Polymerization processes reactive extrusion

Because of the accuracy of the calculation method only an estimation of the cost comparison can be made, but from the results of these calculations it can be seen that reactive extrusion can be competitive with conventional processes. Reactive extrusion with one kneader with a diameter of 200 mm is economically more attractive when compared to a batchwise solution polymerization for a capacity of 5000t/year. When calculated with the... 

Reactive extruders and extrusion dies of different designs can be easily included in standard technological scheme of polymer production plants, such as those for polycaproamide synthesis, as shown in Fig. 4.39. In this case, a reactive material premixed in a tank 1 is fed into a static device 2 for prepolymerization, where part of the polymerization process takes place. Then the reactive mixture enters the extruder-reactor 3. The necessary temperature distribution is maintained along the extruder. Transfer of the reactive mass proceeds by a system of two coaxial screws mounted in series in a common barrel. Controlling the relative rotation speed of both screws provides the necessary residence time for the reactive mass in the extrader, so that the material reaching the outlet section of the die is a finished polymer. 

Reactive extrusion takes place when the twin screw system is designed to incorporate one or more chemical reactions during the process, such as grafting or even polymerization. Grafting is the process of attaching pendant molecules onto the backbone of a polymer chain. For example, a small concentration of maleic anhydride can be incorporated into polypropylene to make the... 

The ring-opening polymerization of PLA is traditionally realized during a discontinuous batch-process, but recently continuous processes have been developed. As another alternative to continuous polymerization processes the reactive extrusion of PLA was realized. By combining Lewis-acid catalysts with cocatalysts it is possible to increase the catalytic activity and to reduce the polymerization time [18]. 

Xanthos, M. (1992) Process analysis from reaction fundamentals.Examples of polymerization and controlled degradation in extruders, in Xanthos, M. (Ed.) Reactive Extrusion Principles and Practice, Munich Hanser-Verlag. 

The term reactive processing is used to describe a polymer processing that involves chemical reactions. In principle, any processing operation can be conducted as a reactive process, viz. reactive injection molding (RIM). However, most often the term refers to reactive extrusion, and in particular, to the reactive compatibilization of immiscible polymer blends, usually conducted in a TSE. During the last 50 years, the latter machines have been used as chemical reactors for the polymerization, depolymerization (chemical recycling), polymer modification and compatibilization [Brown, 1992, Xanthos, 1992 Utracki, 1989, 1991, 1994, 1997]. 

Generally, polymer nanocomposites can be obtained through two routes the first one is the polymerization of monomers in contact with the exfoliated clay and the second one uses existing transformation processes to produce nanocomposites, for example, by a reactive extrusion. There are, however, problems present due to the lack of affinity of the clay-polymer system because of the hydrophilic character of the particles. It is then necessary to treat the clay chemically to increase its affinity with the polymer matrix. This constitutes another whole area of research in the nanocomposites production. 

Figure 11.3 Processing and screw concept used for reactive extrusion polymerization of polylactide. Reproduced from ref. 90 with permission of Elsevier.

Table 11.2 Comparison of two types of poly-L-lactide potymerized in glass ampoule bulk batch polymerization technology and using a single-stage reactive extrusion potymerization process, both catalyzed with an equimolar Sn(0ct]2 TPP complex with an initial monomer to tin molar ratio of 5000 at 180°C...

Table 11.3 Influence of different processing parameters during reactive extrusion polymerization on the resulting molecular polymer parameters...

Schmack et al. [126] spun PLA fibers through the reactive extrusion polymerization of L-lactide (92 wt%) and meso-lactide (8 wt%). In many potential textile technological applications (e.g., for nonwoven materials) the fiber forming process is of general importance. An effective polymer synthesis requires also an effective spinning process to reduce the still high cost of the PLA fibers compared with those of established synthetic fibers. 

Table 11.4 Influence of the addition of hydroxyl terminated oligo- -caprolactone (OCL, M = 4000 g/mol,<5 = 1.5] and polyethylene glycol [PEG, Mn = 1500 g/mol] on the polymerization of PLLA in a reactive extrusion process...

Gallos et al. [6] synthesized stereocomplexed polylactide using reactive extrusion process. The stereocomplexed PLA obtained in a two-step polymerization of L-lactide and D-lactide process to yield poly-L,D-lactic acid multiblocks. In the first step, DSM Micro 15... 

A new process has been developed for the production of PLA using reactive extrusion polymerization based on a new catalytic system, which not only enhances the ROP kinetics of L-lactide but also suppresses side and degradation reactions such as intermole-cular transesterification reactions. Co-rotating closely intermeshing twin-screw extruders have often been used for polymerization reactions, but in any case, the reaction time was sufficiently smaller than the residence time in the extruder. In the case of ROP of lactide, the extraordinary effect of triphenylphosphine on the efficiency of Sn[Oct)2 as a catalyst was the key point to ensure further enhancement of the polymerization reaction. Thus, it was feasible... 

Jacobsen et al. reported a new catalytic system and a reactive extrusion polymerization process, which can be used to produce PLA continuously in larger quantities and at lower costs than before. This extrusion polymerization process has been developed and tested with laboratory scale machines and the possibilities to extend this polymerization process to lactide-based block copolymers have been investigated [11]. 

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. 

To make an economically viable PLA, Jacobsen et al. [21] developed a continuous one-stage process based on reactive extrusion with a twin-screw extruder. This technique requires that the bulk polymerization be close to completion within a very short time (5—7 min), which is predetermined by the residence time in the extruder. 

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