DEVELOPMENT OF ON-LINE SENSOR FOR PROPERTIES OF MOLTEN POLYMER USING NEAR INFRARED SPECTROSCOPY

点击翻译按钮获取中文摘要

Two new on-line sensors using near infrared (NIR) spectroscopy are developed in this project. One is for monitoring density of molten polyethylene polymer and the other is for monitoring CO2 concentration dissolved in the molten polymers.Density and melt index are two key properties in grading commercial polyolefin polymers. For quality assurance, these properties must be controlled as accurately as possible in the production plant. However, the lack of suitable in-line sensors for these properties makes feedback quality control difficult. In this project, an in-line density sensor using near infrared (NIR) spectroscopy was developed. The NIR spectra of molten pokyethylene in flow are collected by a fiber-optic device attached to a single screw extruder. By the ratio of the absorption intensity at 1170 nm to that at 1213 nm, the densities of 14 grades of polyethylene were successfully measured.By installing the same NIR probe at the foaming extruder, where carbon dioxide is introduced to make polymeric foams, concentration of carbon dioxide dissolved into the molten polymer could be measured on-line from the NIR spectra. The calibration curve relating the absorbance spectrum at 2019 nm to the dissolved gas concentration is derived so as to infer dissolved CO2 gas concentration form measured NIR spectra. Experimental reults show the developed sensor can successfully estimate dissolved CO2 concentration in at most three kinds of polymer, polyethylene, polypropylene and polybuthylene succinate.Those two developments illustrate that the NIR on-line sensing technique is among the more promising method for quality control of polymer production processes.