Diffusion of curing agent through the thickness of a bi-layer EPDM system during the cure

Two EPDM rubber layers with different level of curing agent (2 and 10%) pressed and cured together exhibit interesting properties when immersed in toluene. In spite of the large swelling taking place, different for each of the two layers, leading to a strong flexural force, the two components of the bi-layer remain bonded. Simultaneously, a hardness gradient has been measured through the thickness of the final material. This hardness gradient is assumed to result from the diffusion of the curing agent through the thickness of the bi-layer system during the cure process. Deeper insight into the phenomenon is obtained in making calculations by taking into account these facts, either on the process of cure of the bi-layer system or on the process of absorption of liquid leading to large assymmetric swelling. Application of this phenomenon could be made in re-treading old tyres with a roller band made of a new rubber.     

Ultrasound-assisted adsorption of Pb ions by carbonized/activated date stones from singles/mixed aqueous solutions

This work aims to assess the adsorption efficiency of date stones biowaste subjected to carbonization and activation processes for the removal of Pb ions from single and mixed solutions. Several techniques have been used for characterization of adsorbents such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), methylene blue index and point of zero charge (pHpzc). An excellent adsorption capacity of 97.43% is achieved at an initial concentration of 300 ?mg/L, solution volume 75 ?mL of Pb nitrate, adsorbent mass of 0.7 ?g, temperature of 30 ?°C, a stirring speed of 500 ?rpm/min, a contact time of 180 ?min and pH 6. Specifically, a comparison has been conducted between carbonized/activated date stones “CADS” and commercial activated carbon “CAC” besides investigating the influence of the presence of Co ions and the utilization of ultrasound radiation. A higher adsorption rate of 98.16% is reached under ultrasound radiation at Pb(II) initial concentration of 100 ?mg/L for a contact time of 3 ?h. Nevertheless, the temperature has shown a negative effect; the adsorption rate decreases from 98.31% at 18 ?°C to 92.70% at 60 ?°C. The modeling of the experimental adsorption data manifests a type-L isotherm characteristic of Langmuir and Freundlich models. The kinetic study has shown that the experimental data are well described by a pseudo-second-order rate model and controlled by the internal diffusion, a limiting-step that controls the transfer rate of Pb(II) to the adsorbent surface. The calculated thermodynamic parameters (ΔG⁰, ΔH⁰, ΔS⁰) indicate that the adsorption of Pb(II) is spontaneous and exothermic process.