,the maximum degradation temperature(Tmax)of sheet-like nanocrystal-Zinc oxide nanohybrid with the addition of 5 mmol Zn2+ ions(CNC-Zn O5.0)nanohybrid was improved by 23.1 ℃,and its limiting oxygen index increased up to 49.6%.This work provides a simple preparation procedure of sheet-like CNC-Zn O nanohybrids with good antimicrobial,photocatalytic and thermal properties for attractive applications as biomedical materials and flame-retardants.2)Sheet-like cellulose nanocrystal-Zn O nanohybrids as multifunctional reinforcing agentsin biopolyester composite nanofibers with ultrahigh UV-Shielding and antibacterialperformances.The uses of inorganic metal oxide and Zn O nanohybrids as UV absorbershave potential to increase the production of UV-protective textile,which will also overcome the drawbacks of organic molecules and prevent negative impacts on human health and environment.In this work,sheet-like cellulose nanocrystal-Zinc oxide(CNC-Zn O)nanohybrid was successfully developed by a one-step hydrothermal method.The obtained CNC-Zn O nanohybrids as UV absorber and antibacterial agents were introduced into biopolyester(poly(3-hydroxybutyrate-co-3-hydroxyvalerate,PHBV)by using electrospinning process.The addition of sheet-like CNC-Zn O can greatly enhance PHBV thermal stability and crystallization ability.In addition,excellent antimicrobial ratios of Escherichia coli and Staphylococcus aureus,and high absorbency of solution A(9.82 g/g)were obtained for the composite nanofibers with 5 wt % CNC-Zn O.Moreover,most of the UV irradiations were blocked out for both UVA(99.72%)and UVB(99.95%)with high UPFvalue of 1674.9 in the resulting composite nanofibers with 9 wt % CNC-Zn O.This study provides a novel method to produce sheet-like CNC-Zn O with multifunctional properties and its nanocomposite for potential uses as wound dressings and other functional biomaterials.3)In vitro degradation and possible hydrolytic mechanism of PHBV nanocomposites byincorporating cellulose nanocrystal-Zn O nanohybrids.Fabrication and characterization ofbiodegradable nanocomposites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV)matrix reinforced with cellulose nanocrystal(CNC-Zn O)nanohybrids via simple solution casting process for possible use as antibacterial biomedical materials is reported.The obtained nanocomposites exhibited good antibacterial ratio of 95.2-100% for both types of bacteria namely S.aureus and E.coli and showed 9-15% degradation after one week.The addition of CNC-Zn O showed a positive effect on hydrophilicity and barrier properties.More significantly,the nanocomposites with 10 wt% CNC-Zn O showed enhancement in tensile strength(140.2%),Young’s modulus(183.1%),and the maximum decomposition temperature(Tmax)value increased by 26.1 ℃.Moreover,this study has provided a possible mechanism for using such nanofillers on the hydrolytic degradation of PHBV,which was beneficial to obtain the high-performance nanocomposites with modulated degradation rate for antibacterial biomaterials.4)Sun-light and thermo-sensitive responsive of PHBV phase change materials withfunctionalized Cellulose nanocrystal-Zn O nanohybrids for thermal energy storage andcontrollable drug release behavior.In this study,we demonstrated sunlight andthermo-sensitive responsive functionalized cellulose –Zn O nanohybrids based PHBV phase change fiber composites(PCF)for thermal energy storage and controllable drug release behavior.It is found that under sunlight irradiation,the PCF composite could absorb light and then transformed light into heat and stored in the PCF composite to produce energy withefficiency between(46.3-34.2%)for the PCF sample without/with the addition of CNC-Zn O nanohybrid.It is found that when the temperature is close to melting point temperature at 60 ℃,the PCF composite with the addition of 5 wt% CNC-Zn O showed percentage of sustained release more than 40.5% and 78.9% of Tetracycline hydrochloride(TH)drug were released over the two weeks with the low and high loading of TH drug content of(10,30 wt%).Thus,the responsiveness of PCF composite aligned with heating has high responsive to temperature-sensitive for controllable accumulative drug release behavior.It is interesting to mention that the high thermal stability of PCF composite as prepared in this work could make them more beneficial and promise in the practical applications for thermal storage and drug delivery.