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Size Matters In Particulate Additives

March 28, 2018

Yep, it’s true: size matters.

But in the case of particulate additives, (unlike, ahem, other instances) smaller is definitely more beautiful.  In fact, nano-sized or even particles measured in micrometers are much less problematic for fabricated plastic products than adding pure organic polymers.  The smaller particulate additives  not only can lower the cost of plastic products, but also improve their “functionalities” (electrical conductivity, thermal resistance and tensile strength).  In contrast, the particulate additives in organic polymers have a tendency to “agglomerate,” forming  “hydroclusters” during injection molding or extruding due to inter-particle interactions.

This agglomeration has huge implications for small plastic injection-molding processes and 3D printers, which in recent years have become the darling of the industrial press and even general public.  These machines have truncated, relatively narrow nozzles which can get easily gummed-up by particulate additive hydro-clusters.

The real problems begin during the actual machine operation.  That’s because, in order to optimize the effects of using particulate additives, they must be well-dispersed.  So, to reduce their propensity to agglomerate, the surfaces of these additives are typically coated with various modifiers.  One of the most frequently-used surface modifiers is stearic acid, or one of its salts.  The coating process for this class of modifiers is frequently based on wet chemical processes.

Polymer, recently published a paper on this subject.  The paper told the story of researchers who selected SiO2 nanoparticles and polyethylene (PE) as the base materials for the plastic composites.  They confirmed that a polydimethylsiloxane coating on SiO2 can aid the scattering of SiO2 nanoparticles in injection-molded plastic composites.

Researchers altered the surface of SiO2 nanoparticles with polydimethylsiloxane (PDMS) by one of two thermal vapor deposition (TVD) methods without using any solvents. Moreover, the PDMS layer on the SiO2 showed greater chemical stability than a stearic acid layer, as well as good thermal stability that could stand up to the exigencies of the injection-molding and extruding processes.

These results, researchers suggest that the thermal vapor deposition of PDMS is a potential method for solving the dispersion problem of inorganic additives in polymer composites. Furthermore, this method also can help facilitate the fabrication of extruded or injected-molded composite materials.


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