Page 173 - Handbook of Adhesives and Sealants

Standard Test Methods 143

A simple, but not very quantitative, hardness test has been used for
hundreds of years—the fingernail indentation test. The indentation
that a fingernail makes in the edge of an adhesive bond or in the body
of a sealant can often be used as an approximate indication of hard-
ness of the material.

4.3.1.7 Solids content. The solids content of an adhesive or sealant
should be checked to assure that formulation or dilution errors have
not been made. ‘‘Solids’’ can refer either to the non-volatile component
of the adhesive or the inorganic component of the adhesive.
The nonvolatile solids content is usually determined by weighing a
small amount of material in a clean container, heating or curing until
a constant weight is obtained, and then weighing the container again.
The percentage of solids may be determined as the ratio of the sample
weights before and after curing 100. The percent solids is an indi-
rect measurement of the amount of volatile material in the sample
that was driven off during the heating cycle. The volatile material may
be solvent, water, or other additives. ASTM D 1489 offers a test
method for determining the non-volatile content of aqueous adhesives.
The solids content provides a measurement of the non-volatile ma-
terials that are contained within the formulation. Addition of solvent
can be used to ‘‘correct’’ the viscosity of adhesives to account for var-
iabilities in the manufacturing process or inconsistent base materials
in the resin formulation. Measurement of solids content will generally
identify such practices.
The ash test is a measure of the total inorganic content in a sample.
In this test, a weighed sample is placed in a muffle furnace at ap-
proximately 1000 F for 30 min or at a temperature and time long
enough to completely pyrolize any organic matter. The remaining ma-
terial is inorganic filler, reinforcement, etc. ASTM D 5040 provides a
method of measuring the ash content of adhesives. Ash content will
determine the amount of inorganic fillers that are in an adhesive or
sealant sample. The manufacturer can adjust the filler content, like
the solids content, to correct for errors or inconsistency in formulation.
Higher concentrations of solvent or filler are also often used to lower
the cost of the adhesive or sealant system.

4.3.2 Adherends and other materials used
in the bonding process
Fundamental property tests are also commonly used to characterize
the substrate and provide a ‘‘signature’’ for lot to lot comparisons. In