Study Of A Thermoplastic Polyimide Modified Poly (Ether Ether Ketone) Resin

Specialized engineering plastics were born as support to the needs ofstructural materials with heat resistance, excellent mechanical propertiesand light weight as the aerospace industry developed rapidly. The mostspecial property is the long-term use under temperature higher than150℃,several types of polymer materials were reported then, includingpolyether sulfone (PES), polyphenylene sulfide (PPS), polyaromatic etherketone (PAEK), polyimide (PI), polybenzimidazole (PBI), liquid crystalpolymer (LCP). More and more research attention has been focused onspecialized engineering plastics as they are widely used in thecutting-edge industry for their outstanding combined properties.Poly (etherether ketone)(PEEK), as a main member in the family ofPAEK, has been widely used in the industry of electronic devices,machinery instrumentation, transports and aerospace field. Meanwhile,PEEK is a polymer with crystallization ability, the crystallization degreecan be controlled in the range of0-48%depending on the processingconditions. As the performance of polymer materials are affected by the morphological structures of the polymer chains, the properties of PEEKcan be tailored by conditioning the processing parameters.The glass transition temperature of PEEK is low, which limits thematerial's performance, severe softening is observed above200℃,making PEEK unavailable under high-temperature conditions. It isnecessary to modify PEEK to enhance its properties, especially theperformance at high temperatures.Polyimides (PI) have found various applications in the high-techfields for the high-temperature resistance. In the family of polyimides,thermal plastic polyimides (TPI) have the similar thermal properties asthe other polyimides, and the good thermal processing properties, e.g.shaped by thermal molding, extrusion and injection methods. It isexpected to use TPI as the modifier of PEEK to enhance the resin's hightemperature performance by melt blending TPI/PEEK.The properties of PEEK, especially those properties at hightemperature, were studied in this dissertation. Thermal analysis, dynamicmechanical analysis, thermomechanical analysis, X-ray diffraction andtensile analysis were applied to characterize PEEK molded with variousprocessing conditions. The results showed that the processing conditionsaffected the morphology structures, which in turn affected theperformance of PEEK. The morphology turned from amorphous, lightlycrystallized to highly crystallized, mechanical properties results showed that tensile modulus and maximum tensile strength became higher as thecrystallization degree increased, and elongation at break turned lower,this could be attributed to the rigidity of the crystallized regions. Anotherpoint to note is, even for the highly crystallized PEEK prepared fromannealing treatment, which had tensile modulus of1.5GPa at150℃, thetensile modulus dropped down to300MPa when the temperature raised to200℃, indicating the performance was severely damaged at highertemperature range. Meanwhile, dependence of the dimensional stabilityon the processing conditions was observed by TMA analysis, especiallyat high temperature, the annealing sample had a CTE value of144ppm/K,implying again that PEEK' properties at temperatures higher that200℃was limited.A thermal plastic polyimide containing flexible groups (sulfone,m-phenylene and ether link) were synthesized as a modifier for PEEK,using a diamine4,4'-(3-amino-phenoxy) diphenyl sulfone (m-BAPS),and the TPI's properties were studied. Thermal and mechanical propertieswere evaluated and the results showed that this type of TPI had goodthermal and mechanical properties, with a glass transition temperature of260℃, dynamic mechanical analysis showed that the polyimide chainswere highly active during glass transition for the storage modulusunderwent decrease of three-order magnitude, implying a high degree ofthermal plasticity. Melt viscosity results showed that this type of polyimide had low viscosity when melted, the melt viscosity values were240pa.s,1200pa.s and2300pa.s for the molding compound withmolecular weights of15k,30k and45k, respectively, showing that meltprocessing can be conducted to this TPI, which laid the foundation ofmelt blending with PEEK as a modifier.After the pre-blending of PEEK and as-synthesized TPI, the resinwas extruded by the torque rheometer and the properties of modifiedPEEK were studied. TGA analysis showed good thermal stability of theresin, DSC results showed two glass transitions and an endothermic peakowing to the melting of crystallization, the intensity of the transition orthe peak changed systematically as the composition changed, implying anincompatible system. Study on the morphology structures of the modifiedresin showed the crystallizztion of PEEK chains, and the diffraction peakschanged successively as the PEEK component changed. DMA analysisgave the impression of incompatibility again and, mechanical propertiesat high temperatures and the retention of storage modulus at hightemperature ranges increased as the modifier component increased,indicating the high-temperature performance of the resin was improvedcompared to that of pure PEEK. Dimensional stability was also enhancedas the modifier was incorporated.