Influence of silicon dioxide addition and processing methods on structure, thermal stability and flame retardancy of EVA/NR blend nanocomposite foams

Abstract

Rubber nanocomposite foams based on 60/40 ethylene vinyl acetate (EVA)/natural rubber (NR) were melt-mixed with flame retardant silicon dioxide (SiO2) (20 parts per hundred rubber, phr), and foamed by compression molding process. In this study, the effect of mixing phenomena of SiO2 through two different compounding techniques such as direct mixing (DM) and phase selective mixing (PSM) methods on structure, thermal stability, combustility and flame retardancy of EVA/NR blend nanocomposite foams were investigated. DM method is a melt mixing of EVA, NR, layered silicate and SiO2, followed by foaming. PSM is a new method based on pre-mixing EVA with SiO2, then melt mixing of EVA/SiO2 masterbatch with NR and layered silicate, and finally foaming. Based on TEM technique, it was found that the SiO2 was exclusively located in dispersed NR phase for the sample prepared by DM method, and the SiO2 was preferably dispersed in continuous EVA matrix when PSM method was employed. However, the different mixing methods did not significantly alter their cellular structures. The thermal stability and char residue content of foamed samples with SiO2 increased obviously when compared with those of corresponding foams without SiO2. The results based on limiting oxygen index (LOI) test and oxygen bomb calorimetry indicated that the foams combined with SiO2 had better combustion resistance and flame retardancy due to barrier effect of thermally stable silicon-based char layer. Further, the SiO2 filled foamed system obtained from the PSM method showed a higher degree of improvement in thermal stability, combustion resistance and flame retardancy than that of DM method because the homogeneous dispersion of SiO2 in EVA matrix rather than the selective dispersion in NR phase. This resulted in the continuity of flame retardant EVA/SiO2 phase in the 60/40 EVA/NR nanocomposite foams, which exerted more efficient fire barrier of the silicon-based char layer.

Enhancing cellular structure, mechanical properties, thermal stability and flame retardation of EVA/NR blend nanocomposite foams by silicon dioxide-based flame retardant

“…As given in Table 3, there was an increase in the LOI values of EVANRSiO 2 foams with increasing SiO 2 loading, indicating that the flame retardancy of foamed materials were improved. According to previous work, 19 it was proved that the addition of SiO 2 filler (20 phr) in the EVA/NR blend nanocomposite foams could improve the thermal resistance by creating an insulating silicon dioxide-containing char layer on their burning surfaces. When the SiO 2 loading was increased, the silicon dioxide-based char layer with higher thermal resistance was obtained.…”

“…The average domain size of the NR in the EVANRSiO 2 -0 was about 2.58 ± 1.16 µm, while the average size of the NR domain in the EVANRSiO 2 -20 and EVANRSiO 2 -40 was around 2.27 ± 0.86 and 1.29 ± 0.24 µm, respectively. Based on the sequence of filler addition (Figure 1) and the TEM images (Figure 2), it is suggested that a number of flame retardant SiO 2 transferred from the EVA toward the NR preferred phase due to its low affinity, 19 and some SiO 2 fillers were absorbed at the EVA/NR interfaces of EVANRSiO 2 -20 and EVANRSiO 2 -40 as indicated by arrows. In an immiscible polymer blend, the solid fillers confined at the interface of two polymers act as physical barrier to prevent the coalescence of the minor phase.…”

“…In the 60/40 EVA/NR blend nanocomposite foams, the EVA is mainly the phase that controls combustility and fire behavior. 19 Therefore, in this study, we employed two steps of mixing method which is based on pre-mixing EVA with SiO 2 , then melt blending of EVA/SiO 2 mixture with NR and additives as depicted in Figure 1. The preparation of 60/40 EVA/NR/SiO 2 blend nanocomposites were carried out by using Brabender plastograph model 815653 (Brabender GmbH & Co., Germany) at a temperature of 70°C and rotor speed of 60 rpm.…”

“…15-18 Recently, we studied the effect of SiO 2 incorporation in reference with various processing methods on structure, thermal stability and fire performance of the EVA/NR blend nanocomposite foams. 19 The incorporation of SiO 2 at 20 phr apparently increased the thermal and fire resistance of the foamed blend nanocomposites, and the level of increment in both properties depended on the incorporation routes of SiO 2 . Furthermore, the results showed that the enhanced fire performance is mainly driven by the formation of a heat barrier due to SiO 2 addition.…”

Synthesis of Novel Arginine-Based Flame Retardant and Its Application in Lyocell Fabric

“…Silicone-containing flame retardants form an amorphous silicon protective layer on the surface of the material after burning to isolate the transfer of air and oxygen. Amorphous silica dioxide (SiO 2 ), due to its high heat resistance, inert and non-toxic properties, is considered as a potential and safe flame retardant [21]. The combination of silicon with other flame retardants will play a synergistic flame-retardant effect.…”