| Low melting point polyester is a kind of modified polyester, its melting point is lower than conventional polyester, the range of the melting point is from 90 ? to 240 ?, when Tm under 200 ?, it can be produced to sheath-core composite staple and filament, otherwise can be prepared for various polyester masterbatch. Along with low melting point polyester used in non-woven fabric and hot melt adhesive gradually, preparation of low melting point polyester has become a new research field of PET modification.At present, the synthesis of low melting point polyester mainly concentrated in adding Isophthalic Acid(IPA), but this kind of low melting point polyester is hardly crystallization and influences the stability of the subsequent processing and molding. So the goal of this project is the preparation of crystalline low melting point polyester and synthesizing two kinds of specifications of the low melting point polyester through blending modification and copolymerization. Adding ester exchange catalyst(Zn Ac2), PET and PBT were blended with different ratio(100/0,75/25, 50/ 50, 25/75, 0/100) by twin-screw extruder. Due to the action of implementation reaction, melting point of blending products was different. Copolymerization method is to choose Adipic Acid(AA) and 1, 2- propylene glycol(?-PG) as a modified monomer, according to the acid alcohol mole ratio of different polymerization preparation for a series of low melting point polyester. The structure, thermal behavior and adhesion stress were tested. The results were as follows.Blending method is based on the quality of PET/PBT = 25/75 ratio, adding 0.2% of transesterification catalysts Zn Ac2, blending 3 min in 275 ?, the low melting point polyester of 210.1? was prepared. The blending products' thermal behavior and crystal properties were analyzed by Differential Scanning Calorimetry(DSC), the structure was analyzed through nuclear magnetic resonator(1H-NMR and 13C-NMR). Through the analysis of 13C-NMR, PET and PBT blending system reacted ester exchange reaction after adding transesterification catalysts(Zn Ac2), the actual blending ratio is 27/73 through the calculation of 1H-NMR. The non-isothermal crystallization kinetics of blending products was analyzed through J method, Avrami index(n) was above 3. Mo method was suitable for description of blending products' non-isothermal crystallization process. F(T) increased with the increase of the value of X(t) and increased from 2.39 to 2.39.The copolymers' structure was invested by Fourier transform infrared spectrometry(FT-IR) and 1H-NMR. The thermal behavior and crystal properties of copolymers were researched by DSC and Thermo Gravimetric(TG). The bond strength of copolymer was analyzed by Universal Testing Machine. DSC analysis was carried out on the copolymerization of low melting point polyester. Results showed that adding 10% per mole ratio of AA, the melting point of polymer reduce 20 ?, and adding 5% per mole ratio of ?-PG, the melting point of polymer reduce 5?. In the copolymerization system AA and ?-PG had a synergistic effect on reducing melting point. As a result of the copolyesters obvious secondary crystallization, J method only could describe the primary crystallization process. Avrami index was approximately equal to 3. Because of unable to ignore the secondary crystallization, Mo method was used to describe the non-isothermal crystallization of low melting point copolyesters. F(T) increased with the increase of the value of X(t), F(T) increased from 11.94 to 11.94. Ziabicki theory investigated copolymerization modification monomer for copolymerization modification system crystallization ability. Through the comparison of crystallization ability constant Gc, ?-PG influenced on the crystallization properties of polyester, AA can adjust the crystallization properties of polyester. The analysis of FT-IR was that ?-PG has realized the copolymerization reaction; Through results of 1H-NMR, the ratio of charge is basically equal to the ratio of copolymerization; Adhesive strength of low melting point polyester could reach 3.483 MPa.Through to the 170 ? low melting point polyester samples rheological analysis, copolymer has good fluidity, and the shear viscosity decreases with the increase of shear rate, showing the typical shear thinned pseudoplastic fluid behavior. Non-newtonian index of LPET is larger than that of conventional polyester, and the dependence of shear viscosity to shear rate is more obvious. E? of conventional polyester ranges from 68 k J/mol from 113 k J/mol, and E? of low melting point polyester ranges from 18.78 k J/mol to 28.65 k J/mol, this means that the low melting point polyester melt can be flowed steady under the low temperature. At 220 ?,the structure viscosity index of sample is 0.297,this value is the same as the conventional PET spinning structure viscosity index. Combined with non-newtonian index and flow activation energy, the best spinning temperature is 220 ?.170? low melting point polyester sample was spinning at 220 ?. With 4 times of drawing ratio, the strength of low melting point polyester fiber was 2.07 c N/dtex. Its strength is 4 times than these low melting point fiber synthesized by IPA. |
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