Fabrication of a mechanically tough and strong SiO2@EPOSS modified novolac phenolic network by simultaneously improving its crosslinking inhomogeneity and crosslinking density

New Strategy to Construct Mechanically Strong and Tough Phenolic Networks by Considering the Effect of Curing Reactions and Physical States on the Cross-Linking Density and Cross-Linking Inhomogeneity

“…Novolac phenolic resin (NR) was purchased from Shandong Shengquan Chemical Co., Ltd. Hexamethylenetetramine (HMTA) and ethanol were obtained by Tianjin Chemical Reagent Company. GO and ES were prepared according to our previous study. , …”

“…Thermosetting resin with high mechanical strength and toughness is critical for its application in the aerospace, automotive, construction, chemical, and transportation industry. − However, the mechanical strength and toughness of thermosetting resin are often mutually exclusive. ,− Many natural materials like nacre, , bones, and spider silk fibers are equipped with outstanding fracture toughness, large breaking strain, and high tensile strength. Inspired by the relation between the microstructure and the unique mechanical combination involved in these natural materials, two-dimensional inorganic additives and their derivatives, such as boron nitride, graphene, MXene, and more, are introduced into thermosetting resin to construct mechanically strong and tough thermosetting nanocomposites. − However, it remains a challenge to generate thermosetting nanocomposites with high mechanical strength and toughness owing to the fact that the mechanical properties of thermosetting nanocomposites are essentially determined by their cross-linking networks. , Cross-linking density and cross-linking inhomogeneity are the two main characteristic parameters of cross-linking networks. , Generally speaking, increasing the cross-linking density will increase the mechanical strength and weaken the fracture toughness of thermosetting nanocomposites. − Besides, cross-linking networks of thermosetting resin inevitably display spatial inhomogeneity, which is composed of nodular regions with relatively higher cross-linking density surrounded by an interstitial phase with lower cross-linking density. − The cross-linking inhomogeneity can weaken the mechanical strength owing to the existence of microstructural defects, but it is beneficial for fracture toughness accompanying significant energy dissipation in the fracture process. , Thus, the key to achieving high mechanical strength and toughness for thermosetting nanocomposites is to accurately regulate cross-linking density and cross-linking inhomogeneity.…”

“…21,22 Cross-linking density and cross-linking inhomogeneity are the two main characteristic parameters of crosslinking networks. 23,24 Generally speaking, increasing the cross-linking density will increase the mechanical strength and weaken the fracture toughness of thermosetting nanocomposites. 25−29 Besides, cross-linking networks of thermosetting resin inevitably display spatial inhomogeneity, which is composed of nodular regions with relatively higher crosslinking density surrounded by an interstitial phase with lower cross-linking density.…”

GUS Aerogel Modified Phenolic Nanocomposites: Effects of Inhomogeneous Cross-Linking Characteristics and Interfacial Phase Properties on the Mechanical Behavior

“…Novolac phenolic resin ( m / z = 306–731 Da) was obtained from Shandong Shengquan Chemical Co., Ltd. Hexamethylenetetramine (HMTA), tetrahydrofuran (THF), and ethanol were supplied by Tianjin Chemical Reagent Company. 4,4′-Methyl diphenylene (MDI) and dibutyltin dilaurate (DBTDL) were obtained from Shanghai Aladdin Bio-Chem Technology Co., Ltd. Poly­(oxycarbonyloxy-1,6-hexanediyl) (PCDL) was purchased from Dongguan Hongsui Industrial Investment Co., Ltd. GO and ES were prepared according to our previous study. , …”

“…The conflict between mechanical strength and toughness of thermosetting polymers is a vital deficiency for their application even though massive efforts have been made by introducing various nanoparticles into thermosetting polymers. − Indeed, this deficiency is derived from difficulty in balancing the conflict effect of cross-linking density and cross-linking inhomogeneity on the mechanical strength and toughness of thermosetting polymer nanocomposites (PNCs) . Generally, thermosetting PNCs with higher cross-linking density could contribute to a higher mechanical strength but at the expense of loss of toughness. − Moreover, cross-linking inhomogeneity of thermosetting PNCs can improve the toughness but sacrifice mechanical strength. − …”