**1. Introduction**

*Cannabis* is classified into the family of Cannabaceae and initially encompassed three main species: *Cannabis sativa*, *Cannabis indica*, and *Cannabis ruderalis* [1]. Nowadays, Cannabis has only one species due to continuous crossbreeding of the three species to generate hybrids. In fact, all plants are categorized as belonging to *Cannabis sativa* and classified into chemotypes based on the concentration of the main cannabinoids. Depending on the THCA/CBDA ratio, some chemotypes have been distinguished. In particular, chemotype I or "drug-plants" have a TCHA/CBDA ratio >1.0, plants that exhibit an intermediate ratio are classified as chemotype II, chemotype III or "fiber-plants" have a THCA/CBDA ratio <1.0, plants that contain cannabigerolic acid (CBGA) as the main cannabinoid are classified as chemotype IV, and plants that contain almost no cannabinoids are classified as chemotype V [2–5].

Recently, in Italy the interest in *Cannabis sativa* L. has increased mainly due to the latest legislation (Legge n. 242 del 2 dicembre 2016) [6]. As a consequence, there is a request to develop cost-e ffective and easy-to-use quantitative and qualitative methods for analysis of cannabinoids.

The Italian regulatory framework has classified two types of *Cannabis sativa* L. depending on the content of Δ9-THC. In particular, fiber-type plants of *Cannabis sativa* L., also called "hemp", are

characterized by a low content of Δ9-THC (<0.2% *w*/*w*). If the content of Δ9-THC is >0.6% *w*/*w*, it is considered as drug-type, also called "therapeutic" or "marijuana".

Industrial hemp is used in several sectors, such as in the pharmaceutical, cosmetic, food, and textile industries, as well as in energy production and building. In general, fiber-type plants are less used in the pharmaceutical field, where drug-type plants are more often employed [5]. However, there is also an increased interest in hemp varieties containing non-psychoactive compounds. In fact, the European Union has approved 69 varieties of *Cannabis sativa* L. for commercial use [7].

Hemp has a complex chemical composition that includes terpenoids, sugars, alkaloids, stilbenoids, quinones, and the characteristic compounds of this plant, namely cannabinoids. *Cannabis sativa* L. has several chemotypes, each of which is characterized by a different qualitative and quantitative chemical profile [5]. The cannabinoids, terpenes, and phenolic compounds in hemp are formed through secondary metabolism [3,8]. The term "cannabinoid" indicates terpenophenols derived from *Cannabis*. More than 90 cannabinoids are known, and some are derived from breakdown reactions [8]. Gaoni and Mechoulam [9] were the first to define cannabinoids "as a group of C21 compounds typical of and present in *Cannabis sativa*, their carboxylic acids, analogs, and transformation products". Currently, cannabinoids have been classified according to their chemical structure, mainly seven types of cannabigerol (CBG); five types of cannabichromene (CBC); seven types of cannabidiol (CBD); the main psychoactive cannabinoid Δ9-tetrahydrocannabinol (Δ9-THC) in nine different forms including its acid precursor (Δ9-tetrahydrocannabinolic acid, Δ9-THCA); Δ8-tetrahydrocannabinol (Δ8-THC), which is a more stable isomer of Δ9-THC but 20% less active; three types of cannabicyclol (CBL); five different forms of cannabielsoin (CBE); seven types of Cannabinol (CBN), which is the oxidation artifact of Δ9-THC; cannabitriol (CBT); cannabivarin (CBDV); and tetrahydrocannabivarin (THCV) [10,11]. THC, CBD, CBG, CBN, and CBC are not biosynthesized in *Cannabis sativa*, and the plant produces the carboxylic acid forms of these cannabinoids (THCA, CBDA, CBGA, CBNA, and CBCA). Cannabinoid acids undergo a chemical decarboxylation reaction triggered by different factors, mainly temperature. This decarboxylation reaction leads to the formation of the respective neutral cannabinoids (THC, CBD, CBG, CBN, and CBC) [12,13].

There are several methods to quantify cannabinoids [14–21], some of which require expensive mass spectrometry detectors [22–25]. Furthermore, there is a great deal of uncertainty around the use of gas chromatography (GC) for the titration of cannabinoids due to the high temperature of the injector and detector that can lead to the decarboxylation of cannabinoid acids if not derivatized correctly [26]. Moreover, recent studies have reported that cannabinoid acid decarboxylation is only partial, and as result the actual value is underestimated. An HPLC system allows for determination of the actual cannabinoid composition, both neutral and acid forms, without the necessity of the derivatization step [13].

It is necessary, in addition to honed methods, to develop new procedures with a view to discriminate different *Cannabis* varieties in order to identify and titrate cannabinoids in a simple way. These methods should ideally be fast, easy, robust, and cost-efficient as they can be used not only by research laboratories but also by small companies with a view on quality control.

This study focuses on the development, validation, and step-by-step explanation of a rapid and simple HPLC-UV method for identification and quantification of the main cannabinoids in hemp inflorescences that can be easily reproduced and applied. The method described is focused on the quantification of CBD but can also be applied to check the levels of THC.

#### **2. Results and Discussion**


**5. Conclusions**

The study shows the significance of the EU pressures for aligning the health systems of a small country, like Estonia, with the climate adaptation goals of building resilience to future increases in, e.g., projected storminess and length of heatwaves. However, the effect of these external pressures remains short-lived, when the political salience of climate change and the related political will is low to mainstream climate change into policies, and to invest scarce resources in adaptation policy programmes, monitoring, and protective responses. Although efforts are being made in emergency preparedness and rescue, which, as a co-benefit, increase the ability to cope with the health risks of climate-related extreme events, the state has limited avenues for pressuring the private domains of primary care and hospitals. There are significant opportunities to gain synergistic benefits from conducting risk and vulnerability analyses, and from building community resilience through mainstreaming climate change over related policy fields, including rescue services, health, environment, social care, and even education. In a situation where there is lack of issue ownership, policy integration and mainstreaming could be facilitated by appointing a responsible institution. Institutional responses resonate with people's perception and the demand for adaptation measures. As characteristic of a small health system, the shortage of regionally specific scientific assessments and lack of pressure from other organised interest groups, attenuate the social and political urgency for adaptation. Nevertheless, growing experience with extreme weather events, particularly among increasing urban and minority populations who are detached from traditional coping strategies, may increase demand for the provision of state support for health adaptation.

**Author Contributions:** K.O. conceived the research questions and design; conducted the analysis and did most of the writing of the manuscript; M.T. conducted expert interviews and participated in their analysis; K.L.E. provided advice on the data analysis and helped in writing the manuscript; H.O. conducted the population-based survey and contributed to writing the manuscript.

**Funding:** K.O.'s work on the preparation of this article was supported by the HEALTHDOX project (MSHUH14155) financed by NORFACE Programme. H.O.'s work on the preparation of this article was supported by the Estonian Ministry of Education and Research grant IUT34-17.

**Conflicts of Interest:** The authors declare no conflict of interest.


Hardwood Tannin: Sources, Utilizations, and Prospects

*Atanu Kumar Das, Md. Nazrul Islam, Md. Omar Faruk, Md. Ashaduzzaman, Rudi Dungani, Enih Rosamah, Sri Hartati and Alfi Rumidatul*

## **Abstract**

Tannins are found in widely distributed species of plants, and it protects plant from predators and pests. There are three major groups of tannins, that is, hydrolyzable, complex, and proanthocyanidins. Tannins are being used as a significant element for the tanning of animal hides in the leather production industry from the beginning of tannin industry. Then, these have been used for mineral absorption and protein precipitation purposes since the 1960s. Tannins are used for iron gall ink production and wood-based industry as adhesive and anticorrosive, recovering uranium from seawater and removing mercury and methylmercury from solution. In addition, tannins are considered as bioactive compound in nutrition science, and their possible effects on health are to be identified. This chapter outlines the structural and biological properties of hardwood tannins to indicate the positive utilization of them. It also describes the contemporary information on tannins.

**Keywords:** tannin, structural properties, biological properties, utilization

#### **1. Tannin and its classification**

Plants are protected from herbivores and diseases due to the accumulation of a wide range of "secondary" compounds, together with alkaloids, terpenes, and phenolics. Phenolic metabolism helps to produce a wide variety of compounds ranging from the familiar anthocyanidins (flower pigments) to lignin (complex phenolics of the plant cell wall). Generally, the chemical and biological criteria of phenolic compounds are called as tannins which are different from other plant secondary phenolics. The word "tannin" originates from the ancient Celtic word for oak [1].

Seguin has introduced the term "tannin" to explain the ability to convert hide or skin into leather by organic material extracted from certain plant tissues in 1796 [1]. Tannin is a chemical component obtained from plant, and it has been used for the benefit of human being from the beginning of its development. To get the idea about its complete nature, a lot of research work is needed till today, and that is why it is considered the "dark continents" of science. Tannin has the ability to make proteins and other polymers like pectin [2].

Tannins are the main polyphenolic secondary metabolites distributed widely in the range of 5–10% of dry plant material in vascular plants. They are found mainly in the bark, stems, seeds, roots, buds, and leaves [3]. Tannins are either galloyl

**Figure 1.** *Classification of tannins.*

esters, or they are oligomeric and polymeric proanthocyanidins. They protect trees from fungi, pathogens, insects, and herbivorous animals [4].

Tannins in softwood and hardwood are different as softwood and hardwood dust particles can be separated based on their tannin content [5].

The term "tannin" is difficult to define concisely as it is found in plant chemistry. Generally, tannin contains precise physical and chemical components, which help to convert hide or skin of animal into impermeable non-rotting leather. Broadly, the definition of tannin covers a whole mass of components which give overall phenolic reactions [2].

Bate-Smith has defined tannins in this way: "tannins are water soluble phenolic compounds with molecular weight of 500 and 3000, capable of precipitating gelatin, alkaloids and other proteins and provide the typical phenolic reactions" [1, 6]. Tannins having a high molecular weight of 20,000 have shown complex with some specific polysaccharides [1, 6]. Scientists have also used the term "polyphenol" in place of "tannin" to emphasize the diversity of phenol groups which characterize these compounds [7, 8].

Natural tannins are generally categorized as either condensed or hydrolyzable tannins (**Figure 1**). Hydrolyzable tannins are subdivided into gallotannins and ellagitannins [4].

Condensed tannins have a wide range of molecular weight from 500 to over 20,000 [9]. Condensed tannins are composed of flavolans or polymers of flavan-3-ols (catechins) and/or flavan 3:4-diols (leucoanthocyanidins) [10]. Phlobaphene, a water insoluble product, is possible to be produced by polymerization of condensed tannins. Condensed tannins have the ability to react with aldehydes to generate polymeric materials [9]. The hydrolyzable tannins contain glucose or other polyhydric alcohols esterified with gallic acid (gallotannins) or hexahydroxydiphenic acid (ellagitannins) [11]. Acid hydrolysis of hydrolyzable tannins helps to get gallic acid, ellagic acid, or other similar species [7]. The most important condensed tanning materials are wattle or "mimosa," quebracho, mangrove, and hemlock, whereas the hydrolyzable tanning materials are chestnut wood (*Castanea sativa* and *C. dentata*) and dry myrobalan fruits (*Terminalia chebula*) [10].

#### **2. Hardwood tannin**

#### **2.1 Condensed tannin**

Condensed tannins are polymeric flavonoids, and most of them are based on the flavan-3-ols (**Figure 2**) (−)-epicatechin and (+)-catechin [1].

**5**

**Figure 3.**

*Common modes of coupling of condensed tannins [1].*

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

**Figure 2.** *Flavan-3-ols [1].*

The best categorized condensed tannins are linked by C8 of the terminal unit and C4 of the extender. The four common modes of coupling are called B-1, B-2, *Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

**Figure 2.** *Flavan-3-ols [1].*

*Tannins - Structural Properties, Biological Properties and Current Knowledge*

from fungi, pathogens, insects, and herbivorous animals [4].

dust particles can be separated based on their tannin content [5].

esters, or they are oligomeric and polymeric proanthocyanidins. They protect trees

Tannins in softwood and hardwood are different as softwood and hardwood

The term "tannin" is difficult to define concisely as it is found in plant chemistry. Generally, tannin contains precise physical and chemical components, which help to convert hide or skin of animal into impermeable non-rotting leather. Broadly, the definition of tannin covers a whole mass of components which give overall phenolic

Bate-Smith has defined tannins in this way: "tannins are water soluble phenolic compounds with molecular weight of 500 and 3000, capable of precipitating gelatin, alkaloids and other proteins and provide the typical phenolic reactions" [1, 6]. Tannins having a high molecular weight of 20,000 have shown complex with some specific polysaccharides [1, 6]. Scientists have also used the term "polyphenol" in place of "tannin" to emphasize the diversity of phenol groups which characterize

Natural tannins are generally categorized as either condensed or hydrolyzable tannins (**Figure 1**). Hydrolyzable tannins are subdivided into gallotannins and

Condensed tannins have a wide range of molecular weight from 500 to over 20,000 [9]. Condensed tannins are composed of flavolans or polymers of flavan-3-ols (catechins) and/or flavan 3:4-diols (leucoanthocyanidins) [10]. Phlobaphene, a water insoluble product, is possible to be produced by polymerization of condensed tannins. Condensed tannins have the ability to react with aldehydes to generate polymeric materials [9]. The hydrolyzable tannins contain glucose or other polyhydric alcohols esterified with gallic acid (gallotannins) or hexahydroxydiphenic acid (ellagitannins) [11]. Acid hydrolysis of hydrolyzable tannins helps to get gallic acid, ellagic acid, or other similar species [7]. The most important condensed tanning materials are wattle or "mimosa," quebracho, mangrove, and hemlock, whereas the hydrolyzable tanning materials are chestnut wood (*Castanea*

*sativa* and *C. dentata*) and dry myrobalan fruits (*Terminalia chebula*) [10].

flavan-3-ols (**Figure 2**) (−)-epicatechin and (+)-catechin [1].

Condensed tannins are polymeric flavonoids, and most of them are based on the

The best categorized condensed tannins are linked by C8 of the terminal unit and C4 of the extender. The four common modes of coupling are called B-1, B-2,

**4**

reactions [2].

**Figure 1.**

*Classification of tannins.*

these compounds [7, 8].

**2. Hardwood tannin**

**2.1 Condensed tannin**

ellagitannins [4].

**Figure 3.** *Common modes of coupling of condensed tannins [1].*

B-3, and B-4 (**Figure 3**). Besides these dimers, related dimers which are linked by C6 of the terminal unit and C4 of the extender have been separated [1].

Proanthocyanidin is becoming more popular to describe flavonoid-based polyphenolics instead of condensed tannins. Anthocyanidin pigments are derived from proanthocyanidins by oxidative cleavage in hot alcohols (**Figure 4**) [1].

Unmodified terminal units are produced by the acid butanol reaction, and the extender units produce the colored anthocyanidins. Procyanidins are produced by catechin- and epicatechin-based polymers. Delphinidin is the yield of gallocatechin- and epigallocatechin-based polymers, whereas pelargonidin is the product of the rare mono-substituted flavan-3-ol-based polymers.

There is an available branch in 5-deoxy-flavan-3-ol polymer-condensed tannins due to having the reactivity of the 5-deoxy A ring, and these are an important group of condensed tannins. In the case of quebracho and acacia tannin preparations, profisetinidins and prorobinetinidins are observed as the major tannins. Acid butanol reaction helps to produce the 5-deoxy anthocyanidins fisetinidin and robinetinidin (**Figure 5**) [1].

Tannins are broadly available in all over the plant kingdom, while the condensed tannins are distributed in the Archichlamydeae division of the

**7**

**Table 1.**

*Condensed tannins in hardwood.*

**Figure 5.**

*Extracted tannins by acid butanol reaction [1].*

**Family Genus** Casuarinaceae *Casuarina* Salicaceae *Salix* Betulaceae *Betula*

Lauraceae *Persea* Rosaceae *Prunus*

Fagaceae *Castanea*, *Lithocarpus*, *Quercus*

Leguminosae *Acacia*, *Cassia*, *Robinia* Meliaceae *Carapa*, *Xylocarpus* Euphorbiaceae *Excoecaria*

Anacardiaceae *Astronium*, *Rhus*, *Schinopsis*

Rhizophoraceae *Bruguiera*, *Carallia*, *Ceriops*, *Candelaria*, *Rhizophora*

Bombacaceae *Camptostemon* Sterculiaceae *Heritiera* Dipterocarpaceae *Hopea* Lythraceae *Pemphis* Sonneratiaceae *Sonneratia*

Combretaceae *Laguncularia* Myrtaceae *Eucalyptus*, *Tristania*

Verbenaceae *Avicennia*

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

**Figure 4.** *Proanthocyanidin and its derivative [1].* *Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

*Tannins - Structural Properties, Biological Properties and Current Knowledge*

C6 of the terminal unit and C4 of the extender have been separated [1].

proanthocyanidins by oxidative cleavage in hot alcohols (**Figure 4**) [1].

the rare mono-substituted flavan-3-ol-based polymers.

robinetinidin (**Figure 5**) [1].

B-3, and B-4 (**Figure 3**). Besides these dimers, related dimers which are linked by

Proanthocyanidin is becoming more popular to describe flavonoid-based polyphenolics instead of condensed tannins. Anthocyanidin pigments are derived from

Unmodified terminal units are produced by the acid butanol reaction, and the extender units produce the colored anthocyanidins. Procyanidins are produced by catechin- and epicatechin-based polymers. Delphinidin is the yield of gallocatechin- and epigallocatechin-based polymers, whereas pelargonidin is the product of

There is an available branch in 5-deoxy-flavan-3-ol polymer-condensed tannins due to having the reactivity of the 5-deoxy A ring, and these are an important group of condensed tannins. In the case of quebracho and acacia tannin preparations, profisetinidins and prorobinetinidins are observed as the major tannins. Acid butanol reaction helps to produce the 5-deoxy anthocyanidins fisetinidin and

Tannins are broadly available in all over the plant kingdom, while the condensed tannins are distributed in the Archichlamydeae division of the

**6**

**Figure 4.**

*Proanthocyanidin and its derivative [1].*

#### **Table 1.**

*Condensed tannins in hardwood.*

Dicotyledonae. Scientists examined condensed tannins by paper chromatography in their previous studies [12–16]. In Australia, the attractive source of condensed tannins are extracts from barks of *Bruguiera* and *Rhizophora* species (mangrove species) and *Eucalyptus astringens* (brown mallet) and the heartwood and bark of *E. wandoo* and *E. accedens* (wandoos). **Table 1** shows the distribution of condensed tannins in hardwood.

#### *2.1.1 Utilization of condensed tannin*

#### *<IP_ADDRESS> Tanning industry*

In general, condensed tannin material is the major component of commercial tanning chemical, which is used for tanning leather in tannery. The major contributors for the world's supply of condensed tannin are extract of mangrove and wattle and quebracho used in heavy leather manufacture. Condensed tannin materials are selected based on their tanning quality for heavy leather production. Condensed tannins have high resistance power to detanning [17]. Quebracho and wattle tannins are more resistant to concentrated urea solution than to hydrolyzable tannins [18].

Though tannin materials are dissimilar based on pH, salt content, and natural conditions of acid content, it can be controlled maintaining proper conditions [19, 20]. pH in tan liquors is relatively high due to the absence of phenolic in tan liquors. Mangrove extracts contain sodium chloride, whereas sulfited quebracho extracts possess sodium sulfate, and the salt content contributes to the salt material in tannin materials [21].

#### *<IP_ADDRESS> Preservative for fishing net*

Preservation of fishing nets by various condensed tannin materials is popular in Indo-Pacific countries. It is used to prevent cellulose degradation by bacterial and fungal cellulases. Fishing nets are submerged in hot tannin solution, and this method is repeated for several times. Tannin-impregnated nets are further treated with either hot ammoniacal copper sulfate or dichromate solution for some cases [22, 23]. Condensed tannin materials are extracted from Burma cutch from *Acacia catechu* heartwood, Malayan (mangrove) cutch from *Carapa obovata* and *Ceriops candolleana* barks, and Borneo (mangrove) cutch from *Ceriops candolleana*, *Rhizophora candelaria*, and *R. mucronata* barks [21].

#### *<IP_ADDRESS> Preparation of plastics and adhesives*

Condensed tannins are phenolic raw materials which react with formaldehyde; these can be used for the production of synthetic resins [21]. Nico [24] studied the suitability of quebracho-formaldehyde resins for adhesives and plastics. Molding powders are produced by pressing mixtures of accurate quebracho and wattle tannins, paraformaldehyde, and plasticizer [21]. Though these moldings have short flow period, these follow all the characteristics of phenol-formaldehyde moldings as per the specifications of British standards [25]. These molding powders show very stable and waterproof properties, and the mixture is catalyzed with either acid or alkali at temperature 250°F [25].

Various condensed tannins as plywood and particle board adhesives have been studied by many researchers [26–30]. Adhesives prepared from bark of *Tsuga heterophylla*, *Acacia mollissima*, and *Callitris calcarata* have less strength and higher water resistance properties than those obtained from commercial adhesives [31, 32]. Strong and waterresistant adhesives for plywood are prepared by mixing of paraformaldehyde, filler, and sulfited tannin solutions obtained from *Eucalyptus crebra*, *Pinus radiata*, wattle extract,

**9**

**Figure 6.**

*Precursors of gallotannins [1].*

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

*<IP_ADDRESS> Oil and ceramic industry*

tannins in the casting of bone China [21].

underground iron pipes and tubes [35].

*<IP_ADDRESS> Anticorrosive of metals*

tion of nonferrous metal [39].

**2.2 Hydrolyzable tannin**

and quebracho extract [25, 33]. Adhesives prepared from Australian mangrove tannin extracts in addition with a small proportion of commercial phenol-formaldehyde, resorcinol-formaldehyde, or phenol- and resorcinol-formaldehyde comply with Australian and British standard for synthetic adhesives for plywood [21, 34].

The main problem is to maintain the flow and suspension characteristics of bentonite oil well muds in the United States [21]. In oil well drilling, quebracho tannins are used widely to control the viscosity of the mud; annual consumption of quebracho extract is 30,000–40,000 tons for this purpose [35]. In the United States, it is accounted for about 40% of the total tannin consumption in 1950 [36, 37].

Scientist has reviewed the incorporation of condensed tannins into the ceramic industry. Quebracho extract enables the use of higher solid mixer in the casting of clay slip by lowering the viscosity of the clay-water mixes. Condensed tannins save the plaster molds from deterioration by increasing the tensile strength of clay casts and eliminating the silica from the mixture, with consequent saving in the deterioration of plaster molds. The suspending power of the slip is enhanced by quebracho

Tannins protect the iron materials from sulfate-reducing bacteria by exerting a bacteriostatic action [38]. Mangrove tannin is economically viable to protect the

Tannate films of tannin extract is formed on iron and steel surfaces to protect it from atmospheric corrosion [25]. Actually a protective film is formed during the submersion of aluminum in tannin solutions, and it can be used for the preserva-

Hydrolyzable tannins are esters of a sugar with one or more polyphenolic carboxylic acids; sugar is mainly glucose, but polysaccharides or branched-chain sugars are available for some cases. The hydrolyzable tannins are generally classified based on the hydrolyzed product, and these are either gallotannins, are simple polygalloyl esters of glucose. Pentagalloyl glucose, has five identical ester linkages that involve aliphatic hydroxyl groups of the core sugar (**Figure 6**). Alkalies, acids, or enzymes like tannase

and takadiastase hydrolyze the ester linkages in hydrolyzed tannins [40].

and quebracho extract [25, 33]. Adhesives prepared from Australian mangrove tannin extracts in addition with a small proportion of commercial phenol-formaldehyde, resorcinol-formaldehyde, or phenol- and resorcinol-formaldehyde comply with Australian and British standard for synthetic adhesives for plywood [21, 34].

### *<IP_ADDRESS> Oil and ceramic industry*

*Tannins - Structural Properties, Biological Properties and Current Knowledge*

densed tannins in hardwood.

*<IP_ADDRESS> Tanning industry*

*2.1.1 Utilization of condensed tannin*

*<IP_ADDRESS> Preservative for fishing net*

*Rhizophora candelaria*, and *R. mucronata* barks [21].

*<IP_ADDRESS> Preparation of plastics and adhesives*

alkali at temperature 250°F [25].

Dicotyledonae. Scientists examined condensed tannins by paper chromatography in their previous studies [12–16]. In Australia, the attractive source of condensed tannins are extracts from barks of *Bruguiera* and *Rhizophora* species (mangrove species) and *Eucalyptus astringens* (brown mallet) and the heartwood and bark of *E. wandoo* and *E. accedens* (wandoos). **Table 1** shows the distribution of con-

In general, condensed tannin material is the major component of commercial tanning chemical, which is used for tanning leather in tannery. The major contributors for the world's supply of condensed tannin are extract of mangrove and wattle and quebracho used in heavy leather manufacture. Condensed tannin materials are selected based on their tanning quality for heavy leather production. Condensed tannins have high resistance power to detanning [17]. Quebracho and wattle tannins are more resistant to concentrated urea solution than to hydrolyzable tannins [18]. Though tannin materials are dissimilar based on pH, salt content, and natural conditions of acid content, it can be controlled maintaining proper conditions [19, 20]. pH in tan liquors is relatively high due to the absence of phenolic in tan liquors. Mangrove extracts contain sodium chloride, whereas sulfited quebracho extracts possess sodium sulfate, and the salt content contributes to the salt material in tannin materials [21].

Preservation of fishing nets by various condensed tannin materials is popular in Indo-Pacific countries. It is used to prevent cellulose degradation by bacterial and fungal cellulases. Fishing nets are submerged in hot tannin solution, and this method is repeated for several times. Tannin-impregnated nets are further treated with either hot ammoniacal copper sulfate or dichromate solution for some cases [22, 23]. Condensed tannin materials are extracted from Burma cutch from *Acacia catechu* heartwood, Malayan (mangrove) cutch from *Carapa obovata* and *Ceriops candolleana* barks, and Borneo (mangrove) cutch from *Ceriops candolleana*,

Condensed tannins are phenolic raw materials which react with formaldehyde; these can be used for the production of synthetic resins [21]. Nico [24] studied the suitability of quebracho-formaldehyde resins for adhesives and plastics. Molding powders are produced by pressing mixtures of accurate quebracho and wattle tannins, paraformaldehyde, and plasticizer [21]. Though these moldings have short flow period, these follow all the characteristics of phenol-formaldehyde moldings as per the specifications of British standards [25]. These molding powders show very stable and waterproof properties, and the mixture is catalyzed with either acid or

Various condensed tannins as plywood and particle board adhesives have been studied by many researchers [26–30]. Adhesives prepared from bark of *Tsuga heterophylla*, *Acacia mollissima*, and *Callitris calcarata* have less strength and higher water resistance properties than those obtained from commercial adhesives [31, 32]. Strong and waterresistant adhesives for plywood are prepared by mixing of paraformaldehyde, filler, and sulfited tannin solutions obtained from *Eucalyptus crebra*, *Pinus radiata*, wattle extract,

**8**

The main problem is to maintain the flow and suspension characteristics of bentonite oil well muds in the United States [21]. In oil well drilling, quebracho tannins are used widely to control the viscosity of the mud; annual consumption of quebracho extract is 30,000–40,000 tons for this purpose [35]. In the United States, it is accounted for about 40% of the total tannin consumption in 1950 [36, 37].

Scientist has reviewed the incorporation of condensed tannins into the ceramic industry. Quebracho extract enables the use of higher solid mixer in the casting of clay slip by lowering the viscosity of the clay-water mixes. Condensed tannins save the plaster molds from deterioration by increasing the tensile strength of clay casts and eliminating the silica from the mixture, with consequent saving in the deterioration of plaster molds. The suspending power of the slip is enhanced by quebracho tannins in the casting of bone China [21].

#### *<IP_ADDRESS> Anticorrosive of metals*

Tannins protect the iron materials from sulfate-reducing bacteria by exerting a bacteriostatic action [38]. Mangrove tannin is economically viable to protect the underground iron pipes and tubes [35].

Tannate films of tannin extract is formed on iron and steel surfaces to protect it from atmospheric corrosion [25]. Actually a protective film is formed during the submersion of aluminum in tannin solutions, and it can be used for the preservation of nonferrous metal [39].

#### **2.2 Hydrolyzable tannin**

Hydrolyzable tannins are esters of a sugar with one or more polyphenolic carboxylic acids; sugar is mainly glucose, but polysaccharides or branched-chain sugars are available for some cases. The hydrolyzable tannins are generally classified based on the hydrolyzed product, and these are either gallotannins, are simple polygalloyl esters of glucose. Pentagalloyl glucose, has five identical ester linkages that involve aliphatic hydroxyl groups of the core sugar (**Figure 6**). Alkalies, acids, or enzymes like tannase and takadiastase hydrolyze the ester linkages in hydrolyzed tannins [40].

**Figure 6.** *Precursors of gallotannins [1].*

#### **Figure 8.** *Ellagitannins [1].*

Gallotannins, the simplest hydrolyzable tannins, are simple polygalloyl esters of glucose. The ideal gallotannin is comprised esters of β-1,2,3,4,6-pentagalloyl-*O*-D-glucopyranose (pentagalloylglucose) (**Figure 6**). Pentagalloylglucose (PGG) has five identical ester linkages having aliphatic hydroxyl groups of the core sugar [21].

PGG has many isomers having the same molecular weights (940 g/mol) (**Figure 7**). Although the molecular weights are same, chemical properties and biochemical properties are different from each other due to having different structures. Therefore, their properties like susceptibility to hydrolysis, chromatographic behavior, and ability to precipitate protein are varied for different isomers [21].

Gallotannins are converted to the related ellagitannins by the oxidative coupling of galloyl groups (**Figure 8**). The simple ellagitannins are esters of hexahydroxydiphenic acid (HHDP). In aqueous solution, HHDP impulsively lactonizes to ellagic acid [21].

HHDP is formed by intramolecular carbon-carbon coupling C-4/C-6 (e.g., eugeniin) and C-2/C-3 (e.g., casuarictin, also has C-4/C-6) having polygalloyl glucoses

**11**

in the more stable <sup>4</sup>

*Hexahydroxydiphenic acid (HHDP) [1].*

**Figure 9.**

C1 conformation (**Figure 9**). On the other hand, intramolecular

C4 conforma-

coupling occurs at C-3/C-6 (e.g., corilagin), C-2/C-4 (e.g., geraniin, also has C-3/C-

Some commercial hydrolyzable tannins presented in **Table 2** develop the present

tion for a few plants (**Figure 9**). In addition, geraniin is characterized by partial

knowledge on the chemistry of the hydrolyzable tannins. Hydrolyzable tannins are available in the leaves and sapwood of a tree [40, 41]. Ellagitannins (or ellagic acid) are found in the leaves of species of the orders *Fagales*, *Myrtiflorae*, *Rosales*,

6), or C-1/C-6 (e.g., davidiin) with polygalloyl glucose the less stable <sup>1</sup>

oxidation of the C-2/C-4 HHDP to dehydro-HHDP [21].

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

*Tannins - Structural Properties, Biological Properties and Current Knowledge*

Gallotannins, the simplest hydrolyzable tannins, are simple polygalloyl esters of glucose. The ideal gallotannin is comprised esters of β-1,2,3,4,6-pentagalloyl-*O*-D-glucopyranose (pentagalloylglucose) (**Figure 6**). Pentagalloylglucose (PGG) has five identical ester linkages having aliphatic hydroxyl groups of the core sugar [21]. PGG has many isomers having the same molecular weights (940 g/mol) (**Figure 7**). Although the molecular weights are same, chemical properties and biochemical properties are different from each other due to having different structures. Therefore, their properties like susceptibility to hydrolysis, chromatographic behavior, and ability to precipitate protein are varied for different isomers [21].

Gallotannins are converted to the related ellagitannins by the oxidative coupling of galloyl groups (**Figure 8**). The simple ellagitannins are esters of hexahydroxydiphenic acid (HHDP). In aqueous solution, HHDP impulsively lactonizes to ellagic acid [21]. HHDP is formed by intramolecular carbon-carbon coupling C-4/C-6 (e.g., eugeniin) and C-2/C-3 (e.g., casuarictin, also has C-4/C-6) having polygalloyl glucoses

**10**

**Figure 7.** *Isomers of PGG [1].*

**Figure 8.** *Ellagitannins [1].*

#### **Figure 9.**

*Hexahydroxydiphenic acid (HHDP) [1].*

in the more stable <sup>4</sup> C1 conformation (**Figure 9**). On the other hand, intramolecular coupling occurs at C-3/C-6 (e.g., corilagin), C-2/C-4 (e.g., geraniin, also has C-3/C-6), or C-1/C-6 (e.g., davidiin) with polygalloyl glucose the less stable <sup>1</sup> C4 conformation for a few plants (**Figure 9**). In addition, geraniin is characterized by partial oxidation of the C-2/C-4 HHDP to dehydro-HHDP [21].

Some commercial hydrolyzable tannins presented in **Table 2** develop the present knowledge on the chemistry of the hydrolyzable tannins. Hydrolyzable tannins are available in the leaves and sapwood of a tree [40, 41]. Ellagitannins (or ellagic acid) are found in the leaves of species of the orders *Fagales*, *Myrtiflorae*, *Rosales*,

#### *Tannins - Structural Properties, Biological Properties and Current Knowledge*

#### **Table 2.**

*Name of commercial hydrolyzable tannins and sources.*

**13**

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

**Family Genus**

Punicaceae *Punica*

Diapensiaceae *Galax*

Campanulaceae *Centropogon* only Compositae *Tagetes* only Amaryllidaceae *Hypoxis*

*Name of family and genus containing ellagitannins or ellagic acid.*

Lythraceae *Lagerstroemia*, *Lythrum*

Rhizophoraceae *Cassipourea* (*Rhizophora* in lit.) Combretaceae *Combretum* (*Terminalia* in lit.)

Haloragaceae *Gunnera*, *Haloragis*, *Myriophyllum* Ericaceae *Arbutus* (*Arctostaphylos*, *Vaccinium*, in lit.)

Myrtaceae *Agonis*, *Angophora*, *Callistemon*, *Eucalyptus*, *Eugenia*,

Melastomataceae *Bertolonia*, *Heterocentron*, *Medinilla*, *Tibouchina* Onagraceae *Dircaea*, *Fuchsia*, *Jussieua*, *Lopezia*, *Oenothera*

*Melaleuca*, *Metrosideros*, *Myrtus*, *Psidium*

nins or ellagic acid is presented in **Table 3**.

*2.2.1 Utilization of hydrolyzable tannin*

tanning in leather industries [2].

*<IP_ADDRESS> Tanning industry*

**Table 3.**

*<IP_ADDRESS> Medication*

*<IP_ADDRESS> Other applications*

ings, gallic acid, etc. [2].

*2.2.2 Prospectus of the utilization of tannins*

The potential uses of tannins are in the following.

*Sapindales*, and *Geraniales* [42]. Gallotannins and ellagitannins have been detected in the tissues of many hundreds of species of dicotyledons [40]. Source of ellagitan-

For leather manufacturing process, the conversion of animal hide or skin into leather is considered as the main art of tanning in leather industries. To provide leather, tannin cross-links with the collagen chains located in the hide during tanning process. Hydrolyzable tannins obtained from plant extract are widely used for

Biological activities of hydrolyzable tannins confirm the beneficial effect on the health of human being, and these are used as antimutagenic, anticancer, and antioxidant. Furthermore, hydrolyzable tannins help to diminish serum cholesterol

Tannic acid is used in dye industry and water treatment process for purifying water. It is also used for manufacturing ink, plastic resins, adhesives, surface coat-

There are several uses of tannins for the welfare of human being, and continuous research is being carried out for increasing the diversity of utilization of tannins.

and triglycerides and suppress lipogenesis by insulin [43, 44].

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

#### **Table 3.**

*Tannins - Structural Properties, Biological Properties and Current Knowledge*

Sumac tannin Leaves of *Rhus coriaria* (Anacardiaceae) Myrobalans Fruit of *Terminalia chebula* (Combretaceae) Turkish tannin Galls on wood of *Quercus infectoria* (Fagaceae)

Oak extract Wood of various *Quercus* species (Fagaceae) Chestnut extract Wood of *Castanea sativa* and *C. dentata* (Fagaceae) Tara extract Pods of *Caesalpinia spinosa* (Leguminosae) Divi-divi Pods of *Caesalpinia coriaria* (Leguminosae) Algarobilla extract Pods of *Caesalpinia brevifolia* (Leguminosae)

Chinese tannin (tannic acid) Galls on leaves of *Rhus semialata* (Anacardiaceae)

Valonea extract Acorn cups of *Quercus valonea* or *Q. macrolepis* (Fagaceae)

**Family Genus** Casuarinaceae *Casuarina* Juglandaceae *Pterocarya* Betulaceae *Alnus*, *Carpinus*

*Name of commercial hydrolyzable tannins and sources.*

**Table 2.**

**Tannin Source**

Loranthaceae *Nuytsia* Nymphaeaceae *Nuphar* Cercidiphyllaceae *Cercidiphyllum* Droseraceae *Drosera* Saxifragaceae *Francoa*, *Ribes* Hamamelidaceae *Liquidambar*

Geraniaceae *Geranium* Tremandraceae *Tetratheca*

Empetraceae *Empetrum* Coriariaceae *Coriaria* Cyrillaceae *Cyrilla* Corynocarpaceae *Corynocarpus*

Melianthaceae (Anacardiaceae in lit.) *Greyia*, *Melianthus*

Elaeagnaceae *Elaeagnus*, *Hippophae*

Vitaceae *Vitis* Elaeocarpaceae *Aristotelia*

Frankeniaceae *Frankenia* Tamaricaceae *Tamarix* Bixaceae *Bixa* Stachyuraceae *Stachyurus*

Fagaceae *Castanea*, *Nothofagus*, *Quercus*

Leguminosae *Pterocarpus* (*Caesalpinia* in lit.)

Euphorbiaceae *Acalypha*, *Euphorbia*, *Ricinus*

Aceraceae *Acer monspessulanum* (*A. ginnala* in lit.)

Theaceae *Camellia*, *Cleyara*, *Gordonia*, *Thea*

Rosaceae Rosoideae (*Geum*, *Fragaria*, *Potentilla*, *Rosa*, *Rubus*) only

**12**

*Name of family and genus containing ellagitannins or ellagic acid.*

*Sapindales*, and *Geraniales* [42]. Gallotannins and ellagitannins have been detected in the tissues of many hundreds of species of dicotyledons [40]. Source of ellagitannins or ellagic acid is presented in **Table 3**.

#### *2.2.1 Utilization of hydrolyzable tannin*

#### *<IP_ADDRESS> Tanning industry*

For leather manufacturing process, the conversion of animal hide or skin into leather is considered as the main art of tanning in leather industries. To provide leather, tannin cross-links with the collagen chains located in the hide during tanning process. Hydrolyzable tannins obtained from plant extract are widely used for tanning in leather industries [2].

#### *<IP_ADDRESS> Medication*

Biological activities of hydrolyzable tannins confirm the beneficial effect on the health of human being, and these are used as antimutagenic, anticancer, and antioxidant. Furthermore, hydrolyzable tannins help to diminish serum cholesterol and triglycerides and suppress lipogenesis by insulin [43, 44].

#### *<IP_ADDRESS> Other applications*

Tannic acid is used in dye industry and water treatment process for purifying water. It is also used for manufacturing ink, plastic resins, adhesives, surface coatings, gallic acid, etc. [2].

#### *2.2.2 Prospectus of the utilization of tannins*

There are several uses of tannins for the welfare of human being, and continuous research is being carried out for increasing the diversity of utilization of tannins. The potential uses of tannins are in the following.

### *<IP_ADDRESS> Tanning industry*

Tannins were the major tanning material for converting animal hide/skin into leather. At present, inorganic salts especially chrome salts are used to produce 70–85% leather. Replacing toxic chrome salts with less toxic and environmentally friendly tanning materials is possible by polymerization of tannins with other synthetic materials [11].

### *<IP_ADDRESS> Wood composite industry*

Tannins as wood adhesives have been confirmed by a number of patents. Synthetic adhesives are hazardous to environment. Therefore, tannins can be used as alternative source of adhesive in wood composite industry. Cost-effectiveness and high level of consistency should be considered for the replacement of existing harmful adhesives with tannins [11].

#### *<IP_ADDRESS> Water and waste water treatment plant*

Tannins have a positive potentiality to be used as water treatment chemicals. For municipal water treatment, floccotan, a commercial product, has been used to eradicate suspended colloidal matter like clay and organic matter. Chelating ability of tannin is important to remove metallic ions, that is, Cr, Ni, Zn, or Cd, from waste water [11].

*Acacia mearnsii* cryogel obtained from the extraction of *A. mearnsii* tannin with formaldehyde in alkaline medium is used as absorbent of heavy metal (**Figure 10**). Extraction of *A. mearnsii* tannin by epichlorohydrin in N,N-dimethylformamide medium, followed by grafting with diethylenetriamine and triethylamine, yields a cationic adsorbent. This cationic absorbent is also used for heavy metals (**Figure 11**) [45].

*A. mearnsii* cryogel is also applicable for the removal of dyes. The dyes absorption capacity by *A. mearnsii* cryogel is presented in **Figure 12**. It is noted that cationic dyes have higher adsorption efficiency than anionic dyes, like tartrazine and alizarin violet. On the other hand, cationic adsorbent has a high efficacy for many anionic dyes, even for a cationic dye such as methylene blue (**Figure 13**) [45].

**Figures 14** and **15** show the various pesticides and pharmaceutical absorption capacity of cationic tannin adsorbent. Cationic compounds, like 2,4-D, clofibric acid, MCPA, acetylsalicylic acid, diclofenac, ketoprofen, naproxen, etc., are absorbed effectively, whereas cationic products, such as atrazine, amoxicillin, trimethoprim, are adsorbed ineffectively [45].

**15**

**Figure 13.**

**Figure 11.**

**Figure 12.**

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

*Comparison of the adsorption capacity of heavy metals on cationic tannin adsorbent [45].*

*Comparison of the adsorption capacity of dyes on* Acacia mearnsii *cryogel [45].*

*Comparison of the adsorption capacity of dyes on cationic tannin adsorbent [45].*

**Figure 10.** *Comparison of the adsorption capacity of heavy metals on* Acacia mearnsii *cryogel [45].*

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

#### **Figure 11.**

*Tannins - Structural Properties, Biological Properties and Current Knowledge*

Tannins were the major tanning material for converting animal hide/skin into leather. At present, inorganic salts especially chrome salts are used to produce 70–85% leather. Replacing toxic chrome salts with less toxic and environmentally friendly tanning materials is possible by polymerization of tannins with other

Tannins as wood adhesives have been confirmed by a number of patents. Synthetic adhesives are hazardous to environment. Therefore, tannins can be used as alternative source of adhesive in wood composite industry. Cost-effectiveness and high level of consistency should be considered for the replacement of existing

Tannins have a positive potentiality to be used as water treatment chemicals. For municipal water treatment, floccotan, a commercial product, has been used to eradicate suspended colloidal matter like clay and organic matter. Chelating ability of tannin is important to remove metallic ions, that is, Cr, Ni, Zn, or Cd, from waste water [11]. *Acacia mearnsii* cryogel obtained from the extraction of *A. mearnsii* tannin with formaldehyde in alkaline medium is used as absorbent of heavy metal (**Figure 10**). Extraction of *A. mearnsii* tannin by epichlorohydrin in N,N-dimethylformamide medium, followed by grafting with diethylenetriamine and triethylamine, yields a cationic adsorbent. This cationic absorbent is also used for heavy metals (**Figure 11**) [45]. *A. mearnsii* cryogel is also applicable for the removal of dyes. The dyes absorp-

tion capacity by *A. mearnsii* cryogel is presented in **Figure 12**. It is noted that cationic dyes have higher adsorption efficiency than anionic dyes, like tartrazine and alizarin violet. On the other hand, cationic adsorbent has a high efficacy for many anionic dyes, even for a cationic dye such as methylene blue (**Figure 13**) [45]. **Figures 14** and **15** show the various pesticides and pharmaceutical absorption capacity of cationic tannin adsorbent. Cationic compounds, like 2,4-D, clofibric acid, MCPA, acetylsalicylic acid, diclofenac, ketoprofen, naproxen, etc., are absorbed effectively, whereas cationic products, such as atrazine, amoxicillin,

*<IP_ADDRESS> Tanning industry*

synthetic materials [11].

*<IP_ADDRESS> Wood composite industry*

harmful adhesives with tannins [11].

*<IP_ADDRESS> Water and waste water treatment plant*

trimethoprim, are adsorbed ineffectively [45].

**14**

**Figure 10.**

*Comparison of the adsorption capacity of heavy metals on* Acacia mearnsii *cryogel [45].*

*Comparison of the adsorption capacity of heavy metals on cationic tannin adsorbent [45].*

**Figure 12.** *Comparison of the adsorption capacity of dyes on* Acacia mearnsii *cryogel [45].*

**Figure 14.** *Comparison of the adsorption capacity of pesticides on cationic tannin adsorbent [45].*

**Figure 15.** *Comparison of the adsorption capacity of pharmaceuticals on cationic tannin adsorbent [45].*

#### *<IP_ADDRESS> Metal protective agents*

Tannins have been used as a corrosion inhibitor for carbon steel and copper in oil and gas facilities with treated *Rhizopora mucronata* tannin. Sulfonated tannins can be used to remove scale-forming cooling water pipes and boilers. In the protective coating industry, tannins have been used for protecting metal surfaces as a primer/undercoat/topcoat. In Chile, pine tannin has been used as a commercial anticorrosive product. Black wattle extract has been used as a polyurethane-type coating for wood [11].

#### *<IP_ADDRESS> Building construction purpose*

Tannins are used as a viscosity modifier of mud for the production of residential and architectural bricks [11].

**17**

**Author details**

Atanu Kumar Das1

Rudi Dungani3

Indonesia

Indonesia

East Kalimantan, Indonesia

, Md. Nazrul Islam2

, Sri Hartati5

Generally, condensed tannins preserve lignocellulosic materials naturally. Therefore, condensed tannins can be used as potential wood preservatives and

Tannins have antiviral, anticancer, antibacterial, anti-inflammatory, and antioxidant properties, and these are the driving forces to be a potential source of medicinal products. A large amount of research is being undertaken currently to

1 Technical Division, PT. Indiah Kiat Pulp and Paper Tbk, Serang, Banten,

3 School of Life Sciences and Technology, Institut Teknologi Bandung, Bandung,

4 Faculty of Forestry, Mulawarman University, Campus Gunung Kelua, Samarinda,

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 School of Life Sciences, Khulna University, Khulna, Bangladesh

5 Faculty of Agriculture, Universitas Padjadjaran, Bandung, Indonesia

\*Address all correspondence to<EMAIL_ADDRESS>
provided the original work is properly cited.

, Enih Rosamah4

\*, Md. Omar Faruk<sup>2</sup>

and Alfi Rumidatul3

, Md. Ashaduzzaman<sup>2</sup>

,

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*

*<IP_ADDRESS> Eco-friendly preservatives*

develop medicine from tannin [11].

biocides [46].

*<IP_ADDRESS> Medical science*

*Hardwood Tannin: Sources, Utilizations, and Prospects DOI: http://dx.doi.org/10.5772/intechopen.86003*


Social Aspects of Ageing - Selected Challenges, Analyses, and Solutions

*Edited by Andrzej Klimczuk*

Published in London, United Kingdom

Social Aspects of Ageing - Selected Challenges, Analyses, and Solutions http://dx.doi.org/10.5772/intechopen.100694 Edited by Andrzej Klimczuk

### Contributors

Alice Nga Lai Kwong, Ana Louro, Barbara Mikołajczyk, Eduarda Marques da Costa, Hamish Robertson, Marcela Barata, Mariana Dias, Ntobeko Bambeni, Nuno Marques Da Marques da Costa, Raymond Saner

### © The Editor(s) and the Author(s) 2024

The rights of the editor(s) and the author(s) have been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights to the book as a whole are reserved by INTECHOPEN LIMITED. The book as a whole (compilation) cannot be reproduced, distributed or used for commercial or non-commercial purposes without INTECHOPEN LIMITED's written permission. Enquiries concerning the use of the book should be directed to INTECHOPEN LIMITED rights and permissions department (permissions@intechopen.com).

Violations are liable to prosecution under the governing Copyright Law.

Individual chapters of this publication are distributed under the terms of the Creative Commons Attribution 3.0 Unported License which permits commercial use, distribution and reproduction of the individual chapters, provided the original author(s) and source publication are appropriately acknowledged. If so indicated, certain images may not be included under the Creative Commons license. In such cases users will need to obtain permission from the license holder to reproduce the material. More details and guidelines concerning content reuse and adaptation can be found at http://www.intechopen.com/copyright-policy.html.

#### Notice

Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published chapters. The publisher assumes no responsibility for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained in the book.

First published in London, United Kingdom, 2024 by IntechOpen IntechOpen is the global imprint of INTECHOPEN LIMITED, registered in England and Wales, registration number: 11086078, 167-169 Great Portland Street, London, W1W 5PF, United Kingdom

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library

Additional hard and PDF copies can be obtained from<EMAIL_ADDRESS>
Social Aspects of Ageing - Selected Challenges, Analyses, and Solutions Edited by Andrzej Klimczuk p. cm.

This title is part of the Education and Human Development Book Series, Volume 16 Topic: Human Development Series Editor: Katherine K.M. Stavropoulos Topic Editor: Tal Dotan Ben-Soussan

Print ISBN 978-1-80356-506-4 Online ISBN 978-1-80356-507-1 eBook (PDF) ISBN 978-1-80356-508-8 ISSN 2755-9513


*2.2. Datasets*

#### 2.2.1. Satellite Reflectance Data

The MODIS MCD43A4 Nadir Bidirectional Reflectance Distribution Function (BRDF) Adjusted Reflectance (NBAR) product with a 500 m resolution was used in this study to remove the viewing angle effects from directional reflectivity [42]. A total of 366 images from 1 January 2020 to 31 December 2020 were freely downloaded from the NASA Land Processes Distributed Active Archive Center (LP DAAC, http://lpdaac.usgs.gov (accessed on 10 July 2021)), which were processed to UTM/WGS-84 projection and 500 m resolution. Based on repeated manual tests, missing values of 50 consecutive days would introduce significant errors in reconstructing the VI trajectory. To eliminate errors caused by missing

values in the daily NBAR products, pixels with more than 50 consecutive days of missing data were flagged as poor-quality pixels and excluded from subsequent analysis, which accounted for only 3.34% of the study area. Reflectance in the red, green, near-infrared (NIR), and shortwave infrared (SWIR) bands was used to calculate the different VIs and to further determine the SOS dates.


*2.2. Analysis of RUNX1 Methylation and mRNA Levels*

We previously analyzed the DNA methylation and mRNA expression at the level of genome using the Infinium HumanMethylation450 BeadChip and the HumanHT-12 expression BeadChips (Illumina, San Diego, CA, USA), respectively, in 42 surgically resected tumor and matched normal tissues, 136 bronchial washings, 12 sputums, or 6 bronchial biopsy specimens obtained from a total of 118 NSCLC patients and 60 cancer-free patients [13]. We used the reported data for the analysis of methylation and mRNA levels of *RUNX1*. Preprocessing such as background or batch effect correction, probe filtering, and adjustment of the background signal difference between types I and II probes was conducted using the R software package called wateRmelon [14]. Methylation level (β-value), ranging from 0 (no methylation) to 1 (100% methylation), was estimated as the ratio of fluorescence signal intensity between methylated alleles and the sum of methylated and unmethylated alleles at each CpG locus. The levels of mRNA expression from HT-12 chips were normalized using the R lumi package (https://bioconductor.org/biocLite.R).

#### *2.3. Feature Selection for Prediction of Lung Cancer*

To select candidate CpGs for lung cancer prediction among differentially methylated CpGs and to build models for lung cancer prediction, we divided the normal and tumor tissues from 42 patients into training and test datasets, according to a 7:3 ratio. Supervised machine learning algorithms were applied to select features in the training dataset. Age-related CpGs or any CpGs that were significantly correlated in the normal or tumor tissues were removed during the model building. Supervised machine learning algorithms for feature selection and model building were applied using RapidMiner Studio version 8.2 (RapidMiner Inc, Boston, MA, USA).


**1. Introduction**

Society is increasingly aware of the usage of sustainable energy sources that protect the environment, such as renewable energy resources, whose viability is demonstrated. At the same time, it is necessary that energy storage devices also meet the same requirements of sustainability and efficiency, making the entire process of generation and consumption of energy as clean as possible. Nanotechnology has become one of the main subjects in science nowadays, offering exciting new possibilities in the field of renewable energy production/conversion and storage. An energy storage device is characterized by two main magnitudes. The first one is the energy density, which gives an account of the total energy that the device could store. The other magnitude refers to the time

necessary for the device to store or supply a certain amount of energy to attend to the demand, which is known as power density.

Within storage systems, capacitors are those that have higher power densities, but the lowest energy density. Supercapacitors, apart from maintaining the power density of the usual capacitors, are able to reach higher energy density values of about one or two orders of magnitude above those achieved by usual energy storage devices. Therefore, by improving the energy storage capacity of these capacitors, devices with good performance both in autonomy and power density can be obtained, which present a wide range of applications in industry, electronics, or inclusively in means of transport [1,2]. Specifically, supercapacitors have direct application in those electrical systems that demand high power supply in short times, such as the engine of an electric car during vehicle acceleration. Another possible application would be the supply of extra power to the electricity network in specific periods of peak energy demand, which would tackle one of the main disadvantages of renewable energy. In addition, supercapacitors are small gadgets, so it would be possible to introduce this type of device into electronic circuits, causing capacitors to become increasingly smaller and improving their performance due to their high capacitance. Capacitors are usually classified into two types: electrolytic or electrostatic. For the first type, electric charge storage is produced by electrochemical processes. However, the electrolytic acid medium limits the lifespan of these devices as they end up being depleted or even oxidizing the capacitor's own electrodes, rending it out of service. In addition, these devices have a great disadvantage regarding their ecological footprint, because at the end of their lifetime, they generate non-usable chemical residues. On the other hand, the storage of electrical charge on electrostatic capacitors occurs by the electric polarization of an insulating or dielectric material, when a voltage is applied between the conductive electrodes of the capacitor. From the environmental point of view, their advantages over electrolytic batteries or capacitors are clear: a longer (or even unlimited) lifetime and the non-generation of chemical waste at the end of its working time.

In recent years, several investigations based on nanotechnology have achieved important improvements in energy storage capacity of electrostatic capacitors [3,4]. Manufacturing of devices with high storage capacities and energy densities of up to 4 Wh/kg has been demonstrated [5,6], while maintaining the high power density characteristic of electrostatic capacitors. This type of device is called a super-electrostatic nanostructured capacitor (super-ENC) [7]. The use of nanoporous anodic alumina membranes (NAAMs) as a patterned support for the manufacture of super-ENCs that is proposed in this work is a widely contrasted technique that offers good results not only for the manufacturing of electrostatic capacitors [8], but also for other types of energy storage devices [9,10].

$$\mathbf{C} = \varepsilon\_0 \varepsilon\_\mathbf{r} \mathbf{S} / d \tag{1}$$

Equation (1) summarizes the main factors to be taken into account when evaluating the storage capacity of an electrostatic capacitor, where *C* is the capacitance, ε0 the dielectric permittivity of the vacuum, εr the relative permittivity of the dielectric medium of the capacitor, and *d* is the thickness of such medium. Despite the apparent simplicity of this expression, it can be considered as an approximation to estimate the order of magnitude for a super-ENC's capacitance. As shown in Equation (1), the capacitance is enhanced by a larger surface area (*S*) of the electrodes. In order to increase the parameter by sizing up the dimensions of the device, NAAMs are used as a substrate, as they offer a high open surface area. By using electrochemical anodization techniques, it is possible to grow hexagonally self-ordered pores whose geometrical parameters can be properly tuned, thus obtaining a highly ordered nanoporous surface with well-defined dimensions, grown on the starting aluminum substrate. The atomic layer deposition (ALD) technique represents an important tool within the nanomaterials additive manufacturing owing to its enhanced possibilities like the fabrication of thin oxide films over micro- or mesoporous surfaces by covering them conformally [11]. The use of the ALD technique allows one to take advantage of the internal surface inside the NAAM's pores to deposit the three layers that make up the typical structure of the capacitor, that is, the upper and the lower electrode and, between them, the dielectric material. The goal of ALD employment is to reduce the thickness of the dielectric material (*d*) to the order of nanometers, which results in a consequent increase of capacitance (see Equation (1)). This technique allows one to make coatings of oxide materials over porous substrates, achieving the deposition of layers with thicknesses in the range of nanometers on the internal surface of the nanopores [11,12]. Through ALD performance, it is possible to guarantee a uniform thickness substrate coating [13,14], able to be carried out on porous surfaces with diverse morphologies, whether they are micro-, meso-, or macroporous substrates [15]. Within the storage of energy, ALD is a widespread technique and has a wide range of applications depending on the substrate on which the ALD is made, from the treatment of porous carbon to form a cathodic material that can be implemented with batteries [16], to the coating of ZnO nanowires as electrostatic capacitors [17]. This technique is also used to form supercapacitor devices over multiple substrates. There is a detailed study that applies ALD on NAAMs [4–7] in a very similar way to what was conducted in this work, developing new electrostatic supercapacitor devices, in which ALD becomes essential in the conformation of its electrodes and dielectric material. However, its range of application goes further, as ALD has been successfully used in recent years for electrochemical capacitor manufacturing over bundles of carbon nanotubes (CNT) [18,19], or TiO2 nanoparticles [20]. One of the main advantages provided by ALD is the performance of electrodes with greater mechanical and chemical stability, owing to the deposition of conformal coatings, which are adapted, in many cases, in the form of nanowires [21,22].

In this work, the manufacturing process of electrostatic supercapacitors by combining the ALD technique and electrochemical anodization of nanoporous anodic alumina templates as starting substrates is reported. The so-formed electrostatic capacitor structure, which consists of a top electrode, a dielectric material, and finally a bottom electrode, has been reduced to nanoscale dimensions by depositing the required materials over patterned nanoporous anodic alumina membranes using the ALD technique. A thin layer of aluminum-doped zinc oxide, 6 nm in thickness, is used as both the top and bottom electrodes' material, while two different dielectric materials were tested. On the one hand, a triple-layer made by successive combination of a 3 nm in thickness for each layer of silicon dioxide (SiO2), plus titanium dioxide (TiO2), and silicon dioxide (SiO2) again, forming the three-layered SiO2/TiO2/SiO2 dielectric medium, and on the other hand, a single layer with 9 nm in thickness made of alumina (Al2O3).

Regarding the selection of dielectric materials, two criteria have been taken into account. Firstly, the material needs to have a high relative permittivity in order to increase the capacitance. The second criterion is related to the energy gap between its valence and conduction bands, which should be as high as possible, to avoid leakage currents and to reach the maximum working voltage of the capacitor. Among the different insulating materials characterized in the work of [23], the one with the highest relative permittivity (TiO2) and the one with the largest gap (SiO2) are extracted. Unfortunately, these two properties are opposed, with TiO2 being the material with the lowest gap, and SiO2 being the dielectric with the lowest permittivity, as can be seen in Table 1. For this reason, in this work, the combination of these two materials in a triple layer of SiO2/TiO2/SiO2 dielectric is proposed, in such a way that this new material can provide the high performance of permittivity and insulation that TiO2 and SiO2 display by themselves. The electrical behavior of this new multilayered capacitor is compared with the performance of a single layer capacitor, which is conformed by Al2O3 as the dielectric layer. This last dielectric is a material whose ALD deposition has been widely characterized [4–6,11,14,24,25], and which also exhibits an intermediate permittivity and band gap values with respect to TiO2 and SiO2.

**Table 1.** Values of the relative permittivity, εr, and band gap of the different materials employed as dielectric layers for the supercapacitors. The given values are those collected from the work of [23].

Both oxide materials (Al2O3 and SiO2/TiO2/SiO2) have 9 nm in total thickness and play the role of insulating layers of the capacitors. The electrical properties of these capacitors were tested under different experimental configurations, by measuring characteristic magnitudes such as the impedance and capacitance on the AC and DC frequency regime. In order to give a complete overview on the electrical behavior of these capacitors, breakdown voltage values along with leakage currents are also studied. This demonstrated the ability of using nanostructured materials for designing energy storage supercapacitor devices.

#### **2. Experimental**

#### *2.1. NAAMs Manufacturing*

NAAMs have been grown on high-purity (99.999%) Al square plates with 2.5 cm sides and 0.5 mm thickness. The pre-anodization treatment consists of immersing the Al plate in an isopropanol bath and then an ethanol bath, both processes applying ultrasound for 5 min. At this point, a series of electrochemical anodization processes begin, using a Keithley 2400 Source-Meter power supply (Tektronix, Inc., Beaverton, OR, USA). Once washed, electropolishing is carried out in an electrochemical cell for 5 min, applying a DC voltage of 20 V and placing the Al plate as the anodic electrode and a Pt mesh as the cathode. A mixture of perchloric acid and ethanol (1:3 vol) at 5 ◦C is used as electrolyte, which was mechanically stirred during the process.

The growth of the highly ordered porous alumina is carried out through a double process of electrochemical anodization, as reported in the literature [26,27]. The first anodization is carried out in the electrochemical cell by applying a potentiostatic voltage of 40 V between the electrodes, again placing the aluminum plate on the anodic electrode, and a Pt mesh as the cathode, while mechanically stirring throughout. This process takes 24 h and is performed with a 0.3 M oxalic acid electrolyte at 2 ◦C. Although during this step, a nanoporous alumina membrane has been produced over the aluminum substrate, the pores of which start to become randomly disordered at the sample surface, it is possible to generate the set of honeycomb self-ordered concavities in the Al substrate. In order to access to the Al substrate, the alumina membrane is then removed through selective chemical etching by an aqueous mixture of chromium trioxide and phosphoric acid for 24 h at room temperature. The second anodization is carried out under the same conditions as the first one, but for a time of 45 min, in which the pores already grow in a hexagonally self-orderly manner, by replicating the honeycomb pattern induced in the substrate by first anodization. Two geometrical parameters of the membrane are fixed when applying this procedure, obtaining pores with a height (*h*) of 1.2 ± 0.1 μm and placed at a horizontal distance between their centers, or interdistance axes (*R*CC), of 105 ± 5 nm [4] (Figure 1).

**Figure 1.** (**a**) Top view of the nanoporous anodic alumina membrane (NAAM) patterned platform supporting the electrostatic nanostructured capacitor (ENC) structure, showing the honeycomb symmetry acquired by the pores. Geometrical parameters are also shown, such as the distance between centers (*R*CC = 105 ± 5 nm) and the diameter of the pores (*D* = 65 ± 3 nm). (**b**) Side view of the NAAM showing the height (*h* = 1.2 ± 0.1 μm) of the pores as well as their parallel alignment.

After the second anodization, the diameter of the pores is approximately 35 nm, whereby a widening of the pore size is performed by chemical etching after immersing the membrane in a 5% weight phosphoric acid solution at 30 ◦C for 35 min. The final average pore diameter (*D*) of 65 ± 3 nm has been obtained [4]. Thus, the pore radius (*r*p) is around 32.5 nm. Figure 1 displays two scanning electron microscope (SEM, JEOL JSM-5600, JEOL Ltd., Akishima, Tokyo, Japan) images of the NAAMs obtained, showing the morphology and geometrical lattice parameters of the patterned alumina membranes employed in this work.