Use of hygrothermal decomposed polyester-urethane waste for the impact modification of epoxy resins

Hygrothermally decomposed polyurethane (HD-PUR) of a polyester type was use d as an impact modifier in tri- and tetrafunctional epoxy (EP) resins. Betw een 5 and 80 wt % of the PUR modifier was added to the EP prior to its cros slinking with a diamine compound (diaminodiphenyl sulfone, DDS). The mean m olecular weight between crosslinks (M-c) was determined from the rubbery pl ateau modulus of the dynamic mechanical thermal analysis (DMTA) spectra. Th e fracture toughness (K-c) and energy (G(c)) of the modified resins were de termined on static-loaded compact tension (CT) specimens at ambient tempera ture. The change in the K-c and G(c) as a function of M-c followed the pred iction of the rubber elasticity theory. The efficiency of the HD-PUR modifi er was compared with that of a carboxyl-terminated liquid nitrile rubber (C TBN). Attempts were also made to improve the functionality of the modifier by hygrothermal decomposition of PUR in the presence of glycine and E-capro lactam, respectively. DMTA and fractographic results showed that HD-PUR fun ctions as an active diluent and a phase-separating additive at the same tim e. As HD-PUR can be regarded as an amine-functionalized rubber, it was used as the hardener (by replacing DDS) in some EP formulations. (C) 2000 John Wiley & Sons, Inc.