Processing reinforced thermoset

Figure 5.83 Example of vent locations in a compression mold processing reinforced thermoset plastics...

ALLYL ESTER RESINS. The allyl radical (CH2CH=CH2) is the basis of the allyl family of resins. Allyl esters arc based on monobasic and dibasic acids and are available as low-viscosity monomers and thermoplastic prepolymers. They are used as crosslinking agents for unsaluraied polyester resins and in the preparation of reinforced thermoset molding compounds and high-performance transparent articles. All modem thermoset techniques may be used for processing allyl resins. 

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. 

As an example. Fig. 34 gives the temperature — time diagram for different stages of the process of obtaining glass-reinforced thermoset [130, 131]. Regions I-IV in this diagram actually correspond to different parts of the viscosity curve... 

Fig. 34. Temperature-time diagram at different stages of processing of a glass-reinforced thermoset [130]...

Melby, E.G. Castro, J. M. (1989) Glass-reinforced thermosetting polyester molding materials and processing, in Allen, G. (Ed.) Comprehensive Polymer Science, Oxford Pergamon. Mijovic, J., Bellucci, F. Nicolais, L. (1995) J. Electrochem. Soc., 142, 1176-1182. 

Open-mould processes are thermoset moulding processes with open moulds in the male or female form. In this process the mould is made from a pattern and the reinforced thermoset is applied to the mould to reproduce the shape and finish of the mould. Typical examples would be boat hulls made from fibreglass-reinforced gel coats. Figure 6.10 shows the basic contact-moulding process. 

Fig. 11-3. Detailed guide to reinforced thermoset plastics process selection.

Two processes for the forming of reinforced thermosets (a) pultrusion and (b) filament winding. 

Although thermoplastics, thermosets and elastomers can be used as matrix of polymer composites, thermosets are more widely used mainly due to the processing techniques employed in their manufactme, that allow for the easy use of long fibers, mats and fabrics as reinforcement. Thermosets are also generally more thermally stable than thermoplastics, and these two reasons lead to products with significantly higher mechanical properties which are less affected by thermal variations than thermoplastic composites [1,2,12],... 

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