Katja Nevalainen

Performance of epoxy filled with nano- and micro-sized Magnesium hydroxide

Magnesium hydroxide (MDH) particles are often used as fillers to improve the flame retardancy of polymers. However, achieving the balance between the enhanced fire resistance and reduced mechanical properties, especially toughness, is still a challenge to the composite community. In this study, the effect of the particle size and silane surface modification of MDH particles on the flame retardant, thermal, and mechanical properties of epoxy was studied. Both nano- and micro-sized MDH particles were modified by a silanization reaction with γ-aminopropyltrietoxysilane in an aqueous solution and filled into epoxy matrix by a high-shear mixer and a three-roll mill. Results show that nano-MDH filled epoxy composites yielded better mechanical properties than their micro-MDH filled counterparts. Furthermore, the adhesion between nano-sized MDH and the matrix was improved by the silane surface modification. When comparing the flame retardant properties, enhancements in heat release rates and total heat released were observed for MDH filled epoxy composites.

Mechanical and tribological property comparison of melt-compounded nanocomposites of atomic-layer-deposition-coated polyamide particles and commercial nanofillers

Mechanical and tribological properties of melt-compounded titanium dioxide nanocomposites of atomic-layer-deposition (ALD)-coated polyamide particles and commercial nanofillers were compared. The nanofiller dispersion in the polyamide matrix was studied using transmission electron microscopy showing very different morphology for the ALD-created and the traditional nanocomposites: former appearing as ribbons in the matrix whereas latter composing from spherical clusters. The effect of such morphology change on the specimen’s mechanical response subjected to tensile and impact loading was investigated. The results demonstrated that ALD-created nanocomposites possess significantly higher Young’s modulus than pure and traditionally filled polyamide matrix. However, transition from ductile to brittle behavior occurs especially for the ALD-created nanocomposites. Notched impact strength experiments supported this, suggesting that the impact strength of ALD-created composites decreased significantly compared to ...