| Rise straw (RS), a waste agriculture material, is the most important, and among the largest productions of renewable biomass resources in China. It can be directly burned as a fuel but that will be not only wasteful, but also can cause serious air pollution. Now, it can be used to produce a variety of clean fuels by biomass conversion technologies. As reproducible natural polymer carrier, it is also a perfect source of material. Its modified composite materials can be a substitute for conventional organic materials.This topic is envisaged to use polyethylene glycol as modification reagent to modify rice straw by the way of cellulose modified method. We use 4,4-diphenyl methane diisocyanate (MDI) of high activity as a bridging compound to introduce a certain amount of the polyoxyethylene soft segments to the straw fiber through chemical coupling reaction by ultrasonic-microwave radiation technology. It can effectively reduce the connection between macromolecules and change the physical and chemical structure of straw, making modified rice straw thermoplastic material.The influences of microwave power, ultrasonic power, reaction time, temperature and amount of PEG on the grafting percentage were investigated. So we obtained the optimum conditions of MDI modified straw and determined the best conditions of the ultrasonic-microwave synergistic straw graft PEG copolymerization respectively. Straw-MDI grafting process:straw and PEG mass ratio 1:2; microwave power 300 W, ultrasonic power 270 W, reaction temperature 60℃, reaction time 60 min; Straw-MDI-PEG grafting procedure: microwave power 300 W, ultrasonic power 360 W, temperature 60℃, time 70 min. We analyses the physical and chemical structure of grafted straw using FT-IR, NMR (1H-NMR, 13C-NMR) and XRD. Thermal analysis (TG and DSC) characterization results indicate that the thermal stability of the modified rice straw has been improved and the thermoplastic property has been gotten. In addition, in the DSC curve of the modified straw at about 120 ℃-180℃ appeared a broad melting peak. Above 180℃, the modified products can be compressed into sheets without any plasticizer. The modified straw powder mixed with elastic polyurethane (TPU) can be made into straw/TPU composite material with high strength and elastic modulus under certain temperature and pressure. |
