Forestry 485Forestry 485

Lecture 2-5: Specific Types of Lecture 2-5: Specific Types of AdhesivesAdhesives

Chemical Nature of Wood Chemical Nature of Wood AdhesivesAdhesives

Organic, Polymeric ChemicalsOrganic, Polymeric Chemicals Natural origin, e.g., blood protein, milk protein, starch Natural origin, e.g., blood protein, milk protein, starch

(carbohydrate)(carbohydrate) Synthetic origin, e.g., phenol formaldehyde, Synthetic origin, e.g., phenol formaldehyde,

isocyanate, polyvinyl acetate (“Elmer’s glue”)isocyanate, polyvinyl acetate (“Elmer’s glue”)

Thermoplastic (soften upon heating, harden Thermoplastic (soften upon heating, harden upon cooling, re-soften upon heating)upon cooling, re-soften upon heating)

Thermosetting (chemically reactive, once Thermosetting (chemically reactive, once hardened, they do not soften upon subsequent hardened, they do not soften upon subsequent re-heating)re-heating)

Polymers

from Latin Poly = Many; Meros = Units

General Definition – molecules with high molecular weight composed of many smaller repeating units.

Classification by OriginClassification by Origin

NaturalNatural CarbohydrateCarbohydrate

StarchStarchCelluloseCellulose

ProteinProteinPlant-based (e.g., soybeans)Plant-based (e.g., soybeans)Animal-basedAnimal-based

Protein from hides, bones, Protein from hides, bones, sinewsinew

Liquid (“hide” glue)Liquid (“hide” glue)Solid (“hot animal Solid (“hot animal glues)glues)

BloodBlood Casein (milk)Casein (milk)

Lignocellulosic ExtractsLignocellulosic ExtractsTanninsTanninsLigninLignin

SyntheticSynthetic Polyvinyl acetate (PVA)Polyvinyl acetate (PVA) Elastomeric contact adhesives Elastomeric contact adhesives

(e.g., styrene butadiene)(e.g., styrene butadiene) Elastomeric mastic Elastomeric mastic

(construction adhesives)(construction adhesives) Hot meltsHot melts EpoxyEpoxy Urea formaldehydeUrea formaldehyde Phenol formaldehydePhenol formaldehyde Polymeric isocyanatePolymeric isocyanate ResorcinolResorcinol MelamineMelamine PolyurethanePolyurethane

Vick, 1999. Table 9-3

Classification by Use CategoryClassification by Use Category

StructuralStructural Fully ExteriorFully Exterior

Phenol formaldehydePhenol formaldehydeResorcinol formaldehydeResorcinol formaldehydePRFPRFIsocyanate emulsionIsocyanate emulsionMelamine formaldehydeMelamine formaldehyde

Limited ExteriorLimited ExteriorMUFMUFIsocyanateIsocyanateEpoxyEpoxy

InteriorInteriorUrea formaldehydeUrea formaldehydeCaseinCasein

Semi-structuralSemi-structural Cross-linked PVACross-linked PVA PolyurethanePolyurethane

NonstructuralNonstructural PVAPVA Animal protein (except Animal protein (except

casein)casein) Plant proteinPlant protein Elastomeric constructionElastomeric construction Elastomeric contactElastomeric contact Hot meltHot melt Starch/carbohydrateStarch/carbohydrate

Vick, 1999. Table 9-2

Major Synthetic Major Synthetic Resins Used in Resins Used in Composite Panels:Composite Panels: Phenol formaldehydePhenol formaldehyde Urea formaldehydeUrea formaldehyde IsocyanateIsocyanate

White, 1995

Adhesive AdditivesAdhesive Additives

Catalysts: Increase chemical reaction rate of adhesive Catalysts: Increase chemical reaction rate of adhesive during cure (e.g., ammonium chloride used for UF during cure (e.g., ammonium chloride used for UF resins)resins)Extenders: Low cost additives that enhance adhesive Extenders: Low cost additives that enhance adhesive handling, flow, or working characteristics and provide handling, flow, or working characteristics and provide some adhesive function (e.g., wheat flour)some adhesive function (e.g., wheat flour)Fillers: Low cost additive that modify adhesive working Fillers: Low cost additive that modify adhesive working characteristics but do not provide adhesive function characteristics but do not provide adhesive function (e.g., corn cob powder)(e.g., corn cob powder)Other additives may include plasticizers, tackifiers, Other additives may include plasticizers, tackifiers, antioxidants, formaldehyde scavengers, colorants, antioxidants, formaldehyde scavengers, colorants, wetting agents, defoamers, etc. wetting agents, defoamers, etc.