A masterbatch may be blended with virgin polymer to add desired color or other properties to the virgin polymer prior to further processing. Methods and processes for producing an antimicrobial and/or antiviral polymeric masterbatch that may be used to add antimicrobial, antiviral and/or antifungal properties to a virgin polymer without significantly degrading the properties of the virgin polymer. The masterbatch may be extruded into pellets or formed into other particles for subsequent blending with the virgin polymer to add antimicrobial and antiviral properties to the polymeric materials.The method includes a heat treatment after compounding the base polymer with the antimicrobial, antiviral and/or antifungal are compounded together. The heat treatment comprises heating the masterbatch blend to a temperature between the glass transition temperature and the melting point of the base polymer.