Study On The Effect Of Diethylene Glycol On The Melting And Crystallization Behavior Of Pet Copolyester Hot-melt Adhesive

With tetrabutyl titanate(Ti(OBu)4) as the catalyst, poly (ethylene-co-diethylene terephthalate-co-isophthalate)(PEDTI) was prepared by the directed esterification and polycondensation of terephthalic acid(PTA), isophthalic acid(PIA), ethylene glycol (EG) and diethylene glycol(DEG). The methods of gel permeation chromatography(GPC), infrared spectroscopy(IR), thermogravimetric analysis(TGA) and differential scanning calorimeter method(DSC) were used to characterize copolyester samples.In the experiments,with other synthetic experimental conditions unchanged, the amount of DEG was gradually increased, and the effect of DEG on synthesis of copolyesters were researched. The results showed that the thermal stability of copolyesters decreased with increasing DEG content. Melting point(Tm), initial melting point(Tim), equilibrium melting temperature(Tm0)and glass transition temperature(Tg) were also decreased as DEG increased, and the reduction of melting point was larger. When DEG content reached26%mol, crystallization melting peak disappeared, it indicated that crystalline polymer had been modified into an amorphous polymer under the experimental conditions.With DSC methods and Avrami dynamic equation and its correction models, isothermal and non-isothermal crystallization process of copolymers were studied. The process of isothermal crystallization of PEDTI and PETI were described by Avrami equation. The results indicated that the increase in DEG hindered the isothermal crystallization from the melt and the crystallization rate was decreased. For the isothermal crystallization from the glassy state, the addition of DEG promoted the crystallization. The Avrami equation modified by Khanna-Taylor and Mo were used to describe the behaviors of the non-isothermal crystallization. The results showed that the two methods were suitable for describing the system.