Polymer reactive-processing

The modern discipline of Materials Science and Engineering can be described as a search for experimental and theoretical relations between a material s processing, its resulting microstructure, and the properties arising from that microstructure. These relations are often complicated, and it is usually difficult to obtain closed-form solutions for them. For that reason, it is often attractive to supplement experimental work in this area with numerical simulations. During the past several years, we have developed a general finite element computer model which is able to capture the essential aspects of a variety of nonisothermal and reactive polymer processing operations. This "flow code" has been Implemented on a number of computer systems of various sizes, and a PC-compatible version is available on request. This paper is intended to outline the fundamentals which underlie this code, and to present some simple but illustrative examples of its use. 

Reactive polymer processing that produces polymer monoliths by low-pressure injection and mixing of low viscosity precursors into moulds. 

Note 3 Reaction injection moulding and reinforced reaction injection moulding are types of reactive polymer processing. 

Reactive polymer processing modifies or functionalizes the macromolecular structure of reactor polymers, via chemical reactions, which take place in polymer processing equipment after the polymer is brought to its molten state. The processing equipment then takes on an additional attribute, that of a reactor, which is natural since such equipment is uniquely able to rapidly and efficiently melt and distributively mix reactants into the very viscous molten polymers. The operation is shown schematically in Fig. 1.3. 

Fig. 1.9 Conceptual breakdown of polymer compounding, blending, and reactive polymer processing (27). Designer pellets are processed in extruders or injection molding machines to form products, with the possibility of further structuring or destructuring .

Classes of Polymer Chain Modification Reactions, Carried out in Reactive Polymer Processing Equipment, 604... 

Mixing Considerations in Multicomponent Miscible Reactive Polymer Processing Systems, 623... 

The equipment in which reactive polymer processing is carried out, is in fact a chemical reactor. The performance, design, analysis, and control of such reactors have been dealt... 

CLASSES OF POLYMER CHAIN MODIFICATION REACTIONS, CARRIED OUT IN REACTIVE POLYMER PROCESSING EQUIPMENT... 

There are many polymer chain modification reactions of different types that have been carried out on polymer melts processed in single and twin rotor extruders. This activity, (4-6) in the analysis of polymerization reactors, driven by market forces seeking to create value-added polymers from commodity resins, started in the mid-1960s in industrial research laboratories (7). Indeed much of the early work is to be found in the patent literature.1 Although in recent times more publications, both industrial and academic can be found in the open literature, there is still a good deal of industrial secrecy, because the products of reactive polymer processing are of significant commercial value to industry. Below we will deal briefly with two important examples of such reactions. 

Reactive polymer processing has been used extensively in the manufacture of carboxyl-containing polymers (8). The carboxylation of unsaturated polymers with maleic anhydride (MAH) proceeds through the ene reaction where succinic anhydride is attached to the polymer with a shift of the double bond to the adjacent site. 

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. 

Ryu et al. (37) and Xanthos et al. (38) prepared thin films of sintered PP, 200-300 micron diameter, precoated at room temperature with POX E . The films were allowed to react in a constant-temperature oven and samples were withdrawn and analyzed to determine Mw and MWD. It was found that the reduction rates of the M v and MWD became essentially zero after six to seven half-lives of POX E as measured in dodecane. The conclusion is, since there is no mixing during reaction, the diffusion rate of the POX coating onto the PP particulates is not rate controlling, that is, CR-PP for those coated 200-300-pm PP powder particulates is not diffusion controlled. In reactive processing one should strive for process conditions and reaction kinetics where the reactive polymer processing environment is uniform, resulting in uniform product. We discuss this in Sections 11.2 and 11.3. 

Chain addition polymerizations have a typical value of e 4 x 10-2, and for such batch reactions re increase 106 times from 0 = 10 1 to 0 = 10, with the plateau region at 0 values that are 1010 times higher. It is for this reason that chain addition polymerization reactions, although experimentally studied, as with methyl methacrylate (41,42), are rarely carried out in reactive polymer processing equipment. 

MIXING CONSIDERATIONS IN MULTICOMPONENT MISCIBLE REACTIVE POLYMER PROCESSING SYSTEMS... 

In this example of model reactive polymer processing of two immiscible blend components, as with Example 11.1, we have three characteristic process times tD,, and the time to increase the interfacial area, all affecting the RME results. This example of stacked miscible layers is appealing because of the simple and direct connection between the interfacial layer and the stress required to stretch the multilayer sample. In Example 11.1 the initially segregated samples do create with time at 270°C an interfacial layer around each PET particulate, but the torsional dynamic steady deformation torques can not be simply related to the thickness of the interfacial layer, <5/. However, the initially segregated morphology of the powder samples of Example 11.1 are more representative of real particulate blend reaction systems. 

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