Stearate/LDH

Fig. 22 Image plate study of a stearate/LDH cast film. Reprinted with permission from [151]. Copyright American Chemical Society...

FIGURE 9 IR spectra of ZnsAl-Stearate-LDH with stearate monolayer packing (A) and bilayer packing (B). 

In the case of stearate ions intercalated in Mg/Al LDHs, the electron density shows a pronounced minimiun in the center of the interlayer region, which is consistent with the presence of a bilayer of guest molecules [151,152], The electron density distribution for an anionic azobenzene derivative intercalated in an Mg/Al LDH has also been reported [ 153]. 

Chlorine-containing polymers such as poly(vinyl chloride) PVC undergo an autocatalytic dehydrochlorination reaction under the influence of elevated temperature and UV radiation. Since the HCl originating from the dehydro chlorination of the PVC chains is believed to sustain this autocatalytic process, stabilizers that irreversibly bond HCl can thus inhibit the degradation. Heavy metal compounds such as cadmium stearate or lead stearate are currently used for this purpose. However, alternatives are required due to environmental problems associated with the use of heavy metals. Indeed, the largest current application of LDH materials is in the polymer industry, mainly to stabilize PVC [3,229-232]. 

Kyowa Chemical Industries (Japan) were the first to demonstrate that adding Mg/Al LDHs to PVC in combination with other additives such as zinc stearate and tin maleate leads to an enhancement in thermal stability of the resin [231]. The role of the LDH in absorbing HCl was confirmed experimentally by Van der Ven et al. [232], who measured the capacity of LDHs... 

Figure 6.5 Time evolution of the FTIR spectra of QUV (accelerated weathering tester) films containing 0.10% Mn Al-LDH-stearate. Reprinted from Polymer Degradation and Stability, Vol. 94, Bhelki Magagula, Nontete Nhlapo and Walter W. Focke, Mn Al-LDH-and COjAl-LDH stearate as photodegradants for LDPE film, pp. 947-954, 2009, with permission from Elsevier.

Even the properties of PVC are improved if organomodified LDH is dispersed by a solution-assisted process compared to samples without addition of LDH. Two different ions, DS and stearate, were used as intercalating ion showing inaeased stability of nanocomposites prepared with MgAl-LDH-stearate which reached 20 times the stability of neat PVG. There it was suggested that the basicity of the interlayer anion plays a oucial role in the dechlorination process of PVG due to the absorption of HGl. 

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