Ingeniero quimico

Plastics Industry

The term “plastic” encompasses a broad range of materials. In addition, each has its own special properties and variations when it comes to properties such as hardness, heat tolerance, and resiliency. Nonetheless, each of them is made of organic condensation or addition polymers and can be made into fibers, films, or objects.

Classifying Plastics
There are many methodsused to classify plastics. The most common method is to classify them according to their polymer backbone. Plastics can, however, also be classified according to the glass transition temperature or thermoplastic versus thermoset.
No matter the classification, all plastics are polymers, which is a long chain of atoms that are bonded to one another. These chains are comprised of monomers, which arerepeating molecular units. Most plastics are made of carbon polymers or carbon polymers combined with nitrogen, oxygen, sulfur, or chlorine in the backbone, which is the main path linking the units together. Plastic is then customized by “hanging” different molecular groups to the backbone.
Methods of Processing Plastic

There are a variety of methods used to process plastic. Each method hasits advantages and disadvantages and are better suited for specific applications. These methods include: injection molding, blow molding, thermoforming, transfer molding, reaction injection molding, compression molding, and extrusion.
Injection Molding
The main method used for processing plastic is injection molding. With this process, the plastic is placed into a hopper. The hopper then feedsthe plastic into a heated injection unit, where it is pushed through a long chamber with a reciprocating screw. Here, it is softened to a fluid state.
A nozzle is located at the end of the chamber. The fluid plastic is forced through the nozzle into a cold, closed mold. The halves of the mold are held shut with a system of clamps. When the plastic is cooled and solidified, the halves open and thefinished product is ejected from the press.
Thermosetting materials usually are not processed with injection molding because they will soften, they harden to an infusible state. If they are processed with injection molding, they need to be moved through the heating chamber quickly so they do not set.
Blow Molding
Blow molding is used when the plastic item to be created needs to be hollow. Amolten tube is created with blow molding by using compressed air, which blows up the tube and forces it to conform to the chilled mold. Variations of blow molding include injection, injection-stretch, and extrusion blow molding.
With injection blow molding uses a perform, which is taken to a blow mold and filled with compressed air. As a result, it conforms to the interior design of the blow mold.With injection-stretch blow molding, a the plastic is stretched prior to being formed. Otherwise, it is essentially the same as the injection process.
With continuous-extrusion, a molten plastic tube is continuously created. At the appropriate times, the tube is pinched between two mold halves. Then, a needle or a blow pin is inserted into the tube and blows compressed air up the part in orderto force it to conform to the mold interior. With accumulator-extrusion, the molten plastic material is gathered in the chamber before it is forced through a die in order to form a tube.
Thermoforming
Thermoforming uses a plastic sheet, which is formed with the mold by applying air or through mechanical assistance. The air pressure used can be nearly zero psi, or several hundred psi. At 14 psi,which is equivalent to atmospheric pressure, the pressure is created by evacuating the space between the mold and the sheet. This is known as vacuum forming.
Transfer Molding
Transfer molding is generally used only for forming thermosetting plastics. It is similar to compression molding because the plastic is cured into an infusible state through pressure and heat. Unlike compression molding,...