Mechanical and morphological properties of organic–inorganic, hybrid, clay‐filled, and cyanate ester/siloxane toughened epoxy nanocomposites

Abstract

Organic-inorganic hybrids involving cyanate ester and hydroxyl-terminated polydimethylsiloxane (HTPDMS) modified diglycidyl ether of bisphenol A (DGEBA; epoxy resin) filled with organomodified clay [montmorillonite (MMT)] nanocomposites were prepared via in situ polymerization and compared with unfilled-clay macrocomposites. The epoxy-organomodified MMT clay nanocomposites were prepared by the homogeneous dispersion of various percentages (1-5%), and the resulting homogeneous epoxy/clay hybrids were modified with 10% HTPDMS and g-aminopropyltriethoxysilane as a coupling agent in the presence of a tin catalyst. The siliconized epoxy/clay prepolymer was further modified separately with 10% of three different types of cyanate esters, namely, 4,4 0 -dicyanato-2,2 0 -diphenylpropane, 1,1 0 -bis(3-methyl-4-cyanatophenyl) cyclohexane, and 1,3-dicyanato benzene, and cured with diaminodiphenylmethane as a curing agent. The reactions during the curing process between the epoxy, siloxane, and cyanate were confirmed by Fourier transform infrared analysis. The results of dynamic mechanical analysis showed that the glass-transition temperatures of the clayfilled hybrid epoxy systems were lower than that of neat epoxy. The data obtained from mechanical studies implied that there was a significant improvement in the strength and modulus by the nanoscale reinforcement of organomodified MMT clay with the matrix resin. The morphologies of the siloxane-containing, hybrid epoxy/clay systems showed heterogeneous character due to the partial incompatibility of HTPDMS. The exfoliation of the organoclay was ascertained from X-ray diffraction patterns. The increase in the percentage of organomodified MMT clay up to 5 wt % led to a significant improvement in the mechanical properties and an insignificant decrease in the glass-transition temperature versus the unfilled-clay systems.

Modification of epoxy resin with polyether-grafted-polysiloxane and epoxy-miscible polysiloxane particles

“…When the modifier content increased to 8 wt% and 10 wt%, modified polysiloxanes aggregation happened in the modified epoxy resins, the size of second phase is so big that it may seriously affect the crosslinking density of the epoxy networks. The improvement in the impact strength is observed with the incorporation of both FPMS and EMPP, and this may be due to high-energy absorption, and resilient behavior of the flexible siloxane molecule, 30 as well as the defects and the lower crosslinking density of the network caused by the incorporating polysiloxanes.…”

Morphologies and mechanical and thermal properties of highly epoxidized polysiloxane toughened epoxy resin composites

“…Impact strength and K IC values of modified epoxies first increased with the increase in HEPSO2 content before 4 phr, which may be due to high-energy absorption, and resilient behavior of the flexible siloxane molecule, 34 as well as the defects and the lower crosslinking density of the network caused by the incorporating polysiloxanes. When the modifier content increased to 8 wt% and 12 wt%, the dispersed polysiloxane particles were so many that the particles seem to be contacted each other, as shown in Figure 5(c) and 5(d) (above), which might affect the crosslinking structure of the epoxy networks, and consequently the lower impact strength and K IC values.…”

Processing and Characterization

“…Wooster et al [17] found that the crack resistance of the cyanate ester is improved by 80% by the addition of 4 wt% nanoclay without a sacrifice of flexural strength. Others have shown that the incorporation of nanoclay has similar enhancement on mechanical properties, toughness, and thermal properties of cyanate ester modified epoxy resin or cyanate/epoxy blends [18][19][20][21].…”

“…The gaps between rollers of the three-roll mill (Exakt 80E) used in this study were electronically adjustable [20]. Figure 3.17 shows pictures of the three-roll mill and how it works.…”

“…Since the gaps between rollers were small, the product was essentially free of air bubbles after milling. [20] and (right) how a three-roll mill works [21].…”