Rheological behavior of bamboo fiber compound plastic

Size: px

Start display at page:

Download "Rheological behavior of bamboo fiber compound plastic"

Posy Clarke
5 years ago
Views:

1 Rheological behavior of bamboo fiber compound plastic H. Yamaguchi', H. Muramatsu' & S.Tagami2 'Departmentof Mechanical Engineering, Doshisha Univen&y, Japan. 'Eastern Hiroshima Prefecture Industrial Research Institute, Japan. Abstract Rheological characteristics of bamboo fiber compound plastic were examined experimentally. h the present study, rheological data for the shear viscosity, the storage modulus and the loss modulus of compound plastic of polypropylene with maleic acid mixing with various contents of bamboo fiber, were reported in comparison with equivalent glasfiber compound plastic. According to SEM visual information, bamboo fibers have short rod-like structure with high fiber-fiber interaction in the compound, while the glass fibershave long needle structure fomg entanglement m the compound. It was obtained that the rheological data showed clear difference based on the different structures in the compounds Rheological characterization was achieved by considering the natural bamboo fiber-fiber interaction, with which a rheological correlation is derived based on data obtained in the present investigation. 1 Introduction The fiber reinforced plastics (FRP) were utilized in many fields of engineering due to their superiorities against their counterpart, the metal materials. There are many types of FRP available in industrial production, depending on the combination of fibers and compounds. Until recently fibers used in FRP are mostly artificially made such as glass fiber, owing to mass

138 ISBN High1-85312-904-6 Pet$mnance Structwes and C omposites production with advantage of superior material properties.

2 138 ISBN High Pet$mnance Structwes and C omposites production with advantage of superior material properties. However, the problem is aroused when they are disposed to natural environment, and also there is a diflkulty of recycling of FW. Recently enormous movements toward the environmental problem activate a research for FRP using natural (biological) fibers, with which the FRP can be disintegrated itself in the natural environment with bacteria decomposition. To date, there were some reports available for bio-decomposable resin [l]and FRP with jute fiber [2]. In the present investigation, we employed bamboo fibers [3] as the reinforced material for FRP due to their natural reproductivity and relative toughness (31 against glass fibers. Bamboo FRP may be useful for environmental problems, but also contributes to enhance planting bamboo field to absorb CO2. In thistudy particularly, we report rheological characteristics of melted bamboo FRP. In order to characterize the bamboo FRP,ordinary glass FRP was tested for a sake of comparison, using the same compound material, i.e. polypropylene with 5wt% maleic acid. Various concentrations of fiber contained in the compound materials were examined in the melt. Rheological data were obtained with a plate-plate rheometer for the simple shear and dynamic moduli. 2 Experiment 2.1 Test materials Test bamboo FRP was made by mixing dried bamboo fibers with melted polypropylene with 5wt% maleic acid at 180 C for 10 mutes. The bamboo fiber, whose nominal diameter is 330,U m ( tim) and noma1length is 1000tim ( tim), was extracted by Mousou Bamboo tree commercially. Six test pieces of bamboo FRP were made for rheological measurement by mixing bamboo fibers of 5, 10, 20, and 3Owt% concentration. Prior to mixing with the compound material the bamboo fibers were sufficiently dried in an electric furnace at 80 C for 12 hours. For a comparison reason, ordinary glass FRP test pieces were also made using the same compound material. The glass fiber used in the test pieces is 13tim diameter and 3000,Um nominal length. The glass FRP test pieces were made by the same procedure as the bamboo FRP test pieces. 2 types of test pieces of glassf were prepared by alteringthe mixing concentration of fibersat 5 and lowt%. 2.2 Experimental apparatus Fig.1 shows the experimental arrangement of rheological measurements. Plate-plate rheometer (Haake Rheatress : R!3759 was used for measurements of the shear viscosity 77 vs. the shear rate y,the storage modulus G and tie loss modulus G vs. oscillating angular velocity W. The prepared test FRP pieces were melt m the rheometer and measurements were taken at C for y =O.l-lO[l/s] and CO

3 Iligh Petfiornzance Strmztwes mdcomposites 139 = [rad/s].Test pieces were placed between the plate (2Omm diameter of upper plate (sensor plate) and lower plate (measuring plate)) as shown m Fig.2 and heatedthroughthebothplatesatthemeasuringtemperature.theplatetoplate distance were kept at l.hm, with which the rheological data are independent from the gap distance (plate to plate distance). Particular attention was made so that the temperatureof test pieces was kept constant throughout measurement by insulatmg the test section with pdex glass (Fig.2). To gam the reproducibility each measurement was repeated three times and data were recorded as mean value. By examining the reproducibility it was obtained thathe measuring error of test pieces was approximately maximum f3%. arheometerrsrt ~Sensorshaft control Control Figure 1: Experimental apparatus Figure 2 : Detail of test section

140 ISBN High 1-85312-904-6 Performance Structures and Composites 3 Result and discussion Fig.

4 140 ISBN High Performance Structures and Composites 3 Result and discussion Fig.3 shows typical features of (a)-1 bamboo fiber and (b)-l glass fiber at the magnification shown in theeach figure. In Fig.3also,thestructural arrangements of fibers in the test pieces, (a)-2 bamboo FRP and (b)-2 glass FRP, are displayed. As seen in Fig.3 (a)-1 and (b)-l, the bamboo fiber has irregularsurfacestructure (it isnotedthatthebamboofiberused in the present study is the flux of thin wooden fibers of bamboo stem), while the glass fiber has smooth surface. Similarly in comparison with Fig.3 (a)-2 and (b)-2, which are typically seen in the test pieces when they were made, it is seen that the bamboo FW has dispersed rod-like structure in the compound material,whiletheglass FRPhasentangledlongneedlestructure in the compound material. So it is easily speculated thathese fundamental difference oftheinternalstructure of fibers in thetestpieces may yield substantial differencein rheological measurements. (a)-1 Bamboo Fiber (b)-l Glass Fiber (a)-2 BambooFRP (lowt%) (b)-2 Glass FRP (lowt%) Figure 3 : SEM photograph 1 In Fig.4, the shear characteristics (shear viscosity vs. shear rate) are depicted for (a) bamboo FW and (b) glass FRP. It is noted here that in both cases, the shear characteristic of the compound material itself (without fibers) is superimposed for a sake of comparison. As seen from Fig.4 (a), there are two major trends in the rheological data, depending upon the concentration of fibers and the shear rate. When the shear rate is lower than y =6[l/s] ; it can

IIigh Perfimmwre Structures and Composites 141 be defined the lower shear rate region in the present study, the viscosity becomes higher than compound material for BFlO%, 20% and 30% (by

5 IIigh Perfimmwre Structures and Composites 141 be defined the lower shear rate region in the present study, the viscosity becomes higher than compound material for BFlO%, 20% and 30% (by concentration differences). This would be due to the hydrodynamics friction [4], [5]between fibers and the melt since the fiber concentration of rod-like solid yields increasing order of viscosity. The shear-thinning characteristic largely came from the nature of the compound melt itself. However, when the shear rate is increased beyond y =6[l/s], the trend (the shear characteristic) comes to opposite order, i.e. the large drop of shear viscosity occurs for higher concentration FRP such as BF30% and there exists cross over point at the shear rate of Y =6[l/s]. This is very interesting and peculiar trend obtained in the present investigation, and which can be explained phenomenologically by the following speculation. When the shear rate is low, each bamboo fiber tends to rotate with fiber to fiber collision interaction, keeping dispersed state as a whole. On the other hand, when the shear rate is high, bamboo fibers tend to coagulate together aligning themselves toward flow direction due to strong fiber to fiber interaction. Aligned and coagulated fibers form the laminate state, reducing frictional force (stress) between melt, and thus result in dropping viscosity. The evidences of the changing internal structure of fibers under the shear motion are depicted in Fig.S(a)-l and (a)-2, which were taken at lower shear rate y = 1 and higher shear rate y =8 respectively. As seen in FigS(a)-Z, fibers are agglomerated and aligned toward flow direction, while in Fig.S(a)-l the fibers are fairly dispersed evenly. In comparison with the bamboo FRP, similarly the typical cases for the glass FEW are displayed in Fig.S(b)-l and (b)-2. Unlike the bamboo FRP, the glass FEU shows unified distribution for the range of shear rate y s 10[l/s] as shown in Fig.S(b)-l and (2). This evidence would lead a thought that the entangled structure is responsible for the rheological trend a shown in Fig.4(b), where the entangled structure of long needle glass fibers sustains the stress independent from the t"-'=f shear rate (in the experimental range), keeping the structure unchanged. r-----l ]"I 4 I, 1 BF?O% --. BF30%...- a v GFSW GFlQI I I IO Y [ h 1 (a) Bamboo FRP 7 [ W (b) Glass FRP Figure 4 : Shear viscosity (200 C)

6 (a)-1 Bamboo FW (lowt%) (a)-2 Bamboo FRP (lowt%) lowshear(j =l) high shear ( y = 8 ) (b)-l Glass FRP (lowt%) (b)-2 Glass FRP (lowt%) lowshear(j -1) high shear ( y = 8) Figure 5 : Distribution orientation of fibers In Fig.LF(a), measured data are fitted by the following empirical correlation. where eqn(1) was derived from Krieger-Dougherty equation [6] for short rod-like fiber mixture and $m is the maximum filling rate, (b the fiber volume rate and [v]the material constant. In eqn(l), v, is the shear viscosity of compound material and in the present study the Carreu-Yasuda correlation [7] is used for as follows : 55 = h- a J [ l + W +% ] ~ (2) where v,, is zero shear viscosity,? )m the infinite shear viscosity (second Newtonian viscosity), h the relaxation constant, n the power index and a the material constant. In eqn(l), the last term (Y indicates the fiber-fiber interaction and coagulation parameter. In the present study, (Y is written in

7 High Perjornzance Str.uc/ures and C'omposites 143 the following formula for bamboo fibers, a=p.q wherep and q may be written in the following form : (3) Itis mentioned that p determines the effect atlow shear region while q determines the effect at high shear region. In fitting the rheological data for the bamboo FRP the following constants are determined, q, =380, qm=lo, A "0.25, ~ ~ 1. r1=1.93,&,, 6, EO.79, v,=6 (cross over shear rate). As seen in Fig.4(a), reasonable data fitting were obtained by eqn(l), showing that the fiber-fiber interaction and coagulation parameter is quite effective. In particular, for the highest concentration case, i.e. BF30%, the dominant effect of the fiber-fiber interaction and coagulation is evident at high shear rate. In Fig.6, measured moduli are displayed for (a) bamboo FRP and (b) the glass FRP, and in each case the storage modulus and the loss modulus is depicted. As seen in Fig.6(a)-l and (a)-2, there exists the basic elastic character due to the compound material. The noticeable difference isthat there are so called the second plateaus [8] at low frequency region for the bamboo FRP. This would be due to the large relaxation of fiber orientation against fluid oscillation of melt at low frequency oscillation. This tend can be seen in the loss modulus as shown in Fig.6(a)-2 (though the magnitude is small). However, as displayed in Fig.6(b)-l and (b)-2, such phenomena were not obtained in the moduli data of the glass FRP. It is finally mentioned that for the glass FRP the viscoelastic effect is quite high compared with the bamboo FRP since the G' has fairly large value. This would be again due to the structural difference in the compound, where in the case of the glass FRP the entanglement of fibers forms strong structure, excerting high elastic behavior in the viscoelastic data for G' and G". 1 m,, 1 l I IU!W W [rad:%) (a)-1 Storage modulus (Bamboo FRP) (a)-2 Loss modulus (Bamboo FRP) U

8 144 Hig-hPe~fornzmceStructures and Composites IOYXU,., yxkk7 i t i l[ ; I IO IW (b)-l Storage modulus (Glass FRP) W Iralbrl (b)-2 Loss modulus (Glass FRP) Figure 6 : Moduli (200 C) 4 Conclusion In the present study, following conclusions were obtained in rheological measurements of the bamboo FRP and the glass FRP. (1) Both bamboo and glass FRP show the shear thinning character. Substantial difference in rheological character exists for the bamboo FRP, particularly in high shear region. This would be due to the strong fiber-fiber interaction and coagulation derived from the nature of bamboo fibers. (2) Correlation formula including effects of the fiber-fiber interaction and coagulation could fit the data of shear viscosity satisfactory. (3) The measurements of moduli indicated the relaxation phenomena of orientating bamboo fibers at low frequency region. Acknowledgment This work was supported by a grant of New Engineering Development Research Project to Doshisha University from Ministry of Education, Culture, Sports, Science and Technology Japan. References [l]j.jiang, K.Okubo, T.Fujii, Fabrication of bio-decomposable composites using natural fibers and their strength properties, 31 International SAMPE Technical Conference, pp , [2] A.K.Rana, B.C.Mitra, Short jute fiber-reinforced polypropylene composites, Journal of Applied Polymer Science vol. 71, pp ,

9 High Perfornzance ~Stmctwesand Composites [3] S.Jain, R.Kumar, Mechanical behavior of bamboo and bamboo composite, Journal of Materials Science27, pp , [4] R.G.Larson, The Structure and Rheology of Complex Fluids, Oxford University Press, pp , [5] J.K.Kim, J.H.Song, Rheological properties and fiber orientations of short fiber-reinforced plastics, Journal of Rheology 41(5), [6] H.A.Barnes, JXHutton, K.Walters, An Introduction to Rheology, Elsevier, pp , [7] R.B.Bird, R.C.Armstrong, O.Hassager, Dynamic of Polymeric Liquids, Wiley-Interscience Vol.1, pp , [8] T.Matsumoto, Rheology of Dispersed System, High Molecular Pub. Soc., Japan, ~76,1997.

Modeling the Rheology and Orientation Distribution of Short Glass Fibers Suspended in Polymeric Fluids: Simple Shear Flow

Modeling the Rheology and Orientation Distribution of Short Glass Fibers Suspended in Polymeric Fluids: Simple Shear Flow Aaron P.R. berle, Donald G. Baird, and Peter Wapperom* Departments of Chemical