Cell morphology, bubbles migration, and flexural properties of non‐uniform epoxy foams using chemical foaming agent

Abstract

Epoxy foams with different densities and microstructures were prepared by changing the process parameters including the foaming temperature, chemical foaming agent (CFA) content and precuring extent. The microstructure of foams reveals a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher precuring extent. However, the cell size and distribution are not affected by the foaming temperature and CFA content without precuring process. In addition, the bubbles migration, which resulted in non-uniform cell density distribution, was promoted by increasing the foaming temperature and depressed by increasing the CFA content and precuring extent. The flexural properties of the non-uniform epoxy foams were also studied. Results showed that the flexural modulus was related to the cell morphology, while the flexural strength was affected by both the cell morphology and the position of the specimens during test. It was also found that the relative flexural modulus and strength exhibited a power-law dependence with respect to the relative density.

Study on Foaming Quality and Impact Property of Foamed Polypropylene Composites

“…The G” is a key index for material viscosity. Generally, the greater the loss modulus of the material, the better the viscosity of the material [24,25,26,27]. Moreover, Figure 5c further indicates that the viscosity of PP/TPR and PP/POE is higher than that of PP in the low-frequency region.…”

“…Meanwhile, for the PP/POE composites, the POE and PP matrix exhibit two continuous interlocking structures (Figure 2c). The well-dispersed second phase (TPR or POE) can supply large numbers of interfacial heterogeneous nucleation sites in the PP matrix, which can significantly increase the nucleation sites of cells and facilitate cell generation [22,24]. Moreover, the good dispersion of the elastomer may have a significant role in promoting the viscoelasticity and impact property of the PP composites.…”

Thermosetting polyester foams by infiltration in soluble preforms

“…Wang et al have prepared epoxy foams with different densities and microstructures by changing the process parameters such as foaming temperature, chemical foaming agent content, and pre-curing time. 2 They have discussed that bubble migration strongly affects the foam structure, resulting in non-uniform cell density distribution. As a valid alternative, Ren and Zhu have developed a novel approach to epoxy foaming by using CO 2 as latent blowing agent.…”

“…Apart from the case of solid state foaming, 10 all the other contributes refer to epoxy systems. [1][2][3][4][5][6][7][8][9] UP resins are very difficult to foam because of the low roomtemperature viscosity (lower than epoxies) and the fast polymerization kinetics. Recently, Zhang et al have evaluated urea-activated 4,4 0 -oxibis-(benzenesulfonyl hydrazide) OBSH as foaming agent to produce UP foams.…”

Cell characteristics of epoxy resin foamed by step temperature-rising process using supercritical carbon dioxide as blowing agent

“…8,9 In spite of the lower mechanical properties, polymer foams with open-cell structures are often served as coating. 10 Furthermore, the mechanical properties of foams, such as compression, tensile and flexural strength, vary with different cell sizes. Wang et al.…”