Novel terephthalamide diol monomers synthesis from PET waste to Poly(Urethane acrylates)

Due to its excellent properties, poly(ethylene terephthalate) (PET) is one of the most produced and consumed polymers. Among plastics, it represents the main contributor to environmental pollution. Following the circular economy model, the chemical upcycling of PET reduces the amount of waste generated and transforms it into high-value products. The depolymerization of poly(ethylene terephthalate) into oligomers or monomers leads to forming a library of reactive molecules involved in different polymerization processes to obtain compounds with improved properties. Herein, several β-hydroxy amines were synthesized and used for the chemical recycling of water bottle waste by an environmental benefit aminolysis process to get very useful new terephthalamide diol monomers. The recycled diol monomers were subsequently exploited to synthesize poly(urethane acrylates) (PUAs) UV-curable coatings, and their chemical, thermal and mechanical characterizations were performed. The results show the great potential of the developed synthesis protocols to obtain PUAs with final properties that can be modulated to meet the requirements of different applications.

Degradation of vinyl ester resin and its composites via cleavage of ester bonds to recycle valuable chemicals and produce polyurethane

Vinyl ester resins (VER) and its composites are widely used in chemical industry and municipal engineering. However, its dense three-dimensional network structure makes its degradation and recycling a great challenge. Herein, a novel, efficient and green degradation system gamma-valerolactone (GVL)-H₂O/p-toluene sulfonic (PTSA) was developed to degrade VER and its composites. VER was completely degraded in the GVL-H₂O/PTSA at 210 °C and 0.6 MPa. By combing SEM-EDS, IR, NMR, GPC and MALDI-TOF-MS analysis, it was clarified that VER swelled well in GVL, allowing the transfer of PTSA and H₂O through the resin matrix. The ester bonds in VER were cleaved via hydrolysis with H₂O catalyzed by the sulfonic acid of PTSA, and high value-added polymer products, i.e., copolymer of styrene and methacrylic acid (SMAA) and bisphenol-A diglycidyl ether (DGEBA), were recycled, which accounted for ca. 87.0 wt% of raw VER. DGEBA can be recycled to prepare a new PU material. The GVL-H₂O/PTSA system was also effective for degrading UPR and VER-containing composites. This work provides a practical strategy for chemical degradation and recovery of thermoset VER resins.

Back-to-monomer recycling of polycondensation polymers: opportunities for chemicals and enzymes

The use of plastics in a wide range of applications has grown substantially over recent decades, resulting in enormous growth in production volumes to meet demand. Though a wide range of biomass-derived chemicals and materials are available on the market, the production volumes of such renewable alternatives are currently not sufficient to replace their fossil-based analogues due to various factors, in particular cost-effectiveness. Hence, the majority of plastics are still industrially produced from fossil-based feedstocks. Moreover, various reports have clearly raised concern about the plastics that are not recycled at their end-of-life and instead end up in landfills or the oceans. To avoid further pollution of our planet, it is highly desirable to develop recycling processes that use plastic waste as feedstock. Chemical recycling processes could potentially offer a solution, since they afford monomers from which new polymers can be produced, with the same performance as virgin plastics. In this manuscript, the opportunities for using either chemical or biochemical (i.e., enzymatic) approaches in the depolymerization of polycondensation polymers for recycling purposes are reviewed. Our aim is to highlight the strategies that have been developed so far to break down plastic waste into monomers, providing the first step in the development of chemical recycling processes for plastic waste, and to create a renewed awareness of the need to valorize plastic waste by efficiently transforming it into virgin plastics.

Chemo-Biological Upcycling of Poly(ethylene terephthalate) to Multifunctional Coating Materials

Chemo-biological upcycling of poly(ethylene terephthalate) (PET) developed in this study includes the following key steps: chemo-enzymatic PET depolymerization, biotransformation of terephthalic acid (TPA) into catechol, and its application as a coating agent. Monomeric units were first produced through PET glycolysis into bis(2-hydroxyethyl) terephthalate (BHET), mono(2-hydroxyethyl) terephthalate (MHET), and PET oligomers, and enzymatic hydrolysis of these glycolyzed products using Bacillus subtilis esterase (Bs2Est). Bs2Est efficiently hydrolyzed glycolyzed products into TPA as a key enzyme for chemo-enzymatic depolymerization. Furthermore, catechol solution produced from TPA via a whole-cell biotransformation (Escherichia coli) could be directly used for functional coating on various substrates after simple cell removal from the culture medium without further purification and water-evaporation. This work demonstrates a proof-of-concept of a PET upcycling strategy via a combination of chemo-biological conversion of PET waste into multifunctional coating materials.

Valorization of Plastic Wastes for the Synthesis of Imidazolium-Based Self-Supported Elastomeric Ionenes

Imidazolium-based ionenes are known to be high-performance materials for a great variety of applications. The preparation of these polymers requires the use of bis-imidazole starting monomers, which are commonly prepared by using toxic chloride reagents. In this study, bis-imidazole monomers are synthesized by organocatalytic chemical recycling of discarded plastics through chemical depolymerization. By using poly(ethylene terephthalate) and bisphenol A polycarbonate as starting materials, different monomers containing amide or urea functionalities are prepared to produce high-molecular-weight ionic polymers. These novel ionenes show excellent elastomeric and self-healing behavior, serving as a promising means to expand the exploration of plastic wastes as a source of new materials.

Aminolytic upcycling of poly(ethylene terephthalate) wastes using a thermally-stable organocatalyst

We report the potential of thermally stable acid-base mixtures for the upcycling of PET in the presence of amines.

Novel polyester diol obtained from PET waste and its application in the synthesis of polyurethane and carbon nanotube-based composites: swelling behavior and characteristic properties

Novel PUs and PU/CNTs were prepared from PET bottle waste and were characterized by a wide range of characterization methods.