potential for biobased adhesives in wood bonding ppt.pdf · tannin structure has many available...
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Potential for Biobased
Adhesives in Wood
Bonding
CHARLES FRIHART, US FOREST PRODUCTS LABORATORY, USA
59TH SWST INTERNATIONAL CONVENTION, MARCH 6–11, 2016
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History of biobased adhesives –
main component
Ancient
Animal glues (collagen)
from hides and bones
Blood
Paints – egg whites and milk
Pitches for sealant
adhesives
Up to 1700
Casein from milk
Fish (collagen)
1700-2000
Commercial adhesives
Highly alkaline soy flours
Honeymoon soy-RF
Tannin
2000’s
Slightly basic soy flour with co-reactant
Soy with magnesium oxides
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Additive role (extender, modifier,
filler)
Proteins
Wheat gluten, soy, blood
Tannin with PF
Lignin
Walnut shell flour, etc.
Not considering urea and formaldehyde since they are
made synthetically, although they can also be biobased
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Casein glulam - FPL 1935 to 2010
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What makes bonding wood hard?
Complex surface structure that varies greatly from location to location (density, moisture content, cellular fracture, rays, reaction wood, juvenile wood, etc.)
Many wood species are used, but they have significantly different structural properties and extractive chemicals
Properties of surface vary rapidly with time (contact angles and extractives) leading to decreased bond strength
Moisture durability required in most cases, which changes the wood’s dimensions
Creep resistance, often under significant load, requires the use of thermoset adhesives
Temperature durability required in some cases (roof deck, attic, fire)
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Moisture durability
Changes in moisture causes the wood to swell and shrink
The bonded portion needs to accommodate the dimensional
changes or failure will occur
Internal forces in
addition to
applied forces
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Response of the adhesives to wood
swelling
In-situ polymerized,
infiltrate cell wall to
reduce swelling
Pre-polymerized,
need right flexibility
to flex but to not
creep
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Adhesive classes
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Typical wood surfaces
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Why adhesive interaction with
wood is important
Lumen filling does not
reduce impact of swelling
Cell wall infiltration reduces
swelling and its impact
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How do biobased materials fit into
these adhesive classes?
Tannins and lignins are in-situ polymerized
Thus need to infiltrate cell wall to reduce swelling
Proteins, oil-based polyurethane, and carbohydrates are pre-
polymerized
Need flexibility as well as strength
Biobased additives generally do not enter the cell wall and usually
change the properties of the adhesive on the surface
Best current review is A. Pizzi, Bioadhesives for Wood and Fibres: A
Critical Review, Rev. Adhesion Adhesives, Vol. 1, No. 1, February
2013
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Condensed
tannins
structure
model
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Condensed tannin – PF adhesives
Tannin structure has many available reactive phenol
groups
Including resorcinol type groups giving it high reactivity
It has significant molecular weight and thus is unlikely to
infiltrate the cell wall
Limited availability makes it useful only in certain locals
where PF is less available and more expensive
Used commercially
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Condensed tannin (non-PF)
adhesives
Formaldehyde
Urea-formaldehyde
Hexamethylenetetramine
Methylolated aminoparafins or methylolated nitroparafins
Acid or base self-condensation
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Lignin structure
(generalized
model)
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Lignin sources
Sodium hydroxide pulping of wood
Sulfite pulping of wood
Complete acidulation of Kraft black liquor (50,000 ton/year
Partial acidification of Kraft black with carbon dioxide (70,000 ton/year)
Organosolv pulping of wood or grasses
Biofuel ethanol production by product from wood or grasses (6 projected plants using corn stover, DDG, corn cobs and bagasse)
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Lignosulfonate
structure
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Ligninosulfonates
The largest volume for lignin is lignosulfonates
Originally produced from bisulfite pulping of wood
Now also produced by sulfonating Kraft lignin
Lignin contains varying degrees of sulfonation
Markets for about 1 million tons/year include:
Dispersant for concrete admixtures
Animal feed binder
Oil well drilling mud
Dust control for road work and mineral mining
Many minor applications as surfactant, including PF adhesives
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Lignin uses
Largest current demand is for lignosulfonate
Market reports
Frost and Sullivan (2012) projects $130 Bn/yr market
Lux Research (2014) projects $242 Bn/yr market
This would be equivalent to about 186 Million/tons on
average
However, these projections seem overly positive with
current plans for lignin utilization
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Lignin-phenol-formaldehyde
adhesives
Many papers have shown that a wide variety of lignins can replace
up to 40% of the phenol in Pf resins, with the usual amount in the 20-
30% range, especially if methylolated first.
There are reports that lignin was at one time used in PF resins
Today thee does not seem to be any lignin used in PF resins in the US
or Europe
Why lignin is not used
Slow curing makes it more of a filler than an extender
No real incentive for PF manufacturers to complicate their process,
especially since PFs are already specialty products
Need development work to make LPF more viable
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Other lignin adhesives
Lignin with hydrogen peroxide
Enzymatically activated lignin
Methylolated lignin with polymeric diphenyl methylene
diisocyanate
Lignin glyoxal
Tannin-lignin-formaldehyde adhesive
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Other potential lignin markets
Functional Fillers Polymeric Composites
RecycleWood uses lignin at 25-30% loading to make compostable garbage bags
Asphalt Emulsifiers
Lignin-polyamine condensates can make 70% asphalt emulsions
Polyurethanes
Lignin can partially replace polyols to make stiff PU foams for insulating panels
Wastewater Treatment Polymers
Lignin can be cross-linked to form effective flocculants
Carbon Fiber
WHEN successful, this will be a HUGE market for lignin
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Protein adhesives
Most of the research has been on their properties in food applications, which has some relation to adhesives
However, the problem comes in that protein properties are very dependent upon processing and the protein used in individual studies is usually quite vague
For most grain and oil seed proteins, the proteins are globular and therefore colloidal properties are very important
Work on chemical modification has been good, but it lacks understanding of real protein properties
Interesting work on the properties of adhesives used by sea creatures
More potential in proteins than has been unlocked so far
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Wood-derived adhesives
Besides wood components being used in adhesives,
Liquidified wood or bark
Biooil
Biochar
These are often used in PF adehsives
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Tree and plant oils
Epoxidized oil resins for use in polyurethanes
Acrylic epsxidized soy oil resin
Transformations include epoxy, carboxyl, hydroxyl,
vinyl, amine, etc.
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Thank you for your kind
attention
Questions?