Here we report the use of a one-step process of reactive melt mixing to prepare starch-based superabsorbent polymers (SBSAPs) for the slow release of urea as a fertilizer. A modified twin-rotor mixer, with improved sealing to establish an oxygen-free environment, was used to study the chemical and physical reactions during the melt-processing through monitoring the temperature and torque. The effects of the initiator (ceric ammonium nitrate, or CAN), crosslinker (N,N'-methylene-bisacrylamide, or N,N'-MBA) and saponification agent (NaOH) under different reaction conditions (time, temperature, and shear intensity) were systematically studied. Also investigated was the effect of starch with different amylose content. Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) confirmed that using this simple technique, SBSAPs were successfully prepared from either high-amylopectin starch (waxy corn starch) or high-amylose starch (Gelose 50) grafted with AM and crosslinked by N,N'-MBA. Gel strength was evaluated by rheometry, which revealed a significant increase in storage modulus (G') obtained in the crosslinked high-amylose SBSAP gels. Also, scanning electron microscopy (SEM) images showed a more sophisticated structural network with a smaller pore size in the crosslinked high-amylose gels. Urea as a fertilizer was embedded in the SBSAP gel network, and this network controlled the urea release in water. The release rate of urea depended on the gel strength, gel microstructure and water absorption capacity (WAC) of SAP, which was affected by the reaction conditions and degree of saponification.
New ruthenium complexes of two tridentate ligands 2,6-bis( benzimidazol-2-yl)pyridine ( L7) and 2,6bis( 1 -methylbenzimidazol-2-yl)pyridine (La) have been synthesised. Proton and 13C NM R spectroscopy served well for their characterization, and the observed change. Proton chemical shift yields information about the electron distribution accompanying deprotonation of the ligands. The [ RuL7Jn+ chelate acts as a tetrabasic acid, with pK, ranging from 2.5 to 10.7, depending on the ruthenium oxidation state. The absorption spectra and oxidation potentials are consequently sensitive to solution pH and to solvent. The proton-coupled oxidative electron-transfer reactions of the complexes afford stable higher oxidation states such as Ru'". The properties of the complexes are discussed in comparison to those of previously reported bis(tridentate 1igand)ruthenium compounds.
Waste
water resulted from polymer flooding oil recovery generally
has a bad impact on the subsequent process of enhanced oil recovery.
Separating residual oil from oil/water (O/W) emulsion with suitable
kinds of demulsifier is one strategy generally adopted by oil companies.
Because of the existence of large amounts of ultrafine oil droplets
with the average diameter less than 2 μm, the emulsions can
be extremely difficult to break up. To solve this problem, an amine-based
dendrimer demulsifier PAMAM (polyamidoamine) was synthesized in this
study, and the efficiency of the demulsifier in dealing with O/W emulsions
with ultrafine oil droplets was investigated. Because of its strong
interfacial activity and relatively good solubility in water, the
dendrimer-based demulsifier can easily attach to emulsified oil droplets
in a stable diesel-in-water emulsion. The influences of temperature,
settling time, and concentration of the demulsifier used on the efficiency
of the demulsifier were investigated in detail. The optimal operating
condition under which more than 90% oil was removed from the original
emulsion by the demulsifier was found. In contrast, less than 2% oil
was removed from the emulsion without applying the demulsifier under
the same conditions. Micrographs showed that the PAMAM demulsifier
could lead to the breakup of diesel-in-water emulsions with ultrafine
oil droplets by flocculation and coalescence. The surface tension
and interfacial tension at the diesel–water interface were
also measured to give a basic understanding of the demulsification
mechanism. Though not perfect in dealing with emulsions with the average
oil droplets less than 2 μm due to the relatively high demulsifier
dosage, its relatively simple synthetic procedure and mild operating
conditions showed a great promise in industrial applications with
unique advantages over traditional physical methods.
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