Emerging bio based materials for surface coatings

Excerpt: A bio-based material is a material intentionally made from substances derived from living (or once-living) organisms whereas biopolymers are macromolecules derived from plants, trees or other sources.

## Emerging bio-based materials for surface coatings

| | |
| --- | --- |
| Ashish A Pradhan | Rajesh M Shah |

Ashish A Pradhan* and Rajesh M Shah
Asian Paints Pvt. Ltd.
Research & Technology Centre, Turbhe, Navi Mumbai - 400 703

*Principal Author: - All the communication may be addressed
Queries and Responses: author.paintindia@gmail.com


ABSTRACT

A bio-based material is a material intentionally made from substances derived from living (or once-living) organisms whereas biopolymers are macromolecules derived from plants, trees, bacteria, algae, or other sources. They are long chains of molecules linked together through a chemical bond and are usually able to perform the functions of traditional petroleum-based products. Biopolymers exist in nature as cellulose (in cotton, wood, wheat, etc.), proteins, starches, and polyesters. The potential for using these materials to make synthetic polymers was identified in the early 1900s, but they have only recently emerged as a viable material for large-scale commercial use.

While biopolymers can be made from an almost unlimited range of bio-based materials, most of the currently marketed biopolymers are made from vegetable oils and natural polymers such as cellulose & starch. Bio-based materials have the potential to produce fewer greenhouse gases, require less energy, and produce fewer toxic pollutants over their lifecycle than products made from fossil fuels. They may also be recyclable or compostable depending on the biomaterial and how they have been produced.

As the cost of petroleum resources increases, making products with biobased materials is increasingly attractive. Increased demand for agricultural and forest-based feedstocks also offers new resource-based economic development opportunities for farmers and struggling rural communities and manufacturing sectors. Moreover, societal benefits from a shift to biobased materials could be enormous from long term sustainability point of view.


Introduction

“BIOMATERIAL” or a “Bio-based material” is any material derived from current living organisms including agricultural crops and residues, trees, and algae. There are many raw materials which are bio-based and used in coating industry since many years e.g. vegetable oils and their derivatives. The motivation of the introduction of such material was always economic feasibility of the product.

Nowadays the view point towards the bio based raw materials has been changed. In past few years throughout the world, environmental awareness among people is considerably increased and also after introduction of the stringent environment acts in European countries people are trying to move towards more and more green products.

Another aspect of moving to bio- based raw materials is increasing crude oil prices. Crude oil and natural gas are the starting points for nearly all chemicals used in manufacturing paints and coatings. The chemicals industry uses natural gas not only as an input for fuel and power, but also as the raw material for feedstocks. Conventional route of synthesis of fossil fuel based raw materials used in paints and coatings industry is shown in Fig. 1.


Fig. 1: Conventional route of synthesis of fossil fuel based raw materials used in paints and coatings industry[1]

In this review, an attempt is made to illustrate the classification of bio based raw materials either as a natural polymers or based on the various bio- processes. It also focuses on important concepts such as oil based acrylated monomers and use of naturally occurring materials in coatings and corrosion protections. The paper also emphasizes that if we want to move away from crude oil routes and to introduce more and more renewable Carbons to paints and coatings, then shifting to bio-based raw materials is the only option for a sustainable economy.

Classification of bio-based raw materials used in paints and coatings

  1. Vegetable oil & fatty acid based materials
  2. Biobased or natural polymers
  3. Biobased monomers or building blocks
  4. Biobased solvents and additives
Vegetable oil & fatty acid based raw materials

Vegetable oils have been used as binders or additives in coatings for at least 30,000 years, going back to the days of cave paintings. The primary use of vegetable oil or fatty acid in coatings is for drying. Drying oils are highly unsaturated oils that will oligomerize or polymerize when exposed to the oxygen in air usually in the presence of a catalyst. The result is an increase in the molecular weight as a consequence of cross- linking. Some of the common fatty acids found in oils include myristic, palmitic, stearic, oleic, linoleic, linolenic, pinolenic, ricinoleic and α-eleostearic which are obtained from various vegetable oils such as Coconut, Soybean, Sunflower, Castor, Linseed etc.[2] are known to industry for decades however there are some emerging oils and fatty acids which can be used in paints and coatings

Lesquerolic acid

Lesquerolic acid is a hydroxy acid that occurs naturally In Paysonia lasiocarpa and other Paysonia & Physaia species. It is chemically similar to Ricinoleic acid, but with two additional carbons at the carboxyl end of the carbon chain.


Fig. 2: ricinolic acid and lesequerolic acid

Like castor oil, it was found that lesquerella oil is having an –OH group in its fatty acid chain so it is non-drying. It is expected that chemical dehydration and lesquerella oil produces oil that is similar in drying properties of dehydrated castor oil[3] . Lesquerolic acid, like other hydroxy fatty acids, has important industrial uses, including making resins, waxes, nylons and plastics.

Because of longer chain length (as shown in fig. 2), alkyds and polyesters obtained from lesquerella oil have lower solution viscosity as compared with castor oil alkyds and polyesters.

The hydroxyl group of lesquerella oil can be exploited to make acrylates. Lesquerella oil acrylates impart excellent gloss to wood, aluminum, and steel and have good adhesive properties.

The hydroxyl groups of lesquerella and castor oil also react with cycloethers such as propylene oxide, epichlorohydrin, and ethylene oxide. As a result of these reactions, novel polyhydroxy compounds of much improved reactivity can be obtained. These polyhydroxy compounds can be used as polyols and can be reacted with polyacids in the production of various resins.

Vernonia oil

Vernonia oil is extracted from the seeds of the Vernonia galamensis (or ironweed), a plant native to eastern Africa. The seeds contain about 40 to 42% oil of which 73 to 80% is vernolic acid (12,13–epoxy-9-Octadecenoic acid) (fig.3)

Products that can be made from vernonia oil include epoxies for manufacturing adhesives, varnishes, paints and industrial coatings. As these oils contain multiple functionalities, they provide an alternative to petroleum as a chemical feedstock. The epoxide moieties of vernonia oil play an important role in making acrylates, useful in making UV curing formulations.

Fully epoxidized soybean and linseed oils are not as good as vernonia oil for making reactive diluents for coatings because of their higher viscosities and melting points. Vernonia oil is used as a crosslinker for several polymers containing moieties known to react with epoxy groups. In all cases, the vernonia did indeed act as a crosslinker, producing films with high methyl ethyl ketone double rub resistance if baked for


Fig. 3: Vernonia Oil

a sufficient time. The films cured thermally also had higher glosses. The studies showed that vernonia oil has three important attributes of a reactive diluent, reasonable solvating power, good reactivity and suitable viscosity.[4]

Calendula oil

Calendula commonly known as Marigold is a genus of about 15–20 species of herbaceous plants. They are native to southwestern Asia, western Europe, Macronesia & the Mediterranean. Popular herbal and cosmetic products are available under name 'calendula'. Calendula oil (59–65% calendic acid, 29% linoleic acid, 4% oleic acid, 4% palmitic acid) is obtained by extraction of the seeds of Calendula officinalis.

Calendic acid (see fig.4(a) offers potential to come to vegetable oil based paints with improved drying characteristics. Calendic acid is structurally related to unsaturated fatty acid α-eleostearic acid which is present in tung oil (see fig.4(b) therefore, Calendula oil can be used as cheaper alternative to Tung oil.


Fig. 4 a): Caledic acid (8,10-trans, 12-cis octadecatrienoic acid) b) -eleostearic acid (9-cis,11,13-trans octadecatrienoic acid)

Transesterifications of calendula oil with alcohols (Fig. 5) such as methanol, ethanol, and isopropanol give the respective calendula oil esters, which can be used as reactive diluents for alkyd resins in coating formulations.

Especially ethyl and isopropyl calendula oil esters showed good properties, including low viscosity and good drying performance. The reduction or even the substitution of organic solvents is an important contribution to the necessary reduction of Volatile Organic Content (VOC) [5].

Use of Castor oil as acrylated monomer


Fig. 5: transesterification of calendula oil with merhanol in the presence of sodium methoxide as caralysts to give methyl calendulate.

Castor oil on suitable acrylation can be converted to Castor acrylated monomer (CAM) which acts as a co- monomer in emulsion polymerization. They can be used in acrylic latexes for low VOC, low odor, ambient cure, architectural coatings. It can also be used as as a potent non-volatile plasticizer, improving latex film formation which can reduce organic cosolvent requirements in latex coating formulations. CAM also possesses an internal isolated double bond which functionalizes latex polymers for auto-oxidative polymerization after application.[6]

Bio-based natural polymers

The first generation of bio-based polymers focused on deriving polymers from agricultural feedstocks such as corn, potatoes, and other carbohydrate feedstocks. However, the focus has shifted in recent years due to a desire to move away from food-based resources and significant break throughs in biotechnology. Bio-based polymers offer important contributions by reducing the dependence on fossil fuels and through the related positive environmental impacts such as reduced carbon dioxide emissions. The legislative landscape is also changing where bio- based products are being favored through initiatives such as the Lead Market Initiative (European Union) and BioPreferred (USA). As a result, there is a worldwide demand for replacing petroleum-derived raw materials with renewable resource-based raw materials for the production of polymers.[7]


Fig. 6

Bio-based polymers similar to conventional polymers are produced by bacterial fermentation processes by synthesizing the building blocks (monomers) from renewable resources, including lignocellulosic biomass (starch and cellulose), fatty acids, and organic waste. Natural bio-based polymers are the other class of bio-based polymers which are found naturally, such as proteins, nucleic acids, and polysaccharides (collagen, chitosan, etc.). These bio-based polymers have shown enormous growth in recent years in terms of technological developments and their commercial applications.

There are three principal ways to produce bio-based polymers using renewable resources:

  1. Using natural bio-based polymers with partial modification to meet the requirements (e.g., starch)
  2. Producing bio-based monomers by fermentation/conventional chemistry followed by polymerization (e.g.,polylactic acid)
  3. Producing bio-based polymers directly by bacteria (e.g., polyhydroxyalkanoates).

* Starch*

Starch is a unique bio- based polymer because it occurs in nature as discrete granules. Starch is the end product of photosynthesis in plants - a natural carbohydrate-based polymer that is abundantly available in nature from various sources including wheat, rice, corn, and potato. Essentially, starch consists of the linear polysaccharide amylose and the highly branched polysaccharide amylopectin. (shown in fig.7)


Fig. 7: Structure of the amylopectin molecule

Finger painting is one of the application in which starch is used. Because of non toxicity of starch, it can be used in finger painting.

Starch is also used in paper coatings as one of the binders for the coating formulations which include a mixture of pigments, binders and thickeners.[8]

Cellulose

Cellulose is the predominant constituent in cell walls of all plants. Cellulose is a complex polysaccharide with crystalline morphology. Cellulose differs from starch where glucose units are linked byβ-1, 4-glycosidic bonds, whereas the bonds in starch are predominantly α-1,4 linkages. (Fig. 8)


Fig. 8: Cellulose

The most important raw material sources for the production of cellulosic plastics are cotton fibers and wood. There are currently two processes used to separate cellulose from the other wood constituents.[9]

Regenerated cellulose is the largest bio-based polymer produced globally for film applications. Films obtained from regenerated cellulose (from cotton linter) by coating Castor oil polyurethane/benzyl konjac glucomannan semi-interpenetrating polymer networks were water resistant and biodegradable.[10]

Indesirable quantities, it may be used as a modifier rendering toughness in fragile coatings. The primary hydroxyl groups present in the chain may further facilitate adhesion to the substrate Hydrophoebically modified hydroxyethyl cellulose used in WB coatings and paints provided good gloss, levelling and sag resistance.[11]

It has been reported that Amoxicillin doped cellulose acetate films showed good corrosion resistance on Aluminium AA2024-T3 substrate.[12]

Chitosan

Chitin and chitosan are the most abundant natural amino polysaccharide and valuable bio-based natural polymers derived from shells of prawns and crabs(Fig.9). Currently, chitin and chitosan are produced commercially by chemical extraction process from crab, shrimp, and prawn wastes.[13]


Fig. 9: Chitosan

Chitosan displays interesting characteristics including biodegradability, biocompatibility, chemical inertness, high mechanical strength, good film-forming properties, and low cost[14][15][16] Chitosan is being used in a vast array of widely varying products and applications ranging from pharmaceutical and cosmetic products to water treatment and protection.

For each application, different properties of chitosan are required, which changes with the degree of acetylation and molecular weight.

Chitosan can be modified with poly(itaconic acid) containing two negatively charged carboxylic acid Groups. The -COOH from poly(itaconic acid) and and –NH2 groups Chitosan forms (hydrophoebic) secondary amide linkages, which lead to the grafting of Polyitaconic acid on Chitosan backbone, and at higher temperature crosslinking occurred. Increased “grafts” and “crosslinks” formed coatings that were less susceptible to moisture and prevented the penetration of corrosive electrolyte species, providing good corrosion protection to the substrate.[17]

Corn-starch derived dextrin modified Chitosan with CHTO:dextrin ratio 70/30 provided low moisture resistance and could withstand salt spray test upto 720 h for aluminium surface.[18]

It has been found that Chitosan is having wound healing property so Chitin can also be used for 'coatings of normal biomedical materials'.[19]

Pullulan

Pullulan is a linear water-soluble polysaccharide mainly consisting of maltotriose units connected by α-1,6 glycosidic units (Fig.10). Pullulan was first reported by Bauer (1938) and is obtained from the fermentation broth of Aureobasidium pullulans. Pullulan is produced by a simple fermentation process using a number of Feedstocks containing simple sugars.[20] [21] [22] Pullulan can be chemically modified to produce a polymer that is either less soluble or completely insoluble in water. The unique properties of this polysaccharide are due to its characteristic glycosidic linking.


Fig.10: Pullulan

Pullulan is easily chemically modified to reduce the water solubility or to develop pH sensitivity, by introducing functional reactive groups.

Due to its high water solubility and low viscosity, pullulan has numerous commercial applications including use as a food additive, a flocculant, a blood plasma substitute, an adhesive, and a film.[23] [24] 25]

The pullulan is extremely high in film- forming ability and can give a film excellent in strength, elasticity, hardness and gloss, and thus is entirely different from the polysaccharides or derivatives thereof which have no functionally excellent film-forming ability. Pullulan possesses oxygen barrier property and good moisture retention, and also, it inhibits fungal growth. Further, the pullulan can make a solution which is stable over a long period of time and brings about no gelation nor so-called “aging” phenomenon, unlike in the case of starches. A film formed from the pullulan is extremely high in transparency and is excellent in adhering property, heat resistance and weather resistance. Further, the pullulan film shows markedly low oxygen permeability coefficient, and hence is effective to coat or protect a pigment or adjunct susceptible to oxidation, or a substrate susceptible to oxidative degradation characteristics which are fundamental properties of paints.[26]

Alginates

Alginate is a linear polysaccharide that is abundant in nature as it is synthesized by brown seaweeds and by soil bacteria.[27]

Sodium alginate is the most commonly used alginate form in the industry since it is the first by-product of algal purification.[28]

Sodium alginate consists of α-l-guluronic acid residues (G blocks) and β-d-mannuronic acid residues (M blocks), as well as segments of alternating guluronic and mannuronic acids.

Although alginates (Fig. 11) are a heterogeneous family of polymers with varying content of G and M blocks depending on the source of extraction, alginates with high G content have far more industrial importance.[29]


Fig. 11: Alginate

Alginates have various industrial uses as viscosifiers, stabilizers, and gel- forming, film-forming, or water-binding agents.[30]

It is estimated that the annual production of alginates is approximately 38,000 tons worldwide.[31]

Sodium alginate based coatings are also used for temporary field lines and logos for sports complexes and roadway markings, as well as coatings for plants, fruit, and the body are a few examples that underscore where removable coatings could be applied.[32]

Sodium Alginate gel is used in fire retarding coatings.[33]

Biobased monomers or building blocks

Typically, scientists look for ways to isolate monomers from plant based materials that can be used as building blocks for various resins. Monomers can be derived from sources such as biomass, cellulose (e.g., cotton, wood and help), sugar, etc. It is not necessary always to find alternate bio-based raw material over the chemically synthesized one but we can also develop 'bio-based processes for production of such raw materials so as to improve renewable Carbon of the polymer or final product, and to reduce crude oil dependency.

* Acrylic acid*

Acrylic acid is used in synthesis of acrylic polymer, the polymer made from acrylic acid, in which the double bond in acrylic acid is used for acrylic polymerization and the side chain is formed by an acid group that is negatively charged in water in neutral conditions. Acrylic polymer is mainly used in adhesives and coatings (like latex and acrylic paint). Copolymers of Polyacrylic acid can absorb a lot of water and are used as super absorber in incontinence products and as a thickening agent.

Following processes which are used to get acrylic acid (Fig. 12):-

  1. Fermentation of sugars to 3-HPA (3-hydroxypropionic acid), followed by dehydration into acrylic acid[34]

  2. Catalytic dehydration of lactic acid

  3. Conversion of glycerol (via acrolein) to acrylic acid

  4. Oxidation of biobased propylene

The process via lactic acid has the benefit that lactic acid is already being produced at a commercial scale, while the process via glycerol has potential because of the wide availability of glycerol as a raw material. The current process for acrylic acid involves the oxidation of petrochemical propylene. If bio-based propylene is produced on a large scale in the future, it is possibly a raw material for acrylic acid as the required infrastructure is already in place.

Succinic acid

Bio-based succinic acid has emerged as one of the most competitive of the new bio-based chemicals. As a platform chemical, bio-based succinic acid provides researchers and product developers a valuable and sustainable platform chemical building block to enable innovative development of differentiated high performance materials. One significant opportunity to improve the bio-based carbon content of alkyd formulations is by replacement of aromatic diacids and anhydrides with organic acids from renewable, non- petrochemical feedstocks.


Fig. 12: Manufactruing process of acrylic acid from various routes

The preliminary findings suggest bio- based SA can replace between 20-35% of the PA producing a polyester alkyd resin with improved color values while maintain adequate drying time and Persoz hardness values when formulated into matt based alkyd paints.

The fermentation of glucose to bio- succinic acid (Fig. 13) is a process that has a greatly enhanced Life Cycle Analysis (LCA), improved greenhouse gas (GHG) reduction and energy utilization. The fermentation of sugar feedstocks results in excellent utilization of the sugar based carbon and sequestration of CO2 to produce bio- based succinic acid in high yield and purity.

Bio-based succinic acid can be used to increase the bio-content of alkyd resins without compromising the color of the alkyd resin. The use of bio-based succinic acid in place of phthalic anhydride helps to broaden the formulation flexibility of the alkyd resins. Bio-based succinic acid can effectively replace 25-35% of the phthalic anhydride and enable matt alkyd coatings with improved yellowing resistance, color fastness with equivalent formulated hardness, gloss and cut adhesion.[35]

Styrene

Styrene (vinyl benzene) is currently produced from petroleum. It is mainly used as monomer for the production of polymers and as a reactive solvent for polyester resins.

There are various possibilities for the production of styrene from biomass.[36]

  1. Yeast fermentation from sugars to ethanol, conversion into buta diene followed by dimerisation into styrene

  2. Pyrolysis (heating at a high temperature without the presence of oxygen) of biomass to a mixture of benzene, toluene and xylene (BTX). Benzene can then be converted into styrene via a reaction with ethylene

  3. Chemical (catalytic) conversion from sugars to BTX and further conversion of benzene into styrene via reaction with ethylene

  4. Isolation of aromatic compounds from proteins or lignin. [37]

Styrene has applications in latex based emulsion paints, acrylic paints, modifications of alkyd resins, Polystyrene, etc.

Itaconic acid, methacrylic acid and methyl methacrylate

Itaconic acid is an unsaturated dicarbonic acid which has a high potential as a biochemical building block, because it can be used as a monomer for the production of various products including resins, plastics, paints. Some Aspergillus species, like A. itaconicus and A. terreus, show the ability to synthesize this organic acid.


Fig. 13: The fermenation of glucose to bio-succinic acid


Fig. 14: Process of manufacturing of bio based styrene

Itaconic acid (IA) is an unsaturated dicarbonic organic acid. It can easily be incorporated into polymers and may serve as a substitute for petrochemical- based acrylic or methacrylic acid. It is used at 1-5% as a co-monomer in resins and also in the manufacture of synthetic fibres, in coatings, adhesives, thickeners and binders. The another production process which can be said as favoured production process is fermentation of carbohydrates by fungi (shown in fig.15)[38]


Fig. 15: Process of manufacturing of bio based Methacrylic Acid and Methyl Methacrylate

Itaconic acid is seen as a highly interesting chemical building block due to its resemblance to maleic acid, a compound commonly used in acrylates and resins.

It has been shown that itaconic acid is stored in the tubers of potato plants[39]. Energy crops like switch grass, grown for the production of bio-ethanol, can also produce itaconic acid.[40].

There are various developments in the field of biobased methyl methacrylate. These developments are all at R&D stage and not yet ready for production. There are two routes for the development of bio based methyl methacrylate those are

  1. Using biomass for feedstock in the existing production processes
  2. Using a novel route via fermentation process of biomass.[41].

Sucrose Polyester


Fig. 16: Surose Polyester

Sucrose polyesters (SPE) essentially consist of a sucrose backbone and natural fatty acid residues linked to sucrose through ester bonds ( Fig 16). They are the esters prepared from renewable feedstocks by esterifying sucrose with fatty acid methyl esters (FAME). It can be tailored for different applications by selecting the right FAME blends to achieve desired oil content, fatty acid chain length distribution, unsaturation level and degree of esterification. The use of all-natural ingredients in its development and processing, with materials derived from vegetable oil and sugar, results in a material that is: non-persistent, non- toxic & 100% biodegradeable. The use of natural, renewable materials provide a sustainable solution versus petro-derived triglycerides.

Since one to eight fatty acid chains can be attached onto sucrose, the physical properties and reactivity of sucrose polyesters may be tailored by the degree of esterification and by choosing the appropriate natural oils to achieve the right fatty acid chain length distribution and unsaturation level. Thus, sucrose polyesters offer a unique chemical platform by controlling their unique molecular architecture and functional density enabling the compact cross linking structure to an auto oxidizing paint system. Sucrose polyester help to develop high solid alkyd resin.

Polylactic acid

Polylactic acid is currently the most important biobased polymer used in polyester and one of the most attractive examples of a fully biobased material. Lactic acid, building block for polylactic acid, is obtained via fermentation of sugars (see Fig. 18).


Fig. 17: Process of manufactruing of biobased lactic acid


Fig. 18: Lactide to polyactic acid PLA

While various micro-organisms can also produce lactic acid, actobacillus is most commonly used in commercial applications. During the fermentation process, two molecules of lactic acid are formed from one molecule of glucose via glycolysis; this results in a theoretical yield of 100%[43].

Lactic acid is then dimerised into lactide, followed by ring-opening polymerisation to PLA. PLA is an example of a polymer that is only produced from renewable raw materials via a biotechnological process.

Lactic acid is currently commercially produced from sugar-rich and starch- rich biomass, such as sugar cane, maize and tapioca. For a sustainable production process on a scale that meets future demands for bioplastics like PLA, however, the use of non-food biomass such as lignocellulose is crucial. Compared to biomass that is rich in sugar and starch, lignocellulose is a complex source of sugars, and several steps (like a pretreatment) are required to isolate the sugar and make it suitable for fermentation into lactic acid.[44].

. In paint industry Lactides which are esters of lactic acid has wide applications. In polysters and alkyds, lactide enhances coating performance by improving properties, such as; stiffness, adhesion, impact resistance, balance between hardness and flexibility, chemical resistance, gloss and gloss retention, and tuning of drying time.

Bio-based solvents and additives

There are many bio-based solvents and additives currently used in paints and coatings industry. Out of that bio-based surfactants continue to gain market share owing to concerns about sustainability and the long-term availability of petrochemical feedstocks.

New technologies are making it easier than ever to make such products from nonfood feedstocks. Technically, everything that can be made from petroleum-based feedstocks can now be made from biomaterials, with the dream of going 100% bio being limited only by nontechnical factors such as price, reliability of supply, and labeling.

BTX is the abbreviation for the aromatics benzene, toluene and xylene; components that are mainly used as solvent as well as in the production of polyamides, polyurethanes and polyesters. The current production volumes in Europe are around 13,000k ton/year[45]. (Para-xylene can be isolated from BTX. (Fig. 19)


Fig. 19

Para-xylene is one of the three isomers of xylene (the X in BTX). It is an important building block as oxidation of para-xylene yields terephthalic acid. Para-xylene can be produced from BTX but also via fermentation of isobutanol. Terephthalic acid is obtained by oxidation of para-xylene. As described above, a large number of companies and research institutes is working on biobased terephthalic acid.

Ethanol is a building block that is currently produced mainly by yeast fermentation of sugar-rich and starch- rich biomass like sugar cane (Brazil) or maize (North America), so-called first generation biomass. Globally, some 86,000 kton of bio-ethanol is produced each year[46]

The industrial production of ethanol from second generation biomass such as lignocellulose is rapidly developing.[47] Ethanol is widely used as a solvent for paints.

Isopropanol is currently mainly used as a solvent in coatings, but it can also serve as a raw material for propylene. The fermentation of sugars into isopropanol and this is described in a number of patents[48] [49]

n-Butanol is a chemical building block with a current production volume of 2,300 kton/year[50] Like isobutanol it is one of the isomers of butanol. It is used as a solvent in paints and coatings. n- butanol can also be used as a chemical building block for the production of e.g. 1-butene.

Tannic Acid is commercial form of Tannin. It is a polymer of Gallic acid molecules and glucose. It is contained in roots, husks, galls and leaves of plants. It is also found in bark of trees (oak, walnut, pine, mahogany). Tannic Acid is used in tanning of leather, staining wood, a mordant for cellulose fibers, dyeing cloth. It is used as conversion coating to prevent corrosion of iron, zinc, copper and their alloys. The (ortho) hydroxyls react with metals forming metal-tannic acid complexes, which protect metal from rusting.[51]

Lignin is produced worldwide annually as residue in paper production processes.Lignin contains hydroxyl, carboxyl, benzyl alcohol, methoxyl, aldehydic and phenolic functional groups. It adsorbs on the metal surface and is capable of forming a barrier between the metal and corrodents[52] .

Challenges

Biobased raw materials form an essential part of our sustainability approach as they can contribute to a reduction of our environmental footprint and our reliance on oil. Like many other positive potential contributors, biobased raw materials have a potential downside, they have been blamed for deforestation (sometimes causing excessive CO2 emission), reducing biodiversity and rising food prices. There are many more matters to consider before committing resources to the development of bio materials for coatings. The following is a discussion on some of these issues.

Cost

From a practical basis, the process of synthesizing the polymer competes with the conversion cost of prevailing polymerization techniques. The cost/performance balance may skew negatively if the bio-based process costs more than using petroleum-based monomers.

Quality & performance

Regardless of where the monomers come from and how the resins are produced, the ultimate product has to perform to become a commercial reality. In most cases, the bio-renewal product has been inferior in color stability and durability. These shortcomings truly are show-stoppers for the formulator and customers and would remain challenge for the adaptation of bio-materials and bio-based synthesis processes.

Impact on the food chain

Another key issue is how using a plant-based material for industrial products will affect the food supply chain. The use of corn to product starch, which subsequently is converted into sugars (mainly glucose) then diacids or glycols, will have an impact on food supply. Interestingly, the vast majority of corn production is used for livestock feed. Then it will become more difficult to justify the use of food items for industrial production.

Conclusion and path forward

A lot has been talked about renewable and biodegradable materials. They differ in the way that renewable materials are substances derived from a living tree, plant, animal or ecosystem which has the ability to regenerate itself whereas Biodegradable materials are substances that will decompose in a natural environment. However, the new buzz word in the coating industry is “Sustainable Biomaterials” which covers the entire spectrum of their origin (plant, forest etc) along with manufacturing practices without hazardous inputs and recycling or composting abilities.

Factors such as limitations and uncertainty in supplies of fossil fuels, environmental considerations and technological developments have accelerated the advancement of bio- based materials and products.

Use of bio based materials in coating is still a challenge in the coming years include management of raw materials, performance of bio-based materials and their cost of production. However, a number of institutions and organization are working towards building a competitive, secure and sustainable bio- based economy that is less dependent on fossil resources and with a positive global climate effect.

Developing a sustainable bio-based economy that uses eco-efficient bio- processes and renewable bio-resources will be one of the focus areas in near future for coating industry.

Acknowledgement

We express our deep sense of gratitude towards management of 'Asian Paints Ltd.' for providing us necessary resources in reparing the paper. We are thankful to Dr B P Mallik - Vice President, Technology and Dr. R K Jain – Chief Manager, Technology for the valuable guidance and encouragement. We are also thankful to Mr Nilesh Phalke, Mr Anand Kondalkar and Mr Vivek Patil for their help during writing and framing the Paper.

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