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.

The results on testing application of ground tire rubber (GTR), as potential filler for butyl rubber, are presented. The GTR content variation, within the range of 10-90 phr, was studied with respect to the vulcanization process, static mechanical properties (tensile strength, elongation-at-break, hardness and resilience), dynamic mechanical properties and the morphology of the obtained vulcanizates. Butyl rubber was characterized by its low compatibility to other elastomers [i.e., natural rubber and styrene–butadiene rubber (SBR) -the main ingredients of tires] and low degree of unsaturation. To evaluate the impact of these factors on curing characteristics and mechanical properties of butyl rubber vulcanizates filled with GTR, the same compositions of SBR compounds, cured under identical conditions, were used as reference samples. Based on the obtained data, it can be stated that butyl rubber vulcanizates containing 30 phr of GTR as filler revealed the highest tensile strength and elongation-at-break. The microstructural analysis of a sample containing 30 phr of GTR revealed strong interactions between the butyl rubber matrix and GTR. This phenomenon resulted mainly from two factors. First, the cross-link density of the butyl rubber matrix was affected by its competition against GTR for cross-linking agents. Secondly, the migration of carbon black particles from GTR into the butyl rubber matrix had a significant impact on properties of the obtained vulcanizates.

Background and Aim: Recycling of brackets can significantly reduce the price of fixed orthodontic appliances but if the bond is more prone to failure during treatment, this potential benefit will disappear. The aim of this study was to investigate the effect of chemical recycling on bond strength of metal orthodontic brackets and failure pattern of recycled brackets. Material and Methods: In this experimental study Instron machine was used to measure shear bond strength (SBS) of brackets in two stages on 60 human maxillary first premolars using No-Mix composite. Shear bond strength and pattern of failure were compared between recycled and new brackets in two stages. Data were analyzed by ANOVA and Duncan tests. Adhesive Remnant Index was evaluated in different groups by Pearson Chi-square test. P<0.05 was considered as the limit of significance. Results: Statistical analysis showed that the mean values of SBS for new bracket group was 12.00 MPa and for recycled group and double recycled group, 9.94Mpa and 10.00 MPa respectively. A significant reduction (about 18%) in bond strengths of brackets was observed at the first time of recycling. Recycling at the second time had no significant influence on the bond strength. Pattern of bond failure of these brackets showed that a great amount of residual adhesive material was remained on the teeth surfaces after debonding of recycled brackets which indicates that cleaning the teeth surfaces after debonding of recycled brackets is more time consuming. Conclusion: Based on the results of this study, before using recycled brackets, several advantages and disadvantages must be considered.

Recycling of waste rubbers is developing due to environmental concerns and continuous increasing raw materials price. The EPDM (ethylene-propylene-diene rubber) rubber is the rubber base of the non tire automotive rubber articles and their recycling is necessary for resources saving and the environment protection. A mechanical recycling technique, a twin screw extruder with the aid of a de-vulcanizing agent, TMTD (tetramethylthiuram disulfide) was used to de-vulcanize waste rubber powder from discarded EPDM automotive parts. The de-vulcanized rubbers, subsequently, re-vulcanized in a semi-efficient (SEV) curing system and correspondent curing and mechanical properties including hardness, tensile strength and elongation at break were measured and the results were compared and discussed. The results showed that the waste rubber de-vulcanized with used technique efficiently. The direct relationship was observed between increasing de-vulcanization percent and also the crosslink density reduction of the waste cured rubbers with improving the curing and mechanical properties of re-vulcanized compounds. The optimum de-vulcanization operating conditions were obtained by a design of experiment software at rotor speed of 180 rpm at a constant operative temperature, 220. The main challenge for using the outcomes of this study in commercial scale was the difference between waste rubbers composition because they provided from various sources.

There have recently been several initiatives to develop eco-sustainable materials because of the growing concern over ecological contamination caused by the overuse of synthetic materials. Previous studies in literature have explored the development of rice straw waste-based epoxy composites. Another waste hazard of concern in the current times is that of waste tire rubber. The present study investigates the physico-mechanical properties of a unique hybrid composite consisting of recycled waste tire rubber and rice straw reinforced composite, which has not been investigated in the literature. Their density, water absorption, hardness, tensile and flexural strengths were examined with variations in the proportion of rubber particles and rice husk. Increase in the rubber content resulted in proportional rise in the water uptake, hardness, tensile strength, and flexural strength. The composite with 25 wt.% of rubber and 5 wt.% of rubber showed the highest tensile strength and strain of 12.5 MPa and 0.015, respectively. The composite with 15% RS and WTR showed a 14.26% increase in flexural strength, with the neat composite exhibiting the highest strength. The composite material can be used as structural panels for instruments or devices in low load bearing applications. The developed sustainable material with waste generated from used tires and rice husk can aid in decreasing the harmful effects caused on the environment and human health during their disposal.

Hypothesis: The primary method for recycling waste tires is grinding them into fine particles and then mixing them with various matrices to improve their properties. For example, ground tire rubber (GTR) can be used to enhance the impact resistance of brittle polymers such as polystyrene (PS). However, weak interactions between the two components may lead to a decline in mechanical properties. Polymer grafting onto GTR is a successful method for rubber modification. The unique advantage is the graft polymer can be selected based on the matrix polymer. Namely, polystyrene grafted onto the surface of GTR, PS-g-GTR, can be used as a compatibilizer for the PS/GTR blend. Methods: In this study, styrene monomer was in-situ polymerized in the presence of GTR to synthesize PS-g-GTR in bulk and solution environments. The variation in monomer conversion and grafting efficiency was investigated by increasing the temperature in bulk polymerization and increasing the initiator concentration in solution polymerization. Findings: The highest grafting efficiency (57%) and grafting degree (247%) were achieved in solution polymerization at 90 °C, with a molar ratio of initiator to monomer equal to 1% and a weight percentage of GTR to monomer equal to 13. A comparison of Fourier Transform Infrared Spectroscopy (FT-IR) spectra for GTR and PS-g-GTR clearly showed the appearance of peaks corresponding to benzene rings after grafting. Based on thermogravimetric analysis (TGA), the synthesized PS-g-GTR contained 56% polystyrene by weight. By calculating the cooperatively rearranging region (CRR) length scale at the glass transition temperature using differential scanning calorimetry (DSC), the molecular weight of the grafted chains was estimated to be greater than 104 g mol-1. This graft polymer appears to significantly improve the impact resistance of PS by enhancing compatibility between polystyrene and GTR.