8.Summary,Conclusions and Recommendations This report has examined the evolving field of high performance thermoplastic resins and their composites.Thermoplastic polymers of various chemical familles having the potential to be used as matrix for composites in aircraft structural applications have been identified and presented.The chemical families include polyketones,polyarylene sulfides, polyamides,polyimides,polysulfones,liquid crystalline polymers,polybenzimidazoles and polyphenylquinoxalines.Discussions on the performance of neat and continuous fibre reinforced thermoplastic resins in terms of their chemical properties,room temperature and elevated temperature mechanical properties,damage tolerance,environmental and chemical resistance and faugue and creep behavior have been provided.The interrelationships between morphology and properties of semi-crystalline thermoplastic composites have been addressed as well as the factors influencing the morphology.The techniques to combine fibres and matrix,to produce laminates,to form three-dimensional parts and to join thermoplastic composite parts have been described.Many conclusions have been reached and the ones considered to be the most important are provided below along with recommendations for future research and development work. 8.1 Neat Thermoplastlc Resins There is considerable interest in advanced thermoplastic composites in the aerospace community.Already.an interesting choice of these novel materials is available in the marketplace for use as matrices for composites in aircraft structural applications;and others are expected to emerge.In general,high performance neat thermoplastic resins exhibit mechanical properties comparable to those of thermosets but they are characterized by outstanding toughness.higher ductility reflected by high tensile strain to failure and lower moisture absorption.In general,they exhibit good temperature capability as they possess high glass transition temperature (Tg).But the very high desired Tg leads to high melt viscosity which renders the complete impregnation of the fibres by the matrix difficult and thus impeding the avallability of some thermoplastic resins in the prepreg form.The development of very flowable high performance thermoplastics that possess enhanced elevated temperature performance is highly desirable and should be investigated. 8.2 Morphology The morphology of semi-crystalline thermoplastic polymers is a fundamental issue.It is important to know how mechanical properties are affected by the morphology of the polymer and how the morphology of the matrix of the composite of interest is influenced by processing conditions.The effects of exposure to solvents encountered in aircraft applications on the morphology of semi-crystalline thermoplastics should be investigated.Special attention has to be paid to non-uniform heating during the processing of semi-crystalline 1528. Summary, Conclusions and Recommendations This report has examined the evolving field of high performance thermoplastic resins and their composites. Thermoplastic polymers of various chemical families having the potential to be used as matrix for composites in aircraft structural applications have been identified and presented. The chemical families include polyketones. polyarylene sulfides, polyamides, polyimides, polysulfones. liquid crystalline polymers, polybenzimidazoles and polyphenylquinoxalines. Discussions on the performance of neat and continuous fibre reinforced thermoplastic resins in terms of their chemical properties, room temperature and elevated temperature mechanical properties, damage tolerance, environmental and chemical resistance and fatigue and creep behavior have been provided. The interrelationships between morphology and properties of semi-crystalline thermoplastic composites have been addressed as well as the factors influencing the morphology. The techniques to combine fibres and matrix, to produce laminates, to form three-dimensional parts and to join thermoplastic composite parts have been described. Many conclusions have been reached and the ones considered to be the most important are provided below along with recommendations for future research and development work. 8.1 Neat Thermoplastic Resins There is considerable interest in advanced thermoplastic composites in the aerospace community. Already, an interesting choice of these novel materials is available in the marketplace for use as matrices for composites in aircraft structural applications: and others are expected to emerge. In general, high performance neat thermoplastic resins exhibit mechanical properties comparable to those of thermosets but they are characterized by outstanding toughness, higher ductility reflected by high tensile strain to failure and lower moisture absorption. In general, they exhibit good temperature capability as they possess high glass transition temperature (Tg). But the very high desired Tg leads to high melt viscosity which renders the complete impregnation of the fibres by the matrix diificult and thus Impeding the availability of some thermoplastic resins in the prepreg form. The development of very flowable high performance thermoplastics that possess enhanced elevated temperature performance is highly desirable and should be investigated. 8.2 Morphology The morphology of semi-crystalline thermoplastic polymers is a fundamental issue. It is important to know how mechanical properties are affected by the morphology of the polymer and how the morphology of the matrix of the composite of interest is influenced by processing conditions. The effects of exposure to solvents encountered in aircraft applications on the morphology of semi-crystalline thermoplastics should be investigated. Special attention has to be paid to non-uniform heating during the processing of semi-crystalline 152