By Shell Polymers on Sep 01, 2021
Increase Supply Confidence By Substituting Polypropylene with Polyethylene
With U.S. polyethylene production volumes totaling 22.67 million metric tons1 and polypropylene at 7.65 million metric tons2 in 2019, these are two of the most commonly used plastic resins3 . With the plastic shortages affecting converters, having the ability to use polyethylene as a replacement for polypropylene when supplies are low is critical to a business’ bottom line. While they may seem similar, each type of plastic has well-defined characteristics that provide different benefits for converters and, ultimately, consumers. To understand polyethylene’s ability to substitute in for polypropylene, it’s important to know each material's advantages and properties.
Polyethylene Properties and Advantages
Polyethylene is known for its lightweight nature, durability and affordability. It is commonly used as a material for trash and grocery bags, bottles, pipes, and playgrounds with high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) being the most common forms.
Both forms of polyethylene can be mixed with additives to make them opaque and offer UV protection. Plus, both materials have high versatility as they can be made into different forms for different use cases across various industries. In fact, with the right design and supplier, it is possible to permanently replace polypropylene with polyethylene. In order to do that, it’s important to understand how the two materials compare to one another.
How PE and PP compare4
Imagine this: a converter is used to making polypropylene bottle caps and is in the midst of a supply shortage due to unforeseen circumstances. Without a reliable supply of resin, they’ll be unable to meet their customer’s demands. While they haven’t used polyethylene in the past and may be wary of switching materials, there is a lot polyethylene can do as a substitute for polypropylene. In fact, it’s the closest material to substitute in for polypropylene and is often a more cost effective choice. And, depending on the end product being made polyethylene can lead to the same quality that end-users are looking for. But to understand how that can happen, we need to look at the attributes of both materials.
First, let’s look at how the two materials deal with temperatures. From a cold perspective, polyethylene is more durable at low temperatures, holding its characteristics all the way down to -112°F while a specific form of polypropylene, polypropylene impact copolymer, must be used for the same results. Using the example of the bottle cap converter above, they’d have products that are more cold-resistant, opening up new ways for their customers to store these materials in colder environments.
When looking at flexibility, it’s important to note that polyethylene is an elastic material while polypropylene is much less flexible. That can be an added benefit for converters making flexible products like packaging or toys. And from a sustainability perspective, both materials are thermoplastics that can be recycled, but polyethylene is the more widely recycled of the two. That’s due to how difficult and costly recycling polypropylene is. Because of the difficulty and expense of sorting, transporting, cleaning and reprocessing plastics of all kinds, in many places it is only economically viable to recycle a few select types which includes high-density polyethylene and not polypropylene and its many variations.
Understanding the advantages and comparisons above, polyethylene becomes a great substitute for use cases where production or use happens in temperatures between -112°F and 239°F. Polyethylene is also more flexible than polypropylene and can therefore be used for many polypropylene applications where flexibility is needed; plus, polyethylene is more frequently recycled, giving converters a greener material to work with to satisfy brand owner demands around sustainability.
Replacing one material with another also brings with it technical difficulties. For example, the shrinkage of polypropylene versus polyethylene is very different. These technical differences make switching from one material to another expensive and time-consuming. Getting the switch to work requires technical expertise to make the transition as painless and cost effective as possible.
Finding a New Supply
When plastic supplies run low due to things like weather-related events, creative solutions must be drawn up. In the case of global material shortages, like with polypropylene, polyethylene can be used as a replacement material in certain use cases.
The plastics industry suffered a number of setbacks and supply shortages due to the pandemic, hurricanes, winter storms, and labor shortages. The lockdown due to COVID-19 caused both polyethylene and polypropylene inventory levels to fall. Right after that, Hurricane Laura stopped 10% to 15% of US polyethylene and polypropylene production in its tracks5. There was also the labor and truck shortages6 that has continued to affect the industry and still cause supply chain disruptions to this day.
With the winter storm that made both polyethylene and polypropylene supplies run low, having both materials on-hand gives converters flexibility to use either material and maintain production levels. That increased supply of materials may help alleviate supply shortage concerns, as converters can get each material from different suppliers, diversifying and strengthening their supply chain. To do that, though, converters will need a reliable polyethylene supplier.
The Need for a Reliable Supplier
To combat supply shortages and get the maximum benefits from their resin, converters need a reliable supplier. Shell Polymers can be that supplier by aiming to provide consistent batches of polyethylene by qualifying our resin to ensure all attributes are within a narrow range. We know lot-to-lot consistency is critical for converters so we've taken steps to ensure our products are consistent each and every time.
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We aim to make sure that the product in every rail car is as consistent as possible, lowering the inconsistency between lots and providing our customers with a reliable supply. We’ll also be producing to unique specifications by testing resin in our Polymers Science Lab to meet
regulations and standards. That includes our Analytical Lab where we’ll analyze the properties and ingredients that go into product streams during production as well as test the final resin.
This in-depth testing will help provide converters with transparent, in-depth information that will help them make the right decisions for their business. It’s hard enough to deal with supply shortages and increasing customer demand without having to also worry about inconsistent resin. So if a polypropylene shortage is affecting your business, look at how adding polyethylene to your supply chain can alleviate supply disruptions and shortages in the future to help reduce downtime and production delays.