Facile preparation and characterization of fibrous carbon nanomaterial from waste polyethylene terephthalate

Effects of Temperature, Ionic Strength and Humic Acid on the Transport of Graphene Oxide Nanoparticles in Geosynthetic Clay Liner

With the wide application of graphene oxide nanoparticles (GONPs), a great amount of GONP waste is discarded and concentrated in landfills. It has been proven that GONPs have strong toxicity and could gather toxic substances due to their high adsorption capacity. GONPs will seriously pollute the surrounding environment if they leak through the geosynthetic clay liner (GCL) in landfills. To investigate various factors (temperature, ionic strength (IS) and humic acid (HA)) on the transport and retention of GONPs in the GCL, a self-designed apparatus was created and column tests were carried out. The experimental results show that GONPs could be transported through the GCL. The mobility and sorption ratio of GONPs in GCL decreased with an increase in temperature and IS, and increased with an increase in HA. The temperature had little effect on the deposition ratio of GONPs in the GCL. The deposition ratio of GONPs in the GCL increased with IS, and decreased with an increase in HA. The transport of GONPs in GCL, glass beads and quartz sand was compared, and the results show that the retention ability of the GCL is much better than other porous materials. The experimental results could provide significant references for the pollution treatment in landfills.

Commercialization potential of PET (polyethylene terephthalate) recycled nanomaterials: A review on validation parameters

Polyethylene Terephthalate (PET) is a polymer which is considered as one of the major contaminants to the environment. The PET waste materials can be recycled to produce value-added products. PET can be converted to nanoparticles, nanofibers, nanocomposites, and nano coatings. To extend the applications of PET nanomaterials, understanding its commercialization potential is important. In addition, knowledge about the factors affecting recycling of PET based nanomaterials is essential. The presented review is focused on understanding the PET commercialization aspects, keeping in mind market analysis, growth drivers, regulatory affairs, safety considerations, issues associated with scale-up, manufacturing challenges, economic viability, and cost-effectiveness. In addition, the paper elaborates the challenges associated with the use of PET based nanomaterials. These challenges include PET contamination to water, soil, sediments, and human exposure to PET nanomaterials. Moreover, the paper discusses in detail about the factors affecting PET recycling, commercialization, and circular economy with specific emphasis on life cycle assessment (LCA) of PET recycled nanomaterials.

Metal-free recycling of waste polyethylene terephthalate mediated by TBD protic ionic salts: the crucial role of anionic ligands

The structure-activity relationships of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) based protic ionic salts for polyethylene terephthalate (PET) glycolysis by ethylene glycol (EG) were comprehensively investigated through theoretical prediction and experimental verification. The proton capture ability of the anionic ligand from EG is positively correlated with the activity of the catalyst, as the generation of EG- was crucial for the chain breaking reaction via nucleophilic attack on the carbonyl group. Furthermore, density functional theory calculations demonstrated that the HTBD cation and anionic ligands work in a cooperative manner in the PET glycolysis reaction, where the ligands abstract a proton from EG to generate EG- and provide a proton to produce the bis(hydroxyalkyl)terephthalate (BHET) product. The rate-determining step is the nucleophilic attack step, where the Gibbs energy barriers (ΔG≠) increase in the order of 29.7 kcal mol-1 (HTBD-OAc) < 30.2 kcal mol-1 (HTBD-CH3CH2COO) < 31.4 kcal mol-1 (HTBD-HCOO) < 35.7 kcal mol-1 (HTBD-CH3COCOO) < 36.9 kcal mol-1 (HTBD-NO3). This is confirmed from the experimental results that the BHET yields decrease in the order of 84.8% (HTBD-OAc) > 82.4% (HTBD-CH3CH2COO) > 80.2% (HTBD-HCOO) > 73.6% (HTBD-CH3COCOO) > 4.7% (HTBD-NO3). These findings offer valuable guidance for designing more efficient metal-free protic ionic salts, promoting sustainable PET recycling.

Optimization of Ti-BA efficiently for the catalytic alcoholysis of waste PET using response surface methodology

A titanium benzoate (Ti-BA) catalyst was prepared by hydrothermal method, which has an ordered eight-face structure, and was used for polyethylene terephthalate (PET) depolymerization. With bis(2-hydroxyethyl)terephthalate (BHET) as the target molecule and ethylene glycol (EG) as the solvent, the best reaction conditions for catalytic alcoholysis via a PET alcoholic solution were investigated via response surface experiments and found to be a EG/PET mass ratio of 3.59, temperature of 217 °C and reaction time of 3.3 h. Under these conditions, the amount of the catalyst required was only 2% of the mass of the PET, and the yield of BHET reached 90.01% and under the same conditions, the yield of BHET could still reach 80.1%. Based on the experimental results, the mechanism of alcoholysis, Ti-BA catalyst activated ethylene glycol deprotonation to achieve the progressive degradation of polymers. This experiment provides a reference for the degradation of polymer waste and other transesterification reactions.

A facile, alternative and sustainable feedstock for transparent polyurethane elastomers from chemical recycling waste PET in high-efficient way

Polymers with excellent optical and mechanical performance fabricated from renewable resources, have been paid an increasing attention in recent years. Here, high-performing polyurethane elastomers with significant mechanical properties, crystallinity, excellent stretchability and good transparency are prepared by a synergistic molecular design in the soft and hard segments. Using the liquid glycolysis degradation product (LGOP) as a chain extender, polyurethane elastomer is synthesized from polyethylene terephthalate (PET) waste bottles. The results suggest that the degradation products from waste PET can be directly used as feedstock for preparing polyurethane elastomers with significant performance. The polyurethanes exhibited excellent optical transparency of near 90%, and can be stretched up to 670% without any treatment to return to original size. It is assumed that the symmetrical hard domain composed of aromatic rings and ester groups in LGOP creates sufficient chain fluidity for the dynamic exchange of hydrogen bonds and urethane. This paper has devoted to achieve a complete and mature system from waste PET to polyurethane products, to create a closed loop of waste PET plastic recycling and regeneration, and to realize the polyurethane industrial chain of raw material self-supply.

Strategic Approach Towards Plastic Waste Valorization: Challenges and Promising Chemical Upcycling Possibilities

Plastic waste, which is one of the major sources of pollution in the landfills and oceans, has raised global concern, primarily due to the huge production rate, high durability, and the lack of utilization of the available waste management techniques. Recycling methods are preferable to reduce the impact of plastic pollution to some extent. However, most of the recycling techniques are associated with different drawbacks, high cost and downgrading of product quality being among the notable ones. The sustainable option here is to upcycle the plastic waste to create high-value materials to compensate for the cost of production. Several upcycling techniques are constantly being investigated and explored, which is currently the only economical option to resolve the plastic waste issue. This Review provides a comprehensive insight on the promising chemical routes available for upcycling of the most widely used plastic and mixed plastic wastes. The challenges inherent to these processes, the recent advances, and the significant role of the science and research community in resolving these issues are further emphasized.

Plastic waste associated with the COVID-19 pandemic: Crisis or opportunity?

Coronavirus Diseases 2019 (COVID-19) pandemic has a huge impact on the plastic waste management in many countries due to the sudden surge of medical waste which has led to a global waste management crisis. Improper management of plastic waste may lead to various negative impacts on the environment, animals, and human health. However, adopting proper waste management and the right technologies, looking in a different perception of the current crisis would be an opportunity. About 40% of the plastic waste ended up in landfill, 25% incinerated, 16% recycled and the remaining 19% are leaked into the environment. The increase of plastic wastes and demand of plastic markets serve as a good economic indicator for investor and government initiative to invest in technologies that converts plastic waste into value-added product such as fuel and construction materials. This will close the loop of the life cycle of plastic waste by achieving a sustainable circular economy. This review paper will provide insight of the state of plastic waste before and during the COVID-19 pandemic. The treatment pathway of plastic waste such as sterilisation technology, incineration, and alternative technologies available in converting plastic waste into value-added product were reviewed.

Cellulose-based polymers

The presented chapter deals with structure, morphology, and properties aspects concerning cellulose-based polymers in both research and industrial production, such as cellulose fibers, cellulose membranes, cellulose nanocrystals, and bacterial cellulose, etc. The idea was to highlight the main cellulose-based polymers and cellulose derivatives, as well as the dissolution technologies in processing cellulose-based products. The structure and properties of cellulose are introduced briefly. The main attention has been paid to swelling and dissolution of cellulose in order to yield various kinds of cellulose derivatives through polymerization. The main mechanisms and methods are also presented. Finally, the environmental friendly and green cellulose-based polymers will be evaluated as one of the multifunctional and smart materials with significant progress.

Flexible temperature sensors based on carbon nanomaterials

Flexible temperature sensors based on carbon nanomaterials can be attached to the surface of human skin or curved surfaces directly for continuous and stable data measurements, and have attracted extensive attention in myriad areas.