Epoxy resin composites

Synthesis and properties of epoxy resins and their application as composites

1. EPOXY RESINS Presented By, Vishal K P

2. INTRODUCTION Epoxy resins are low molecular weight pre-polymers or high molecular weight polymers containing at least two epoxide groups Mainly used for surface coatings and composite applications Gives thermosetting polymer with high mechanical property, temperature and chemical resistance

3. PREPARATION FROM BIS-PHENOL A E poxy resins are obtained by the reaction products of Bis -phenol A and Epichlorohydrin - bispheniol A diglycidyl ethers Bisphenol -A is prepared by Acetone and Phenol

4. FORMATION OF DIGLYCIDYL ETHER General formulae for glycidyl ether resin:

5. Bisphenol A with MP 153ᵒC is adequate for preparation Commercial liquid resins consist of low M.W Bisphenol A diglycidyl ether along with high M.W polymers The Diglycidyl ether has a M.W of 340 and it can be increased by raising the Bisphenol A- Epichlorohydrin ratio Commercially epoxy resin is available at 98% purity and as colourless mobile liquid

6. Laboratory Scale P reparation 1 mole of bisphenol A is dissolved in 4 moles of epichlorohydrin and heat to 105-110ᵒC under nitrogen atmosphere Solution is stirred for 16 h and 30% aqueous solution of NaOH is added The resulting organic layer is separated , dried with sodium sulphate Diglycidyl ether is obtained by fractional distillation under vaccum

7. CURING OF GLYCIDYL ETHER RESINS Three dimensional cross-linked structures are obtained when epoxy resins are cured Cross-linking is carried out using either epoxy groups or hydroxy groups.

8. The Epoxy-Hydroxyl reaction is as follows: The product will contain new hydroxyl group that can react with other epoxy rings

9. AMINE HARDENING SYSTEM Amine hardeners will cross-link epoxy resins either through catalytic mechanism or bridging. 1° and 2° amines acts as reactive hardeners and 3° amines as catalytic. Diethylenetriamine and triethylenetetramine are highly reactive amines with 5-6 hydrogens available for cross-linking

10. Primary aliphatic amines provide fast curing hardeners

11. ANHYDRIDE HARDENING SYSTEM They require heat to initiate full cure Anhydride curing agents reacts with epoxy resins to form esters. The carboxyl group formed by opening of anhydride ring reacts with epoxy groups for cross-linking

12. They are more thermally stable and provides better electrical insulation than he linkage formed in an amine cure. Reaction of carboxyl group with epoxy group Etherification of epoxy groups by hydroxyl groups Reaction of mono ester with hydroxyl groups Hydrolysis of anhydride to acid by water release Hydrolysis of mono ester with water to give acid and alcohol 1. 2. 3. 4. 5.

13. ACID HARDENING SYSTEM Acid cure system are less skin sensitive and gives low exotherm than the amine cure system. Acid anhydrides are preferred to acids as the latter releases more water during cure which causes foaming. Same mechanism for that of the anhydride hardening. Main hardeners are Phthallic anhydride, Maleic anhydride, etc..

14. PROPERTIES Heat resistant Corrosion resistance Flexible and rigid Transparent and opaque Chemical resistant Excellent electrical properties Mechanical properties

15. EPOXY COMPOSITES Wide variety of composites are made using epoxy as matrix. Broadly classified into: 1.Fibre reinforced plastic (FRP) composites 2.Particulate composite 3.Nanocomposites Reinforcements used are Glass, Carbon, Kevlar, Basalt fibres etc.

16. Carbon- fibre reinforced EC’s Carbon- fibre reinforced EC’s are light weight, high strength composite material. Are made by filament winding. Resin and hardener are dissolved in a solvent. Hardener used can be amine/acid/anhydride system. Solvent used is methyl ethyl ketone.

17. Tensile strength:1900-3400N/mm sq. Modulus:240-645KN/mm sq. Applications: aircrafts, automobiles etc.

18. Glass-fiber reinforced EC’s T hey have strength equal to steel, higher stiffness than Al and specific gravity one quarter of steel. Glass fibre can be in the form of long fibres, woven mat & chopped fibres. Are made by compression molding, hand lay-up and hot press techniques.

19. They are light weight and translucent in nature. Applications : foundations, sculptures, panels, roofs, domes, helmets etc.

20. REFERENCES PLASTICS MATERIALS- J.A.Brydson -Butterworth Heinmann : Seventh Edition. HANDBOOK OF COMPOSITES- George Lublin, Van Nostrand , New York , 1982. TP Sathish Kumar, S Satheesh Kumar, J Naveen ; Glass-fiber reinforced polymer composites-A review; Journal of reinforced Plastics and Composites; SAGE Publications.

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