Interpenetrating polymer networks based on castor oil polyurethane/cellulose derivatives and polyacrylic acid

Castor oil, 2,4-tolylene diisocyanate (2,4 TDI), cellulose acetate, and hydroxiethyl cell u- lose, based polyurethane (PU) - polyacrylic acid (PAA) sequential interpenetrating polymer networks (IPN's) were synthesized. PU's were prepared by reaction of hydroxyl groups from castor oil, and ce l- lulose acetate or hydroxiethyl cellulose with 2,4 T DI, using dibutyl tin dilaurate (DBDTL) as catalyst. PU's were swollen in acrylic acid monomer solution and subsequently polymerized by radical polymeri- zation initiated with 4,4-azobis(4-cyanovaleric aci d) (ACVA), and N,N '-methylenebis acrylamide (NNMBA) as crosslinking agent. Series of three PU/PAA ratios (75/25, 50/50, 25/75) were prepared. Viscoelastic properties were studied by means of dynamic mechanical analysis (DMA), showing a maximum modulus for IPN with 25% PAA content. Tan δ curve showed two main peaks, and γ γ γ γ relaxa- tion which is due to lateral chains of PU, suggesti ng phase separation. The existence of two T g in each IPN was also confirmed by differential scanning calorimeter DSC). Morphology of samples was ob- served using a scanning electron microscope (SEM), which revealed different fracture surfaces between the compatible and incompatible PU/PAA ratios studied. Fractures were decreasing to turn into roughness surfaces when the PAA was increasing within the IPN's.