Toners for laser printers are an unusual material that many people may be exposed to if they get near them at all because they are an extremely fine dust, in the nanoparticle range, meaning less than a tenth of a micrometer in size. They are made from various chemicals to give them their plastic properties and various pigments to give them their colors. To find out some technical properties, go to Toner on the Wikipedia website. These plastic chemicals can be toxic if inhaled and some loss of lung function has been described in the literature for people who are exposed to airborne dusts. They may become airborne in unexpected ways, such as being rubbed off of printed pages.*
Nevertheless, my interest here is not primarily the toxicity of these materials, but their place in the pantheon of reused and wasted materials. Manufacturers play a series of games with regard to toners. They pretend that every machine and every brand makes use of vastly different toners. This gives them a chance to charge extremely high prices for brand adjusted toners. I have never seen any suggestion in the commercial sphere that any toner can resemble any other toner or that any toner can actually be substituted for another. This would suggest to the user that these materials are capable of being understood and sorted in the same way, for example, that metallic alloys are understood in terms of their compositions and can be specified by composition by users and buyers. Every attempt is made to keep toner composition secret and proprietary. This is a marketing mechanism directed at profit.
This is not to say that there are not a fair number of different parameters that can be adjusted to maximize utility of toners. But in the long run, they are just fine powdered plastic that must be attracted to paper using static electricity and then melted into place. This suggests some constitutive properties like average particle size, density of the plastic material, the melting point of the plastic material, the pigment being used and additives such as finely divided silica used to keep the particles from clumping (much the way that a coarser silica is used in table salt or baking powder for the same purpose). These are not really a lot of parameters. Different plastics may have similar values of these critical parameters. If, for example, a given laser printer uses a particular temperature to melt the toner onto the page, that puts certain limits on the toner that can be substituted, but there may be a broad range of different polymers that meet the temperature requirements besides the one that the manufacturer recommends.
I don’t know, because up to now there has been no public discussion of the interchangeability of different toners, but I am guessing that if the physical properties of toners were to be revealed, we would be amazed at how subject to mixing and matching toners actually are. Then generic manufacturers could produce generic toners to fit into specified use categories for much cheaper prices. Of course this is the time to recall that standardization applied to other parts of printers would also pay huge benefits to the public. Instead of having five hundred different cartridge designs, for enormous prices, there could be a much smaller number of cartridges all being made by, and bought from, central sources. I am reminded of the similar situation for automotive head and taillight assemblies, which all perform the same functions but are made unique for no good reason except the ability to charge supernatural prices to replace them when they are broken. But the number of applications yearning for standardization is astronomical.
To wrap up, toner prices are kept artificially high by hiding their intrinsic physical properties and by pretending that every one is uniquely formulated for a particular model of laser printer. Someday, I assume, they will be bought far more cheaply and easily by specifying a number of physical properties that must be matched. In fact, since the physical properties can be measured today by scientists, I imagine that many of the replacement toners sold for refilling cartridges are already being supplied by intelligent substitution. However, there is a strong incentive for even the replacement toner manufacturers to go along with the model based deception to keep prices high.
One last observation: everything that was said above about toners would also apply to liquid based inks used in dot matrix printers.
* Nanoplastics. It has been widely reported that nano sized plastic dusts are ubiquitous in our environment and that we even have significant amounts in our own bodies. Their effect has not yet been identified. Most of them come from the breakdown of all the plastic in our environment but with toner we have a nano plastic being made on purpose. To the extent it escapes into the atmosphere, we must necessarily be breathing a few particles with every breath.