LAB COMPOUNDERS | PLANNING EXPERIMENTS
it is possible to compound this material at all. The customer should understand that this is a ‘trial,’ not a demonstration. The result of the trial for a new material may be that the material cannot be compounded as expected.
Above: Arranging feeding equipment around small lab-scale
machines can present a challenge. This image shows a CPM CXE26 lab compounding extruder with four gravimet- ric feeders
CW: What are some best practices for planning a compounding trial? McHouell: Communication about the raw materi- als and the final goals of the experiment are key. Does the mix just need to be distributed evenly? Or is it an additive that needs exfoliation and dispersive mixing? Is the material shear or heat- sensitive? We can draw on our past experience as a starting point for screw design depending on the type of mixing needed, materials being used and the desired final properties of the compound. Safe handling and properties of the material should be communicated ahead of time. Details are not always available on the safety datasheets. With some liquid additives, one concern could be knowing the flash point in comparison to the processing temperatures needed for the base material. Another question (not related necessarily to safety) is whether we need to be concerned about moisture before or after compounding. For bio-based materials, in particular, how much starting moisture is in the material is critical to know for optimising the process to give us the best chance of success. Also, these materials may be best pro- cessed using dry pelletising instead of water cooling to eliminate moisture wicking during this process. Having the correct feeder for the material is critical for a successful trial. If you know the flow characteris- tics of the material ahead of time, you can make sure you have the right feeder for the job. You might need a solid-wall feeder with a bridge breaker, a flexible- wall feeder, or a single or twin-screw feeder, as examples. The feeders might need a different augur or pitch to dose the material accurately. Dreiblatt: The first essential practice is to define clear objectives for the trial—and to put them in writing. The definition of success depends on the type of experiment. If you’re working with a brand-new material, you are first trying to find out if
48 COMPOUNDING WORLD | December 2022
Another essential is to plan in advance to have the necessary auxiliary and feeding equipment, especially if the materials are not a standard pellet or powder. For example, is a liquid feeder needed, and does it need to be heated to be pumped? Is a screen changer needed? Are the materials free- flowing or are special feeders needed? Just having an extruder is not enough for a successful trial—all the needed pieces of equipment must be available. The raw material format is an important compo- nent to plan and to communicate. The material format shouldn’t be a surprise on the day of the trial. We were once surprised to receive a gaylord of whole post-industrial parts as a raw material for a trial. Another time, an additive raw material arrived as a large, solid block of rubber, rather than as granules. Companies requesting trials must remem- ber that an extruder is not a grinder! We have often seen cases where the raw material is too big to feed into an extruder, especially as companies are trying to use recycled materials. Post-industrial recycle material may be ground, but it is often not ground to small enough particle sizes for extrusion. A large production-sized twin-screw extruder (TSE) has a 0.50 inch [12.5mm] channel at the largest, and a laboratory-sized machine might have a 0.25 inch [6.4mm] channel. The smaller the machine, the more the material size will affect the process. All incoming raw materials should be clearly identified (after non-disclosure agreements are signed, if necessary) with safety datasheets to ensure the safety of those running the process. For example, if materials are flammable, they would require specialised explosion-proof equipment and facilities. The trial plan should also include the disposition of materials after the trial—where they should be shipped, for example.
CW: What are some best practices for conducting a successful trial? Dreiblatt: A successful trial is a symbiotic relation- ship between the test facility and the customer—the customer should have experience with the material and the process engineer understands the equip- ment and process. The reality, however, is that many start-ups are doing unique things with materials they’ve never used before, and so material experience that would be beneficial to the trial is often not available. The customer and process engineer must work together and be
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IMAGE: CPM EXTRUSION GROUP
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