1. CHAPTER 2 POLYMERIZATION MECHANISMBy Nur Isfarina binti Ismail

2. DEFINITION POLYMER: are macromolecular (large molecule)which are long chain made up of combination of many repeating units. MONUMER: small molecules that will bepolymerization to become polymer. HOMOPOLYMER: a polymer that derived frompolymerization of a single monomer. COPOLYMER: a polymer derived frompolymerization of more than one monomer. 3. MECHANISM OF ADHESION CHEMICAL BONDING- primary bond: ionic, covalent, metallic bond. - secondary bond: hydrogen bond, Van der Waals bond. PHYSICAL BONDINGMechanical interlocking 2. Diffusion theory 3. Adsorption theory 4. Electrostatic 1. 4. CHEMICAL BONDING Mechanism chemical bonds may across theinterface. Strong and significant contribution to the adhesion in some across. Can be derived into 2 type: 1. Primary bond: ionic, covalent and metallic. 2. Secondary bond: hydrogen, Van der Waals 5. PHYSICAL BONDING 1. MECHANICAL INTERLOCKING When surface are held together with adhesive and the adhesive penetrate through the cavities or porous. Anchored the substrate and adhesive while solidification. The weakest part can be the strength of adhesive when it bonded. Rough surface increase area of physical contact. 6. 2. DIFFUSION THEORY Based on solubility of one material to another. The adhesive can diffuse into adherent surface if it content adherent solvent with interlocking of molecules. One end of the molecules diffuses into the other material. Strong enhanced by heat and pressure. 7. 3. ADSORPTION THEORY Bonding process of intermolecular attraction between adhesive and adherent at interface. The surface form are Van der Waals force. The adhesive should have lower surface tension than adherent to wet solid surface. The adhesive applied to adherent spread spontaneously when joined is formed. 8. ELECTROSTATIC The difference in electronegativity of adhering material. Adhesive force attribute to the transfer of electrons to form electrical charge at joint. Usually used in coating industry. 4. 9. MECHANISM FAILURE IN BONDED JOINT Predominant mechanism of failure in adhesivebonded are adhesive, adhesive-cohesive and cohesive failure. It is cause by stress, fatigue, temperature and etc. 10. CRITERIA OF GOOD ADHESIVE BOND Adhesive must be soluble in adherent. Adhesive spontaneously wet the surface. Adhesive with right viscosity to the right adherent. The surface has microscopic roughness. Surface treatment 11. WETTING OF THE SURFACE The adhesive must wet the surface and applied inliquid form. The viscosity of adhesive is critical to wetting, low viscosity make more easy to wet to the surface.