PLASTIC

Plastic is a material consisting of any of a wide range of synthetic or semi-synthetic organics that are malleable and can bemolded into solid objects of diverse shapes. Plastics are typically organic polymers of high molecular mass, but they often contain other substances.

The world’s first fully synthetic plastic was bakelite, invented in New York in 1907 by Leo Baekeland who coined the term ‘plastics’. Many chemists contributed to the materials scienceof plastics, including Nobel laureate Hermann Staudinger who has been called “the father ofpolymer chemistry” and Herman Mark, known as “the father of polymer physics”.

Common plastics and uses

A chair made with a polypropylene seat

  • Polyester (PES) – Fibers, textiles.
  • Polyethylene terephthalate (PET) – Carbonated drinks bottles, peanut butter jars, plastic film, microwavable packaging.
  • Polyethylene (PE) – Wide range of inexpensive uses including supermarket bags, plastic bottles.
  • High-density polyethylene (HDPE) – Detergent bottles, milk jugs, and molded plastic cases.
  • Polyvinyl chloride (PVC) – Plumbing pipes and guttering, shower curtains, window frames, flooring.
  • Polyvinylidene chloride (PVDC) (Saran) – Food packaging.
  • Low-density polyethylene (LDPE) – Outdoor furniture, siding, floor tiles, shower curtains, clamshell packaging.
  • Polypropylene (PP) – Bottle caps, drinking straws, yogurt containers, appliances, car fenders (bumpers), plastic pressure pipe systems.
  • Polystyrene (PS) – Packaging foam/”peanuts”, food containers, plastic tableware, disposable cups, plates, cutlery, CD and cassette boxes.
  • High impact polystyrene (HIPS) -: Refrigerator liners, food packaging, vending cups.
  • Polyamides (PA) (Nylons) – Fibers, toothbrush bristles, tubing, fishing line, low strength machine parts: under-the-hood car engine parts or gun frames.
  • Acrylonitrile butadiene styrene (ABS) – Electronic equipment cases (e.g., computer monitors, printers, keyboards), drainage pipe.
  • Polyethylene/Acrylonitrile Butadiene Styrene (PE/ABS) – A slippery blend of PE and ABS used in low-duty dry bearings.
  • Polycarbonate (PC) – Compact discs, eyeglasses, riot shields, security windows, traffic lights, lenses.
  • Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS) – A blend of PC and ABS that creates a stronger plastic. Used in car interior and exterior parts, and mobile phone bodies.
  • Polyurethanes (PU) – Cushioning foams, thermal insulation foams, surface coatings, printing rollers (Currently 6th or 7th most commonly used plastic material, for instance the most commonly used plastic in cars).

Classification

Thermoplastics and thermosetting polymers

There are two types of plastics: thermo-plastics and thermo-setting polymers. Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be molded again and again. Examples include polyethylene, polypropylene, polystyrene and polyvinyl chloride. Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as repeat units, derived from monomers; each polymer chain will have several thousand repeating units.

Thermosets can melt and take shape once; after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization of rubber is a thermosetting process. Before heating with sulfur, the polyisoprene is a tacky, slightly runny material, but after vulcanization the product is rigid and non-tacky.

THERMO-SETTING PLASTICS

Thermoset Curing Process

Thermoset plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product remelting when heat is applied, making thermosets ideal for high-heat applications such as electronics and appliances.

Features & Benefits

Thermoset plastics significantly improve the material’s mechanical properties, providing enhances chemical resistance, heat resistance and structural integrity. Thermoset plastics are often used for sealed products due to their resistance to deformation.

Pros

  • More resistant to high temperatures than thermoplastics
  • Highly flexible design
  • Thick to thin wall capabilities
  • Excellent aesthetic appearance
  • High levels of dimensional stability
  • Cost-effective

Cons

  • Cannot be recycled
  • More difficult to surface finish
  • Cannot be remolded or reshaped

THERMO PLASTICS

Thermoplastics Curing Process

Thermoplastics pellets soften when heated and become more fluid as additional heat is applied. The curing process is completely reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be remolded and recycled without negatively affecting the material’s physical properties.

Features & Benefits

There are multiple thermoplastic resins that offer various performance benefits, but most materials commonly offer high strength, shrink-resistance and easy bendability. Depending on the resin, thermoplastics can serve low-stress applications such as plastic bags or high-stress mechanical parts.

Pros

  • Highly recyclable
  • Aesthetically-superior finishes
  • High-impact resistance
  • Remolding/reshaping capabilities
  • Chemical resistant
  • Hard crystalline or rubbery surface options
  • Eco-friendly manufacturing

Cons

  • Generally more expensive than thermoset
  • Can melt if heated

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One comment

  1. Sayan Munshi · December 2, 2015

    Reblogged this on curator.

    Like

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