Nina Bellucci Butler of More Recycling states correctly in a Sept. 27 article in Plastics Recycling Update that “we have capacity to purchase HDPE, PET, PP and other resins. We don’t have the capacity to take the material from the MRF [and] further segregate it so we can get those discrete resins to market.”
But compatibilizer technology now allows us to take the material from the MRF and process it without segregating it into discrete resins. The end product is suitable for consumer and automotive products. Key hurdles to widespread adoption of the technology remain, however, including current markets and a need for capital investments in processing equipment.
Why the incompatibility?
The reason why the segregation issue is a challenge is that HDPE, PP, and PET are intrinsically incompatible with each other, and small amounts of contamination cause processing and quality issues in finished parts. For example, although HDPE and PP are polyolefins and classified as addition polymers, more than 5 percent PP blended into HDPE will cause delamination issues when injection molding the blend.
Also, PET, PBT, PC, and PA are condensation polymers and are incompatible with addition polymers.
To date, conventional compatibilizers can be used only when the MRF or post-consumer resin is segregated into distinct resins, as Butler stated. For example, bi-polar thermoplastics will compatibilize two dissimilar polymers of known polarity or may be “coupled” with maleated polymers. For more details, see this white paper from the Plastics Industry Association.
The problem arises when there are more than two polymers, which occurs in non-segregated PCR streams. For example, if the stream contains PET, PBT, PC, PA and other condensation polymers, maleic anhydride (MAH) will depolymerize them, reducing mechanical properties.
Additionally, fillers, such as calcium carbonate and carbon black, affect mechanical properties such as elongation and impact strength. Considering all of the above, these are the reasons why – to date – streams of non-segregated PCR containing HDPE, PET, PP and a host of other filled and unfilled polymeric materials cannot be used for any kind of value-added performance molded or extruded product, particularly those subject to consumer liability issues.
A solution – and continuing challenges
A small amount of a new pellet additive dubbed Ken-React CAPS KPR 12/L acts as a Z-N/Metallocene catalyst in the melt to compatibilize the non-segregated resins, as well as the fillers in the resins. The product is able to catalyze both addition and condensation polymers and at the same time couple and disperse fillers such as calcium carbonate and carbon black. Doing so significantly reduces segregation requirements to a practical level as filler levels can be in the 20 to 40 percent loading range without detracting from stress/strain properties.
The new product is based partly on a neoalkoxy titanate coupling agent, which is a known REPOLYMERIZATION catalyst for unfilled polymers (I was issued a U.S. Patent for the REPOLYMERIZATION technology in 1987). The product is also based on replacing the inert silica in the KPR powder and pellet masterbatches with a mixed-metal filler. Doing so gives a synergistic boost for reacting/polymerizing in the PCR melt. The new KPR catalyst allows the melt processing extruder to act similar to a polymerization reactor, where the monomer is polymerized in the presence of a catalyst.
The focus on developing the new catalyst product took several years and began when there was a confluence in the market of an emphasis on sustainability and high pre-shale oil prices, which allows for the cost of recycled feedstock preparation, additives, and melt processing into usable pellets for molding.
Solving the technical challenge still leaves two major PCR market obstacles. The first is economics: The additives add 7 to 10 cents to the cost in a market suppressed by low shale-oil resin prices and China’s recent restrictions on baled recyclables. The other is processing savvy: The PCR stream must be granulated and melt processed so that the polymer catalysis and filler coupling chemistry of the additive can go to work in the extruder melt.
The recycling industry can fulfill all the potential PCR demand if the price of virgin resin increases to provide a financial space for the cost of the additive/melt processing and/or the use of PCR is mandated and subsidized by a customer that can move the market to do the capital investment needed to support processing with the new additive technology. In the interim, the post-industrial market would certainly benefit immediately from using the additive chemistry for certain niche applications such as automotive.
Salvatore J. Monte is president of Kenrich Petrochemicals, Inc.
The views and opinions expressed are those of the author and do not imply endorsement by Resource Recycling, Inc. If you have a subject you wish to cover in an op-ed, please send a short proposal to [email protected] for consideration.
To receive the latest news and analysis about plastics recycling technologies, sign up now for our free monthly Plastics Recycling Update: Technology Edition e-newsletter.