Reactive extrusion determination

No IR absorption bands of Rf-COOH and Rf-CO-F are detectable in IR spectra of the PTFE PA-6 product after reactive extrusion. Additionally, spectra of an unirradiated PTFE (black line) and an irradiated PTFE (1,000 kGy) (red line) are shown for comparison in Fig. 8. All spectra were normalised to the CF2 band at 2,365 cm IR spectroscopy can be used for the determination of the turnover of carboxylic acid groups after reactive extrusion. 

The first results of degradation of polyamides shown above are based on fast melt modification reactions. The determination of the gross kinetical reaction rate was impossible. Only a very vague estimation could be made during reactive extrusion processes. 

In reactive processing, such as reactive extrusion of thermoplastics, the use of DSC may be seen in determining the stability of the polymer formulation by measuring the oxidation induction time (OIT) (Bair, 1997). This is an isothermal experiment in the presence of air... 

For the tests of preparing dynamic vulcanizates in the continuous process of reactive extrusion a twin-screw mixer-extruder DSK 42/6D manufactured by Brabender was used. The vulcanizates were produced dynamically in the process of one-stage or two-stage extrusion process, setting the favorable operating parameters for the device, which had been determined based on multiple tests distribution of temperatures in each heating area... 

The reaction diagram for a single component reaction, as shown in Fig. 7.2 has two adjustable parameters, the amount of initiator and therefore the radical concentration and the temperature, all other parameters depend on changes in these two primary variables (2). Due to the deeomposition kinetics, the radical concentration depends of course also on the temperature of the reacting mixture. In reactive extrusion this temperature is affected by the wall temperature and the heat transfer coefficient but also by the reaction velocity, which, in turn, is influenced by the radical concentration and the temperature. The reaction velocity, together with the residence time determines the conversion, which has its effect on the viscosity of the reacting mixture. The viscosity is also affected by the average... 

During all experiments the stability of the process was checked by measuring the throughput leaving the die at regular intervals and comparing it to the amount of material fed to the extruder. This way it could be determined whether the reactive extrusion process reached a stable situation for every adjustment of throughput and screw rotation rate or not. 

A more accurate method is the direct determination of the reactivity ratios. In literature, a number of studies is reported, where several copolymerizations are studied. Unfortunately, many of these studies are performed at low temperatures and therefore not applicable to reactive extrusion. 

According to Jakisch et al. [79], FTIR spectroscopy is the preferred method for in-line investigation polymer melts and polymer melt reac-tions/kinetics, allowing quantitative determination of all components. FTIR analysis of compound melts enables additive level stability and effectiveness to be observed over multiple extrusion passes. The use of the ATR principle is suitable for in-line analysis of polymer melts in the extruder. The exit of the extruder was equipped with an on-line IR transmission process control system consisting of a 150 /um thick ZnSe melt flow cell. Characteristics of such systems have been described [71,74]. Another process spectrometer with an in situ ZnSe-ATR dipper probe was mounted at different positions in the extruder. For in-line ATR the residence time plays no role. Only the first 5 /xm (corresponding to the penetration depth of the IR radiation) are examined. Minor components are thus detected with difficulty. Jakisch et al. [79] monitored the conversion of styrene-maleic anhydride copolymers (SMA) with fatty amines into styrene-maleimide copolymer (SMI) during reactive extrusion by means of FTIR. In principle, both mid-IR and near-IR spectroscopy with ATR, transmission and diffuse reflectance probes are suitable for quantitative on- and in-line process analysis of multicomponent polymer... 

The process time is determined by the technical parameters heatup, application, and cooling It is very short compared to the process times of reactive adhesives. Processing is done with so-called sticks, spreadable powders, extrusions, nets, or films. Hotmelt adhesives in the form of films in particular are among the heat-activated or heat seal adhesives. In film and textile composites the term used is laminate adhesives. 

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