Near infrared spectroscopy as a tool for in-line control of process and material properties of PLA biopolymer

In the field of polymer processing NIR spectroscopy has been increasingly applied for an on-/in-line monitoring mainly at lab scale process development but also for production of high value materials. In this paper the bio-polymer polylactide (PLA) was investigated by NIRS in the range of 1.2 to 2.4 μm in order to identify additives like nanofil® and nano titanium oxide. A twin screw extruder (Haake Polylab PTW 16) was used to extrude polymer pellets mixed with the additives. The optical sensor probes (glass fibers) were placed between screw and nozzle to achieve a good optical throughput and to withstand typical temperature and pressure conditions during the extrusion (up to 220◦ C and a few 10 MPa). The on-line NIR spectroscopy enabled a real time information which might be used for process control or feeding control on the compound characteristics continuously. The chemometric data evaluation was able to quantify the measured values, especially the content of the additives in the compounds. The established statistical models predicted the actual values with high correlation coefficients (> 0.99). The additives altered viscosity of the melt and mechanical properties (Young´s modulus) of injection moulded test samples of the compound.