Research On Nano-Cellulose Crystals/Poly(Lactic Acid)In-situ Composites

Poly?lactic acid??PLA?is one of the most important biodegradable polymer with biocompatibility and biodegradability,but its application is limited for its hy-drophobicity and uncontrollable degredation rate.With wonderful hydrophilic and good biodegradability,cellulose nanocrystal?CNC?are normally compound with PLA to improve properties of PLA composites,but compatibility between CNC and PLA is poor for hydrophobocity of PLA and hydrophilic of CNC.The CNC/PLA in-situ composties were prepared by in-situ melt-solid state polymerization to improve the compatibility between CNC and PLA.The primary research in bone tissue engineer-ing scaffolds was performed.The main contents and results are as follows:First,the CNC/PLA in-situ composites were obtained by in-situ melt/solid state condensation using lactic acid?LA?and CNC suspention as raw materials which pre-pared by acid hydrolysis of medical absorbent cotton with 64%sulfuric acid.To op-timize the technology parameters,the effect of reaction temperature reaction time of melt and solid polymerization,prescystalline time,precrystalline temperature and content of CNC on the molecular weight of PLA in CNC/PLA in-situ composites were discussed.The results show that the appropriate reaction conditions of conden-sation are as follows:in the melt state,synthesized at 180? for 10h;in the solid state,polymerized at 105? for 20h with 3h of precrytalline time and 105? of precrystal-line temperature.The structures and properties of CNC and CNC/PLA in-situ composites were charactertized by transmission electron microscope?TEM?,fourier transfer infrared spectroscopy?FTIR?,gel permeation chromatography?GPC?,differential scanning calorimetry?DSC?,thermo-gravimetric analysis?TG?,wide angle X-ray diffraction?WAXD?.The results show that the LA are successfully grafted onto the surface of CNC due to the chemical reaction between PLA and CNC;the molecular weight of PLA in in-situ composites increases and decreases with increasing time and tempera-ture for solid state polycondensation?SSP?and content of CNC;the molecular weight distribution of PLA in in-situ composites increases with increasing CNC content and reaction temperature for SSP while increases and then decreaseds with increasing re-action time for SSP;The heat resistance of CNC/PLA in-situ composites are better than that of common CNC/PLA composites and when the content of CNC is 0.4%,the heat resistance,degree of crystallinity and structure of crystals are optimal;the dis-persity of CNC in CNC/PLA in-situ composites is improved.CNC/PLA in-situ composites porous scaffolds were prepared by thermally in-duced phase separation method.The effect of coarsening time,coarsening tempera-ture and content of PLA and CNC on porosity and compression modulus of CNC/PLA in-situ porous scaffolds were studied.The pore connectivity of the scaffolds was ob-served by scanning electron microscope?SEM?.The results show that the pore con-nectivity of composites porous scaffolds is lower in comparison with that of pure PLA porous scaffolds;The porosity of scaffolds increases and then decreases while com-pression modulus of scaffolds decreases and then increases with increasing coarsening time;The porosity of scaffolds increases and then decreases while compression mod-ulus of scaffolds increases and then decreases with increasing content of CNC;when the content of CNC is 0.8%,the porosity of scaffolds is 78%and the compression modulus is 87MPa which increases about 183%in comparison with that of pure PLA porous scaffolds;the porosity and compression modulus of in-situ composites porous scaffolds increases with increasing molecular weight of PLA.Capacity of protein absorption and blood biocompatibility of CNC/PLA in-situ composties were performed and degradation of in-situ composites porous scaffolds in simulated body fluid?SBF?was discussed.The structures and properties of CNC/PLA in-situ composites porous scaffolds after degradation in SBF were charactertized by fourier transfer infrared spectroscopy?FTIR?,scanning electron microscope?SEM?;wide angle X-ray diffraction?WAXD?.The results show that the capacity of protein absorption of the scaffolds increases and then decreases with increasing content of CNC which reaches the highest value of 8.44mg/g when the content of CNC is 0.8%,which increases about 182%in comparison with that of pure PLA porous scaffolds whose is 4.61mg/g;With increasintng content of CNC and molecular weight of PLA,the hemolysis ratio of in-situ porous scaffolds decreases and increases,respectivity,but both are less than 0.5%which means that the in-situ porous scaffolds are not toxic;under the same conditions,the degradation of high molecular weight of scaffolds and low content of CNCs scaffolds is slower than that of low molecular weight and high content of CNCs;The surface of scaffolds becomes rough due to the deposition of ion of Ca²⁺?CO₃^2-?PO₄^3-and degree of crystallinity of scaffolds decreases.