Transcript Forestry 485 - Iowa State University

Forestry 485
Lecture 2-5: Specific Types of
Adhesives
Chemical Nature of Wood
Adhesives
Organic, Polymeric Chemicals
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Natural origin, e.g., blood protein, milk protein, starch
(carbohydrate)
Synthetic origin, e.g., phenol formaldehyde,
isocyanate, polyvinyl acetate (“Elmer’s glue”)
Thermoplastic (soften upon heating, harden
upon cooling, re-soften upon heating)
Thermosetting (chemically reactive, once
hardened, they do not soften upon subsequent
re-heating)
Polymers
from Latin
Poly = Many; Meros = Units
General Definition – molecules with high
molecular weight composed of many smaller
repeating units.
Classification by Origin
Natural

Synthetic
Carbohydrate
Starch
Cellulose
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Protein
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Plant-based (e.g., soybeans)
Animal-based
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Protein from hides, bones,
sinew
Liquid (“hide” glue)
Solid (“hot animal
glues)
Blood
Casein (milk)
Lignocellulosic Extracts
Tannins
Lignin
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Polyvinyl acetate (PVA)
Elastomeric contact adhesives
(e.g., styrene butadiene)
Elastomeric mastic
(construction adhesives)
Hot melts
Epoxy
Urea formaldehyde
Phenol formaldehyde
Polymeric isocyanate
Resorcinol
Melamine
Polyurethane
Vick, 1999. Table 9-3
Classification by Use Category
Structural
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Fully Exterior
Phenol formaldehyde
Resorcinol formaldehyde
PRF
Isocyanate emulsion
Melamine formaldehyde
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Interior
Urea formaldehyde
Casein
Cross-linked PVA
Polyurethane
Nonstructural
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Limited Exterior
MUF
Isocyanate
Epoxy
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Semi-structural
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PVA
Animal protein (except
casein)
Plant protein
Elastomeric construction
Elastomeric contact
Hot melt
Starch/carbohydrate
Vick, 1999. Table 9-2
Major Synthetic
Resins Used in
Composite Panels:
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Phenol formaldehyde
Urea formaldehyde
Isocyanate
White, 1995
Adhesive Additives
Catalysts: Increase chemical reaction rate of adhesive
during cure (e.g., ammonium chloride used for UF
resins)
Extenders: Low cost additives that enhance adhesive
handling, flow, or working characteristics and provide
some adhesive function (e.g., wheat flour)
Fillers: Low cost additive that modify adhesive working
characteristics but do not provide adhesive function
(e.g., corn cob powder)
Other additives may include plasticizers, tackifiers,
antioxidants, formaldehyde scavengers, colorants,
wetting agents, defoamers, etc.