Purer Grade of ABS Makes for Better Parts and Processes

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ABS (acrylonitrile butadiene styrene) made with the mass polymerization process offers an array of benefits beyond what you’d expect from this venerable material. Whiter, purer, easier and less expensive to process all add up to a high-value engineering resin.

ABS is acrylonitrile butadiene styrene. The ABS resin pellets here show the difference in pigment prior to adding a colorant additive.

ABS has been around a long time and for good reason. It’s durable, tough and inexpensive. It works well in multiple processes including injection molding, extrusion, 3D printing and especially thermoforming. ABS can be fabricated in its natural color or with a color additive, and thus lends itself to a wide range of opaque applications. So, it’s no wonder that ABS is still a popular solution in a wide variety of applications such as toys, device enclosures and automotive parts.

What many plastics processors may not know, however, is that all ABS quite literally is not made the same. ABS made with a process called mass polymerization results in a higher grade of engineering resin. That difference can result in substantial advantages in injection molded, extruded or thermoformed component properties in addition to a lower cost to manufacture those parts. The enhanced properties offered by this material include:

  • Excellent color stability
  • Whiter base color
  • Purer with less residual monomers, gels and VOCs
  • Excellent lot-to-lot consistency
  • Wider processing window

Because of these enhanced properties, mass polymerization ABS is widely used in automotive, medical devices, consumer electronics, and high-end extrusion and thermoforming applications, such as with housings and enclosures that require advanced performance and aesthetics.

 

 

Mass Polymerization vs. Emulsion Polymerization

Traditionally ABS has been made with a multi-step emulsion batch reaction process. The result is that there can be significant variability in the material from batch to batch. Perhaps more consequential, the emulsion process requires the use of several processing additives such as emulsifiers and salts. Impurities from the additives typically remain in the finished material in detectable levels, which contributes to the resin’s yellowish tint.

Mass polymerization is a continuous process that uses few additives, resulting in clean, pure ABS material with high consistency.  

 

Mass polymerization is a continuous process that uses few additives, resulting in clean, pure ABS material with high consistency.  

 
 
 
 
 
Emulsion polymerization uses a batch reaction process requiring emulsifiers and salts that remain in the ABS at detectable levels.

 

Emulsion polymerization uses a batch reaction process requiring emulsifiers and salts that remain in the ABS at detectable levels.

 

 

 

 

With mass polymerization, resins are produced in a single, continuous process that uses very few process additives. This yields a much more consistent, purer product with less color. The combination of these attributes offers a variety of advantages in the processing of the material as well as in the properties of the final products. Moreover, because mass polymerization is a continuous process, the material has much less variability in comparison to resins made with batch processes.

This difference is exemplified in the line of MAGNUM™ ABS resins from Trinseo, a former business of The Dow Chemical Company, and global manufacturer of plastics, latex binders, and synthetic rubber.

 

Purer Resins Make Better Parts

When compared with emulsion ABS (eABS), ABS produced with mass polymerization technology has substantially lower volatile organic compounds.

A disadvantage of emulsion polymerization is all the residuals that remain in the material. The result is ABS with measurable levels of impurities, VOCs and gels and that can negatively impact downstream processes as well as the final products. As this VOC graph shows, when compared with emulsion ABS (eABS), ABS produced with mass polymerization technology has substantially lower volatile organic compounds.

Residuals and impurities may intensify the aging process in injection molded parts, losing their color and finish sooner. Higher levels of VOCs raise regulatory concerns, create swirling residue in the extrusion process, and raise the odor level of finished parts, not to mention odor in places where those parts are processed. (That new car smell may be appealing to some, but it’s the VOCs they’re sniffing.)

Gels become a problem in the surface quality of parts, particularly in sheet extrusion, creating visible imperfections on the surface of the plastic part.
Unmelts in ABS, also called gels, can cause aesthetic surface defects because gels do not melt during extrusion and may form a surface irregularity.

Gels become a problem in the surface quality of parts, particularly in sheet extrusion. Gel particles may not even be noticeable in the sheet, but then appear in a secondary process—such as in thermoforming—creating visible imperfections on the surface of the part.

Because the mass polymerization process never introduces many of these contaminants to begin with, MAGNUM™ ABS exhibits fewer of these issues. A purer ABS also reduces the likelihood of substance migration from the plastic, which is particularly important in sensitive applications such as with medical devices.

 

Brighter Colors with Less Pigment

Trinseo MAGNUM ABS resins in multiple colors

The most striking feature when you see MAGNUM™ ABS in its natural state is how white it is. Because there are fewer impurities, the material is much brighter than conventional ABS, and stays whiter longer in a final product, even through multiple regrinds. You can add whitener to lighten conventional ABS but will not be able to reach the level of whiteness that can be achieved with MAGNUM™ without using additives at all.

This low, base color allows the processor to use less pigment yet still achieve a rich color with the end result, particularly with lighter colors. Being able to color parts closer to the target aesthetics with less pigment brings significant cost savings to processors. It’s also easy and cost-efficient to use masterbatches, enabling smaller lot production in different colors. Adopting self-coloring allows processors to avoid keeping and managing many different lots of colors.

 

Better Stability In-Process and Over Time

Another benefit of the mass polymerization process is that it yields a material that is more thermally stable. MAGNUM™, for example, can be processed at temperatures above 250°C, which—combined with its low melt temperature—offers an exceptionally wide processing window. Good thermal stability also results in less color shift, which is important to injection molding shops running the same part across different machines.

MAGNUM ABS resins (bottom) shows less discoloration over the number of regrind passes, demonstrating higher thermal stability.

This image shows how granules change in color after various re-extrusion passes. Pass 1 is the original granule color. The yellow of the eABS is clearly more pronounced than MAGNUM™. Further, MAGNUM™ shows less discoloration over the number of regrind passes, demonstrating higher thermal stability.

The material also exhibits less property shift over time. Compared to emulsion ABS, it has an improved resistance to UV light such that less UV additive is needed to stabilize molded, extruded and thermoformed parts. In accelerated QUV-A weathering tests, the material demonstrated a 50 percent slower aging rate than conventional ABS. This means parts retain their color and surface appearance longer, which is critical for materials exposed to sunlight.

Simulating indoor conditions, QUV-A tests are used to demonstrate results of accelerated UV exposure of the ABS resins.

This graph shows the evolution of the delta E value when exposed to a QUV-A accelerated weathering test. The delta E value is a numerical value that expresses the total color change compared to the original color before the test. The emulsion ABS color ages twice as fast as the MAGNUM ABS. That means, in theory, that MAGNUM ABS needs about half the amount of UV absorber compared to eABS for indoor exposure conditions.

 

Who is Trinseo?

While well known in the automotive industry, the name Trinseo might not ring a bell to some processors serving other markets. Trinseo was formed in 2010 by combining four businesses of The Dow Chemical Company:

  • Polycarbonate and Compounds & Blends
  • Paper and Carpet Latex
  • Synthetic Rubber
  • Styrenics (polystyrene, ABS/SAN resins)

Today the company has over $4.4 billion in revenue and approximately 2,200 employees in 25 countries. It has a global footprint with 15 manufacturing sites and 10 R&D labs across the world.

Learn more about MAGNUM™ ABS resins or Trinseo plastics products.