Synthesis And Characterization Of Poly(Ethylene Terephthalate) Copolyester Modified By Polyol

Poly(ethylene terephthalate)(PET) is a kind of high performance thermoplasticpolyesters. Due to its good chemical and physical properties, PET has been used widely inmany fields such as synthetic fibers, films, engineering plastics and so on. After nearly30years of development, China has become the world’s largest polyester producer, but how toexpand the application fields of polyster products and enhance the value-added product ofpolyster is a real problem to be solved at present for polyester industry. PET can bemodified by physical or chemical routes. Physical modification (blending modification) iseasy to operate and costs less, while chemical modification (copolymerization) has a goodmodification effect and convenient access to achieve large-scale industrial production andso on.In this paper, we use terephthalic acid (PTA), ethylene glycol (EG) as raw materials toproduce PET which modified with pentaerythritol (PENTA) and trimethylol propane (TMP)as the third monomer by chemical modification. Further, by improving the polymerizationprocess, the polyol modified PET copolyester has been carried out through theconventional melt polycondensation procedure by using a5L and10L polycondensationreaction reactor. Ubbelohde viscometer, gas chromatography, photometric titrator,differential scanning calorimetry (DSC) and extrusion capillary rheometer and othermethods are used to analyze and characterize basic physical parameters, crystallization andrheological properties of the PET copolyester modified with polyol.The basic physical parameters of the sample test results show that copolyestersamples have a higher intrinsic viscosity and carboxyl end groups and diglycol are in linewith GB standards of PET pellets. DSC results show that the glass transition temperature,melting temperature and the thermal crystallization temperature of PET is not affectedstrongly by adding a small amount of PENTA and TMP. Non-isothermal crystallizationkinetics of copolyesters are studied by Jeziorny theory, Ozawa theory and Mo theory. Theresults show that the Jezinorny and Mo method can appropriately describe thenon-isothermal crystallization kinetics of synthesized copolyesters, whereas the Ozawa method fails to do the same ideally. It is because the Ozawa method considered the effectof cooling rate on the dynamics, making the data a poor relationship between the linear.Jeziormy’s results, the Avrami exponent has been increased by the addition of polyol, thecrystallization rate has been slowed; Mo’s results show that the value of α was almostconstant while Fz(T) is increased with increasing Xt.The results of polyester sample’s rheological tests show that the synthesized sampleshave rheological properties of pseudo plastic non-Newtonian fluid, exhibiting theshear-thinning viscosity property obviously. Compared with unmodified PET, melt shearviscosity is increased by adding PENTA and TMP, while the non-Newtonian index ofcopolyester fluid is decreased and non-newtonianism is enhanced under the sameconditions.