4.17.
MIXED PLASTIC EMBEDDING
127
4.17. Mixed Plastic Embedding
Plastic resins, even when they belong to different families, often are
mutually compatible, and yield polymerizable hybrid plastics. The
number of possible variants is so nearly limitless that it would be fruitless to try and consider them except as individually they have demonstrably advantageous physico-chemical properties, or seem useful for
some special characteristic.
Perhaps the most interesting reason for using a mixed plastic is to
take advantage of differential solubilities or volatilities in the final sections, which makes it possible eventually to remove one component.
The other plastic component then is left behind as structural support.
This of course produces great gain in contrast, and is apt to permit very
easy and intense subsequent "staining" (Chapter 7). To be useful, the
residual support must be adequate so that no structural collapse of the
specimen results which otherwise would lead to artifact. Experience with
this technique has been so limited, however, that those who would experiment should use caution and have interpretive knowledge.
Low and Clevenger (1962) first developed some of the possibilities of
this technique in working with mixtures of Selectron and methacrylate.
Normally, they advocated mixing 40% butyl methacrylate with a mixture
of 50% Selectron 5003 and 10% of Selectron 5214 (this is a discontinued
product, and now it would be necessary to substitute Selectron 5208).
Low and Clevenger (1962) have particularly emphasized "clearing"
the sections by volatilizing most of the methacrylate with furnace heat,
but solvent action also works, and has proved to be much more reliable
and satisfactory in the hands of the present writer. Acetone and ether in
equal proportions, or carbon tetrachloride are the solvents originally
recommended by Low and Clevenger. Toluene and methacrylate monomer also are effective. When heat is used, Low and Clevenger recommend elevating the temperature slowly to 200°-250°C, and then maintaining this for one hour. Certainly, a small-order artifact has been
visible in some of the micrographs of heat-treated sections that Low and
Clevenger have exhibited at national meetings, so that this procedure
must be used judiciously if at all. [Low (1960) reported that similar heat
treatments partially "cleared" pure Vestopal W sections.]
Kushida (1961a and 1962) developed a mixture of styrene and butyl
MIXED PLASTIC EMBEDDING
127
4.17. Mixed Plastic Embedding
Plastic resins, even when they belong to different families, often are
mutually compatible, and yield polymerizable hybrid plastics. The
number of possible variants is so nearly limitless that it would be fruitless to try and consider them except as individually they have demonstrably advantageous physico-chemical properties, or seem useful for
some special characteristic.
Perhaps the most interesting reason for using a mixed plastic is to
take advantage of differential solubilities or volatilities in the final sections, which makes it possible eventually to remove one component.
The other plastic component then is left behind as structural support.
This of course produces great gain in contrast, and is apt to permit very
easy and intense subsequent "staining" (Chapter 7). To be useful, the
residual support must be adequate so that no structural collapse of the
specimen results which otherwise would lead to artifact. Experience with
this technique has been so limited, however, that those who would experiment should use caution and have interpretive knowledge.
Low and Clevenger (1962) first developed some of the possibilities of
this technique in working with mixtures of Selectron and methacrylate.
Normally, they advocated mixing 40% butyl methacrylate with a mixture
of 50% Selectron 5003 and 10% of Selectron 5214 (this is a discontinued
product, and now it would be necessary to substitute Selectron 5208).
Low and Clevenger (1962) have particularly emphasized "clearing"
the sections by volatilizing most of the methacrylate with furnace heat,
but solvent action also works, and has proved to be much more reliable
and satisfactory in the hands of the present writer. Acetone and ether in
equal proportions, or carbon tetrachloride are the solvents originally
recommended by Low and Clevenger. Toluene and methacrylate monomer also are effective. When heat is used, Low and Clevenger recommend elevating the temperature slowly to 200°-250°C, and then maintaining this for one hour. Certainly, a small-order artifact has been
visible in some of the micrographs of heat-treated sections that Low and
Clevenger have exhibited at national meetings, so that this procedure
must be used judiciously if at all. [Low (1960) reported that similar heat
treatments partially "cleared" pure Vestopal W sections.]
Kushida (1961a and 1962) developed a mixture of styrene and butyl