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Composites Design and Manufacture (BEng) - MATS 324 Thermoplastic polymers. |
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Thermoplastic polymer components can be produced in a heat-form-cool cycle and hence thermoplastic composite materials can potentially be recycled at the end-of-life. However, it is likely to be difficult to effectively deply the layers of a laminate and hence the material will perhaps be granulated (at high energy cost due to the material toughness arising both from the matrix and from its reinforcement with fibres) for extrusion or injection moulding and the material properties of continuous fibres composites will be severely degraded in the second cycle of use.
A variety of thermoplastic polymers (the list below is not exhaustive) find use as the matrix for composite materials, including:
Typical properties of some common (and some specialist) thermoplastics are listed in the table below. The Society for the Plastics Industry (SPI) in the United States of America proposed the Voluntary Plastic Container Coding System in which an equilateral triangle formed of three curved arrows encloses a number (as in column three of the Table) with the acronym below the triangle. The six specified generic materials cover 95% of the current domestic plastic waste produced. The number 7 is allocated to all other polymers:
| Polymer | Acronym | Coding | SMB001 specimen colour | Tg (ºC) | Tm (ºC) | Morphology |
| Low-density polyethylene | LDPE | 4 | Yellow | -130 | +105 | partially crystalline |
| High-density polyethylene | HDPE | 2 | Red | -125 | +135 | partially crystalline |
| Polypropylene | PP | 5 | Brown | -27 .. -10 | +165 ..+170 | partially crystalline |
| Polyamide (nylon) 6,6 | PA6,6 | --- | White | +55 | +255 | partially crystalline |
| Glass-fibre reinforced polyamide | GF/PA | Black | ||||
| Polyvinylchloride | PVC | 3 (V) | +75 .. +80 | --- | amorphous | |
| Polystyrene | PS | 6 | Transparent | +90 .. +100 | --- | amorphous |
| High-impact PS (toughened with polybutadiene microparticles) |
HIPS | Blue | ||||
| Polyester (polyethylene terephthalate) | PET | 1 (PETE) | +67 .. +80 | 265 | partially crystalline | |
| Polycarbonate | PC | Green | +145 .. +150 | --- | amorphous | |
| Polyoxymethylene (acetal) | POM | --- | +180 | partially crystalline | ||
| Polyurethane | PU | +140 | --- | amorphous | ||
| Poly ether ether ketone | PEEK | 144 | 367 | partially crystalline |
Molten thermoplastic polymers typically have viscosities far in excess of those used for RTM. However, in recent years there has been increasing use of in-situ polymerisation to produce thermoplastic matrix composites by Resin Transfer Moulding albeit usually at elevated temperatures. The principal systems are caprolactam (e.g. DSM Fiber Intermediates APA-6) to produce polyamide 6, laurolactam (e.g. EMS-Grivory APLC12) to produce polyamide 12 and cyclic butylene terephthalate oligomers (e.g. Cyclics Corporation) to produce PBT polyester.
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