Effect of atmospheric plasma treatment on mechanical properties of jute fiber and interface adhesion between fiber and resin

201 Journal of Chemistry, Vol. 45 (5A), P. 201 - 206, 2007 EFFECT OF ATMOSPHERIC PLASMA TREATMENT ON MECHANICAL PROPERTIES OF JUTE FIBER AND INTERFACE ADHESION BETWEEN FIBER AND RESIN Received 16 August 2007 Ta Thi Phuong Hoa, Nguyen Thi Thanh Binh, Nguyen Chau Giang Polymer Center, Hanoi University of Technology Summary The surface treatment by physical method of jute fiber using air plasma was investigated. Fiber was treated by the atmospheric plasma with various conditions of power 50W and different treatment times (from 1 min to 7 min). After treatment, the characteristics of fiber changed remarkably and fiber surface observed by SEM analyze showed a better morphology for adhesion. The result showed that tensile strength and Young’s modulus of jute fiber were slightly improved, however there was a remarkable improvement interface adhesion between fibers and polypropylene (PP) resin. Especially, when combine physical method and chemical method, the interfacial adhesion and mechanical properties of jute fibers were significantly improved. I - Introduction Natural fiber reinforced composites have recently increased concerns of scientists and technologists because of many advantages. Natural fibers are abundant with various species, can be recyclable and biodegradable and therefore are very potential in manufacturing environmental friendly polymer composite. It is however important to improve interface adhesion properties between natural fiber and resin. Among several fiber treatment methods, plasma treatment is a new physical method which is regarded as a dry surface processing method for adhesion improvement without waste liquid. Moreover, plasma treatment can modify surface without obstructing basic properties of fiber. In this research, atmospheric plasma treatment has been applied to improve adhesion properties between jute fiber and polypropylen (PP) resin. II - Experimental 1. Material - Jute fiber: silk jute and roll of jute supplied from Hanoi Jute Company. - MAPP - Compatibilizer polypropylene -g- maleic anhydride with 0.8% of maleic anhydride was synthesised at Polymer Center, Hanoi University of Technology, Vietnam. - Technical potassium hydroxide was used for alkali treatment. - Acetic acid from China with density and concentration of 1.05 g/ml and  99.3% respectively. 2. Fiber preparation Raw jute fiber obtained locally was scoured by treating with a 1% solution of a detergent at 70oC for 1 h to remove weaving size (potato starch and waxes), then by washing in distilled water and drying. 202 3. Alkali treatment Jute fibers were soaked in beakers containing potassium hydroxide concentration in 0.5N for 2h, 4h, 6h and 8h. The fibers were then washed with dilute acetic acid to neutralize excess of sodium hydroxide and thoroughly rinsed with distilled water and dried. 4. Plasma treatment The plasma experiment system used for this study is shown in figure 1. Figure 1: Experimental system creates plasma Two Plane-parallel metal electrodes are separated by an atmospheric environment in which silent discharge environment at the gap. The electrodes are connected to a power supply with high frequency and power of 12 KHz and 50W. Fiber was treated under conditions as showed in table 1. Table 1: Plasma treatment condition Gas Air Pressure and temperature Atmospheric pressure, room temperature Intensity and frequency of power 50W and 12 KHz Treatment time 1 to 7 min 5. Morphology study The morphology was observed by using SEM. 6. Tensile test of jute fiber The average diameters of fiber were measured in microscope which magnifying index comes to 40 times. Figure 2 shows the dimensions of the fiber specimen. One of the jute fibers was glued on the sheet of paper working as an attachment for the specimen. Then, the gage positions of the paper were cut after checking it on LLOYD (5000 N) equipment at a crosshead speed of 2 mm/min. 7. Microdroplet test Single fiber composite (SFC) of jute fiber and PP was prepared, then the interfacial shear strength (IFSS) was measured by microdroplet Power supply 12-20 KHz 0-200 W Enclosure Electrode Gas exhaust Vacuum pump Dielectric 203 test on LLOYD (5000 N) at a crosshead speed of 2 mm/min. Figure 2: Tensile test of fiber Figure 3: Microdroplet test III - Results and Discussion 1. Effect of alkali treatment on the tensile properties of Jute fiber Table 2 presents tensile properties of jute fiber after alkali treatment with various conditions. Table 2: Tensile properties of untreated and alkali treated Jute fiber Alkali treatment conditions Tensile strength, MPa Young’s Modulus, GPa Untreated 198 21.920 KOH 0.5 N, 2h 239.15 23.290 KOH 0.5 N, 4h 274.95 24.471 KOH 0.5 N, 6h 287.6 28.432 Jute fiber KOH 0.5 N, 8h 241.95 22.292 The results show the change of tensile properties when changing the treatment condition. An explanation is that rupture of alkali - sensitive bonds existing between the different components of the fiber as a result partial removal of the hemicelluloses, lignin and Adhesive agent Jute fiber Paper tab will be cut 5 cm 0.7 cm 2 cm 2 cm Jute fiber PP Adhesive agent Blade Paper tab will be cut 204 other substances. They have amorphous structure, inhomogeneous property and can respond to low stress. Treated fiber becomes more homogeneous and capable of rearranging themselves along the direction of tensile deformation. Consequently, tensile properties of treated fiber increase. Especially, in case the alkali treatment of 0.5 N in potassium concentration and 6 hours in treatment time, the average value of tensile strength and Young’s modulus increased 45.25% and 29.71%. 2. Effect of atmospheric plasma treatment on the tensile properties of jute fiber Changes of tensile properties of jute fiber after atmospheric plasma treatment are shown in table 3. Table 3: Tensile properties of untreated and atmospheric plasma treated jute fiber Kind of fiber Atmospheric plasma treatment condition Tensile strength, MPa Young’s Modulus, GPa 1 min 227.92 22.436 3 min 254.60 23.527 Untreated 5 min 265.39 25.145 1 min 308.90 29.774 5 min 335.26 33.720 Alkali treated KOH 0.5N,6h 7 min 313.30 27.315 In case the atmospheric plasma treatment, highest tensile properties achieved at treatment time of 5 min. That is suitable treatment condition. Especially, the combination of alkali treatment and atmospheric plasma treatment leads to increases of 69.32 % and 53.83 % in the average value of tensile strength and Young’s modulus. Effect of atmospheric plasma treatment on the tensile properties of fiber is however slight. It may be that atmospheric plasma treatment strafed on fiber surface caused a partial removal of lignin and hemicelluloses. As known that plasma treatment can modify only fiber surface without obstructing basic properties of fiber. 3. Effect of atmospheric plasma treatment on interfacial adhesion between Jute fiber and MAPP The effect of atmospheric plasma treatment on interfacial adhesion between jute fiber and MAPP is indicated in figure 4. As shows in this figure, the interfacial adhesion between two phases improved significantly by atmospheric plasma treatment. Plasma treatment showed higher effect than alkali treatment. In the case of combination of atmospheric plasma treatment of 5 min and alkali treatment of 0.5 N KOH in 6 hours, the interfacial adhesion is 30.96% higher than that between untreated fiber and MAPP. 2.061 2.562 2.323 2.669 1.5 2 2.5 3 Untreated Plasma treated, 5 min Plasma treatment condition IF SS ,M Pa Untreated Alkali treated, KOH 0.5N, 6h Figure 4: Effect of atmospheric plasma treatment on interfacial adhesion between Jute fiber and PP resin 205 4. Effect of plasma treatment and alkali treatment on the surface morphology The SEM images of untreated and treated fiber surface are shown in figure 5. Figure 5: SEM images of Jute fiber surface It showed that jute fiber consists of many individual fibers which are bonds together closely by adhesive substances. After alkali treatment, individual fiber becomes more oriented and has cleaner surface. After atmospheric plasma treatment of 5 min, fiber surface became rougher comparing to the surface of untreated fiber. 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