How is recycled polypropylene made?
Polypropylene fiber is made from thermoplastic polymer and is used in a variety of products. One of the most important properties of polypropylene is that it is recyclable in nature. Polypropylene is used mostly in packaging materials. Since it is non-biodegradable in nature i.e. they take 20 to 30 years to decompose, hence most of its products end in landfills. This not only pollutes the environment, but even the toxic chemicals used in its manufacturing like lead and cadmium are also bad for the ecosystem.
Polypropylene or PP can be recycled in a total of five steps which are:
• Collecting: At first the used and thrown away polypropylene bags or containers are collected.
• Sorting: The next step is sorting. In this step, the collected plastics are sorted as per the ‘resin code’ printed on them. Resin code has significant importance during the recycling process of plastics as they tell the type of plastic. This not only helps during the sorting process but also makes the process easy.
Using the ‘sink-float’ method polypropylene is separated from other types of plastic polymer. In this technique, all the plastics are put in the water. Where due to the difference in the specific density of polymers and polypropylene, the polypropylene floats on the surface while the other polymers sink. For light-colored plastics Near Infrared Radiation (NIR) techniques and melt flow index are used to separate the different kinds of plastics.
• Cleaning: In this step, any type of contamination is removed from polypropylene so that during the reprocessing phase there is no foreign material struct between the fibers.
• Reprocessing: In the reprocessing phase, the collected polypropylene products are fed into an extruder and then melted at a temperature of 4640F (2400C). Due to the high temperature inside the extruder, the bonds between hydrogen and carbon molecules become weaker, which results in a change of structural intensity of the PP. After which the materials are cut into small chips or pellets.
• Producing new products: Generally, these small chips or pellets are mixed with virgin polypropylene and are used to produce polypropylene yarns which are then converted into various products like clothes or equipment.
A European company Nextek has developed an innovative process that uses only two steps in the recycling of polypropylene. In the first stage, to get rid of contaminated molecules, the polypropylene is melted at a temperature of 250 °C (500 °F). And in the second step vacuum is used to remove residual molecules. After which the material is solidified at a temperature of 140 °C (280 °F). The final material obtained is used in various products by blending it with 50 percent of the virgin polypropylene