As straight forward that question sounds, it’s not entirely simple. Why? Because “Microspheres” may be one of the most misunderstood additives on the market today. Part of the blame is due to the secretive nature around its use. They are often cloaked inside a “proprietary” formula. When customers contact us for the first time about the technology, most are surprised how many different products already contain spheres. And ours is only one of multiple technologies out there. It’s the additive that few people know a lot about and virtually nobody talks about.
Add to that misconceptions that all microspheres perform the same basic function. It’s true there are similarities. They have small surface area to volume ratios, they have minimal viscous drag and lower resin viscosity. But that’s where the similarity ends for the most part.
The confusion may just come down to the term “microsphere”. It isn’t a genericized trademarklike Kleenex® to facial tissue or LEGO® to building blocks. It’s more akin to using the term “automobile” to describe both an F150 and 911 Carrera. Technically speaking both are automobiles but….
There are assumptions that all microspheres lower weight, reduce cost, increase abrasion resistance, prevent creep, extend resin etc.. That’s just not the case, at least not within a single technology. It’s product and application dependent. They are almost never interchangeable without substantial trade-offs. For example, you could substitute a glass microsphere (bead) with a polymer microsphere to lower weight. However, if that product relies on the high crush strength of glass beads, you have a problem.
Cenospheres, Ceramic and Glass (Solid and Hollow) Microspheres and Expandable Polymer Microspheres
Cenospheres (Fly Ash):
Used commonly in Syntactic Foams and Low Density Concrete. Cenospheres are a byproduct of coal combustion. The aluminosilicate spheres form naturally from oxide decomposition. They form low density (0.2 to 0.8 g/cm3) spheres making them easy to harvest from ash ponds because of natural separation. However, because they are a byproduct vs. an engineered, there can be some variability; either facility to facility or on the consistency of the coal burned.
Used commonly in architectural paints and coatings for their durability and resistance to sag. Made from alkali aluminosilicate with a density of 2.4 g/cc they are UV transparent and have the highest crush strength of any sphere formed additive.
Solid Glass Microspheres:
Their retroreflectivity characteristics make them ideal for construction paints. At 1.59G-2.5 g/cc solid glass spheres are one of the heavier additives used as a resin extender. They provide stability, high compressive strength and combat shrinkage in materials like Nylon 6/6. Different production methods including heating irregularly shaped glass and using fusion flow breaking to produce glass droplets.
Hollow Glass Microspheres:
Used for pipeline thermal insulation, drilling cements their buoyancy (0.4-0.6 g/cc) makes them ideal for a number of offshore applications. Different production methods including heating irregularly shaped broken glass coupled with a foaming agent. The interfacial tension during condensation forms hollow spheres.
Expandable Polymer Micro spheres:
(Kureha’s product): Used widely in flexible PVC in conjunction with a high lode of plasticizer concentration for density reduction to 0.5-0.65. Also used in thermoplastics, thermosets, glass and polypropylene composites. Polymer microspheres lower weight, extend resin and provide a closed cell foam with good durometer and surface finish control. They also have ultra-low expanded densities ranging from 0.004≦to 0.036≦g/ml.
Some technologies are more narrowly focused while others have a broader application range. There are limitations with every microsphere technology, the trick is connecting the right technology to the right application.
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|Title||What Are Microspheres?|
|Description||The confusion (about what Microspheres do and don’t do) may just come down to the term “microsphere” itself. It isn’t a genericized trademarklike Kleenex® to facial tissue or LEGO® to building blocks. It’s more akin to using the term “automobile” to describe both an F150 and 911 Carrera. Technically speaking both are automobiles but….|