4.4.
INFILTRATION
87
non-reactive solvent seems required for such reasons, xylene can be used
(Birbeck and Mercer, 1957), or better, the more volatile toluene. Acetone
also is used by some investigators, and recently we have been using
styrene.
Polyester resin mixtures are not miscible in alcohol, and so a different
dehydrant or an intermediate solvent must be used. Acetone originally
was advocated by Ryter and Kellenberger (1958). It is also quite possible
to use propylene oxide, but the ideal intermediate solvent for all polyesters would seem to be styrene. Its use for this purpose was first suggested by Kurtz (1961), who did not, however, seem to appreciate that
this was a "reactive solvent" when used with polyesters, and serves as a
copolymer. Indeed, it is common industrial practice to include up to
70% styrene in polyester resin mixtures, and Vestopal W already contains
a substantial quantity. In compounding casting resins, styrene is used
specifically to reduce viscosity. Small variations in the amount of styrene
are not expected to affect importantly the physico-chemical properties of
the final cured plastic; therefore, residual traces of this solvent left in
the specimen do not matter. Thus, styrene can be regarded as the intermediate solvent of choice between a dehydrating agent, such as alcohol,
and a polyester mixture.
4.4.
Infiltration
Infiltration of the tissue with the monomer mixture is not a problem
when the latter is very fluid, as is methacrylate. The tissue blocks then
are passed from absolute alcohol through one or two changes of the
monomer with added catalyst before moving them into gelatin capsules
filled with embedding mixture. The latter ordinarily serve as individual
containers for polymerization. If the tissue blocks are as small or as thin
as they should be, no more than 10-15 minutes need be allowed for each
bath, particularly if the containers are agitated on a shaker during the
infiltration process.
Infiltration of viscous embedments poses more difficult problems, and
inevitably the original descriptions of handling different
embedding
mixtures have outlined varied and often unnecessarily conservative infiltration schedules. Experience in our own laboratory indicates that a
single generalized schedule is applicable to almost all embedments.
With viscous embedding mixtures we always use an appropriate inter-
INFILTRATION
87
non-reactive solvent seems required for such reasons, xylene can be used
(Birbeck and Mercer, 1957), or better, the more volatile toluene. Acetone
also is used by some investigators, and recently we have been using
styrene.
Polyester resin mixtures are not miscible in alcohol, and so a different
dehydrant or an intermediate solvent must be used. Acetone originally
was advocated by Ryter and Kellenberger (1958). It is also quite possible
to use propylene oxide, but the ideal intermediate solvent for all polyesters would seem to be styrene. Its use for this purpose was first suggested by Kurtz (1961), who did not, however, seem to appreciate that
this was a "reactive solvent" when used with polyesters, and serves as a
copolymer. Indeed, it is common industrial practice to include up to
70% styrene in polyester resin mixtures, and Vestopal W already contains
a substantial quantity. In compounding casting resins, styrene is used
specifically to reduce viscosity. Small variations in the amount of styrene
are not expected to affect importantly the physico-chemical properties of
the final cured plastic; therefore, residual traces of this solvent left in
the specimen do not matter. Thus, styrene can be regarded as the intermediate solvent of choice between a dehydrating agent, such as alcohol,
and a polyester mixture.
4.4.
Infiltration
Infiltration of the tissue with the monomer mixture is not a problem
when the latter is very fluid, as is methacrylate. The tissue blocks then
are passed from absolute alcohol through one or two changes of the
monomer with added catalyst before moving them into gelatin capsules
filled with embedding mixture. The latter ordinarily serve as individual
containers for polymerization. If the tissue blocks are as small or as thin
as they should be, no more than 10-15 minutes need be allowed for each
bath, particularly if the containers are agitated on a shaker during the
infiltration process.
Infiltration of viscous embedments poses more difficult problems, and
inevitably the original descriptions of handling different
embedding
mixtures have outlined varied and often unnecessarily conservative infiltration schedules. Experience in our own laboratory indicates that a
single generalized schedule is applicable to almost all embedments.
With viscous embedding mixtures we always use an appropriate inter-