Manufacturing processes commonly used in conjunction with the production of epoxies include filament winding, pultrusion, infusion molding, resin transfer molding (RTM), vacuum assisted RTM (VARTM), and wet lay-up or vacuum bag techniques.
Polyoxyalkylene amines, or “polyetheramines” as they are sometimes called, are useful as curing agents in epoxy systems to improve flexibility, and to lengthen working time in the manufacture of fiber-reinforced composites. The “working time” is defined as the time period between when the reactive components of the epoxy resin are first mixed with one another and when the mixture is no longer suitable for processing. During the working time, the resin or article containing the resin remains in a pourable, flexible, pliable or otherwise moldable form.
Lower functionality polyetheramines, such as those based on diols and triols, and including commercial products such as the JEFFAMINE® brand amines, have been utilized as epoxy curing agents. Increasing the molecular weight of these lower functional amines yields lower glass transition temperatures (Tg) when used to polymerize standard, liquid epoxy resins, such as those predominantly containing the diglycidyl ether of bisphenol A. Increasing the molecular weight of lower functionality polyetheramines also leads towards undesirably long gel times and related problems such as the reaction of the amines with carbon dioxide and water in the case of surfaces exposed to the atmosphere during curing. The oily surface phenomenon that results from this exposure is often referred to as “amine blushing.”
On the other hand, high functionality, lower molecular weight amines have shortened gel times and higher exotherm temperatures because of the higher concentration of reactive groups. Often, higher exotherm temperatures limit the cross-sectional thicknesses of parts that may be molded due to the onset of thermal degradation within the thick sections. Such thermal degradation may be manifested as charring or may result in undesirable mechanical properties.