The as filler material. Generally employed in electrical moldings,

The
word plastic originates from ‘plastikos’ which means to mold in Greek. The
capability to preserve deformation, after the removal of the load that produced
this deformation, is called Plasticity, as we saw in The Properties of Metals. 

Before the use of synthetic plastic materials, translucent
slices of animal horns were used for lantern windows. The Palaquium Gutta tree possessed
latex called gutta-percha, which was used extensively for cable insulation. The
lac bug’s secretion called shellac was also used.              

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The first synthetic plastic was developed by John Wesley Hyatt.
It was a cheap replacement for ivory. Created from plant cellulose, it was
named Celluloid and patented in 1869.   

 

 

 

    John
Wesley Hyatt

         (1837 – 1920)

Leo Henricus Arthur Baekeland founded
the modern plastic industry by developing a material named Bakelite. The first
completely synthetic plastic material. It was created from phenol-formaldehyde.
It is quite brittle and generally used with mica, asbestos or wood flour as
filler material. Generally employed in electrical moldings, wire insulation,
brake pads etc.     

        Leo Baekeland

    
(1863 – 1944)

However,
nowadays the word plastics has become a generic name used to define carbon
polymers (molecules with long chains), whether synthetic or natural, that can
take any shape by being cast, pressed or molded. They can also be employed as
fibers when elongated into filaments. 

Thermoplastic and Thermosetting compositions are two important
groups of plastics but Elastomers, which are synthetic rubbers, are also
accepted as a component of the plastic industry. 

 

Thermoplastic materials become soft and malleable when heated,
hence their prefix thermo- (which is Greek for heat), but in contrast they are
hard in their normal state. Thermoplastic materials moldable and they can be
given any desired shape when softened. Once cooled, they preserve their new shape.
This procedure can be applied again and again as long as their heat limit isn’t
exceeded.

Aircraft
windshields and side windows are made from two kinds of transparent
thermoplastic material, which are generally called cellulose acetate and
acrylic. 

Cellulose acetate plastic was used in outdated aircraft because
of its light weight and transparency but it has some disadvantages like its
inclination to shrink and become discolored over time, thus it has been almost
been completely phased out. 

Particularly
when aged, it can be recognized by its tint which is slightly yellow and also
the black smoke and sputtering it causes while burning. Some materials like
acetone will also cause it to react and soften upon contact.

The
trade names used to identify acrylic plastics is Perspex in the UK is
Plexiglass in the USA. Compared to cellulose acetate it is more transparent,
stiffer and basically without color. If burned, it has a clear flame and has a
rather pleasant smell. Although application of acetone may leave white stains,
it will have no impact on the material’s hardness.    Specific
tree extracts, as well as other plants are used to obtain natural resins. They
are used in lacquers, linoleum, adhesives and food glazing agents thanks to
being translucent, clear, amber, brown and solid/semi-solid agents. As expected
they are also used in plastics.   Although
resins and plastics are words that are used interchangeably, in actuality they
are very different. Plastics are used to point out the material in the
completed items and resins are usually in flake, pellet, syrup or powder form.
They are the raw materials. Although
resins may be used by themselves to create plastic, generally some additives
are used to support the molding quality of raise the quality of the end
product. The
supplement of inert fillers, in order to condense the resin, can be used to
fill out holes and cracks in the structure. Cotton, glass flock, micro balloons
and fumed silica (aerosol) are common filler materials. Other
typical additives used with resins are stabilizers, flame retardants, antioxidants,
antimicrobial, thickeners,anti-stats,
and impact modifiers. Lubricants and coupling agents are used as processing
aids in addition to various other additives. 
Resins alone lack strength so various synthetic fibers or
‘cloths’ like paper and linen are used in conjunction. Resin is used to
impregnate these fibers. Aircraft control cable pulleys are, for a very long
time, constructed from thermosetting resins, reinforced with layers of linen
cloth. Using high temperatures, these pulleys are cured in a mold and thus
possess high strength and don’t damage to the control cables.    As thermosetting resin like phenol-formaldehyde or urea-formaldehyde
is used to impregnate layers of paper, it can be molded into flat sheets or any
other shape. This material is used as terminal strips or printed circuit boards
since it becomes an extraordinary electrical insulator when hardened.  Polyester
resin can be cast into different shapes or woven into fabric such as nylon when
pressed into fine filaments. It can also be used as a lacquer that is heat
resistant. For
their weight, glass fibers and mat for instance possess great strength but don’t
have enough rigidity. Thus they are impregnated with polyester resin and molded
into any desired form in order to be used as structural materials.  Polyesteris distinct from other materials which cure by evaporation of a
solvent or oil, since polyester cures by chemical action. A styrene monomer is
added to the polyester to make it easier to work on by thinning it because it’s
usually thick and unmanageable.   Inhibitors are used to delay the mixture of polyester and
styrene from curing into a solid mass, which it does eventually when left
untouched, thus these inhibitors improve shelf life. When the inhibitors aren’t wanted any longer and the curing
process will be started, a catalyst is needed. Depending on the mass of the
resin and temperature, an accelerator will of course reduce the curing time of
the resin.  When the catalyst and accelerator produces heat within the resin
through a chemical reaction, the actual cure of the polyester resin takes
place. When a thick layer cures faster than a thin layer, this exothermic
reaction can be observed. The chemical reaction’s heat may cause the material to ‘run
down’, especially if placed vertically, since it becomes less viscous. In order
to increase viscosity, a thixotropic agent is combined with the resin. This
gain in viscosity lets it stay in place.  
In laminated structures, epoxy resin can also be employed,
instead of polyester. Small percentage of shrinkage, capability to adhere to
many types of materials and strength to weight ratio are important
characteristics of epoxy resin.   Epoxy resins need a curing or hardening agent without the
requirement for heat, which is in contrast to  
polyester resins that need a catalyst. Epoxy and polyester resin mixing ratios also vary. In order to
harden, polyester resin has a ratio of 64:1 resin to catalyst ratio while it is
4:1 in the case of epoxy resin.

Traditional materials such as wood, metal and natural rubbers are being
succeeded by plastics. Its use is ever expanding. The properties plastics have,
compared to regular aircraft materials, make them a better choice. Their
popularity can be explained by the