Advances in plastic polymer heating

Opportunities for process efficiencies, quality control through heat exchange technology

Authors: Jill Caskey, Gerald Marinitsch and Albert Bedell

Plastic polymers play an important part of our daily lives – from toys to medical devices, clothing to food packaging and virtually everything in-between (even chewing gum!).

They have also led to incredible innovation across countless industries – from sustainable shipping pallets and fully recyclable packaged goods to a new lightweight material developed by researchers at MIT that’s stronger than steel.

Not surprisingly, plastic polymer manufacturers have become increasingly focused on quality control at every stage of the process to avoid poor product performance or even consumer safety risks.

Heating plastic polymers has traditionally been an energy-intensive processes, but newer thermal technologies are now allowing manufacturers to maintain high-quality standards while increasing process efficiencies.

But first, what are plastic polymers?

Plastic polymers – also known as manufactured or synthetic polymers – were introduced on the heels of the Industrial Revolution. The first synthetic polymer was actually invented in 1869 by John Wesley Hyatt, who was inspired by a New York firm’s offer of $10,000 for anyone who could provide a substitute for ivory.

Synthetic polymers differ from natural polymers in that they are manufactured using natural building blocks, rather than being found in nature. Common synthetic polymers such as nylon, polyester and polyethylene all contain organic compounds – “organic” meaning their molecular structure contains carbon.

There are eight common types of synthetic organic polymers commonly found in consumer products, including both low- and high-density polyethylene (LDPE and HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon and Teflon.

How is plastic made?

It begins with crude oil, which is separated into fractions of differing mixtures of hydrocarbon chains, varying in size and structure. These hydrocarbon chains are used to produce synthetic polymers through the processes of polymerization and polycondensation.

Polymerization is a chemical reaction between monomers to form a polymer chain. Common monomers such as ethylene and propylene are often linked together in this process to create polyethylene and polypropylene.
Polycondensation, meanwhile, is the formation of a polymer chain by removing water to link the molecules together.

Converting the polymer chains produced in polymerization or polycondensation into finished products can be done through a few different processes, which will depend on the application, production rate and types of plastic.

That said, it typically involves some form of:

Heating: This helps transition the stiffer solid to a softer material that’s more pliable for shaping/forming. When heat is applied to the material, the space between the molecules increases, thereby making it more flexible.
Shaping/forming: This is typically done either through an extrusion or injection molding process. In extrusion, the plastic is melted and forced out a die-shaped opening to form the final product. With injection molding, the molten plastic is ejected at a high pressure into a cold, closed mold.
Cooling: In both examples above, the final product is cooled through different processes so that it can retain its shape. This is often referred to as crystallization.

Heating polymers

Polymer materials are often kept in storage prior to processing in products for sale, where temperatures of the material are subject to fluctuating ambient temperatures. This, in turn, can adversely affect the shaping/forming process.

For example, Solex Thermal Science worked with a U.S.-based company that produces PEX (cross linked polyethylene) tubing for residential and commercial use. The customer was receiving its polyethylene powder in rail cars, which were parked outdoors.

Polymer heat exchanger During the winter months, the powder could get as cold as -7°C. At that temperature, the cold powder tended to pick up moisture, which adversely affected the shaping/forming process and correlated to a much higher percentage of rejected and discarded tubing. The issue reached the point where production had to be halted numerous times, resulting in a considerable negative economic impact for the plant.

To avoid these process problems, the customer required the powder to be consistently heated to room temperature or 21°C.

The role of MBHEs

Moving bed heat exchangers (MBHEs) based on vertical plate technology provide manufacturers with the ability to better control polymer temperatures prior to processing, regardless of ambient conditions and variable supply temperatures.

In this process, the polymer feed material flows by gravity between a series of hollow, stainless-steel plates in which hot water flows countercurrent within the plates, heating the passing material via conduction.

The highly dense heat transfer area within the MBHE — combined with the unique design of each plate that makes it suitable for low velocity of water within recovery loops — allows manufacturers to use waste heat from elsewhere in their operations for this heating step. This replaces the primary energy, typically electrical, that is currently used by heaters that rely on hot air.

In fact, air is not used within a vertical plate MBHE, which not only reduces energy consumption but also virtually eliminates emissions. The result is a final product with an accurate and stable output temperature that is ready for the next processing step.

Lastly, because the product is fully contained within the MBHE, it is not subject to degradation and has minimal exposure to ambient air, while the controlled mass flow rate guarantees a consistent quality and throughput.

Results

In the U.S. example above, Solex installed an MBHE that used 50 USGPM of 60°C water to indirectly heat 2,000 kg/hr of polyethylene powder from -7°C to 21°C. The small footprint of the equipment, approximately 1.5 x 2.5 x 12.5 feet, allowed the customer to accommodate it in a small corner of the plant.

Instead of having to shut down production on cold winter days, the MBHE allowed the customer to continue producing plastic tubing product at the desired capacity while achieving high production quality. This provided a more predictable production capacity year-round and a more consistent revenue stream.

The installation was such a success that when the customer decided to increase their capacity, they returned to Solex to purchase a second unit capable of processing 4,000 kg/hr.

Learn more

Learn more about how MBHEs can work for your polymer processes by visiting our Polymers page.

Ready to talk specifics? Contact a Solex team member today.

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About the experts

Jill Caskey, Global Sales Director

Jill offers broad experience with many markets and application guidelines, including in-depth experience with fertilizer applications and equipment design. Contact Jill

Gerald Marinitsch, Global Director, Industrials & Energy

Gerald leads Solex's efforts in creating tailored and process integrated solutions within industrial applications such as chemicals, metals and minerals and sands. Contact Gerald

Albert Bedell, Regional Director, Asia Pacific

Albert provides support to customers both directly and through Solex’s extensive agency network in the Asia Pacific region. He also works closely with Solex's partner, Chemequip Industries, within the People’s Republic of China. Contact Albert