4.5.
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91
viscous so that important quantities would be expected to remain on
the pipette side walls.
The remnants of viscous mixtures are hard to clean off glassware, and
the recent advent of disposable plastic laboratory utensils in considerable
variety promises to be a boon to us. Now, graduated beakers and syringes
are available, as well as containers of almost all sizes with lids. There
are even disposable plastic gloves to protect the hands. This laboratory
equipment is being made presently from a variety of different plastics
which complicates knowing whether or not there will be reaction with
the resin mixture of interest. However, in general, polyethylene, polypropylene, and polystyrene laboratory utensils seem resistant to the
epoxy resin blends and solvents. This is not as true with the polyester
mixtures, however, for these can be expected to include substantial
amounts of styrene monomer which possesses great solvent action, particularly dissolving polystyrene. Thus, disposable polystyrene syringes can
be used very conveniently for filling capsules with epoxy embedding
mixtures, but cannot be so used with most polyesters.
When glassware is used with viscous resin mixtures, and then must be
cleaned, we find it best to begin by draining the containers on paper.
Then we soak these in an organic solvent bath consisting of approximately equal parts of alcohol and acetone. After this, the glass is cleaned
in a sulfuric acid-potassium dichromate bath, and washed and dried. The
alcohol-acetone mixture is intended to remove only the bulk of the adhering organic film, so that this bath is not changed often, but is allowed
to accumulate substantial quantities of resins, impurities, dirt, and
water. This treatment works equally well for glassware that contains
either epoxy or polyester resins.
People who deal with the commercial utilization of epoxy resins have
long recognized that most of these substances are more or less toxic.
Perhaps the gravest danger is that a permanent allergic sensitivity will
develop, particularly from skin contacts. Tepper (1962) indicates that
the main trouble comes from the aliphatic amine hardeners which, of
course, are used in considerable quantities, and are not easily removed
from the skin. Accelerators, such as DMP-30, are also toxic and have
relatively high vapor pressures. Tepper stresses that one should use soap
and water to remove resin or catalyst from the skin. His argument is that
if organic solvents are used for this purpose they tend to spread contamination. Disposable plastic gloves which recently have appeared on
HANDLING THICK EMBEDDING MEDIA
91
viscous so that important quantities would be expected to remain on
the pipette side walls.
The remnants of viscous mixtures are hard to clean off glassware, and
the recent advent of disposable plastic laboratory utensils in considerable
variety promises to be a boon to us. Now, graduated beakers and syringes
are available, as well as containers of almost all sizes with lids. There
are even disposable plastic gloves to protect the hands. This laboratory
equipment is being made presently from a variety of different plastics
which complicates knowing whether or not there will be reaction with
the resin mixture of interest. However, in general, polyethylene, polypropylene, and polystyrene laboratory utensils seem resistant to the
epoxy resin blends and solvents. This is not as true with the polyester
mixtures, however, for these can be expected to include substantial
amounts of styrene monomer which possesses great solvent action, particularly dissolving polystyrene. Thus, disposable polystyrene syringes can
be used very conveniently for filling capsules with epoxy embedding
mixtures, but cannot be so used with most polyesters.
When glassware is used with viscous resin mixtures, and then must be
cleaned, we find it best to begin by draining the containers on paper.
Then we soak these in an organic solvent bath consisting of approximately equal parts of alcohol and acetone. After this, the glass is cleaned
in a sulfuric acid-potassium dichromate bath, and washed and dried. The
alcohol-acetone mixture is intended to remove only the bulk of the adhering organic film, so that this bath is not changed often, but is allowed
to accumulate substantial quantities of resins, impurities, dirt, and
water. This treatment works equally well for glassware that contains
either epoxy or polyester resins.
People who deal with the commercial utilization of epoxy resins have
long recognized that most of these substances are more or less toxic.
Perhaps the gravest danger is that a permanent allergic sensitivity will
develop, particularly from skin contacts. Tepper (1962) indicates that
the main trouble comes from the aliphatic amine hardeners which, of
course, are used in considerable quantities, and are not easily removed
from the skin. Accelerators, such as DMP-30, are also toxic and have
relatively high vapor pressures. Tepper stresses that one should use soap
and water to remove resin or catalyst from the skin. His argument is that
if organic solvents are used for this purpose they tend to spread contamination. Disposable plastic gloves which recently have appeared on