Question # 1:
PET (Polyethylene terephthalate)
Polyethylene terephthalate which is commonly known as PET is a type of thermoplastics polymers resins. When PET is used in fabrics then it is also called as Polyester which is just like a clothing fabric. PET is lightweight, economical, non reactive and shatterproof that’s why it is highly valued packaging material. Despite its name it does not contain polyethylene. Polyethylene terephthalate (PET) consists of polymerized units of the ethylene terephthalate, with repeating units of C10H8O4
PET may exist both as invisible and also in semi colours.
PET used in many different things such as ...view middle of the document...
It also has low co efficient of friction which makes it superior from other plastics. PET does not leak into liquid that’s why it is used for food storage.
Polyethylene terephthalate (PET) is manufactured by two processes as given below
Ethylene glycol or Dimethyl terephthalate (transesterification)
Terephthalic acid (esterification)
Dimethyl Terephthalate process:
In this process this compound and excess of ethylene glycol are reacted in the melt at 150-200 °C with Methanol which is removed by distillation to drive reaction. Excess ethylene is distilled off at high temperature. The first step is:
C_6 H_4(CO_2CH_3 )_2+2HOCH_2 CH_2 OH→C_6 H_4 (CO_2 CH_2 CH_2 OH)_2+2CH_3 OH
And the second step is:
nC_6 H_4 (CO2CH2CH2OH)2 → [(CO)C6H4(CO2CH2CH2O)]n + n HOCH2CH2OH
Terephthalic acid process:
In this process esterification is conducted directly at pressure of (2.7 - 5.5 bar) and at temperature of 220-260 C and in this water is also eliminated directly by distillation and following step takes place:
n C6H4 (CO2H)2 + n HOCH2CH2OH → [(CO)C6H4(CO2CH2CH2O)]n + 2n H2O
Page # 3
PET is subjected to various types of degradation processes. Some of the degradation during process is thermal, thermal oxidation and hydrolytic. When degradation occurs several thing occurs:
Formation of acetaldehyde
Discoloration occurs due prolonged treatment at elevated temperature. Acetaldehyde is colorless substance with a fruity smell. It can cause off taste the water bottle. It is formed by degradation of mishandling of material. In water bottles acetaldehyde off tastes the water because it diffuses with the walls of container and mixed with water but in fruit juices and shampoo because acetaldehyde is already used in them.
Bottle processing equipment:
There are two fundamental embellishment routines for PET containers, one-stage and two-stage. In two-stage shaping, two different machines are utilized. The primary machine infusion forms the perform, which looks like a test tube, with the jug top strings effectively shaped into spot. The assortment of the tube is altogether thicker, as it will be swelled into its last shape in the second step utilizing stretch blow shaping.
In the second step, the performs are warmed quickly and afterward expanded against a two-part form to structure them into the last state of the flask. Reforms (uninflected containers) are currently additionally utilized as...