Handbook of Solvents - George Wypych - ChemTech - Ventech!

848 George Wypych
methyl amyl ketone, butyl acetate, methyl ethyl ketone, 2-ethoxyhexyl acetate as solvents),
these adhesives can be made without solvents.
Pressure sensitive and contact adhesives are made from a variety of polymers including
acrylic acid esters, polyisobutylene, polyesters, polychloroprene, polyurethane, silicone,
styrene-butadiene copolymer and natural rubber. With the exception of acrylic acid
ester adhesives which can be processed as solutions, emulsions, UV curable 100% solids
and silicones (which may contain only traces of solvents), all remaining rubbers are primarily
formulated with substantial amounts of solvents such as hydrocarbon solvents (mainly
heptane, hexane, naphtha), ketones (mainly acetone and methyl ethyl ketone), and aromatic
solvents (mainly toluene and xylene).
Melt adhesives and plastisols do not contain solvents. The solution adhesives group
includes products made from the following polymer-solvent systems: nitrocellulose (typical
solvents include solvent combinations usually of a ketone or an ester, an alcohol and a
hydrocarbon selected from isopropanol, 2-butylhexanol, amyl acetate, acetone, methyl
ethyl ketone), nitrile rubber (main solvent - methyl ethyl ketone), polychloroprene (which is
usually dissolved in a mixture of solvents including a ketone or an ester, an aromatic and
aliphatic hydrocarbon selected from naphtha, hexane, acetone, methyl ethyl ketone, benzene,
toluene), and polyvinyl acetate (water).
In addition to the solvents used in adhesives, solvents are needed for surface preparation
4 and primers. Their composition may vary and is usually designed for a particular substrate,
often using fast evaporating solvents and environmentally unfriendly materials with
significant adverse health effects.
Detailed data on the total amount of solvents used by adhesive industry could not be
found. The adhesive manufacturing industry continues to grow at a very fast pace. Total adhesive
production, according to Frost & Sullivan, was $18.25 billion in 1996 and this is expected
to grow to $26.2 billion in 2003. 5 Solvent-based materials in 1995 constituted 13%
of total production in North America, 14% in Europe, 15% in Japan, and 25% in the Far
East. 6 Many industries which use solvent-based adhesives have moved to South America
and Asia where regulations restricting emissions are less severe. 5 The shoe industry is now
concentrated in South America. There are many initiatives to decrease solvent emissions.
For example, World Bank’s assistance program for developing countries focuses on this
issue. 5 But in spite of the fact that solvent-based adhesives lost some of their markets (3.3%
during the period of 1994-1996), 5 they still hold 14-15% of the European market. 6 It is estimated
that the use of solvents contributes 24% of all VOC emissions. According to one
source adhesives were responsible for a 6% share in these emissions in 1993. 7 Another
source 8 blames adhesives for 7% of total VOC emissions in Germany in 1995.
Sealants are divided into groups according to the generic names of polymer base. The
main groups include: polyurethanes, silicones, acrylics, polysulfide and others (PVC,
polybutylene, styrene-butadiene-styrene copolymers, polychloroprene, and several others).
The amount of solvent used in sealants is controlled by the standards which previously divided
sealants into two groups: these below 10% VOC and those above. Recently, a provision
was made to include water-based acrylics and the limit of VOC for class A sealants was
increased to 20%. Polyurethane sealants and structural adhesives can be made without solvent
(the first solvent-free polyurethane sealant was made in 1994). 9 Solvents are added to
reduce sealant viscosity and to aid in the manufacture of polymer. Typical solvents used are
mineral spirits, toluene, and xylene. A small amount of solvent is emitted from curatives