Glass transition temperature chitin

Nanofibers based on poly(vinyl alcohol) as the matrix, and nanocrystals of a-chitin (ca. 31 nm in width and ca. 549 nm in length) as the nanofiller were prepared by Junkasem et al. [51]. The average diameters of the electrospun fibers ranged between 175 and 218 nm. The addition of increasing amounts of the whiskers caused the crystallinity of poly(vinyl alcohol) within the nanocomposite materials to decrease and the glass transition temperature to increase. 

GLASS TRANSITION TEMPERATURE (a-RELAXATION) CONTROVERSY IN CHITIN, CHITOSAN, AND PVA... 

In semicrystalline polymers, such as chitin and CS, the value of the glass transition temperature characteristic of the amorphous material was controversial even as to whether polysaccharides exhibit a glass transition temperature (Eg). For many natural polymers, Eg is above the thermal degradation temperature [10]. For chitin, some authors have not observed a glass transition [11], while others report an apparent a-relaxation at 236 °C for a-chitin [12] and 170 °C for P-chitin [13] using DMTA measurements. Lee et al. [14] report an apparent a-relaxation at 182 °C for 3-chitin by dielectric measurements. 

For most polymers, the relationship between the glass transition temperature 7g and T), is 7g = T), -E C where C is a constant that in many dielectric studies is about 50 K [9, 73, 74]. On the basis of the usual uncertainty in C and the above Tq = 285 K, we estimate that Tg for dry annealed chitin is 62 10 °C. This low value for the 7g of a stiff polymer such as a-chitin is slightly surprising, but it is consistent with the low Ig s found in polypeptides (-70 to -50°C) [75-77]. The common denominator between polysaccharides and polypeptides is extensive hydrogen bonding significant thermal dismption of H-bonding and the onset of main chain molecular motions are probably closely related. 

The a-relaxation in dry annealed a-chitin can be observed by DS measurements. On this basis, the glass transition temperature was estimated at 61 10 °C. Moisture content is a key factor to observed the glass transition in chitin and it could be related to the controversy about the glass transition temperature detection and designation in this biopolymer... 

The 1 wt% of chitin nanociystals were added to poly(lactic acid) plasticized with glycerol triacetate plasticizer in blown film application. The addition of chitin nanocrystals increased the tear strength by 175% and the puncture strength by 300%. Also, the glass transition temperature increased by 4°C and the films degree of ciystallinity was... 

NILS chiral and biodegradable ionic liquids can be synthesized from natural amino acids [45], Some characteristics of these RTILs, such as good ntiscibiUty with organic solvents, high ionic conductivities, and low glass transition temperatures (Tg), have been reported. For example, Chitosan is obtained by full or partial deacetylation of chitin (Fig. 7.7). 

The two different temperature dependencies described above for giass-forming liquids are present in a-chitin, and the simiiarity between dc conductivity and relaxation time for the two low frequency relaxations is clearly observed in Figure 2.12a and b. Both dependencies (dc conductivity (a, .) and relaxation time (t) versus T plots) show the same features an Arrhenius type relaxation will yield a straight line above 80 °C, whereas a non-Arrhenius relaxation will manifest as a curved line that suggests a VFTH type or glass transition below 80 °C in dry annealed samples. For wet and dry samples, the decrease of conductivity as the temperature is increased from 20 to 80 °C is likely due to the motion of water-polymer complex since water could be modifying the relaxation mechanism of the matrix material. 

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