276 A. B. Irez et al. rubber or rigid fillers [8–14]. In this respect, to manufacture various cost-effective consumer products, recycled rubbers can be used as soft fillers. Blending the recycled rubber with epoxy enables its shaping to beneficial products at a low cost. This idea can be achieved by mixing powdered scrap rubber with epoxy as well as necessary additives. The manufacture of recycled rubber modified composites is realized by means of continuous processes, such as injection molding or pultrusion of thermosets. Another important point is that addition of rubber to plastics also promotes some key properties of plastics especially impact resistance and ‘good feel’ behavior. Second, the modification of epoxies also done by the incorporation of some inorganic–particulate fillers such as silica [6, 7] and alumina [8–11]. They generally improve the material properties such as fracture toughness [12, 15–23, 25], resin stiffness [14–19] and wear resistance [24, 25]. In this study alumina was used as a rigid filler. In particular, alumina has good thermal conductivity, inertness to most acids and alkalis, high adsorption capacity, thermal stability and electrical insulation, and so on. Also, it is inexpensive, non-toxic and highly abrasive [16–18, 26]. More specifically, in this study alumina has been used in fibre form and it has advantages compared to particle form. This work presents processing of recycled rubbers blended with epoxy resin to create novel composites in an economic way. Main objective of this research is to determine the mechanical properties and toughening mechanisms of these composites. During this study, physical properties such as glass transition temperature were determined with dynamical mechanical analysis (DMA). Then, bending tests were realized with single edge notched beam (SENB) and smooth specimens. At the end, fracture surfaces were observed by means of scanning electron microscopy (SEM) to study the toughening and damage mechanisms. 34.2 Experimental Procedure 34.2.1 Material Processing Recycled rubber modified epoxy based composites were prepared according to following procedure. First Bisphenol A-type Huntsman™ Araldite DBF epoxy resin was heated to 65 ◦C in order to decrease its viscosity. Then the alumina fibers were added to epoxy resin. This blend was mixed by using a high shear stirrer for 1 h at 65 ◦C to homogenize the mixture. The temperature of the mixture was controlled by a digital thermometer during the mixing process. Next, EPDM rubbers were added gradually to the mixture and mixing of this blend was continued for an additional 2 h, again at 65 ◦ C to prevent agglomerations. The recycled rubber powders are obtained from the unused scrap parts obtained during sportive equipment manufacturing. It means that they are fresh, clean and completely free of other materials that is present in ground tire. After mixing procedure, the mixture was cooled down to room temperature and the hardener was added. Because, addition of hardener at higher temperatures results in rapid solidification which may lead to uncompleted cross-linking reaction in some regions of the composite. When the mixture cooled down to room temperature, the hardener (Huntsman™ HY-952) was added regarding the stoichiometric ratio and this final compound was mixed for 15 min. Afterwards, the mixture was degassed in a vacuum chamber at room temperature for about 30 min. Then, the mixture was poured into silicon molds which have been cleaned previously and molds were left at room temperature for 24 h to complete the curing. After bulk composites were manufactured, test specimens were prepared by machining of the bulks according to test standards (Table 34.1). 34.2.2 Experimental Procedure Dynamic properties, storage modulus (E’) and mechanical loss angle tangent (tan δ) of the epoxy based composites were investigated using a Dynamic Mechanical Thermal Analyser Q800 system (TA Instruments). The data were obtained at a Table 34.1 Composition of the EPDM rubber modified epoxy based composites LRAL composites Alumina fiber content Rubber content 0% 5% 7.50% 10% 20% LR20 LR2AL5 LR2AL7.5 LR2AL10
RkJQdWJsaXNoZXIy MTMzNzEzMQ==