Plastics Reference book

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Reference book for engineers and designers regarding design of plastics.

Text of Plastics Reference book

  • CHAPTER CHAPTER NAME

    1. Plastics

    History

    Composition

    Polymerization process

    Composition

    Properties of plastics

    Common plastics & uses

    Different manufacturing processes for Plastics:

    Injection Moulding.

    Compression Moulding.

    Blow Moulding.

    Compression Moulding.

    Plastics Extrusion.

    Thermoforming.

    Slush Moulding.

    Transfer moulding.

    Calendaring.

    Gate type

    Design Rules For Plastic Parts:

    Maximum wall thickness

    Corners

    Draft

    Ribs

    Bosses

    Undercuts

    Threads

    TYPICAL NOMINAL THICKNESS FOR VARIOUS

    CLASSES OF THERMOPLASTICS

    DEFECTS of PLASTICS

    Welding Techniques

    Hot gas welding

    Heat seal

    Freehand welding

    Speed tip welding

    Extrusion welding

    Contact welding

  • Hot plate welding

    High frequency welding

    Injection welding

    Ultrasonic welding

    Friction welding

    Spin welding

    Laser welding

    Transparent Laser Plastic Welding

    Solvent welding

    Welding rod

    PLASTICS Growing demand in the automotive sector

    Plastics In Automotive Markets Today

    Abbreviations

  • PLASTICS:

    A plastic material is any of a wide range of synthetic or semi-synthetic organic solids

    that are mouldable. Plastics are typically organic polymers of high molecular mass, but they

    often contain other substances. They are usually synthetic, most commonly derived from

    petrochemicals, but many are partially natural.

    History

    Early plastics were bio-derived materials such as egg and blood proteins, which are

    organic polymers. Treated cattle horns were used as windows for lanterns in the Middle

    Ages. Materials that mimicked the properties of horns were developed by treating milk-

    proteins (casein) with lye. In the 1800s the development of plastics accelerated with Charles

    Goodyear's discovery of vulcanization as a route to thermoset materials derived from natural

    rubber. Many storied materials were reported as industrial chemistry was developed in the

    1800s. In the early 1900s, Bakelite, the first fully synthetic thermoset was reported by

    Belgian chemist Leo Baekeland. After the First World War, improvements in chemical

    technology led to an explosion in new forms of plastics. Among the earliest examples in the

    wave of new polymers were polystyrene (PS) and polyvinyl chloride (PVC). The

    development of plastics has come from the use of natural plastic materials (e.g., chewing

  • gum, shellac) to the use of chemically modified natural materials (e.g., rubber,

    nitrocellulose, collagen, galalite) and finally to completely synthetic molecules

    (e.g., bakelite, epoxy, polyvinyl chloride).

    Bakelite

    The first so called plastic based on a synthetic polymer was made

    from phenol and formaldehyde, with the first viable and cheap synthesis methods invented in

    1907, by Leo Hendrik Baekeland, a Belgian-born American living in New York state.

    Baekeland was looking for an insulating shellac to coat wires in electric motors and

    generators. He found that combining phenol (C6H5OH) and formaldehyde (HCOH) formed a

    sticky mass and later found that the material could be mixed with wood flour, asbestos, or

    slate dust to create strong and fire resistant "composite" materials. The new material tended

    to foam during synthesis, requiring that Baekeland build pressure vessels to force out the

    bubbles and provide a smooth, uniform product, as he announced in 1909, in a meeting of the

    American Chemical Society.[12]

    Bakelite was originally used for electrical and mechanical

    parts, coming into widespread use in consumer goods and jewelry in the 1920s. Bakelite was

    a purely synthetic material, not derived from living matter. It was also an early thermosetting

    plastic.

    ASTM: American Standard Test Methods; is a scientific organisation defining standards on

    physical and mechanical testing of materials to obtain objective characteristics used for

    comparison purposes and for design of articles. The standards are partly used to formulate

    ISO (International Standards Organisation) ones.

    Composition

    Most plastics contain organic polymers. The vast majority of these polymers are

    based on chains of carbon atoms alone or with oxygen, sulphur, or nitrogen as well. The

    backbone is that part of the chain on the main "path" linking a large number of repeat units

    together. To customize the properties of a plastic, different molecular groups "hang" from the

    backbone (usually they are "hung" as part of the monomers before linking monomers

  • together to form the polymer chain). The structure of these "side chains" influence the

    properties of the polymer. This fine tuning of the properties of the polymer by repeating unit's

    molecular structure has allowed plastics to become an indispensable part of the twenty-first

    century world.

    Additives

    Additives: these are in general low molecular weight chemicals added to plastics and

    rubbers to improve certain characteristics such as ultraviolet absorbers, antioxidants and heat

    stabilisers, lubricants, plasticisers, flame retardants, cross-linking and blowing agents,

    pigments and dyes. Impact modifiers are polymeric materials added to improve the impact

    resistance of e.g. PVC, PP, PBT, PA. A separate class of additives are the fillers such as

    talcum, wood flour, and reinforcing agents like glass and carbon fibres.

    Alloys: strictly speaking, alloys refer to metals and do not exist in plastics. The term is used

    interchangeably with blends for mixtures of two or more polymers. Examples are alloys or

    blends of polycarbonate (PC) with ABS or with polybutylene terephthalate (PBT).

    Blend" an intimate mixture of two or more polymers to obtain the good properties of each,

    for example semi-crystalline polypropylene (PP) mixed with 10 to 30% rubbery EPDM

    results in a blend with good heat resistance and extraordinary impact resistance. Also the mix

    of polycarbonate (PC) with ABS terpolymer results in a blend with the good heat resistance

    of the PC part and the low temperature impact resistance of the ABS. Instead of the term

    blend, trade literature and producers also use alloy. Blends are made passing the components

    in powder or pellet form in a dry blender followed by a heated twin screw extruder to obtain

    an intimate blend.

    Polymerization process Plastics are one group of polymers that are built from relatively simple units called

    monomers (or mers) through a chemical polymerization process. This process is illustrated

    below. Processing polymers into end products mainly involves physical phase change such as

    melting and solidification (for Thermoplastics) or a chemical reaction (for Thermosets).

    Structure of polymers The basic structure of a polymer molecule can be visualized as

    a long chain of repeating units, with additional chemical groups forming pendant branches

    along the primary "backbone" of the molecule. Although the term plastics has been used

    loosely as a synonym for polymer and resin, plastics generally represent polymeric

    compounds that are formulated with plasticizers, stabilizers, fillers, and other additives for

    purposes of processability and performance. Other polymeric systems include rubbers, fibers,

    adhesives, and surface coatings. A variety of processes have been employed to produce the

    final plastic parts,

  • Polymer family, the formation of plastics, and the polymerization process

    Classification

    Plastics are usually classified by their chemical structure of the polymer's backbone

    and side chains. Some important groups in these classifications are

    the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also

    be classified by the chemical process used in their synthesis, such as condensation, poly-

    addition, and cross-linking.

    There are two types of plastics: thermoplastics and thermosetting polymers.

    Thermoplastics are the plastics that do not undergo chemical change in their composition

    when heated and can be molded again and again.

    Thermoplastics

    A Thermoplastic, also known as a thermosoftening plastic, is a polymer that

    becomes pliable or moldable above a specific temperature, and returns to a solid state upon

    cooling. Most thermoplastics have a high molecular weight, whose chains associate

    through intermolecular forces; this property allows thermoplastics to be remolded because the

    intermolecular interactions spontaneously reform upon cooling. In this way, thermoplastics

    differ from thermosetting polymers, which form irreversible chemical bonds during the

    curing process; thermoset bonds break down upon melting and do not reform upon cooling.

    Thermoplastic materials can be formed into desired shapes under heat and pressure and

    become solids on cooling.

    If they are subjected to the same conditions of heat and pressure, they can be reprocessed

    into new shapes.

    Thermoplastics based on their crystallization are classified into

  • Amorphous Thermoplastics

    Some thermoplastics donot crystallise on heating and are termed as amorphous plastics

    Used in applications where clarity is important.

    They a