Fabio L. Barcia

Synthesis and properties of epoxy resin modified with epoxy-terminated liquid polybutadiene

Abstract Epoxy resin networks have been modified with block copolymer of polybutadiene and bisphenol A diglycidyl ether (DGEBA)-based epoxy resin. Block copolymers prepared from isocyanate-terminated polybutadiene (NCOPBER) resulted in cured transparent epoxy networks with no discernible phase-separated morphology, as indicated by scanning electron microscopy. Epoxy resin modified with block copolymer derived from carboxyl-terminated polybutadiene (CPBER) presented an opaque aspect with dispersed rubber particle diameters in the range of 0.5–3μm. This value is substantially smaller than that found in epoxy matrix modified with hydroxyl-terminated polybutadiene. The different morphological characteristics observed in these modified systems were attributed to the different times to achieve the gelation (gel time) and also to the different structures of the block copolymers. The visual homogeneity of the NCOPBER block copolymer-modified network cannot be attributed to the presence of dissolved rubber, since the glass transition temperature of the epoxy matrix (determined from dynamic mechanical analysis) has not been substantially influenced by the presence of this block copolymer. The epoxy resin modified with the different block copolymers presented an improved impact resistance. The best mechanical performance in terms of flexural and tensile properties was achieved with the block copolymer derived from carboxyl-terminated polybutadiene, whereas a more flexible material has been obtained with NCOPBER block copolymer-modified network.

Characterization of nanostructured epoxy networks modified with isocyanate-terminated liquid polybutadiene

Polybutadiene-block-epoxy prepolymer (DGEBA-b-PBNCO) copolymers with multi-branched topological structure were prepared by reacting isocyanate-multifunctionalized liquid polybutadiene (PBNCO) with DGEBA prepolymer and used to develop nanostructured rubber-modified epoxy thermosets cured with triethylene-tetramine (TETA) as the aliphatic amine. The nanoscopic structure was obtained with the addition of as high as 20 phr of rubber component and successfully demonstrated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The glass transition temperature of the rubber-modified epoxy networks was slightly higher than the neat epoxy system. In addition, a unique combination of outstanding toughness and increased modulus and T(g) was achieved in these modified systems, which was attributed to the peculiar morphology associated with a strong interfacial adhesion imparted by the reaction between the isocyanate and hydroxyl groups present in the PBNCO and epoxy resin, respectively. The effect of the PBNCO on the gelation time of the epoxy/TETA system was investigated by rheological techniques. The NCO-functionalized polybutadiene decreased the gelation time, indicating an accelerating effect on the curing process, probably because of the urethane groups formed by the reaction between PBNCO and the epoxy resin during the PB-b-ER block copolymer preparation.

Estudo das Propriedades de Compósitos de Polianilina e Resina Epoxídica

The conductive composites of polyaniline (Pani) and epoxy resin were prepared by polymerization of aniline in the presence of epoxy resin, using a direct, one step in situ polymerization method. The polymerization of aniline was performed in an emulsion system comprising water and toluene containing epoxy resin in the presence of dodecylbenzene sulfonic acid, which acts as surfactant and a dopant for Pani. The electrical conductivity of Pani/ epoxy resin reached values as high as 2 x 10-3 S/cm at a Pani content corresponding of 7 wt% of Pani. The Pani content in the mixtures was calculated by means of elemental analysis. The relationships between glass transition temperature (Tg) and Pani.DBSA content obtained by two different cured methods were also investigated.

Composite materials based on modified epoxy resin and carbon fiber

Epoxy resin networks have been modified with block copolymer of polybutadiene and bisphenol A diglycidyl ether (DGEBA)-based on epoxy resin. The epoxy resin modified with carboxyl-terminated polybutadiene presented improved impact resistance and outstanding mechanical performance in terms of flexural and tensile properties because of the presence of rubber particles homogeneously dispersed inside the epoxy matrix. This modified system also resulted in an improvement of mechanical properties of the corresponding carbon fiber based composites. The outstanding properties were attributed to a better interaction fiber-matrix, as indicated by SEM micrographs.

Modificação de fibra de carbono com PBLH e sua utilização em compósitos com resina epoxídica

Carbon fibers containing 1,4 e 2,1 mmol/g of carboxyl and phenolic hydroxyl groups, respectively, were modified through the reaction with TDI. The presence of isocyanate groups at the fiber surface made possible the fiber modification with hydroxyl terminated polybutadiene (HTPB). These modified and unmodified carbon fibers were employed in the preparation of epoxy resin-based composites. A substantial improvement in the impact properties was observed in the composites with HTPB-grafted carbon fibers when compared to unmodified carbon fibers. These results may be attributed to a higher interfacial adhesion promoted by reactions between the functional groups present at the modified carbon fiber surface and the epoxy matrix.