Near infrared spectroscopy as an alternative method for rapid evaluation of toluene swell of natural rubber latex and its products

Abstract

Toluene swell or equilibrium swelling is universally used by rubber factories to measure the degree of crosslink of their compounded or prevulcanized latices at different stages of production. To apply near infrared spectroscopy for rapid and accurate quality control, spectral acquisition of prevulcanized latex, thin film and thick film was performed using a Fourier transform near infrared spectrometer in diffuse reflection mode across the wavenumber range of 12,500-3600 cm À1. For prevulcanized latex an effective model was developed using partial least squares regression with preprocessing (first derivative þ straight line subtraction method). The coefficient of determination (r 2), root mean square error of cross validation and bias of the validation set were 0.71, 3.93% and À0.005%, respectively. For the thin film model the r 2 , root mean square error of cross validation and bias were 0.65, 4.01% and À0.028%, respectively. Whereas for the thick film model the r 2 , root mean square error of cross validation and bias were 0.70, 4.00% and À0.006%, respectively. Three models including prevulcanized latex, thin film and thick film were validated by 23 unknown samples, providing standard error of prediction and bias of 5.357 and 2.494, 4.565 and 1.001 and 3.641 and À0.961%, respectively, for prevulcanized latex, thin film and thick film. The model developed for the thick film spectra gave the best results.

Classification of the Crosslink Density Level of Para Rubber Thick Film of Medical Glove by Using Near-Infrared Spectral Data

“…The studies by Lim and Sirisomboon of crosslink density of natural rubber film developed from prevulcanized latex model which was created by PLSR using the spectra scanned by FT-NIR spectrometer [ 3 ], the natural rubber thin film model provided the r 2 , root mean square error of cross validation and bias of 0.65, 4.01%TSI and −0.028%TSI, respectively, using the wavenumber range of 6102–5446.3 cm −1 and 4428–4242.9 cm −1 (1639–1836 nm (included natural rubber absorption bands) and 2258–2357 nm), whereas for the natural rubber thick film model the r 2 , root mean square error of cross validation and bias were 0.70, 4.00%TSI and −0.006%TSI, respectively, using the wavenumber range of 6102–4597.7 cm −1 (1639–2175 nm (included natural rubber absorption bands)). By using the low-cost VIS/NIR diode array spectrometer in the wavelength range of 450–1000 nm using a fiber optic probe scanned on the thin and thick film, the models for crosslink density indicated by prevulcanisate relaxed modulus (PRM) had poor results, as indicated by the R 2 of calibration and RMSEC of 0.02 and 17.31 × 10 4 N/m 2 and 0.05 and 16.63 × 10 4 N/m 2 , respectively [ 43 ].…”

“…Toluene swell index (TSI) or equilibrium swelling values are determined by immersing a latex film in the solvent, usually toluene, and measuring the increase in linear dimensions at equilibrium [ 3 ]. TSI is directly related to the crosslink density, but the procedure is relatively slow and requires toluene, a hazardous chemical, and the total time for the test, including drying of the film, is about 1 h or more [ 3 ].…”

Near infrared spectroscopy and machine learning classifier of crosslink density level of prevulcanized natural rubber latex

“…The toluene swell method is normally used for measuring the crosslink density of compounded or PV latex and toluene swell product. Analysis of toluene swell followed [3]. The percentage toluene swell was calculated from equation (1).…”

“…NIR spectroscopy have been studied for feasibility determination of cross link density of rubber latex such as cross link density determined by prevulcanisate relaxed modulus (PRM) test [1] using NIR Fourier Transform spectrometer (FT-NIR) and [2] using low cost spectrometer (LCS) and toluene swell test [3] using FT-NIR, when reference methods has been used in rubber latex factory. For prevulcanized latex an effective model was developed using partial least squares regression with preprocessing (first derivative + straight line subtraction method).…”

Designing and controlling the Ni2+-activated (Zn, Mg)Al2O4 spinel solid-solution for phosphor-converted broadband near-infrared illumination

“…The changes in optical signals such as absorption or reflection triggered by near-infrared light (NIR, 900-2000 nm) irradiating the surface of the material can reveal the inherent structural information of a particular material, and the wavelength distribution of the reflected light collected by the detector can be used to detect the presence or quantity of certain composition and are widely used in the fields of food industry, agriculture, and medicine. [1][2][3][4][5][6][7][8] Currently, the devices for NIR spectrometry are moving toward miniaturization and portability. 9,10 Therefore, the new generation of NIR lighting sources should have the following features: smooth and continuous spectral characteristics, ultrawide coverage, easy adjustability, small size, long life, and flexible packaging.…”