Pattara Aiyarak and Piti Sunheem

pp. 713 - 718

Abstract

An accurate, quick and practical method for measuring the dry rubber content (DRC) in natural rubber latex is
proposed and investigated experimentally, based on microwaves. The concept exploits the microwave absorption of water
molecules to infer the DRC. However, various design aspects had to be experimentally investigated. In this study, rectangular
waveguide antennae were used for microwave transmission. The latex was placed between two antennae, and the signal was
analyzed by a vector network analyzer (VNA). A calibration curve was fitted with least squares regression for sample DRCs
ranging from 10.26% to 60.63%. The best linearity with 0.9996 correlation between attenuation and DRC was obtained at 2.36
GHz. To validate this measurement technique, 17 fresh local rubber latex samples were measured both with the slow reference
gravimetric determination of DRC that involves oven drying, and with the microwave transmission technique. The measurements had a 0.43 mean error in %DRC, and a 0.9047 correlation to the gravimetric DRC. The study supports potential design
and construction of a prototype DRC measurement device for field use.

Keywords

• dry rubber content
• latex
• microwave
• waveguide