98 High Performance Thermoplastic Resins and Their Composites polymerized before having been combined with fibres and that they are relatively inert renders the achievement of a good adhesion between the matrix and the fibres generally difficult.In contrast.Leeser and Banister [77]affirm that most thermoplastics show an affinity to carbon resulting in good fibre-matrix interfaces without the addition of a coupling agent.However,for weaving operations,sizing is requtred for protecting the fibres during the process;usually a small amount of a matrix polymer is applied to the fibre prior to weaving.These authors [77] also affirm that with glass fibres.a coupling agent is needed since most thermoplastics do not adhere well to glass due to the inert nature of the glass surface. Fibre treatment is a means to promote and enhance adhesion.The extensive work reported in the literature dealing with fibre treatment is almost exclusively on thermosets.In addition,most fibre treatment processes for thermoplastic composites are proprietary [1951. The choice of the proper fibre treatment is complex.It depends both on the type of fibre and on the nature of the thermoplastic involved [1].It may include cleaning,etching and oxidizing of the fibres to provide reactive sites for adequate bonding to the sizing and the application of the sizing itself [1951.These operations are often accomplished at the same time as the fibre or prepreg formation in order to reduce the handling of the fibres.If a sizing has to be applied.it must be non-volatile,easy to apply,compatible with the matrix and thermally stable.A fibre treatment tailored for thermoset composites may not be suitable or optimized for thermoplastic composites [1].The possible degradation of the sizing at the high processing temperature of high performance reinforced thermoplastics is also an important issue.At temperatures close to 400C.none of the epoxy sizings will resist degradation. Turner and Cogswell [169]have evaluated the mechanical properties of PEEK based composites with a variety of fibres and have explored the varying interfacial properties that result from the differing fibre types.The fbres included E,R and S glass fbres,aramid fibres (Kevlar).high strength (HS),high modulus(HM),intermediate modulus (IM)and ultra high modulus (UHM)carbon fibres.Mechanical properties with the R glass and aramid fibres were particularly low.It is believed that in the case of R glass fibre,the manufacturer's size may have degraded while in the case of aramid fibres,degradation of the fibres may have occurred due to the high processing temperature which is close to the decomposition temperature of Kevlar. 5.4 Combination of Fibres with Matrix There are several techniques reported in the literature for combining fibres with thermoplastic matrix [1.8.55.71,77,98,195.197-204].They include hot melt coating. solution processing,in-situ polymerization of monomers or pre-polymers,film stacking. powder coating and fibre hybrldization.Some of these are well established since they are employed with thermosets while others have been recently developed especially to overcome the difficulty of fibre impregnation due to the high melt viscosity of the matrix.Depending on98 High Performance Thermoplastic Resins and Their Composites polymerized before having been combined with fibres and that they are relatively inert renders the achievement of a good adhesion between the matrix and the fibres generally difficult. In contrast, Leeser and Banister 1771 affirm that most thermoplastics show an affinity to carbon resulting in good fibre-matrix interfaces without the addition of a coupling agent. However, for weaving operations, sizing is required for protecting the fibres during the process: usually a small amount of a matrix polymer is applied to the fibre prior to weaving. These authors [77] also aifirm that with glass fibres, a coupling agent is needed since most thermoplastics do not adhere well to glass due to the inert nature of the glass surface. Fibre treatment is a means to promote and enhance adhesion. The extensive work reported in the literature dealing with fibre treatment is almost exclusively on thermosets. In addition, most iibre treatment processes for thermoplastic composites are proprietary [ 1951. The choice of the proper fibre treatment is complex. It depends both on the type of fibre and on the nature of the thermoplastic involved [ 11. It may include cleaning, etching and oxidizing of the fibres to provide reactive sites for adequate bonding to the sizing and the application of the sizing itself [195]. These operations are often accomplished at the same time as the fibre or prepreg formation in order to reduce the handling of the fibres. If a sizing has to be applied, it must be non-volatile, easy to apply, compatible with the matrix and thermally stable. A fibre treatment tailored for thermoset composites may not be suitable or optimized for thermoplastic composites [ 11. The possible degradation of the sizing at the high processing temperature of high performance reinforced thermoplastics is also an important issue. At temperatures close to 400’ C, none of the epoxy sizings will resist degradation. Turner and Cogswell [ 1691 have evaluated the mechanical properties of PEEK based composites with a variety of fibres and have explored the varying interfacial properties that result from the differing fibre types. The fibres included E, R and S glass fibres, aramid fibres (Kevlar). high strength (HS). high modulus (HM), intermediate modulus (IM) and ultra high modulus (UHM) carbon fibres. Mechanical properties with the R glass and aramid fibres were particularly low. It is believed that in the case of R glass fibre, the manufacturer’s size may have degraded while in the case of aramid fibres, degradation of the fibres may have occurred due to the high processing temperature which is close to the decomposition temperature of Kevlar. 5.4 Combination of Fibres with Matrix There are several techniques reported in the literature for combining tlbres with thermoplastic matrix (1, 8, 55, 71, 77, 98, 195, 197 - 2‘041. They include hot melt coating, solution processing, in-situ polymerization of monomers or pre-polymers, film stacking, powder coating and ilbre hybridization. Some of these are well established since they are employed with thermosets while others have been recently developed especially to overcome the difficulty of fibre impregnation due to the high melt viscosity of the matrix. Depending on