The effect of montmorillonite modification and the use of coupling agent on mechanical properties of polypropylene–clay nanocomposites

In this work, polypropylene (PP)–clay nanocomposites obtained by melt blending were investigated. Different commercial montmorillonites (MMTs), such as unmodified MMT, octadecyl ammonium-modified MMT, and dimethyl dialkyl ammonium-modified MMT, have been used. Maleic anhydride–polypropylene (MAPP) copolymer has been used as a coupling agent, and the effect of clay modification as well as MMT: MAPP ratio on final nanocomposites performance was studied. The transmission electron microscopy was used to evaluate the incorporation of clays into the PP matrix. The isothermal crystallization behavior of neat PP and different nanocomposites was studied by differential scanning calorimetry and polarized optical microscopy. Only nanocomposites based on organically modified MMT showed mechanical performance improvements. Nanocomposite reinforced with 5 wt% of organically modified MMT without MAPP showed modulus and strength values of 871 and 29.3 MPa, respectively, these values being higher, around 23% and 4.6%, respectively, than modulus and strength values of neat PP. The incorporation of MMT into the PP matrix produced an increment on the crystallinity rate with respect to neat PP. The half crystallization time of nanocomposites without MAPP was, at least, two times faster than for a neat PP system.

On the Removal and Desorption of Sulfur Compounds from Model Fuels with Modified Clays

The presence of sulfur compounds in fossil fuels has been an important concern in recent decades as an environmental risk due to the increase of greenhouse gases in the atmosphere and accentuation of acid rain. This study evaluates modified clays as low-cost and efficient adsorbents for the removal of dibenzothiophene (BT) and 4,6-dibenzothiophene (DBT). Adsorption was investigated in a batch system with synthetic fuels (gasoline and diesel) as a function of type of clay modification, adsorbent dosage, initial concentration of the pollutants, desorption, and isotherm modeling. Maximum adsorption was observed with clays modified with benzyltrimethylammonium ion (BM), achieving a maximum adsorption capacity (qmax) of BT of 11.3 mg/g in gasoline and 31.3 mg/g in diesel. The formation of Van der Waals interaction as well as aromatic forces as the main mechanism is proposed based on the results. A 40% desorption was accomplished in 0.1 N HCl. Adsorbents were characterized by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FT-IR), indicating their optimum properties as adsorbents in fuels. This work highlights the potential use of reverse polarity clays in the elimination of sulfur compounds from model fuels as a low-cost and environmentally friendly purification technique.

Increases in organic carbon concentration and stock after clay addition to sands: validation of sampling methodology and effects of modification method

Plant growth on sands is often constrained by water repellence, low fertility and low water-holding capacity (WHC). These soils also have low organic carbon (OC) concentration, particularly in a bleached A2 horizon. Addition of subsoil clay to sands (clay modification) can overcome these constraints and increase WHC; however, little is known about the effect on OC concentration. Clay addition is predicted to increase OC storage via increased OC input from improved plant growth and increased stabilisation of OC by binding to clays. The objectives of this study were (i) to validate the number of soil samples required within a 25-m grid for accurate OC and bulk density measurement in clay-modified soils and (ii) to determine OC concentration, bulk density and OC stocks in clay-modified compared with unmodified soil. The study was carried out on two agricultural properties in South Australia, where unmodified controls (sands with 1–3% clay) were compared with three methods of modification using clay (clay spread, delved and spaded). Soil cores to 50cm depth were collected after harvest within a 25-m grid. The study showed that clay modification could increase OC stocks (0–30cm) by up to 14tha–1 in the South East and 22tha–1 in the Eyre Peninsula. However, the magnitude of the OC stock increase was influenced by the modification method and depended on concentration and depth of incorporation of the added clay and organic matter.