Polyethylene terephthalate (PET, PETE or PETP or PET-P) is a thermoplastic polyester resin and is used in synthetic fibers, beverages, food and liquids; can be injection molding to shape; and in the industry often associated with glass fiber.
- PET is one of the materials used in the manufacture of handmade yarns.
- The characteristics of PET are determined by heat treatment, which can exist both as amorphous (transparent) and as crystalline (opaque white). Monomers of PET can be synthesized by the esterification between terepthalic acid and ethylene glycol to produce water, or transesterification reactions between ethylene glycol and dimethyl terepthalate, as methanol. Polymerization is carried out by a monomeric condensation process (immediately after esterification or transesterification) with ethylene glycol as the product (ethylene glycol recovered in production).
- Most of the world's PET is synthetic fibers (60%), which supplies about 30% of the world's demand.
- In the field of yarn, PET is used as polyester in combination with cotton. Mostly, PET is applied extrusion products.
PET is produced under the trade names Arnite, Impet and Rynite, Ertalyte, Hostaphan, Melinex and Mylar films, and Dacron, Diolen, Terylene and Trevira fibers.
- PET can be covered by hard shell or hard shell, which is determined by the layer thickness and the amount of resin required. It forms a very good gas-permeable membrane.
PET bottles contain beverages such as alcohol and others that are durable and resistant to impact. PET is a natural color with high transparency.
- PET can be drawn into thin films (often referred to as mylar). PET is often coated with aluminum to reduce its magnetic conductivity, making it reflective and opaque.
PET bottles are a very good container and are used extensively for liquid drinks. PET or Dacron is also used as a layer of insulating material outside the International Space Station (ISS). In addition, PET insertion between the polyvinyl alcohol film increases the oxygen permeability.
When reinforced with glass or particles, it becomes more rigid and durable. PET is a semi-crystalline form, traded under the trade names Rynite, Arnite, Hostadur & Crastin.
The sails are usually made of Dacron, a type of PET fiber, light in color, lightweight tools usually made of nylon.
- PET was discovered in 1941 by the Calico Printer 'Association of Manchester. PET bottles were produced in 1973.
The properties of PET
One of the important characteristics of PET is its viscosity. The viscosity of the substance is decilit / gram (dl / g) depending on the length of the polymer circuit. The longer the length of the polymer, the higher the solids, the higher the viscosity. The length of a polymer can be adjusted through polymerization.
- Viscosity of some forms:
+ 0.6 dl / g: fiber form.
+ 0.65 dl / g: thin film.
+ 0.76-0.84 dl / g: bottle.
+ 0.85 dl / g: rope type.
- PET can absorb moisture. When moistened, during PET processing, hydrolysis takes place at the contact surface between water and PET, which reduces the molecular weight of PET (or viscosity) and its mechanical properties. . So before the plastic is processed, the moisture must be removed from the plastic. This can be done by using a desiccant or drying agent prior to commissioning.
The process of PET drying
In the oven, hot air is blown from the bottom onto the floor containing the cut PET plates, which are suspended in hot air so that the moisture can be removed. The hot and humid air is taken off the floor and passes through the chiller to remove moisture. Finally, the air is reheated and is returned to the initial PET drum as the cycle is repeated. The moisture content of plastic products must be less than 40 parts per million (one part per million parts by volume) to meet the quality requirements prior to processing. The drying time should not be shorter than 4 hours, because the drying time is less than 4 hours, the temperature of the PET plate is lower than 160oC. At this temperature, the hydrolysis takes place inside the PET particles before they are dried.