Novel phosphorus-containing hardeners with tailored chemical structures for epoxy resins: Synthesis and cured resin properties

• Published in: Journal of applied polymer science Vol. 105; no. 5; pp. 2744 - 2759
• Main Authors: Perez, R. M., Sandler, J. K. W., Altstädt, V., Hoffmann, T., Pospiech, D., Artner, J., Ciesielski, M., Döring, M., Balabanovich, A. I., Knoll, U., Braun, U., Schartel, B.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 05.09.2007; Wiley
• Subjects: Applied sciences; Chemical properties; Composites; Exact sciences and technology; flame retardance; Forms of application and semi-finished materials; fracture toughness; organo-phosphorus compounds; Polymer industry, paints, wood; Properties and testing; Technology of polymers; Fiber reinforced material; Curing agent; Epoxy resin; Organic phosphinate; Mechanical properties; Flame retardant; Organic phosphonate; Curing (plastics); Experimental study; Mineral fiber; Property processing relationship; Composite material; Phosphorus polymer; Fracture toughness; Thermal properties; organo-phosphorus compounds; Tertiary phosphine oxide; flame retardance; Flammability; Organic phosphate; Kinetics; Organo non metallic polymer; Carbon fiber
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.26537

A comparative evaluation of systematically tailored chemical structures of various phosphorus‐containing aminic hardeners for epoxy resins was carried out. In particular, the effect of the oxidation state of the phosphorus in the hardener molecule on the curing behavior, the mechanical, thermomechanical, and hot‐wet properties of a cured bifunctional bisphenol‐A based thermoset is discussed. Particular attention is paid to the comparative pyrolysis of neat cured epoxy resins containing phosphine oxide, phosphinate, phosphonate, and phosphate (with a phosphorus content of about 2.6 wt %) and of the fire behavior of their corresponding carbon fiber‐reinforced composites. Comparatively faster curing thermosetting system with an enhanced flame retardancy and adequate processing behavior can be formulated by taking advantage of the higher reactivity of the phosphorus‐modified hardeners. For example, a combination of the high reactivity and of induced secondary crosslinking reactions leads to a comparatively high Tg when curing the epoxy using a substoichiometric amount of the phosphinate‐based hardener. The overall mechanical performance of the materials cured with the phosphorus‐containing hardeners is comparable to that of a 4,4′‐DDS‐cured reference system. While the various phosphorus‐containing hardeners in general provide the epoxy‐based matrix with enhanced flame retardancy properties, it is the flame inhibition in the gas phase especially that determines the improvement in fire retardancy of carbon fiber‐reinforced composites. In summary, the present study provides an important contribution towards developing a better understanding of the potential use of such phosphorus‐containing compounds to provide the composite matrix with sufficient flame retardancy while simultaneously maintaining its overall mechanical performance on a suitable level. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007