Improved mechanical, thermal and flame resistant properties of flexible isocyanate-based polyimide foams by graphite incorporation

Abstract

In order to improve the mechanical, thermal and flame-resistant properties of polyimide foams (PIFs), in the present study, flexible polyimide (PI)/graphite composite foams were prepared with dianhydride and isocyanate as the starting materials and graphite as the filler. The experimental results showed that most cells of PIFs possessed an open cell structure, and the open cell content decreased by graphite incorporation. While with the increase in graphite, the distribution of cellular size became uneven and the size distribution became broad. The compressive strength increased initially and then decreased and reached the maximum value of 26.4 kPa when the graphite content was 1.98 wt%, but all the composite foams exhibited higher strength than the neat PIF. In addition, the limiting oxygen index increased from 31% to 34.8% with the increase in graphite from 0 wt% to 3.25 wt%. The peak heat release rate of composite foams was 2.3% to 24.7% lower than the neat PIF and reached a minimum value of 42.36 kW m−2 with the graphite content of 1.98 wt%. Considering the above analysis, it is feasible to improve mechanical properties, thermal stability and flame-resistant properties of PIFs by graphite addition.

Graphite effect on the mechanical and fire‐retardant performance of low‐density polyethylene and ethylene‐vinyl‐acetate foam composites

“…All samples showed two decomposition stages. The first step presents the maximum rate of weight loss at 354°C of EVA 0 foaming and decreased slightly because of the graphite addition, as the graphite increases, the thermal conductivity of EVA at low temperature 25 reaching a value of 351°C for the foaming of EVA 12 , which is observed with the derivative of weight loss (Figure 1(b)). The second step of weight loss has the same effect described, having the maximum speed of weight loss at 461°C for EVA 0 and 456°C for EVA 12 foam.…”

“…Thus, the fire retardancy of foams can be improved by the carbonaceous char layer formation during the combustion process; where the char acts as a heat insulator and a mass transport barrier, limiting the heat transfer from combustion and the oxygen access to the polymer 24 . In addition, the high thermal conductivity of graphite decreases with increasing temperature, becoming a thermal insulator at high temperatures 25 …”

“…Several reports about incorporating graphite have explained the mechanical and fire‐retardant properties and showed that graphite is a very efficient fire retardant additive. For example, Tian et al 25 investigated the effect of graphite incorporation (0.6, 1.3, 1.9, 2.6 and 3.2 wt%) on properties of flexible isocyanate‐based polyimide foams. The optimal flammability was obtained with graphite at 1.9 wt%, the reduction in the pHRR was almost 25% compared to the neat polymer and the compressive strength achieving a maximum value of 26 KPa when the filler content was 1.9 wt%, finally, they concluded that the graphite addition forms a layer during the burning of the foam surface.…”

Polyethylene glycol: An effective agent for isocyanate-based polyimide foams with enhanced foaming behavior and flexibility

“…Polyimide foam is one of the foams with excellent comprehensive properties of thermal stability, chemical stability, radiation resistance, flame retardance, and electrical insulation, [1][2][3][4][5][6] and hence, is widely used in aerospace, shipbuilding, high-speed railway, and nuclear power in the field of noise reduction and heat insulation areas. [7][8][9][10][11] Different methods of producing polyimide foams, such as using polyimide precursor and powders, hollow polyimide microspheres, dianhydride and isocyanate, and so on, have been reported in previous works. [12][13][14][15][16][17] The method using dianhydride and isocyanate was considered to be a simple one to fabricate polyimide foams, in which the preparation method is similar to that of polyurethane foams being prepared by mixing the polyol and isocyanate.…”

One‐component photoinitiator based on benzophenone and sesamol

“…All the results suggest that BPBDO is an effective PI for the free radical polymerization of acrylic basic monomers. In contrast to a typical dual‐component PI, BPBDO does not require an additional amine coinitiator for the initiation and is biocompatible and applicable in nonamine resin systems …”