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    Comparison of Electrical Conductivity in Compounds of Carbon Black With Natural and Butadiene Rubbers
    (Frontiers Media Sa, 2019) Sancaktar, Erol; Basan, Satilmis
    Carbon black (CB) filled butadiene (BR) (Cis-1,4-polybutadiene) and natural (NR) (Cis-1,4-polyisoprene) rubber compounds containing CB in 60-100 per hundred (phr) proportions were investigated for their pressure/time-dependent electrical conductivity. Due to their high deformability, the percolation thresholds for CB-BR and CB-NR compounds were functions of pressures (compression loads) applied. Resistivity of such compounds decreased with time and compressive load levels. Storage moduli, G', as well as the loss moduli, G and the dynamic viscosities, eta* of the compounds were evaluated to assess viscoelastic response of the compounds' conductivities under pressure. The storage and loss moduli values for both the CB-BR and the CB-NR compounds decreased with increasing strain levels, indicating that the rate of increase in conductivity is expected to increase at higher compressive loads. The storage moduli increased with increasing frequency (rate), indicating that the rate of increase in conductivity should be lower at higher rates of compressive load application. Comparison of variations in conductivity between the CB-BR and CB-NR compounds as functions of time and pressure, however, revealed that, overall, the conductivity levels are also strongly dependent on the nature of the molecular structure of these rubber materials and their initial interactions with CB during compounding, and the resulting dispersion levels of CB. Once such dispersion structure is established, the overall difference in conductivity levels for the CB-BR and CB-NR compounds remain approximately unchanged for given time and pressure conditions for the cases where high CB fill levels (similar to 90 phr) are used and asymptotic conductivity values are reached. The experimental results revealed that because of the presence of higher number (similar to 2-fold) of hydrogen side atoms on the linear BR chains, CB-BR compound forms more physical crosslinks (mostly due to hydrogen bonding) in comparison to the CB-NR compound resulting in more effective CB dispersion and higher conductivity. Such higher efficiency in CB dispersion and percolation in BR is further implied by higher conductivities despite higher G' and eta* values for the CB-BR compound in comparison to the CB-NR compound.
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    Physical properties of LLDPE and PP filled with wood flours
    (American Society of Mechanical Engineers (ASME), 2015) Baş, Gamze Sultan; Sancaktar, Erol; Karadurmuş, Erdal
    In this study, composites of polypropylene (PP), as well as linear low density polyethylene (LLDPE) thermoplastics filled with wood flour have been investigated to study the effect of size and amount of wood flour on their mechanical, thermal and aging properties. PP and LLDPE were mixed with five different types of wood flour, i.e., cedar, maple, oak, poplar, and select pine, by adding different percentages of wood flour at 30, 40 and 50 weight percentages. Mixing was done using a mini compounder at 180-210ºC and dog-bone shape samples were produced by using a mini-injection molding machine. Two different sizes of wood flour labeled as thin (425 – 500 µm) and thick (600 – 710 µm) were compared for PP-wood and LLDPE-wood composites. Mechanical properties of blends were investigated by tensile testing and thermal behaviors of blends were characterized by using DSC analyses. Poplar and maple show better tensile results among other wood types with 543.7 MPa and 600.5 MPa Young’s modulus and 21.05 MPa and 24.53 MPa tensile strength for LLDPE when comparing thick and thin wood flour blends, respectively. In the case of PP; poplar and select pine gave higher Young’s modulus and tensile strength results. Samples were also aged in acid and water solution for 3 days, and their weight and dimensional changes were recorded and compared with neat polymer samples to show physical stability
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    Role of adhesion in sandpaper failure progression
    (Elsevier Ltd, 2016) Tunalıoğlu, Mert Şafak; Sancaktar, Erol
    In this study, different grit sizes of sandpapers were used under controlled rubbing experiments using a rheometer to investigate the role of adhesion in failure progression by particulate separation. Frictional shear forces were induced on sandpaper samples of different grit sizes by frictional rubbing of the same and different grit size sandpaper samples. Comparison of failure rates under different normal forces, grit sizes, as well as grit size mismatch, provided insight on the role of particulate adhesion to the sandpaper's backing sheet on the loss of wear function for different grit-size sandpapers. In conclusion, it is considered that the wear/failure mechanism for the cases corresponding to similar/reasonably close wear ratios are likely to have occurred under similar mechanism, most probably adhesion failure on the abrasive particles. © 2015 Elsevier Ltd. All rights reserved.