Processing of Polymers: How to Solve for Unique Characteristics
Justin Klinger, Dec 2, 2021 10:12:00 AM
Polymers, both natural and synthetic, play important roles in product formulations across nearly every industry, so polymer milling is a critical step in manufacturing.
Natural polymers like starch, cellulose, and pectin – and synthetic polymers such as nylon, polytetrafluoroethylene (PTFE), polyethylene, and epoxy – are large-molecule materials made up of many smaller units (monomers).
Polymers are typically selected as additives in formulas, contributing specific characteristics, or serving purposes such as:
- Thickening agent
- Corrosion protectant/chemical resistance
- Strength enhancer
- Pharmaceutical delivery system
- And more
But what does proper polymer grinding entail, and are there special polymer processing techniques to consider?
In this article, we’ll take a look at special considerations that may apply to the milling and processing of polymers.
How Material Characteristics Inform Polymer Processing Techniques
As with any raw feed for milling, material scientists and engineers on your toll processing team will first want to know as much as possible about the raw material’s properties and the intended particle size goals. Do the particles need to be granulated or micronized? Do they need to be co-milled with another material?
The more information you can provide about the end use of the formulation, the better.
Understanding the intended benefits to the formulation can help the team optimize processing to achieve those specific characteristics. Yet, experienced toll processors often work with customers on projects requiring non-disclosure agreements (NDAs), and have amassed the technical expertise to get to your desired specifications with the information you can provide.
Polymers are Selected for Their Properties and Applications
Many natural polymers’ characteristics make them important food formulation ingredients to alter viscosity, create gels, and control flavor release. Other important polymer properties can include high specific strength, tensile strength, flexibility, elasticity, transparency, and adhesive qualities.
Novel polymers are always being engineered and introduced to deliver specific, optimal properties to products. The characteristics that make polymers so useful in formulations are often the same characteristics that pose challenges in milling and processing.
When developing a polymer milling process, a toll processing team will consider these characteristics first:
- Starting particle size and goal size; initial bulk density versus goal bulk density; or initial particle morphology (shape) versus goal morphology
- Friability — a material’s tendency to be easier or harder to break into smaller particles on contact or under stress
- Glass transition temperature — the temperature range where the polymer changes from rigid to flexible, measured in terms of stiffness
- Melting point — polymers’ very long molecules and very strong covalent bonds mean they have higher melting points than many other organic molecules
When materials are more friable, they may be good candidates for jet milling; but softer, more flexible materials are unlikely to break apart in the collisions that take place inside a jet mill. Some polymers are quite friable, while others are selected for their respective applications specifically because they’re flexible and tough instead of friable.
That’s why understanding glass transition temperature is important. Cooling a polymer below its glass transition temperature can make it more rigid and likely to break down in a milling process. Consider, for example, how plastic items sometimes become rigid and crack under extreme cold conditions in winter.
Similar consideration may be needed for melting points, especially for polymers processed on mechanical milling equipment. The friction created in mechanical mills causes heat, which can alter the polymer’s characteristics and make it more flexible and harder to mill. Polymers with low melting points could pose problems in high heat environments. Exposure to heat can also impact a polymer’s color, texture, and other important characteristics.
At least as important is explosivity data for the product in its final particle size. Without this critical information, a milling project won’t go forward.
Sometimes, these challenges can be mitigated by simply milling certain polymers in colder seasons. For more extreme cooling needs, nitrogen can be introduced into the milling process to help maintain cooler temperatures. Cryomilling, or cryogenic milling, uses liquid nitrogen to subject the material to very cold temperatures — and of course, this special process increases a project’s cost.
Polymer Processing Techniques Used for Particle Size Reduction
The choice of mill type is determined by considering all the milling project needs in a holistic way. Size specifications, particle surface characteristics, glass transition temperature, melting points, and other issues contribute to the choice between mechanical mill types, such as universal mills and hammer mills, jet mills, or wet media mills for micronization projects, achieving sizes as small as 1 to 5 microns.
Each polymer milling project is a potentially unique combination of material characteristics, specifications, conditions, and end use application. The best way to start any new milling project is to consult with a technical expert. It’s often possible to experiment with processes at smaller scales before scaling up to production quantities.
The decision to include a polymer in your product formulation is typically driven by the advantages the material can deliver, so even a challenging raw feed material can make commercial sense — if your processing team has the know-how and capabilities to mill to specification in a cost-effective way. Learn more about the many types of milling processes available, their advantages and most common applications, and much more with our Milling Methods Comparison Guide. Click the link below for your copy.