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.

Further reading

  1. Gert Strobl, Crystallization and melting of bulk polymers: New observations, conclusions and a thermodynamic scheme, Progress in Polymer Science, 2006, 31(4), 398-442.
  2. SP Nalawade, F Picchioni and LPBM Janssen - Supercritical carbon dioxide as a green solvent for processing polymer melts: Processing aspects and applications, Progress in Polymer Science, 2006, 31(1), 19-43.
  3. Andrzej Galeski - Strength and toughness of crystalline polymer systems, Progress in Polymer Science, 2003, 28(12), 1643-1699.
  4. ML Di Lorenzo and C Silvestre - Non-isothermal crystallization of polymers, Progress in Polymer Science, 1999, 24(6), 917-950.
  5. Yu Long, Robert A. Shanks and Zbigniew H. Stachurski - Kinetics of polymer crystallisation, Progress in Polymer Science, 1995, 20(4), 651-701.

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Updated by John Summerscales on 02 September 2011 18:00. Terms and conditions. Errors and omissions. Corrections.