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Plastics recycling is an important component of the circular economy. In mechanical recycling, the recovery of high-quality plastics for subsequent reprocessing requires plastic waste to be first sorted by type, color, and size. In chemical recycling, certain types of plastics should be removed first as they negatively affect the process. Such sortation of plastic objects at Materials Recovery Facilities (MRFs) relies increasingly on automated technology. Critical for any sorting is the proper identification of the plastic type. Spectroscopy is used to this end, increasingly augmented by machine learning (ML) and artificial intelligence (AI). Recent developments in the application of ML/AI in plastics recycling are highlighted here, and the state of the art in the identification and sortation of plastic is presented. Commercial equipment for sorting plastic recyclables is identified from a survey of publicly available information. Automated sorting equipment, ML/AI-based sorters, and robotic sorters currently available on the market are evaluated regarding their sensors, capability to sort certain types of plastics, primary application, throughput, and accuracy. This information reflects the rapid progress achieved in sorting plastics. However, the sortation of film, dark plastics, and plastics comprising multiple types of polymers remains challenging. Improvements and/or new solutions in the automated sorting of plastics are forthcoming. 

The growing textile industry is polluting the environment and producing waste at an alarming rate. The wasteful consumption of fast fashion has made the problem worse. The waste management of textiles has been ineffective. Spurred by the urgency of reducing the environmental footprint of textiles, this review examines advances and challenges to separate important textile constituents such as cotton (which is mostly cellulose), polyester (polyethylene terephthalate), and elastane, also known as spandex (polyurethane), from blended textiles. Once separated, the individual fiber types can meet the demand for sustainable strategies in textile recycling. The concepts of mechanical, chemical, and biological recycling of textiles are introduced first. Blended or mixed textiles pose challenges for mechanical recycling which cannot separate fibers from the blend. However, the separation of fiber blends can be achieved by molecular recycling, i.e., selectively dissolving or depolymerizing specific polymers in the blend. Specifically, the separation of cotton and polyester through dissolution, acidic hydrolysis, acid-catalyzed hydrothermal treatment, and enzymatic hydrolysis is discussed here, followed by the separation of elastane from other fibers by selective degradation or dissolution of elastane. The information synthesized and analyzed in this review can assist stakeholders in the textile and waste management sectors in mapping out strategies for achieving sustainable practices and promoting the shift towards a circular economy. 

Xanthan gum (XG) is a carbohydrate polymer with anionic properties that is widely used as a rheology modifier in various applications, including foods and petroleum extraction. The aim was to investigate the effect of Na+, K+, and Ca2+ on the physicochemical properties of XG in an aqueous solution as a function of temperature. Huggins, Kraemer, and Rao models were applied to determine intrinsic viscosity, [η], by fitting the relative viscosity (ηrel) or specific viscosity (ηsp) of XG/water and XG/salt/water solutions. With increasing temperature in water, Rao 1 gave [η] the closest to the Huggins and Kraemer values. In water, [η] was more sensitive to temperature increase (~30% increase in [η], 20–50 °C) compared to salt solutions (~15–25% increase). At a constant temperature, salt counterions screened the XG side-chain-charged groups and decreased [η] by up to 60% over 0.05–100 mM salt. Overall, Ca2+ was much more effective than the monovalent cations in screening charge. As the salt valency and concentration increased, the XG coil radius decreased, making evident the effect of shielding the intramolecular and intermolecular XG anionic charge. The reduction in repulsive forces caused XG structural contraction. Further, higher temperatures led to chain expansion that facilitated increased intermolecular interactions, which worked against the salt effect. 

The anionic hydrocolloid polysaccharide xanthan gum is widely used in the food and petroleum industries (among others) as a viscosity enhancement polymer due to its high viscosity at low concentrations and moderate temperatures. The physical properties of microbial polysaccharide xanthan gum aqueous solutions were investigated using temperature dependent viscosity measurements. Specifically, the effect of thermal history on the solution viscosity was investigated. Heating and cooling cycles were assessed in two ways, by using a “sawtooth” and “triangle” pattern, which essentially differed in the rates of cooling. The sawtooth method used a cooling rate of 2.0 ◦C min􀀀 1 whereas the triangle pattern had a cooling rate of 0.20 ◦C min􀀀 1. The sawtooth cooling rate was controlled by the speed at which the Peltier device could cool the sample, and the triangle rate was governed by the time required to measure the viscosity at each temperature on return to the initial value. Cycles measured using the sawtooth pattern for 16 mg/kg xanthan gum in water showed an 8–10% overall decrease in the viscosity over four complete cycles. Comparatively, at 320 mg/kg the xanthan gum solution showed a 25% decrease in viscosity over four cycles. The observed temperature dependent viscosity variation suggested minor modifications in the physical network structure of xanthan gum. When using a triangle heating/cooling pattern, the overall decrease in the xanthan gum solution viscosity was 5–7% for 16 mg/kg and only 10% change for 320 mg/ kg solutions. The activation energy of viscous flow for the aqueous xanthan gum solutions by either method was ~15.0 kJ/mol under all conditions. The data showed that temperature and heating cycles influence xanthan gum viscosity and thermal history, which depends more strongly on xanthan gum concentration than solution temperature. 

ABSTRACT Elucidating the crystalline‐amorphous interface during decrystallization processes in semi‐crystalline polyethylene (PE) is crucial for the advancement of polymer theory and plastic‐to‐plastic recycling technologies. In this study, we carried out an in‐depth investigation of PE thin films undergoing melting or dissolution using a temperature‐controlled liquid flow‐cell experimental setup which provided in situ mid‐infrared (MIR, 4000–700 cm⁻¹) and near‐infrared (NIR, 6000–4000 cm⁻¹) spectra in real time. The spectroscopic results yielded molecular‐level information regarding PE decrystallization and chain disentanglement via fundamental vibrations, combination bands, and overtones which were correlated using hetero‐spectral two‐dimensional correlation spectroscopy (2D‐COS). A quantitative procedure for the calculation of PE degree of crystallinity was developed to track transformations of crystalline domains during melting and dissolution. This semi‐empirical model achieved a strong linear correlation of at least +0.93 in four spectral regions: 750–700 cm⁻¹, 1500–1400 cm⁻¹, 3000–2800 cm⁻¹, and 4400–4200 cm⁻¹. This analysis revealed important spectral trends about the interfacial solvation environment during these processes. Lastly, the time evolution of the unraveling, terminal methyl (CH₃) groups of PE cilia was examined in relation to the decrystallization mechanism of PE. The insights obtained from this study advance the fundamental understanding necessary for developing new depolymerization and dissolution‐precipitation recycling strategies. 

Recycling plastic is an important step towards a circular economy. Attaining high-quality recycled plastics requires the separation of plastic waste by type, color, and size prior to reprocessing. Automated technology is key for sorting plastic objects in medium- to high-volume plants. The current state of the art of commercial equipment for sorting plastic as well as challenges faced by Material Recovery Facilities (MRFs) to sort post-consumer plastics are analyzed here. Equipment for sorting plastic recyclables were identified using publicly available information obtained from manufacturers’ websites, press releases, and journal articles. Currently available automated sorting equipment and artificial intelligence (AI)-based sorters are evaluated regarding their functionality, efficiency, types of plastics they can sort, throughput, and accuracy. The information compiled captures the progress made during the ten years since similar reports were published. A survey of MRFs, reclaimers, and brokers in the United States identified methods of sorting used for plastic, sorting efficiency, and current practices and challenges encountered at MRFs in sorting plastic recyclables. The commercial sorting equipment can address some of the challenges that MRFs face. However, sorting of film, multilayered, blended, or mixed-material plastics is problematic, as the equipment is typically designed to sort single-component materials. Accordingly, improvements and/or new solutions are considered necessary.