Sorina Alexandra Gârea

Characterization of Novel Epoxy Composites Based on Hybrid Inorganic/Organic Polyhedral Oligomeric Silsesquioxane

New nanocomposites were synthesized by the reaction between a polyhedral oligomeric silsesquioxane (POSS) with eight epoxy groups (epoxy-POSS) and diglycidyl ether of bisphenol A (DGEBA) using Jeffamine D230 as curing agent. The reactivity of the systems was extensively studied by Raman spectroscopy. The hybrid materials were characterized by different techniques like thermogravimetric analysis, dynamical mechanical analysis, X-ray photoelectron spectroscopy, differential scanning calorimetry, and scanning electron microscopy. The “Si‒O‒Si” cages of the POSS component form aggregates, which was shown by the conversion data obtained from the Raman spectra and confirmed by the DSC curves, XPS spectra, and SEM images.

Effect of POSS-NH2 functionalization of MWNTs on reinforcing properties in epoxy nanocomposites

The research focuses on multiwalled carbon nanotubes (MWNTs) functionalization with aminoethyl aminopropyl polyhedral oligomeric silsesquioxane to increase their compatibility with epoxy polymers and enhancement of interface adhesion. Functionalization of MWNTs consisted of a three-stage reaction by oxidation and further amidation through acylation with thionyl chloride. The new nanomaterials were dispersed as reinforcing agent in a weight ratio of 0.3% related to the epoxy matrix, which was further cured with an aromatic polyamine. Characterization of functionalized MWNTs by infrared spectroscopy revealed the presence of POSS cages bonded to the MWNTs through the formation of amide groups, these findings were also proved by transmission electron microscopic images. Although catalytic influence of the reinforcing agent on the curing reaction was not significant at this level of reinforcement, scanning electron microscopic images of the nanocomposites fracture surface revealed strong interfacial adhesion and crack retardant effect of POSS-functionalized MWNTs.

The Influence of the Organic Substituents from the Polyhedral Oligomeric Silsesquioxane (POSS) Cage on the Epoxy-POSS Hybrid Materials Properties

This paper reports the synthesis of new reinforcing agents based on sodium montmorillonite modified with some polyhedral oligomeric silsesquioxanes. The modified montmorillonite was extensively characterized using different techniques such as Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and X-ray photoemission spectroscopy. The obtained reinforcing agents were used for the synthesis of epoxy-based nanocomposites. The nanocomposites were studied using thermal analysis, dynamic mechanical analysis, differential scanning calorimetry and thermogravimetric analysis to conclude that the type of radicals on the POSS cage may influence the properties of the final nanocomposites.

New Hybrid Materials Based on Modified Halloysite and Unsaturated Polyester Resin

New hybrid materials based on unsaturated polyester resin and modified halloysite with different coupling agents were synthesized. The effect of functional groups grafted on the surface of halloysite against the properties of the final hybrids was studied using different characterization methods. The results of dynamic mechanical analyses showed that the glass transition temperature value of hybrids was strongly influenced by the halloysite modifier type. The concentration of halloysite and the modifier agent type influence the thermal stability of final hybrid materials.

Kinetics of benzoxazine polymerization studied by Raman spectroscopy

Raman spectroscopy was used to monitor the curing process of a benzoxazine monomer. The reaction follows an autocatalytic mechanism. The autocatalytic model described in Kamal equation was employed. The activation energy and the pre-exponential factor were determined as: E a = 60.52 kJ mol−1 and A = 6.09 × 105 min−1. The overall reaction order was found to be 1.731 (n = 1.078; m = 0.653). The kinetic model characterized by these values is in good agreement with the experimental values.

Advanced Polybenzoxazine Structures Based on Modified Reduced Graphene Oxide

Two new polybenzoxazine products based on a reduced graphene oxide (rGO) were synthesized. The synthesis process started with an rGO with amino functionalities. Benzoxazine structures were synthesized with oxazine rings attached to the surface of rGO and were fully characterized by FT-IR, 1H–NMR, XPS and XRD. The presence of polybenzoxazine chains was pointed out by 1H–NMR and it correlated with XRD data which show a partial exfoliation of the graphene oxide layers. The degree of polymerization plays a significant role against the exfoliation process. A higher yield of the ring-opening process for benzoxazine rings leads to a low degree of exfoliation, as the inner covalent bonds within the polybenzoxazine chains keep the graphene oxide sheets together.

Clay–Polymer Nanocomposites for Controlled Drug Release

Abstract The classical pharmaceutical forms involve a fast drug release with a significant fluctuation of plasmatic drug concentration that requires repetitive administrations (especially for drugs with short half-life). The development of new pharmaceutical formulations is encouraged to solve these limitations and therefore achieve an increase of therapeutic effect.

Chapter 40 – Polybenzoxazine-Clay Nanocomposites

This chapter describes the preparation, characterization, and properties of polybenzoxazine-clay nanocomposites. The structure of intercalating agents, and the preparation and organophilization methods available for anionic and cationic clays are presented as key factors that significantly influence the structure and properties of polybenzoxazine-clay nanocomposites.