Microspheres are spherical particles used in plastics and other materials as fillers and reinforcing agents. They are made of glass or ceramics or resins. There are two different kinds of glass microspheres — solid and hollow. Solid spheres, made of soda-lime glass, range in size from 4 to 5000 | m in diameter and have a specific gravity of about 2.5. Hollow glass microspheres have densities ranging from 80 to 801 kg/m3 and diameters from 20 to 200 | m.
The spheres in plastics improve tensile, flexural, and compressive strength and lower elongation in water absorption. They also serve as thermal and sound insulators. Plastic micro-spheres are used mostly in the production of syntactic foams. Polyvinylidene chloride micro-spheres are excellent resin extenders and are used in sandwich construction of boat hulls. Epoxy microspheres are used as low-density bulk fillers for plastics and ceramics, and were developed for use in submerged deep-water floats. They can withstand hydrostatic pressures 68 MPa. Phenolic microspheres filled with nitrogen are used for production of polyester foams and syntactic epoxy foams. Polystyrene microspheres are also used to produce syntactic foams.
