Air-plasma treatment of bamboo fiber for polypropylene composite application

Journal of Chemistry, Vol. 45 (5A), P. 196 - 200, 2007<br /> <br /> <br /> Air-plasma treatment of bamboo fiber<br /> for polypropylene composite application<br /> Received 16 August 2007<br /> Ta thi Phuong Hoa, Do Thi Cuc, Nguyen Hoang An<br /> Polymer Centre, Hanoi University of Technology<br /> <br /> <br /> summary<br /> In this study, the air-plasma generated by radio-frequency was used to treat bamboo fiber.<br /> The treatment parameters were studied to find the suitable condition. The testing on tensile<br /> strength, tensile modulus, module Weibull and elongation to break of the fiber, the measurement<br /> of contact angles and the SEM analysis showed that at the high frequency of 12 kHz, power 50 W<br /> and treatment time of 5 minutes, after air- plasma treatment the tensile strength and tensile<br /> modulus of bamboo fiber increased more than double (101.1% and 101.5%), the contact angles<br /> increased remarkably and treated fibers have cleaner surface. The adhesion between bamboo<br /> fiber and polypropylene (PP) as well as PP containing maleic anhydride grafted PP evaluated by<br /> droplet method showed that the interfacial shear strength (IFSS) of the treated fiber increased<br /> 18.2% at PP and 39.4% at PP-MA-PP compared with untreated fiber; SEM image showed a<br /> better adhesion between fiber and polymer. Compared to treatment by silane coupling agent, air-<br /> plasma treatment can improve both the mechanical properties of fiber and adhesion while silane<br /> coupling agent only the adhesion.<br /> <br /> <br /> I - Introduction treatment, which is environmental friendly, is<br /> considered as a promising physical treatment<br /> In recent years there has been renewed the method to modify the fiber surface for a better<br /> interest in using the natural fiber to replace glass adhesion. In this paper air-plasma has been used<br /> fiber to get polymer composite which is eco- to treat bamboo fiber surface for PP-composite<br /> friendly. Vietnam is the country where bamboo application. The mechanical properties,<br /> is abundantly available and of diversified morphology of fiber and adhesion between fiber<br /> species, polypropylene (PP) has a wide range of and PP have been investigated and compared<br /> application and a high value of property/price with that of silane treatment [1, 2, 4].<br /> therefore there is a good potential to use<br /> bamboo fiber for polypropylene composite II - Experimental<br /> application to get a motivated combination of<br /> environmental friendliness and economical 1. Material<br /> feasibility. However, due to very different<br /> - Bamboo fiber was separated from bamboo<br /> natures of natural fiber and polymer there is a<br /> using mechanical method.<br /> poor wet ability and weak interfacial adhesion<br /> between fiber and polymer which leads to poor - Polypropylene.<br /> mechanical properties of composite. Surface - Yeniosil Silane GF31.<br /> treatment of reinforcement fiber is one of the<br /> effective solutions. Recently cold plasma 2. Plasma treatment<br /> 196<br />  Usually surface treatment is under low- 4. Tensile test of fiber<br /> pressure. However this study is carried out at<br /> atmosphere pressure and room temperature in Bamboo fibers were separated from bamboo<br /> order to simplify as much as possible the and cut approximately 40 mm in length. Both<br /> technology for application. fiber ends were glued on the pieces of paper<br /> (paper tabs of size 40x40 mm) for handing<br /> Plasma is generally created by supplying a purposes. During pulling, the specimens were<br /> sufficient amount of energy to a volume handled only by paper tabs and the working<br /> containing a neutral gas. The energy may be zone of the fiber was not touched. Before<br /> supplied in the form of electrical energy, heat, experimenting, fiber diameter was measured on<br /> ultra violet radiation or particle beams. In optical microscope with an optical objective of<br /> technical plasma device, the input energy is 4-40 times magnification. The test was carried<br /> generally supplied as electrical energy [1, 2]. out on a computer connected LLOYD LRX Plus<br /> The major structural components of self- machine. Measurements of load and<br /> made plasma device for this study are a bell displacement were used to compute stress strain<br /> (chamber) and an excitation source (Fig. 1) curves for the fibers. All tests were<br /> connecting with gas line, vacuum pump and displacement controlled with the loading rate of<br /> pressure controller. 2 mm/min.<br /> 5. Determination of Fiber to Resin Interfacial<br /> Shear Strength<br /> The mechanical adhesion between<br /> reinforcing fibers is usually characterized by the<br /> interfacial shear strength (IFSS) determined by<br /> such test methods as fiber pull-out,<br /> microdebond test, fiber fragmentation test etc.<br /> In this study droplet pull-out test was conducted<br /> to evaluate the interfacial shear strength (IFSS)<br /> between the fiber surface and resin.<br /> Fibers were dried to allowable moisture<br /> content and mounted on the cardboard. Drops of<br /> Fig. 1: Plasma treatment device<br /> PP resin was heated to melting point and then<br /> dripped directly on the fiber. It would solidify in<br /> Bamboo fibers reside directly in the<br /> several seconds. The maximal dimension of the<br /> chamber housing the plasma. The chamber was<br /> drops and embedded length of the fiber were<br /> filled by air. Plasma excitation sources in this<br /> measured using an optical microscope with a<br /> test having high frequency of 12 KHz with the<br /> gratitude.<br /> plasma power of 50 W. The investigation was<br /> carried out at room temperature, atmospheric The separation of the droplet from the fiber<br /> pressure. surface was made possible by use of two blades<br /> adjusted laterally using vernier gauges.<br /> 3. Silane treatment Resistance of the droplet against the blades<br /> The bamboo fibers were treated with a provided the necessary force for generating the<br /> silane solution (the ratio 10 water to 90 shear stress between the resin droplet and the<br /> methanol, 0.5% dicumine peroxide, 3% silane fiber surface.<br /> by weight). CH3COOH solution was used for The IFSS, , is estimated as :<br /> adjusting the pH of around 3.5 to 4. After 1 hour<br /> .d<br /> treatment fibers were dried at room temperature =<br /> and then heated for 1 hour at 120 degree 2 lC<br /> Celsius.<br /> <br /> 197<br /> where: d is the fiber diameter, m; is the The results show a significantly increase of<br /> average fiber strength at critical, MPa; lC is the tensile property of fibers after air-plasma<br /> critical length related to the average fiber length treatment. Namely, mean tensile stress of<br /> at saturation fragmentation process, l as: untreated fiber was 181.84 MPa and of treated<br /> were 357.87 MPa (after 1 minute) and 365.77<br /> 4<br /> lC = l MPa (after 5 minutes), respectively. Thus, stress<br /> 3 increased more than double after treated 5<br /> minutes (up to 101.1%)<br /> with lC is the average embedded length [3].<br /> In the same conditions, Young’s modulus<br /> increased 101.5% and elongation decreased<br /> 25.6%.<br /> The tensile fracture surface of bamboo fiber<br /> was observed in the scanning electronic<br /> micoroscope and shown on the figure 2. We can<br /> see that each bamboo fiber was even if small<br /> (the average diameter was about 0.1 to 0.4 mm)<br /> also set from many single fibers. The fiber<br /> bundles arranged quite tightly and isotropic so<br /> that sensating as a single fiber. However, the<br /> orientation and bond on the whole fiber wasn’t<br /> Fig. 2: Pull-out test the same and fiber would be demolished at the<br /> point that the bond was weakest.<br /> III - Results and discussion<br /> <br /> 1. Effect of plasma treatment on the<br /> mechanical properties of fiber<br /> Table 1 presents some mechanical properties of<br /> bamboo fibers after plasma treatment with<br /> various times.<br /> <br /> Tab.1: Effect of plasma treatment on the Fig. 3: SEM image of the tensile fracture<br /> mechanical properties of bamboo fiber surface of bamboo fiber<br /> Plasma treatment time, min When producing plasma, there are not only<br /> charged and neutral particles bombarding<br /> 0 1 5 7 samples, but it also produced light, such as UV<br /> and others which may cause the polymerization<br /> Mean stress of lignin, making a significant increase in<br /> ( ), MPa 181.8 357.8 365.7 235.9<br /> mechanical properties of fiber due to<br /> Young’s polymerized lignin- cellulose composite fiber<br /> modulus, GPa 19.72 27.79 39.73 26.32 structure.<br /> ,% 2. Contact angle<br /> 2.00 1.84 1.48 1.55<br /> It can be seen that plasma treatment can<br /> Weibull improve the contact angle of fiber with ethylene<br /> modulus (m) 1.54 1.52 1.44 1.38<br /> glycol at nearly the same level as silane<br /> Normalizing treatment, however less in the case of water.<br /> stress ( 0), kPa 15.57 16.81 25.38 98.15<br /> <br /> 198<br />  Tab. 2: Contact angle of bamboo fiber with untreated fiber surface (a), plasma treated (b)<br /> water and ethylene glycol and silane treated (c). Plasma treatment caused a<br /> cleaner and smoother fiber surface as showed in<br /> Ethylene<br /> Water Fig. 4.<br /> glycol<br /> Untreated 39.3 39.1 Tab. 4: IFSS between bamboo fibers with PP<br /> 1 56.4 42.4 grafted MAPP<br /> Silane<br /> treatment, 2 64.5 43.2 Plasma<br /> %silane treatment time, Silan<br /> 3 66.9 44.5 Adhesion Un-<br /> treatment<br /> Plasma treated min<br /> 49.4 44.0 (3%w)<br /> treatment, 1min 1 5 7<br /> <br /> 3. Interfacial Shear Strength (IFSS) Specific<br /> The results in the table 3 show the slightly shear<br /> 2,08 2,1 2,27 2,94 2.76<br /> strength,<br /> increasing of IFSS value between bamboo fibers<br /> MPa<br /> with resin after air plasma treatment.<br /> Tab. 3: IFSS between bamboo fibers with PP IFSS,<br /> 3,12 3,31 3,41 4,35 4.13<br /> Plasma MPa<br /> Adhesion Un- treatment time, min Silan<br /> treatment In addition, plasma treatment lost the sets of<br /> treated<br /> 1 5 7 (3% w) non-orientation on the fiber’s surface.<br /> Specific Therefore, the single fibers in the fiber’s bundle<br /> shear would be oriented more closely. That’s fit to<br /> 2,06 2,25 2,28 2,18 2.72 increase significantly strain strength of fiber<br /> strength,<br /> MPa after treated. Simultaneously, the interstice<br /> between very close two single fibers also<br /> IFSS,<br /> 3,09 3,38 3,41 3,09 4.3 became wider and deeper creating conditions<br /> MPa<br /> adherence better with resin but unremarkably.<br /> With un-modified PP, IFSS between fiber Silane treatment also lost the sets of non-<br /> and resin increased from 3.085 MPa of orientation on the surface of fiber but the effect<br /> untreated fiber to 3.38 MPa after 1 minute got lower at plasma treatment. Silane treatment<br /> treatment, to 3.41 MPa after 5 minutes treatment only made fiber’s surface changed but without<br /> and then decreased to 3.09 MPa (plasma treated changing the inner fiber’s structure, therefore,<br /> for 7 minutes). strain strength of silane treated wasn’t almost<br /> changed.<br /> With PP grafted MAPP (5% MA),<br /> adherence increased from 3.12 MPa to 3.31 IV - Conclusions<br /> MPa of 1 minute treatment, to 3.41 MPa at 5<br /> minutes and got the highest value of 4.35 MPa Air plasma treatment has increased<br /> with plasma treated for 7 minutes, higher than remarkably the tensile properties of bamboo<br /> that of silane treatment. It can be seen that for fiber. Both mean stress and Young’s modulus in<br /> PP plasma treament can increase IFSS only suitable condition increased more than 101.15<br /> 9.7%, however for PP grafted MAPP 39.52%. and 101.5%.<br /> 4. Bamboo fiber surface morphology Plasma treatment also has changed the<br /> There was clear difference on the plasma surface of fibers for a better adhesion.<br /> <br /> 199<br />  PP grafted MAPP is higher than at PP, however<br /> less than that of silane treatment at suitable<br /> treatment condition of 5 minutes.<br /> <br /> References<br /> <br /> (a) (b) 1. Essay (2005). Low-Temperature Plasma<br /> Processing of Materials: Past, Present and<br /> Future. Plasma Processes and Polymers,<br /> Vol. 2: 7 - 15 (2005).<br /> 2. D. Sun, G. K. Stylios. Textile Research<br /> Journal. Vol. 75(9), P. 639 - 644 (2005).<br /> (c) 3. Arnold N. Towo, Martin P. Ansell. Third<br /> International Workshop on Green<br /> Fig. 4: SEM showing the surface of fiber Composites. P. 190 - 194 (2005).<br /> untreated (a), plasma treatment (b) and silane 4. X. J. Dai, L. Kviz. Study of Atmospheric<br /> treatment (c) and Low Pressure Plasma Modification on<br /> the Surface Properties of Synthetic and<br /> The adhesion between bamboo fiber and PP Natural Fibres, Textile and Fibre<br /> has improved. The effect of plasma treatment at Technology (2001).<br /> <br /> <br /> <br /> <br /> 200<br />