Poly(methyl methacrylate) (PMMA) is a synthetic thermoplastic polymer that is obtained by the additional polymerization process of methyl methacrylate (MMA). It shows unique properties such as being highly transparent, having very lightweight, and being resistant to expansions and contractions in hot and cool temperatures, respectively [1, 2]. These properties make it a really good alternative for a typical glass. However, its application is not excluded from this and it is used in various industries such as resins and coatings or even in inks [3, 4]. It is also an inexpensive alternative for polycarbonates (PC) because not only the toxic bisphenol-A material does not exist in its structure, but also shows better characteristics such as polishability ability and laser cutting than those of PC [5, 6]. The lack of the bisphenol-A in the structure of the PMMA makes it a good candidate in biomedical, and other applications. A series of NCs including the PMMA and Ti-Mo-Cu were synthesized to compensate for the mechanical weakness of porous Ti-Mo-Cu alloys in tissue engineering. The results showed a significant increase in the compressive strength of the newly obtained NCs in comparison with Ti-Mo-Cu alloys, which helped them to be appropriate for tissue engineering [7]. However, being susceptible to scratches and brittleness and showing low resistance to strong solvents in its pure state limit its usage in different applications [8–10]. Therefore, it must be combined with some fillers such as mesoporous organic material (MOM)s and ordered mesoporous carbon (OMC) to compensate for its drawbacks.
MOMs (size 2-50 nm) have been widely utilized as fillers for polymers because of their specific features. Their structure consists of the well-ordered arrays of uniform channels in the nano dimension, high mechanical and thermal stability, being inert to a variety of chemicals, high surface to the volume ratio and also, their large pore volume and being in a diversity of forms such as powders, foams, and fibers which make them widely used in applications such as adsorption of dyes and heavy metals in the contaminated water [11, 12].
OMC is a porous material with interconnected channels which can be fabricated by direct carbonization of organic-organic nanocomposites [13]. Like MOMs, OMCs also possess similar characteristics such as the high surface area to the volume ratio, significant chemical and thermal stability, and hydrophobicity. They are widely utilized in the adsorption applications like the adsorption of dyes and act as an adsorbent in hydrogen or carbon monoxide for gas storage purposes [14]. For example, a series of OMCs were prepared via the hard-templating method in a mesoporous silica template (KIT-6) and their application in the removal of AV90 dye was also examined. The results revealed the maximum removal of dye at pH 2 and the structure of these materials did not alter after the adsorption process [15].
One of the most common OMCs used as a filler in NCs is FDU-15. FDU-15 possesses a 2-D hexagonal structure and hydrophobic nature having sizeable pore volumes (0.65-0.85 g/cm3) with a high BET surface area between 650 to 1500 m2/g. This structure makes it applicable in water remediation with hydrophobic nature [14, 16]. A study has been done by Wu and his co-workers have shown that the removal capacity of alkaline earth metals increases with the amount of FDU-15. The results revealed that all the alkaline doped FDU-15 possessed significant adsorption capacity and the adsorption process occurred in either the conversion of nitrogen monoxide and oxygen to nitrogen dioxide and then to nitrite or direct oxidation of nitrogen monoxide to nitrite or nitrate [17].
However, there would be trouble using FDU-15 as the reinforcing agent in the polymer matrix. The hydrophobic nature of FDU-15 is not compatible with the polymer matrix and makes it difficult to produce homogenous NCs and finally leads to the accumulation of these mesopores into the matrix [18, 19]. Therefore, they must be modified with some coupling agents such as 3-aminopropyltriethoxysilane (KH-550) to decrease the agglomeration of mesoporous into the polymer matrix. Mohammadnezhad and his co-workers designed a series of NC films based on the PMMA and FDU-15 mesoporous using 3-mercaptopropyl-trimethoxysilane as a modifying agent and studied their thermal stability and mechanical behavior. The result showed that by increasing the amount of FDU-15 mesoporous, the thermal stability and their mechanical behavior rise as well [20].
KH-550 has been extensively used to make a bridge between inorganic fillers and the organic polymer matrix. On the one hand, the oxygen atom on its structure makes a covalent bond with the filler and on the other hand, the primary amine portion reacts with the organic function groups in the polymer matrix [21].
Ultrasonic irradiation as an efficient and green method has widely been exploited to achieve the maximum dispersion of fillers into the NCs. This helps to achieve the maximum interaction between polymer chains and nanoparticles become possible. In a study that was done by Okhovat and his co-worker, a series of NCs based on chitosan-tragacanth blend reinforced with ZnO@Ag nanoparticles were built by the use of ultrasonic irradiation and they were used in bioactivity and antibacterial activity. The result showed that all the NCs are very compatible with hydroxyapatite and also, they showed an extreme antibacterial activity against both gram-negative and gram-positive bacteria [22].
In this project, several kinds of NCs were fabricated by the incorporation of different (0.5, 1, 2, and 3) wt% of the FDU-15s modified with KH-550 (m-FDU) into the PMMA matrix through the in-situ polymerization by the aid of ultrasonic irradiation. Various techniques and instruments were applied to characterize these NCs. Fourier transform infrared spectroscopy (FT-IR) by the aim of investigation of the functional groups, Low angle X-ray diffraction (LXRD) was utilized for the study of the crystallinity, field emission scanning electron microscopy (FE-SEM) for the morphological investigation, and transmission electron microscopy (TEM) to observe the shape and dispersion of m-FDUs into the polymer matrix were used. Moreover, investigation of the influences of these mesoporous structures on the thermal stability of the PMMA was examined by the thermogravimetric analysis (TGA).