TriggeredCatalysts
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Triggered Catalysts
Triggered catalysts need a triggering effect to start their initiator role.
In this section we will list a number of catalyst that will trigger it's desired action through an external input. They have different uses and may be triggered through heat, UV-light, visible light, electron beam radiation, moisture exposition etc.
For each catalyst I will describe a number of applications where it can be used, although the list is virtually endless. I have chosen the catalysts for their ease of use, price and availability, and have tried to use the safest available. Nevertheless, all precautions on manipulating chemicals apply! These compounds will probably always be noxious, flammable, irritant, and may even cause cellular damage. Use gloves (plastic or rubber gloves will do fine) and I recommend wearing some kind of protective clothes (painter suit or such).
Ultraviolet Photoinitiators
Benzophenones
These molecules contain two aromatic functional groups that adsorb UV light which puts the molecule in an excited state. Together with amines or even alone, they easily form radicals that trigger the polymerization chain reaction. The average concentration of Benzophenone initiators in the polymer blend lies between 1 and 4 weight percent (wt%). High concentrations speed up the hardening process. Lower concentrations allow a better hardening of deep layers. Benzophenones may be used for hardening of Acrylates, Polyesters and some Epoxy resins.
Benzophenone
(also: Diphenyl ketone or Diphenylmethanone, CAS N� 119-61-9)
http://reprap.org/pub/Main/TriggeredCatalysts/IR_Benzophenone.png
The adsorption spike at 260nm means that it will be triggered by fairly energetic UV light. Energetic UVs tend to travel less deep into the material and remain in the surface boundary, where it is adsorbed very fast. This initiator is to be used in combination with others that adsorb longer wavelengths. Benzophenone is a fairly safe compund to use.
Benzophenone at ACROS Organics
Michlers Ketone
(also: 4,4'-Bis(dimethylamino)benzophenone, CAS N� 90-94-8)
http://reprap.org/pub/Main/TriggeredCatalysts/IR_Michlers_ketone.png
The broad adsorption spike at 380nm and above of this initiator allows it to react at deeper levels of polymer. This is an ideal initiator to mix with Benzophenone, for a fast combined surface and deep curing reaction. Caution! Michlers Ketone has a higher health hazard than Benzophenone. Use gloves and mix it in ventilated areas.
Michler's ketone at Sigma Aldrich
