Extruder reactive-processing

The competition at 200°C between an aliphatic and an aromatic amine toward the formation of an imide is a very selective reaction (Fig. 5.1) for the formation of an aliphatic imide.141 This reaction suggests that the reactive processing in extruder, for example, could be used to transform a melt-processable polyimide with an oligomer end capped with an aliphatic amine. In order to get a perfecdy alternate block polyimide-block siloxane, Rogers et al. used low-temperature transimidization.142 An oligomeric aromatic imide was end capped... 

In the first stage of the investigation the catalyst can be considered in the form of powder in order to derive intrinsic transient kinetics of all the relevant reactive processes. To this purpose, dynamic reactive experiments can be performed in a simple tubular fixed-bed microreactor over small quantities (50-200 mg) of finely powdered catalyst in principle, this guarantees negligible transport limitations and more controlled conditions (e.g. isothermal catalyst bed), hence enabling a direct estimation of intrinsic rate parameters by kinetic fit. Internal diffusion limitations are particularly relevant to the case of bulk (extruded) monolith catalysts, such as vanadium-based systems for NH3/urea SCR however, they... 

Figure 4.31. One-section single screw extruder used in reactive processing (for an explanation of the numbers see text).

Figure 4.33. Twin-screw extruder for reactive processing. Each screw consists of meshing (1) and compressive (2) inter changeable sections.

A possible design of an extruder for reactive processing is shown in Fig. 4.34.240 Two screws are installed on the same axis inside a common barrel 1 but they have independent drives. This design eliminates stagnation zones, where the extruder is obstructed by the polymeric product. Independent drives for both screws permits the choice of optimal rotation speeds, i. e., to synchronize the polymerization rate with the residence times of the reactive mass in both stages of the process. 

Reactive Processing in Counterrotating Twin Screw Extruders... 

The residence time characteristics in an extruder have a great influence on product quality, for instance when processing heat-sensitive products, in reactive processes, and in the case of dispersion and melting. As with all continuous processes, there is no precisely defined residence time in co-rotating twin screw extruders, but rather a residence time distribution. 

An early published example of reactive processing was a description of bulk polymerization of caprolactam in an extruder to give nylon-6.Intense activity in recent years, mostly in industrial laboratories and at extruder companies, has produced more than 600 patents and 60 published papers on the subject of... 

Reactive processing is limited to polymerization or chemical reactions of polymers in conventional singlescrew or twin-screw extruders, excluding processes in oscillatory kneaders, Banbury-type continuous mixers, or Diskpack equipment. Emphasis is placed on continuous processes that have been implemented commercially or that can serve as models for commercial purposes. 

These antioxidants include the hindered phenols and are considered to be most effective when the chain-carrying (propagation) radical is an -oxy radical such as alkyl peroxy, R02. Thus, in reactive processing, they would be expected to be of value in suppressing the oxidation reactions which can occur in the earlier zones of a reactive extruder. The chemistry of these systems has been studied in detail (Al-Malaika, 1989, Scott, 1993b), and it has been found in the case of hindered phenols that the effectiveness of these stabilizers is dependent on the chemistry of the oxidation product rather than the simple donor reaction of the phenol hydrogen atom to the propagating radical. 

To toughen PA, 2-5 wt% of either PO, elastomer, ionomer, acidified or epoxidized copolymer may be added. PA/PO blends of type (2) were developed to improve dimensional stability and to reduce water absorbency of PA. Alloying PA with PO reduces the rate of water migration to and from the blend, but not the inherent water absorption of PA [Utracki and Sammut, 1991, 1992]. The alloying is either a two- or three-step reactive process (1°) acidification of PO, (2°) preparation of a compatibilizer, and (3°) compounding PP, PA, and the compatibilizer. Usually, the reactive blending is carried out in a twin screw extruder [Nishio et al., 1990 Hu and Cartier, 1998], Since it may cause reduction of the blend crystallinity (thus performance), the extend must be optimized. The rigid PA/PP blends usually comprise PA PP =... 

For many years, CORI has been the universal compounder of choice. It operated at higher screw speeds with longer barrel than ICRR, advantageous especially for the reactive processing. However, during the last ten years or so, several manufacturers of these two types of extruders started to demonstrate that unbiased test results frequently show better performance of ICRR as far as the compound quality and the throughputs are concerned. Even at lower screw speed ICRR frequently outperformed CORI. This resulted in renewed interest in redesigning ICRR. Tables... 

Copolymerizations are powerful ways to produce polymers with speeifie properties with well defined strueture. However, they involve the costly modification of existing production facilities of polystyrenes. To satisfy small market niches, modified polystyrenes ean be obtained through grafting reactions by chemical reactions on a polymer melt in an extruder (reactive extrusion) to achieve functionalities on the polymeric chains. Thus, grafting reactions are the preferred methods to achieve functionality commercially because they are low cost alternatives to the eopolymerization processes despite low grafting efficieney. For example, polystyrenes have been grafted with brominated styrene to enhanee the flame resistance of polystyrenes, as shown in Reaction 13. 

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