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Phenolic Resin & Adhesives
- 1. Phenolic Resin Adhesive By TUSHAR KANTI MAITI
- 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
- 4. Synthesis of Phenolic resins
- 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 _________________________________________ * 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
- 10. Epoxy Adhesive Epoxy group Bishenol A NaOH (reactant & catalyst) Epichlorohydrin Epoxy resin
- 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
- 23. Thank You
Editor's Notes
- 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.