What is plastic?Plastic is the term commonly used to refer to a wide range of synthetics or semi-synthetic used in a wide and growing range of applications, ranging from packaging to construction, from cars and medical devices, to that of toys, industry etc.
The word plastic comes from the Greek word "plastikos," which means suitable to be shaped, and that means plastos shaped; and it is precisely the malleability of the material or its plasticity during production, allowing it to be cast, pressed, or extruded into a variety of forms.
The plastic is virtually everywhere, its qualities, such as lightness, versatility, resistance to microorganisms, compatibility with food, make it a material widely used in our daily life.
The plastics are materials that do not exist in nature, but are produced in chemical plants by manipulating the molecules of a raw material, which can be virginnafta or natural gas.
Plastics are those artificial materials with macromolecular structure that under certain conditions of temperature and pressure are permanent changes shape.
Originally many plastics were produced with resins of vegetal origin, e.g. cellulose (cotton), the majority of plastics is currently derived from petrochemicals, easy to use and inexpensive.
The advantageous characteristics of plastics than metals and non-metals are the ease of manufacture, cost-effectiveness, sound insulation, thermal, electrical, mechanical (vibrations), resistance to corrosion and chemical resistance, as well as the water repellency and indifference on the part of mold, fungi and bacteria.
Disadvantageous ones are the attaccabilità from solvents (especially thermoplastics) and acids (in particular the thermosets) and poor resistance to high temperatures.
The polymer are added various auxiliary substances ("positions", additives and plasticizers) depending on the application which the plastic is intended.
These substances have the function (among others) to stabilize, preserve, liquifying, coloring, protect the polymer from oxidation, and generally changing the physical and mechanical properties.
The polymers are divided into three major types (families)
strong > are called thermoplastic Thermoplastic plastics ones who buy malleability, i.e. they soften under the action of heat. At this stage can be shaped or formed into objects and then back to be cooling.
This process theoretically, can be repeated several times depending on the quality of different plastics.
Thermosets The thermosets or resins are a group of plastics which, after an initial phase of softening due to heating, harden for three-dimensional Crosslinking effect; softening time for combined effect of heat and pressure are formabili and once hardened, they have the strength of steel.
If these materials are heated after curing do not return more to soften, but decompose by charring.
The main categories of resins are:
- Epoxy resins
- Phenolic resins
Elastomers Elastomers are synthetic or natural polymers, which possess a characteristic elasticity that allows them, under stress, a lengthening from 1 to 10 times; This is possible thanks to their special molecular structure, composed of large-meshed grids that although strained, as soon as the external force stops work on polymer, immediately return to their initial state.
The main uses of these plastics are:
tires, footwear, adhesives, building components, pipes, electrical cables, components and gaskets for cars.
Figure lists the most common types of polymers and their abbreviations that distinguish them Many plastics (nylon, teflon, plexiglas etc.) lend themselves well to industrial production processes with machine tools in a completely analogous to metals; for this reason they are often produced in semi-finished products such as bars, rods, plates; from which the finished products are then obtained by mechanical processes.
ES. HDPE high density polyethylene PS polystyrene or styrofoam PA polyamide (nylon)
Among the works to which they are subjected, plastics include:
Many plastics (nylon, teflon, plexiglas etc.) lend themselves well to industrial production processes with machine tools in a completely analogous to metals; for this reason they are often produced in semi-finished products such as bars, rods, plates; from which the finished products are then obtained by mechanical processes.
Compression moulding; is a manufacturing process used for the thermosetting plastics.
It is with special presses (called "injection moulding machines"), which merges the plastic granules and inject at high speed and pressure in molds, where the polymer, cooling, assumes the desired geometry. The injection molding process is used both in the case of thermoplastic materials that thermosets.
Extrusion blow Moulding; the material is pushed through a screw through an opening. The final form of the polymer depends on the geometry of the opening. Such as plastic pipes are produced via this process.
Calendering; is a continuous process like extrusion, used for the production of sheet and film still from thermoplastic resins, is also applied in coating processes of textiles, paper and other materials.
Blow moulding; (Blow Molding) process used to produce hollow bodies (such as bottles, drums, tanks, containers for liquids of any kind in plastic). Is to expand a certain portion of resin cylindrical shape with a jet of air under pressure, up to make it adhere to the walls of a mold.
The product is then cooled and extracted from the mold.