A novel and multifunctional flame retardant synergist, N-alkoxy hindered amine containing silane (Si-NORs), was synthesized by combining N-alkoxy hindered amine and silane coupling together through sol−gel reaction. The composition of Si-NORs was characterized by FTIR and XPS. Intumescent flame retardant polypropylene (IFR−PP) composites were prepared with different contents of Si-NOR and characterized by the limiting oxygen index (LOI), vertical burning tests (UL-94 tests), TGA, the Yellowness Index (YI), mechanical properties, and SEM measurements. The results showed that IFR−PP composites with 1 wt % Si-NORs and 25 wt % intumescent flame retardant could reach a V-0 rating in the UL-94 tests. Moreover, the thermal stability, UV stability, mechanical properties, compatibility, and char residue structure were also improved significantly, which proves Si-NOR as a multifunctional flame retardant synergist. The possible synergistic mechanism of Si-NORs was also discussed.
This paper reports our investigation of the existence of physical cross-links in modified polypropylenes (PPs) containing long chain branches (LCBPPs) or amine moiety (PP-g-NH 2 ). By varying the stoichiometric ratio of maleic anhydride grafted polypropylene (PP-g-MAH) and ethylenediamine (EDA), a series of modified PPs with different degrees of branching and side-group polarities were prepared. Extensive rheological studies were conducted after baseline characterization of the chemical and molecular structures of these materials using Fourier transform infrared (FTIR) spectroscopy and size exclusion chromatography (SEC), respectively. The results strongly suggest the presence of physical cross-links in a majority of the materials studies herein, which significantly impacts their rheological behaviors. The physical cross-links can be argued to be in the form of phase-separated domains and hydrogen bonding, which has been reported in the literature.
In this work, reactive twin screw extrusion was conducted to synthesize long chain branched polypropylenes (LCB-PPs) in a “one-pot” process in which dicumyl peroxide (DCP) initiated maleic anhydride (MAH) grafting onto the linear PP, and the concomitant coupling reaction between ethylene diamine (EDA) and MAH grafted polypropylene (PP-g-MAH) proceeded in series. Fourier transfer infrared spectroscopy (FTIR) on the prepared materials confirmed the occurrence of both reactions. A series of LCB-PPs were prepared using different amounts of EDA, MAH and DCP to study their effects and determine the optimal synthesis conditions. The prepared materials were characterized by size exclusion chromatography (SEC) and rheological analysis to ascertain the polymer microstructure. The foamability of the LCB-PPs by supercritical carbon dioxide (scCO2) foaming and foam morphology were investigated. The LCB-PPs were found to have vastly improved foamability and cellular morphology. Under optimal conditions, a foam expansion ratio of over 20 was achieved.
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