1.3 Processing of Composite Materials 9 matrix composites are traditionally far more common,but thermoplastic-matrix composites are currently the focus of rapid development.The advantages of thermoplastic-matrix composites compared to thermoset-matrix composites in- clude the following: Lower manufacturing costs: ·No cure Unlimited shelf-life Reprocessing possible(for repair and recycling) Fewer health risks due to chemicals during processing ·Low moisture content .Thermal shaping possible .Weldability(fusion bonding possible). Better performance: High toughness(damage tolerance) Good hot/wet properties High environmental tolerance. The disadvantages of thermoplastic-matrix composites include the following: Limitations in relation to processing methods High processing temperatures ·High viscosities Prepreg (collection of continuous fibers aligned to form a sheet that has been impregnated with the polymer or polymer precursor)is stiff and dry when a solvent is not used (ie.,not drapeable or tacky) Fiber surface treatments less developed. Fibrous polymer-matrix composites can be classified according to whether the fibers are short or continuous.Continuous fibers have much more effect than short fibers on the composite's mechanical properties,electrical resistivity,thermal conductivity,and on other properties too.However,they give rise to composites that are more anisotropic.Continuous fibers can be utilized in unidirectionally aligned tape or woven fabric form. Polymer-matrix composites are much easier to fabricate than metal-matrix, carbon-matrix,and ceramic-matrix composites,whether the polymer is a ther- moset or a thermoplastic.This is because of the relatively low processing temper- atures required to fabricate polymer-matrix composites.For thermosets,such as epoxy,phenolic,and furfuryl resin,the processing temperature typically ranges from room temperature to about 200C;for thermoplastic polymers,such as poly- imide(PI),polyethersulfone(PES),polyetheretherketone(PEEK),polyetherimide1.3 Processing of Composite Materials 9 matrix composites are traditionally far more common, but thermoplastic-matrix composites are currently the focus of rapid development. The advantages of thermoplastic-matrix composites compared to thermoset-matrix composites in￾clude the following: Lower manufacturing costs: ￾ No cure ￾ Unlimited shelf-life ￾ Reprocessing possible (for repair and recycling) ￾ Fewer health risks due to chemicals during processing ￾ Low moisture content ￾ Thermal shaping possible ￾ Weldability (fusion bonding possible). Better performance: ￾ High toughness (damage tolerance) ￾ Good hot/wet properties ￾ High environmental tolerance. The disadvantages of thermoplastic-matrix composites include the following: ￾ Limitations in relation to processing methods ￾ High processing temperatures ￾ High viscosities ￾ Prepreg (collection of continuous fibers aligned to form a sheet that has been impregnated with the polymer or polymer precursor) is stiff and dry when a solvent is not used (i.e., not drapeable or tacky) ￾ Fiber surface treatments less developed. Fibrous polymer-matrix composites can be classified according to whether the fibers are short or continuous. Continuous fibers have much more effect than short fibersonthecomposite’smechanicalproperties,electricalresistivity,thermal conductivity, and on other properties too. However, they give rise to composites that are more anisotropic. Continuous fibers can be utilized in unidirectionally aligned tape or woven fabric form. Polymer-matrix composites are much easier to fabricate than metal-matrix, carbon-matrix, and ceramic-matrix composites, whether the polymer is a ther￾moset or a thermoplastic. This is because of the relatively low processing temper￾atures required to fabricate polymer-matrix composites. For thermosets, such as epoxy, phenolic, and furfuryl resin, the processing temperature typically ranges from room temperature to about 200°C; for thermoplastic polymers, such as poly￾imide (PI), polyethersulfone (PES), polyetheretherketone (PEEK), polyetherimide