Chitin films

Chitin films can be manufactured from DMAc solutions or by other approaches, for example, blend films of beta-chitin (derived from squid pens) and poly(vinyl alcohol) (PVA) were prepared by a solution casting technique from corresponding solutions of beta-chitin and PVA in concentrated formic acid. Upon evaporation of the solvent, the film having 50/50 composition was found to be cloudy [224]. 

Yusof NL, Lim LY, Khor E (2004) Flexible chitin films structural studies. Carbohydr Res 339(16) 2701-2711... 

Yusof NL et al (2003) Flexible chitin films as potential wound-dressing materials wound model studies. J Biomed Mater Res A 66(2) 224—232... 

Muzzarelli et al. (2000) described a method for coating prosthetic articles with chitosan-oxychitin. Plates of titanium (Ti) and its alloys were plasma sprayed with hydroxyapatite and glass layers, and subsequently a chitosan coat was deposited on the plasma-sprayed layers using chitosan acetate. These layers were treated with 6-oxychitin to form a polyelectrolytic complex. This complex was optionally contacted with l-ethyl-3-(3-dimethylami-nopropyl) carbodiimide at 4°C for 2 hours to form amide links between the two polysaccharides, or acetylation with acetic anhydride in methanol to obtain a chitin film. In all cases, the modified coats were insoluble, uniformly flat, and smooth. Prosthetic materials coated with chitosan-oxychitin were capable of provoking colonization by cells, osteogenesis, and osteointegration. 

Figure 23 Dielectric spectra of wet chitin films at different bias applied voltage. Contact effect is observed when applied voltage is changed from 0 V to 3 V in the quasilinear response (outside the semicircle). Source Reproduced with permission from Gonzalez-Campos JB, Prokhorov E, Luna-Bdrcenas G, Mendoza-Galvdn A, Sanchez 1C, Nuno-Donlucas SM, Garcia-Gaitan B, Kovalenko Y. J Polym Sci B Polym Phys 2009 47 932 [5]. Copyright 2009 John Wiley and Sons, Inc.

These films are cooled under vacuum from 120 °C to room temperature (20 °C) and then a second measurement is performed in the dry annealed films. To calculate water content on these films, TGA measurements were performed in dry samples (heated at 120 °C in oven overnight). After 1 h at 120 °C (dry annealed films), no further change in weight is observed the films were cooled to 20 °C and reheated. The second TGA scan for dry annealed chitin films shows free water content of circa 0.1% (dash-dotted line. Fig. 2.5). Using the same annealing methodology in the dielectric and TGA measurements, we can monitor the water content in the samples. 

Modulated DSC thermograms (Fig. 2.7) for chitin films after water removal were scanned a second time from 20 to 250 °C. The objective was to see whether a glass transition would manifest. However, as stated in Section 2.1, controversy centers on whether a glass transition can be detected. In our case, there is no clear evidence of the glass transition hence, it is not possible to draw any conclusion from the thermal analysis. As explained earlier, some authors assign no for chitin [11], while others... 

Figure 2.9 shows the complex Cole-Cole plot for wet (Fig. 2.9a) and dry annealed chitin films (Fig. 2.9b) measured at 25, 50, 70, and 130 °C, respectively. A Cole-Cole type plot of Z" versus Z for wet films exhibit characteristic semicircles at high frequencies and a quasilinear response at low frequencies. This behavior is due to the presence of water in the samples, that is, water reduces the resistivity of films and could be modifying the relaxation mechanism of the matrix material. 

The same dielectric behavior in dry annealed and wet samples is developed above 110°C. These observations are very important since they suggest an extra relaxation process [16] in the absence of water, which is analyzed in detail in the next section. On the other hand, the linear response at low frequencies in wet and dry chitin can be associated with interfacial polarization in the bulk films and/or surface and metal contact effects [47]. To analyze the dielectric relaxation of chitin films is necessary to understand the nature of the low frequency part of dielectric spectrum. 

It is well known that contact metal-polymers for many systems can be interpreted as Schottky barriers [55-57] or heterojunction [58, 59]. To test the influence of gold contact on the chitin dielectric spectra, a nonsymmetrical contact array was prepared in the following manner a circular chitin film was covered on one side with a piece of gold sheet with a small circular orifice in the center during gold-sputtering. The other side of the film was totally gold-sputtered. This way a top surface available for electrode contact is circa 0.008 cm. The bottom surface area is circa 0.75 cm. Because of contact surface area differences, the current depends on the properties of the top electrode. 

Specific examples using STEM include structural studies over chitin gels used to produce chitin films. The results of the tests performed revealed that shrinkage resulted in a coarser microstructure. This morphology affected the tensile properties. It was also observed that shrinkage was proportional to the ductility and roughness of the meterial [53]. 

Qin, Y., Lu, X., Sun, N. and Rogers, R.D. (2010) Dissolution or extraction of crustacean shells using ionic liquids to obtain high molecular weight purified chitin and direct production of chitin film and fibers. Green Chemistry, 12,968-971. 

An attempt was also made to prepare the chitin film using l-butyl-3-methy-limidazolium acetate, which was reported as another ionic liquid dissolving chitin as aforementioned (Wu et al., 2008), according to the same procedure using AMIMBr as described. However, the regenerated chitin was not dispersed in... 

The weight loss of samples, prepared by acetic acid, buried in soil is listed in Table 9.2. The weight loss of chitin films buried in red clay reached 83.8%, 99.0%, and 100% after 1,1.5, and 2 months. 

Soil Type (Months) Chitin Film Chitosan Film... 

It is also possible to prepare a chitin gel using a recently found calcium chloride dihydride saturated methanol [22]. If chitin powder is suspended in this solvent and stirred, it becomes a viscous solution. Upon casting this solution onto a glass plate and deforming, a gel-like chitin film is obtained by immersing the casting into a mixed solution of 20% sodium... 

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