154 High Performance Thermoplastic Resins and Their Composites 8.4 Processing There are major benefits in processing thermoplastic composites compared to thermoset composites including the unlimited shelf life.generally short processing times (some require long and elaborate processing cycles with the evolution of volatiles)and the ability to be remelted and reprocessed.The main drawbacks are high melt viscosity,high processing temperature and the lack of tack and drape of most prepregs. The interfaclal adhesion between fibres and matrix is generally lower than that observed for epoxdes.Fibre treatment used for thermoset polymers to promote adhesion to the fibres may be inappropriate for thermoplastics.Means to improve the interfacial adhesion and their effects in controlling mechanical properties should be investigated. Residual stresses arc an important issuc when proccssing high pcrformancc thermoplastic composites since they are likely to be higher than those found in thermoset composites due to the higher processing temperatures.Care should then be taken regarding void formation and matrix cracking due to residual stresses formed during processing. Some of the processing routes followed to produce high quality thermoplastic composite parts are well established as they are used with thermosets or borrowed from metal forming technology while other techniques are new and still require improvement.The etfects on mechanical properties of the techniques used to combine fibres with thermoplastic matrix as well as the techniques used to produce consolidated laminates should be investigated further.Major effort should be placed on the development of cost-effective processes to offset the high cost of raw thermoplastic material.Automated processes such as tape laying.filament winding and pultrusion are very attractive processing techniques from an economical point of view. Thermoplastic composites can be machined by conventional means,parts with defects can be reprocessed and scrap material can be reused.However,the effects of processing history on morphological structure.chemical and mechanical properties should be more thoroughly invcstigated. 8.5 Jolning A wide range of techniques to join thermoplastic composites is avallable.The composites can be mechanically or adhesively joined and due to their ability to be remelted. they can be joined by local consolidation at the joint interfaces using a varlety of novel techniques.These new promising welding techniques are still in an early stage of development and need further improvement,but they may provide new opportunities in the repair of thermoplastic composite structures cspecially for acronautical applications.154 High Performance Thermoplastic Resins and Their Composites a4 Processing There are major benefits in processing thermoplastic composites compared to thermoset composites including the unlimited shelf life, generally short processing times (some require long and elaborate processing cycles with the evolution of volatiles) and the ability to be remelted and reprocessed. The main drawbacks are high melt viscosity, high processing temperature and the lack of tack and drape of most prepregs. The inter-facial adhesion between fibres and matrix is generally lower than that observed for epoxies. Fibre treatment used for thermoset polymers to promote adhesion to the fibres may be inappropriate for thermoplastics. Means to improve the interfacial adhesion and their effects in controlling mechanical properties should be investigated. Residual stresses are an important issue when processing high performance thermoplastic composites since they are likely to be higher than those found in thermoset composites due to the higher processing temperatures. Care should then be taken regarding void formation and matrix cracking due to residual stresses formed during processing. Some of the processing routes followed to produce high quality thermoplastic composite parts are well established as they are used with thennosets or borrowed from metal forming technology while other techniques are new and still require improvement. The effects on mechanical properties of the techniques used to combine fibres with thermoplastic matrix as well as the techniques used to produce consolidated laminates should be investigated further. Major effort should be placed on the development of cost-effective processes to offset the high cost of raw thermoplastic material. Automated processes such as tape laying, filament winding and pultrusion are very attractive processing techniques from an economical point of view. Thermoplastic composites can be machined by conventional means, parts with defects can be reprocessed and scrap material can be reused. However, the effects of processing history on morphological structure, chemical and mechanical properties should be more thoroughly investigated. A wide range of techniques to join thermoplastic composites is available. The composites can be mechanically or adhesively joined and due to their ability to be remelted, they can be joined by local consolidation at the joint interfaces using a variety of novel techniques. These new promising welding techniques are still in an early stage of development and need further improvement, but they may provide new opportunities in the repair of thermoplastic composite structures especially for aeronautical applications