| Although the glass fiber composites is widely used for its advantages such as excellent mechanical properties and low cost, they have caused some environmental problems. It consumes a lot of energy in the production process of glass fiber, and will bring a heavy burden for the ecological environment after it abandoned. In the world of advocating low-carbon environmental protection, the development of environment-friendly natural fiber reinforced composites have become an inevitable trend. Due to the poor adhesion properties between natural fiber and resin, the paper studied the interfacial properties of ramie reinforced polypropylene composites. Ramie fibers were treated with ethanol followed by atmospheric plasma treatment to modify the surface properties, thereby improving the interfacial properties of the composites. On this basis, the water aging properties of the composites was studied, and a model was built to discuss the failure mechanism of the interface. The main work includes:(1) Ramie fibers were treated with plasma under different powers. Ramie fiber were treated with 120 W, 140 W, 160 W plasma after ethanol pretreatment. Single fiber strength and water contact angle were measured and compared. The data showed that there was no significant difference between the treated group and untreated group in fiber strength. While the surfaces of the ramie fibers changed from hydrophilic to hydrophobic after the treatment. Changes in surface morphology was observed by environmental scanning electron microscopy(ESEM), it was apparent that the surface of the fiber has more pit and debris after plasma treatment. And the greater the processing power, the rougher the surface. X-ray photoelectron spectroscopy(XPS) was used to test the change of surface chemical elements and chemical bonds. The O/C bond content decreased significantly, and C/C bond content increased significantly, C/O bond and C=O bond reduced after the plasma treatment.(2) Ramie fibers were treated with plasma under different powers, and then made into ramie fiber/PP(polypropylene) micro composite. The draw rate of the micro-drop was optimized, data showed that the tensile strength values was relatively stable when the tensile rate was 5 mm/min. scanning electron microscopy(SEM) was used to observe the surface morphology after pullout test of the micro-drop. Interfacial shear strength(IFSS) value was measured to characterize the mechanical properties of the composites. The results showed that, the IFSS increased by 30% under the treatment power of 120 W, while the IFSS has no significant improvement when the treatment power is 140 W and 160 W. The SEM analysis also showed that the debonding area of 120 W treated group had residual debris, while the other groups were relatively smooth, which matched well with IFSS analysis.(3) According to the experimental results above, 120 W plasma was chosen to treat ramie fibers. And we compared the water aging properties of 120 W plasma treated group and untreated group. The IFSS values of both group decreased dramatically after 15 min’s aging. The longer the more obvious the IFSS declined, and the value stabilized after a certain length of time, which means the interface was broken gradually and the ramie fiber was degradating in the process.(4) We established a model based on the water aging test, and derive the moisture regain to break the interface between ramie and PP. According to the aging data, it was calculated that when the moisture regain of ramie reach 65.65%, the interface will be destroyed.In conclusion, ethanol pretreatment followed by plasma treatment can effectively improve the interfacial properties of ramie/ PP composites. Compared with the control group, the IFSS value increased by 30% when the treatment power is 120 W, and the SEM analysis matched well with the result. In addition, the IFSS values decreased dramatically after 15 min’s aging, and the value stabilized after a certain length of time. Substitute the aging data into the interface broken model, it can be deduced that when the fiber absorption reaches 65.53%, the interface will be destroyed. And this paper provides new thoughts and methods for the interfacial research of natural fiber reinforced composites. |
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