JEC COMPOSITES MAGAZINE - Issue #104 - April/May 2016 - 49

Tab.1: Results of MW curing for different resins and gelcoats with susceptors a,
b and c

Tab. 2: Tensile strength results for POLRES 305BV and CRYSTIC VE 676-03 with
the best susceptors

Test piece

Maximum
resistance (σ)

Deformation (є)

Polyester resin

9.77 (± 2.34)

0.26 (± 0.11)

Polyester resin + susceptor c

17.1 (± 2.04)

0.26 (± 0.095)

122.4

Vinyl ester resin

13.3 (± 3.00)

0.21 (± 0.13)

10.6

87.2

Vinyl ester + susceptor a

11.4 (± 1.82)

0.19 (± 0.072)

Polyester resin + susceptor c

6.0

125.1

Vinyl ester

20.5

112.6

Vinyl ester + susceptor a

70.4

Vinyl ester + susceptor b

11.9

95.2

Vinyl ester + susceptor c

13.0

72.4

Polyester gelcoat

18.9

86.5

Polyester gelcoat + susceptor a

8.7

94.0

Polyester gelcoat + susceptor b

10.2

86.7

Polyester gelcoat + susceptor c

13.4

78.0

Epoxy gelcoat

13.3

73.0

Epoxy gelcoat + susceptor a

6.3

81.5

Epoxy gelcoat + susceptor b

4.7

83.8

Epoxy gelcoat + susceptor c

3.8

83.1

Time to
exothermic
peak (min)

Exothermic
peak (°C)

Polyester resin

12.3

100.5

Polyester resin + susceptor a

7.6

Polyester resin + susceptor b

Shore D

constant MW power was recorded for each system (resin and
gelcoat with susceptors). An example of the resulting graph
can be seen in figure 5.
The graphs were compared in order to choose the most suitable susceptors in terms of interaction with the microwave
radiation. 24 hours after the MW curing, Shore D hardness
was measured for each sample in order to determine the influence of the susceptors on the mechanical properties of the
resin/gelcoat.
Table 1 shows the time necessary for each system to reach the
exothermic peak, the temperature of the exothermic peak and
the Shore D value of the samples. The addition of susceptors
reduces the time needed for the resin to achieve the exothermic peak by 46-71%, which is a very good result.

Apart from Shore D, tensile strength was also measured with
the best susceptor for each resin (figure 6). The results are
shown in table 2. For the polyester resin, it can be seen that
susceptor c does not influence the tensile strength properties as the maximum resistance is 7.33 units higher with the
susceptor. For the vinylester resin, the results are a bit worse
as the maximum resistance with the susceptor is 1.9 units less
than for the pure resin, but the standard deviation is 3 units.
Then, it can be concluded that the susceptors do not influence
the mechanical properties of the resins (tensile strength and
shore D hardness).

Conclusions
The addition of susceptors reduces polymerization time during microwave curing of resins and gelcoats. The best susceptors, with the right conditions, make it possible to reduce the
polymerization time of resins and gelcoats by 46-71%. The
addition of susceptors to improve MW absorption and reduce
polymerization time does not influence the mechanical properties of the resins. n
References
[1] A. C. Metaxas, R. J. Meredith. 1983. Industrial Microwave
Heating. Institute of Electrical Engineers. London: Peter
Peregrinus, Ltd.
[2] Dr. F. Parodi. Smart catalysts for microwave-enhanced
polymerization processes. http://www.fpchem.com/
fap_6a3-en.html
[3] P. Alazard, M. Palumbo, A. Gourdenne. Curing under
continuous microwaves (2450 MHz) of thermosetting epoxy
prepolymers: final statement. Macromol.
Symp. 2003, 199, 59-72.
[4] I. Gómez, J. Aguilar. Estudio del comportamiento de
materiales cerámicos expuestos a un campo de microondas.
Ciencia UANL 2005, Vol. VIII, n° 2, abril-junio.
[5] J. Slama, A. Gruskova, R. Vicen, S. Vicenova, R. Dosoudil,
J. Franek. Composite material with substituted Li ferrite for
high-frequency applications. Journal of magnetism and
magnetic materials 2003, Vol. 254, 642-645.

More information:
www.aimplas.es

Fig. 6: MW antenna curing of tensile test pieces with a robot

No104 April - May 2016 /

jec composites magazine 49

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