Measurement of cross link densities of prevulcanized natural rubber latex and latex products using low-cost near infrared spectrometer

Abstract The objective of this project is to use the four models to predict the crosslink densities based on reference method of PRM 300% using portable low-cost visible and shortwave near-infrared (Vis/SW-NIR) spectrometer across wavelengths of 350-1100 nm. The degrees of crosslink reflect on the properties of the prevulcanized (PV) latices and latex products produced and hence useful for quality control in the process of production. The four models were optimized using partial least squares regression (PLSR) that the spectra were collected from PV, PV50, thin and thick films. The use of thin and thick films was to emulate the latex products that used the PV latices. The results showed that there were almost no difference in the PV and PV50 models by the coefficient of determination (R2) and root mean square error of calibration (RMSEC) of 0.70 and 9.04 × 104 N/m2 and 0.75 and 8.59 × 104 N/m2, respectively. Among the four models, thin and thick film models had poor results indicated by the coefficient of determination (R2) and root mean square error of calibration (RMSEC) of 0.02 and 17.31 × 104 N/m2 and 0.05 and 16.63 × 104 N/m2, respectively. Based on these results, only the models of prevulcanized (PV) latices could be used for quality assessment. Hence the Vis/SW-NIR spectrometer could be a cheap alternative for crosslink density determination of PV latices and would be a beneficial tool for monitoring the process of vulcanization in the rubber industry.