The Study of Natural Rubber Coagulum Quality Evaluation … · Evaluation by Ultrasonic Method ... Ultrasonics could also be used to find the elastic parameter of a material ... The

International Journal of Applied Agricultural Research ISSN 0973-2683 Volume 3 Number 1 (2008) pp. 55–66 © Research India Publications http://www.ripublication.com/ijaar.htm

The Study of Natural Rubber Coagulum Quality Evaluation by Ultrasonic Method

*Dadi R. Maspanger1, Hadi K. Purwadaria2, I Wayan Budiastra2 and Amoranto Trisnobudi3

1Bogor Research Centre for Rubber Technology - IRRI, Jalan Salak 1,

Bogor 16151, Indonesia *E-mail : [email protected]

2Dept of Agriculture Engineering - IPB , Kampus IPB Darmaga, P.O. Box. 220, Bogor 16680 - Indonesia

E-mail : [email protected], [email protected] 3Dept. of Engineering Physics – ITB, Jalan Ganesha 10,

Bandung 40132, Indonesia E-mail : [email protected]

Abstract

Ultrasonic method, as a non-destructive means could be considered for the evaluation of coagulum quality. The objective of this research were to assess the relationship of coagulum quality with the rubber elasticity and the properties of ultrasonic wave, and to develop a mathematical model to relate the coagulum quality with the acoustic characteristics. Test samples were based on model, made by coagulating fresh latex with formic acid and the addition of foreign materials, that were limited to sand, rubber wood shavings, and their mixtures.

The result showed that increasing moisture content caused the increasing of Young modulus, as well as decreasing attenuation and wave velocity. The increase of sand content caused an increase of Young modulus, attenuation, and decrease of wave velocity. The increase of wood shavings caused the increasing of wave velocity and attenuation. The developed mathematical equation to determine the moisture content, dirt content and Young’s modulus were expresed as function of density, attenuation, and wave velocity. This preliminary research result is expected to give useful information to develop further investigation for using ultrasonic method in rubber quality evaluation. Experiments are still to be carried out to investigate the effect of other contaminants to ultrasonic wave properties, to serve as base for engineering

56 Dadi R. Maspanger et al

design of practical scale ultrasonic equipment. Keywords: NR coagulum, moisture, dirt content, ultrasonic, wave velocity, attenuation

Introduction Ultrasonic wave is a mechanic-acoustic wave with a frequency above 20 kHz. Sound waves (sonic) range from 20 Hz to 20 kHz could be heard by human beings. At the time being, the ultrasonic technology has been applied in a lot of fields, such as medical diagnostics on fetus, human organs, nerve system, identification of physical properties of soil, oil, depth in geology, material testing, detection of flow velocity, and separation process in industry [1]. Application of ultrasonic method in agriculture has been done Mulet et. al. [2] and also by Sarkar and Wolf [3] to determine the ripeness of apples. Mizrach, et al. [4] tried to find a correlation between ultrasonic velocity and attenuation on apples and avocado. Budiastra, et al. [5] determined the ripeness and damage of tropical fruits. Haryanto, et al. [6] and Rejo, et al. [7] determined the ripeness of durian by studying the ultrasonic wave and physicochemical properties of the fruit. In polymer-composite field, White, et al. [8] used ultrasonic wave to observe the vulcanization process of glass fiber. Doring and Stark [9] observed the formation of urea-formaldehyde and epoxy. Turkachinsky, et al [10] succeedeed in performing a devulcanization of used tyre rubber, and Levin et al. [11] of styrene butadiene rubber (SBR). Ultrasonics could also be used to find the elastic parameter of a material such as Young modulus, Shear modulus, and Poisson ratio. Trombino [12] and Navarrete, et al. [13] used ultrasonics for peat moss mixture, polymers, and silica sand. Indonesia is one of the main natural rubber producing country. Most of the raw rubber materials mainly come from smallholders, mostly in the form of wet coagulum, specially prepared as raw materials to produce TSR 10 or TSR 20. Because of various form and size of coagulum and also various kind and contaminant composition or distribution, quality evaluation by sampling and objective method is still difficult to practice. At the crumb rubber factory, thick raw materials were sorted by slicing it, the dry rubber content (DRC) roughly estimated, and the dirt content determined just by visual subjective judgement. Based on earlier experiments on several agricultural commodities, ultrasonic method could likely be developed to identify the quality of rubber coagulum. Analysis procedure by ultrasonic wave is an objective, non-destructive and fast testing method. It could be applied on the spot to the material tested. A comprehensive research will take a long time because the contaminant in coagulum varies is shape, size, and composition and also the method used in coagulating latex by the smallholders are very variable. This research attempts a model, using testing samples of coagulum prepared in the laboratory and the foreign material is limited to sand and rubber wood shavings. The choise to use sand and

The Study of Natural Rubber Coagulum Quality Evaluation 57

rubber wood shavings was because these were the most common contaminant found in coagulum from smallholders. The objective of this research was to assess the relationship of coagulum quality, expressed as dirt, moisture and DRC with the rubber elasticity and the properties of ultrasonic wave i.e. attenuation and ultrasonic wave velocity, also to develop a mathematical model to relate the coagulum quality with the acoustic characteristics. Materials and Methods The ultrasonic testing was done in the Ultrasonic Laboratory, Department of Engineering Physics - ITB. Preparation of NR coagulum testing sample and measurement of physical properties and elasticity were conducted in the laboratory of Bogor Research Centre for Rubber Technology. Test materials were prepared from field latex tapped in the experimental garden in Bogor, Indonesia. Latex was coagulated, and deliberately contaminated with sand, 0.5-1 mm, rubber wood shavings 3-5 mm size, and their mixture as foreign materials. Latex was poured into a PVC pipe with inner ∅ of 5 cm and height of 5-10 cm. With continuous stirring a 1% formic acid was added at the amount of 0.4 mL/g dry rubber. Foreign materials added was 0-20% w/w to dry rubber. Stirring was terminated jus before the latex coagulated. Figure 1 shows the scheme of ultrasonic equipments to measure the acoustic properties of rubber coagulum, and the scheme of tensometer equipments to measure the Young's modulus of rubber coagulum. The ultrasonic wave was generated in a Signal generator USIP 12 (Krautkramer Branson), transferred to a transducer piezoelektrik 2 MHz. After passing the rubber sample, signal was transformed into digital data by digital osciloscope ETC M621 and into a personal computer (PC). On the monitor, the ultrasonic wave curve was shown. From this curve, the amplitudo could be calculated from wave travel time, and attenuation from wave amplitude. The following equation were used :

= (1) Where CL = longitudinal velocity of ultrasonic wave, m/s ; L = thickness of coagulum, m, and Δt = wave travel time in coagulum, second.

(2) Where I = wave attenuation, dB/m ; A = wave amplitude in the material, mV ; A0 = wave amplitude of standard sample, mV ; and L = coagulum thickness, m.


Figure 1 : Scheme of ultrasonic equipments to measure the acoustic properties of rubber coagulum (a), and scheme of tensometer equipments to measure the Young's modulus of rubber coagulum (b) Result and Discussion The effect of moisture and dirt on ultrasonic wave properties The relationship between moisture and dirt content to elasticity of coagulum (expresed as Young's modulus, E) is shown in Figure 2. Experimental results showed that increase of moisture content up to 18-43% w/w, in general decrease of E value from about 1.2 MPa to 0.3 MPa. On the contrary, increasing of sand content caused an increase of E. The Increasing of E value was probably due to by increased stifness of coagulum with increasing volume fraction of the sand. The value of Young at high moisture (43% w/w) was much different for low and high content of dirt, because coagulum was still soft and easy to be break apart.

Figure 2 : The effect of moisture and dirt content on elasticity of rubber coagulum


The relationship between moisture and dirt content to wave velocity, are shown in Figure 3, 4 and 5, for sand, wood shavings and their mixtures, respectively. Research result showed that increasing moisture content up to 18-43% w/w, caused increasing ultrasonic wave velocity. The increase of sand up to 20% w/w caused the decreasing of wave velocity from 1516 m s-1 to 1441 m s-1 (Figure 3). The increase of wood shavings up to 20% w/w caused the increasing of wave velocity from 1481 to 1545 m s-1 (Figure 4).

Figure 3 : Distribution of wave velocity on different moisture and dirt contents (sand)

Figure 4 : Distribution of wave velocity on different moisture and dirt contents (wood shavings)


The contrary effect of sand and wood shaving, caused the composition of their mixture to have different effect on wave velocity. On Figure 5 showed that the mixture where the quantity of sand was higher than quantity of wood shavings (• and � symbols) tend to decrease wave velocity, while the mixture where quantity of wood shavings was higher than quantity of sand (∗ and Δ symbols) tend to increase wave velocity.

Figure 5 : Distribution of wave velocity on different moisture and dirt contents (mixture of sand + wood shavings) According to Gent and Mason [14] and Gooberman [1], the velocity of ultrasonic wave in rubber is 1400-1479 m/s, in water 1497-1500 m/s, so the increase of moisture content in rubber will increase the wave velocity. Barkan [15] informed that wave velocity in sand is 300-550 m/s, therefore the increasing of sand content caused the decreasing of wave velocity. Kinsler and Frey [16] informed that wave velocity in wood depended on the kind and density of the wood. The velocity in cork and balsa wood (density 0.13-0.24 g/cm3) is 500-1150 m/second, while in pinewood (density 0.45-0.72 g/cm3) is 3500-4000 m/second. No information available of the ultrasonic wave velocity in rubber wood shavings. If it was assumed that density was more than 0.6 g/cm3, the velocity in wood shavings would be more than the velocity in water or rubber, hence the increase of wood shavings would increase the wave velocity in coagulum. The result showed that increasing moisture content of 18-43% w/w resulted in decreasing attenuation of the ultrasonic wave. The increase of sand up to 20% w/w caused increase of attenuation from 504 to 1520 dB m-1. Also, increasing wood shavings up to 20% w/w caused the increase of attenuation from 504 to 1108 dBm-1. Figure 6 showed that was a relationship between moisture and mixture of dirt to ultrasonic wave attenuation. Caused by the same effect for both sand and wood


shavings, increasing the sum amount of dirt (sand+wood shaving) will increase wave attenuation.

Figure 6 : Distribution of wave attenuation on different moisture and dirt contents (mixture of sand + wood shavings) The increase of attenuation with the increasing of dirt content was probably caused by scattering, reflection or refraction of the wave by dirt particles, hence there was a lower energy level noted by the decrease of wave amplitude ( Figure 7 ). The wave amplitude in a contaminated coagulum was lower than in a clean coagulum.

Figure 7 : Amplitude of ultrasonic wave in (a) a clean coagulum and (b) contaminated coagulum The mathematical model of coagulum quality as a function of density and acoustic properties The developed mathematical equation to calculate Young’s modulus (E, MPa ) was expresed as hyperbolic function : E = (1.072 10-10 pCL

2) /(1+ 1.265 10-14 I 2CL2) (3)


where ρ = density (kg m-3), I = attenuation (dB m-1), CL = wave velocity (m s-1). Figure 8 showed that mathematically there was high relationship for both linear and parabolic correlation, indicated by high value of determination coefficient (R2) , where R2 = 0.9598 and R2 = 0.9674 for linear and parabolic correlation respectively.

Figure 8 : Linear (a) dan parabolic (b) correlation of Young’s modulus (E) as hyperbolic function of density (ρ), wave velocity (CL) dan attenuation (I). The developed mathematical equation to determine the moisture content (Ka, % w/w) was expresed as geometric function : (100-Ka)1/3 = 1.412 10-9p 0.867 CL

1.868 I -0.097 (4) where ρ = density (kg m-3), I = attenuation (dB m-1), CL = wave velocity (m s-1). Figure 9 showed that mathematically there was high relationship for both linear and parabolic correlation, indicated by relatively high value of determination coefficient (R2) , where R2 = 0.9519 and R2 = 0.9522 for linear and parabolic correlation respectively.

Figure 9 : Linear (a) and parabolic (b) correlation of moisture content (Ka) as geometric function of density (ρ), wave velocity (CL) dan attenuation (I).


The developed mathematical equation to determine the dirt content (Kkot, % w/w) was expressed as geometric function : 0.3Ka2 –4Kkot = - 0.007 x2 + 0.586 x - 37.14 (5) with x= 8.08 10-9 p 0.82 CL1.87 I -0.055 , where ρ = density (kg m-3), I = attenuation (dB m-1), CL = wave velocity (m s-1). Using the values of moisture and dirt content, dry rubber content was calculated by simple equation (6). First, moisture content was calculated from equation (4), and further used to calculate dirt content using equation (5). K3 = 100 – (Ka + Kkot) (6) Result of validation Figure 10 showed that the results of validation indicated highest deviation of 20% for the Young’s modulus value prediction, with an RMSE = 0.0522 Mpa, and 80% data performed a deviation below 10%. For the moisture content, showed that the results of validation indicated highest deviation of 27% for the value prediction, with an RMSE = 1.98%, and about 86% data performed a deviation below 10% ( Figure 11 ). For the dry rubber content, the results of validation indicated a maximum deviation of 12%, indicated for the value prediction, with an RMSE = 3.0722 and about 94% data performed a deviation below 10% ( Figure 12 ).

Figure 10 : Deviation of Young's modulus estimated by mathematical model (= E prediction) to true value (= E target)


Figure 11 : Deviation of predicted moisture content from their true value (= Ka target)

Figure 12 : Deviation of dry rubber content value (predicted by mathematical model) to target value Conclusions The result of this experiment showed that moisture and dirt content in the coagulum had a significant influence on the ultrasonic wave properties passing through the sample. The increasing of moisture caused the increasing wave velocity and decreasing of attenuation. The increase of sand content resulted in decreasing wave


velocity and an increase of attenuation, whereas increasing wood shavings content caused increase in attenuation and wave velocity. The developed mathematical model, though with relatively high deviation, gave an indication that moisture and dirt content could be predicted based on rubber viscoelasticity theory. Modification of the model should involve the effect of contaminant shape, and homogeneity of the contaminant in the coagulum matrix. This research would have a commercial value if ultrasonic testing were done to field coagulum. There is a necessity for doing some adjustment on frequency, transducer, and signal generator. A combination of longitudinal and transversal waves should come into a consideration to be studied. This research is hoped to be a good stimulant for developing other investigations to apply ultrasonic in rubber quality analysis. Other types of foreign materials, that usually exist in coagulum such as pebbles, fiber, and other extrameous things not included sand and wood shaving, which have influence on rubber elasticity and ultrasonic wave properties, should be studied. References [1] Gooberman, G. L., 1968, Ultrasonic Theory and Applications, The English

Press, Ltd, London, UK. [2] Mulet, A., Benedito, J., Bon, J., and Rocello, C., 1999, “Ultrasonic Velocity in

Cheddar Cheese as Affected by Temperature. J. Food Sci., 64(6),1038-1041. [3] Sarkar, N., and Wolf, R.R., 1983, “ Potential of Ultrasonic Measurement in

Food Quality Evaluation,” Trans of ASAE, St Joseph, MI, USA. [4] Mizrach, A., Flitsanov, U., El-Batsri, R., and Degani, C., 1999,

“Determination of Avocado Maturity by Ultrasonic Measurements,” Scientiae Horticulturae, Vol. 80, pp. 173-180.

[5] Budiastra, I. W., Trisnobudi, A., and Pujantoro, L., 1998, “Development of Ultrasonic Wave Technology for Determination of Damage and Maturity of Tropical Fruits by Non Destructive Methods,” Report of RUT V, Fateta-IPB, Bogor.

[6] Haryanto, B., Budiastra, I. W., Purwadaria, H. K., and Trisnobudi, A., 2001, “Determination of Acoustic Properties of Durian Fruit,” Proc. 2nd IFAC-CICR Workshop on Intelligent Control for Agricultural Applications, Bali, Indonesia.

[7] Rejo, A., Suroso, Budiastra, I.W., Purwadaria, H.K., Susanto, S., and Nazaruddin, Y.Y., 2001, “Model for Predicting and Classification of Durian Fruit Based on Maturity and Ripeness Using Neural Network,” Proc. 2nd IFAC-CICR Workshop on Intelligent Control for Agricultural Applications, Bali, Indonesia.

[8] White, S.R., Mather, P.T., and Smith, M.J., 2002, “Characterization of Cure State of DGEBA-DDS Epoxy Using Ultrasonics,” Pol. Eng. and Sci., 42(1), pp. 51-67.


[9] Döring, J., and Stark, W., 1998, ”On-Line Process Monitoring of Thermosets by Ultrasonic Methods,” NDT-net, 3(11), pp. 1-4.

[10] Turkachinsky, A., Schworm, D., and Isayev, A., 1996, “Devulcanization of Waste Tire Rubber by Powerful Ultrasound,” Rubb. Chem. and Tech. , 96(1), pp. 92-103.

[11] Levin,V., Kim, S., and Isayev, A., 1996, “Ultrasound Devulcanization of Sulfur Vulcanized SBR,” Rubb. Chem. and Tech., 96(1), pp. 104-114.

[12] Trombino, C., 1998, “Elastic Properties of Sand-Peat Moss Mixtures from Ultrasonic Measurement,” Lawrence National Laboratory, Dept. of Energy, USA.

[13] Navarrete, M., Pozos, G., Castaneda, R., and Pillagran, M., 1998, “Recovery of the Elastic Constants from Wave Speed Measurement Using the Photoacoustic Method in Viscoelastic Composites,” J. Mexican Society of Instrumentation, Instrumentation and Development, 4(5), pp. 70-75.

[14] Gent, A. N., and Mason, P., 1963, Viscoelastic behavior, Bateman, L., ed., The Chem & Physics of Rubber Like Substances, John Willey & Sons, New York. pp. 197-224.

[15] Barkan, D.D., 1960, Dynamics of Bases and Foundations, McGraw Hill, New York, pp 32-33.

[16] Kinsler, F., and Frey, A., 1962, Fundamentals of Acoustics, John Wiley & Sons, New York, pp.18-20

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The Study of Natural Rubber Coagulum Quality Evaluation … · Evaluation by Ultrasonic Method ... Ultrasonics could also be used to find the elastic parameter of a material ... The