Diluent, an inert substance added for dilution when processing raw materials into powder or to facilitate spraying. For example: clay, kaolin, clay, talc powder, etc. Thermosetting resins require the addition of diluents to reduce their viscosity and facilitate further processing. These diluents are actually cheaper organic solvents than resins, thus also playing a cost-effective role in reducing processing costs. For example, non active diluents commonly added to epoxy resins include acetone, methyl ethyl ketone, cyclohexanone, benzene, toluene, xylene, n-butanol, styrene, etc. For thermoplastic resins, the main purpose of adding solvents is to meet process requirements, as the addition of solvents can serve as a temporary measure to reduce the viscosity of polymers, in order to process them into products. For example, suitable solvents can dissolve polymers and play a bonding role, polymer solutions can be used as coatings, and solvents need to be added for wet spinning.
However, the dissolution characteristics of polymers are significantly different from those of small molecule compounds: low molecular weight crystals such as sucrose have a dissolution - expressed in grams of soluble sucrose per liter of solvent; But for amorphous polymers, their solubility usually does not exist, that is, they can dissolve with solvents in any proportion.

The essence of polymer dissolution can be understood as the "pores" between polymer molecular chains caused by thermal motion immediately occupied by more active solvent molecules, and this process can continue until all polymer molecules are separated from each other and become "solutions". The process of dissolving polymers can also be seen as a controlled diffusion process, and sometimes the concept of determinism can be said to be that the polymer dissolves the solvent rather than the opposite.
If the polymer molecules are cross-linked, the movement of the chain segments is restricted, and a lightly cross-linked polymer will swell or slightly dissolve in the solvent until the osmotic or diffusive forces are balanced by the elastic contraction force of the stretching molecules of the polymer, but it will not dissolve into a mobile solution. Highly cross-linked polymers do not undergo chain segment movement or absorb this liquid, so they cannot swell or partially dissolve. There is usually a critical dissolution temperature for soluble polymers, below which the system is divided into two phases: insoluble swelling polymers and almost pure solvents.
A large amount of non solvent can often be added to polymer solvents without precipitating the polymer. Adding these non solvents to the solution can improve solubility, and they are often referred to as latent solvents. There is often a situation where a mixture of two non solvents is a good solvent for a certain polymer, such as nitrocellulose, where the solvent is an ether alcohol mixture, while the opposite situation also exists, such as cellulose acetate, which can be dissolved in aniline or strong acids respectively, but not in their mixture.
A useful way to increase the dissolution rate of powdered polymers is to first suspend the powdered material in a non solvent, and then add a real solvent. This operation process can prevent aggregation between polymer particles; The second is to use heating to accelerate the dissolution rate.
Keyword: Diluent