Abstract
Metal ions present on smectite clay (montmorillonite) platelets have preferential reactivity towards peroxy/alkoxy groups during polyamide 6 (PA6) thermal decomposition. This changes the decomposition pathway and negatively affects the ignition response of PA6. To restrict these interfacial interactions, high-temperature-resistant polymers such as polyetherimide (PEI) and polyimide (PI) were used to coat clay layers. PEI was deposited on clay by solution-precipitation, whereas PI was deposited through a solution-imidization-precipitation technique before melt blending with PA6. The absence of polymer-clay interfacial interactions has resulted in a similar time-to-ignition of PA6/PEI-clay (133 s) and PA6/PI-clay (139 s) composites as neat PA6 (140 s). On the contrary, PA6 with conventional ammonium-based surfactant modified clay has showed a huge drop in time-to-ignition (81 s), as expected. The experimental evidences provided herein reveal the role of the catalytic activity of clay during the early stages of polymer decomposition.
Highlights
Polymer/clay nanocomposites show a significant reduction in peak heat release ratesduring combustion [1,2]
In our recent systematic investigations on this topic [7,11], we showed that by amplifying the content of a specific cation, thermal decomposition and combustion reactions of polyamide 6 (PA6) could be affected
Coated clay (PEI-clay) and PI coated clay (PI-clay) platelets are shown in Figure 1, highlighting the differences in the uniformity of coating on organoclay with PEI and PI
Summary
Polymer/clay nanocomposites show a significant reduction in peak heat release rates (up to 70%)during combustion [1,2]. In our recent systematic investigations on this topic [7,11], we showed that by amplifying the content of a specific cation (which are inherently present in the clay structure), thermal decomposition and combustion reactions of PA6 could be affected. Al3+ -rich PA6/clay nanocomposites ignited early with a lower onset temperature of decomposition under oxidative conditions; while an Mg2+ -rich composite displayed the maximum thermo-oxidation stability and gave the highest residue. This suggested that the chemical interaction of the PA6 matrix and/or its intermediate decomposition products with the clay surface changes the decomposition pathway of PA6. It has been observed that the nature of intermediate products depends on the type of interacting and/or coordinating metal ions
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