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Main Sources for Recycled Powders from Other Areas Potentially Useful for Filler Applications

Glass

Glass of various types is widely available in recycled form and can be theoretically converted into powders for polymer filler use. The main limitations to its widespread adoption as a filler are due to water sensitivity of the commonest glass compositions and their relatively high hardness, which can cause unacceptable wear rates on conventional equipment designed for use with other fillers.

Glass is a mixture of various oxides, of which the principle one is silicon dioxide. There are a number of different compositions in bulk use; the main ones being:

  • • Commercial glass (soda-lime glass)
  • • Borosilicate glass
  • • Glass fiber
  • • Lead glass

Commercial Glass (Soda-Lime Glass)

This is the most common glass form and is used in bottles and jars and flat glass for windows. The main constituent of commercial glass is sand. While sand by itself can be fused to produce glass, this requires high temperatures (about 1,700 °C) and other ingredients are added to lower this.

The principal additive is sodium carbonate (Na2CO3), known as soda ash, but this would on its own make the glass too soluble and so other oxides such as calcium and magnesium are also added (usually in the form of limestone).

Most commercial soda-lime glasses have roughly similar chemical compositions of:

70-74% SiO2 (silica) 12-16% Na2O (sodium oxide) 5-11% CaO (calcium oxide) 1-3% MgO (magnesium oxide) 1-3% Al2O3 (aluminum oxide)

 
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