**3. Chitosan- raw materials obtained from chitin**

Chitosan is obtained as a result of the hydrolysis of chitin N-acetylamide groups (partial deacetylation of chitin). The main advantage of chitosan is its much better solubility in aqueous acid solutions, especially organic acids. Chitin deacetylation by chemical or enzymatic methods allows for obtaining materials with various degrees of hydrolysis (**Figure 9**). However, it is assumed that at least 50% chitin deacetylation is necessary for the material to be classified as chitosan. The degree of deacetylation (DD) is defined as the ratio of the number of free NH2 groups to the initial number of NHCOCH3 groups present in chitin and is presented in the equation:

$$DD = \frac{N\_{NH\_2}}{N\_{NH\_2} + N\_{NHCOCH\_3}} \cdot 100\%$$

where N - the number of specific units (structural units) in the polymer. The value of DD affects the biological and physicochemical properties of the polymer, such as solubility, swelling and stability, as well as reactivity.

Chitosan obtained by chemical (concentrated NaOH) or enzymatic (chitin deacetylase) deacetylation of chitin. The first step of preparation of chitosan

*Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

of porous structures obtained by the porophor agent washout method.

*Microscopic picture of porous structures obtained by the porophor agent washout method.*

*Picture of porous structures obtained by the porophor agent washout method.*

tests confirmed the porous structure of pores, which are negative for the crystals of the inorganic porophor agent used. In addition, the pores are open pores, which increases the effectiveness of water adsorption. **Figure 7** shows microscopic picture

Dressings made of butyryl-acetyl chitin co-polyester (**Figure 8**) are intended for wounds of various etiologies, including chronic wounds, where the healing process is disturbed by comorbidities. In order to accelerate the healing of deep wounds, a dressing in the form of a backfill has been designed. Wounds are often accompanied by a bacterial infection, therefore, apart from the dressing in the form of a membrane made of chitin co-polyester only, there is also a variant containing the addition of silver, showing a bactericidal effect in the wound environment. Silver may appear in various forms, however, it has been assumed that only the ionic form of silver has a bactericidal effect. Any other form of silver must be converted to its ionic form. Hence, metallic silver with a small particle size after oxidation and hydrolysis is characterized by the highest antibacterial activity. Silver in ionic form also has the ability to interact with proteins. It has been found that the ionic form of silver has a higher protein binding capacity compared to nanoparticles [32–36]. The presence of pores and microcapillaries in the structure of membrane dressings allows drainage of wound exudate. Dressings made on the basis of chitin co-polyesters are characterized by high biocompatibility. Biological tests confirmed the lack of cytotoxic, irritating and allergenic effects. These dressings are degraded

**140**

**Figure 8.**

**Figure 7.**

**Figure 9.** *Chitosan formation from chitin by chitin deacetylation.*

is mechanical grinding of the raw chitin, and subsequent process of removing proteins, color compounds and inorganic salts takes place. The deproteinization process is usually performed with a dilute aqueous solution of sodium hydroxide at an elevated temperature [4, 5]. For protein removing also proteolytic enzymes were used [39, 40], but in the case of papain, trypsin and chymotrypsin, it was found that they did not completely remove the protein fraction. After deproteinization process, the residue is treated with dilute aqueous hydrochloric acid to dissolve the calcium carbonate. A similar effect can be obtained by using HCOOH, HNO3, H2SO4 or EDTA [5]. The decolorization process is based on extraction with ethanol, acetone or treatment with oxidizing reagents (KMnO4, NaOCl, H2O2). These activities allow to obtain chitin of required purity for its further transformation into chitosan. Chitosan from chitin obtained by chemical deacetylation is obtained at high temperature (above 100°C), under high pressure and in the presence of concentrated (40–50%) strong bases (usually NaOH). A typical industrial chitosan production process provides almost complete recovery of proteins, calcium oxide or calcium carbonate, carotenoid pigments and sodium acetate under the conditions of using sodium hydroxide as the deacetylating agent. However, this process has several disadvantages. It is not environmentally friendly as it consumes a large amount of energy and is also difficult to control leading to a heterogeneous product. The use of chitin deacetylase for the production of chitosan oligomers and polymers can potentially eliminate most of these drawbacks [41]. The advantages of enzymatic deacetylation are more pronounced in the processing of chitin oligomers, as these substrates are soluble in the aqueous medium and are therefore more susceptible to enzymes. The downside is the high cost of the enzyme and the requirement to use pre-processed chitin. The conditions of the chitin deacetylation process have a significant impact on the distribution of N-acetyl-D-glucosamine and D-glucosamine groups in the polysaccharide chain. Their location in the chain has a significant impact on the physicochemical properties of the material, such as crystallinity, solubility and susceptibility to degradation [3]. Depending on the final use, chitosan can be formed into a hydrogel, membranes, fibers, sponges and micro/ nanoparticles [42].

**143**

*Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining…*

Chitosan is a polysaccharide composed of randomly distributed acetylated and deacetylated units of D-glucosamine. Chitosan exists in five different crystal forms, four of which are hydrated and one is anhydrous. Microcrystalline chitosan is

Most of the properties of chitosan depend on two parameters: degree of deacetylation and molecular weight distribution. Depending on the source and method of preparation, the deacetylation degree varies from 30 to 95%, and the molecular weight from 300 to over 1000 kDa [43]. The solubility of chitosan strongly depends on the deacetylation degree, which translates into the number of free amino groups. Chitosan is soluble in acidic solutions due to its susceptibility to protonation and formation of ammonium salts. It is soluble in acetic, formic, citric, lactic and hydrochloric acid and insoluble in most organic solvents. Chitosan, as a biodegradable polymer, is easily broken down by microorganisms into simple chemical compounds such as carbon dioxide (CO2) and ammonia (NH3). Like other biopolymers, it is susceptible to many chemical and physical factors leading to its degradation. The degradation process also depends on the degree of deacetylation

Chitosan has many valuable properties, such as: biocompatibility, biodegradability, non-toxicity, the ability to create polycations in an acidic environment, the possibility of modification, high affinity for metals, dyes and proteins, hydrophilicity, ability to create membranes and others [3, 5, 44]. These features make it applicable in medicine and pharmacy, in various industries, in environmental protection, including water treatment and separation processes. [5, 45, 46]. Chitosan also has a number of properties that limit its use in certain areas. It swells strongly in water (especially in an acidic environment), and in the swollen state it is characterized by low mechanical strength. The use of chitosan is also limited due to its high viscosity. The reduction of the viscosity of chitosan solutions can be achieved by increasing the deacetylation degree while reducing the molecular weight and increasing the temperature or ionic strength [5, 47]. The key problem with the use of chitosan is its susceptibility to external factors (humidity and temperature) and processing conditions (heating or sterilization), which can affect its structure and cause its degradation. Parameters such as molecular weight or the presence of impurities have a significant impact on the processing of chitosan [48]. This causes difficulties in maintaining the stability of chitosan (no changes in molecular weight) for a long time at room temperature [49]. The influence of many factors, such as increased temperature, the presence of strong acids, mechanical shear or radiation, on the molecular weight of chitosan was demonstrated. It is also believed that high molecular weight chitosan is more stable. The lack of reproducibility in the processing of chitosan is also due to significant differences in molecular weight, deacetylation degree and purity level depending on the source of the raw material. The level of chitosan purity may affect both biological properties, such as biodegradability or immunogenicity, as well as its solubility and stability [48, 50].

Chitosan is a non-toxic polysaccharide containing randomly distributed acetylated and deacetylated units of D-glucosamine. The results of many studies confirm

*DOI: http://dx.doi.org/10.5772/intechopen.95815*

**4.1 Physio-mechanical parameters of chitosan**

and the molecular weight of the polymer [3, 5].

**4.2 Biological parameters of chitosan**

characterized by better biodegradability and bioactivity.

**4. Chitosan parameters**

*Modulating the Physicochemical Properties of Chitin and Chitosan as a Method of Obtaining… DOI: http://dx.doi.org/10.5772/intechopen.95815*
