According to Faruk et al.35 the main disadvantages of natural fibers in reinforce­ment of composites are the poor compatibility between the fiber and the matrix and their relative high moisture absorption. Therefore, natural fiber modifications are considered in modifying the fiber surface properties to improve their adhesion with different matrices. There are several treatments to modify natural fibers including physical, chemical, and enzymatic. These behaviors can be applied to other wood — based materials.

14.5.7 FIBER TYPE (OR CELLULOSE-BASED MATERIAL TYPE) AND CONTENT

The type of the cellulose-based materials such as natural fibers, nanocrystals, and nanofibrillated materials, and their content can affect the distribution of these mate­rials on the composite structure to affect mainly the mechanical, thermal, and sur­face energy properties of these composites.

Coir fibers treated with water, alkali (mercerization) and bleaching were incor­porated in starch/ethylene vinyl alcohol copolymers (EVOH) blends and were stud­ied by Rosa et al. (2009).53 Mechanical and thermal properties of starch/EVOH/coir biocomposites were evaluated. The results showed that all treatments produced sur­face modifications and improved the thermal stability of the fibers and consequently of the composites. The best results were obtained for mercerized fibers where the tensile strength was increased by about 53% as compared to the composites with untreated fibers, and about 33.3% as compared to the composites without fibers. The authors believe that the mercerization improved fiber-matrix adhesion, allowing an efficient stress transfer from the matrix to the fibers.

Venkateshwaran, Perumal, and Arunsundaranayagam54 treated the surface ba­nana fibers with alkali solution to change the fiber hydrophilic nature and the me­chanical and viscoelastic behavior of the resultant composites with an epoxy matrix were evaluated. The alkali (NaOH) concentrations used were 0.5%, 1%, 2%, 5%, 10%, 15% and 20%. They found that 1% NaOH treated fiber reinforced composites behaved superiorly in terms of mechanical properties as opposed to other treated and untreated fiber composites. The authors concluded that the alkali treatment plays a significant role in improving the mechanical properties and decreasing the moisture absorption rate.

The effect of the nanocrystalline cellulose concentration of cotton fiber on the properties of starch-based nanocomposites was studied by Lu et al. (2005).55 These authors found a positive correlation with the resistance (from 2.5 MPa to 7.8 MPa), with the modulus (from 36 MPa to 301 MPa) and with the surface energy, for 0% to 30% NCC concentration.

The study of the orientation effect of NCCs in the poly(3-hydroxybutyrate-co3- hydroxyvalerate)-(PHBV) matrix by using an electric field on the nanocomposite mechanical anisotropy was done by Ten et al.56 These authors showed that NCC concentration strongly influenced the degree of NCC alignment under the electric field. High NCC concentration (>4 wt.%) led to high viscosity of the suspension and high restraint on CNW mobility. This caused the electric field to become ineffective in aligning the nanocrystalline cellulose particles. The aligned PHBV/NCCs nano­composites showed substantial mechanical anisotropy. The authors suggest that the method developed in their paper can be used to prepare NCC nanocomposites with desired directional reinforcement.

The effect of the sulfuric hydrolysis time of the pea hull fibers on the isolated nanocrystalline cellulose structure and on the pea starch-based nanocomposite made by each NCC dispersion properties was reported by Chen et al. (2009).57 The results revealed that the hydrolysis time had a great effect on the structure (including length (L), diameter (D) and aspect ratio values (L/D)) of the nanocrystalline cellulose par­ticles, as well as on the structure and performance of the resulting nanocomposites. The authors found a negative correlation with the hydrolysis time length and the diameter of the nanocrystalline cellulose pea. The nanocomposite films exhibited higher ultraviolet absorption, transparency, tensile strength, elongation at break, and water-resistance than both the neat pea starch film and the nanocomposites with pea hull fibers without hydrolysis treatment.

Three different cellulose-based materials were used to reinforced acrylic films, acacia pulp fibers, nanocrystalline cellulose and nanocellulose balls, and their strength properties were evaluated.58Nanocrystalline cellulose reinforced compos­ites had enhanced strength properties compared to the acacia pulp and nanoball composites. AFM analysis indicated that the nanocrystalline cellulose reinforced composite exhibited decreased surface roughness.

Silverio et al.59 studied the effect of sulfated nanocrystalline cellulose from corn­cob using three different hydrolysis times (30, 60 and 90 min) in the mechanical and thermal properties of polyvinyl alcohol (PVA) as the polymeric matrix. They found that the NCC from 60 min. hydrolysis time resulted in nanoparticles with larger reinforcing capability. Also, the composites with these nanoparticles improved sig­nificantly the tensile strength of 140.2% when only 9% (wt.%) of these were incor­porated. These particles presented a needle shaped nature, high crystallinity index (83.7%), good thermal stability (around 185 °C), an average length (L) of 210.8 ± 44.2 nm and a diameter (D) of 4.15 ± 1.08 nm, giving an aspect ratio (L/D) of around 53.4 ± 15.8. Comparing to the others NCC times, this aspect ratio of the nanocrystalline cellulose from time hydrolysis of 60 min was intermediary. Because of this, the authors concluded that the material crystallinity index was a more impor­tant parameter to consider than the aspect ratio.

Biodegradable nanocomposites prepared by casting with natural rubber and sugar cane bagasse nanocrystalline cellulose in different ratio were studied by Bras et al. (2010)60. The incorporation of nanocrystalline cellulose into rubber resulted in composites with enhanced thermo-mechanical properties and biodegradability. Significant improvement of Young’s modulus and tensile strength was observed as a result of NCC addition to the rubber matrix especially at high whiskers’ loading.

The use of NCC with hydrophobic polymer matrix such as rubber deteriorates its resistance to water vapor permeation

As mentioned above, chitosan is being explored for wound healing, antibacterial, antifungal, drug delivery, wound healing and absorption of organic and inorganic pollutants.17,19,47-51

Antimicrobial properties: Since bacterial infections (such as from Listeria monocytogenes) are the leading cause for foodborne human infection and diseases, the development of antimicrobial packaging material is still growing. Antimicro­bial packaging materials can be classified into three following categories (a) first category antimicrobial packaging materials involves the direct use of antimicrobial additive in the packaging film, (b) in the second category, a carrier for antimicrobial additive can be used as a coating, while (c) the more advanced option is the use of cationic polysaccharide, which can make membranes and possess antimicrobial activity.14,52,59

In this regards, chitosan, notably possess a polycationic structure that interacts with anionic bacterial cell membrane, thereby disrupting the integrity of bacterial cells. Similar antimicrobial activity can be expected from chitin, which is the raw material of chitosan, but never been explored, despite the fact that chitin nanocrys­tals accelerate wound healing.17,60,61

Multicomponent nanocomposite films of polysaccharides (starch, chitosan and cellulose nanofibers) were shown to have bactericidal activity against S. aureus, depending on chitosan content. Since the chitosan (CH) and water soluble CH are the only components responsible for antimicrobial activity, the bactericide activ­ity strongly depend on the CH and WCH content.62 In comparison of NFC, BC nanofibers did not significantly affect the bactericidal activity. Recently, the nano­composites of bacterial cellulose nanofibers and chitin nanocrystals prepared via both in-situ biosynthesis of BC and solution casting were demonstrated to possess superior antibacterial properties against E. Coli.63 The antibacterial activity of nano­composites increased with increasing deacetylated chitin content, by forming strong interaction with bacterial cellulose network which indicates them suitable for anti­microbial applications.

A novel polyelectrolyte-macroion complex composed of chitosan and cellulose nanocrystals have been examined for its potential drug delivery applications.64 As shown in Fig. 16.6, the particles were primarily composed of cellulose nanocrys­tals only and are governed by the strong mismatch in the densities of the ionizable groups of the two components. Further, higher cellulose nanocrystals concentration in the composite leads to the formation of larger and highly aggregated particles.

The structural investigations were performed by scanning electron microscope (SEM, LEO 1540 XB) and transmission electron microscope (TEM, Philips CM — 20). The eggshell structure (Fig. 2.3a) is relatively compact with average grain size about 3 дш. The XRD measurement of the calcined eggshell confirmed mainly the CaO (JCPDS-PDF 0371497) phase (Fig. 2.3b).

The effect of various milling was observed after attritor and ball milling17,27. SEM image of structure prepared by attritor is shown in Fig. 2.4a. The structure pro-

duced by ball milling is shown in Fig. 2.4b. The SEM investigation confirmed that the attritor milling is more efficient in grain size reduction compared to ball milling. Thus, smaller particle size with homogeneous size distribution may be achieved with attritor milling. In both cases, the grains were agglomerated. The XRD mea­surements of powders prepared by two different milling showed different phases (Fig. 2.5). In the both cases, the powders are consisted of hydroxyapatite (HAp, JCPDSPDF 74-0565), calcite (CaCO3, JCPDS-PDF 05-0586), calcium hydroxide (Ca(OH)2, JCPDS-PDF 01-0653).

The reduction of average particle size of milled powders from few hundred nm to 100 nm was observed after heat treatment at 900 °C during 2h. The agglomeration is still present, but the size of agglomerates is enhanced (Fig. 2.6). Smooth surfaces are evolving after heat treatment at 900 °C in the cases of ball milling.

Figure. 2.7 shows X-ray diffractograms of the milled powders after heat treat­ment at 900 °C during 2h. Only two phases were observed; the main phase hydroxy­apatite (HAp) and minor phase calcium oxide (CaO, JCPDS-PDF 037-1497).

In order to check the presence of trace elements in addition to the diffractograms energy dispersive X-ray microanalysis (EDS) measurements were performed on the milled powder samples. As the hydrogen content can not be analyzed by X-ray methods, furthermore the irregular and porous samples do not allow rigorous cor­rection of the EDS spectra, the results can be considered as semiquantitative ones. The spectra were collected in a JSM-25 S-III SEM using Bruker Si(Li)EDS detec­tor and Quantax system using area scan mode for averaging. The collection times were typically25-60 min (live lime) on a single 1 mm2 area of each sample, then the data were turned into numerical composition values using the no-standard P/B

ZAF package of the Quantax system. The normalized mass percent output values of the P/B ZAF program are summarized in Table 2.2. Zirconia may be found in the samples prepared by attrition milling only, because of wearing of zirconia milling parts (balls, tanks). Other elements found by EDS are sodium and silicon (as shown in Tab.2.1).

These elements are characteristic trace elements of eggshell. Sulfur and chlo­rine are other contaminants. As observed by EDS the chlorine can be found only in attrition milled samples. Although the EDS results are semiquantitative ones, it is interesting to see that magnesium is found. Increasing concentration of Mg in HAp has the following effects on its properties: (i) decrease in crystallinity, (ii) increase in HPO42- incorporation, and (iii) increase in extent of dissolution 28. Mg is one of the main substitutes for calcium in biological apatites. Enamel, dentin and bone con­tain, respectively, 0.44, 1.23, and 0.72wt.% of Mg 28; Mg-substituted HAp materials (denoted hereafter as Mg-HAp) are expected to have excellent biocompatibility and biological properties 29.

The phase composition of powders was studied by Fourier transform infrared spectroscopy (FTIR-Varian Scimitar FTIR spectrometer equipped with broad band MCT detector). The FTIR spectrum after attritor milling (Fig. 2.8a) resembles the characteristic spectral feature of bone mineral. The spectrum is dominated by the typical PO4 bands of poorly crystalline apatite phase components of the triply de­generated u3PO4 asymmetric mode at 1021 and 1087 cm-1 (shoulder), nondegener­ated symmetric stretching mode of o4PO4 at 962 cm-1 and components of the triplet of u4PO4 bending mode at 599 and 562 cm-11727. Carbonate bands are also observed at 1550-1350 cm-1 (u3), 873 cm-1 (u2) and 712 cm-1 (u4). By analogy with bone min­eral, the position of carbonate bands (1456, 1415and 872 cm-1) indicates the forma­tion of a carbonated apatite with B-type substitution (in tetrahedral positions) 30. The

broad band of low intensity in the range 3000-3400 cm-1can be attributed to traces of water incorporated to the structure, together wit the very weak, broad band around 1640 cm-1 of H-O-H bending mode. In the OH stretching vibration region, beside the uOH of HAp, surface OH band at 3644 cm-1also appears, probably con­nected to CaO occurring on the surface. In the case of attritor milled and treated powder, the intensity of surface OH band also increases with increasing the tem­perature (Fig. 2.8a).

FTIR spectrum of ball-milled powders shows a complex mixture of differ­ent calcium phosphate phases (Fig. 2.8b). This band decreases in matured bone apatite and in highly crystalline HAp31. The pure HAp phase with some carbonate substitution is formed only after 900 °C. However, surface OH bands are also present in the spectrum. After heat treatment, spectral features of the apatite phase become dominant and above 800-900 °C beside some peaks of carbonate (u3 at 1466 and 1409 cm-1, u2at 874 cm-1, u4 at 713 cm-1) and surface — OH (nOH at3640 cm-1) typical bands of well-crystallized HAp can be observed (u3PO4 at 1086 and 1018 cm-1, u1PO4at 961 cm-1 and the triplet of u4PO4 at 626, 599 and 561 cm-1) 30. No traces for acid phosphate (HPO42-peak around 540-530 cm-1), characteristic for immature bone mineral or incomplete apatite phase can be observed 32.

Noise can be defined as any kind of undesired sound. It is the specific circumstances and attitudes of those who are exposed to the sound, which makes the distinction between noise and other sounds. However, loudness is never of secondary relevance for annoyance by noise. Sound pressure levels exceeding 85 dB may cause tem­porary or permanent damages in the hearing organ. Levels exceeding 60 dB can negatively affect blood circulation and metabolism. Annoyance,10 fatigue,22 sleep disturbance,23 interference with speech,22 and decrease in school and work perfor­mance23 are some of the other unwanted effects of noise. There are regulations on noise levels in working environments to limit exposure of workers.14 Consequently, in order to prevent the unwanted effects of noise, and to meet regulations, noise control measures have to be taken.

For sound, or noise, to be produced, three components are needed: a sound source, a medium, and a detector. The sound source is a vibrating body that pro­duces a mechanical movement or sound wave. The medium, such as air, transfers the mechanical wave. The detector, such as an ear, detects the sound wave.24

ASTM describes sound absorption as “the process of dissipating sound energy” in ASTM C 634.24 Every sound wave is subject to continuous reduction by cer­tain dissipative processes whether it is propagating through air or porous materi­als. However, the sound dissipation during propagation through porous materials is much stronger than it is through air.10

Thermogravimetric test is used to determine the temperature at which the thermal degradation starts and determines the usable temperature range of treated jute felts. Thermogravimetric analysis (TGA) of raw and natural rubber treated jute felts was carried out in nitrogen gas atmosphere at a heating rate of 10°C/min from 45°C to 60°C temperature using a Differential Thermal Analyzer (DTA). Using the first de­rivative of the TGA line, a DTG curve was obtained to identify the start, peak, and end temperature. From TGA it was found that thermal stability of raw jute felt is till 260.92°C whereas treated jute felt is till 269.3°C. This indicates that jute and its derivative can be used in applications up to a temperature of 260°C, which can be further enhanced with suitable chemical treatment.

Visually, some tows on the preform seem to be very tight. This is particularly the case of the vertical yarns passing by the triple point (top of the tetrahedron). A local analysis of the tensile strains using the mark tracking method is carried out on those tows to investigate if failure strain has not been overcome.

Figure 7.19 shows the position of the tested yarns and the place between which the strain was measured. Figure 7.20 shows the values of the strains measured on the five considered yarns for one face of the tetrahedron shape. The results show that the strain rises in a nonuniform way during the sheet forming process. At the beginning of the test, no strain is observed as the punch is not in contact with the fabric. Once in contact, the strain in the different tows rises in a regular manner up to values above which the strain increases with a lower slope. Figure 7.20 also shows that the strains measured on the tows passing by or close to the triple point (top of the tetrahedron) are higher than the other ones. Moreover, the tensile strain decreases as a function of the increasing distance from the triple point. A ratio of 1/2 is observed between the strain measured at the end of the test for tow 5 and the strain measured on tow 1.

The maximum strain values measured at the end of the forming process indi­cated that these ones are all within the range 5-9.5%. These values seem to be rela­tively high in comparison to values evaluated for glass fiber fabric73 and it is there­fore important to investigate the mechanical behavior of the fabric independently of the process to find out if local failure in the tow took place during the forming test. Local failure in the tow causes local movements of the fibers within the tow, and this may lead locally to lower fiber density. This can certainly be a problem for the final composite part if the fiber density is not kept homogeneous as these places could be zones of weakness.

As reinforcement 1 is not balanced, the tensile strain has also been measured in the case of orientation 90° for the tow passing by the triple point of the Face C. Fig­ure 7.21 shows the evolution of the tensile strains of the tows passing by the triple point for orientation 0 and 90° for Face C.

For orientation 90°, the tensile strain values are much lower than the ones mea­sured on the equivalent tow for orientation 0° and same process parameters. This may be explained by the fact that reinforcement 1 is not balanced. For orientation 0°, the vertical weft tows are more submitted to the crimp effect than the warp tows (vertical for orientation 90°). Because of the crimp (the fact that a tow passes above and then below the perpendicular tows) the tow is not completely tight when the fabric is not loaded. The phenomenon depends on the number of perpendicular tows met by the tow. In our case, the vertical weft tows for orientation 0° meet more perpendicular tows than the vertical warp tows for orientation 90°. A ratio of 1/3 is observed between the maximum tensile strains of the tows passing by the triple point for orientation 90° and 0°.

Figure 7.22 shows that for the reinforcement 2 and orientation 0° that the tensile strains are relatively lower than for equivalent tows of reinforcement 1. This may be due to the fact that the tows of reinforcement 2 are stiffer and therefore less strained than the tows of reinforcement 1. Figure 7.22 also shows that the tensile strains are symmetrical in both sides of the tows passing by the triple point.

Tensile strain measurements have also been carried out on tow -1 at different location from the top (close to the triple point) to the bottom of the tow. Figure 7.23 shows that the tensile strains raise when the measurement is performed close to the top of the shape.

This therefore means that the highest strains are recorded in the top zones of the shape close to the triple point. As a consequence, it may be expected that due to the

high strains recorded in these tows that fiber movements within the tow takes place with some possible loss of fiber density. To confirm this hypothesis, it is important to investigate from which tensile strain these fiber movements may take place.

Leman et al.3 conducted series of tensile tests to determine the maximum stress of SPF reinforced epoxy composites. The composites were fabricated using SPF treated with seawater and freshwater for different time periods (6, 12, 18, 24, and 30 days). The aim of their study was to examine whether SPF can be effectively used in the marine sector as a potential substitute for the conventional glass fiber for manufacturing fishing boats. The results proved that SPF treated with seawater for 30 days had the highest stress value (23042.48 kPa), followed by freshwater treated SPF for 30days (21266.5 kPa). The SPF/epoxy composite strength improved by 67.26 and 54.37% for seawater and freshwater treated SPF for 30 days, respectively, as compared to the untreated SPF. The SPFs that were treated for 30 days with sea­water or freshwater had the smoothest surfaces. This was attributed to the removal of their first surface layers, which consisted of hemicelluloses and pectin. Therefore, the adhesion between SPF and epoxy polymer matrix significantly improved, lead­ing to higher tensile strength.

The effect of alkaline treatment on tensile and impact properties of SPF/epoxy composites was reported by Bachtiar et al.112 The treatment was conducted using two different sodium hydroxide solution concentrations (0.25 and 0.5 M) and three different soaking times (1, 4 and 8 h). The alkali treatment in all conditions (differ­ent alkali concentration and soaking time) significantly enhanced the tensile proper­ties of SPF/epoxy composite particularly for tensile modulus. SPF treatment with alkali removed the hemicellulose and lignin content, making the fiber relatively ductile and provided rougher fiber surface than the untreated SPF. This created better interlocking mechanism between the fiber and matrix surface. However, the treatment had a negative effect on the tensile strength of SPF/epoxy at higher alkali concentration. Very high alkali solution for fiber treatment certainly cause damage to the fiber and consequently decrease the tensile strength of fiber and also their composites.110 On the contrary, higher alkali concentration provided better impact performance for the SPF/epoxy composite. At strong alkali concentration treatment, the lignin and hemicellulose were washed out enabling better exposure of the fiber to epoxy matrix, leading to better bonding between their surfaces.107112115

Injection molded specimens, ASTM D638 Type I tensile bars, were tested for tensile modulus and strength using a universal testing machine (UTM), Instron Model 1122 (Instron Corporation, Norwood, MA). The speed of testing was 50 mm/min, which corresponds to a strain rate of 1 mm/mm/min at the start of the test. Specimen thick­ness was measured with a digital micrometer, Model 49-63 (Testing Machines Inc., Amityville, NY). Initial samples (dry) were conditioned for approximately 240 h at standard room temperature and humidity (23°C and 50% RH) prior to any test evaluations.

Three point bending flexural tests were completed according to ASTM-D790 on an Instron UTM Model 1122. The flexural tests were carried out using Procedure B with a crosshead rate of 13.5 mm/min, which corresponds to a rate of straining of the outer fiber equal to 0.1 mm/mm/min. The maximum flexural stress (flexural

strength, Oj-J and modulus of elasticity in bending (Eb) were calculated using the following formulas:

where P is the maximum applied load, L is the length of support span, m is the slope of the tangent, and b and d are the width and thickness of the specimen bars, respectively. Five specimens of each formulation were tested. The average values and standard errors were reported.

Notched impact tests were conducted with an IZOD impact tester, Model Resil 5.5, P/N 6844.000 (CEAST, Pianezza, Italy) conformed to ASTM D256-84. Speci­men bars were obtained by cutting the flexural specimens in half to 12.7 mm W x 64 mm L x 3.2 mm thickness and then notched.

Benzophenone is the organic compound with the formula (C6H5)2CO, generally ab­breviated Ph2CO (see Fig. 15.5). Benzophenone is a widely used building block in organic chemistry, being the parent diarylketone. Benzophenone is used as a flavor ingredient, a fragrance enhancer, a perfume fixative and an additive for plastics, coatings and adhesive formulations; it is also used in the manufacture of insecti­cides, agricultural chemicals, hypnotic drugs, antihistamines and other pharmaceu­ticals. Benzophenone an important class of organic UV filters, are widely used in sunscreen products due to their ability to absorb in the UVA and UVB ranges

15.1.4.1 ABSORPTION PROCESS

Absorption of visible and/or ultraviolet light by a molecule introduces energy suf­ficient to break or reorganize most covalent bonds. From the relationship E = hc/A, we see that longer wavelength visible light (400 to 800 nm) is less energetic (70 to 40 kcal/mole) than light in the accessible shorter wavelength (200 to 400 nm) near ultraviolet region (150 to 70 kcal/mole). Consequently, ultraviolet light is most often used to effect photochemical change. Care must also be taken to construct lamps and reaction vessels from glass that is transparent to the desired wavelength range. The low wavelength cut-off for some common glass types are given in the table on the right. The light required for a photochemical reaction may come from many sources.

Sunscreens may be defined as agents that protect the skin by absorbing damag­ing light rays and dissipating their energy in some harmless manner (1). When an organic compound absorbs radiation, it is either raised to a higher energy level or disassociated. An excited molecule may dissipate the absorbed energy by collision, fluorescence, or a reaction with other molecules at collision (2). The photochemistry of polyatomic molecules is quite complex and very little is known about photo­chemical mechanisms of organic compounds.

Chitin, a natural polymer, is the second most abundant organic resource on the earth next to cellulose. It is an exoskeleton of crustacean, cuticle of insects, cell wall of fungi and micro organisms. It consists of 2-acetamido-2-deoxy-p-1, 4-D-glucan through the P-(1-4)-glycoside linkage.79 Chitin can be degraded by chitinase. Chitin fibers have been used for making artificial skin and absorbable sutures. Although chitin is structurally similar to cellulose, much less attention has been paid to chitin than cellulose, primarily due to its inertness. Therefore, it has remained an almost unused resource. Deacetylation of chitin yields chitosan, which is relatively reac­tive and can be produced in numerous forms, such as powder, paste, film, fiber, and more. The materials are biocompatible and have antimicrobial activities as well as the ability to absorb heavy metal ions. They also find applications in the cosmetic industry because of their water-retaining and moisturizing properties. Using chitin and chitosan as carriers, a water-soluble prodrug has been synthesized.80

Chitosan is polysaccharides comprising copolymers of glucosamine and N — acetylglucosamine. Chitosan is usually prepared from chitin and chitin has been found in a wide range of natural resources (cruslaceans, fungi, insects, annelids, molluscs, coelenterate, etc.). Chitosan has interesting biopharmaceutical character­istics such as pH sensitivity, biocompatibility and low toxicity.81 Moreover, chitosan is metabolized by certain human enzymes, especially lysozyme, and is considered as biodegradable.82 Due to these favorable properties, the interest in chitosan and its derivatives as excipients in drug delivery has been increased in recent years. Modified chitosans have been prepared with various chemical and biological prop­erties.83 N-Carboxymethylchitosan and N-carboxybutylchitosan have been prepared for use in cosmetics and in wound treatment.84 Chitin derivatives can also be used as drug carriers85, and a report on the use of chitin in absorbable sutures shows that chitins have the lowest elongation among suture materials consisting of chitin, poly(glycolic acid) (PGA), plain catgut and chromic catgut.86 The tissue reaction of chitin is similar to that of PGA.