Study On Surface Esterification Modification Of Cellulose Nanocrystals And Its Reinforcement Effect On Poly (Butylene Succinate)

In recent years,environmental pollution and oil consumption caused by petroleum-based polymer materials have attracted worldwide attention.Thus,the researches and application of biodegradable polymer materials are promoted.Poly（lactic acid）is the most widely used polyester in degradable polymer,but it’s toughness is poor.Poly（butylene succinate）（PBS）is also a linear degradable aliphatic polyester with excellent toughness and has been successfully applied as degradable plastics and films.However,lower mechanical strength and modulus limit the application of PBS in the field of anti-deformation and tensile resistance.Therefore,it is necessary to find a green nano-reinforced filler with a wide range of sources,biomass and degradability for the development of PBS.Cellulose nanocrystal（CNC）is an ideal filling reinforcing material due to the large stock in nature,light weight,biodegradability,and nanorods crystal properties.Due to the existence of a large number of strongly polar hydroxyl groups on the surface of CNC,CNC is easy to reunite in PBS matrix.Therefore,the surface of CNC was treated by hydrophobic grafting with succinic anhydride and ethyl succinate acyl chloride,respectively.Then,the modified fillers were used to reinforce PBS materials,respectively.The effects of surface structure and content of CNC on the thermal stability and mechanical properties of PBS were studied.1.Succinic anhydride was used modified CNC to improve the compatibility between CNC and PBS matrix.Firstly,CNC with average length of 283.4 nm,and mean diameter of 21.7nm are synthetized by sulfuric acid hydrolysis of microcrystalline cellulose.Succinic acid cellulose nanocrystal（SCNC）was prepared by esterification of CNC with succinic anhydride in anhydrous condition.Then,PBS/SCNC composites were prepared by melt blending.The existence of succinic acid group on SCNC surface is confirmed by Fourier transform infrared spectroscopy（FTIR）spectra and ¹³C solid state nuclear magnetic resonance.Water contact angle and dispersion test prove that CNC changed from strong polarity to weak polarity.Field emission scanning electron microscopy（FESEM）,X ray diffraction（XRD）show that the morphology and size of cellulose nanocrystals before and after modification are very close,and the internal crystal structure remained intact.The effects of CNC and SCNC on the surface morphology,crystallization behavior,thermal stability and mechanical properties of the composites were studied.The dispersion of SCNC in PBS matrix was found to be more uniform than that of CNC by FESEM.The crystallinity of PBS/SCNC composites is slightly lower than that of PBS/SCNC composites,but the original crystalline structure of PBS matrix composites are not be destroyed.Under the same CNC content,the yield strength of PBS/SCNC composites is significantly higher than that of PBS/CNC composites.This is mainly due to the fact that the dispersion of SCNC in the PBS matrix is more uniform than that of CNC,and that the FTIR shows that more hydrogen bond networks formed between SCNC and PBS matrix can significantly enhance the interfacial force between the two phases.The thermal stability of PBS/SCNC composites is obviously higher than that of PBS/CNC composites.The main reason is that the sulfonic group on the surface of SCNC is far lower than that of CNC.On the other hand,the degradation of SCNC can produce barrier effect and delay the degradation of PBS materials.2.Ethyl succinyl chloride was used to modify CNC to improve the compatibility between CNC and PBS matrix.Ethyl succinyl cellulose nanocrystalline（ECNC）are prepared by esterification of ethyl succinate acyl chloride with CNC in anhydrous condition.Finally,PBS/ECNC composites were prepared by melt blending.The dispersion of ECNC in PBS matrix are found to be more uniform than that of CNC by FESEM.Differential scanning amount（DSC）and wide-angle x-ray diffraction（WAXD）show that the crystallinity of PBS/ECNC composites are slightly lower than that of PBS/CNC composites,but the original crystalline structure of PBS composites is not be destroyed.Under the same nano-fillers content,the yield strength of PBS/ECNC composites are obviously higher than that of PBS/CNC composites.When the content of nano-filler is 3 wt%,the yield strength of PBS/ECNC composites increased by 10.7%than that of PBS/CNC composites.This is mainly because the dispersion of ECNC in PBS matrix is more uniform than that of CNC,and that more hydrogen bond networks are formed between ECNC and PBS matrix,resulting in PBS chains entanglement,which improve the interfacial force between the two phases.3.PBS/ECNC composites fibers with different drafting ratios were prepared by melt spinning.And the effects of ECNC axial orientation arrangement,PBS molecular orientation and crystal structure on the mechanical properties of the composite fibers were studied.At the same drafting ratio,the breaking strength of PBS/ECNC composite fibers is higher than that of PBS/CNC composite fibers.This is mainly due to the good dispersion of ECNC in PBS matrix as verified by FESEM results.With the increase of the drafting ratio of PBS composite fibers,the tendency of ECNC arrangement along its axial direction is more obvious in the cross-section morphology of PBS/ECNC composite fiber,and the side of the composite fiber is more smooth and smooth.In addition,the sonic velocity orientation value of the composite fiber at high drafting ratio is obviously higher than that of the low drafting ratio composite fiber with the same component,which indicates that the PBS molecular chains is oriented at high drafting ratio,and the nanoparticles will be arranged along the fiber axis.It is helpful to improve the breaking strength of composite fiber.