The aim of this study was to investigate the effect of replacing carbon black (CB) with inexpensive and environmentally friendly fillers – bentonite (BNT) and modified bentonite (M-BNT), on the curing properties of natural rubber (NR) composites. A control sample (unfilled NR) and thirteen NR composites filled with varied proportions of CB (x1), M-BNT (x2), and BNT (x3) based on a third degree – simplex lattice mixture design of experiment (DOE) were prepared in this study. Rheometric results showed that 33% substitution of CB with M-BNT provides the highest elastic torque values. Mixture of 10phr CB and 5phr M-BNT (CB/M-BNT/BNT 10/5/0) produces synergistic effect on curing. The presence of CB increases vulcanization rate due to its high basicity and low oxygen content while M-BNT serves as vulcanizing accelerator due to the present amine groups. Coefficients of reduced hierarchical models showed that the main factors contributed mainly on the curing parameters: β1for the torque values, β2for the scorch and curing time, and β3for CRI. High values of coefficient of determination (r2) were computed particularly for MH(98.20%), ΔS (99.13%), ts2(95.68%), tc90(95.70%) and CRI (95.97%) establishing best fit between the model and experimental values.

No abstract

The aim of this study was to investigate the effect of each ternary filler component: carbon black (CB), modified bentonite (M-BNT), and raw bentonite (BNT), and their interactions, on the mechanical properties of natural rubber (NR) composites, using a third degree-simplex lattice mixture design of experiment. The efficiency of the two-step organic modification to produce M-BNT was confirmed by the results of Fourier transform infrared with attenuated total reflectance (FTIR-ATR) spectroscopy and x-ray diffraction (XRD) analysis. Synergistic effect between CB and M-BNT on the mechanical properties of NR composites with ternary filler composition 10/5/0 was observed. Reinforcement of NR matrix using this ternary filler enhanced its tensile properties: strength (69.43%), modulus (47.01%), stress at 100% strain (34.67%), stress at 200% strain (41.88%), and stress at 300% strain (50.82%), as well as its compressive properties: strength (40.89%), modulus (40.05%), stress at 20% strain (41.10%), stress at 40% strain (37.57%), and stress at 60% strain (40.79%). Significant improvement in the mechanical properties was also attributed to the surface modification of M-BNT resulting to better dispersion to NR matrix. The addition of pure BNT filler resulted to lowest tensile and compressive performance due to high clay loading and incompatibility with NR matrix. Trends of the generated contour plots based on reduced hierarchical models demonstrated synergy between CB and M-BNT as well as deterioration of mechanical properties upon addition of pure BNT filler 0/0/15.

The effect of carbon black (CB) substitution with raw (BNT) and modified (M-BNT) bentonite on the thermal aging resistance of natural rubber (NR) composites was investigated in this study. NR composites were prepared at varied proportions of CB, M-BNT, and BNT using a three-component, third degree simplex lattice mixture design of experiment (DOE). M-BNT was produced by modifying sodium-activated bentonite with tetradecyldimethylamine (TDA) salt and cocamide diethanolamine (CDEA). Thermal aging was performed at 70 and 100°C for 168 and 336 h. Substitution of CB with 5 phr M-BNT gave the highest values of tensile properties (modulus and strength) for both unaged and aged samples. This is attributed to the synergistic effect of CB and M-BNT fillers on the tensile properties of NR composites. In terms of property retention (%), composites filled with M-BNT and BNT clay fillers attained the highest values which signified their excellent thermal aging resistance. This observation proves the barrier effect of clay platelet structure which hinders oxygen diffusion in the rubber. Reduced hierarchical models as function of CB, M-BNT, and BNT proportions were used to generate contour plots for tensile properties of NR composites after 168 h of aging at 70 and 100°C.

Magnetic citric acid-modified cellulose was successfully produced and tested for the removal of copper in aqueous solution. Initially, the cellulose material was reacted with citric acid solution. The modified cellulose was then attached to the Fe2O3nanoparticle producing an adsorptive magnetic material. Characterization using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy indicated successful binding and chemical modification of the cellulose. Its adsorption was also studied to evaluate its potential in removing heavy metals such as copper. Removal of copper was as high as 84.74% in solution containing 25 mg/L copper. The sorption of copper in the magnetic sorbent follows second-order kinetics and best fits Freundlich isotherm model. The developed material has a strong magnetic response, thus its recovery in the aqueous solution could be easily facilitated using a magnetic field. Regeneration study indicated high recovery efficiency maintaining above 95.7% copper removal efficiency after three cycles of use. Thus, a highly efficient magnetic adsorptive material was produced using simple chemical modification aside from its easy recovery in the water.