Polyethylene microspheres (also referred to as polyethylene spheres, beads, balls, polymer spheres, polymer microspheres, polymer beads, plastic beads or plastic microspheres) are solid spherical microparticles and are the most common type of solid polymer spheres. Hollow glass microspheres represent a class of additives that offer aesthetic, process control and cost benefits, while providing flexibility in a wide range of potential applications. With advances in microsphere manufacturing processes, polymer spheres and hollow glass microspheres are available in comparable grades, particle sizes and prices.
Which microsphere material is right for your application? There are several major differences to keep in mind when selecting microspheres.
1) Melting Point:
Polyethylene Microspheres – The melting point of polyethylene microspheres varies somewhat depending on the grade and molecular weight of the polymer, but is usually between 110C for low molecular weight grades and 130C for higher molecular weight material. The melting point is typically low and sharp, since polyethylene goes through a fast phase transition. This is a very important feature for applications where the spheres are used as a temporary filler but would need to be “melted away” at a later point to create holes or cavities for a sponge effect.
Hollow glass microspheres – The melting point of hollow glass microspheres is from 500C – 800C, depending on the product. High melting point makes hollow glass microspheres attractive for high temperature applications, where the product needs to withstand severe environmental or processing conditions.
2) Density or Specific Gravity of Particles:
Polyethylene Microspheres – Typical densities of 0.95 g/cc – 1.3 g/cc as well as ability to color-code spheres by density make polyethylene spheres suitable as density marker beads. These are small colored microspheres of known mass density that are used for calibrating density gradients and determining density in gradient columns. Density gradients are often used for separations and purifucations of cells, viruses and subcellular particles. Generally a set of several density marker beads covering a range of densities is used. Custom density particles are available in polyethylene formulations. Brightly colored and fluorescent polymer microspheres are specifically designed as particles for water flow visualization and particle image velocimetry (PIV) experiments. Highly spherical microbeads with tight particle size distribution and density of 1g/cc, matching to properties of fresh water, are used as tracer or seeding particles clearly visible as they follow the flow of the liquid.
Hollow glass microspheres – Solid hollow glass microspheres have a high density of about 2.2g/cc for borosilicate hollow glass microspheres, 2.5g/cc for soda lime hollow glass microspheres, and 4.49g/cc for barium titanate hollow glass microspheres. Hollow glass microspheres have densities as low as 0.14 g/cc.Depending on the application requirements, solvents used, desired buoyancy, difference in density between polyethylene and glass microspheres might become a critical factor when selecting the right material.
3) Chemical Stability:
Polyethylene Microspheres – Most grades of polyethylene have excellent chemical resistance and do not dissolve at room temperature because of their crystallinity. Polyethylene microspheres usually can be dissolved at elevated temperatures in aromatic hydrocarbons such as toluene or xylene, or in chlorinated solvents such as trichloroethane or trichlorobenzene. This feature is benefitial if microspheres need to be dissolved at a precise point in the process.
Hollow glass microspheres – Glass has very high chemical resistance and is the right choice for applications where microspheres need to withstand contact with agressive solvents at elevated temperatures.
This article comes from cospheric edit released
