Research
Research on the reduction of plastic pollution
Synthetic polymers (plastic) became ubiquitous in almost every aspect of our life due to their appealing features such as low price, lightweight, easy availability, and durability. None of the commercially used polymers (e.g., polyethylene, polypropylene, polyethylene terephthalate, etc.), are bio-degradable and their natural destruction typically takes hundreds of years. The lack of proper recycling of these plastic materials results in pollution in the form of landfill and their presence in the ocean, the annual accumulation of around 1.1 to 8.8 million tons. An estimated economic loss of 80-120 billion dollars every year results from these billions of tons of plastics that can not be recycled. The situation is so threatening that the research indicates that in 2050, there will be more plastic in the ocean than fish.
While the exhaustive pyrolysis and mechanical recycling of plastic waste provide a partial solution. Wherein the former involves breaking drown the polymer into small useful components.4 The toxic gaseous side products in pyrolysis are one of the major environmental concerns. Mechanical recycling which involves melting the plastic and subsequently reshaping and reusing often results in inferior properties caused by the residual chemical impurities, catalysts, and other contaminants. Such downcycling makes plastic recycling a daunting task. More recently the chemical recycling of plastic has emerged as one of the alternatives due to its advantageous features such as the regeneration of the monomer and production of valued materials from the plastic wastes. Despite the exciting advances, the majority of the chemical recycling processes are not economically preferable; the chemical recycling of PET bottles cost nearly 30 % more than fresh bottle prepared from petrochemical resources. Thus, upcycling plastic which involves the creation of products of higher quality or value than the original plastic is essential for the reduction of plastic pollution.
Scheme: Recycling and upcycling of polyethylene terephthalate (PET) via aminolysis with 2-aminoethanol and generation of valued compound which will be utilized for various purposes as mentioned.
Our current research aim focuses on the chemical upcycling of polyethylene terephthalate (PET) polymer waste (see the scheme). PET is one of the most commonly encountered commercial polymers, used in clothing as fiber and as a container. PET is the sixth most produced plastic, constituting around 18% of the total polymers produced worldwide. It is worth mentioning, that most plastic drinking bottles are primarily made of PET. In 2015, the global production of PET was 56 million tons, nearly 60 % for clothing and 30 % for bottles. The starting monomer for PET, terephthalic acid, and ethylene glycol, both of which are obtained from raw petroleum.
The research aims
1. Generation of valued compounds (e.g aminolysis of PET) and its utilization for the preparation of polymer with targeted properties.
2. Chemical degradation of a plastic (e.g PET) and generation of valued monomer which will be utilized for the preparation of the original polymer.
3. Upcycling of plastic to the plastic derived compounds via dynamic covalent polymer networks (DCPN)
4. Making and breaking of sustainable polymers derived from renewable sources and waste plastic
Research on sustainable polymer
Besides, one of the prime concerns is that the majority of the monomers for common plastics are derived from petrochemical sources. At present nearly 8% of petroleum is produced for this purpose. The demand is increasing monotonically; it is estimated that by 2050 nearly 20% of the total production will be required for the preparation of the polymer. This adds up to the energy crisis occurring mainly due to the increasing demand and faster depletion of fossil fuels which has emerged as a major problem around the world in recent times. The various olefins (e.g. ethylene, propylene, butadiene, etc) and aromatic compounds (such as benzene, toluene, xylene, etc) are obtained from the petrochemical industry via steam cracking of naphtha and alkanes. Some of these monomers are used directly for the preparation of the polymer (e.g. ethylene to polyethylene) and others are used as precursors for the synthesis of other monomers, e.g. ethylene oxide, vinyl chloride, and vinyl acetate prepared from ethylene. The polymer derived from a renewable source (e.g bio sources) would help avoid dependency on petrochemical sources. The recycling of these polymers would minimize pollution. Our other research goal in this context is “Making and breaking of sustainable polymer from renewable sources and waste plastic” (see the figure/cartoon below)
Research of dynamic covalent network
Polymers are generally classified into two categories; thermoplastic and thermoset (see figure 1). Thermoplastic polymers refer to linear polymer chains. Polyethylene, polypropylene, polyethylene terephthalate, nylon, Teflon, etc. are the commonly encountered thermoplastic polymers in our day-to-day life. Thermoplastic polymers are easily malleable, reprocessable, and recyclable but they are not suitable for high temperature and high strength applications. On the other hand thermoset polymers which are typically used for high temperature and high strength applications, consist of a permanent crosslink network structure, and hence cannot be recycled (e.g., tire-to-tire recycling) and reprocessed once a permanent shape is attained. Among many others, thermoset polymers provide thermal, dimensional, and solvent stability over a range of temperatures. The Bakelite is one of the famous examples of the thermoset polymer prepared from the condensation reaction of phenol and formaldehyde and has found widespread applications since the beginning of the 20th century.
Figure: The figure depicts two classes of polymer, thermoplastic and thermoset with their pro and cons. The DCPN which bridges the gap between these two types of the polymer is schematically depicted.
Dynamic covalent polymeric network (DCPN) or covalent adaptable network (CAN) is a special class of polymer, one of the major breakthrough of polymer science in recent times which bridge the gap between the thermoset and thermoplastic by overcoming the limitations and combining the advantages of these two types of polymers. DCPN is the cross-linked polymeric network where the crosslinkers possess a dynamic linkage. The activation of the dynamic bonds in the presence of suitable stimuli (e.g. heat or light) allows the dynamic exchange of the bond and topological rearrangements of the network, enabling the reprocessing and recycling of these thermoset-like materials. Thus DCPNs is a novel cause for the minimization of plastic waste and energy, a greener cause toward sustainability, and a circular economy.
Figure : The various dynamic chemistries that were employed for the development of DCPNs.
At the present, the area encounters few major challenges: A variety of dynamic reactions (functional groups, shown in figure ) e.g. transesterification reaction, disulphide exchange reaction, Diels-Alder reaction, etc. have been explored for the development of DCPN; notably, transesterification is the most commonly used chemistry due to the easy availability of the starting materials. The majority of the functional groups require the addition of an external catalyst (e.g. Lewis acid catalyst for transesterification) to exhibit dynamic behaviors. The catalyst leaching or catalyst inhomogeneity results in poor properties, and loss in dynamicity and could affect end users.12 Besides the majority of these dynamic functional groups undergo unwanted side reactions during multiple recycling steps or reprocessing at a higher temperature, resulting in the loss of dynamic character, material properties, and recyclability. The “creep” is another major downside, limiting its practical and wide-scale commercial applications. Creep is the deformation (e.g. elongation) of solid materials under stress.
Research aim:
1.We are currently developing robust dynamic chemistry which will help to overcome these limitations.
2. Using neighboring group participation (internal catalysis) a new class of DCPN is being developed which would help avoid the addition of external catalysts, thus overcoming the drawbacks associated with the external catalysts.
3. We are developing strategies for enhancing the applicability of DCPN by minimizing creep while maintaining reprocessability and recyclability.
Research on Smart Hydrogels
Our research focuses on the development and application of smart hydrogels, a class of materials with the remarkable ability to respond to external stimuli. These hydrogels can change their properties in response to factors such as temperature, pH, light, and the presence of specific molecules. Through innovative design and synthesis, our aim to create hydrogels that not only adapt to their surroundings but also exhibit precise and controlled behavior. Our investigations span various fields, from drug delivery and tissue engineering to sensors and actuators.
However, challenges persist, notably in enhancing their mechanical strength. Improving the mechanical properties of hydrogels without compromising their biocompatibility remains a significant challenge. Achieving a balance between strength and flexibility is crucial for applications in load-bearing tissues and medical devices. Research into novel crosslinking methods, reinforcing additives, and hybrid materials holds promise in addressing this challenge.
Research Aim
The primary aim of our research is to develop a pH-responsive, temperature-responsive hydrogel with exceptional mechanical strength and self-healing capabilities. To achieve this, we are focusing on the innovative approach of Triple Network synthesis. By integrating three distinct networks within the hydrogel structure, our aim to create a material that can respond to changes in both pH and temperature, while simultaneously exhibiting remarkable mechanical resilience. Our goal is to engineer a hydrogel that not only demonstrates robust mechanical properties but also possesses the ability to autonomously heal when damaged, making it an ideal candidate for a wide range of applications in biomedicine, smart materials, and beyond.
Other research area
1. Bio-derived polymer
2. Organo catalysis in water using polymeric scaffold