Thermosets_ Epoxy, Polyesters, Vinyl esters, Polyurethanes, and Phenolics

1. Thermosets_ Epoxy, Polyesters, Vinyl esters, Polyurethanes, and Phenolics Professor Joe Greene CSU, CHICO

2. ThermosetsReference: Appendix E. Industrial Plastics, Modern Plastics Encyclopedia (p142) • History • Chemistry and Chemical Structure • Applications • Mechanical Properties • Physical Properties • Processing Characteristics • Advantages/Disadvantages • Reinforced thermosets- composites • Other thermosets • Review • Questions

3. Thermoset Definition • Thermoset materials are polymers that under go a chemical reaction to build molecular weight and viscosity. • Thermosets are set or crosslinked with heat and can not be reheated for forming repeated forming.

4. Thermosets History • Thermosets are polymers that undergo a chemical reaction during the polymerization. • Thermosetting reaction is not reversible under heat. • Epoxy • Standard epoxy is based on bisphenol A and epichlorohydrin. • Others based on phenols and formaldehyde or aromatic amines and aminophenols • Curing can occur at room temperature with the use of 2 component systems. Curing at elevated temperature with use of one-component. • Properties include good adhesion to many substrates, low shrinkage, high electrical resistivity, good corrosion resistance, and thermal. • Processing is achieved without generation of volatiles.

5. Thermoset Chemistry Epoxy Chemistry

6. Epoxy Chemistry • Epoxy: O H H C C H + H2N (C) N (C) NH2 H H H H epoxide group + amines (DETA) epoxy • Other epoxy resins • diglycidyl ether of bisphenol A (DGEBRA) • tetraglycidyl methylene dianiline (TGMDA • epoxy phenol cresol novolac • cycloaliphatic epoxies (CA) • Curing agents (hardeners, catalysts, cross-linking agents) • aliphatic or aromatic amines (DETA, TETA, hexamethylene tetramine,etc.) • acid anhydrides (phthalic anhydride, pyromellitic dianhydride, etc.) • Active hydrogen react with epoxide groups. • As much as 15% hardener is needed

7. Epoxy Chemistry

8. Polyester Chemistry O O • Unsaturated Polyesters • Thermoset reaction between a difunctional acid (or anhydride) and a difunctional alcohol (glycol) • At least some of the acid (or anhydride) features double bonds between adjacent carbon atoms for unsaturation. • Characteristic ester linkages are formed, hence the name Polyester C6H4(COOH)2 + (CH2)2(OH)2 -[(CH2)2 -O- C - C-O]- terephthalic acid + ethylene glycol Polyethylene terephthalate (PET) • Acids include: maleic, fumaric, isophthalic, terphthalic, adipic, etc. • Anhydrides include: maleic, phthalic • Glycols include ethylene glycol, diethylene glycol, propylene glycol

9. Polyester Chemistry • Heat or radiation can trigger the cross linking reaction • Catalyst (or initiator) is used. Methyl ethyl ketone (MEK) peroxide, benzoyl peroxide, and cumene hydroperoxide • Accelerators (or promoters) speed up the reaction. • Inhibitors extend shelf life (hydroquinone, tertiary butyl catechol) • Condensation Reaction results in CO2 and H2O • Monomer required to polymerize, e.g., Styrene, to react with the unsaturations in the polyester molecules to form 3-D network. • Styrene at 30% to 50% in commercial polyester systems • vinyl toluene for vinyl ester • methyl methacrylate for methyl methacrylate ester

10. Polyester Chemistry

11. Sheet Molding Compound (SMC) • SMC is the paste that is compression molded • 33% polyester resin and stryrene, which polymerizes and crosslinks • 33% glass fibers (1” fibers) • 33% Calcium Carbonate

12. Polyester Molding Operations • Molding of SMC with compression molder • Molding of BMC with compression molder

13. Materials that are Compression Molded • SMC- Sheet molding compound- Polyester, glass fiber, CaCO3 • BMC- Resin, fiber, and filler • BMC stands for Bulk Molding Compound, • compression molded under high temperature and pressure. • BMC has a solid, uniform constitution. By changing the blend design, the characteristics can be altered to meet a wide range of applications. • We have succeeded in developing BMC as the world's first cultured marble that has the functional specialization for home use.

14. Polyester Use with RTM • RTM: Resin Transfer Molding • The process of injecting a liquid resin trough a glass mat while in a heated mold. • Materials • Polyester • Vinyl ester • Epoxies

15. SCRIMP Process • Used for polyester, vinyl ester, and epoxies

16. Polyurethane Chemistry • Reaction between isocyanate and alcohol (polyol). • Crosslinking occurs between isocyanate groups (-NCO) and the polyol’s hydroxyl end-groups (-OH) • Thermoplastic PU (TPU) have some crosslinking, but purely by physical means. These bonds can be broken reversibly by raising the material’s temperature, as in molding or extrusion. • Ratio between the two give a range of properties between a flexible foam (some crosslinking) to a rigid urethane (high degree of crosslinking). • In PUR foams density can range from 1 lb/ft3 to 70 lb/ft3. • Foams are produced by chemical blowing agents. • Catalyst are used to initiate reaction. • RIM process is used to produce fenders and bumper covers

17. Polyurethane Chemistry

18. Polyurethane Processing • Polyurethane can be processed by • Casting, painting, foaming • Reaction Injection Molding (RIM)

19. Applications for Thermosets • Epoxy • Protective coatings: maintenance coatings for industrial and marine, tank linings, industrial floorings, beer and beverage can coatings, food cans, appliance primers, hospital and laboratory furniture. • Bonding and adhesives: Automotive and aircraft industries adhesive to metals and composites. • Molding, casting and tooling: Molding compounds in electrical and electronic industries, casting resins, potting resins. Prototype and master model tools. • Laminating and composites: Binders in fiber reinforced laminates and composites. Laminates are used in printed wiring boards. Composite applications include filament winding (high performance pipes in oil fields, pressure vessels, tank and rocket motor housings), pultrusion, casting, and molding (graphite composites for aerospace applications) • Building and construction: Flooring (seamless, self-leveling, or epoxy terrazzo floors), repair of bridges and roads with glass and carbon fiber wraps, concrete crack repair, coat reinforcing bars, binders for patios, swimming pool decks, and soil around oil-well drills.

20. Applications for Thermosets • Polyester • Boat hulls, shower stalls, electrical components, appliances • Recreation vehicles, automotive body panels, floor pans; SMC • Soft tooling, patterns • Cultured marble, buttons, corrosion resistant tanks and parts, • Corrugated and flat paneling, simulated wood furniture, bowling balls, polymer concrete, and coatings • Polyurethane • Rigid foams: (MDI) Laminated board stock, Moldings, Bun, Foam in place insulation, sprayed foam, packaging • Semi-flexible foam: (MDI and TDI) Moldings, Integral-skin moldings • Flexible foam:(TDI) Moldings, integral skin molding, carpet underlay • Packaging: (TDI) Furniture cushioning • Microcellular foam: (MDI) RIM parts, shoe soles • Non-foam cast elastomers • Coatings, binders, thermoplastic elastomers, sealants, paints

21. Other Thermosets • Phenolic • Applications • Pistons, Thrust pulleys

22. Mechanical Properties of Thermosets

23. Advantages of Thermosets • Epoxy • Excellent chemical and corrosion resistance • Excellent thermal properties and low creep • High stiffness and modulus properties • Polyester • Rigid, resilient to chemical and environmental exposures, corrosion resistant, and flame retardant • Easily processed in low cost equipment • Polyurethane • High strength to weight ratios, resistance to flame spread, excellent thermal insulation, low cost, easily processed

24. Disadvantages of Thermosets • Epoxy • Moisture absorption, toxicity, not recyclable • Cost • Polyester • Moisture absorption, toxicity, not recyclable • Styrene emmisions • Polyurethane • Moisture absorption, toxicity, not recyclable

25. Additives and Reinforcements to Polyesters • Additives- • UV stabilizers, colorants, heat stabilizers, blowing agents • Catalyst, inhibitors, promotors • Fillers • Talc • Calcium carbonate • Reinforcements • Glass fiber- short fiber (1/8” or long fiber 1/4”) • Mineral fiber (wolastonite) • Mica • carbon fibers

26. Properties of Reinforced Thermosets

27. Processing of Composites • Open Mold processes • Hand lay-up and Spray-up • Filament winding

28. Processing of Composites • Open Mold processes • Vacuum bag, pressure bag, SCRIMP • autoclave: Apply Vacuum Pressure and Heat in an oven which can be 5 feet to 300 feet long

29. Thermoset Reacting Polymers • Process Window • Temperature and pressure must be set to produce chemical reaction without excess flash (too low a viscosity), short shot (too high a viscosity), degradation (too much heat)

30. Processing of Composites • Closed Mold Processes • Compression molding [moderate pressure] • Injection Molding [high pressure] • Resin Transfer Molding (RTM), Structural Reaction Injection Molding (SRIM) [low pressure] • Pultrusion [low pressure]

31. Injection MoldingGlass Reinforced Composites • Plastic pellets with glass fibers are melted in screw, injected into a cold mold, and then ejected. Glass filled resin pellets

32. Composites Have a Fiber Preform • Fiber type • Roving form that can be sprayed into a 3-D preform • Roving form that is woven into a glass sheet and then formed to shape (preform)

33. Compression Molding • Compression molding was specifically developed for replacement of metal components with composite parts. The molding process can be carried out with either thermosets or thermoplastics. However, most applications today use thermoset polymers. In fact,compression molding is the most common method of processing thermosets.

34. Resin Transfer Molding • In the RTM process, dry (i.e.,unimpregnated ) reinforcement is pre-shaped and oriented into skeleton of the actual part known as the preform which is inserted into a matched die mold. • The heated mold is closed and the liquid resin is injected • The part is cured in mold. • The mold is opened and part is removed from mold.

35. Structural RIM • Fiber preform is placed into mold. • Polyol and Isocyanate liquids are injected into a closed mold and reacted to form a urethane.

36. Homework Questions 1. Define PBT and PET chemical structure. 2. Why was Carothers not successful in developing polyesters? 3. Density of PET is _____ which is higher/lower than PBT and nylon?. 4. What is the tensile strength of PET with 0%, 30% glass fibers? What is the tensile modulus? 5. Plot tensile strength and tensile modulus of PET, PBT, Nylon 6, PP, LDPE and HPDE to look like the following 50 xHDPE Tensile Modulus, Kpsi xLDPE 10 2 5 Tensile Strength, Kpsi

37. Homework Questions 6. Four typical Physical Properties of Polyester are Optical = _______, Resistance to moisture= ______ , UV resistance= _____, acid resistance=_______ 7. The Advantages of Polyester are ________, ________, _______, and __________. 8. The Disadvantages of Polyester are ________, ________, _______, and __________. 9. Glass fiber affects Polyester by (strength) ________, (modulus)________, (elongation)_______, (density) __________, and (cost) ____________. 10. What affect does the copolymer have on the crystallinity of polyesters and why?_________________________________ _________________________________________________.