Composites Design and Manufacture (Plymouth University teaching support materials)
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

Black plastic packaging, when coloured using carbon black pigments, cannot be easily identified by the optical/near-infrared (NIR) sorting systems in plastics/material recovery facilities (MRF).

In-situ polymerisation for liquid composite moulding (LCM) processes

Molten thermoplastic polymers typically have viscosities far in excess of those used for LCM.  However, in recent years there has been increasing use of in-situ polymerisation to produce thermoplastic matrix composites during Resin Transfer Moulding or Resin Infusion under Flexible Tooling, albeit usually at elevated temperatures.  The principal systems are:

Monomer Polymer Monomer viscosity (mPa.s) Infusion open time Thermal transitions (polymer °C) [1, 2] Water absorption (cured) Supplier
acrylic acrylic 100 @ 25°C 20 min @ 25°C HDT 109°C 0.5% after 8 days
(ISO 75A)
Arkema Elium 150 
caprolactam polyamide 6 melts 68-71°C
11 @ 71°C [3]
6.5 @ 90°C
  Tg: 52°C (dry)
Tm: 221-225°C
  Fibrant
laurolactam polyamide 12 melts 150-153°C   Tg: 41°C
Tm: 179-210°C
  EMS Grivory
L-lactide & Sn(Oct)2 catalyst PLA
poly(L-lactide)
melts 110°C
moulded 120°C or 185°C 
3-12 min (bulk polymer at 185°C)
40-100 min (bulk polymer at 120°C)
2-3 hours for RTM
Tg: 49-52°C
Tm: 166-176°C
  Louisy et al [5]
ε-caprolactone PCL
32h at 80°C, or 24h at 120°C [7] Tm: 53-59°C [6]    
cyclic butylene terephthalate oligomers polyester 12/11@220°C  33/28@180°C   Tg: 52°C
Tm: 225°C
  Cyclics CBT100 / CBT200
recycled thermoplastic epoxy polymers epoxy     Tg: 40-60°C
Tm: 120-140°C [3]
  Connora Recyclamine*
*  Aditya Birla Chemicals Thailand Limited acquired Connora Technologies’ Recyclamine technology on 22 July 2019 [CompositesWorld].

References

  1. DSC Transitions of Common Thermoplastics, accessed 29 March 2019.
  2. Thermal Transitions of Homopolymers: Glass Transition & Melting Point, accessed 29 March 2019.
  3. Caprolactam, https://cameochemicals.noaa.gov/chris/CLS.pdf, accessed 29 March 2019.
  4. AD La Rosa, I Blanco, DR Banatao, SJ Pastine, A Björklund and G Cicala, Innovative chemical process for recycling thermosets cured with Recyclamines® by converting bio-epoxy composites in reusable thermoplastic - an LCA study, Materials, 2018, 11(353), 1-14.
  5. E Louisy, F Samyn, S Bourbigot, G Fontaine and F Bonnet, Preparation of glass fabric/poly(L-lactide) composites by thermoplastic resin transfer molding, MDPI Polymers, 2019, 11(2), 339.
  6. TJ Corden, IA Jones, CD Rudd, P Christian and S Downes, Initial development into a novel technique for manufacturing a long fibre thermoplastic bioabsorbable composite: in-situ polymerisation of poly-ε-caprolactone, Composites Part A: Applied Science and Manufacturing, June 1999, 30(6), 737-746.
  7. P Christian, IA Jones, CD Rudd, RI Campbell and TJ Corden, Monomer transfer moulding and rapid prototyping methods for fibre reinforced thermoplastics for medical applications, Composites Part A: Applied Science and Manufacturing, July 2001, 32(7), 969-976.

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Updated by John Summerscales on 11-Sep-2019 14:43. Terms and conditions. Errors and omissions. Corrections.