Processing Reinforced Thermoplastics

A practical difficulty which arises during injection moulding of reinforced plastics is the increased wear of the moulding machine and mould due to the abrasive nature of the fibres. However, if hardened tool steels are used in the manufacture of screws, barrels and mould cavities then the problem may be negligible. 

An inherent problem with all of the above moulding methods is that they must, by their nature, use short fibres (typically 0.2-0.4 mm long). As a result the full potential of the reinforcing fibres is not realised (see Section 2.8.5). In recent years therefore, there have been a number of developments in reinforced 

These long fibres give better product performance although injection moulding machine modifications may be necessary to prevent fibre damage and reduce undesirable fibre orientation effects in the mould. 

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Reinforced Thermoplastic Sheet. This process uses precombined sheets of thermoplastic resin and glass fiber reinforcement, cut into blanks to fit the weight and size requirements of the part to be molded. The blanks, preheated to a specified temperature, are loaded into the metal mold and the material flows under mol ding pressure to fiU the mold. The mold is kept closed under pressure until the temperature of the part has been reduced, the resin solidified, and demolding is possible. Cycle time, as with thermosetting resins, depends on the thickness of the part and the heat distortion temperature of the resin. Mol ding pressures are similar to SMC, 10—21 MPa (1500—3000 psi), depending on the size and complexity of the part. 

A wide variety of thermoplastics have been used as the base for reinforced plastics. These include polypropylene, nylon, styrene-based materials, thermoplastic polyesters, acetal, polycarbonate, polysulphone, etc. The choice of a reinforced thermoplastic depends on a wide range of factors which includes the nature of the application, the service environment and costs. In many cases conventional thermoplastic processing techniques can be used to produce moulded articles (see Chapter 4). Some typical properties of fibre reinforced nylon are given in Table 3.2. 

The formation of a fibrillar structure in TLCP blends makes the mechanical properties of this kind of composites similar to those of conventional fiber reinforced thermoplastics [11,26]. However, because the molecular orientation and fibrillation of TLCPs are generally flow-induced, the formation, distribution, and alignment of these droplets and fibers are considerably more processing-dependent. We do not know ... 

With the largest turnover, GMT is certainly the most important semi-product in the group of reinforced thermoplastics. A special production process for natural fiber-reinforced PP semi-products (NMT) has been de-... 

Report 66 Reinforced Thermoplastics - Composition, Processing and Applications, RG. Kelleher, New Jersey Polymer Extension Center at Stevens Institute of Technology. 

Wolf, H. J., Shortening of fibers in processing of fiber reinforced thermoplastics, Kunststoffe, 83, 69-72 (1993). 

Processing of LFRT or LFT - long fibre (reinforced) thermoplastics injection, composite insert moulding, compression moulding, extrusion-compression. 

Grades reinforced with fibres 20 mm and more in length cannot be processed on conventional equipment. It is necessary to use, for example, the extrusion-compression technique. The process differs too much from conventional injection used for short glass fibre reinforced thermoplastics to measure the influence of fibre length alone. 

The integration of the compounding of long glass fibre reinforced thermoplastics on the process line is an example of the globalization and automation of the process. 

Traditional processes can be modified to better industrialize the manufacturing of medium- or short-run manufacturing. In the thermoplastic composite field, the Pressure Diaphorm Process allows the processing of continuous fibre reinforced thermoplastics with low pressures. The press and the moulds (wood, composite or aluminium) can be about 70% cheaper. The process is convenient for short and medium runs in the range of 1000 up to 100000 parts. 

Mitsui Chemicals is launching a new grade of carbon nanotube reinforced thermoplastic poly-imide, Aurum CNT, with supplementary specific properties such as dust reduction and antistatic behaviour. Targeted applications are, for example, processing jigs for semiconductor or hard disk manufacturing, and parts for hard disk drives. 

Two specific areas are covered more comprehensively fibrous glass polyesters and fibrous glass thermoplastics. The advances in reinforced polyesters have been in the materials and process areas. These changes are more profound than those related to mechanical properties. Hence, a treatment of mechanical properties of reinforced polyesters is not attempted. On the other hand, the reinforced thermoplastics advances are essentially in terms of many new reinforced polymers as well as a greater variety of compounds. For these reasons, it seems appropriate to discuss advances in this area in terms of properties. 

Fig. 11.28 The number average fiber length at various axial positions of an injection molding screw. DuPont Alathon 2010 pellets preblended with 3.2 mm chopped fibers and extruded in a 0.75 in diameter, 20.1 L/D, with 3 1 compression ratio extruder. [Reprinted by permission from R. von Turkovich and L. Erwin, Fiber Fracture in Reinforced Thermoplastic Processing, Polym. Eng. Sci., 23, 743 (1983).]... 

Fig. 11.30 Effect of preheating 50% by weight E-glass fiber-filled polyamide pulltruded pellets on fiber lengths at the screw tip of a 300-ton 23.86-oz reciprocating injection molding machine. [Reprinted by permission from C. G. Gogos, C. K. Yoon, and J. Brizzolara, Injection Molding Process Development for Long Fiber Reinforced Thermoplastics, SPE ANTEC Tech. Papers, 40, 384 (1994).]...

R. Turkovich and L. Erwin, Fiber Fracture in Reinforced Thermoplastic Processing, Polym. 

C. G. Gogos, C. K. Yoon, and J. Brizzolara, Injection Molding Process Development for Long Fiber Reinforced Thermoplastics, SPE ANTEC Tech. Papers, 40, 384 (1994). 

The process of injection molding (IM) is used principally for processing unreinforced or glass fiber reinforced thermoplastics (TPs) and thermosets (TSs) (Figure 4.1). Up to at least 90wt% of all plastics processed are TPs. There are many different types or designs of IM machines (IMMs) that permit molding many different products based on factors such as quantities, sizes (such as auto bumpers to medical micro products), shapes (simple to complex), product performances, and/or economics.1,150>157,173 176 476... 

Reinforced thermoset (RTS) plastic B-stage sheet material can be processed with its required heating cycle. However the most popular is to use reinforced thermoplastic (RTP) sheets usually using polypropylene plastics. Compared to injection molding RTPs, these stamped products can provide improved mechanical and physical properties with its longer fibers such as impact strength, heat distortion temperature, and much less anisotropy. 

Back compression is a process based on compression molding (Chapter 14) of a melt strip deposited in an open mold. It describes the process during which a cover stock cutting is placed on a melt strip for simultaneous compression molding and lamination of parts. Melt strip deposition also includes fiber reinforced thermoplastic stock with subsequent compression molding of non-laminated structural parts. 

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