Waste EPDM was recycled by using a twin-screw extruder in the thermo-mechanical method; and the effects of processing parameters were investigated. Barrel temperature (220, 280, 340 and 380oC) and screw speed (60, 100 and 140 rpm) were chosen as the variables. Devulcanized characterizations, such as deVULCANIZATION percent, solvent swelling, and sole fraction were studied. After curing, the properties of revulcanized compounds (including 30 phr devulcanized EPDM) were compared with the reference compound (100% new EPDM compound). At low temperature and low screw speed, deVULCANIZATION was poor while with increasing both of them, deVULCANIZATION occurred very significantly indicated as higher solvent swelling. On the other hand, sole fraction increased as a function of processing conditions. Mooney viscosity decreased for high processing parameters; higher sole fraction, lower Mooney viscosity. Normally, compounds having 30 phr devulcanized rubber showed properties poorer than the reference one, but closer to evaluating deVULCANIZATION conditions. As the temperature or speed increased, stronger tensile behavior, reduced pressure set, and less creep elongation were achieved, meaning more crosslinks breakdown and successful reVULCANIZATION.

Suggestion has been made about the nucleophilic reaction mechanism of a binary accelerator system when derivatives of thiourea are used as secondary accelerators in rubber VULCANIZATION. The idea of our investigation is to give some conclusive evidence to the nucleophilic reaction mechanism proposed. In our studies we found that N- amidino-N"-phenyl thiourea (APT) functions effectively as a secondary accelerator in mercaptobenzothiazyl disulphide-APT, tetramethyl thyuram disulphide-APT, and cyclohexyl benzthiazl sulphenamide-APT binary systems in filled natural rubber (NR) VULCANIZATION. The above binary systems were prepared using carbon black / precipitated silica as filler. Evaluation of cure-characteristics of these mixes showed appreciable reduction in the optimum cure time for the mixes containing APT compared to reference mixes. This indicates a nucleophilic reaction mechanism, as APT is a more active nucleophile compared to the references. Considering the non-reverting characteristics of some of the mixes containing APT, this amidinothiourea derivative seems to function as an anti-oxidant as well. Important physical properties of these vulcanizates were also evaluated. Most of the physical properties of the vulcanizates studied were also found to be better, comparable to those of the reference mixes. Heat aging of these vulcanizates showed good retention of these properties after aging. The optimum dosage of the secondary accelerator required has also been derived.

Polymer blends based on polyacetal (POM) and acrylomtrile butadiene rubber (NBR) were prepared by melt blending technique.The mixing parameters such as temperature, time and speed of mixing were varied to obtain a wide range of properties. The mixing parameters were optimized by evaluating the mechanical properties of the blend over a wide range of mixing conditions. The morphology of the blend indicated a two-phase structure. This study describes an attempt to improve the tensile strength of POM/NBR blends by means of compatibilization and dynamic VULCANIZATION. A commercial compatibilizer, maleic anhydride (MA), has been used to control the phase morphology of the blend system. Dicumyl peroxide is used to dynamically vulcanize the NBR elastomer in the blend. The tensile strength of the compatibilized systems showed improvement. Dynamic VULCANIZATION raises elastic recovery and tensile modulus of the blends, but the elongation at break decreases.

Thermoplastic elastomeric materials have become important because they have many properties of vulcanized rubbers and can be rapidly fabricated as thermoplastics. in this work, selected grade of polypropylene (PP) was modified with dimethylol-phenolic resin and then it was melt-mixed with acrylonitrile-butadiene rubber (NBR) for several weight ratios. After sufficient mixing time additional phenolic resin was added to mixing chamber and the blends were dynamically vulcanized. In order to study the effects of the compositions and dynamic VULCANIZATION on the physical and mechanical properties, simple blends of unmodified polypropylene and NBR were also prepared. The results show that dynamically vulcanized blends have higher tensile strength, elongation at break, solvent and oil resistance.  

In this work, leather fibers were employed as a component of elastomeric compounds based on NBR, CR and EPDM and studied were made on their effects upon curing characteristics and mechanical properties of the prepared compounds. Evaluation of curing characteristics of the compounds demonstrated that leather fibers have no considerable effect on initial viscosity and curing time of the compounds. The study of mechanical properties of the vulcanized compounds showed that inclusion of leather fibers leads to increasing of tensile strength in NBR based compound due to compatibility between NBR and leather fibers. It is also found that increase in tensile strength in NBR compounds depends on the curing system of the compounds. The results of this work showed considerable increase in hardness for all of the prepared compounds. Abrasion resistance and resilience of the compounds were also measured and reported.

Dynamic VULCANIZATION is a well known technique which improves the mechanical properties such as compression set, tensile properties, fatigue, and chemical resistance of thermoplastic elastomers. In this study, three different curing systems (sulphur, peroxide, and phenolic resin) were applied on the polypropylene (PP) /ethylene propylene diene monomer (EPDM) blends. The weight ratio of the blends was PP/EPDM: 40/60. The samples were prepared in an internal mixer at rotor speed of 60 rpm and 190°C. Dynamic rheological parameters such as storage modulus (G') loss modulus (G¢¢), complex viscosity (h*), real and imaginary viscosities (h¢ and h¢¢) damping factor (tan d), and linearity region were determined at 190°C. The nonlinearity region of dynamic vulcanizated samples was shorter than that of the thermoplastic elastomer without applying dynamic VULCANIZATION. The Cole-Cole, Han, and van Gurp-Palmen plots for all samples were drawn to make correlation between rheologies and morphologies of the blends. It was found that the rheological behavior of dynamically cured samples was different from uncured sample, because dynamic VULCANIZATION could affect the morphology of the blends. All samples showed morphology of the EPDM rubber dispersed in the PP matrix (droplet-matrix) with different particle size.