Objectives Montmorillonite (MMT) is a kind of clay mineral having accumulation texture of nanosilicate sheets, so it has excellent mechanical, thermal and gas barrier properties. Three organic ion exchangers were tested in this paper in order to make MMT fully dispersed in polyurethane (PU) matrix, and then used for preparing polyurethane/montmorillonite (PU/MMT) composite materials with excellent mechanical and controlled-release properties.
Methods Three organic modifiers, octadecyl trimethyl ammonium ammoniate (SA1), dodecyl dihydroxyethyl methyl ammonium chloride (SA2) and dimethyl dioctadecyl ammonium chloride (SA3), were used to intercalate the montmorillonite. Then the castor oil-based PU/MMT composite films were prepared by in-situ polymerization. SEM, IR and XRD techniques were used to characterize the morphology and structure of nanoparticles and composite films. The dynamic mechanical properties, the thermal stability and controlled-release performance of PU/MMT composite films were also investigated.
Results The MMT were modified by organic intercalation of the three organic ion exchangers, which brought good dispersal and compatibility of MMT in the matrix of PU matrix. Furthermore, the dynamic mechanical properties and thermal stability of PU/MMT composites were significantly improved due to the addition of nanoparticles. Among the three composites, the PU/SA2-MMT showed the most improvement on the dynamic mechanical properties and thermal stability. The glass transition temperature (Tg) of membrane increased from 30℃ to 80℃, and decomposition temperature increased from 300℃ to 330℃, the reason for it was the double hydroxyethyl structure in SA2 modifier which made MMT more tightly bound to PU. While the PU/SA3-MMT composite coating material performed the best controlled-release property, the time needed for 75% of urea release was increased from 30 d to 75 d, which was mainly caused by the double long chain organic structure of SA3.
Conclusions Intercalation modification of MMT with ion exchangers of dodecyl dihydroxyethyl methyl ammonium chloride and dimethyl dioctadecyl ammonium chloride can effectively loosen its structure and increase its dispersal in polymers. The addition of the modified MMT makes the PU/MMT composite film have excellent thermal stability and satisfactory release properties, which can be used for the manufacture of low price and high quality controlled-release fertilizers.
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