Editorial Feature

Recycling of Polypropylene (PP)

Polypropylene is a polymer plastic that is a member of the ‘polyolefin’ (polymers produced from alkenes) family. It is a highly versatile and rugged material that has many beneficial physical properties, and most importantly it is also recyclable. It resists the action of many chemical solvents.

The PP market is currently projected to reach $133 billion by 2023.

Properties and Applications of Polypropylene (PP)

Polypropylene is an extremely versatile material and can be used for a wide range of applications. PP is tough yet flexible, being classed as semi-rigid. It is extremely resistant to heat, chemicals, and fatigue. Furthermore, it is translucent and has an integral hinge property.

PP has a wide range of uses, including:

  • Clear film packaging
  • Carpet fibers
  • Housewares
  • Rope
  • Labeling
  • Banknotes
  • Stationary
  • Reusable containers
  • Loudspeakers
  • Automotive components
  • Laboratory equipment
  • Thermal underwear

Sandbags made from polypropylene, one of the many applications of this flexible polymer.

Sandbags made from polypropylene, one of the many applications of this flexible polymer. Image Credits: fws.gov

Recycling of Polypropylene

While PP is easily among the most popular plastic packaging materials in the world, only around 1% is recycled, which means most PP is headed for the landfill. These decompose slowly over 20-30 years. 

To determine how recyclable polypropylene is, companies have undertaken ‘life cycle’ studies that look at the plastic from the raw material production to the final stages of waste management to assess the sustainability of the product. The general consensus from these studies is that PP has considerable potential as a sustainable product.

To make the recycling of polypropylene economically viable, several factors must be taken into account, most importantly its difficulty and expense.

There are five steps in PP recycling, namely, collecting, sorting, cleaning, reprocessing, and producing new products.

Plastics will often have a printed ‘resin code’ (5 for PP), which is useful during recycling, as they indicate what type of plastic it is. This ensures separation and efficient recycling of different plastic types.

First, the polypropylene must be separated from other plastic polymers. This is achieved by ‘sink-float’ separation, based on the unique specific density of PP (0..93-0.95g/cm3), which allows it to float while other polymers such as PET (specific density 1.43-1.45 g/cm3) will sink.

Another separation technique is based on the melt flow index, while a third is based on dissolution and reprecipitation of PP. A simple way to identify PP is by using Near Infrared Radiation (NIR) techniques. It must be noted that this cannot work with dark-colored plastics as they absorb the radiation.

PP reprocessing includes melting at a temperature above 400 F in an extruder, followed by granulation for use in new production. Polypropylene is eventually affected by thermal degradation, which compromises the structural intensity of the plastic due to the bonds between hydrogen and carbon becoming weaker. This varies with the use of the PP, but in general, four closed loops of recycling are considered possible before the negative impact of thermal degradation is perceptible.

Recycled PP is generally mixed with virgin PP at up to 50% to produce new products such as clothes or playground equipment.

The resin identification code for polypropylene.

The resin identification code for polypropylene. Image Credit: dnr.wi.gov

The Environmental Benefits of Recycling PP

Recycling of polypropylene is emerging as an important, and economically viable, option on a large scale.

The main benefit of recycling PP is the reduction in the consumption of raw, finite resources such as oil and propane gas. It is estimated that around 8% of the oil used worldwide (around 400 million tons) is utilized in the traditional methods of plastic production, with 4% as ‘feedstock’ and another 4% in manufacturing.

Relative to production from oil and gas, energy use can be reduced by 88% when plastic is produced from plastic.

Given its inherent flexibility, PP can be recycled back into many different products, including:

  • Clothing fibers
  • Industrial fibers
  • Food containers
  • Dishware
  • Compost bins
  • Speed humps
  • Gardening apparatus (compost bins, garden edging, and plant pots)

About 30% of polypropylene is recycled from major industries, but a significant proportion is still dumped into landfills. It is currently not as economically viable to recycle PP as it is to recycle other polymers, in particular, HDPE, LDPE, and PET. It is hoped that this will be changed in the near future with advancements in recycling technology.

On the other hand, it is recognized that materials recycling is not always the most cost-effective recycling method. In such cases, it would be better to use plastics for direct combustion or chemically recycle them into synthetic fuels at the expense of some embedded energy, reducing landfill significantly.

Sources and Further Reading

This article was updated on 14th June, 2019

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

G.P. Thomas

Written by

G.P. Thomas

Gary graduated from the University of Manchester with a first-class honours degree in Geochemistry and a Masters in Earth Sciences. After working in the Australian mining industry, Gary decided to hang up his geology boots and turn his hand to writing. When he isn't developing topical and informative content, Gary can usually be found playing his beloved guitar, or watching Aston Villa FC snatch defeat from the jaws of victory.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Thomas, G.P.. (2022, November 24). Recycling of Polypropylene (PP). AZoCleantech. Retrieved on July 19, 2024 from https://www.azocleantech.com/article.aspx?ArticleID=240.

  • MLA

    Thomas, G.P.. "Recycling of Polypropylene (PP)". AZoCleantech. 19 July 2024. <https://www.azocleantech.com/article.aspx?ArticleID=240>.

  • Chicago

    Thomas, G.P.. "Recycling of Polypropylene (PP)". AZoCleantech. https://www.azocleantech.com/article.aspx?ArticleID=240. (accessed July 19, 2024).

  • Harvard

    Thomas, G.P.. 2022. Recycling of Polypropylene (PP). AZoCleantech, viewed 19 July 2024, https://www.azocleantech.com/article.aspx?ArticleID=240.


  1. Nilesh Parikh Nilesh Parikh India says:

    We wants to wash used pp disposable glasses , we had wash with costic soda, resulting while extrusion materials turn brown.

  2. Jini Patel Thompson Jini Patel Thompson Canada says:

    Here's the problem: Hay bale twine is made from polypropylene. I have been searching for SIX MONTHS to find a facility that will recycle my perfectly clean, color-sorted hay bale twine here in BC Canada (which is supposed to be eco-friendly) and no one will take it! There are 1 million horses in Canada, there are 9.5 million horses in the USA. Each horse eats half a bale (2 strings per bale) per day. That is a MASSIVE amount of PP going into landfills across the continent. And no solutions. 30 years ago all the hay sellers baled using Sisal twine - no problem! Totally biodegradable and a great material to re-use for all kinds of things. Seems to me we have technology backwards... shouldn't we FIRST make sure we have a way to deal with a substance, BEFORE making it widely available to users who have no concern beyond their own profits and efficiency?

    • Stephane Boisjoli Stephane Boisjoli Canada says:

      Jini, it's worse than that.  Most "disposable" plastics are #5, polypropylene.  That means all the plastic the fast foods are pumping out are usually #5 and cannot be recycled in any manner, in most cities.  They are more landfill waste.
      So far the best usage for them is to burn them (for heat or electricity generation), which is far from ideal.
      As for the Sisal twine - I suggest you complain to the manufacturers involved.  If you can, get a petition going and pass it among the customers who use the hay.  If you get enough signatures, eventually the makers will notice.
      As for having no idea how to dispose - that would be a great law, wouldn't it? Force companies to make sure their product can be recycled first before they market it?

      • Viva Yo Viva Yo United Kingdom says:

        2022 and still no law, no infrastructure, and no market has been created to incentivize the recycling of PP flexibles. Unbelievably irresponsible. This is a matter of global responsibility, not just local or national. Disgusted with decision makers.

    • Matt Cowling Matt Cowling United States says:

      I would take all of your PP twine and recycle it, but logistics is always the issue.  PP is very cheap to make- with the amount of excess natural gas and the cheap cost of oil, PP is so easy and cheap to make, it becomes tricky as nobody would want to pay the shipping costs for the twine, which honestly is not that much plastic. In the scope of things, the twine is a blip- but heck, I would love to recycle it and use it in my products.  As far as Stephane comments above- in the USA we recycle PP foodservice containers and cups, and many QSR's are looking at closed loop recycling- thus allowing us to re-use the cups over and over.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoCleantech.com.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Your comment type

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.