Epoxy resins are one of the most commercially successful materials known especially as composite matricx but also as coating materials and adhesives[1]. Among them, resins based on the diglycidyl ether of bisphenol A (DGEBA) are particularly well studied and most widely used.
After decades of successful production, this kind of epoxy resins now confrontsan intractable safety issue. Concerns have been growing that bisphenol A(BPA), which constitutes the backbone of DGEBA, may adversely affect humans[2]. BPA is an endocrinedisruptor that has been shown to be harmful in laboratory animal studies.Due to itswidespread human exposure and toxicity, Restrictions on the use of BPAin certain consumer products, ranging from manufacture, sale and distributions, have been suggested and implemented in many countries[3].Accordingly, a series of researches looking for alternatives have been carried out since then.
Many candidates alternatives have been proposed and studied, among them, Bisphenol S (BPS) and bisphenol F (BPF) are endowed with high hopes. Nonetheless, recent study shows that neither of them are safe replacements of BPA[4]. The bisphenol series of A, S and F are reported to be unsafe for human health, all of which contains aromatic rings in their backbones. These results remind us of the fact that the toxicity may derive from the aromatic rings that constitutes the backbone of the polymer. Considering this situation, we seek to hydrogenation of the BPA to transform the aromatic rings to cyclohexyl groups, thus eliminating the origins of toxicity.
The absence of aromatic rings will surely weaken the mechanical properties of the epoxy resinsthemselves, but, on the other hand, the hydrogenated diglycidylether of Bisphenol A epoxy resin (HDGEBA) turns out to be a good polymer matrix to well disperse stacked clays in, which will in return generate more chances to compensate the mechanical strength loss by adding inorganic clays.
The system of epoxy-claynanocomposites has been intensively investigated and commercialized for their unique physical and chemical properties, such as high modulus, high thermal stability, decreased flammability, and barrier properties[5–10]. The final properties of nanocompositesrely on the quality of clay dispersion in the polymer matrix. A fully exfoliated structure is most desirable but the most difficult to get.An effective approach to improve the degree of clay exfoliation is to adjust polymer/clay interaction.In our previous work, the effect ofpolymer/clay interaction on the clay exfoliation, clay orientation and disorientationwas well elucidated by the rheology experiments, which has attracted considerable interest recently[6, 11–16]
One frequently used strategy is to modify inorganic clay using organic additives in order toameliorate the compatibility between polymer and clay[17].The hydrogenated resin exhibits lower polarity than DGEBA for the presence of flexible cyclohexyl groups instead of rigid aromatic rings [18]. Due to the lower polarity of the hydrogenated resin, HDGEBA is expected to be more compatible with the organically modified clay.Il-Nyoung and co-workers found that nanomaterial reinforced HDGEBA/D230 adhesives were transparent[19]. María and co-workers reported that magnetite nanoparticles of about 10 nmin diameter modified with oleic acid exhibit a good dispersion in the matrix of HDGEBA[18].
In our study, we managed to adjust the polarity of the polymer to be more compatible with organo-clay by hydrogenating the unsaturated bonds of the aromatic rings in BPA.The hydrogenated diglycidylether of Bisphenol A epoxy resin (HDGEBA) wassuccessfully made and then employed to prepare nanocomposites with a more homogeneous distribution of clay, compared to that of bisphenolA epoxy resin (DGEBA)/clay system. Nanocomposites, with amounts up to 7.5 wt% of Organo-clay, were synthetized by means of “slurry-compounding” method and followed by a curing process with cis-1,2-Cyclohexanedicarboxylic anhydride and Glutaric Anhydride as the curing agent.The enhance dispersion of clay in HDGEBA was investigated with a series of experiments.
In this article, we focus our attention on the effect of hydrogenation of epoxy resin on the dispersion of organo-clay in the epoxy resin matrix. Organo-clay is found more easily to get exfoliated in the matrix of hydrogenated epoxy resin by a combined characterization of X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, we find there is stronger interaction between HDGEBA and organo-clay rather than DGEBA and organo-claywith the help of compatibility and rheology experiment.