This document provides information on phenolic resin adhesives and epoxy adhesives. It discusses that phenolic resins are thermoset polymers produced from reactions of phenol or substituted phenols with formaldehyde. They are used for applications like bonded abrasives, coated abrasives, and friction elements. The document also describes the synthesis and applications of epoxy resins, which include their reaction with hardeners, modifiers, fillers to produce one component or two component adhesives. Examples of formulations for general purpose, quick cure, and one component epoxy adhesives are also provided.
2. It low molecular wt. raw polymeric materials
It is used for binders, curable molding compositions adhesives and
coatings.
They normally have a melting or softening range, are brittle in the solid
state.
Resins : natural resins and synthetic resins.
Synthetic resins:
phenol-formaldehyde resins*, urea-formaldehyde,
melamine-formaldehyde resins, polyesters resins,
silicone resins, epoxy resins, acrylic resins and alkyd resins.
Resins
Thermoset type polymers.
Prepared as prepolymer and than in the second stage they are cross-
linked by the effect of catalyst, heat and pressure.
Phenolic resins are thermoset type polymers.
3. Phenolic Resin Adhesive
Phenolic resin: reaction products of phenol and /or substituted
phenols with formaldehyde (HCHO)
Unlimited variety of resin:
1. choice of phenols
2. the phenol : formaldehyde ratio
3. type of and amount of catalyst
4. time and temperature of reaction
Different types of phenol
Phenol Cresol Xylenol Para phenyl phenol
5. Condensation reaction: Acid or base catalyst
Novolac Resin
Formaldehyde/Phenol ratio 1 : 0.75-0.95
pH 0.5-1.5
Temp. 100oC
Reaction time 3-6 hrs
Pressure Atmospheric
Two step resin: need to add hexamethylene tetramine (6-15%)
(Hexa) for further reaction or curing.
No water reaction evolved during curing.
Acid catalyst: Novolac
6. Condensation reaction: Acid or base catalyst
Base catalyst: Resole
Resole Resin
Formaldehyde :Phenol ratio 1 : 0.75-0.95
Catalyst NaOH
Temp. 80-100oC
Reaction time 1-3 hrs
Single step resin: heating require for
further reaction or curing.
7. Application of Phenolic Resin Adhesive
Bonded Abrasives:
Three-dimensional products composed of abrasive grain
held together by various binders
Grinding wheels are the most important type bonded abrasive
Grain: Aluminum oxide, silicon carbide, quartz, iron oxide, TiO2 depending
on applications
Coated Abrasives:
Sandpaper: a layer of abrasive grain bonded to a flexible backing
of paper, cloth or combination of these two.
Available in : abrasive belts, coated abrasive wheel, bands, sleeves
rolls and discs
8. Typical abrasive formula
Hot-pressed coarse abrasive Snagging wheel Test*
Aluminum oxide 780
Powder phenolic two-step resin 120
Cryolite (Na3AlF6) 97
Calcium oxide 3
**Creosote oil 12
Hot pressed density (g/cc) 3.03
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* Parts by wt.
**wood-tar creosote and coal-tar creosote
9. Friction Elements
Binders for asbestos in friction materials:
brake linings, brake blocks, disc pads,
clutch facings
Foundry
Binder for sand in the manufacturing of shell molds
and cores
11. Important Characteristics of Epoxy
Hardener or curing agent: Primary and / or secondary amine groups
Adhesion: High adhesion properties to metals, glass and ceramics
(Hydroxyl, amine and other polar groups)
Cohesion: Cohesion strength is also great to metals, glass and
ceramics (Hydroxyl, amine and other polar groups)
12. Reaction with mercaptans (-SH)
+ -SH -S-CH2-CH-
OH
This reaction is accelerated by t-amine, make feasible the incorporation
of thiol terminated polysulfides or polymercaptan as flexibilizing agents
13. Characteristics of Epoxy
100 % solids-no by-products during reaction
Resistance to moisture and solvents
Low creep: Cure epoxies, like other thermoset resins maintain their shape
under prolong stress
Low shrinkage: It can also reduced to a fraction of 1% incorporation of silica,
aluminum, or other inorganic filler
Can be cure at room temp within 5 min by selecting special curing agents
Epoxy can formulated for use in cryogenic (-270 C) and high temp. 260 C)
Disadvantages: Toxicity,
Low pot and shelf-life
Moderate high cost
14. Epoxy resin intermediates
Bis-Epi Resins: Derived from bisphenol A and epichlorohydrin with caustic
soda as both reactant and catalyst.
For commercial resins, n varies from 0 to 20,
and when n =2 or more, it becomes solid at RT.
Hydroxyl groups increase the rate of cure of the resin with amine
Increase adhesion of the cured epoxy to metals and other polar substrates
This –OH group also react with anhydrides curing agents, less common
Araldite 6010- Ciba-Geigy, D.E.R 331-Dow
15. Epoxy Novolac Resins:
Epoxy group + thermal resistance phenolic backbone
Novolac resin: phenol and formaldehyde
Epoxide groups varies from 2.2 to 3.8.
Higher epoxide functionality than Bis-Epi resin –higher density crosslinks,
results high heat resistance
DEN 439- Dow (phenol Novolac), Epi-Rez 5155 (Momentive)
16. Flexible Epoxy Resins:
Derived from polyols and glycerine
Low viscosity and flexible
D.E.R 732 (Dow) from propylene glycol
Epon 812 (Shell) from glycerin.
Usually used with the bis-epi resins
17. Specialty Epoxy Resins:
Solid resin derived from tetrakisphenyl ethane. Use for high temperature adhesive.
Epon 1031 : Shell. Similar products-Araldite 0163 from Ciba-Geigy
18. Compounding of Epoxy Adhesive
Resin, filler, modifier and hardeners
One component system: 100% nonvolatitle liquid, solvent solutions,
pastes, sticks or powder
Two component system: Resin and hardener in separate containers
in liquid or paste form
Usually cure at RT
Curing agents:
Amideamines-dicyandiamide, polysulfides, polyamine
with tertiary amines as accelerators
* Early days, diethylenetriamine, triethylenetrtramine are used but highly toxic, irritating
19. Diluents:
Reduce the viscosity of the resin systems.
May be reactive or nonreactive
Reactive Nonreactive
Butyl glycidyl ether Dibutyl phthalate
Phenyl glycidyl ether Pine oil
Triphenly phosphite Coal tar
Solvent type
Ketones
Esters
Toluene
20. Modifiers:
Enhance flexibility, impact resistance
Flexibilizers enter the reaction with epoxide groups and increase the distance
b/w crosslinks, thereby making the product flexible.
• Incorporation of polysulfides into the formulation
Or using Flexible epoxy resin derive from long chain acids or aliphatic polyols
c.g., glycol based epoxy resin
Modification with synthetic polymers for film or tape adhesive
Epoxy phenolic (resole) (sold as tapes and used in aerospace applications)
Thermoplastic polyurethane modified epoxy systems
Nylon epoxy (30-50 wt% epoxies): high tensile shear and peel strength
21. Fillers:
Lower cost, less shrinkage, lower thermal expansion,
greater heat resistance, better thermal conductivity
Better electrical and fire retardance properties
Property Filler, reinforcement or additive
Mechanical Asbestos, silica, alumina, etc.
Shrinkage and thermal Silica, Quartz, calcium carbonate, etc.
expansion
Heat resistance Mica, asbestos, glass flake, etc.
Electrical conductivity Cu, Ag, graphite powder
Fire retardance Antimony Oxide
Lower cost Sand, Calcium carbonate, etc.
22. Formulation of Epoxy based adhesive
General purpose adhesives: (rigid)
Epoxy resin 100 parts
Versamid 115* 70 parts
Fillers as desired
Versamide: high viscosity, Reactive
polymeric resin based on dimerized
Fatty acid polyamines
General purpose adhesives: (flexible)
Component I Epoxy resin 100 parts
Component II Thiokol LP 3 175 parts (polysulfide, flexibilizer)
Cab-O-Sil 8 parts (colloidal silica)
DMP-30 10 parts (2,4,6 tri dimethyl amino phenol)
Cures overnight at RT or 2 hrs 71 degree C
Quick cure adhesives:
Epoxy resin 100 parts
Silica flour 60 parts
Black 0.1 parts
Asbestos 3 parts
One component adhesives:
Epoxy resin 100 parts
Bentone 34 25 parts
Alumina 25 parts
Dicyandiamide 6 parts
Cures at RT for 7-8 mins. Cures at 1-1.5 hr 176 degree C
To make a resole resin, an alkanine catalyst such as sodium hydroxide is added to the phenol and formaldehyde before heating to 80-100 deg. C.
To make a resole resin, an alkanine catalyst such as sodium hydroxide is added to the phenol and formaldehyde before heating to 80-100 deg. C.
Epoxy, epoxide, oxirane or ethoxyline group is a three membered ring consisting of an oxygen atom attached to two connected carbon atom. The term époxy resin’ usually refers to an intermediate molecule which contains at least two reactive epoxy group.
Aliphatic primary and secondary amines react with epoxy groups rapidly at room temperature, but aromatic amines require elevated temperature cures. Each H-atom attached to N-atom is capable of opening an epoxy ring. In order X-link a diepoxide, the primary amine must be a polyamine. The amount of amine required may be calculated by allowing one amino H-atom per epoxy group.
When the resin is properly cured, the cohesive strenght withen the glue line is so great, and adhesion of the epoxy to other materials so good, that failure under stress often occurs in one of the adherents rather than in the epoxy or at the interface. This happens with glass and aluminium as well as with weaker adherents such as concentrate and wood
Properties of epoxy can be modify by 1. selection of base resin and curing agent, b) alloying epoxy with another resin or c) compounding with fillers
Disadvantanges: Amine curing agents are toxic. Cure epoxy are not deleterious to health.
Most two component adhsive formulations must be mixed shortly before use. Some film and tape adhesives must be stored at low temp. for extended life.
This idealized formula shows two epoxide end groups. In practice, side reactions intervene so that commercial resins average between 1.9 and 1.3 epoxides per molecules.
Its idealized structure shows 4 epoxides per molecules.
Earlier days, diethylenetriamine, triethylenetetramine are used as curing agent but they are volatile and highly toxic, irritating. To overcome these drawbacks amine epoxy aadducts have been used with are less volatile.