Gum tragacanth (GT) was exploited to create a series of novel hydrogel membranes with diverse swelling properties. The films of this biopolymer were crosslinked with applying heat only, as well as application of four types of chemical crosslinking reagents, including glycerin, ethylene glycol, triethylene glycol, and glutaraldehyde. The effects of the crosslinking agent concentration, crosslinking reaction temperature (57-97 C) and reaction time (2-24 h) on the equilibrium swelling of each series of the synthesized hydrogels were investigated by the aid of Taguchi method of experimental design. This approach facilitated the study of interaction of a large number of variables spanned by factors and their levels with a small number of experimental runs. In all cases, it was found that by increasing the concentration of each type of the crosslinking reagent and extension of the crosslinking reaction time, the swelling capacity of the prepared hydrogel films decreased. However, by increasing the crosslinking temperature, the equilibrium swelling capacity changed by passing through a minimum. As a whole, the equilibrium swelling values of the hydrogels proved that a broad range of hydrogel membranes having the crosslinking densities of 0.83-23.87 Â 10 À6 mol/cm 3 and swelling capacities of 120-1580 g/g was achieved successfully from GT. Thus, GT was assigned as a promising biopolymer for preparing membranes with diverse structural and swelling characteristics.

Hydrogel membranes based on gum tragacanth (GT), with a wide range of crosslinking densities (0.83-23.87 Â 10 À6 mol/cm 3 ) and swelling capacities (120-1580 g/g), were prepared with the aid of heat alone and four crosslinking reagents according to a procedure reported in our previous article. In this article, we report on the comprehensive evaluation of the swelling behavior of the prepared hydrogel membranes. These include the swelling kinetics, swelling behavior in terms of the pH and ionic strength of the swelling media, water absorbency under load (AUL), swelling as a function of sample size, deswelling behavior, and successive swelling and deswelling cycles. The swelling kinetics of the hydrogel membranes with higher crosslinking densities and lower swelling equilibria were closer to those of the case II transport mechanism; this is desirable in the field of drug-delivery systems (DDSs). Furthermore, higher crosslinking densities, and hence stronger structures, of the membranes led to higher AUL values and more stable performances in the successive swelling and deswelling cycles. Moreover, because of the anionic nature of the gum, the prepared GT hydrogels showed pH-and ionic-strengthdependent swelling behavior. All of these results reveal that GT could be a promising material for the preparation of hydrogel membranes for applications in the fields of DDS, tissue engineering, and the separation of small molecules.

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Galbanic acid (GA) is known as an effective photo-sensitizing agent in polyethylene. This paper reports the comparative studies on photo-oxidative degradation of LLDPE films in the presence of varying amounts of galbanic ferric salt (Fe-GA), tetrabromo galbanic acid (Br-GA), GA at the optimum concentration of 0.2% (w/w) and the pure polymer film, exposed to Ultra-Vitalux sun lamp. The degradation rate was monitored through the changes in mechanical properties (retained elongation at break and retained tensile strength) and also carbonyl index. The results obtained revealed that Fe-GA efficiency in enhancing oxidation rate of polymer upon UV exposure is remarkably much more than of GA. In contrast, Br-GA is responsible for initiating photo-oxidation of the polymer and has negligible effects on the rate of degradation. Based on the results obtained, it was proposed that the photo-activity of GA in the polymer arises from the C=C bond present in the side group attached to aromatic lacton rings of additive molecule, probably through its reaction with singlet oxygen and subsequent generation of hydroperoxide. This mechanism in combination with catalytic effect of iron (III) accounted for the higher effect of Fe-GA in accelerating photo-oxidation rate of the polymer.