Nanoclay Polymer Composites Research Articles

Synthesis and characterization of nanoclay–polymer composites from soil clay with respect to their water‐holding capacities and nutrient‐release behavior

ABSTRACTWater and nutrients are two important inputs to agriculture that need to be used judiciously with higher efficiency to save these limited resources. For these purposes, a series of nanoclay–polymer composite (NCPC) superabsorbent nutrient carriers were prepared. These NCPCs were based on the reactions of different types of nanoclays (10 wt %) with partially neutralized acrylic acid and acryl amide by a free‐radical aqueous solution copolymerization reaction with N,N′‐methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator. The nanoclays isolated from three different types of soils were dominant in kaolinite (clay I), mica (clay II), and montmorillonite (clay III), and a portion of each was freed from amorphous aluminosilicate. Thus, there were six different types of nanoclays used, namely, those dominated by kaolinite, mica, and smectite with and without amorphous aluminosilicate. Fourier transform infrared spectroscopy and X‐ray diffraction (XRD) investigations showed evidence of interaction between the clays and polymer. XRD investigation also showed that the reaction between the polymer and clays I and II occurred on the surface of various clay particles without intercalating into the stacked silicate galleries, whereas in the case of clay III (the smectite‐dominated clay), evidence indicated the intercalation of polymer into the stacked silicate galleries of the clay and the exfoliation of the clay. The water absorbency decreased in the NCPCs compared to that of the pure polymeric hydrogel. In case of the pure polymer, the entire amount of nutrient loading released within 15 h of incubation; this was higher than that of the NCPCs. In the initial stage (up to 15 h), no significant differences in nutrient release were observed among the different polymer/clay composites, but there were differences in later stages. Among the different NCPCs, the percentage release of nutrients at 48 h ranged from around 70% in the polymer/clay III composite to 90% in the polymer/clay I composite. The presence of amorphous aluminosilicates in clay did not make any difference in the nutrient‐release rate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39951.

Mesomechanical Modeling of Polymer/Clay Nanocomposites Using a Viscoelastic-Viscoplastic-Viscodamage Constitutive Model

In this study, damage evolution in a nanocomposite containing the polymethyl methacrylate polymer (PMMA) embedded with silicate nanoclay particles is simulated by using a nonlinear viscoelastic, viscoplastic, and viscodamage constitutive model. Mesomechanical two-dimensional representative volume elements (RVEs) of fully intercalated and fully exfoliated nanoclay polymer composites have been arbitrarily generated assuming a uniform dispersion of nanoclay particles with random length, aspect ratio, and orientation. Proper size of the RVE has been determined by studying the effect of the RVE size on the stress-strain response and toughness. Several simulations including different intercalated and exfoliated nanoclay weight fractions under different strain rates at room temperature have been conducted. It is concluded that the strength of exfoliated nanoclay composite is higher than intercalated one due to more distributed damage within many narrow localized zones for the case of exfoliated nanoclay polymer composite.

Modelling stiffness of polymer/clay nanocomposites

Aligned nanoclay particles can be distributed randomly in a polymer matrix even at high volume fractions, but randomly oriented particles cannot be randomly distributed at high volume fractions. Instead a nanocomposite where there are clusters of nearly aligned particles is obtained. The clusters of nearly aligned particles form an effective particle with lower aspect ratio. This phenomenon which produces a nanocomposite of less stiffness than might have been expected has implications for the processing of nanoclay polymer composites. It is shown by comparing two-dimensional to three-dimensional finite element studies that the two-dimensional model, often used because it is simpler, does not accurately predict the stiffness. The Mori–Tanaka model is shown to give a reasonably accurate prediction of the stiffness of clay nanocomposites whose volume fraction is less than about 5% for aligned particles but underestimates the stiffness at higher volume fractions. On the other hand for randomly oriented particles the Mori–Tanaka model overestimates the stiffness of clay nanocomposites.

Cluster size effect in hardness of nanoclay/epoxy composites

The mechanical and thermal properties of nanoclay polymer composites have been experimentally investigated over the last decade. Most of the research has been focused mainly on the control of their interplanar structures, which govern the global properties of the composites. In reality, these structures (both exfoliated and intercalated patterns) are hardly achieved through the use of conventional manufacturing process for plastic products. Different sizes of clusters mixed by nanoclays and matrix would be easily formed, particularly in the extrusion of polymer-based components. This paper experimentally studied the hardness and interlaminar shear properties of nanoclay/epoxy composites with different amount of nanoclay content, which formed different sizes of nanoclay/epoxy clusters after mixing in an extruder. The results showed that the micro-hardness of the composites could be enhanced when a small amount of nanoclay was added into the epoxy. However, there was an optimal limit in which the hardness was dropped by continuously increasing the nanoclay content. Microscopic observation on the fracture surfaces showed that the size of the clusters varied with the amount of nanoclays used in the composites. Although previous literatures have reported that the use of nanoclays in polymer-based composites could enhance their mechanical properties, the interlaminar shear test indicated that the short beam shear strength of the composites decreased after adding the nanoclays into the matrix.