TECHNOLOGY | FUNCTIONAL FILLERS
Figure 3: Calcium carbonate coated with stearic acid can increase impact resistance of a polymer through the process of filler debonding
Source: Chris DeArmitt/ Kirk-Othmer Encyclopedia of Chemical Technology
IMAGES: CHRIS DEARMITT/ KIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY
Thoughts on wear and nanocomposites
Phantom Plastics founder Chris DeArmitt, who features in this article, recently contributed a chapter on fillers and filled plastics to the latest edition of the Kirk-Othmer Encyclopedia of Chemical Technol- ogy (which is published by Wiley). These selected excerpts present his thinking on equipment wear and nanocomposite potential.
Where is the wear coming from? “In the plastics industry, people observe wear of their equipment and attribute that wear to the filler. Even soft minerals such as talc and calcium carbonate are blamed for wear. This is intuitively nonsense because talc is so soft that it is scratched by a fingernail. So, what is the explanation? Studies have proven that almost all wear observed is due to traces of hard impurities, usually quartz, in the mineral. Larger amounts of quartz and larger quartz particles cause excessive wear that can be avoided by using purer grades of filler.”
And what about nano-composites? “A lot of hype has sprung up around the topic of nanofillers. This is surprising for a couple of reasons. Firstly, because nanofillers are not new. Nano-silica and carbon black have been in our tyres for decades, colloid scientists have understood the nano/surface realm for over half a century. “The small particle size actually turns out to be the least impor- tant factor. Small size can lead to some useful properties such as transparent composites but, usually, the size is a problem because small particles give rise to huge viscosity and severe difficulties with dispersion. The high surface area, often in the hundreds of m2
leads to higher strength but also requires very large amounts of surface treatment to cover the surface. “Platy nanoclays have very high aspect ratio making for excel-
lent reinforcement. However, they can only be used at low loadings and do not perform better than standard reinforcements. The extreme level of interest in [these] nano-composites is therefore unwarranted.”
38 COMPOUNDING WORLD | June 2020
stearic acid coating, a foam is created.” This is shown in the micrograph images in Figure 3. A new sustainable calcium carbonate has been launched by Arctic Minerals under the AquaFlex tradename. “Unlike standard calcium carbonate, which is mined from ancient deposits, AquaFlex is newly deposited and very pure. Because it is deposited at a vastly greater rate than it is mined, the calcium carbonate is fully renewable,” DeArmitt says. “Many companies have set targets for renewable content without any clear plan on how to reach those targets. For them, AquaFlex is a dream come true. Everyone is comfortable with calcium carbonate filler used at 20-40 wt% in polyolefins, so it is a drop-in solution.”
Targeting barrier Joe Lichtenhan, Vice President of Business Develop- ment at Hybrid Plastics, highlights an interesting effect it has seen when its polyhedral oligomeric silsesquioxane (POSS) is loaded at ppm levels into PE, which could lead to the possibility of single- layer PE barrier films. “We get improved mechani- cals and oxygen permeation barrier,” he says. Lichtenhan and Dr Angel Romo-Uribe, who
/g, means huge contact area with the surrounding polymer. This
works in the R&D department at Johnson & Johnson (J&J) in Jacksonville, Florida, US, shared some details with Compounding World of a joint project that has demonstrated that just 80 to 400ppm of POSS nanochemical melt blended with PE can form nanostructured films with a more than 100% increase in tensile modulus. “Strikingly, at these concentration levels there is no penalty on the extensibility of the films, as usually seen in reinforced (nano) composites. Furthermore, other important mechanical properties like toughness, yield stress, tear and puncture resistance were also enhanced at this rather low POSS content,” they say. See Figure 4 for effect on modulus. The investigation determined that the dispersion of POSS into the polyethylene matrix at nearly
www.compoundingworld.com
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