Keerthi Sasikumar1, 2 and K. Madhavan Nampoothiri1, 2 *
1Microbial Processes and Technology Division (MPTD), CSIR- National Institute for Interdisciplinary Science and Technology, Trivandrum – 695019, India.
2Academy of scientific and Innovative Research (AcSIR), Ghaziabad -201002, India
*Correspondence: Tel: +91- (0) 471-2515366 Fax: +91-(0)471-2491712; firstname.lastname@example.org
Nylon is the commercial name for a kind of polyamide thermoplastic. The Polyamide nylon has varying supremacy that makes it an ideal candidate for a wide range of applications. It was first developed in the mid-1930s and the global nylon market is expected to grow at a compound annual growth rate of 6.2% from 2018 to 2025 to reach USD 41.1 billion by 20256. Polyamides, better known under the generic name nylons, are a major class of engineering plastics and they are produced via polycondensation of a diacid and a diamine, or ring-opening polymerization of a lactam (a cyclic compound with an amide group) (Fig.1). The backbone of nylon is characterized by recurring units (−CO−NH−) of diamines and dicarboxylic acids that may contain different numbers of carbon atoms rendering varying material properties 2.
Polyamides are named after the number of carbon atoms of each of the monomers, in which the first number corresponds with the diamine and the second with the diacid. Nylon comes in four main grades of polyamide nylon: nylon 66, 11, 12 and 465. Due to the various advantages (Table1), the nylon market is segmented into automobiles, electrical and electronics, engineering plastics, textile, and others. Automotive held the largest market share in 2019; The Asia Pacific was the dominant regional segment occupying over 42.95% of the revenue share in 2019 followed by Europe and North America.
Every year polymers constitute a major fraction of industrial petrochemicals. However, during the current decade, bio-based processes from renewable resources have come into a priority (Fig.2.), as they open routes to value-added chemicals and supreme materials.
Biopolymers produced from renewable raw materials provide an environmentally friendly alternative to conventional petroleum-based polymers and exhibit new interesting properties, such as low water uptake, high mechanical resistance, high melting point, and crystallization rate1. Vegetable oils derived from non-edible plants are good alternative chemical feedstock due to their specific reactivity and biocompatibility2. They are vastly used for durable biothermoplastics, such as biopolyamides which have huge demand as they show promising mechanical and thermal properties.
The growth in the polyamide market is driven by the polyamide 6 and polyamide 66 segments due to their usage in a wide range of products across several industries. The bio-based and specialty polyamide type segment is projected to be the fastest-growing type segment of the polyamide market from 2016 to 2021. The demand for organic materials is expected to rise globally due to the rise in prices of petrochemical-based raw materials. Bio-based polyamides are a high-quality alternative to substitute petro-based materials and some of the leading industries involved in bio-based polymers and chemicals are shown in Table 2
Bio-polyamides are synthesized from monomers or comonomers, which belong to amino acid, cyclic amide (lactam), dicarboxylic acid, and diamine families. Three main groups of monomers for the production of biopolyamides are (i) diamines and diacids undergoing polycondensation, where both monomers and only diacid come from renewable feedstock, (ii) amino-carboxylic acids capable for polycondensation and (iii) lactams transformed into polyamides via ring-opening polymerization. Table 3 shows some of those monomers and the raw material used.
Monomers used in biopolyamides synthesis can be obtained partially or fully from biomass 2. Currently, biomass-derived monomers with the highest industrial meaning for the synthesis of biopolyamides are 11-aminoundecanoic acid, 1, 8-octanedicarboxylic acid, 1, 10-decanediamine, adipic acid, caprolactam and 1, 4-butanediamine.
The main source of bio-based monomers for polyamides is castor oil, which makes up 40–60% of the castor bean. Fatty acids present in vegetable oils can be converted by simple reactions into suitable bifunctional monomers for the production of polyamides by a simple polycondensation process. Among the most known biomonomers are 11-aminoundecanoic acid and sebacic acid produced by conversion of ricinoleic acid derived from castor oil. Typically, raw castor oil is hydrolyzed to give ricinoleic acid, which is then converted to sebacic acid in a reaction with potassium or sodium hydroxide at high temperature 12. The 1,12-dodecanedioic is most often prepared from petrochemical butadiene, but potentially it can be obtained by an x-oxidation process of lauric acid catalyzed by yeast strain. Undecane-1, 11-dicarboxylic acid and 11-aminoundecanoic acid were also reported as potential monomers 12.
Bio-polyamides, e.g., 1, 5-diaminopentane (cadaverine), pentamethylenediamine, or tetramethylenediamine, are naturally occurring substances or they can be produced by microbial biosynthesis (e.g., by decarboxylation of amino acids (lysine, ornithine)11,17 and polymerization with substances from microbial fermentation (such as succinate)15. Monomers used in biopolyamides synthesis can be obtained partially or fully from biomass. Currently, biomass-derived monomers with the highest industrial meaning for the synthesis of biopolyamides are 11-aminoundecanoic acid, 1,8-octanedicarboxylic acid, 1, 10-decanediamine, adipic acid, caprolactam and 1,4-butanediamine etc 9,10.
A large number of the polyamide monomers can be produced, in principle, by bio-based routes, which led to the availability of a variety of different polyamides with excellent properties. Corynebacterium glutamicum in which the L-homoserine dehydrogenase gene (hom) was replaced by the L-lysine decarboxylase gene (cadA) of Escherichia coli showed great potential for the production of the glutamate-derived diamine putrescine, a monomeric compound of polyamides. So far, putrescine has been produced using engineered E. coli and C. glutamicum. Putrescine was also produced from alternative carbon sources such as crude glycerol13 biomass hydrolysates14 , amino sugars and juices etc. In one of the recent studies, the methylotrophic and thermophilic bacterium Bacillus methanolicus was engineered for the production of the platform chemical cadaverine (1, 5-diaminopentane) from methanol7. This was achieved by the heterologous expression of the E. coli genes cadA and ldcC encoding two different lysine decarboxylase enzymes, and by increasing the overall L-lysine production levels in this host.
A new metabolic pathway for the production of 5-aminovalerate (5AVA) from l-lysine via cadaverine as an intermediate was also established 8 and this three-step-pathway comprises l-lysine decarboxylase (LdcC), putrescine transaminase (PatA) and γ-aminobutyraldehyde dehydrogenase (PatD). Upon expression of ldcC, patA and patD from E. coli in C. glutamicum wild type, production of 5AVA was achieved for the synthesis of cadaverine from glucose by fermentation. Moreover, 5AVA production from the alternative feedstocks such as starch, glucosamine, xylose and arabinose was also established. Thus, a large number of the polyamide monomers can be produced, in principle, by bio-based routes, which led to the availability of a variety of different polyamides (Table 4) with excellent properties.
To summarize, nylon polymers have found significant commercial applications in fabric /fibers, molded parts for cars, electrical equipment, food packaging and medical devices. Sustainable technologies of extraction and synthesis of a variety of biomass-derived chemicals and monomers of polymers are reported in the recent past and the development of bio-based feedstock is rudimentary for the future progress in bioplastic production and is considered a unique and fast-evolving field of chemical technology. The need for sustainable, bio-based approaches to material precursors is an area of business attraction. Through carefully drafted fermentation processes, industrial biotechnology rather called white biotechnology can make many wonders. It has been demonstrated by the researchers that using a synthetic biology approach and with genetically engineered microorganisms it is possible to produce many of the monomers of the polyamides from biomass-derived sugars including the abundantly present pentose sugar Xylose of the biomass and it is an economic opportunity for the industries to look in to. The real challenge is of the translation step, how all these laboratory studies can be successfully converted to the commercial scale. Many of the new biotechnological processes combine an enzymatic catalytic step with one or more chemo-catalytic steps and is popularly known as green chemistry which helps to derive new pathways that did not exist and is a tremendous opportunity.
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About the Authors
Mrs. Keerthi Sasikuamr is MSc Microbiology rank holder and currently working as ACSIR PhD scholar in Microbial processes and technology Division of CSIR NIIST. Her research focus is on utilization of biomass for the production of value added chemicals such as the building blocks of polyamides using genetically engineered Corynebacterium glutamicum strains. She is author in seven research papers.
Dr K. Madhavan Nampoothiri, PhD FBRS, is presently working as Senior Principal Scientist in the Microbial processes and technology division of CSIR-NIIST, Trivandrum. He obtained his PhD in Microbial Biotechnology and he worked as Alexander von Humboldt (AvH) fellow at IBT1 , Forschunzentrum , Juelich in Germany and as Welcome Trust fellow in the University of Newcastle upon Tyne, England. In 2001 he joined in CSIR-NIIST, Trivandrum. He has nearly 190 publications with google citation more than 11800. In 2016, he was elected as Fellow of the BRSI. His Research interests are in the areas of bioprocess and microbial products, Industrial and therapeutic enzymes functional genomics and infectious diseases, probiotics and biopolymers etc. Google scholar: https://scholar.google.co.in/citations?user=cQ09vN8AAAAJ&hl=en (cQ09vN8AAAAJ)