Study On The Regulation Of Crystallization Behavior Of Poly(ethylene Terephthalate) And Its Properties

In this work,bicyclo[2.2.1]heptane-2,3-dicarboxylic acid disodium salt(HPN-68L),sodium citrate(SC)and thermoplastic polyester-ether elastomer(TPEE)were used as modifiers to mediate the crystallization behaviors of poly(ethylene terephthalate)(PET)via melt blending method to improve the mechanical properties of PET,which aimed to resolve the problems of slow crystallization rate and poor toughness of PET.The effect of HPN-68L,SC and TPEE on the crystallization behaviors,crystal structure,spherulite morphology,impact fracture surface and mechanical properties of PET were systematically by using DSC,WAXD,SAXS,POM,SEM and mechanical test.Firstly,in order to overcome low caystallization rate of poly(ethylene terephthalate)(PET),bicyclo[2.2.1]heptane-2,3-dicarboxylic acid,disodium salt(HPN-68L),a metal carboxylate nucleating additive was selected to replace the special nucleate agent of PET to improve PET crystallization.It was found that HPN-68L had a significant nucleation effect on PET.The crystallization temperature and the nucleation efficiency of PET were increased by approximately 14 °C and 68.4%at a very low content of 0.6 wt%HPN-68L.Moreover,the half-time of crystallization and isothermal crystallization activation energy decreased with the addition of HPN-68L.The long period of PET decreased and the number of spherulites increased after adding HPN-68L,while the crystal form of PET did not change.In addition,the nucleation mechanism of HPN-68L induced PET crystalliyzation was studied and chemical nucleation mechanism was proposed.The flexural strength and modulus of PET/HPN-68L composite materials were improved,whereas the impact strength decreased to a certain extent with the addition of HPN-68L.Secondly,the influence of another metal carboxylate nucleating agent(SC)on the crystallization behaviors,crystal structure,spherulite morphology and mechanical properties of PET was investigated.The results showed that SC had a significant nucleation effect on PET.When the SC content reached 0.6 Wwt%,the crystallization temperature increased by about 8.4 °C,the nucleation efficiency reached up to 38.2%and the crystallization rate increased by 1 time compared with pure PET.The crystal structure of PET did not change with the addition of SC,but the long period of PET decreased with the increasing of SC content.The addition of SC effectively increased the nucleation density of PET.At the same time,the addition of SC can effectively improve the impact toughness and tensile properties of PET,and when the SC content reached 0.6 wt%,the notched impact strength was about 1.3 times and tensile strength was about 1.2 times higher than that of pure PET.Thirdly,TPEE is selected as a modifier to mediate the crystallization behaviors and mechanical properties of poly(ethylene terephthalate)(PET)at different levels by melt blending method,wich is mainly aimed at the problems of poor toughness of PET.DSC tests showed that the introduction of TPEE could hinder the crystallization of PET process.Moreover,both of crystallization temperature and crystallization rate of PET decreased with the increase of content of TPEE.TPEE had little effect on the crystal structure of PET,but the increased of TPEE contents would extend the long period of PET.In addition,the addition of TPEE would depress the rigidity of PET,but it would distinctly improve the impact toughness and the elongation at break of PET.When the TPEE content reached 50 wt%,the notched impact strength increased about 2.8 times than pure PET.Finally,HPN-68L(or SC)and TPEE were selected as modifiers,and ternary composite materials with different compositions were prepared by melt blending method.It was found that adding HPN-68L(or SC)and TPEE at the same time can improve the crystallization and toughness of PET.DSC results showed that adding HPN-68L(or SC)in the PET/TPEE composite materials would increase the crystallization temperature,crystallinity and crystallization rate of PET.Meanwhile,the long period of PET increased after adding HPN-68L(or SC)and TPEE,but it has certain influence on the crystal structure of PET.In addition,the spherulites arranged more closely and the size was more uniform after adding the nucleating HPN-68L(or SC)to PET/TPEE composite materials.In mechanical properties testing,with increasing the TPEE content,the flexural strength and flexural modulus of ternary composite materials were decreased,but the toughness of ternary composite materials was greatly improved.