Partially miscible blends of epoxy resin and epoxidized rubber: Structural characterization of the epoxidized rubber and mechanical properties of the blends

Abstract

SYNOPSISThe cure process and the mechanical properties of blends of diglycidyl ether of bisphenol-A-based epoxy resin and hydroxyl terminated, internally epoxidized polybutadiene rubber have been studied. Internal oxirane groups are characterized by a main absorption a t 885 cm-' in the infrared spectrum while the terminal oxirane groups of the diepoxide monomer absorb a t 913 cm-'. In the absence of prereaction of the rubber, gelation of the epoxy matrix occurs much faster than any reaction involving the internal oxirane groups or the terminal hydroxyl groups. Therefore, only weak chemical bonding between the rubber particles and the epoxy matrix exists and the fracture toughness of the blends does not show any significant improvement. Upon prereaction of the rubber with an excess diepoxide monomers, a 40% improvement in the value of the critical stress intensity factor is obtained.However, dynamic mechanical spectra of these blends acquired in the rubbery plateau region uniquely demonstrate that this improvement is due to the incorporation of the rubber into the epoxy network rather than to the presence of phase-separated rubber particles. 0 1994 John Wiley & Sons, Inc. INTRODUCTIONIt is well known that a small amount of rubber can greatly improve the fracture toughness of epoxy resins by forming discrete rubbery particles that are chemically bonded to the matrix. The toughening effect is generally accompanied by a relatively small loss of thermomechanical properties. A review of the literature indicates that both chemistry ',* and thermodynamic^^'^ play an essential role in determining the final properties of these rubber/epoxy blends. Thermodynamics include issues of miscibility and phase separation. Initially, the rubber must be able to dissolve in the monomer/curing agent/ catalyst mixture. However, miscibility must not be too great because phase separation of the rubber before gelation of the epoxy matrix is also required for efficient toughening. Too good of a miscibility leads to a diluent effect rather than a toughening effect. The balance between phase separation and polymerization depends on the solubility of the rubber in the epoxy resin, the initial fraction of rubber, and the cure conditions. This balance, in turn, determines the particle size distribution and the composition of the epoxy-rich and rubber-rich phases and, thus, directly influences the mechanical properties. Chemistry of the rubber includes issues of selectivity and reactivity. Functional groups must be present on the rubber backbone in order to selectively react with the epoxy matrix. Indeed, chemical bonding between the rubber particles and the epoxy matrix is necessary for efficient stress transfer. It has been proposed' that the rubbery particles are composed of a mixture of linear rubber-epoxy copolymers and crosslinked epoxy resin. In the absence of chemical bonding or curing, only van der Waals attractive and/or hydrogen bonding type of forces are present and not much toughening is expected. If, on the other hand, the reactivi...

Epoxy–urethane copolymers: Relation between morphology and properties

“…[1][2][3][4] The toughening increases with the volume fraction of dispersed phase, but it also depends on the ductility of the continuos phase because the mechanisms of deformation are related to the characteristics of the matrix. 5 As clearly explained by Bussi and Ishida, 6 when the elastomer co-reacts with the epoxy segments, the ductility of the system is increased as a result of the incorporation of a flexible, rubbery molecule as part of the polymer network. Similarly, Mulhaupt and Buchholz 7 refered to polymer compatibility as determining phase separation and/or flexibilization of the matrix.…”

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

“…However, so far no studies have been performed to establish unambiguously the nano-scale structure of these networks. Several other works in the literature report the use of polybutadiene functionalized with hydroxyl [50][51][52][53][54][55], epoxide [56][57][58][59], carboxyl [49,[60][61][62], and amine [63,64] as modifiers for the epoxy matrix, but all systems presented phase-separated morphology in the cured state because of the great incompatibility between polybutadiene and the epoxy matrix. In this sense, it appeared us that the confirmation of the totally nanoscopic character of the structure of the blends prepared by using PBNCO would be an interesting contribution for future development of technical applications.…”

Particle Surface Design using an All‐Dry Encapsulation Method

“…Comparing the FTIR spectrum of a PGMA standard with that of the PGMA-coated nanotubes in Figure 1C, there is an excellent match between the spectral signatures, with the presence of the strong carbonyl peak characteristic of a methacrylate group at 1727 cm -1 , and the peaks specific to the oxirane ring of the glycidyl group at 905 and 841 cm -1 , representing the asymmetric and symmetric in-plane ring-deformation modes, respectively. [39,40] iCVD provides a useful way to surface functionalize nanotubes in a noncovalent fashion without destroying the sp 2 nature of the nanotubes, which will help preserve essential nanotube properties like electrical conductivity and tensile stiffness. Aside from carbon nanotubes, symmetric particles like microspheres have also been successfully encapsulated using the ) and PGMA-coated carbon nanotubes (bottom), showing an excellent match with the polymer standard.…”