Correlation between dry rubber content in field …

1 Original ArticleCorrelation between dry rubber content in field latexand viscosity measured with efflux time methodPanu Danwanichakul*, Paitoon Lertsurasakda and Rachatham WiwattanasitDepartment of Chemical Engineering, Faculty of Chemical Engineering,Thammasat University, Klong Luang, Pathum Thani, 12120 15 February 2012; Accepted 11 September 2012 AbstractViscosity of field latex was determined with a horizontal capillary viscometer connected to a vertical reservoir flow behavior shows that the viscosity of rubber latex increased exponentially with dry rubber content (DRC).

2 The linearrelation between viscosity and DRC was obtained when DRC is less than 8 wt%. However, further dilution seems to givemore discrepancies because of experimental errors. Therefore, the maximum DRC that is still on the linear relation should beapplied in order to minimize the experimental errors while making the effect of dissolved solids in rubber latex viscosity of diluted latex was also checked with the rotational viscometer, which gave the confirmation that dilutioncould shield the effect of dissolved solids. The experiment showed that the efflux time method could predict the DRC well inthe range of 9-10 wt%.

3 Keywords: natural rubber , latex , dry rubber content , viscosity , efflux timeSongklanakarin J. Sci. (5), 551-555, Sep. - Oct. 20121. IntroductionThailand ranks among the top countries in exportingnatural rubber products to the world market. Natural rubberis the raw material in the production of tires, toys, rubbergloves, and other rubber products. rubber is usually sold inthe market either in the form of dry rubber blocks or concen-trated rubber latex . Both are made from field rubber latex ,which is traded in the rubber field or at the cooperativeorganization in the village.

4 The price of the field latex dependson the rubber content in the latex . Therefore, it is necessaryto determine the dry rubber content (DRC) before methods used nowadays are those correlated with thespecific gravity of the natural rubber and the standardmethod of ISO 126-2005. latex as much as 700 cm3 is used inthe former method, while it takes significant time and needschemicals in the preparation of the latter method. A newmethod is proposed here since it needs small amount of latex ,takes a short time and needs no chemicals in the viscosity of the solution or suspension is mainlyrelated to contents in the liquid.

5 This concept was appliedvery early by Einstein in his hydrodynamic study of thesucrose molecules in the aqueous solution. There are manystudies pertinent to the flow of suspensions of colloidalparticles. For example, Hernandez et al. (2006) proposed anequation to explain the viscosity of a dilute suspension ofSiO2, Al2O3 and TiO2 as a function of pH because pH couldchange the interactions among colloidal particles. Anotherexample involved the dilute gelatin system. Olivares et al.(2006) applied the technique of horizontal capillary tomeasure the viscosity to study the entanglement of gelatinchains when they were subjected to temperature measurement has been widely applied for otherhydrocolloids such as mulberry extract to study the effect ofthe concentration on the solution viscosity .

6 It was foundthat the relation was non-linear due to the entanglement ofpolymer chains in water. In addition, viscosity is an indicator*Corresponding Danwanichakul et al. / Songklanakarin J. Sci. Technol. 34 (5), 551-555, 2012552for the effect of charged polymers in water (Lin and Lai, 2009)and for the effect of the particle shape, which could changeunder shear stress. This situation is possible for a system athigher concentration or higher density. Interestingly, for theflow of polyethylene oxide (PEO) together with polystyreneparticles in a micro-capillary, the particles get bigger whenthe PEO is attached to their surfaces so they move faster inwater (Amnuaypanich et al.)

7 , 2007).Up to present, there has been no work investigatingthe viscosity of natural rubber latex as to determine therubber content . Therefore, in this work, we explored thepossibility of applying this method to determine the DRC ofthe field rubber latex . However, there are many methodsavailable to determine liquid viscosity . For example, in rota-tional flow, the torque is applied and measured . In sedimen-tation, drag force of the sediment is correlated with liquidviscosity. In this study, the viscosity is easily obtained fromcapillary flow where pressure drop could be expressed asa function of viscosity , Hagen-Poiseuille should be noted that the Hagen-Poiseuille equation is basi-cally derived from the laminar flow of Newtonian fluid.

8 Wethen assume first that the dilution of rubber latex couldoppress the non-Newtonian nature of the Research MethodologyThe apparatus was set up according to the onesuggested by Hernandez et al. (2006), where the horizontalcapillary was applied as shown in Figure 1. The liquid ispoured into the vertical tube with a radius (R0) of cm upto a specified point. The flow is then initiated and passingthrough the horizontal capillary, which is made of a glasstube with a radius (Rc) of mm. The time is recorded whenthe liquid front moves down to any specified value of H (elevation) is then plotted with theefflux time (t) as expressed by the Equation 1, where L is thelength of the capillary tube, which is 30 cm and is thedensity of the liquid.

9 The equation could be derived basedon the assumption that the flow is steady, the mechanicalenergy is conserved (Bernoulli s equation) and the laminarNewtonian flow can be applied (Hagen Poiseuille equation).402exp4cot gRHHLR (1)When ln(H) is plotted against the efflux time (t), the linearline is obtained, of which the slope (M) is related with theviscosity as shown in Equation (2)The experiments were performed for various dilutionratios, water volume: latex volume ratio of 100:0, 75:25,50:50, 40:60, 25:75, 20:80, 12:88, 9:91, 6:94, 3:97, 1:99.

10 In eachexperiment, the viscosity is obtained from Equation 2. Thevalue of experimental DRC was from the standard methodof acid coagulation. Briefly, rubber particles suspending inthe latex coagulate upon adding sulfuric acid solution. Thecoagulum is then dried in the oven and the weight of driedrubber is obtained. The DRC is reported as the ratio of dryrubber weight to total weight of rubber Results and of rubber latexThe field latex from the Thai rubber latex Corpora-tion (Thailand) PCL at Rayong has the properties as thefollowing.