Revision 1. 6
1.17
General
1
Even if the mixing ratio is absolutely correct, some molecules which have not found a reaction
partner will still be left behind, as in any chemical reaction. However, for optimum strength it is
necessary to achieve the highest possible degree of cross-linking. In addition to adhering precisely to
the required mixing ratio, you can achieve almost 100% cross-linking by controlled heating
(annealing). However, the resin must be heated carefully under controlled conditions in order to
avoid warping.
If done properly, the annealing enhances the mechanical strength and, in particular, raises the
temperature at which resins begin to distort. For these reasons annealing is mandatory e.g. for
structural parts in aircraft construction.
Annealing Fiber Composite Parts
When using cold-curing epoxy resin systems, you can first leave the parts to cure at room
temperature and then finish them, if necessary. Anneal all fiber composite parts before painting.
Place all parts in suitable room in such a way that they are not distorted or stressed and heat them
slowly. Do not raise the temperature by more than 20°C (28°F) per hour. Maintain the target
temperature for at least 18 hours. The epoxy resin system used for the Twister (lamination resin L285
/ hardener H286) requires 18 hours of annealing at 80°C (176°F).
1.4 Safety
Over the last few years epoxy and polyester resins have become increasingly important and are now
used in a wide range of applications. Despite this, so far no severe health problems have been
reported which could be attributed to dermatological or toxic effects of liquid plastics. These positive
results were made possible by appropriate safety precautions, i.e. compliance with industrial hygiene
regulations and selection of compatible resin/hardener systems.
Years of experience in processing epoxy resin systems have shown that health risks can be prevented
by adopting the usual general precautions for handling chemicals and following the health and safety
precautions recommended by the manufacturers of epoxy resin systems and stipulated by the
authorities.
Two cases have to be distinguished:
a)
the effects of resins and the hardeners in their pure, unmixed state
b)
the effects of the mixture of resin and hardener, as it is processed
Toxicity data (like LD
50
values, etc.) of the individual products do not necessarily provide reliable
information as to whether a system is compatible when processed in practice.
Provided that the processing instructions like mixing ratio and curing conditions have been observed,
the molded materials are completely inert and harmless after curing.