With the progress of science and technology and the improvement of people's health awareness, implantable medical devices are more and more widely used in clinic. Polyether ether ketone (PEEK) composite has a broad application prospect in the medical field because of its low imaging interference, light weight, high strength, modulus closer to human tissue, excellent dynamic load performance, corrosion resistance and wear resistance.

PEEK composite hot press molding needs to overcome three main difficulties:

The low melt flow rate and high forming temperature of high performance thermoplastic resins such as PEEK are not conducive to the impregnation of fibers.

(2) Thermoplastic prepreg has no viscosity and high stiffness at room temperature, so that its coating property is not as good as thermosetting prepreg; (3) Temperature and pressure control, cooling and heat treatment during the molding process have complex effects on the porosity generation of composite materials and the condensed state structure of resin.

Prepreg, as an intermediate material for manufacturing composite materials, is an important link in the preparation of continuous fiber reinforced PEEK composite materials. The following describes several preparation methods for thermoplastic prepreg of PEEK composite materials.

Hot melt impregnation method

Commonly used fiber and resin composite method. As shown in the figure, PEEK resin is melted into a melt by a screw extruder and transported to a closed mold, and the fiber bundles are impregnated through the resin melt to prepare the prepreg.

This method requires the resin to have a lower viscosity in the molten state and a better wettability with the fiber. It is particularly important that the resin has basically no crosslinking reaction in the molten state, and must have good chemical stability and small viscosity fluctuations. Because the solvent is not used, the problem of high pore content caused by volatile components is avoided. The disadvantage is that in the process of resin melting impregnated fibers, higher temperatures and pressures are usually required. The prepared prepreg has poor softness and drape property.

Mixed impregnation method

First, the thermoplastic resin is processed into fine fibers, and then the resin fiber and the reinforced fiber are mixed into plain or satin fabrics, or the thermoplastic yarn and unidirectional fiber are directly combined to form a mixed fiber yarn and then woven. Due to the good softness and drapes of the fibers, a certain degree of sliding and rotation can occur between the resin fiber and the reinforced fiber in the mixed fabric. It has certain deformation ability. In the preparation of complex surface structures, the tight mold can be achieved by the relative slip between fibers, the rotation at the joints and the deformation of the mesh. During the molding process, the thermoplastic resin fiber is melted at high temperature and the resin infiltrates the fiber under pressure.

For the parts with complex surface or fine structure, the shear deformation in the surface and the relative Angle change between the layers will occur in the process of forming the surface, which has good overlay property. However, it is easy to cause damage to the reinforced fiber in the mixing process, and the impregnation effect still needs to be improved because of the high viscosity of spinnable resin melt. A relatively large number of reinforced fibers in the reinforced fiber bundle cannot fully contact with the resin matrix, resulting in poor interfacial properties of the composite.

Electrostatic powder preleaching method

The basic principle is that the conductive fiber bundles are fluffed and dispersed in the electrostatic fluidized bed, and the bundles are stretched and thinly so that the thermoplastic resin powders can be filled between the fibers, and the thermoplastic powders are fixed on the fiber bundles by preheating and consolidation method. Electrostatic powder impregnation speed is fast, the production efficiency is high, if the use of ultrafine powder can obtain relatively soft prepreg.

Suspension powder prepreg method

Using water from a wide range of sources and no pollution to the environment as a dispersion medium, the fine powder of thermoplastic resin is uniformly dispersed and permeated into the fiber bundle, and then the resin is fully melted and impregnated by heating, which is a technical route that is expected to prepare high performance and high quality thermoplastic prepreg.

Foreign enterprises such as Solvay, Hershey, BASF and so on are using suspension powder impregnation method to prepare thermoplastic prepreg.

Compared with the traditional hot melt impregnation method, the flow distance of resin after hot melt is reduced, and the PEEK thermoplastic prepreg with more full infiltration and more collimating fiber is obtained. The interfacial properties of the composite prepared by the prepreg are excellent, and the interlayer shear strength is more than 105MPa, which is in the international leading level. The toughness and fatigue properties lost by traditional hot melt method to reduce the viscosity of resin are avoided. Excellent quality, uniform and controllable, low risk.

The widespread application of new medical implant materials will be a slow and cautious process. PEEK composite has been developed as an ideal substitute for metal implants due to its low imaging interference, high mechanical strength, good dynamic load performance, modulus closer to bone, excellent corrosion resistance and wear resistance. At present, the application prospects are broad, but there are also many problems and challenges: at present, the structural design of continuous fiber PEEK composite implants is conservative, and it is still carried out with reference to existing commercial metal implants, which is difficult to give full play to the performance advantages of PEEK composite materials.

The manufacturing of PEEK composite materials for medical implantation in China is still in its infancy, and relevant research will promote the development of the level of medical materials in China and the replacement of implantable devices, improve the health of patients, reduce the burden on patients, which is related to the happiness of everyone and every family.

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