Epoxy formulations, processing equipment

Epoxy resins are an important class of polymers used for reactive processing. However, it is rather difficult to find a formulation which provides sufficiently high process rates to be useful in the modern processing equipment used for the RIM-process. 

Castable polyurethanes can be formulated to contain conventional crosslinks, as in rubbers and epoxies. They may be either in the form of the liquid system or in the form that requires conventional rubber-processing equipment. The introduction of conventional cross-links will break the formation of the hydrogen bonds and normally reduce the hardness of the finished product. In very hard grades, they are used to increase the compression resistance. 

The following section looks at the processes and equipment commonly used in the compounding of epoxy adhesive systems. Since they can be utilized by either the formulator or the end user, there will be no strict division of the discussion by user. Hazards and safety issues related to these materials and processes are discussed somewhat in this chapter, but a more thorough discussion is found in Chap. 18. Test methods, quality control processes, and standards that are commonly used at the formulation level are addressed in Chaps. 19 and 20. 

Chapters 17 through 20 describe the various processes and equipment employed in the formulation or end use of epoxy adhesives. Health and safety issues regarding the use of these materials are discussed. The importance of quality control methodologies and specification preparation is also noted. Finally, test methods that are commonly used by both the formulator and the end user are identified. 

VE polyurethane resins have mechanical properties similar or superior to those of conventional VE and epoxies. Characteristics include a heat distortion temperature of 120C (248F). Ultimate elongation of an unreinforced molding compound without fillers is 5.5% tensile strength is 80 MPa and flexural strength 150 MPa. The resins can be custom-formulated. Applications include customized automobile parts, recreational vehicles, outdoor equipment, tubs/showers and electrical parts. The resins are suitable for standard molding processes some were specifically developed for pultrusion, RIM, foam, adhesive, and polymer concrete applications. 

The vinyl ester fimctionality of the epoxy vinyl esters provides outstanding hydrolysis and chemical resistance properties, in addition to the inherent thermal resistance and toughness properties of the epoxy backbone. These attributes have made epoxy vinyl esters a material of choice in demanding structural composite applications such as corrosive chemicals storage tanks, pipes, and ancillary equipment for chemical processing. Other applications include automotive valve covers and oil pans, boats, and pultruded construction parts. Significant efforts have been devoted to improve toughness and to reduce levels of styrene in epoxy vinyl ester formulations because of environmental concerns. In addition to Dow Chemical, other major suppliers of epoxy vinyl esters include Ashland, AOC, DSM, Interplastic, and Reichhold (DIG). 

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