Polyetherimide-modified epoxy networks: Influence of cure conditions on morphology and mechanical properties

Abstract

ABSTRACT:The morphologies and mechanical properties of thermoplastic-modified epoxy networks generated through the reaction-induced phase separation procedure were studied as a function of isothermal cure conditions. The selected model system was diglycidyl ether of bisphenol A cured with 4,4-methylenebis [3-chloro,2,6-diethylaniline] in the presence of a nonfunctionalized polyetherimide. Appropriate precuring and postcuring schedules were selected. The precure temperature had a strong effect on final morphologies because it affected the viscosity of the system at the cloud point and the extent of the separation process. The morphologies generated are discussed in connection with phase separation mechanisms. The ratio of the height of the loss peaks corresponding to each phase was an appropriate parameter to qualitatively predict the shape of morphology and to determine if the system was phase-inverted or not. The fracture toughness, K Ic was significantly improved only when bicontinuous or inverted structures were generated, resulting from the plastic drawing of the thermoplastic-rich phase. Before phase inversion, K Ic was hardly higher than that of the neat matrix due to poor interfacial adhesion. Nevertheless, the thermoplastic-rich particles constitute obstacles to the propagation of the crack and contribute to the toughening of the material, measured through impact resistance measurements. The observation of fracture surfaces revealed the occurrence of microcracking and crack-pinning. Strain recovery experiments showed that particle-induced shear yielding of the matrix was present as well.

Toughness of syndiotactic polystyrene/epoxy polymer blends: microstructure and toughening mechanisms

“…Thirdly, previous thermoplastic/epoxy blends have employed amorphous, rather than semi-crystalline, thermoplastics to improve the fracture performance of polymer blends. However, large increases in the value of K Ic are generally only measured when a cocontinuous or phase-inverted microstructure is formed, and 20 to 30 wt.% of amorphous thermoplastic is typically required to achieve the optimum mechanical properties [11,13,[15][16].…”

“…The thermoplastics employed have typically been functionalized poly(ether sulfone) [6,[9][10][11], poly(ether imide) [7,[15][16], polyimide [17], polysulfone [18][19] and polyester [11], which are all amorphous polymers. Semi-crystalline thermoplastics have been used previously, but as preformed particles; and all processing was conducted below the melting point of the thermoplastic [20][21][22].…”

High Performance Thermoplastic/Thermosetting Composites Microstructure and Processing Design Based on Phase Separation

“…It is understood more and more that the rigidity and toughness of matrices are also of practical importance. The high rigidity & toughness require multi-scale controllable inhomogeneity of composites including bi-continuous and/or phase inverted micro-network with adjustable interface (Girard-Reydet et al, 1997;. After the concept of CIPS was proposed in 80s of last century (Inoue 1995), many experimental and theoretical investigations have been carried out to study the CIPS process in mixtures of tightly crosslinked TS matrices with ductile TP which is now assumed a promising alternative to rubber toughening approach, particularly when high value of elastic modulus, strength and glass transition temperature Tg are required.…”

“…Poor adhesion will render the TP phase premature de-bonding before expected deformations occur, while over strong adhesion between TS and TP interface will restrain the extent of ductile deformation undergone by TP phase because of the excessive constraint brought by TS phase. This constraint would limit the amount of material which could be involved in the bridging and deformation process (Williams, 1997;Girard-Reydet et al 1997;. Therefore the modifier TP must be chose in such a way that optimal affinity between TP and TS components is ascertained properly whereby CIPS can occur freely while cracking and/or delaminating can be restraint.…”

Propiedades mecánicas de un sistema epoxi modificado con ABS

“…Son muchos los termoplásticos que han sido utilizados como modificadores de los sistemas epoxi, entre ellos polietersulfonas (2), polisulfonas (3) y polieterimidas (4).…”