Post curing effect of poly epoxy on visco‐elastic and mechanical properties of different sandwich structures

Abstract

Poly epoxy is a high performance room temperature cured epoxy system which provides excellent physical and mechanical properties. However, the effects of post curing of this resin system on the properties of different sandwich structures are unknown. This study aims to evaluate the effect of post curing (at 70°C for 2 hr) on the edgewise compressive and flexural strengths of a sandwich structure, constructed with Styrofoam and honeycomb as core materials and a plain weave carbon fabric as face sheet. Tested factors evaluated from edgewise compressive tests were as follows: peak load, compressive strength, and crash energy absorption of sandwich structures while core shear stress and bending stress of sandwich structures were determined and compared with flexural tests. It was observed that post curing affects significantly on the bending and compressive strengths of the sandwich structures. However, the data obtained for crash energy absorption suggested that the effect of post curing on the core shear strength and the total deflection was statistically insignificant. The matrix polymer was also inspected using dynamic‐mechanical thermal analysis to assess the changes in glass transition temperature and degree of conversion due to post cure. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers

A very low concentration of polybenzimidazole film interleaved bismaleimide/diallyl bisphenol a system with outstanding improvement in impact strength and excellent allround properties

“…3‐layer PBI film interleaved BMI/DBA system shows the optimal flexural strength and modulus, which are 22.5% and 11% higher than those of BMI/DBA, respectively. The improvement in mechanical property for PBI film interleaved BMI/DBA system can be attributed to the sandwich structure that can lead to the effective energy dissipation of PBI film with excellent damage resistance and the strong interface adhesion between PBI film and BMI/DBA matrix resulting from the reaction of NH in PBI and CC in BMI/BA prepolymer . The reaction between BMI/DBA and PBI can disturb the crosslinked networks of BMI/DBA, which has an adverse influence on the flexural strength and modulus of matrix.…”

“…The reason can be attributed to the advantage of sandwich structure of BMI/DBA/5PBI‐F system. The sandwich structure can dissipate significantly more energy as compared to the conventional structures of thermoplastic‐modified polymers, owing to the permanent deformation and shear fracture of thermoplastic PBI film .…”

“…As shown in Figs. e and f, PBI films in the interleaved BMI/DBA with sandwich structure can completely shield against the heat in in the longitudinal direction, whereas the dispersed PBI particles in BMI/DBA matrix can partly insulate the heat for the existence of BMI/BDA matrix between PBI particles, therefore, PBI film in sandwich structure can provide the more effective thermal insulation or barrier to prevent heat diffusion into the matrix than PBI particles , leading to the higher thermal stability of the interleaved BMI/DBA.…”

“…For most interleaf toughening thermosetting polymer composite methods, the thermoplastic interleaves are completely or partly dissolved in thermosetting resins during the curing process at elevated temperature, and the phase separated morphology can be formed. Compared to the conventional thermoplastic toughening method, a small amount of the thermoplastic film or fiber interleaf toughening the thermosetting resin is an effective method to improve the mechanical property because the sandwich‐like structure of the interleaved system can use the interleaf as a shield or barrier against large amounts of energy in the longitudinal direction .…”

Electro‐induced Cationic Polymerization of Vinyl Ethers by Using Ionic Liquid 1‐Butyl‐3‐methy­limidazolium Tetrafluoroborate as Initiator

“…It is well known that the active centers in cationic polymerizations can survive for extended time periods, which is evident from the post-curing that occurs in cationic polymerization. [28][29][30] A solution of ethylene glycol monovinyl ether containing 0.5 wt% BMIMBF 4 was exposed to a voltage of 6.0 V for 1 min to begin the electro-induced polymerization process while conversion was monitored during and continuing after the electric fi eld was removed as a means to investigate the post-curing process. As shown in Figure 5 , the doublebond conversions were only 11.9%, when the electric fi eld was turned off; however, conversion reached 31.1% within 16 min.…”