•A novel couple agent was synthesized, and used to link phenolic and polysiloxane.•Co-continuous structure in tens of nanometers was first obtained in this system.•Enhanced oxidation resistance and higher residual weight was achieved in hybrid.Co-continuous structure with tens of nanometers was obtained in polysiloxane modified phenolic resin by using of a novel couple agent. The couple agent was synthesized through addition reaction between resorcinol and isocyanatopropyltrimethoxysilane; then, it was introduced into the mixture of silane monomers, phenol and formaldehyde solution, in situ coupled the silane and phenolic during the polymerization reaction, and hybrid resin was obtained. Structure of the couple agent and hybrid resin was characterized by FTIR and NMR measurements. Through varying the amount of the couple agent, different morphology was obtained. The co-continuous structure of the cured hybrid with relatively higher amount of couple agent was confirmed by TEM and AFM observation, with the periodic length being about 50–65 nm. The oxidation resistance of the hybrid resin was greatly enhanced, the residual weight after oxidation at 1000 °C was much higher than that of pure phenolic resin.Download high-res image (287KB)Download full-size image

Carbon nanotube/carbon (CNT/C) composites derived from entangled CNT network and different precursors, phenolic or pitch, were fabricated in this work. Multi-step mechanical stretching, repeated polymer infiltration pyrolysis and graphitization were subsequently performed for the preparation. CNT alignment was accomplished in CNT/C derived from both phenolic and pitch precursors, while aligned carbon matrix could be only found in CNT/pitch derived CNT/C composites. Such phenomenon provided direct evidence for the promoting effect of CNT alignment on the graphitization of the carbon matrix. Mechanisms for the stretching induced alignment and the formation of aligned carbon matrix were proposed and discussed. The planar configuration of pitch molecules and its Pi–Pi stacking with CNT walls were considered beneficial for the stress induced graphitization, thus the carbon matrix could be aligned along the CNT walls. Based on the tensile and electrical conductivity measurements, we believed that CNT alignment dominated both mechanical and conducting performances of cured (stabilized) and carbonized CNT/C composites; while the alignment of carbon matrix played the decisive role in graphitized CNT/C. In addition, the carbonized composites could exhibit tensile strength as high as 1.2 GPa, while the electrical conductivity of graphitized samples was in the scale of 105 S/m.

Crystallization behaviors and kinetics of iPP in an in-situ prepared isotactic polypropylene/graphene (iPP/G) composites were studied in this paper. In samples used in this study, the graphene fillers were well dispersed, and the interfacial adhesion exhibited enhanced features between graphene and iPP components. The thermal stability of the composites was improved by about 100 °C compared to the pristine iPP. It was found that the crystallization morphology, crystallization rate and kinetics of the iPP/G composites were significantly influenced by the presence of graphene. The nucleation and epitaxial growth of iPP on the graphene surface were observed and studied in detail. It was observed that the nucleation of iPP favored to occur at the wrinkles and edges due to the good match of the lattice parameters and the weak spatial hindrance compared to the smooth surface. Numerous nuclei epitaxially formed and the size of the crystals was very small. The schematic diagram was also proposed for the nucleation and growth process of iPP on the graphene surface in the iPP/G composites. Meanwhile, the overall crystallization kinetics and crystals growth were analyzed through Avrami equation. The obtained Avrami index n decreased with the graphene loadings and was close to 2 for the iPP/G composites, which implied that the growth of iPP in the composites was in two-dimension. And this was caused by the structure of graphene and the spatial confinement effect of graphene platelets in the iPP/G composites.

The correlation between rheological behavior and time evolution of the phase separation patterns was investigated in the epoxy/thermoplastic blends. Before and during the induction period of phase separation, the storage and loss modulus initially increased with epoxy curing reaction and the concentration fluctuation. At the late stage of phase separation, the modulus values also increased and showed a sharp enhancement around the epoxy gel point. However, the time evolution during the reaction induced phase separation process differed a lot at various thermoplastic (TP) concentrations. At the low TP concentrations, the rheological parameters decreased with the coarsening of sea-island structure. At the high TP concentrations, the TP-rich continuous structures initially formed and maintained until the end, resulting in a continuous increase for the rheological characters. At middle TP concentrations, formation and evolution of the three-layered structure displayed a complicated rheological behavior. It was found that the storage modulus quickly increased, reached a vertex, then rapidly decreased, reached a minimum, and increased again afterwards. Although the rheological behaviors were almost phenomenologically similar as that in the normal dynamically symmetric system, driving force for the variation was fundamentally different. Especially for the case of middle TP concentrations, the behavior of the holistic volume shrinking of the slow dynamic TP-rich network and the flowing out of the fast dynamic epoxy-rich phase from the network during this period, as radically transformed the nature of the matrix from an elastic network to a macro-phase separated layer structure and caused the dramatic change of the rheological behaviors.

Morphological structure development of the in-situ polymerized isotactic polypropylene/graphene nanocomposites was investigated during the annealing process. The material was prepared via an in-situ slurry polymerization method with graphene-supported Ziegler–Natta catalyst. An interpenetrating network was observed at a relatively low graphene concentration after the sample was annealed for a long period (one to several hours). Alternative Conductivity impedance spectroscopic measurements showed a remarkable electrical conductivity increase of several orders of magnitude after the network was formed. At very low graphene content, although macroscopic network cannot be formed, the electrical conductivity can be enhanced through annealing as well. It implied that the rearrangement of the clusters or aggregates was necessary and such rearrangement favored the network formation. The network forming process was investigated through optical and electron microscopy methods and discussed based on the viscoelastic phase separation model. The effect of network on the crystallization behaviors was also investigated. It showed that the overall crystallization was improved by the presence of graphene platelets, but depressed after the network was formed, which was due to the spatial confinement and the decrease of total surface area available for heterogeneous nucleation.

The reaction induced phase separation behavior was investigated in various epoxy/thermoplastic (TP) blends. Several morphological structures, including the sea-island, dual morphological (epoxy-rich particles may disperse in the TP-rich domains, while TP-rich particles can also have some dispersions in the epoxy-rich phase) or three-layered (TP-rich continuous domains mainly located in the middle part of the sample while outer layers are mostly composed of epoxy-rich matrix) and nodular structure, were observed with the increase of the TP concentrations. In the middle TP concentration ranges, when the TP with low glass transition temperature (Tg) was used, dual morphological structures were formed. While for the epoxy/TP blends with high Tg thermoplastics, three-layered structures were observed. High Tg and the large molecular weight of the TP was considered to cause the dynamic asymmetry, which dominated the phase separation mechanism and formed such an unusual structure. Through the in-situ investigation on time evolution of phase separation process, ubiquitous nature of this formation mechanism of the three-layered structure were discussed, which may have some important implications on the applications of the epoxy/TP blends.

A thermoplastic polysulfone was used to blend with epoxy resin, and both the curing reaction and phase separation of the epoxy/polysulfone blend were investigated. Polysulfone did not alter the mechanism of curing reaction; however, it did depress the reaction rate. The details of the dynamically asymmetric phase separation, which was caused by the large differences in viscoelastic properties between epoxy and polysulfone component, were observed and studied. During the structure evolution, volume-shrinking behavior of the dynamically slow polysulfone component always existed even at fairly low (but still above the entanglement concentration) concentrations. More interestingly, when the curing temperature was higher than the glass transition temperature of polysulfone, volume shrinking with the consequence of layered structure formation was also observed as long as the viscoelastic asymmetry was maintained. These results indicated the generality of the mechanism of the dynamically asymmetric phase separation in this type of reactive system. Also, the influence of curing temperature was studied, and it was found that phase separation was promoted more than the curing reaction as the temperature was increased.

In an epoxy/polysulfone blend, the reaction-induced phase separation behavior and the final morphology were investigated. Three distinct morphological structures were obtained. Sea-island and nodular structures were observed at lower and higher polysulfone contents, respectively. A three-layered structure was obtained in the middle polysulfone concentration range. In order to understand the formation of three-layered structure, phase separation process was studied using time-resolved light scattering, phase-contrast optical microscope and scanning electron microscope. Bicontinuous structure formed uniformly in the whole sample at the beginning of phase separation. After the phase structure grew for a certain time, large domains formed and developed. Then, the large epoxy-rich domains gradually flew to the outer space of the sample film. This process assisted the formation of the three-layered structure. The mechanism of the formation of the three-layered structure was discussed based on the different viscoelastic properties of the components.