BORON IN ADHESIVES
ARUN K. CHATTOPADHYAY
Etimine USA, Inc., Pittsburgh, PA
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ADHESIVES
Surfaces & Interfaces
Solid/air; Solid/Solid; Solid/Liquid; Air/Liquid &
Liquid/Liquid
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ADHESIVE: A Substance Capable of Holding
Materials Together by Surface Attachment
MULTI BILLION $ BUSINESS
>750 COMPETING INDUSTRIES
Boron Compounds – Little Usage
Significant Role
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Be
B
C
SMALL PRESENCE – BIG MAGICAL
CHANGES IN MATERIAL
PROPERTY
Agriculture to Aerospace
‘Mummies to Cancer Therapy’
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Adhesives and Boron – Is the Connection Historic?
First Known Adhesive: 4000BC
Pre-Historic Artefacts Glued with Tree Saps/Resins
In Babylonian Temples: Glued Ivory Eyeballs
1-500AD: Greeks/Romans: Veneering & Marquetry
Developed Animal Glue: Fish/Blood/Bones/Hide
1500-1700AD: Term ‘Adhesive’ as Specific Substance
1700AD+: Industrial Revolution: Rapid Growth
1900AD+: Synthetic Resins
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BORON’S CONNECTION?
Art of Making Mummies Involved : NATRON
A Boron Based Mineral for Preservation;
Bonding;
Lamination
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Regardless of the Type :
Plant, Starch, or Animal Based
A Common Substance in Glue Recipe:
Borax or Some form of Borates
As Preservatives or Adhesive Enhancer?
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Chemistry Behind Its Marvel:
B : 1s22p1 : sp2 Hyb : Trigonal Planar
LEWIS ACID
Chattopadhyay, Arun K.; J. Adhesion Sci and Technol (in press, 2014)
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Trigonal Planar sp2 ↔ sp3 Tetrahedral
H3BO3 + H2O
Stereo Chemically They Can Be Both Tetrahedral and Trigonal Planar
B4O72-(aq) + H2O(l)
↔
HB4O7-(aq) + OH-(aq)
B4O72-(aq) + 5H2O(l) + 2H+(aq)
↔
4H3BO3 (aq)
B(OH)3 (aq) + H2O(l)
↔
B(OH)4-(aq) + H+(aq)
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Tetrahedral B(OH)4- Undergoes Bridging and Gels
With Polyol, Cellulose, Polysaccharide,
Glycoprotein etc.
This is the basis for its importance in adhesives.
Chattopadhyay, Arun K.; J. Adhesion Sci and Technol (in press, 2014)
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The Prime Importance for Adhesion to A Substrate:
Wetting or Surface Force
For which the molecular structure of an adhesive
especially:
1. Chain length
2. Presence of any branched chains
3. Presence of polar groups
4. Viscosity
are the most important aspects to consider for the
performance of an adhesive.
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Chattopadhyay, Arun K.; J. Adhesion Sci and Technol (in press, 2014)
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ROLE OF BORATES/BORIC ACID?
In Water Borne Adhesive Formulations:
1.Increases molecular weight of starch
or poly saccharides, casein,
glycoproteins, and poly-ol type of
molecules after forming complexes.
2.Modifies Viscosity to a desired extent
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STARCH BASED ADHESIVES
APPLICATIONS: Paper Bonding and paper products:
Bookbinding, Corrugated Boxes,
Paper Bags, Wallpaper pastes etc.
Typical Formulation:
Cooking Starch-Dextrin (35%) with Water (~58%),
Borax (6%), Defoamer, Alkali, preservatives etc.
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ADVANTAGES OF BORATED ADHESIVES:
1. Gives required viscosity and structure
2. Increases tack.
3. Improves film formation of the starch
based glue onto the papers.
4. Improves water holding of the glue
5. Minimizes water penetration (paper)
6. Improves high temperature stability
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ANIMAL GLUE: One of the Oldest Arts Known
Method: Extraction of Water Miscible Proteins
By Boiling Blood,Bones, Hoofs, Horns, Hides –
Extracted Protein Undergo Hydrolytic
Degradation Forming Collagen and then
Gelatin – A Denatured Collagen Type-1
Collagen Type-1
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Glycoprptein
Boric Acid and Borax In Animal Glues:
1.
2.
3.
4.
Modify Rheology
Provide High Temperature Tolerance
Improve Water Resistance
Resist Fungal, Bacterial and Insect Attacks
APPLICATIONS: Wood & Furniture Industries
Often Formulated With Casein
T. E. Rolando, Rapra Review Report, vol 9 (5), 1-20 (1995).
L. A. Varghese and E. T. Thachil, J. Adhesion Sci. Technol., 18, 181 and 1217 (2004).
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Neutral Plastic Adhesive: HCl, tar, Congo gum, and
urea, and cooking with an animal glue, casein,
borax, sodium benzoate, oil of Wintergreen and
water.
Addition of casein provides improved plasticity to the adhesive by bridging
with glycoprotein via B(OH)4- ion forming a massive H-bond network
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RUBBER BASED CONTACT ADHESIVES
1.
2.
3.
4.
5.
6.
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Pressure Sensitive Adhesive Tapes
Floor Tiles and Carpets
Contact Adhesives for Plastic Laminates
Self Sealing Envelops
Rubber Cements
LEATHER INDUSTRIES
Due to Increasing Stringency Towards Solvents:
Water Borne Rubber Adhesives Are on the Rise
Use of Boric Acid Improves:
1.
2.
3.
4.
Set Time
Storage Stability
Tensile Strength
High Elongation Characteristics
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Chattopadhyay, Arun K.; J. Adhesion Sci and Technol (in press, 2014)
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SYNTHTIC ADHESIVES:
1. NON REACTIVE (Solvent and Water Based)
2. REACTIVE
Direct & Indirect Use of Boron Compounds
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1. Solvent based adhesives that get cured as the
solvent evaporates.
e.g. white glue, contact adhesives, rubber
cement etc.
2. Polymer dispersion types, like polyvinyl acetates
(PVAc)
Extensively Used In Wood & Packaging Industries.
In water borne PVAc adhesive systems: Ester
Groups of PVAc Hydrolyzes Forming Hydroxy
Components of the polymer.
Using Borax or Boric Acid Under an Alkaline
Condition Causes the Polymer to Crosslink.
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Chattopadhyay, Arun K.; J. Adhesion Sci and Technol (in press, 2014)
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REACTIVE ADHESIVES:
Reactive adhesives mainly include Urethanes,
Epoxies, and Cyanoacrylates.
Urethanes:
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A Small Addition Borax
Reduces Formaldehyde
Emission.
EPOXIES:
BF3 is Used as a Catalyst for
Homo-Polymerization of
Epoxy Resins for High Temp
Curing.
Epoxy Adhesives of High Thermal Conductivity:
BN Used as Filler For High Performance Bonding,
Sealing, Coating and Potting.
BN Based Epoxies Are Lighter in density Particularly
Desirable for Aerospace & Defense and for
microelectronic
assemblies
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HOT MELT ADHESIVES:
THERMOPLASTIC SOLID
POLYMER Liquefy At
Elevated Temperature
The Major Use: Carton Sealing
Frozen Food Packages,
Breakfast Cereal, Laundry Detergent,
Beer Cartons, etc.
Tri-Phenyl & Tri-Fluoro Boranes are Used for
Synthesis of Co-Polymerized Ar.Vinyl-co-Sty.Butadiene
Silicones Based Reactive Systems: Boron Halides are
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Used for Curing
In Cyanoacrylates (Super Glue):
Boron Oxide and Boron Tri Fluoride Complexes
Are Used as Acid Inhibitor & Stabilizer for the
Synthesis of Cyanoacrylates.
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Silicone Adhesives:
Boron oxide and boric acid are used as fillers in
silicone adhesives.
Organometallic derivatives of boronic acids are used as
photo-initiators in UV curable compositions.
Boron nitride is used in thermally conductive silicone adhesives.
Self-adhering silicon rubbers of improved surface properties are
synthesized using boric acid (<0.5 wt%) for the manufacture of
pressure sensitive adhesive elastomers.
It is well known that addition of boric acid to silicones
improves adhesion to metal
Hot melt adhesive composition containing α-olefin/aromatic vinyl compound random copolymer; US Patent US 6235818 B1.
Adhesive Compositions for Medical Use: Single Additive as Both the Thickening Agent and the Accelerator; USPTO Patent
Application US 2012/0264846 A1.
Viscous alpha-Cyanoacrylate Compositions; Patent Application US 2009/0326095 A1.
Acid chelate of boric acid or a derivative thereof with a poly-hydroxy compound; US Patent
US4182823 A.
Ashton Acton (Ed), in ‘Boron Compounds - Advances in Research and Application’, Scholarly Edition (2013).
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Questionable Health Concerns with Boron Compounds
Opened New Vistas to Search for Substitutes to Replace
Boron.
In many Cases Such Attempts are Found to be No Less
Damaging to Environment and Health, and Often They Are
Costlier.
e.g.: Boron Compounds are Replaced by Chlorine
and Enzymes in Detergents
Li Compounds Are Used to Replace Borates in
Enamels & Glass Products
Amm.Sulphate/Magnesium Sulphate Used As
Alternate to Borate For Fire Retardation
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DESPITE ALL UNPLEASANT ATTEMPTS TO DISPLACE
BORON COMPOUNDS, WHICH HAVE BEEN IN USE
FOR CENTURIES, CAN EASILY OUTLAST SUCH
CONCERNS AND MEET THE DEMAND FOR MANY
COMING YEARS.
THE FUTURE OF BORON IS ONLY LIMITED
BY OUR IMAGINATION
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