Resin is a fascinating substance, used to create all the plastics around us. As we explored in an earlier blog, What is Plastic Resin?, the creation of resin involves a sophisticated industrial process. The results are tiny plastic pellets, then melted and molded into whatever product is required.

That process broadly referred to as cracking, takes primary chemical ingredients and catalysts to create certain types of plastic. The plastic properties are also altered through the length and pressures of the process.

But there is a third part to resin that makes a huge difference: additives. Additives can help determine the final properties of plastic: if it will melt, bend under pressure, resist sunlight and more. A basic understanding of additives is useful to selecting the best resin for your plastic product.

What are additives?

hand in resin

Additives most commonly come in powder form and can be added at different stages of the plastic process. Some are added early into the mix to be part of the resin itself. Others might be added when the resin is melted to create a plastic object (the processing stage), and some additives can even be added after processing.

Some additive can give multiple properties to a plastic. For example, Aluminium trihydroxide can add bulk, reduce shrinkage and make a plastic more resistant to flames. Many resins are already modified to meet certain criteria in a turnkey fashion.

Nonetheless, it is important to ensure the plastic you choose will have the properties your product needs. For example, if you are making plastic spatulas, they need a level of heat resistance.

What type of additives are there?

Additives are divided into several classes:

Plasticizers: Plastics are not naturally elastic. The difference in flexibility between a lawn chair and the insulation around an electrical wire depends on this type of additive.

Impact modifiers: Plastics can be quite brittle, so this additive class strengthens the material.

Lubricants: These additives most often help with the molding process, ensuring the plastic is distributed evenly and damage to the mold is limited.

Fillers: Fillers give plastics more mass, making them heavier and stronger. It is very common to add fillers to resin.

Flame retardants: The name says it all – these additives reduce the impact of heat and flames on plastic.

Antioxidants: This is a broad class, covering nearly everything that will help plastics withstand wear and tear. If you want to reduce chemical or sunlight damage to plastics, this is the class worth knowing.

Colorants: These quite simply add colour to plastic.

Foaming agents: Simply put, foaming agents add air pockets in plastic. This can have a radical effect, such as turning polystyrene into styrofoam packaging. Foaming agents aren’t always foam-like – some additives are tiny glass balls that make plastics a little less dense and easier to sand.

Antimicrobial: Plastics treated with these additives resist bacterial growth, such as on a shower curtain.

Thickeners: Thickeners add to the viscosity of the plastic, namely its liquid thickness. This can impact the molding process as well as the mixing of other additives such as Colorants.

Anti-stats: Why do some plastics give you a static shock and others don’t? It depends if they include an anti-stat additive.