High temperature shape memory polymers & ionomer modified asphalts.

摘要

This dissertation consists of two research subjects: High Temperature Shape Memory Polymers and Ionomer Modified Asphalts. Current development of thermally sensitive shape memory polymers (SMPs) has focused primarily on relatively low transition temperatures (Tc < 100°C) and elastomeric polymers, such as thermoplastic polyurethanes (TPU), crosslinked polyethylene, poly (epsilon-caprolactone), sulfonated EPDM and polynorbornene. Those materials are appropriate for applications such as biomedical and surgical materials, smart fabrics and heat shrinkable tubing. Materials used as aerospace or structural components often require higher modulus and switching temperatures for shape change and actuation. To the best of our knowledge, there have been no reports of thermoplastic SMPs with controllable switching temperatures above 100°C. There has been research on high temperature SMPs but based on thermoset polymer systems. High temperature thermoplastic shape memory polymers were developed from metal salts of sulfonated PEEK (M-SPEEK, M=Na+, Zn2+, Ba2+, Al3+, Zr4+) ionomer and composites of the M-SPEEK ionomers with a fatty acid salt. M-SPEEKs were prepared by neutralizing sulfonated PEEK acid to metal salts. The glass transition temperatures of M-SPEEK ionomers increased with increasing Coulomb energy of ion pairs and the ionomers were thermally stable to ~320°C. The M-SPEEK ionomers exhibited microphase separated morphologies and the average correlation length was determined by small angle X-ray scattering. Al-SPEEK and Zr-SPEEK showed crosslinked characteristics such as rubbery plateau above Tg and much reduced water uptake. The M-SPEEK ionomers exhibited reasonable shape memory behavior, in which the permanent network was provided by ionic nanodomains formed by the interaction of ionic groups and glass transition temperatures served as the switching temperatures. The relative poor shape efficiency of Na-SPEEK and Zn-SPEEK (80-90%) can be improved by blending M-SPEEK with a low molar mass crystalline compound NaOl. The composites were prepared from 70 wt% M-SPEEK (M = sodium or zinc) and 30 wt% sodium oleate (NaOl). Ionic nanodomains formed by the interactions of ionic groups provided a permanent physically crosslinked network and strong dipolar interactions between the ionomer and a dispersed phase of crystalline NaOl provided the temporary network. A temporary shape was achieved and fixed by deforming the material above the melting temperature (Tm) of NaOl and then cooling under stress to below Tm. The permanent shape was recovered by reheating the material above Tm without applying stress. Shape fixing efficiencies of 96% were achieved and shape recovery reached 100%. Triple shape memory behavior was also achieved for M-SPEEK/NaOl compounds using the glass transition of the ionomer and the melting point of the NaOl as two separate switching temperatures.;Asphalt binders suffer from different kinds of distresses such as low temperature cracking, rutting and fatigue during &;The thermal properties, morphology and viscoelastic behavior of ionomer modified asphalts were studied. The ionomer modified asphalt exhibited much better dispersion and smaller phase separation than did polyethylene modified asphalt. After establishing the linear viscoelastic range of response through strain sweep, frequency sweep tests at a temperature range of 30-80°C were conducted to study the dynamic mechanic properties of the modified blends. The isothermal response curves were reduced to dynamic master curves of modulus and viscosity based on the time-temperature superposition principle. The effects of ionomer concentration and mixing time on the viscoelastic behavior were studied. The addition of ionomer improved the elasticity of the asphalt, but long times were needed to mix the ionomer into the asphalt and properties were very sensitive to mixing time. A series of SuperPave tests were conducted on both ionomer modified and neat asphalt, which simulating the real life temperature and traffic load condition. The performance grade of ionomer modified asphalt was transformed from 64-28 to 69.2-26.5.