Page 474 - Handbook of Adhesives and Sealants

410 Chapter Ten

10.4.3.1 Natural organic resins. Natural organic adhesives are high
polymers like their synthetic counterparts. Many of these adhesives
are used because of their early history and the number of industries
that have adopted and continued to use these systems. They are noted
mainly by their lower cost. In certain applications, they dominate over
synthetic adhesives.
10.4.3.1.1 Glues of agricultural origin. These adhesives are soluble or dis-
persible in water and are produced or extracted from natural sources.
There are several common adhesives that are derived from agricul-
tural sources. These are starch, dextrin, soybean, and oleoresinous
adhesives.
Starch adhesives are derived primarily from the cassava plant, al-
though other sources may be used. The starch is usually heated in
alkaline solutions then cooled to room temperature to prepare the dis-
persion. After cooling, they are applied as cold press adhesives. They
develop their strength by loss of water into porous substrates. Tack
develops rapidly. Normal setting on wood substrates requires 1–2days
at room temperature with contact pressure. Starch adhesives are used
for paper cartons, bottle labeling, and stationery applications. Joint
strengths are low compared to the vegetable types. However, the ad-
hesive is resistant to water and biodeterioration.
Dextrins are degradation products of starch. They are produced by
heating starch in the presence or absence of hydrolytic agents, usually
basic or acid producing substances. They are often mixed with cata-
lytic agents. These adhesives can bond to many different substrates.
Paper and paperboard are the most common substrates. Laminating
adhesives are usually made from highly soluble white dextrins and
contain fillers such as clay.
Soybean glue is derived from protein. These adhesives are cheap
and can be used for making semi-water resistant plywood and for coat-
ing some types of paper. They set at room temperatures.
The most common form of oleoresinous adhesive is made from the
oleoresin of the pine tree. This materials is used either in solvent
solution or as a hot melt mastic. It has poor resistance to water and
oxidation. Bond strengths are moderate and develop rapidly. This ad-
hesive is often used for temporary fastening.

10.4.3.1.2 Glues of animal origin. Many of the most important natural
adhesives occur from animal origin. Almost half of the animal glues
produced go into remoistenable gummed tapes. Common animal-based
glues are derived from casein, blood, bone, and hide byproducts and
fish.
Casein glue is the protein of skim milk. Dry mix casein glues are
simply mixed with water before use. They are used at room temper-