Hygrothermal Aging Properties And Aging Mechanisms Of Plant Fiber Reinforced Polymers Modified By Carbon Nanofillers

Plant fiber reinforced polymers(PFRP)have received more and more attention because of their excellent mechanics,environmental friendly,and low cost.However,the long-term service ability of PFRP in the hygrothermal environment will be seriously degraded due to the structure and composition of plant fibers,which greatly limits the application of PFRP in civil engineering.It is significant to improve the hygrothermal durability of PFRP for expanding its applications in civil engineering.Carbon nanoparticles(carbon nanofibers CNFs,carbon nanotubes CNTs)have been widely used in resin-based composites due to their excellent properties.Lots of studies have proved that carbon nanoparticles have obvious effect on the improvement in properties of FRP composites.In this study,considering the composition characteristics of composite,two modified methods were conducted.First,the resin matrix was modified by filled CNFs.Second,the fiber was modified by grafting CNTs.The modified RFRP are tested for water absorption,mechanical properties and thermodynamic properties.Scanning electron microscopy(SEM),Fourier infrared spectroscopy(FTIR)and were used to characterize the changes of composites.Moreover,the mechanisms of the two modification methods was thoroughly explored.The main conclusions are as follows:(1)Epoxy resin filled with different content of carbon nanofibers(CNFs)kept into distilled water at 23oC,40oC and 60oC for a maximum duration of 180 days.Water absorption test,tensile tests,scanning electron microscopy(SEM)observation,dynamic mechanical analysis(DMA),and Fourier transform infrared spectroscopy(FTIR)analysis were performed to evaluate the effect of hygrothermal aging on the water absorption,tensile and thermodynamic properties of neat epoxy resin and CNFs/epoxy composites.The test results indicated that barrier properties of CNFs in the process of water absorption were characterized by a decrease in the maximum water absorption.The results of the tensile test showed that the long-term tensile properties of CNFs/epoxy composites were better than that of neat epoxy resin.The improvement in glass transition temperature T_g and storage modulus before and after aging showed that the addition of CNFs limited the movement of molecular chains and increased the second cross-link density of epoxy resin.FTIR indicated that the number of-OH functional groups of CNFs/epoxy composites decreased compared with neat epoxy resin,which reveals that CNFs inhibit the hydrolysis of epoxy resin and water immersion.This study demonstrated that CNFs have a positive effect on the long-term hygrothermal durability of epoxy-based composites.(2)The effect of carbon nanofibers(CNFs)addition on hygrothermal aging behaviors of flax fiber reinforced polymer(FFRP)laminates subjected to distilled water immersion was investigated.CNFs/FFRP laminates were fabricated with different content of CNFs(0,0.25wt%,0.5 wt%,1.0 wt%,and 2.0 wt%)by wet lay-up method.Water absorption as well as tensile and thermodynamic properties were measured at specific time intervals.The water absorption of CNFs/FFRP laminates was decreased significantly compared with that of FFRP laminates.A good barrier of CNFs lengthened the diffusion path of water in the epoxy matrix.The long-term tensile strength and elastic modulus of FFRP laminates were improved after the addition of CNFs.Scanning electron microscopy(SEM)observation showed that CNFs played an obvious bridging effect on interior the laminates.In addition,CNFs have also a positive influence on the thermodynamic properties of FFRP laminates due to the increase of the secondary cross-linking network of the epoxy matrix.The whole aging process of FFRP and CNFs/FFRP laminates related to the changes on bands and functional groups were characterized by Fourier transform infrared spectroscopy(FTIR)spectra,which confirmed that the aging degree of CNFs/FFRP laminates was slow down due to the presence of CNFs.(3)The effect of CNTs grafted on ramie fiber to hygrothermal durability of ramie fiber reinforced polymer(RFRP)was studied.Six control groups of RFRP were set up in the test,which were no untreated,and treated with alkali solution,alkali solution and silane coupling agent,and grafted by CNTs.The CNTs concentration grafted on fiber surface was 2 g/m~2,4g/m~2 and 6 g/m~2,respectively.The water absorption,tensile and thermodynamic properties of all RFRP were tested.The test results showed that the RFRP grafted with CNTs has better water absorption,tensile and thermodynamic properties than those treated with other methods.SEM and FTIR were also assisted during test.It can be concluded that CNTs not only strengthen the fiber,delay the aging of the fiber,but also improve the adhesion of the fiber-resin interface to resist the hygrothermal aging.