Toll Processing Spotlight Series: Polymers

KT Brickman, Mar 27, 2020 6:00:00 AM

It’s no exaggeration to say most Americans have had direct contact with a polymer-containing product within the last five minutes.

Polymers cover a huge range of materials that people use in everyday life in a variety of ways: water bottles, grocery bags, paints and coatings, textile fibers, cosmetics, phones/computers, toys. They’re also used in highly technical industries for aerospace and auto parts, implantable medical devices, and artificial joints.

Some polymers bend and stretch (rubber, polyester) while others are hard and solid (epoxies, glass). Although the term “polymer” is often used to describe plastics (which are synthetic/inorganic polymers), natural/organic polymers also exist (such as wood). So, all plastics are polymers, but not all polymers are plastic.

Toll Processing Techniques with Polymers

Various techniques can be used to custom toll process a polymer, depending on its characteristics. And some processing may be applied back-to-back; for instance, extruding a polymer and then jet milling it.

  • Jet Milling — Micronizing with high velocity air to perform autogenous milling in a fluid bed with an adjustable internal classifier to achieve the desired particle size and shape; mills may include hot gas, ceramic lined, and stainless steel varieties.
  • Extruding — Melting the polymer and adding a less-expensive filler can help control costs without sacrificing the polymer’s performance (so quality is also maintained).
  • Cryogenic Milling — Freezing some flexible polymers makes them more brittle and easier to mill; of course, added steps can increase costs.
  • Screening — Sometimes it’s necessary to remove larger or smaller undesired particle from the bulk material by passing it over a screen
  • Classifying — Dispersing the material in air and using an adjustable classifier to control the final particle size to remove oversize or undersize particles from the bulk polymer.
  • Blending — Polymers can be dry or wet blended to create a unique product that is then further handled by extruding, dry milling or wet milling.
  • Wet Milling — Very fine particle sizes are possible by dispersing the polymer in a liquid carrier and/or mixing them with multiple ingredients to create a slurry, either at ambient conditions or heated/cooled, then media milled to the desired size.

Know Your Polymer

Before any toll processing can be attempted, the characteristics of the starting material require examination. Starting with a GHS-compliant Safety Data Sheet (SDS) is always a smart first step. And then documenting everything from current particle size (granular, powder, larger pieces), bulk density, moisture content, combustibility (with explosivity data), and if the material is an allergen.

Has the product been successfully toll processed at some point? If so, a reference sample of the finished product can be studied within particle size analysis equipment (MICROTRAC MRB, Malvern Mastersizer 3000, or HORIBA, Alpine Air Jet Sieve, etc.). Any previous process details can help determine the best way to process the polymer or at least provide some insights. With enough information, a trial may even be skipped, moving the product straight to production, saving money and time.

Two pieces of information are especially valuable when toll processing polymers:

  • Melt Temperature — Extruding involves melting polymer(s) to incorporate a filler, which itself does not melt.
  • Glass Transition Temperature — In order to cryogenically mill a polymer, it needs to be reduced in temperature enough to make it brittle.

The Final Product Takes Shape

An evaluation of the material properties and particle size goals determine the selection of the most efficient processing technology. Asking questions about the characteristics of the final product helps achieve the goals of the polymer.

  • Will toll processing simply blend materials, or is particle size reduction needed? Maybe both?
  • Does the particle shape require changing or just reducing?
  • Is a filler needed? At what percentage?
  • Can existing equipment and processes complete the task? Is a new piece of equipment needed?

Toll processing polymers isn’t always black and white (or easy/difficult). Since polymers have a wide range of characteristics, one may be simple to process while another is far more challenging. A particle size that’s challenging to achieve may have to undergo several steps: cryogenic milling (as pre-grinding) and then jet milling to get to the final particle size.

When it comes to polymers, toll processors rarely help formulate products, but if you have performed bench top trials and are looking to perform larger scale trials, processors can help with that.  Or if a design of experiments in required processors can help define some of the processing changes, while you advise the formula changes.   

The Right Toll Processor for Polymers

One advantage of working with an experienced toll processor is having multiple pieces of equipment available on which to trial products.  The smallest, a feasibility station, performs early initial tests on a polymer material to evaluate how it behaves during processing.

Next largest, a pilot-sized unit can trial small amounts of product (100 - 200 kg minimum) to cost-effectively determine larger-scale production rates. A truckload of material isn’t required to confidently nail down processing moving forward.

Determining the right equipment for the job is easier when they're easily accessible. If a jet milling trial doesn’t hit the mark, a mechanical mill with nitrogen can be rolled in, for instance. In this way, efficiency is maximized, and it’s a shorter path to that polymer’s production.

Another time-saver was mentioned earlier: having the ability to perform multiple processing steps at one location — e.g., extruding/adding filler and then resizing it — at the same toll processor saves time and controls quality.

Polymers are used within cGMP toll processing, yet it requires meeting unique quality standards. Read our blog post, cGMP in Toll Processing: Insights for Food & Pharmaceutical, for the details of toll processing for food and pharmaceutical applications.

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