Karakterisasi mutu koagulum karet alam dengan metode ultrasonik

Abstract

Raw rubber is prepared mostly in the the form of coagulum by the small holders. Its quality is commonly judged subjectively by visual measure to determine the dry rubber content, moisture content and foreign materials. Ultrasonic method, as a non-destructive objective alternative, may be considered for the evaluation of coagulum quality. The objectives of this research were to assess the relationship of coagulum quality with the rubber elasticity and the properties of ultrasonic wave, to develop the mathematical model to relate the coagulum quality with the acoustic characteristics, and to apply neural network in determining dry rubber content. Test samples were based on model, made by coagulating fresh latex with formic acid and the addition of foreign materials. The foreign materials were limited to sand, rubber wood shavings, and their mixture. The result showed that increasing moisture content of 18-43% caused the increasing density, decreasing Young modulus, as well as decreasing attenuation and wave velocity. The increasing of sand up to 20% caused the increasing of density from 930 to 1014 kg m-3, the Young modulus from 0.295 to 1.12 MPa, the attenuation from 504 to 1520 dB m-1, and the decreasing of wave velocity from 1516 m s-1 to 1441 m s-1. The increasing of wood shavings up to 20% caused the increasing of wave velocity from 1481 to 1545 m s-1, the attenuation from 504 to 1,108 dBm-1, and the decreasing of density from 975 to 869 kg m-3.

Bahan olah karet sebagian besar terbentuk koagulum dan berasal dari perkebunan rakyat. Penilaian mutunya secara umum dilakukan subyektif melalui pengamatan visual untuk penentuan kader karet kering, kadar air dan kadar kotoran. Metode ultrasonic, sebagai metode yang bersifat obyektif dan tidak merusak, diharapkan dapat dijadikan metode alternative untuk evaluasi mutu koagulum.