Study Of Two-step Chain Extension Polyester And Its Processing Properties

Polyester is a kind of engineering plastics with excellent comprehensive performance and wide application,which is obtained by condensation polymerization of polyols and polybasic acids.It includes Poly(butylene terephthalate)(PBT)and Poly(butylene succinate)(PBS).In the process of using PBT resin,the problems such as low intrinsic viscosity,low notched impact strength and elongation at break,large molding shrinkage and poor hydrolysis resistance affect the service range and service life.(1)The design starts from the molecular chain structure.High-viscosity,low-crosslinked PBT from organic chain extenders and inorganic particles are prepared.PBT modification adopted from multifunctional,commercially available chain extension containing nine epoxy groups(ADR9)occurred in the first step chain extension;hydroxyl addition modified dioxazoline(BOZ)served as the second-step.Anion stratiform inorganic hydrotalcite(HT)is used to adjust the crystallization behavior and damp-heat aging properties of PBT.Incorporation of chain extender and HT units into the copolymer chains entrapping PBT molecules enabled the formation of the stable cross-linking and branched structure in the PBT matrix.With a fraction of chain extenders in the PBT matrix,the chain-extended PBT exhibited higher mechanical properties,intrinsic viscosity,average molecular weight,and melt viscosity than those of unmodified PBT.Damp-heat aging resistance measurements show correlation with initial carboxyl content in the resin.The tensile strength increased from 51.4 MPa to78.9 MPa,and the elongation at break increased from 18.4%to 77.6%.The intrinsic viscosity and average molecular weight increased from 0.81 d L/g to 1.60 d L/g and 2.4×10⁴ to 5.6×10⁴,respectively.Small angle X-ray diffraction(SAXS)analysis showed that the interface thickness increased from 0.479 nm to 0.899 nm.The results show that the interfacial interaction between inorganic powder and polymer as well as the compatibility is enhanced.The scanning electron microscope(SEM)images show that HT has good dispersion in PBT matrix and no agglomeration.These results show PBT can be modified by two types of chain extenders in combination with HT to obtain the requirements for optical fiber coating.It provides a theoretical guidance for the fabrication of optical fiber coating materials.On the other hand,as a biodegradable resin PBS,the lack of strength and ductility along the stress direction has become the main factor restricting its application in the field of film application.(2)The design starts from molecular chain and aggregation structure.The structure,morphology,fracture toughness and flaw sensitivity length scale of chain-extended PBS with a highly oriented were studied.PBS polyester was modified by means of melting chain extension similar to PBT.PBS was oriented stably by uniaxial tensile at 95?.Time-temperature superposition(TTS)studies confirmed the viscosity and the degree of molecular branching increased sharply.Wide angle X-ray scattering(WAXS)and SAXS experiments were performed for these composites of orientation.The results show that the average size of the crystalline domains decreases from 17.1 to 11.2 nm,while the average distance is calculated to be 44.2 nm increased reach to 53.5 nm.The orientation of the polymer in the pre-stretch state so that its spherulites deformation along the stretching direction.The results determined the fracture toughness??10⁶ J m^-2 and a critical flaw sensitivity length scale of?/W_c?0.01 m,approximately 5 times higher in the chain extension sample during its first-time loading compared to PBS without chain-extension(??2×10⁵ J m^-2,and?/W_c?0.002 m).The research on the chain aggregation structure of PBS has more application prospects in the fields of film,plate and profile.It also provides theoretical guidance for other high toughness materials.