This paper describes the action mechanism of a waterborne epoxy resin (WEP) cross-linked inside wood and its influence on wood dimensional, thermal, and fungal stability. The WEP prepared by phase inversion was impregnated into wood under vacuum-pressure treatment, followed by in situ cross-linking upon heating to form a hydrophobic network inside wood porous structures. The weight gain and volume increment of the treated wood combined with the morphological observation indicated that the WEP components were able to penetrate into wood cell lumens as well as cell walls, cross-link, and finally fix stably inside them. The good fixation of the epoxy resin network formed in wood reduced the leaching into water. Results from Fourier transform infrared (FTIR) spectroscopy confirmed the reaction between the epoxy and wood. In addition, it was found that the dimensional stability, thermal stability, and decay resistance of wood were improved with the WEP modification. The scanning electron microscopy images clearly showed that brown-rot fungus caused more serious damage to the structure of wood than white-rot fungus.

Epoxy/polysufone (PSF) composites cured with 4,4'‐diaminodiphenyl sulfone (DDS) and 4,4'‐diaminodiphenyl methane (DDM) were fabricated, and the effect of dual curing reaction of diamines with epoxy on morphology, mechanical, and thermal performance was investigated. DSC results indicated that DDM was more reactive than DDS and the activation energy decreased with the rising of DDM content. Structures with small domain size at the early stage of phase separation were fixed by the fast epoxy‐DDM reaction. When the DDM content was elevated to a high level, large dual structures were changed to fine bicontinuous structures, which was favorable to improve the mechanical property. The mechanical performance of epoxy composites was enhanced and the maximum values were achieved when the DDM/DDS ratio was located at 75/25 (PSF/DDS0.25‐DDM0.75). The flexural and tensile strength relative to epoxy/DDM system were enhanced more than those relative to epoxy/DDS, while the increase in toughness was the opposite. TGA measurement showed that thermal stability of epoxy/PSF composites was improved because of the restricting effect of continuous PSF domains on thermal motion of epoxy. DMA analysis exhibited two relaxation peaks for PSF/DDS0.25‐DDM0.75, which could be attributed to the formation of phase separated morphology and epoxy network with different cross‐link density.

In this work, the epoxy systems modified with polysulfone (PSF) and cellulose nanofiber (CNF) cured at different temperatures are prepared to investigate the effect of CNF on curing reaction, morphology evolution, rheology, thermal, and mechanical performance of composites. The reaction rate is increased and the activation energy is decreased with CNF incorporation, implying an accelerating effect of CNF on the epoxy-amine reaction. The phase separation and gelation of the epoxy/PSF/CNF system start earlier compared with the binary system of epoxy/PSF. While it is displayed by rheology that both the system viscosity and relaxation time are elevated with CNF, presenting an inhibiting effect on phase evolution. Morphologies with smaller domain size are finally freezed by the epoxy gelation. The enhancement of impact performance for the epoxy/PSF/CNF composites is indicated by 40.2% increase in the impact strength, which is attributed to the finer phase-separated morphology, the uniformly distributed CNF within the polymer matrix and the good load transfer between phases. In addition, the thermal stability of composites is improved as the CNFs existed in the phase-separated polymer matrix can restrict the thermal motion of molecules during decomposition process.

Significant effect of cellulose nanofibers (CNFs) on cure‐induced phase separation in dynamically asymmetric system is reported. An epoxy/polysulfone blends with typical layered structure formation was chosen as the polymer matrix, and morphology evolution and rheological behavior of systems with different nano‐size fiber loadings upon curing reaction were investigated using optical microscopy and rheological measurement. CNF distributed uniformly in the polymer matrix and had good interaction with polymer chains. Curing reaction of epoxy was promoted by CNF, making the system gel and phase separate earlier. Meanwhile, system viscosity was increased with CNF addition, and the movement of polymer chains and component diffusion were constrained, as a result, the structure evolution process was slowed down. The CNF altered the final morphologies, resulting in refined structures with smaller characteristic length scales or even completely change the morphologies from the layered structures to a bicontinuous structure when the CNF concentration reached to a relatively high level. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1357–1366