Once referred to as ‘materials of 1,000 uses’, plastics meet demands in everything from clothing and automotive sectors to the manufacturing of medical equipment and electronics. Concomitant with usage, worldwide generation of plastic solid waste increases daily and is currently around 150 million tonnes per annum. Although recycled materials may have physical properties similar to those of virgin plastics, the resulting monetary savings are limited and the properties of most plastics are significantly compromised after a number of processing cycles. An alternative approach to processing plastic solid waste is chemical recycling, the success of which relies on the affordability of processes and the efficiency of catalysts. In this Review, we describe technologies available for sorting and recycling plastic solid waste into feedstocks, as well as state-of-the-art techniques to chemically recycle commercial plastics. These evaluations are followed by a survey of recent advances in the design of new high-performing recyclable polymers. Many methods exist for the recycling of plastic solid waste. Chemical recycling, which can take many forms from high-temperature pyrolysis to mild, solution-based catalytic depolymerization, can afford enormous economic and environmental benefits. This Review covers the state of the art in chemical recycling and the design of high-performance polymers amenable to such processes.

Chemical recycling of waste plastics for new materials production

Spectroscopy is the study of matter interacting with electromagnetic radiation (e.g., light). The electromagnetic spectrum in Figure 1 illustrates the many different types of electromagnetic radiation, including gamma rays (γ-rays), X-rays, ultraviolet (UV) radiation, visible light, infrared (IR) radiation, microwaves, and radio waves. The frequency (ν) and wavelength (λ) ranges associated with each form of radiant energy are also indicated in Figure 1.

Introduction to Spectroscopy

Electrically conductive polymeric materials have recently attracted considerable interest from academic and industrial researchers to explore their potential in biomedical applications such as in biosensors, drug delivery systems, biomedical implants and tissue engineering. Conventional conductive homopolymers such as polypyrrole and PEDOT show promising conductivity for these applications, however their mechanical properties, biocompatibility and processability are often poor. This has led to more recent attention being directed towards conductive polymeric composites comprised of biostable/biocompatible polymers with dispersed conductive fillers such as graphene, carbon nanotubes and metallic nanoparticles. The major objective of this paper is to provide an up to date review of the recent investigations conducted in the development of conductive polymer composites focussing on the methods of their preparation, underlying concepts of their conductivity and the ways to tailor their properties. Furthermore, recent progress made in conventional conducting polymers and their composites/blends for biomedical applications is also discussed.

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Electrically conductive polymers and composites for biomedical applications

Greener routes to polyurethanes are required and arouse a growing interest in the academic and industrial communities. To this purpose, the depletion of fossil resources exacerbates the need of renewable materials. This review details two main routes to phosgene-free and isocyanate-free pathways to polyurethanes: the transurethanization and the cyclic carbonate/amine routes. A focus is also made on bio-based synthons toward non-phosgene and non-isocyanate PUs.

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Isocyanate-Free Routes to Polyurethanes and Poly(hydroxy Urethane)s.

Spectrometric Identification of Organic Compounds

Conventional polyurethanes involve the use of isocyanates, which require hazardous and toxic phosgene for their manufacture. These monomers cannot be manufactured without elaborate safety devices and huge investment. Isocyanates are also considerably toxic and moisture sensitive. Growing global awareness of the need to protect our environment and continually strive to ensure the safety, health and well-being of those in the industry and consumers has created a demand for environment-friendly products. The cyclic carbonate–primary amine addition reaction which results in hydroxyurethanes is a unique reaction and has been extensively studied over the last few years. This chemistry is now attracting research interest due to its potential application in the preparation of “green”, non-porous, moisture-insensitive, isocyanate free polyurethanes. This review focuses on catalysis, the mechanism involved in the formation of Non-Isocyanate Polyurethanes (NIPU) from five-membered cyclic carbonates and the reaction kinetics for their synthesis. The higher homologues of the cyclic carbonate family, the six-membered cyclic carbonates, are similar to, but more reactive than, the five-membered cyclic carbonates and can also serve as a source for production of isocyanate free polyurethanes. This review also summarizes various application of NIPU in coatings, composites, construction and biochemical fields.

Non-isocyanate polyurethanes: from chemistry to applications

Sol–gel derived organic inorganic hybrid coatings are effective corrosion protective systems for metals. They offer an excellent adhesion to metal as well as to the subsequent coat via strong covalent bond and a three dimensional network of –Si–O–Si– linkages which helps to retard the penetration of corrosive medium through the coating. Unlike conventional surface protection methodology, silane based pre-treatment is an environment friendly technology with number of advantages like room temperature synthesis, chemical inertness, high oxidation and abrasion resistance, excellent thermal stability, very low health hazard etc. Further, the hybrid silane provides required flexibility and an increased compatibility with the subsequent coating in multicoat systems. The performance properties of hybrid systems depend on number of parameters like type of silane (mono or bis), degree of hydrolysis, type and dosage of inhibitive/barrier pigments (in case of pigmented system), application techniques, curing temperature and curing schedule, need to be optimized. A guideline formulation for maximum corrosion resistance with low environmental impact consist of a superprimer (a bis-silane with conventional resins, chrome free inhibitive pigments and additives) followed by epoxy or polyurethane top coat as per the exposure conditions.

Sol–gel derived hybrid coatings as an environment friendly surface treatment for corrosion protection of metals and their alloys

Isocyanate free polyurethanes from new CNSL based bis-cyclic carbonate and its application in coatings

Considering ecological and economical issues in the new generation coating industries, the maximum utilization of naturally occurring materials for polymer synthesis can be an obvious option. In the same line, one of the promising candidates for substituting partially, and to some extent totally, petroleum-based raw materials with an equivalent or even enhanced performance properties, is the Cashew Nut Shell Liquid (CNSL). This dark brown-colored viscous liquid obtained from shells of the cashew nut can be utilized for a number of polymerization reactions due to its reactive phenolic structure and a meta-substituted unsaturated aliphatic chain. Therefore, a wide variety of resins can be synthesized from CNSL, such as polyesters, phenolic resins, epoxy resins, polyurethanes, acrylics, vinyl, alkyds, etc. The present article discusses the potential of CNSL and its derivatives as an environment friendly alternative for petroleum-based raw materials as far as polymer and coating industries are concerned.

Anagha Sabnis

Papers

Non-isocyanate polyurethanes: from chemistry to applications

Sol–gel derived hybrid coatings as an environment friendly surface treatment for corrosion protection of metals and their alloys

Isocyanate free polyurethanes from new CNSL based bis-cyclic carbonate and its application in coatings

CNSL: an environment friendly alternative for the modern coating industry

Effect of incorporation of surface treated zinc oxide on non-isocyanate polyurethane based nano-composite coatings