Contribution of boron compounds and nanoclays on the flame retardancy of aluminium diethylphosphinate in neat and fiber reinforced polyamide-6

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2014
Polat, Osman
The main objective of this dissertation was to investigate contribution of three different boron compounds and nanoclays to the flame retardancy of polyamide-6 and its 15 wt% short glass fiber reinforced composite with and without an organophosphorus flame retardant aluminum diethylphosphinate. All material combinations and nanocomposites were compounded by melt mixing method via twin-screw extruder and the specimens for testing and analyses were shaped by injection and compression molding. In the first part of the thesis, effects of zinc borate (ZB) were investigated. UL-94 vertical burning, limiting oxygen index (LOI) and mass loss cone calorimetry (MLC) analyses indicated that replacement of certain amount of aluminum diethylphosphinate (ADP) with ZB could lead to significant improvements in many flame retardancy parameters. For instance, the suppression in peak heat release rate (PHRR) value of polyamide-6 could be as much as 82%, while it was only 32% when ADP was used alone. Char microscopy, thermogravimetric analyses, X-ray diffraction and evolved gas analyses revealed that the main contribution of ZB to the barrier mechanism of ADP was the formation of additional boron phosphate layers together with aluminum phosphate layers. In the second part of the thesis, effects of both boron oxide (BO) and boric acid (BA) were investigated. In this case, there were no improvements in the values of UL-94 and LOI, but significant improvements in many MLC flame retardancy parameters of especially the neat polyamide-6 specimens. For example, replacement of certain amount of ADP with BO or BA resulted in PHRR suppression of polyamide-6 as much as 84% or 86% respectively, which was only 32% when ADP was used alone. Various analyses indicated that the main contribution of BO and BA to the barrier mechanism of ADP was the formation of additional glassy boron oxide layers and boron phosphate layers. In the third part of the thesis, effects of organically modified montmorillonite type nanoclays (NC) were investigated. Transmission electron microscopy and X-ray diffraction analyses indicated that NC layers had intercalated/exfoliated morphology in the polyamide-6 matrix. UL-94, LOI and MLC analyses revealed that use of only 5 wt% NC could improve many flammability parameters. Contributions of NC silicate layers were much more significant when 5 wt% NC were used together with 15 wt% ADP. Various analyses clarified that the basic flame retardancy mechanism of NC was the formation of insulative barrier via tortuous pathway of silicate layers preventing the underlying polymer from heat and mass transfer during fire. It was also found that, all the mechanical properties lost due to the use of ADP could be compensated when its 5 wt% was replaced with NC.

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Citation Formats
O. Polat, “Contribution of boron compounds and nanoclays on the flame retardancy of aluminium diethylphosphinate in neat and fiber reinforced polyamide-6,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.