| Epoxy resin(EP) is widely used in many fields such as coatings, adhesives, composites because of its excellent cohesiveness, dimensional stability and resistance to chemical corrosion, etc. However, the highly-crosslinked nature of cured resins normally produces an undesirable characteristic: cured epoxies are brittle and show poor resistance to crack growth, which limits its applicaitons. Therefore, epoxy resins must be modified in order to improve their performances.Nanocellulose(CNF) has been attracting particular interest in both academic and industrial fields due to its advantages, renewable nature and outstanding mechanical properties. Therefore, in the first part of this dissertation, the nanocellulose was used to modify the epoxy resin and the effects of CNF on mechanical properties of two kinds of epoxy resins were studied. Mechanical properties involving tensile and impact strength were investigated by the tensile and impact test. The results showed that when the content of CNF is 0.2%, the impact strength reaches the maximum values, 29.94 k J/m2, increasing by 60.96% compared with the impact strength of pure epoxy resin. However, the tensile strength decreased with the CNF addition.In order to improve the mechanical properties of pure EP system further, the thermoplastic polymer(polysulfone), with high glass transition temperature and mechanical properties, was added into the above CNF/EP system. The CNF/polysulfone modified epoxy resin composites were prepared by a combination method of solvent exchange and melt mixing. Mechanical properties involving tensile and impact strength, and the morphological structures of the fractured surfaces for the cured samples were investigated by the tensile and impact test, and the scanning electron microscopy(SEM), respectively. The results showed that for the EP/polysulfone binary system, the impact strength was increased while the tensile strength slightly decreased with the 10wt% polysulfone loading. However, for the EP/polysulfone/CNF ternary system, both the tensile and impact strength were enhanced with the CNF and polysulfone addition. Compared with the pure epoxy resin, the tensile and impact strength were increased by 5% and 39.8%, respectively, when the CNF loading was 0.3wt%. Thermal stability of the composites was also studied using thermogravimetric analysis(TGA). It was indicated that the thermal stability of the epoxy system can be improved by the CNF and PSF addition.Dynamic mechanical property of the composites was also studied by dynamic thermomechanical analysis(DMA). The results indicate that the glass transition temperature(Tg) of the EP/PSF composite system was enhanced with the CNF addition.On the other hand, the low glass transition temperature and mechanical properties of thermoplastic resin such as poly caprolactone(PCL), was also used to modify the epoxy resin to compare with the influence of the PSF. The epoxy resin/poly(ε-caprolactone)/cellulose nanofiber composite was prepared by the method of solvent exchange and melt mixing, during which the cellulose nanofiber(CNF) was uniformly dispersed in the epoxy firstly and then poly(ε-caprolactone)(PCL) was added. The effect of CNF addition on the morphological structure and mechanical property was investigated by SEM and by the tensile and impact test, respectively. The results show that the effect of CNF addition on the morphology and mechanical property is not obvious for the sample with low PCL content, while for the sample with high PCL content, the effect is remarkable. Dual-phase structure is observed for all the samples, and the domain size of both phases decreases with the increase of the CNF contents. Moreover, it is found that both the toughness and strength of the blends are enhanced by the CNF addition. Compared with the system without the CNF addition, the impact and tensile strength of the composites are increased by 91% and 24%, respectively. |
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