No abstract

Determination of melt composition and/or morphology by fast, reliable and accurate in‐line methods is highly desired in polymer industry. In‐line spectroscopic methods like near infrared (NIR), Raman or ultrasonic spectroscopy are such reliable methods for process control without time consuming sampling and off‐line analytics. As the number of in‐line techniques available is increasing, it becomes increasingly difficult for manufacturers and plastic processors to choose the right method or combination of methods for their needs and to keep track of the growing amount of information. Therefore, we combined different in‐line techniques in one slit die in order to compare their potential for various systems such as composites and blends. One installation consists of a combination of NIR and Raman spectroscopy, rheometry and ultrasonic measurements. Another installation bases on a slit die developed for rheology which was equipped with dielectric and ultrasonic sensors. The results of the applied in‐line methods are compared and the specific advantages and drawbacks are discussed.

The paper reviews the state-of-the-art of in-line and on-line monitoring during polymer melt processing by compounding, extrusion and injection moulding. Different spectroscopic and scattering techniques as well as conductivity and viscosity measurements are reviewed and compared concerning their potential for different process applications. In addition to information on chemical composition and state of the process, the in situ detection of morphology, which is of specific interest for multiphase polymer systems such as polymer composites and polymer blends, is described in detail. For these systems, the product properties strongly depend on the phase or filler morphology created during processing. Examples for optical (UV/vis, NIR) and ultrasonic attenuation spectra recorded during extrusion are given, which were found to be sensitive to the chemical composition as well as to size and degree of dispersion of micro or nanofillers in the polymer matrix. By small-angle light scattering experiments, process-induced structures were detected in blends of incompatible polymers during compounding. Using conductivity measurements during extrusion, the influence of processing conditions on the electrical conductivity of polymer melts with conductive fillers (carbon black or carbon nanotubes) was monitored.

The pressure dependence of the order-to-disorder transition in a polystyrene/polyisoprene (PS/PI) (M ) 17 000) and a polystyrene/poly(methylphenylsiloxane) (PS/PMPS) (M ) 29 600) diblock copolymer of symmetric composition has been studied using small-angle X-ray scattering. The orderdisorder transition is investigated with a temperature resolution of 0.1 K. The transition can be resolved in a two-step process with a roughening of the interface preceding the breakdown of the lamellar order. For both systems a pressure-induced ordering transition is observed at constant temperature. The application of small pressures leads to a decrease of the transition temperature for both systems. High pressure shows the opposite effect. The minimum transition temperature for the PS/PI is located around p ) 8 bar.

The phase separation kinetics of fluid mixtures of polyethylene glycol/polypropylene glycol (a system with an upper critical mixing point) is studied after a pressure jump from the homogeneous one-phase region into the two-phase region of the phase diagram. The growth of the emerging domains of the coexisting phases is observed by small angle laser light scattering. In additional measurements the pressure dependence of the phase separation temperature is analyzed. In the kinetic experiments the time-dependent structure function is detected for a mixture with near-critical as well as for a mixture with off-critical composition. For the near-critical mixture an increase of the maximum of the scattering intensity with time has been found, which qualitatively is typical for the intermediate to late stages of spinodal decomposition. A closer analysis of the late stages reveals two maxima in the structure factor with their own set of growth exponents for the scattering vector and for the intensity. The data of the low q maximum are compatible with a two-dimensional growth process which is interpreted as a demixing process in a wetting layer. The data of the high q maximum are according to a three-dimensional process. It is assumed that this maximum reflects the demixing process in the bulk phase. The values of the three-dimensional growth exponents, which are considered to be late stage values, are not compatible with observations on other fluid systems but are close to those for solid systems or, in general, for systems with suppressed hydrodynamic interactions. For the mixture with an off-critical composition the structure function remains constant for larger times (pinning effect). The occurrence of a pinning effect in samples of relatively low molecular weight Mw (Mw⩽1019 g/mol) and the apparently suppressed hydrodynamic interactions in a fluid sample are explained with specific interactions caused by hydrogen bonding (i.e., transient entanglement or a dynamic network).