Polimeros

Plastic (polymer)

A polymer is a chemical compound or mixture of compounds consisting of repeating structural units created through a process of polymerization.The term derives from the ancient Greek word πολύς (polus, meaning "many, much") and μέρος (meros, meaning "parts"), and refers to a molecule whose structure is composed of multiple repeating units, from which originates acharacteristic of high relative molecular mass and attendant properties. The units composing polymers derive, actually or conceptually, from molecules of low relative molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a definition distinct from the modern IUPAC definition. Starch, cellulose, silk and DNA are examples of natural polymers, the most common of these and amongsynthetic polymers find nylon, polyethylene and Bakelite.
Polymerization
The reaction whereby a polymer is synthesized from its monomer is called polymerization. According to the mechanism by which the polymerization reaction occurs to give the polymer, it is classified as a "step polymerization" or "PCR". In any case, the size of the chain depends on parameters such as temperature or reaction time,each chain having a different size, and therefore a different molecular mass; there is talk of average mass of the polymer.
Types of polymerization
Condensation polymerization.
At each junction of two monomers is lost a small molecule, for example water. Because of this, the molecular mass of the polymer is not necessarily an exact multiple of the molecular mass of the monomer. Condensationpolymers are divided into two groups:
Homopolymers.
1. Polyethylene
2. Silicones
Copolymers.
1. Bakelite.
2.Polyesters.
3. Polyamides.
Step polymerization (condensation) takes at least bifunctional monomers. You should know that the polymers can be machinable.
Example: HOOC - R 1 - NH 2
If reacts with itself, then:
2 HOOC - R 1 - NH 2 <----> HOOC - R 1 - NH · · + OC - R1 - NH2 + H2O<----> HOOC - R1-NH - CO - R1 - NH2 + H2O
Addition polymerization.
In this type of polymerization the molecular mass of the polymer is an exact multiple of the molecular mass of the monomer.
They usually follow a three-step mechanism, with hemolytic rupture:
Initiation: CH2 = CHCl + catalyst CH2-CHCl ⇒ • •
Propagation or growth: CH2-CHCl 2 • • ⇒ • CH2-CH2-CHCl-CHCl •
Termination: Freeradicals are joined end to impurities or two chains are joined with a terminal neutralized.

Polymerization of styrene to give polystyrene n indicates the degree of polymerization

Moreover, the polymers may be linear, consisting of a single chain of monomers, or this chain may have branches of varying sizes. Can also form crosslinks caused by the bond between atoms of different chains.
Thechemical nature of the monomers, their molecular mass and other physical properties as well as the structure that present different characteristics determined for each polymer. For example, if a polymer has cross linking, the material will be more difficult to melt if not present any.
Carbon bonds in polymers are not equivalent to each other, so depending on the stereochemical order of links, apolymer can be: atactic (not in order), isotactic (same order) or syndiotactic (alternating order) to this conformation is tacticity flame. The properties of a polymer may be modified depending on their stereochemistry severely.


Waste Management
Plastic is one of the materials to be disposed occupies the largest volume in landfills. Therefore it is very important that this material isrecycled, thus avoiding disposal.
There are different types of plastics: PET, HDPE, PVC, LDPE, PP, PS and others and that is why the separation is the first step in the recycling process (primary).
Then, it proceeds to where the plastic granulate is milled. The third step is the last cleaning and pelleting where the granulated plastic is melted and passed through a thin tube which takes the form of...