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Q&A: Materials

Plastics are materials consisting of a wide range of synthetic compounds including carbon, hydrogen, oxygen, nitrogen, chlorine etc. derived from petroleum, petroleum gas, coal, plant, air, water, salt etc. mixed with additives and fillers as needed.

These are classified or grouped as ;

・Thermosets and Thermoplastics based on thermal characteristics,

・Crystalline and Amorphous based on arrangement of molecules and

・Commodity plastics and Engineering plastics based on heat resistance.

Rubbers, fibers, paints and adhesives are usually not dealt with in plastics.

A polymer is a large molecule composed of many repeated subunits.  Polymers are created by polymerization of many small molecules known as monomers.

Polymers include:

・Plastics such as synthetic polymers, Polyethylene, Polystyrene…,

・Rubbers such as natural/biological polymer, Polyisoprene…,

・Biological macromolecules such as Protein, DNA etc.

There is a group of plastics materials that are used in very large quantities because they are low-cost and suitable for a wide variety of applications. Such plastics are called commodity plastics.

PE, PP, PS, and PVC are typical of this group. They are collectively called the “four major commodity plastics”. Sometimes one of them, PE, is further divided into low-density polyethylene (LDPE) and high-density polyethylene (HDPE). In this case, they are called the ” five major commodity plastics”.  (CT 2-2 P3, METI)

Almost ideal polyethylene (PE) fibers are stronger than steel even if the two materials of equal thickness are compared.

An extremely large is required to tear off the carbon-carbon bonds of polyethylene. So, if we completely aligned the directions in which PE molecules are arranged, the force acting in this direction would be stronger than iron.

The PE fiber produced by the called ultra-drawing or super-drawing is stronger than iron. This fiber is used for applications such as ropes tying  a large ship to port and bullet proof vests etc.

You may not believe that PE is stronger than iron. But, it is no wonder. This fact makes sense because diamond made up of the same carbon-carbon bonds alone is extremely strong.

Engineering plastics are usually defined as “high-performance plastics that are used in industrial applications and that have a heat resistance of over 100 degree C”. Typical examples are Polycarbonate (PC), Polyamide (PA) or Nylon, Polybutyleneterephthalate (PBT), Polyoxymethylene (POM) or Polyacetal and modified Polyphenyleneether (mPPE). These are called “5 major engineering plastics”.