Twin screw extruders reactive processing

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. 

Homopolymers and copolymers from amido-sulfonic acid or salt containing monomers can be prepared by reactive extrusion, preferably in a twin screw extruder [1660]. The process produces a solid polymer. Copolymers of acrylamide, N-vinyl-2-pyrrolidone, and sodium-2-acrylamido-2-methyl-propane sulfonate have been proposed to be active as fluid loss agents. Another component of the formulations is the sodium salt of naphthalene formaldehyde sulfonate [207]. The fluid loss additive is mixed with hydraulic cements in suitable amounts. 

SAN can be modified, for example by grafting. For example, maleic anhydride (MA) can be grafted onto SAN. This process occurs preferably in a twin-screw extruder by reactive extrusion. An advantage of reactive extrusion is the absence of solvent as the reaction... 

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

Reactive Processing in Counterrotating Twin Screw Extruders... 

Recalling the profound differences in the melting mechanisms in SSEs and in corotating twin-screw extruders (Co-TSE) (Chapter 5), we see that the latter one creates all of the melt almost instantaneously, resulting in a very narrow melt age distribution, while in SSE the age distribution is very broad. Thus, Co-TSEs and twin rotor melting devices [e.g., continuous mixers (CMs)] are better suited to be reactors of polymer melts, as is reflected in the current industrial reactive polymer processing practice. 

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. 

The formation of compatibilizer frequently occurs by interfacial reaction of the modified polymers. An example is the use of maleic anhydride grafted to a polyolefin elastomer (EPM/EPM-g-MA) as the interfacial additive for reactive blending with a polyamide, nylon-6 (Van Duin et al., 2001), in a twin-screw extruder. It was found that the consumption of MA occurred rapidly and different blend morphologies were produced. However, it was found that the nylon-6 degraded during processing, due to the reaction of anhydride with the... 

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 =... 

The Use of Twin Screw Extruders in Reactive Polymer Processing... 

Numerous compatibilizers can be produced by grafting monomers (containing some kind of functional groups) in melt onto homopolymers and copolymers of olefins or their blends (25). Reactive extrusion (26) is a basic process for this when the twin-screw extruder is used as a reactor of continuous action (27). 

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... 

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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