Effect of molecular weight and content of PDMS on morphology and properties of silicone‐modified epoxy resin

Abstract

To achieve a stable blend of a bisphenol A type epoxy resin and poly(dimethylsiloxane) (PDMS), reaction between hydroxyl (OH) groups of the epoxy and silanol groups of hydroxyl-terminated(HT) PDMS has been investigated. The chemical structures of the HTPDMS-modified epoxies were characterized by Fourier transform infrared (FTIR) and 1 H-and 13 C-NMR spectroscopy. To allow further understanding of the influence of viscosity and content of HTPDMS on the blend morphology, four different viscosities of HTPDMS were used in three content levels. The morphologies of modified epoxy resins were observed with optical microscopy. The modified epoxies were cured with a cycloaliphatic polyamine. The morphologies of modified epoxies were investigated by using scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) technique.The cured films showed droplet in matrix morphology with different mean droplets size which was influenced by the viscosity and the content of the incorporated HTPDMS. To illustrate the effect of the morphologies of the cured samples on mechanical properties, tensile strength tests were performed. The introduction of HTPDMS into the epoxy altered the tensile behavior according to its viscosity and content. Surface properties of the cured films were evaluated by sessile drop method. The results clearly indicate that the hydrophilic surface of the epoxy turns to a hydrophobic one due to the modification with HTPDMS.

Enhanced Charpy impact strength of epoxy resin modified with vinyl‐terminated polydimethylsiloxane

“…[2][3][4][5] The soft dispersed phase of elastomer, however, provides not only an increase in the toughness (due to the ability to dissipate impact energy), but also an increase in strength under uniaxial tension and with other types of deformation, which is especially effective when thermosetting polymers are filled with elastomer. [2][3][4][5] The soft dispersed phase of elastomer, however, provides not only an increase in the toughness (due to the ability to dissipate impact energy), but also an increase in strength under uniaxial tension and with other types of deformation, which is especially effective when thermosetting polymers are filled with elastomer.…”

“…Toughening of glassy polymers (as, e.g., thermosetting ER) with a soft low-modulus polymers occur when elastomer is introduced into the plastic. [2][3][4][5] The soft dispersed phase of elastomer, however, provides not only an increase in the toughness (due to the ability to dissipate impact energy), but also an increase in strength under uniaxial tension and with other types of deformation, which is especially effective when thermosetting polymers are filled with elastomer. [6][7][8][9][10][11][12][13][14][15] In these cases, the destruction of the material proceeds by the brittle fracture mechanism, as indicated by the small value of elongation at break.…”

“…[1][2][3] In spite of their excellent properties, ERs have inherently low toughness and impact resistance due to their highly crosslinked structure. Epoxy adhesives essentially consist of an ER, often based on diglycidyl ether of bisphenol A (DGEBA).…”

“…Epoxy polymers have been widely used in industrial applications, for example, in automobiles, marine systems, weight-critical aerospace applications as construction materials, adhesives, coatings, and electronic circuit board laminates. [1][2][3] In spite of their excellent properties, ERs have inherently low toughness and impact resistance due to their highly crosslinked structure. 1 This structure leads to brittle behavior and causes the polymers to suffer from relatively poor resistance to crack initiation and growth.…”

“…4 Miwa et al 38 proposed that the optimum volume fraction of silicone rubber particles necessary to improve the impact fracture toughness (2.3 J/m) is 10 wt %. Sobhani et al 2 demonstrated that epoxy modified by 10 wt % of hydroxyl-terminated polysiloxane leads to the highest value of elongation at break (3.55), while the highest fracture energy (150 J) was observed in a sample containing 5 wt % of it. It was found out that, as the elastomer concentration increases up to 20-25 wt %, a state of co-continuity is attained, and a further increase in the concentration leads to phase inversion.…”