The factors that affect weldability of plastics are:
Lubricants such as mold release agents can inhibit the weldability of plastic parts. If mold release agents are used, parts should be cleaned prior to welding.
2) Impact Modifiers
Impact modifiers such as glass fibers can affect weldability of plastics. Because glass fibers melt differently than plastics, weld settings may need to be modified.
3) Foaming Agents
Foaming agents add air to plastic parts to reduce their density. These air pockets can affect weldability.
The pigments in plastic colorants may have an affect on plastic welding requirements. While these can be minor, it is an important consideration if you are welding parts of the same geometry but different colors.
5) Resin Grade
There are many grades of resin for making plastic parts. Resins are designed to flow differently for injection molding, extrusion, blow molding, rotomolding, etc. The differences in flow rate can affect the part’s ability to weld.
6) Resin Age
Some resins change or breakdown over time. Attempting to weld parts of the same resin but different ages can have an effect on weldability.
7) Engineered Resins
In some cases, highly engineered resins may not lend themselves well to welding.