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Effect of high hydrostatic pressure on structure of gelatin gels

Kulisiewicz L., Baars A., Delgado A.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2007

Vol. 55, nr 2

239-244

The present contribution reports on the rheological investigations concerning influence of high hydrostatic pressure on the molecular structure of gelatin gels. For the purpose of the study, a torsional shear wave rheometer for in-situ investigations of viscoelastic substances under high pressure was developed. Small amplitude vibrations generated by piezoelectric elements are used to determine the storage modulus of the investigated medium. The system is able to stand pressures up to 300 MPa. The experiments have been carried out with household gelatin (0.1 w/w aqueous solution). The gelification curves revealed similar time course. However, the values of G' obtained for the gels curing 300 minutes under 100 MPa and 200 MPa were observed to be respectively 2.1 and 4 times higher than at ambient conditions. The increased number of triple helix junction zones is hypothesised to be the cause of this phenomenon as a result of reinforcement of the hydrogen bonds due to pressure. An attempt to cognize the characteristic dimensions of the molecular structure based on the theory of rubber elasticity is made.

Effect of Initial N,N'-Methylene Bisacrylamide Concentration on the Swelling Behaviour of Acrylic-based Superabsorbent Polymers

Mucientes A., Santiago F., Delgado A.

Polish Journal of Chemistry

2005

Vol. 79 / nr 5

897-905

Aseries of superabsorbent polymers based on acrylic acid has been synthesized by a solution polymerization technique at 60°C. The effect of the N,N_-methylene bisacrylamide concentration on the swelling behaviour of these hydrogels in deionized water and saline solution was investigated. Experimental results indicate that the absorbance in deionized water or saline solution decreases on increasing the concentration of crosslinker. Moreover, the amount of swelling in 0.2 wt% NaCl(aq) is smaller than that in deionized water, a result that is due to the decrease in the osmotic pressure (ionic pressure) difference between polymer and external solution at high ionic strength. High swelling and appropriate absorption kinetics can be obtained by altering parameters such as initial monomer concentration, range of neutralization, temperature, initiating system and range of crosslinker concentration. These changes were studied but are not reviewed here. Rates of swelling for these absorbents were found to fit the Voigt expression. Relationships were also established between the ultimate degree of swelling and the ratio of crosslinker to monomer. The results of the investigation involving water or saline solution diffusion in hydrogels approximate to Case II sorption in the early stages of the swelling process and to Case I in the later stages.