The Compression Property Of Phenolic Foam And Its Application In Foam Sandwich Composites

Phenolic foam, a kind of usual sandwich materials of foam sandwich composites, has excellent properties of lightweight, low heat conductivity, noise resistant, high specific strength as well as low price. It is widely used in the construction engineering field. However, the brittleness and poor mechanical property could bring about the damage of sandwich materials, as well as the failure of the whole composite materials, which limit its wide application. In order to solve this problem, we proposed to modify the phenolic foam by different methods, then prepared the 3D woven lattice fabric/phenolic foam sandwich composites.In this paper, we modified the phenolic foam using two methods, homogeneous modification and heterogeneous modification respectively. In the homogeneous modification, the hydroxyl-terminated polysiloxanes were blended with phenolic resin to prepare the phenolic foam. We focused on the effect of viscoelasticity and component compatibility of expandable phenolic resin mixture on cell structure and compressive property of phenolic foam. The experiment was carried out according to the following aspect. Firstly, the physical compatibility of hydroxyl-terminated polysiloxanes and phenolic resin in the mixture was studied from rheological property. The effects of the viscoelasticity on the nucleation, cell growth and stability in the foaming process were discussed. Secondly, the glass transition temperature and storage modulus of phenolic resin splines were analyzed by dynamic mechanical property(DMA). The purpose was to demonstrate the chemical compatibility of hydroxyl-terminated polysiloxanes with phenolic resins. Thirdly, the properties of the phenolic foam matrix were analyzed by fourier transform infrared spectroscopy(FT-IR) and thermogravimetric analysis(TGA), which indicated that the chemical bonds were formed between the hydroxyl-terminated polysiloxane and the phenolic resin during the curing process. And the chemical bond also built a stable interpenetrating network(IPN) structure in the phenolic resin. Fourthly, the cell structure and compressive property of phenolic foam was studied by scanning electron microscopy(SEM) and compression test respectively. And the compressive mechanism of phenolic foam modified by hydroxyl-terminated polysiloxane was discussed. The results showed that 15wt% hydroxyl-terminated polysiloxane could significantly improve the viscoelastic response of the resin mixture, and the chemical bonds between hydroxylterminated polysiloxane and phenolic resin could form an IPN structure. These properties all promoted the formation of small and uniform cell morphography, which brought about the improved compression performance.The heterogeneous modification were prepared by using graphene nanoplates as nucleating agent. We focused on the effect of surface energy and content of nucleating agent on cell structure and compressive property. The experiment was carried out according to the following aspect. Firstly, the surface energy of graphene and oxide graphene was measured by the powder contact angle measurement. Secondly, the interfacial property between graphene(oxide graphene) and resin was analyzed by dynamic rheological property. Thirdly, the mechanism of the effect of graphene(oxide graphene) on the compressive property of phenolic foam was investigated by characterization of cell structure and foam compression. The results showed that the higher surface energy of the oxide graphene could reduce the Gibbs free energy for nucleation, increase the nucleation rate, then reduce the cell size ultimately. While the more nucleating agent in the matrix would block the cell growth, which result in broken hole and more defect. Meanwhile, the graphene and the oxide graphene could transfer the load in the matrix, which promoted the improvement of the compression performance of phenolic foam.The oxide graphene was pre-dispersed in the hydroxyl-terminated polysiloxane, followed by blending with the phenolic resin for foaming. The results of dynamic rheological property, cell structure and compression property showed that a certain amount of oxide graphene and hydroxyl-terminated polysiloxane could play an active role in optimizing the cell structure and improving the compression property of phenolic foam. Based on the preparation process of the modified phenolic foam, the facesheets and composites columns were wetted by infusing the phenolic resin mixture, then they cured together to obtain the 3D woven lattice fabric/phenolic foam sandwich composite. The results showed that the 3D woven lattice fabric played a role in the physical reinforcement. It possesses the ability to transfer the load effectively which could improve the compression performance of the composite materials by making it possible to resist stress as an integral whole.