EBB 220/3 POLYMER ADDITIVES

1. EBB 220/3POLYMER ADDITIVES

2. Introduction • Most of polymers need to add with specific ingredients to obtain desirable properties. • Additives were used: • To improved or modify the mechanical, chemical, and physical properties • To prevent degradation (both during fabrication and in service) • To reduce materials costs • To improve the processability • Each of the additives in formulation has specific functions either during processing or end products applications • Typical additives include • filler materials, • Plasticizer • stabilizers, • colorants • flame retardants.

3. Fillers • Fillers normally add in polymeric materials for economical or technical • Filler materials are most often added to polymers to improve tensile and compression strengths, abrasion resistance, toughness, dimensional and thermal stability and other properties.

4. Fillers • Materials used as particulate fillers  include wood flour (finely powdered sawdust), silica flour and sand, glass, clay, talc, limestone, and even some synthetic polymers. • Particle sizes range all the way from 10 nm to macroscopic dimensions • Because these inexpensive materials replace some volume of the more expensive polymer, the cost of the final product is reduced.

5. Plasticizers • Can be in liquid, half solid or solid form. • It must be compatible with the polymeric materials and other compounding ingredients  incompatibility will results in poor processing properties. • Plasticizer were used for: • ‘extender’ (large amount >20 pphr) to make the end products cheaper • Processing aid (small amount 2-5 pphr) to make the processing easier • Modifier  to modifies some polymeric properties.

6. The aid of additives called plasticizers can : • improved the flexibility, ductility, and toughness • produces reductions in hardness and stiffness • lowers the glass transition temperature  at ambient conditions the polymers may be used in applications requiring some degree of flexibility and ductility. • These applications include thin sheets or films, tubing, raincoats, and curtains.

7. Stabilizers • Some polymeric materials under normal environmental conditions are subject rapid deterioration in mechanical properties. • Most often this deterioration is a result of exposure to light  in particular ultraviolet radiation and oxidation • Ultraviolet radiation  • causes a severance of some of the covalent bonds along the molecular chain • also result in some crosslinking. • Oxidation deterioration is a consequence of the chemical interaction between oxygen atoms and the polymer molecules. • Additives that counteract these deteriorative processes are called stabilizers.

8. Colorants • Colorantsimpart a specific color to a polymer • They may be added in the form of: • dyes • The molecules in a dye actually dissolve and become part of the molecular structure of the polymer. • pigments. • Pigments are filler materials that do not dissolve  but remain as a separate phase; • have a small particle size, are transparent, and have a refractive index near to that of the parent polymer. • Others may impart opacity as well as color to the polymer.

9. Flame retardants • The flammability of polymeric materials is a major concern, especially in the manufacture of textiles and children's toys. • Most polymers are flammable in their pure form  exceptions include those containing significant contents of chlorine and/or fluorine such as polyvinyl chloride (PVC) and polytetrafluoroethylene (PTFE). • The flammability resistance of the remaining combustible polymers enhanced by additives called flame retardants. • These retardants may function by • interfering with the combustion process through the gas phase, or • by initiating a chemical reaction that causes a cooling of the combustion region and a termination of burning.

10. Special purpose additives

11. Example of the exams question • What is the function of additives in polymeric materials? • Discuss the used of fillers as one of polymer compounding ingredients.

12. EBB 220/3MISCELLANEOUS APPLICATIONS

13. Coating • Coating are frequently applied to the surface of materials to serve one or more of the following function: • to protect the item from the environment that may produce corrosive or deteriorative reactions; • to improve the item's appearance • to provide electrical insulation.

14. Many of the ingredients in coating materials are polymers  with majority are organic in origin • These organic coatings fall into several different classifications: • paint, • varnish, • enamel, • lacquer, and • shellac :

15. Adhesives • An adhesive  substance used to join together the surfaces of two solid material (termed "adherends") to produce a joint with a high shear strength • Adhesives may come from either natural or synthetic sources. • Some modern adhesives are extremely strong, and becoming increasingly important in modern construction and industry

16. Polymeric materials that fall within the classifications of thermoplastics, them setting resins, elastomeric compounds, and natural adhesives (animal glue, cast starch, and resin) may serve adhesive functions. • Polymer adhesives may be used to join a large variety of material combinations: metal-metal, metal-plastic, metal-ceramic, and so on. • The primary drawback is the service temperature limitation. • Organic polymers maintain their mechanical integrity only at relatively low temperatures, and strength decreases rapidly with increasing temperature.

17. Some categories of adhesives • Natural adhesives • Adhesives based on vegetable (natural resin), food (animal hide and skin), and mineral sources (inorganic materials). • Synthetic adhesives • Adhesives based on elastomers, thermoplastic, and thermosetting adhesives. • Drying adhesives • These adhesives are a mixture of ingredients  polymer dissolved in a solvent e.g. glues and rubber cements • As the solvent evaporates  the adhesive hardens and they will adhere to different materials to greater or lesser degrees. • These adhesives are typically weak and are used for household applications. Some intended for small children are now made non-toxic. • Hot adhesives (thermoplastic adhesives) • Also known as "hot melt" adhesives • they are applied hot and simply allowed to harden as they cool. • These adhesives have become popular for crafts because of their ease of use and the wide range of common materials to which they can adhere.

18. Adhesives failure • Adhesives may fail in one of two ways: • Adhesive failure is the failure of the adhesive to stick or bond with the material to be adhered (also known as the substrate or adherend). • Cohesive failure is structural failure of the adhesive. Adhesive remains on both substrate surfaces, but the two items separate. • Two substrates can also separate through structural failure of one of the substrates  • this is not a failure of the adhesive. In this case the adhesive remains intact and is still bonded to one substrate and the remnants of the other. • For example, • when one removes a price label, adhesive usually remains on the label and the surface  this is cohesive failure. • If, however, a layer of paper remains stuck to the surface  the adhesive has not failed. • when someone tries to pull apart oreo cookies with the filling all on one side. The goal is an adhesive failure, rather than a cohesive failure.

19. Films • Polymeric materials have found widespread use the form of thin films. • Films having thicknesses between 0.001-0.0005 in (0.025 -0.125 mm) • Used extensively as • bags for packaging food products and other merchandise, • as textile products, and a host of other uses. • Important characteristics of the materials produced and used as films include: • Low density, • high degree of flexibility, • high tensile and tear strengths, • resistance attack by moisture and other chemicals, • low permeability to some gases, especially water vapor.

20. Some of the polymers that meet these criteria and are manufactured in film form are: • polyethylene, • polypropylene, • cellophane, and • cellulose etate. • There are several forming methods: • simply extruded through a thin die slit followed by a rolling operation that serves to reduce thickness and improve strength. • Blown moulding • continuous tubing is extruded through an annular die; and maintaining a controlled positive gas pressure inside the tube, • wall thickness may be continuously reduced( to produce a thin cylindrical film, which may be cut and laid flat. • Some of the newer films  produce using co extrusion that is, multi layers of more than one polymer type are extruded simultaneously.

21. Foams • Very porous plastic materials  produced in a process called foaming • Both thermoplastic and thermosetting materials may be foamed by  including in the batch a blowing agent • upon heating decomposes with the liberation of a gas. • gas bubbles are generated throughout the now-fluid mass remain as pores up cooling and give rise to a sponge-like structure. • The same effect is produced bubbling an inert gas through a material while it is in a molten state.

22. Some of commonly foamed polymers are : • polyurethane, • rubber, • polystyrene, and • polyvinyl chloride. • Foams are commonly used as: • cushions in automobiles and furniture • in packaging and • thermal insulation.

23. Example of the exams question • Discuss two of the various applications of polymeric materials. • What are the polymer characteristic to produced a film?