Polymer Safety Mixing

Many injection molders and extruders process a wide variety of different materials. In most cases, intentional or unintentional mixing of different polymers can result in wasted material, scrap parts, and lost production. However, there are some materials that if mixed together can have very serious consequences. One of the main materials to avoid mixing with other polymers is acetal (POM). If even a few pellets of PVC or TPV gets mixed with acetal, the acidic compounds given off from the PVC or TPV can quickly lead to severe and dramatic degradation of the acetal resulting in off-gassing of formaldehyde and possible pressure build-up in the extruder barrel. In addition to PVC and TPV, there are other polymers and additives that can also cause degradation to acetal. These include, but are not limited to: CPVC, CPE, ionomers, acid copolymers, halogenated flame retardants, some UV stabilizers and metallic copper.

It is recommended that acetal and PVC and TPVs not be processed in the same plant. If that is not possible, they should not be processed on the same molding / extruding equipment. If that is not possible, then the machines should be thoroughly purged and cleaned, as well as all axillary equipment, before transitioning to or from acetal. In addition, extreme caution should be used to ensure that no stray pellets get blown or dropped into acetal boxes or machine processing acetal.

With a little forethought and caution, processing can safely process acetal and other incompatible resins in their manufacturing plants.

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