Multi-material plastic waste streams can now be thoroughly sorted by means of automated methods, and fractions consisting of different chemical classes (e. g. polyesters, polyamides, polyurethanes etc) are obtained in (close to) mono-material form. A most notable exception are polyolefins (PO), namely polyethylene (PE) and polypropylene (PP). Polyolefins are synthetic organic macromolecules that constitutes the largest segment of the plastic market. These materials are everywhere, from packaging to toys and life-saving medical innovations, thereby accounting for more than half of global polymer production and waste. Indeed, the vast majority of polyolefins are fabricated for performance, not for durability and recyclability and if plastic demand follows its current trajectory, the global waste volumes would grow from 260 million tons per year in 2016 to 460 million tons per year in 2030 with a catastrophic impact on the environment. Effective strategies to improve the value-chain of polyolefins and to keep them within the circular economy are mandatory.
PO are also poorly amenable to thermal recycling, due to an exceedingly high chemical stability, whereas mechanical recycling is complicated by the thermodynamic incompatibility of PE and PP. Indeed, the greatest challenge in recycling commingled plastic waste is that most plastics are immiscible with one another, producing phase-separated mixture and fragile interfaces which results in poor mechanical properties (immiscible PO blends have poor application properties). Roughly 5% of the economic value is retained when plastic wastes are recycled. The CORE idea to overcome this limitation is the development an efficient mechanical recycling strategy based on the use of phase compatibilizers (PC) able to control the phase behaviour of polymer mixtures, opening the opportunities for up-cycling without pre-sorting. Phase compatibilizers are multicomponent random or block copolymers, with controlled architecture, presenting tailored thermodynamic interactions with the immiscible polymers in the mixture.
Compatibilizers arrange at the interfaces between the two components of the blend and help to modify the sharp and mechanically weak interfaces. This leads to a system characterized by a fine phase structure with enhanced interfacial adhesion and improved the final mechanical properties (up-cycling).
CORE presents an interdisciplinary research project at the crossover of the different technological areas including: i) design and synthesis of further improved PC structures, ii) development of fast analysis and formulation methods, iii)study of structure-property relationships of compatibilized blends, iiii) study of the effect of mechanical recycling processes on the processability, rheological characteristics, microstructure, mechanical and physico-chemical properties of recycled polymers etc.
The goal is to make more easily recyclable and reusable polyolefin blends for application in furniture and packaging components.
The main targets of CORE correspond to two priority actions towards the New Plastic Economy by EU, i.e., fundamental design and innovation of materials and recycling with improved quality and aims to harness the benefits of plastics while addressing their drawbacks. The successful development of recyclable polyolefin blends could reduce the demand for finite raw materials, alleviate the negative impact of these polymers on the environment and establish a circular economy approach to sustainability.
The final target will be realized through the following intermediate objectives:
1) Design of phase compatibilizers with controlled architecture.
Polymer compatibilizers are generally multicomponent copolymers of various architectures, such as block (linear and graft) or random copolymers.
The scientific aim is to improve our understanding and control of the final properties controlling the phase compatibilizer molecular architecture. Extracting information and guidelines for effective preparation and use of the novel compatibilizers require rationalization of the experimental results and proper preparation of the experiments themselves. Finding a rationale for the relations among synthetic conditions, obtained microstructure and efficacy as a compatibilizer, means to be able to control the entire design of optimal materials.
2) Processing and Recycling: from fundamental understanding to sustainable and circular economy
The main goal is to develop sustainable polyolefin materials which take into account multiple reuse and recycling. The specific objectives are: i) to develop polyolefin materials suitable for applications in furniture, considering a circular perspective, and ii) to compile a guide for selection of most appropriates polymers for final applications. It is expected that all the synthesized polymers will be free of hazardous substances and will keep their properties after several aging and reprocessing cycles. The research will be directed to the attainment of significant advance in understanding the mechanical and physical properties of the phase compatibilizers (pure and blended with PE/PP mixture) as a function of microstructure. In fact, from the fundamental point of view, semicrystalline block copolymers are per se interesting because the phase behavior of block copolymers has been studied in depth only in the case of amorphous systems to date. The presence of a crystallizable component introduces a further complexity due to the contemporarily occurrence of two, often competitive, phase transitions (phase separation and crystallization), but it can be exploited for controlling the final morphology and improving physical properties. The comparison between the structure and properties of the samples (compatibilized and non-compatibilized) will help identifying the optimal microstructure/architecture responsible for the compatibilizing effect, and will eventually simplify/drive the synthetic strategy to be used for their preparation.
We will explore a range of processing conditions and probed the kinetic driving forces associated with interfacial crystallization. Understanding the complex interplay between molecular architecture and processing conditions on interfacial morphology and adhesion provides an avenue to more efficiently use mixed stream recycling feeds for specific product development.
3) Establishing the necessary networking to contact and involve the relevant actors
To achieve this goal, a strategic convergence and collaboration of all actors across the plastic value chain (academia & research, governmental and other organizations) active in the polyolefin market has to be reached in order to create opportunities and mechanisms for coordination between stakeholders. This will enable better information exchange and greater knowledge transfer.
All the above mentioned goals could contribute to accelerate the positive impacts and capacity building by providing support and guidance to plastic designers and manufacturers.