Using 3-[(2,3-epoxypropoxy)-propyl]-trimethoxysilane as a surface modifier, superabsorbent polymers with improved gel strength in their swollen state and saline absorbency under load are synthesized. The products are characterized using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), rheometry, scanning electron microscopy-energy dispersive X-ray analysis, contact angle, thermogravimetric analysis, water absorbency and gel content. The temperature and the duration effect of the surface-treatment process on residual monomer content are also investigated by high performance liquid chromatography. The gel strength (as shown by storage modulus) and absorbency under load are improved up to 3500-4000 Pa, and 30-40 g/g, respectively. It is suggested that the surface of the superabsorbent polymer particles has been modified by two mechanisms: i.e. interpenetrating polymer network and cross-linking. Moreover, the surface modification has enhanced thermo-stability and prohibited undesirable gel blockage. Depending on the post-treatment method used, the wetting behavior of particles is also altered.
Water absorption capacityFree swelling capacity values were measured using the sieve method. [2] The powdered samples (0.10 g) were permitted to Scheme 1. A snapshot of the present research.
The glycerol-lactic acid-based star-shaped modifier (SM) were synthesized and employed for surface modification of hygienic superabsorbent polymer (SAP) hydrogels for the first time. Surface crosslinking was carried out to increase the saline-absorbency under load (AUL) and the swollen gel strength. The surface treatment process was analyzed employing free absorbency and AUL tests, salt sensitivity, attenuated total reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR), oscillatory rheometry, as well as scanning electron microscopy analysis. The effect of the branched architecture and the contents of SM on the properties of the modified SAPs were studied. The implementation of surface treatment leads to increase up to a 28% in the AUL of the modified SAP. Moreover, the loss modulus was surprisingly increased, while the storage modulus was enhanced (possibly due to the star architecture of oligomers). M c and crosslink density values have been estimated based on modified rubber elasticity theory. Salt sensitivity factor ( f ) was calculated; the modified samples showed lower salt sensitivity in NaCl ( f = 0.7) and CaCl 2 ( f = 0.93-0.95) compared with the intact SAP ( f = 0.84 for NaCl, and f = 0.95-0.97 for CaCl 2 ).
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