Biopolymer and biosurfactant-graft-calcium sulfate/polystyrene nanocomposites: Thermophysical, mechanical and biodegradation studies

Biotechnological Plastic Degradation and Valorization Using Systems Metabolic Engineering

Various kinds of plastics have been developed over the past century, vastly improving the quality of life. However, the indiscriminate production and irresponsible management of plastics have led to the accumulation of plastic waste, emerging as a pressing environmental concern. To establish a clean and sustainable plastic economy, plastic recycling becomes imperative to mitigate resource depletion and replace non-eco-friendly processes, such as incineration. Although chemical and mechanical recycling technologies exist, the prevalence of composite plastics in product manufacturing complicates recycling efforts. In recent years, the biodegradation of plastics using enzymes and microorganisms has been reported, opening a new possibility for biotechnological plastic degradation and bio-upcycling. This review provides an overview of microbial strains capable of degrading various plastics, highlighting key enzymes and their role. In addition, recent advances in plastic waste valorization technology based on systems metabolic engineering are explored in detail. Finally, future perspectives on systems metabolic engineering strategies to develop a circular plastic bioeconomy are discussed.

Optimization of Polystyrene Biodegradation by Bacillus cereus and Pseudomonas alcaligenes Using Full Factorial Design

Microplastics (MP) are a global environmental problem because they persist in the environment for long periods of time and negatively impact aquatic organisms. Possible solutions for removing MP from the environment include biological processes such as bioremediation, which uses microorganisms to remove contaminants. This study investigated the biodegradation of polystyrene (PS) by two bacteria, Bacillus cereus and Pseudomonas alcaligenes, isolated from environmental samples in which MPs particles were present. First, determining significant factors affecting the biodegradation of MP-PS was conducted using the Taguchi design. Then, according to preliminary experiments, the optimal conditions for biodegradation were determined by a full factorial design (main experiments). The RSM methodology was applied, and statistical analysis of the obtained models was performed to analyze the influence of the studied factors. The most important factors for MP-PS biodegradation by Bacillus cereus were agitation speed, concentration, and size of PS, while agitation speed, size of PS, and optical density influenced the process by Pseudomonas alcaligenes. However, the optimal conditions for biodegradation of MP-PS by Bacillus cereus were achieved at γ_MP = 66.20, MP size = 413.29, and agitation speed = 100.45. The best conditions for MP-PS biodegradation by Pseudomonas alcaligenes were 161.08, 334.73, and 0.35, as agitation speed, MP size, and OD, respectively. In order to get a better insight into the process, the following analyzes were carried out. Changes in CFU, TOC, and TIC concentrations were observed during the biodegradation process. The increase in TOC values was explained by the detection of released additives from PS particles by LC-MS analysis. At the end of the process, the toxicity of the filtrate was determined, and the surface area of the particles was characterized by FTIR-ATR spectroscopy. Ecotoxicity results showed that the filtrate was toxic, indicating the presence of decomposition by-products. In both FTIR spectra, a characteristic weak peak at 1715 cm⁻¹ was detected, indicating the formation of carbonyl groups (−C=O), confirming that a biodegradation process had taken place.

Biodegradation of polyethylene and polystyrene: From microbial deterioration to enzyme discovery

The global production of plastics has continuously been soaring over the last decades due to their extensive use in our daily life and in industries. Although synthetic plastics offer great advantages from packaging to construction and electronics, their low biodegradability induce serious plastic pollution that damage the environment, human health and make irreversible changes in the ecological cycle. In particular, plastics containing only carbon-carbon (C-C) backbone are less susceptible to degradation due to the lack of hydrolysable groups. The representative polyethylene (PE) and polystyrene (PS) account for about 40% of the total plastic production. Various chemical and biological processes with great potential have been developed for plastic recycle and reuse, but biodegradation seems to be the most attractive and eco-friendly method to combat this growing environmental problem. In this review, we first summarize the current advances in PE and PS biodegradation, including isolation of microbes and potential degrading enzymes from different sources. Next, the state-of-the-art techniques used for evaluating and monitoring PE and PS degradation, the scientific toolboxes for enzyme discovery as well as the challenges and strategies for plastic biodegradation are intensively discussed. In return, it inspires a further technological exploration in expanding the diversity of species and enzymes, disclosing the essential pathways and developing new approaches to utilize plastic waste as feedstock for recycling and upcycling.

Biodegradation of petroleum based and bio-based plastics: approaches to increase the rate of biodegradation

Plastic production and consumption are on the rise due to their variety of uses. Plastics often accumulate in the environment and pose a risk due to the lack of a viable strategy for their safe disposal. Even prohibiting plastic covers does not solve the problems of plastic waste generation. Plastics are degraded by various microbes, although at a very slow rate. In addition, efforts to enhance plastic degradation efficiency by microbes are rarely addressed. This paper describes the biodegradation of both petroleum-based and bio-based plastics, as well as studies on plastic biodegradation in both the Indian and global scenarios. This paper also discusses the biochemical and molecular aspects of plastic biodegradation, which are essential since they disclose more about how bacteria break down plastics. We also shed light on initiatives to boost biodegradation rates using various strategies in this article. Understanding the enzymes and genes involved in biodegradation would also help researchers figure out how to use them to enhance microorganism's ability to degrade plastic.

Photo-catalytic and biotic degradation of polystyrene packaging film: Effect of zinc oxide photocatalyst nanoparticles and nanoclay

Synergistic effect of zinc oxide nanoparticles (ZnO-NPs) as photocatalyst and organonanoclay (ONC) as biodegradable promoter on the degradation of polystyrene (PS) film was investigated. The films were exposed to ultraviolet irradiation under ambient air at room temperature for photo-catalytic degradation and then submitted to biodegradation test in soil using respirometric procedure. Fourier-transform infrared and ultraviolet-visible spectroscopy, thermogravimetric analysis, colorimeter technique, contact angle measurement, and the carbon dioxide evolution results showed higher photo- and biodegradation efficiency of PS-ONC-ZnO nanocomposite compared to the neat PS, PS-ONC and PS-ZnO nanocomposites. Thermal stability, optical band gap, and water contact angle of photo-degraded PS-ONC-ZnO nanocomposite decreased by 11.37, 18.33 and 63.99%, respectively, while that of PS film was only 6.20, 6.44 and 5.84%, respectively. The photo-degraded PS-ONC-ZnO and PS-ZnO film indicated a biodegradation percentage value of 3.3 and 2.1%, respectively, over 16 weeks of incubation in soil. The possible degradation mechanism of nanocomposites was briefly discussed.

Nano-plastics and their analytical characterisation and fate in the marine environment: From source to sea

Polymer contamination is a major pollutant in all waterways and a significant concern of the 21st Century, gaining extensive research, media, and public attention. The polymer pollution problem is so vast; plastics are now observed in some of the Earth's most remote regions such as the Mariana trench. These polymers enter the waterways, migrate, breakdown; albeit slowly, and then interact with the environment and the surrounding biodiversity. It is these biodiversity and ecosystem interactions that are causing the most nervousness, where health researchers have demonstrated that plastics have entered the human food chain, also showing that plastics are damaging organisms, animals, and plants. Many researchers have focused on reviewing the macro and micro-forms of these polymer contaminants, demonstrating a lack of scientific data and also a lack of investigation regarding nano-sized polymers. It is these nano-polymers that have the greatest potential to cause the most harm to our oceans, waterways, and wildlife. This review has been especially ruthless in discussing nano-sized polymers, their ability to interact with organisms, and the potential for these nano-polymers to cause environmental damage in the marine environment. This review details the breakdown of macro-, micro-, and nano-polymer contamination, examining the sources, the interactions, and the fates of all of these polymer sizes in the environment. The main focus of this review is to perform a comprehensive examination of the literature of the interaction of nanoplastics with organisms, soils, and waters; followed by the discussion of toxicological issues. A significant focus of the review is also on current analytical characterisation techniques for nanoplastics, which will enable researchers to develop protocols for nanopolymer analysis and enhance understanding of nanoplastics in the marine environment.

Effect of calcium sulphate nanorods on mechanical properties of chitosan-hydroxyethyl methacrylate (HEMA) copolymer nanocomposites

Copolymers of chitosan and hydroxyetheyl methacrylate (HEMA) were successfully synthesized using ceric ammonium nitrate (CAN) as an initiator, via in situ polymerization method, followed by efficacious preparation of their nanocomposites by incorporating calcium sulphate nanorods via solution blending process. Hydrophilicity studies confirmed that grafting of HEMA in the backbone of the hydrophobic chitosan chains induced the improvement in hydrophilicity of chitosan, while mechanical properties of the nanocomposites were also enhanced significantly up to 20%, due to availability of enlarged surface area and higher aspect ratio of CaSO₄ nanorods. This was supported by FE-SEM and XRD analysis in terms of proper distribution of nanofiller through the copolymer matrix and corresponding rise in percentage crystallanity respectively. Results obtained from biodegradation studies proved the efficiency of CaSO₄ nanofillers to improve biomechanical strength of chitosan nanocomposites, without affecting their normal degradation profile that renders the products to be applicable for biomedical applications.

Biodegradable polymeric nanostructures in therapeutic applications: opportunities and challenges

Biodegradable polymeric nanostructures (BPNs) have shown great promise in different therapeutic applications such as diagnosis, imaging, drug delivery, cosmetics, organ implants, and tissue engineering.