Thermo Setting Plastic 67335

THERMOSETTING -PLASTICS -

A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be done through heat (generally above 200 °C (392 °F)), through a chemical reaction (two-part epoxy, for example),

or irradiation such as electron beam processing. Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductorsand integrated circuits (IC's).

A thermosetting polymer is a prepolymer in a soft solid or viscous state that changes irreversibly into an infusible, insoluble polymer network by curing. Curing can be induced by the action of heat or suitable radiation, or both. A cured thermosetting polymer is called a thermose. Thermosets are permanently set once they are initially formed and cannot be melted. If they are exposed to enough heat, they become brittle and crack or become charred. once a thermosetting plastic object has been formed, it can't be remade into a different object

The linear chains are crosslinked - strongly chemically bonded. This prevents a thermoplastic object from being melted and reformed.

Thermosets are produced in two steps: 1. Linear polymers are formed. 2. The linear polymers are forced into a mold where "curing" takes place. This may involve heating, pressure, and the addition of catalysts. During this process, a cross-linked or

networked structure forms, creating a permanently hard object that is no longer meltable or moldable. Thermosets are good to use for things that will be warmed up such as spatulas and other kitchen tools. They're also used in glues, varnishes, and in electronic components such as circuit boards.

Thermosets are hard to recycle, but today there are methods of crushing the objects into a fine powder form for use as fillers in reinforced thermosets.

Statistics Thermoset materials are generally stronger

than thermoplastic materials due to this 3-D network of bonds, and are also better suited to high-temperature applications up to the decomposition temperature.

Some examples of thermosets are: Polyester fiberglass systems:(SMC Sheet molding compounds and BMC Bulk molding compounds) Vulcanized rubber Bakelite, a phenol-formaldehyde resin (used in electrical insulators and plasticware) Duroplast, similar to Bakelite Urea-formaldehyde foam (used in plywood, particleboard and medium-density fibreboard) Epoxy resin (used as an adhesive and in fibre reinforced plastics such as glass reinforced plastic and graphite-reinforced plastic)

Polyimides (used in printed circuit boards and

in body parts of modern airplanes) Cyanate Esters or Polycyanurates for electronics applications with high demands on dielectric properties

and high glass temperature requirements in composites Mold or Mold Runners (the black plastic part in

Integrated Circuits (IC) or semiconductors) Melamine resin (used on worktop surfaces)

Some methods of molding thermosets are:

Extrusion molding (used for making pipes, threads of fabric and insulation for electrical cables) Reactive injection molding (used for objects like milk bottle crates) Compression molding (used to shape most thermosetting plastics)

Spin casting (used for producing fishing lures and jigs, gaming miniatures, figurines, emblems as well as production and replacement parts)

Injection molding It is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the mold cavity. After a product is designed, usually by an industrial designer or an engineer, molds are made by a moldmaker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entirebody s of cars.

Applications Injection molding is used to create many things such as wire spools, automotive dashboards, and most other plastic products available today. Injection molding is the most common method of part manufacturing.

Some advantages of injection molding are high production rates, repeatable high tolerances, the ability to use a wide range of materials, low labour cost, minimal scrap losses, and little need to finish parts after molding. Some disadvantages of this process are expensive equipment investment, potentially high running costs, and the need to design moldable parts.

Extrusion molding It is a process used to create objects of a fixed cross-sectional profile.

A material is pushed or drawn through a die of the desired cross-section. The two main advantages of this process over other manufacturing processesare its ability to create very complex crosssections and work materials that are brittle,

Because the material only encounters compressive and shear stresses. It also forms finished parts with an excellent surface finish. Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). The extrusion process can be done with the material hot or cold.

Commonly extruded materials include metals, polymers, ceramics, concrete and foodstuffs.

FURTHER CLASSIFICATION OF THERMOSET PLASTICS

Synthetic resins Synthetic resins are materials with similar properties to natural resins—viscous liquids capable of hardening. They are typically manufactured by esterification or soaping oforganic compounds. The classic variety is epoxy resin, manufactured through polymerization-polyaddition or polycondensation reactions, used as a thermoset polymer for adhesives and composites.

Epoxy resin is two times stronger than concrete, seamless and waterproof. Accordingly, it has been mainly in use for industrial flooring purposes since the 1960s. Since 2000, however, epoxy and polyurethane resins are used in interiors as well, mainly in Western Europe.

Lumps of dried resin

Resin in the form of rosin is applied to the bows of stringed instruments (e.g. violin, , sarangi, etc), because of its quality for

adding friction to the hair. Ballet dancers may apply crushed rosin to their shoes to increase grip on a slippery floor. Resin has also been used as a medium for sculpture by artists such as Eva Hesse, and in other types of artwork.

The hard transparent resins, such as the dammars, mastic and sandarac, are principally used for varnishes and cement, while the softer odoriferous oleo-

resins and gum resins containing essential oils (ammoniacum, asafoetida,and scammony) are more largely used for therapeutic purposes and incense.

Polyurethane It is an incredibly resilient, flexible, and durable manufactured material

that can take the place of paint, cotton, rubber, metal, and wood in thousands of applications across all fields. Polyurethane might be hard, like fiberglass, squishy like upholstery foam, protective like varnish,

bouncy like rubber wheels, or sticky like glue. Since its invention in the 40s, polyurethane has been used in everything from baby toys to airplane wings, and continues to be adapted for contemporary technology.

POLYURETHANE FOAM

Polyurethane is a substance categorized as a polymer based on its chemical structure. One manufacturers polyurethane by combining a diisocyanate and a diol, two monomers, through a chemical reaction. This makes a basic material whose variations can be stretched, smashed, or scratched, and remain fairly indestructible. Depending on the different diisocyanates and diol or polyol constituents, the resulting polyurethane might take a liquid, form, or solid form, each with advantages and limitations.

Some polyurethane is categorized as an elastomer. It has elastic properties while maintaining some rigidity, such as in the wheels of a dolly that absorb shock but don't compress too much. It can be extremely flexible when used as a foam insulator

in construction or a foam cushion in upholstery. It can be deformed over and over and still maintain its original shape; in other words

POLYURETHANE MUSHROOM

Uses – Over three quarters of the consumption of polyurethane products is in the form of foams, with flexible and rigid types being roughly equal in market size. Polyurethane materials are also used in coatings and

varnishes used in furniture manufacture, carpentry or woodworking. Polyurethane is also used as an adhesive, especially as a woodworking glue. Its main advantage over more traditional wood glues is its water

resistance. It is also used in making solid tires. Modern roller blading and skateboarding became economical only with the introduction of tough, abrasion-resistant polyurethane parts.

Polyester resin One of a group of synthetic resins which undergo polymerization during curing; advantageous because high pressure is not required for curing; has excellent adhesive properties, high strength, good chemical resistance; esp. used in laminating and impregnating materials.

FREE FLOW POLYSTER RESIN

THERMOPLASTIC What are thermoplastic composites? Thermoplastics are linear or branched macromolecules, which are held together by weak secondary bonds. The macromolecules can be linear or branched. If the polymeric molecules have few branches which increase the distance between the main chains, then the parallel lengths of the chains can form crystalline regions. Due to the limited mobility of the polymer chains, a thermoplastic will never reach a fully crystalline state: the material is at most semi-crystalline. Multi-branched molecules cannot be close together so there will be less crystallinity and the density will be lower. Polymers with low crystallinity are called amorphous.

Schematic representation of currently used thermoplastic polymers. [www.solvayadvancedpolymers.com]

FEATURE OF THE FIGURE •The bottom of the pyramid shows the commodity polymers, while the top shows the ultra-polymers •Typically, the temperature resistance of these polymers is relatively low. More sophisticated thermoplastic polymers can stand higher temperatures and show better mechanical USES properties. •.The commodity polymers are cheap and used in bulk products, for instance polystyrene is used for CD and DVD cases, while polyethylene is used for shopping bags. • The high-performance and ultra polymers, such as polyphenylenesulfide (PPS) or polyetheretherketone (PEEK) are typically used in fibre reinforced parts for

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