Lignocellulosic Biomass: A Sustainable Platform for Production of Bio-Based Chemicals and Polymers Furkan H. Isikgora, C. Remzi Becer*b a Department of Chemistry, Boğaziçi University, Bebek, 34342 İstanbul, Turkey b School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, E1 4NS London, United Kingdom The demand for petroleum dependent chemicals and materials has been increasing despite the dwindling of their fossil resources. As the dead-end of petroleum based industry has started to appear, today’s modern society has to implement alternative energy and valuable chemical resources immediately. Owing to the importance of lignocellulosic biomass for being the most abundant and bio-renewable biomass on earth, this critical review provides insights into the potential of lignocellulosic biomass as an alternative platform to fossil resources. In this context, over 200 value-added compounds, which can be derived from lignocellulosic biomass by using various treatment methods, are presented with their references. Lignocellulosic biomass based polymers and their commercial importance are also reported mainly in the frame of these compounds. The review article aims to draw the map of lignocellulosic biomass derived chemicals and their synthetic polymers, and to reveal the scope of this map in today’s modern chemical and polymer industry. cheaper than any other commodity products. However, the 1. Introduction. competitive price advantage of fossil fuels during the last century has disappeared.5 After crossing the oil production peak, the Modern industrial polymerization technologies make it possible dwindling of fossil resources will further boost the oil price and to produce versatile polymers with highly tunable properties and this situation will drastically impact the cost-effectiveness and broad range of applications. Depending on request, today’s competiveness of polymers. More importantly, mass consumption polymers can be stiff or soft, transparent or opaque, conducting or of petroleum based materials leaves devastating environmental insulating, permeable or impermeable, stable or degradable. problems, which are lethal threats for human beings. Growing Some indispensable and irreplaceable applications of them concerns regarding these issues have inevitably started to enforce include high strenght fibers, composites, construction materials, our society demanding for sustainable and green products. The light weight engineering plastics, coatings, adhesives, packaging European Union has already approved laws for the reduction of materials, microelectronics and novel materials for biomedical environmentally abusive materials and started to put greater applications such as drug delivery systems, implants, membranes efforts in finding eco-friendly materials based on natural for artificial kidneys and water purification, dental fillings, resources. Hence, alternative solutions are sought to develop wound dressing and artificial hearts. No other class of materials sustainable polymers from renewable natural resources for can have such diverse properties and versatile applicability. This decreasing the current dependence on fossil resources and fixing 6, 7 means that modern life would be impossible without polymeric the production rate of CO2 to its consumption rate. materials since they provide high quality of life for all humankind.1-3 Biomass and biomass derived materials have been pointed out to 8, 9 be one of the most promising alternatives. These materials are On the other hand, industrial production of a wide range of generated from available atmospheric CO2, water and sunlight chemicals and synthetic polymers heavily relies on fossil through biological photosynthesis. Therefore, biomass has been resources.4 Dwindling of these resources together with their considered to be the only sustainable source of organic carbon in frightening environmental effects, such as global warming and earth and the perfect equivalent to petroleum for the production littering problems, have started to threaten the future of polymer of fuels and fine chemicals with net zero carbon emission.10, 11 In industry. In the early part of the 19th century, Henry Ford this context, lignocellulosic biomass, which is the most abundant suggested that the implementation of a bio-based economy is a and bio-renewable biomass on earth,10 has a critical importance. logical and necessary option for the growth of any civilization. Many studies have shown that lignocellulosic biomass holds This implementation was postponed because oil has always been enormous potential for sustainable production of chemicals and fuels. Besides, it is a renewable feedstock in abundance and is lignocellulosic biomass, different pre- and post-teratment avaliable worldwide.12, 13 Lignocellulosic biomass has been methods for the degradation of lignocellulosic biomass into its projected as an abundant carbon-neutral renewable source, which components are summarized. Over 200 value-added compounds, can decrease CO2 emissions and atmospheric pollution. Thus, it is which can be derived from lignocellulosic biomass by using a promising alternative to limit crude oil, which can be utilized to various treatment methods, are presented with their references. produce biofuels, biomolecules and biomaterials.14-16 Finally, detailed overviews of the polymers that can be produced Furthermore, the major component of lignocellulosic biomass; mainly from these compounds are depicted. The current research cellulose, is considered as the strongest potential candidate for the studies and commercial product examples of these polymers are substitution of petroleum-based polymers owing to its ecofriendly also explained in order to reveal their indispensable need in our properties like renewability, bio-compatibility and bio- modern society. degradability.7 2. Structure and Sources of Lignocellulosic Sustainability of the production of fuels and chemicals from Biomass. biomass, on the other hand, has been greatly debated. As an example, there are cricital concerns regarding the sustainability of Lignocellulosic biomass is mainly composed of three polymers; current production of bioethanol, which relies on starch and sugar cellulose, hemicellulose and lignin together with small amounts crops. The limited supply of such crops can lead to competition of other components, like acetyl groups, minerals and phenolic with food production.17 Lignocellulosic feedstocks have crucial substituents (Figure 1). Depending on the type of lignocellulosic advantages over other biomass supplies in this manner because biomass, these polymers are organized in complex non-uniform they are the non-edible portion of the plant and therefore, they do three-dimensional structures to different degrees and varying not interfere with food supplies.18 Moreover; forestry, agricultural relative composition. Lignocellulose has evolved to resist and agro-industrial lignocellulosic wastes are accumulated every degradation and this robustness or recalcitrance of lignocellulose year in large quantities. Disposal of these wastes to the soil or stems from the crystallinity of cellulose, hydrophobicity of lignin, landfill causes serious environmental problems, however; they and encapsulation of cellulose by the lignin-hemicellulose could be utilized for the production of a number of value added matrix.16, 26, 27 products.19 From economic point of view, lignocellulosic biomass can be produced quickly and at lower cost than other The major component of lignocellulosic biomass is cellulose. agriculturally important biofuels feedstocks such as corn starch, Unlike to glucose in other glucan polymers, the repeating unit of soybeans and sugar cane. It is also significantly cheaper than the cellulose chain is the disaccharide cellobiose. Its structure crude oil.20 consists of extensive intramolecular and intermolecular hydrogen bonding networks, which tightly binds the glucose units (Figure On the other hand, the development of the conversion of 1). Since about half of the organic carbon in the biosphere is lignocellulosic biomass to fine chemicals and polymers still present in the form of cellulose, the conversion of cellulose into remains a big challange.10 Lignocellulose has evolved to resist fuels and valuable chemicals has a paramount importance.10, 12, 13 degradation. This inherent property of lignocellulosic materials makes them resistant to enzymatic and chemical degradation.16 Hemicellulose is the second most abundant polymer. Unlike For changing the physical and chemical properties of cellulose, hemicellulose has a random and amorphous structure, lignocellulosic matrix, the pretreatment of lignocellulosic which is composed of several heteropolymers including xylan, biomass, which is an expensive procedure with respect to cost galactomannan, glucuronoxylan, arabinoxylan, glucomannan and and energy, is essential.21 Although lignocellulosic materials are xyloglucan (Figure 1). Hemicelluloses differ in composition too; abundant and usually low-priced, the crucial challenge in hardwood hemicelluloses contain mostly xylans, whereas converting lignocellulosic biomass is to produce value-added softwood hemicelluloses contain mostly glucomannans. The chemicals at high selectivities and yields at economical costs.22 heteropolymers of hemicellulose are composed of different 5- and Extensive research is currently being undertaken all over the 6-carbon monosaccharide units; pentoses (xylose, arabinose), world to address this problem.23