Reclamation

Granulation and air classification are generally the first steps in the reclamation process. Following sorting by resin type, whole bottles are ground to a particle size that best suits the reclamation process. The ground plastic resin is referred to as regrind or flake. Most granulation systems employ an air classifying technique, after size reduction, to separate “light” materials, such as labels, from the heavier base resin being recovered. Granulation loosens plastic and paper labels, and begins to free other attachments that might be on a bottle. Excess glue on labels or attachments has a detrimental impact on granulation and “lights” removal. This increases the cost of reclamation by decreasing the wash cycle yield.

Washing the ground flake is the next step in most reclamation operations. The washing may be done at ambient or elevated temperatures and could include the addition of detergents or surfactants to aid the cleaning process. Labels, label inks, adhesives, base cups, closures, closure liners, inserts, layers, coatings, or other attachments that may be present in or on the bottle affect washing efficiency and effectiveness. Labels, labels inks and label adhesives should all be chosen carefully in order not to cause the base resin to be adversely affected. Labels can contaminate the base resin material; label inks can bleed into the wash water tinting the PCR products; and, label adhesives that can’t be removed can coat the plastic regrind and embed unwanted contaminants. Adhesives used to affix other attachments can be difficult to remove and should be applied sparingly. Washing is often followed by another air classification step to remove lighter materials that have been liberated in the wash system.

Most conventional reclamation systems use water in sink/float or hydrocyclone systems to separate the base resin from attachments and contaminants based on differences in the density of the different materials used. Plastic resins with densities greater than 1.0 can be separated from resins with densities less than 1.0 (see table below) in water. However, resins with similar or overlapping densities are difficult to separate in these systems. For example, resins with densities greater than 1.0 cannot be easily separated from each other (i.e., PVC from PET). Likewise, resins with densities less than one cannot be separated from each other either (i.e., PP from HDPE). It is therefore important when selecting plastic resins for attachments or components in a bottle design to avoid any such overlap, or to make them from the base resin in the same color as the bottle.

Rinsing is done to remove residual dirt and detergent from plastic regrind after it is washed and separated. The material is then dried to a level necessary for remanufacturing applications or for further processing stages.

An additional processing stage that may take place at a reclaimer, but is generally done at a converter, is called melt filtering. Melt filtering removes nonmelting, particulate contaminants in plastic regrind that may remain after sorting, washing and separation stages. Melt filtration occurs inside an extruder, where the plastic regrind is melted and filtered through one or more screens as it is passed through the extruder to make pellets. Converting plastic regrind to pellets provides for a more uniform feedstock for remanufacturing applications and lowers transportation costs for the reclaimer or converter.

The Association of Postconsumer Plastic Recyclers supports PCR utilization in the widest range of recycling applications possible to ensure the economic viability of plastic recycling. Better bottle design that incorporates design for recyclability criteria will help improve opportunities for economically viable recycling by reducing the processing costs associated with removing incompatible contaminants and improving the quality of the PCR. Higher value recycling applications require higher quality PCR with excellent performance characteristics. Plastic reclaimers strive to produce the highest quality PCR to access the highest value recycling applications.