Page 471 - Handbook of Adhesives and Sealants

Adhesives Families 407

by crosslinking through the addition of a peroxide or by irradiation.
Curable hot melt adhesive systems are under development.

10.4.2.6 Cellulosic resins. Cellulose derivatives are one of the oldest
and most versatile of adhesives to be originally introduced for house-
hold applications. Cellulose nitrate adhesives are solvent solutions
that bond well to many thermoplastics. They are water resistant and
form a tough bond to a variety of materials such as metal, glass, fabric
and plastics. Cellulose nitrate adhesive formulation was first intro-
duced for bonding plastic models and toys.
Cellulose acetate adhesives are more heat resistant and exhibit bet-
ter aging. However, they are not as moisture resistant as the cellulose
nitrate counterparts. The principal use is bonding cellulose acetate
plastics.
Ethyl cellulose is available as solvent solutions or as hot melts. The
properties can vary considerably with the type of resin used and the
adhesive formulation. Good bonds are formed to porous materials, but
adhesion on nonporous substrates is not outstanding. Water resistance
is only fair.

10.4.2.7 Polyamide. Polyamide hot melt adhesives have lower melt-
ing points than the polyamides used for engineering plastics (nylon).
They have greater temperature resistance than ethylene vinyl acetate
adhesives and require fewer additives. However, they are generally
more expensive. Polyamide terpolymers are used for bonding textile
fabrics and have good resistance to dry cleaning fluids. There are a
great many resins in the polyamide family. They can be varied to pro-
vide hot melts of almost any desired temperature over a span of sev-
eral hundred degrees.
Polyamide resins are also commonly employed as modifiers for both
structural and nonstructural adhesives to improve flexibility and re-
sistance to impact.

10.4.2.8 Polyester. Polyesters, chemically similar to those used in the
synthetic fiber industry, are also used in hot-melt adhesive formula-
tions. One of the earliest applications for hot-melt polyester adhesives
was in the manufacture of shoes. Polyester hot-melt formulations are
commonly found in preformed sticks or coils that are used with hot-
melt extrusion guns. The adhesive is pushed through the heated noz-
zle of the gun, and molten product is applied to the substrate. Hot-
melt polyester adhesives are commonly used for bonding fabrics such
as decorative trim, draperies, etc. Polyester adhesives can be used in
their natural state, but often they are compounded heavily to provide
for increased toughness, peel strength, and open time.