| Natural fiber composite is an environmental friendly and “green†composite material. Sincethe superior advantages, like low density, good sound insulation, high specific strength, recyclable,low price and good human compatibility, the natural fiber composites are widely used inautomobile industry, construction industry and daily consumer goods.Since natural fiber own some advantages, such as wide resources, low price, recyclable andbiodegradable properties. Natural fibers are widely used in natural fiber composite. Ramie fiber isa normal natural fiber in textile industry. Since ramie fiber is very tough and owns good propertiesof high specific strength, low extensibility, antifungal and anti-worn-eaten, ramie fiber is an idealcandidate in natural fiber composite as reinforced material.The definition of thermoplastic resin is the resin which possesses recyclable property ofthermal softening and cooling hardening. This property makes it receive tremendous attentionsfrom scientists, due to recyclable application. Polypropylene is the lightest resin in generalpurpose resin. Polypropylene owns tasteless, non-toxic and light weight. In addition,polypropylene is a superior thermoplastic resin with good mechanic property, chemical stability,good thermo-, acid-and base-resistance and hydrophobicity, which make it a superior candidatein natural fiber composite as matrix.In composite, the properties of composite not only depend on the property of reinforcedmaterial and matrix, also depend on the interfacial property between reinforced material andmatrix. However, the superior wettability of ramie fiber makes undesirable interfacial propertybetween ramie fiber and polypropylene, and swelling of ramie fiber results in failure of naturalfiber composite.Plasma treatment is a novel and effective surface treatment technology. Compared to other vacuum-assisted plasma technology, atmospheric pressure plasma treatment possesses continuousworking, low cost, short treatment time and high flexibility. In addition, the most importantadvantage of atmospheric pressure plasma is that the liquid contained material can be treatedunder this plasma technology, which broadens the applied range of plasma treatment. Since thegood wettability of natural fibers, wet processing in textile industry and high humidity in textileworkshop, the textile product in assembly line owns high moisture content. Atmospheric pressureplasma treatment makes it possible that plasma can be applied in textile industry.Atmospheric pressure plasma is an effective way to modify ramie fiber surface, withimproving roughness and polarity of ramie fiber surface. However, polypropylene is thermoplasticresin and owns hydrophobicity, the improvement of wettability of ramie fiber can lead to thedecrease of interfacial properties between ramie fiber and polypropylene. In order to enhance theinterfacial property between fiber and resin, a new surface modification method need to bedesigned to improve the roughness and reduce the wettability of ramie fiber surface, which canimprove the interfacial property between fiber and resin with enhancing the mechanical propertyof composite. In this project, a novel surface modification treatment combined with alcoholpretreatment and atmospheric pressure plasma treatment is applied to improve the hydrophobicityof ramie fiber surface. Then, the micro ramie-polypropylene composite is fabricated throughmelting, which are tested by micro-drop method to achieve interfacial shear strength (IFSS) tocharacterize the interfacial property between ramie fiber and polypropylene. Finally, othercharacterizations are applied to characterize the property of ramie fiber surface.First, the ramie fibers are pretreated with alcohol. Ethanol, isopropanol and n-butanol areapplied in this project. After that, the pretreated ramie fibers are treated through atmosphericpressure plasma. The radio frequency and discharge power are13.56MHz and40W. The workinggas is pure helium gas (99.99%) which is introduced at a flow rate of20L/min, the working distantis around2mm and working time is in a range of8-24s. Then the scanning electron microscope(SEM) is applied to depict the morphology of ramie fiber surface, the X-ray photoelectronspectroscopy (XPS) is used to show the chemical composition on ramie fiber surface, the staticcontact angle is tested to demonstrate the wettability of ramie fiber surface. The micro compositeare manufactured to be tested to obtain interfacial shear strength (IFSS) which characterizes theinterfacial property between ramie fiber and polypropylene.The scanning electron microscopy (SEM) images show that the surface of ramie fiberbecome rough after surface modification treatment, which can enhance the connections betweenramie fiber and polypropylene; however, with working time increasing, larger amount of cracksare obtained which low the mechanical properties of ramie fiber, leading to the decrease ofmechanical properties of composite. X-ray photoelectron spectroscopy data demonstrate that the content of C-C bond increases after treatment. The results of static contact angles show that thestatic contact angle on modified ramie fiber surface increase which is close to hydrophobicity.After alcohol pretreatment and atmospheric pressure plasma treatment, the “hydrophobic†surfaceof ramie fiber improve the interfacial property between ramie fiber and polypropylene and reducethe water absorption to decrease the damage of interfacial shear strength (IFSS) between ramiefiber and polypropylene. In conclusion, interfacial shear strength (IFSS) between ramie fiber andpolypropylene increase after pretreatment of alcohol and atmospheric pressure plasma treatment;however, with the working time of atmospheric pressure plasma treatment increasing, thereduction of interfacial shear strength (IFSS) is shown. Compared to other alcohol pretreatment,the surface of ramie fibers pretreated by isopropanol, own highest roughness and least hydrophilicgroups, which make it have highest interfacial shear strength. Comparing with wet condition, thesurface of ramie fiber, which is treated by ethanol pretreatment conjunction with atmosphericpressure plasma treatment under dry condition, owns higher roughness and more hydrophobicgroups to achieve higher interfacial shear strength. |
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