Efficient Compatibilization of Isotactic Polypropylene (iPP) and High-density Polyethylene (HDPE) Blends

Current approaches to plastic recycling are limited in their ability to reconstitute functional components, elements, and materials for use in high-value applications. Although iPP and PE constitute nearly two-thirds of the plastic produced worldwide, efforts to recycle them are challenged by their immiscible properties that lead to low- quality blended products. This has led to the investigation of compatibilizers additives, which can be added to such iPP/PE mixtures to improve their structural integrity for future use. However, existing compatibilizers require high additive loadings (5-10 wt%), resulting in plasticization, which deteriorates the physical properties of produced blends and effectively relegates them to limited or downcycling purposes. To overcome the significant challenges associated with recycling PE and iPP from mixed waste streams, Intermix is developing cost-efficient methods to generate novel tapered block copolymers (TPBs) for the compatibilization of PE and iPP, resulting in blends with desired tensile strength characteristics. Enabling upcycling processes, copolymer blocks will be developed to create structures with well-controlled, enhanced properties, even compared to virgin plastics. In Phase I, the team investigated various copolymer block structures, testing them on ocean plastics and demonstrating their strong performance as a compatibilizer for real- world plastic waste. Promisingly, ocean plastics compatibilized with as little as 2 wt% of Intermix’s additive exhibited a strain a break of >800%, as compared to 20% for the un- compatibilized ocean plastic blend and ~1700% for HDPE and ~600% for iPP homopolymers, respectively. Building on the Phase I successes, Intermix’s proposed research will be comprised of three objectives: 1) Development of catalytic system based on chain transfer chemistry, enabling efficient block copolymer synthesis, 2) Investigation of the rheological and impact properties of compatibilized PE/iPP copolymers, informing the development of application-specific compositions, and 3) Production scaleup to multi-kilogram scale, establishing scalability and delivering the compatibilizer volumes needed for pilot testing. Completion of these objectives will establish the commercial feasibility of the technology, demonstrating its processability and scalability and validating its performance in compatibilizing real-world plastic waste. This innovation opens the door for iPP/HDPE blends to be specifically engineered to exhibit desired mechanical properties using the unique characteristics offered by iPP (strength) and HDPE (flexibility), without degrading the resulting blends with high levels of compatibilizer additive. The proposed technology will provide exciting opportunities to recycle the world's top two polymers through simple melt blending, obviating the need for separation and lowering associated costs. Further, the technology will encourage higher recycling rates for these materials while supporting the sustainable production of new materials of equal or increased value, thus addressing critical recycling challenges presented by mixed waste. The successful development and commercialization of this technology will serve to facilitate the transition to a more circular plastics economy, from supplying manufacturers withhigh-value recycledplastics, toenabling the development of novel polymer materials for specialized applications such as transport, aerospace, and defense.