Composites Design and Manufacture (Plymouth University teaching support materials)

First, a couple of definitions:

Dynamic viscosity (mPa.s) Material or Condition Reference
1.0020 Water at 20 °C Kaye & Laby [1]
<20 Cyclic Butylene Terephthalate (CBT) monomer at 180ºC Coll et al [2]
100 - 300 initial viscosity for RTM/infusion polyester, vinyl ester or epoxy resins Dupont et al [3]
<200 - ~400 initial viscosity for vacuum infusion of polyester or vinylester resins Cocquyt [4]
800 upper limit for viscosity in RTM Becker [5]
1000 non-injection point (NIP) in RTM Pearce et al [6]
588-3500 melt viscosity of PLLA Ouagne et al [7]
1500 - 2000 Crystic® 329EPA Class 2 Fire Retardant isophthalic laminating resin Scott Bader data sheet, 02/13.
2500 Crystic® 1035PALSE general prupose orthophthalic low-styrene emission spray-up or hand lamination resin Huntsman Australia data sheet, 01/03.
7500 - 16500 dwell-time window for wet-laid vacuum bagged composites Stringer [8]
100 000 limiting viscosity for film-stacking Riedel et al [9]
100 000 - 1000 000 "preferred [thermoplastic] melt viscosity range for most forming processes" Cogswell [10]
300 000 melt viscosity of PEEK polymer Cogswell [10]
1000 000 limiting viscosity for co-mingled fibre processes Riedel et al [9]
1000 000 000 000 000 vitrimer topology freezing transition temperature (1012 Pa s) Denissen et al [11]

Figure 1:  Melt viscosities and processing temperatures of various matrix materials for both reactive and melt processing.
Figure 13 of K van Rijswijk and HEN Bersee, Reactive processing of textile fiber-reinforced thermoplastic composites: an overview, Composites Part A: Applied Science and Manufacturing, March 2007, 38(3), 666-681.

Effect of temperature on viscosity

Second, as the temperature rises it causes increased motion of the atoms in a polymer chain and thus the polymer becomes more fluid.  For a thermoplastic polymer, there is a direct and reversible relationship between temperature and viscosity (assuming no change in the molecular weight of the polymer due to further polymerisation or to degradation).  For the individual components in a thermosetting resin there should also be a similar reversible relationship between temperature and viscosity, but this will not be true for the mixed materials.  A typical relationship for the variation of viscosity with temperature would be:

.................... (Equation 1)

where η and T are the instantaneous viscosity and temperature respectively and ηo is the viscosity at temperature To.  For a polyester resin, a typical value of a would be -0.04ºC-1 which would result in:

Effect of cure on viscosity

Third, most thermosetting resins start out as a mixture of two low viscosity components which react with one another to form a 3-D cross-linked network.  In consequence, the degree-of-cure and the viscosity increase with time after the mixing of the components. This is normally accompanied by the generation of heat which will act to accelerate the reaction.  In the limit, this may result in smoke and/or fire.

The heat evolved during cross-linking (cure) can be assumed to be proportional to the degree-of-cure of the resin system with the equation to describe the reaction rate having the form: δα/δt = K(1-α)n where K is based upon the Arrhenius equation: K = Ko.exp(-Ea/RT) and where:

For resin systems cured by an addition reaction (e.g. polyester and vinyl ester systems), the Kamal and Sourour [13] model is often used.  It incorporates both n-th order kinetics and an auto-catalytic term (Equation 2 [14]).  

.................... (Equation 2)


For epoxy resin, White [15] modelled the PR286 resin system with the following assumptions:

.................... (Equation 3)


White further demonstrated that the profiles of the isothermal viscosity-time curves of an epoxy resin system were identical when plotted on logarithmic axes.  The effect of temperature was a change in the position of the curve with respect to those axes.  The application of an appropriate shift along the logarithmic time and logarithmic viscosity axes could bring any pair of curves into coincidence.  By implication, it follows that any isothermal viscosity-time curve may be generated from any other by an appropriate scaling of the time and viscosity axes.

Roller [16] presented experimental evidence for the applicability of Equation 4 for the determination of the viscosity of curing B-staged epoxy resins as a function of both time and temperature. 

.................... (Equation 4)


In-process monitoring of viscosity: see the Process Control webpage.


  1. Kaye and Laby Tables of Chemical and Physical Constants,, accessed 15 November 2007.
  2. S Coll, A Murtagh and C Ó Brádaigh, Resin Film Infusion of cyclic PBT composites: consolidation analysis, Proceedings of the Eighth International Conference on Flow Processes in Composite Materials, Newark (USA), 7-9 July 2004, pp 101-106.
  3. L Dupont, M Aguilar and A Poirier, An objective study of resin injection machines for resin transfer moulding of both low cost products and advanced composites, Proceedings of the 9th International Conference on Composite Materials (ICCM-9), Madrid, 12-16 July 1993. Woodhead Publishing, Cambridge UK, 1993, pp 489-496.
  4. A Cocquyt, The VIP (Vacuum Infusion Process) primer, GRPguru website, accessed at 17:14 on Wednesday 28 August 2013.
  5. DW Becker, Tooling for Resin Transfer Moulding, Wichita State University, Wichita – Kansas, no date.
  6. NRL Pearce, FJ Guild and J Summerscales, An investigation into the effects of fabric architecture on the processing and properties of fibre reinforced composites produced by resin transfer moulding, Composites Part A: Applied Science and Manufacturing, 1998, A29(1), 19-27.
  7. P Ouagne, L Bizet, C Baley and J Bréard, Analysis of the film-stacking processing parameters for PLLA/flax fiber biocomposites, Journal of Composite Materials, May 2010, 44(10), 1201-1215.
  8. LG Stringer, Optimization of the wet lay-up/vacuum bag process for the fabrication of carbon fibre epoxy composites with high fibre fraction and low void content, Composites, 1989, 20(5), 441-452.
  9. U Riedel, J Nickel and AS Herrmann, High performance applications of plant fibres in aerospace and related industries, Fibres Seminar, IENICA, Copenhagen, 27 – 28 May 1999.
  10. FN Cogswell, Thermoplastic Aromatic Polymer Composites, Butterworth-Heinemann, Oxford, 1992. ISBN 0-7506-1986-7.  PU CSH Library.
  11. W Denissen, JM Winne and FE Du Prez, Vitrimers: permanent organic networks with glass-like fluidity (minireview), Chemical Science, 2016, 7, 30-38.
  12. K Potter, Resin Transfer Moulding, Chapman & Hall, London, 1997. ISBN 0-412-72570-3.  PU CSH Library.
  13. MR Kamal and S Sourour, Kinetics and thermal characterization of thermoset cure, Polymer Engineering and Science, January 1973, 13(1), 59-64.
  14. CD Rudd, AC Long, KN Kendall and CGE Mangin, Liquid Moulding Technologies, Woodhead Publishing, Cambridge, 1997.  ISBN 1-85573-242-4.  PU CSH Library.
  15. RP White, Time-temperature superpositioning of viscosity-time profiles of three high temperature epoxy resins, Polymer Engineering and Science, January 1974, 14(1), 50-57.
  16. MB Roller, Characterization of the time-temperature-viscosity behaviour of curing B-staged epoxy resin, Polymer Engineering and Science, June 1975, 15(6), 406-414.

On-line resources:

Recommended reading:

The following books, where identified by [name], were suggested by contributors to the Biomimetics JISCmail discussion list:
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Created by John Summerscales on 02 February 2006 and updated on 27-Apr-2020 13:29. Terms and conditions. Errors and omissions. Corrections.