| High pressure can regulate the molecular and interatomic distances of polymers without introducing impurities,and change the crystalline structure and morphology,which is of great theoretical and practical significance for the development of high-strength and high-modulus polymer materials required in sophisticated fields such as astronautics and defense.Pressure-induced rapid solidification is one of the effective ways to prepare amorphous bulk polymers.The principle is that the melt is rapidly loaded from the liquid phase region into the solid phase region by compressing.The melt enters deep supercooled state within very short time(milliseconds time scale),and it finally solidifies to be the amorphous materials.Therefore,the premise of the method is that the melting temperature of the polymers increases with increasing pressure.The thesis includes two experimental studies i.e.,the melting temperature measurement of polymers POM,PEO,and PBT/PC blend,the preparation of amorphous bulk PBT/PC blends by the pressure-induced rapid solidification method.An experimental assembly was designed for studying the melting temperature of polymers under high pressure.The melting and crystal ization temperatures of polymers paraformaldehyde and polyethylene oxide were measured below～300 MPa.The dependence T_m(P)of melting temperature T_m on pressure P was fitted.For the paraformaldehyde,the fitting result was T_m(K)=441.2+0.1044P(MPa)and for polyethylene oxide,the fitting result was T_m(K)=345.1+0.1143P(MPa).The recovered samples were analyzed,and both displayed the same crystal ine structure as that of the solidification product under ambient pressure,indicating that the crystalline structure is stable within 300 MPa.The PBT/PC blends with a mass ratio of 1:1 was prepared by using a torque rheometer.The melting temperature of the PBT/PC blends was measured below～200 MPa by using above designed experimental assembly.It is found that the melting temperature of PBT/PC blends increases with increasing pressure,and the fitting result of T_m(P)was T_m(K)=495.7+0.1501P(MPa).The pressure-induced solidification experiments of PBT/PC blends melt were carried out on the rapid compression apparatus.Amorphous PBT/PC bulk materials with diameter of 24mm were prepared successfully.Thermal analysis showed that the glass transition temperature and crystallization peak temperature of amorphous PBT/PC samples were around 323 K and388 K,respectively.The effect of pressure and temperature preparation conditions on the thermal stability of the amorphous PBT/PC samples were further analyzed.The annealing experiments at atmospheric pressure showed that the products of amorphous PBT/PC isothermal crystal ization at 440 K were theα-phase.Since the solidification of polymer melt is realized by increasing pressure instead of quenching and is consequently not limited by polymer thermal conductivity,it is a promising way to prepare bulk amorphous polymers with large size.By increasing the piston diameter and the force,larger size of amorphous PBT/PC can be prepared.The successful preparation of bulk amorphous PBT/PC is beneficial to the further study the properties and application. |
