Reinforced thermoplastics, heat distortion

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. 

DTUL at 264 psig (Heat Distortion) for Reinforced Thermoplastics. 

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. 

Tefzel is a rugged thermoplastic with an outstanding balance of properties. It can be reinforced with carbon or glass fibers, being the first fluoroplastic that can be reinforced, not merely filled. Because the resin will bond to the fibers, strength, stiffness, creep resistance, heat distortion temperature, and dimer sional stability are enhanced. 

Classification Thermoplastic polyamide Empirical (CioHi8N202)nH20 Formula H[HN(CH2)4NHCO(CH2)4CO]nOH Properties Clear polymer insol. in most soivs. sol. in formic acid si. sol. in trifluoroacetic acid m.w. 22,000-45,000 dens. 1.20 (sol n.-cast film) m.p. 283-319 C heat distort, temp. 149 C (up to 285 C with glass reinforcement)... 

In composites, particulate inorganic fillers or reinforcing materials such as fibres are commonly added to thermoplastic and thermoset polymeric materials to achieve economy while modifying certain properties such as stiffness, heat distortion and mouldability. However, there are certain properties such as toughness and ultimate elongation that usually deteriorate. 

Talc reinforced thermoplastics yield higher heat distortion temperatures and lower thermal expansion. These characteristics indicate an extended service temperature range and improved dimensional stability. In processing, talc builds torque which promotes fusion in rigid vinyls. Talc also provides good hot strength for downstream operations. 

Many thermoplastics can be considered for this application although glass fibre reinforcement provides much greater rigidity, improved strength and a higher heat distortion temperature, these materials are more brittle than the unfilled ductile polymers and have unsatisfactory impact behaviour for this application. The high-temperature creep properties of ABS are unsuitable, and polyamides not only absorb water, which affects properties, but also have poor dimensional tolerances. The three most suitable materials are therefore modified PPO, PC and polyacetal (see Chapter 7) a comparison of their properties indicates that PC is the preferred material. Furthermore, its... 

Over the past few years, however, techniques have been developed to enable continuous reinforcement of thermoplastics. The simplest way is to put a cloth and a plastic sheet on top of each other in a heated press and to carry out impregnation under pressure. More difficult is the forming of an end-product from the sheet produced with conventional sheet-forming techniques the position of the fibres will be distorted in an unacceptable way. As in nearly all processing techniques, the modern finite-element methods with advanced computers are able to present solutions to this problem in principle they can predict the position of the fibres in the sheet-forming operation, so that optimum reinforcement is realised in the end product. 

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