Thermoplastic Prepreg

The carbon fiber has to be coated with a suitable size to aid wetting out and this size can normally be a lower molecular weight version of the thermoplastie polymer applied in a suitable solvent, if possible water based, e.g. low molecular weight nylon, PC and PSU, whilst polyurethane type sizes are also useful. Care must be taken to choose a size that will withstand the processing conditions and for PEEK, it is necessary to use a polyimide size. 

A pre-plied laminate is built up in the required format to provide neeessary strength and stiffness for the specific application. The predried laminates are consolidated in large presses at high pressure and temperature. Typical thermoplastic resins offered by TenCate Advanced Composites are PEI, useful for most applications and PPS, where resistance to MEK or Skydrol is required. The following forming techniques can be used for thermoplastic prepreg  

Thermofolding—a blade heater permits combined pressure and heating to achieve 

Compression molding—the laminate is heated beyond its softening temperature using hot air or infrared and pressed into the required shape. A heated platen press can be used to initially heat the laminate. 

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Table 6.36 displays basic property examples of glass mat thermoplastics (GMT) thermoplastic prepregs and glass or carbon reinforced unidirectional composites. 

APC-2 is a semi-crystalline thermoplastic prepreg. The surface roughness characterization for two different batches of APC-2 prepreg are reported in Table 7.2. Batch I is a 152.4 mm (6in.)-wide prepreg sheet, whereas batch II is 304.8-mm wide. In addition, the... 

Figure 13.11 Idealization of the uneven thermoplastic prepreg surface as a series of rectangles with relative heights and spacing as shown...

Pultrusion fabrication of graphite reinforced thermoplastic prepreg. Reinforced Plastics, 30, (1991). 

Polyamideimides are marketed by Amoco Chemicals under the trade name Torlon. A polyamideimide is also a good candidate for the production of thermoplastic prepregs. 

LN Phillips described the film stacking process [64] to produce thermoplastic prepreg by hot pressing thermoplastic coated carbon fiber interleaved with sheets of thin film of the same polymer such as polysuphone and polyethersufhone. 

The fiber tension is very important as this controls the resin pick-up, normally 35-40% volume fraction. Tensions are about lN/1000 filaments for wet winding and 3N/1000 filaments for other types of winding. If the tension is too high, the fiber does not spread and is damaged by abrasion in the guide and if too low, produces waviness in the applied fiber. The type of fiber size and size content must be carefully chosen to help achieve good resin wet out. The principal matrix materials are epoxy, polyester and vinylester resins, but thermoplastic prepregs such as PEEK can also be applied. 

Thermoset (epoxy, vinyl ester and phenolic resins) or thermoplastic prepreg can be used, as well as wet resin/dry fiber, to give composites with less than 2% voids. An autoclave is not required and epoxy composites can be produced some 10 times quicker. 

Flemming el al [120] have described the production of aligned short carbon fiber reinforced thermoplastic prepreg. 

Hoffman WP, Scanning probe microscopy of carbon fiber surfaces, Carbon, 30, 315, 1992. Flemming T, Kress G, Flemming M, A new aligned short carbon fiber reinforced thermoplastic prepreg, Advanced Composite Materials, 5(2), 151-159, 1996. 

Automated Dynamics Corporation have used PES and PEEK/carbon fiber thermoplastic prepreg for the manufacture of high temperature pipe and down hole components. 

The Westland Group/GKN have undertaken production of many components from thermoplastic prepreg. Griffiths, Damon and Lawson [169] have described their earlier work and Figures 23.47 and 23.48 depict some of these items. 

TSC Thermoplastic sheet compound, can be regarded as thermoplastic prepreg, has no shelf life problems. 

Fiber Innovations Inc., Norwood, Massachusetts, USA—a thermoplastic prepreg manufacturer. 

Sulzer Composites, Winterthur, Switzerland—manufacture thermoplastic prepregs. Sold to the Gurit-Heberlein Group in 2002 and relocated to Fliulingen. 

The family of PKs, also called polyaryletherketones (PAEKs), consists of polyetheretherketone (PEEK), polyetheretherketone-ketone (PEEKK), polyetherketone (PEK), and polyetherketone-etherketone-ketone (PEKEKK). They share similar molecular structures based upon repeating ether and ketone groups in various ratios. Cost of the resins is high but, in RPs with high-performance fibers, there are many appfications in the aerospace and defense industries, electrical and atomic installations, and industrial and electronics products. Compoimds for injection molding are available, but the major area of apphcation is with thermoplastic prepreg materials, using mats, fabrics and/or continuous fiber. 

T Asai, T Ohara, T Tanaka, S Hashizume. Method of Manufacturing Continuous Fiber-Reinforced Thermoplastic Prepregs. U.S. Patent 5529652, June 25, 1996. J-M Charrier, PJ Bates, D Guillon, G Zanella. The Effect of Pin Shape on Spreading Roving Filaments for a Thermoplastic Pultrusion Process. 45th Annual Conference, Composites Institute, SPI, Washington DC, 1990, 18-A, pp 1-4. 

Thermoset prepregs can be formulated and processed to have various degrees of drape. Thermoplastic prepregs are very woody and have little drape therefore, they generally need to be heated to form around sharp mold sections. 

Laser welding has also been used for filament winding of fiber-reinforced composite materials with a thermoplastic prepreg. A defocused laser beam is directed on areas where the prepreg meets the winding as it is being built up. With suitable control over the winding speed, applied pressure, and the temperature of the laser, excellent reinforced structures of relatively complex shape can be achieved. 

Resin cost Low to medium-high, based on resin requirements Low to high. Premium thermoplastic prepregs are more than thermoset prepregs Will decrease for thermoplastics as volume increases... 

Compression molding is a highly nonisothermal process. In the processing of blanks consisting of a thermoplastic reinforced with long fibers, the blanks are preheated and then placed in the mold, which is at a temperature lower than that of the blanks. In the case of thermoplastic prepregs, the... 

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