The Impact Of Small Molecular Substances On The Crystallization,Melting And Mechanical Properties Of Aromatic Polyesters

In this work,the different small molecular substances were selected as modifiers to mediate the crystallization and melting behaviors and mechanical properties of aromatic polyesters at different levels by melt blending method,which is mainly aimed at the problem that the crystallization rate of poly(ethylene terephthalate)(PET)is too slow and for poly(butylene terephthalate)(PBT)is too fast.The effect of additives on the crystallization and melting behaviors,spherulite morphology,crystal structure,intermolecular force and mechanical properties of polymer matrix were systematically investigated by differential scanning calorimetry(DSC),polarized optical microscopy(POM),Wide angle X-ray diffraction(WAXD),Small angle X-ray scattering(SAXS),Fourier transform infrared spectroscopy(FTIR),scanning electron microscope(SEM),and mechanical test.Poly(ethylene terephthalate)(PET)and aryl amide derivative(TMB-5)blends were prepared.DSC results showed that TMB-5 had a significant nucleation effect on PET and especially the nucleation efficiency reached up to 80.7%when the addition of TMB-5 reached 0.6 wt%,the crystallization temperature of PET apparently increased by nearly 20℃ and the crystallization rate increased 11.5 times.WAXD and POM results showed that the addition of TMB-5 remarkably increased the crystallinity and nuclei density of PET.SAXS measurements revealed that the lamellar thickness of PET increased,the amorphous layer of PET decreased and the long period of PET decreased with the increasing of TMB-5 content.Meanwhile,the notched impact strength of PET was improved with the addition of TMB-5.A remarkable improvement in impact strength by approximately 10 times can be achieved when adding 0.4 wt%content of TMB-5.The effect of a low molecular weight Phenyl phosphonic acid salts compound(TMC-210)on the crystallization behaviour and mechanical properties of poly(ethylene terephthalate)were systematically evaluated.The results showed that the incorporation of TMC-210 reflected a significant heterogeneous nucleating effect on the crystallization of PET,it obviously improved the crystallization temperature and accelerated the crystallization rate of PET,the crystal nucleus density increased and the spherulite refinement,these parameters of PET increased with increasing TMC-210 content at the same time.When introducing 0.6 wt%TMC-210 to PET matrix,the nucleation efficiency reached up to 99.8%.To further improve the content of TMC-210,it could find that TMC-210 appeared agglomeration.Meanwhile the crystal structure of PET did not change with the addition of TMC-210.The impact fracture surface of PET developed a brittle ductile transition and thus the impact strength of PET improved significantly,it exhibited an evident enhancement about 12.2 times when the content of TMC-210 reached 0.4 wt%.Additionally,Lauritzen-Hoffman equation was used to discuss the effect of TMC-210 on the fold surface free energy(σe)of PET in the crystallization process and found that the σe values of PET/TMC-210 blends was smaller than that of pure PET.Blends of poly(butylene terephthalate)(PBT)and 4,4’-thiodiphenol(TDP)were prepared through melt blending method and the intermolecular hydrogen-bonding was characterized using Fourier transform infrared spectroscopy(FTIR).The results showed that intermolecular hydrogen bonding formed between the carbonyl group of PBT and hydroxyl group of TDP,the carbonyl and hydroxyl absorption bands shifted to a lower wavenumber and the shape of the hydroxyl peaks became wider asymmetrically with increasing TDP content.This result was verified further by advanced quantum-chemistry calculations.The crystallization behaviors of PBT were significantly inhibited by this hydrogen bonding force.The crystallization rates of PBT/TDP blends were obviously slower than that of pure PBT at the same isothermal crystallization temperature.The crystal structure of PBT did not change with the incorporation of TDP,but the motion ability of PBT chain segments were limited because of the hydrogen bonding crosslinking effect,and as a consequence the crystallinity and the crystal size of PBT decreased with increasing TDP content.The blends of poly(butylene terephthalate)(PBT)and 4,4’-dihydroxyphenyl(DHP)were prepared by melt blending method and the effects of DHP on the crystallization and melting behaviors of PBT were investigated by DSC,WAXD and POM.The results showed that crystallization temperature and crystallinity of PBT apparently decreased with the addition of DHP.A remarkably decline in crystallization rate of PBT was achieved and the blends had higher σe and q values than that of pure PBT as analyzed based on Avrami equation and Lauritzen-Hoffman equation.The addition of DHP did not change the crystal structure of PBT,the elongation-at-break and flexural modulus of PBT was enhanced,while the spherulites size of PBT decreased.