The 7 types of plastics
Mostly obtained by the polymerization of compounds extracted from petroleum, coal and natural gas. There are also plastics that are manufactured by transforming natural substances, such as vulcanized rubber, cellophane or artificial wax.
When heated for the first time, they soften and can be shaped under pressure. But, in this case, the heat initiates an irreversible chemical reaction, so that the plastic becomes rigid and, when heated again, does not soften any more.
The granulate falls down the hopper and enters the auger, which moves it forward. When in contact with the heating belts, the mass is heated until it melts, acquiring a soft, compact and homogeneous structure.
The dough goes through the tronquel (breaker plate) and acquires its final shape. Later the product is cooled by coming into contact with the cooling walls and is then adapted to the product to be manufactured.
The extruder melts the plastic and thanks to a hydraulic piston the closing unit opens and closes the mold, in that way it introduces the melted plastic inside and closes. With the cooling the plastic cools down and becomes solid leaving the desired part.
These changes in the material have a direct impact on its recyclability. Thus, the elements of its composition will determine how possible it is to recover material from these plastics for reuse and establish a less polluting consumption chain.
It is used in beverage bottles such as soft drinks or water, as well as in other light packaging such as food packages, cream jars and other pharmaceutical uses. Its second life is usually new bottles, textiles for clothing, carpets, models, tarpaulins and nautical sails or threads and ropes. Its recyclability level is 1 and the toxic substances it contains are antimony, formaldehyde, acetaldehyde and phthalate. It accounts for 11% of plastic waste on the planet.
It is used in many non-transparent containers such as milk bottles, detergents, food packages and motor oil. Its use after recycling is usually for new packaging, boxes, flower pots, garbage containers, toys, pipes, pieces of urban and garden furniture or new detergent bottles. Although its recyclability level is 1, it is a more resistant material than PET and contains antimony as a toxic substance. It accounts for 14% of plastic waste in the environment.
Types of plastics and their characteristics
Plastic welding is the operation of creating a molecular bond between two thermoplastics that are compatible in nature. Hot gas welding is the process we use most frequently to weld plastics.
We recommend a thermoplastic pipe welding process that uses heat to join two polymer-based products. The heat softens the plastic and then pushes or fuses it together to join the two pieces. This results in a viable and stable bond.
Welding applications: Plastic pipe welding can be done with the use of heat or by using a chemical solvent, depending on the type of plastic being fused. With heat, a plastic is softened to make it flexible. Heat is applied in a variety of ways, including steam, hot gas, a welding rod, a hot plate or a laser. With the plastics softened, they are placed in a press, where pressure is added, causing the edges to come together. Constant pressure is essential to ensure the high quality of a weld.
The thermally induced unidirectional memory effect is an effect classified within the new so-called smart materials. Polymers with thermal memory effect are new materials, whose applications are recently being studied in different fields of science (e.g., medicine), communications and entertainment.
Polymers with thermal memory effect are those polymers that respond to external stimuli and because of this have the ability to change their shape. The thermally induced memory effect results from a combination of appropriate processing and system programming.
In the first step the polymers are processed by means of common techniques, such as injection or extrusion, thermoforming, at a temperature (TAhigh) at which the polymer melts, obtaining a final shape which is called “permanent” shape.
The next step is called system programming and involves heating the sample to a transition temperature (TTrans). At that temperature the polymer is deformed, reaching a shape called “temporary”. Immediately afterwards the temperature of the sample is lowered.