Plastics

1. Plastics

2. Plastics Background • Definition the term plastics, as it is commonly used today refers to a large group of synthetic materials which are made from a number of common substances such as coal, salt, oil, natural gas, cotton, wood, and water • Simple chemicals are pulled from the material to produce monomers. Which are capable of reacting with one another, are produced. • Monomers are then built up in a chainlike molecules called polymers

3. Types of Plastics • Developments have produce over 40 groups or families of plastics. Each with its own characteristics, such as light weight, heavy weight, heat-resistant, hard, soft, clear, or opaque. • Two general classifications • Thermoplastics • Thermosetting plastics

4. Thermoplastics • Become soft when heated and hard when cooled, regardless of the number of times the process is repeated • This is due to the fact that linear molecular chains can move together when heated and cooled. • Types of plastics – acrylics, celluloses, polyethylene, polyvinyl chloride (PVC), polystryrene, polyallomers, polycarbonates, polyimide, polypropylene, polysulfone, phenylene oxide nylons, methyl pentenes, ionomer, fluroplastics, acetal and acrylonitrile butradiene styrene (ABS)

5. Thermosetting plastics • Are also chainlike in molecular structure but the curing and hardening process involves the formation of cross-links between molecules in adjacent chains. Resulting in complex chains that are no longer free to move. • Types – alkyds, aminous (urea and melamine formaldehyde), diallylphthalate (DAP), epoxies, furan, phenolics, polyesters, polyurethane, and silicones

6. Production of Plastics • Process of uniting monomers to form polymers is known as polymerization • Accomplished by either a condensation or an addition process • Raw material can come in any of the following forms • Granules • Powder • Beads • Liquid resins

7. Production of Plastics • The raw material is then produced into the following forms • Sheets • Films • Tubing • Rods • Solid or semisolid shape • Additions to plastics • Plasticizers – added for workability • Fillers – are added to produce bulk • Fibers – added for strength and durability • Hardeners – added to induce setting • Plastics products are formed by a number of methods – injection molding, blow molding, expandable bead molding, compression molding, transfer molding, rotational modeling, form modeling, extrusion thermoforming, laminating, casting, and calendaring

8. Injection Molding • Measured amounts of powder or granules are fed into the intake end of the heated barrel of a molding machine. And forced forwarded by a ram. • Heated to temperatures of 300 to 650 c • Pressure from 5000 to 40000 psi • Thermoplastics and thermosets are used.

9. Blow Molding • Three processes • Extrusion blow molding – an extruder produces a hollow tube called a parison which is captured between the two halves of a hollow mold. The mold is close and air is blown into the tube forcing it to expand. • Injection blow molding – process is same except the tube (parison) is injected molded on a steel rod and the rod is removed prior to closing the mold • Stretch blow molding – involves, stretching the parison in the axial direction before blowing. • Polyethylene is typically used, but PVC, polystyrene, and polypropylene are also used. • Bottles and water cans are typical shapes produced

10. Expandable Bead Molding • Process used to produce lightweight products of polystyrene foam • Small granules together with a small amount of an expanding agent are placed in a rolling drum and steam heated • Heat softens the granules and the expanding agent enlarges their size • Cooled and transferred to a mold • Again heated to 135 c and until they fused together • Flotation equipment, shipping containers, rigid insulation are typical products

11. Compression Molding • Simplest form of molding • A measured amount of powder is place in a heated mold then closed • Heat and pressure are applied to the plastic material which melts and flows to all parts of the mold

12. Transfer Molding • Differs from compression molding in that in the transfer molding process the molding compound is liquefied outside the molding chamber • Transfer to the mold under pressure • There the forming and setting takes place

13. Rotational Molding • Used to form hollow units with complex shapes and heavy walls • A pre measured amount of powder or liquid resin is placed in the bottom half of a cold mold and the mold is closed • Mold is heated and rotated. Then allowed to cooled

14. Form Molding • Made by mixing an expanding agent with either granules or powder and then heating it • Heat melts the plastic and causes the formation of a gas which expands the molten material into foamed structure • Quickly cooled to set the material • Insulation is made in this manner

15. Extrusion Thermoforming • Is used to produce materials which have a constant cross section • Heat material is pushed through a die

16. Laminating • Bonding together a number of layers of materials to form a single sheet.

17. Casting • Liquid plastic are poured into molds and set

18. Calendaring • Form of extrusion • Plastic material is fed to a pair of revolving rollers which extrude a thin film or sheet between them

19. Properties of Plastics • Transparency (acrylics, methyl pentenes, polycarbonates, ionomer, polysulfone) • resistance to discoloration (acrylics) • good resistance to weathering (acrylics, epoxy, silicone, polyvinyl chloride) • good dimensional stability (fluoroplastics, polycarbonates, phenylene, oxide, polyvinyl chloride, urea, melamine) • toughness (Cellulosics, ionomer, nylone, phenoxies, polycarbonates, polyethylene) • high impact resistance (acrylics, ethyl cellulose, polypropylene, polyimide, polycarbonates) • abrasion resistance (nylons, polyallomers, polyimide, polypropylene) • low moisture absorption (fluoroplastics, phenylene oxide, polypropylene, diallyl phthalate, silicone) • ductility (phenoxies, acrylics, nylons) • good adhesive qualities (epoxy, phenolics, amino resins) • good resistance to chemicals (nylons polyethylene, phenylene oxide, polypropylene, polysulfone, diallylphthalate)

20. Additives for plastics • not all properties of plastics are positive ones, additives are necessary to reinforce another property. • Antioxidants • antistatic agents • coloring agents • coupling agents • Fillers • reinforcing agents • flame retardants • foaming agents • Lubricants • Plasticizers • Preservatives • processing aids • ultraviolet stabilizers

21. Plastics in Construction • Structural Applications • For use in structural applications plastics need to be reinforced • Glass fiber, jute, cotton, sisal, asbestos, and synthetic and metallic fibers are used • Flat sheets – glazing • Thermoformed shapes – roof shapes, curtain wall • Glass fiber structural shapes – used where corrosion is a problem (like steel members) • Plastic foam boards – decking, roofing • Fabrics – balloons over a pool • Foamed insulation – insulating materials

22. Nonstructural applications • resilient flooring – vinyl tile, vinyl-cushioned flooring, linoleum, cork tile, rubber flooring • Non resilient flooring – plastic terrazzo – plastic topping – • carpets – tufted carpet – woven carpet -  loomed carpet – knitted carpet – needle punched carpet • interior finishes – wall coverings • moisture control – vapor barriers • plastic pipe – pvc • caulking and sealing compounds • paints and varnishes • lights and sunscreens • adhesives • material coatings