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Theories and Mechanisms of Adhesion
Published in A. Pizzi, K. L. Mittal, Handbook of Adhesive Technology, 2017
Conceptually, the ubiquity of mechanical interlocking has long been a topic of interest in nature, art, and society [7]. In the field of adhesion, mechanical interlocking was first proposed in the early part of the last century [8,9]. There have been changing perceptions on the importance of mechanical interlocking in adhesion as analytical methods to study adhesion and our fundamental understanding have improved [10]. Essentially, mechanical interlocking can be divided into two groups: locking by friction and locking by dovetailing (Figure 1.1). For mechanically interlocked adherends, there are irregularities, pores, or crevices where adhesives penetrate or absorb into, and thus the mechanical properties of the adherends are involved [11]. In addition to geometry factors, surface roughness has a considerable influence on adhesion. Rougher adherend surfaces produce better adhesion than smooth surfaces. High-level adhesion can be attained by improving the adherend surface properties, and mechanical keying can be enhanced by increasing the surface area [12].
Experimental study on the role of moisture in the cold binderless briquetting of low-rank coal
Published in International Journal of Coal Preparation and Utilization, 2022
Toto Hardianto, Adrian Rizqi Irhamna, Pandji Prawisudha, Firman Bagja Juangsa
This mechanism combines adhesion and cohesion forces, surface tension, capillary pressure, and a part of the solid bridge defined by Rumpf (Pietsch 2008; Rumpf 1962). This binding mechanism occurs between two or more particles bonded by an adhesive material acting as a bridge in the particle interstices. This bridge material could be in the solid or liquid phases. Phenomena like adhesion, adsorption layer, capillary pressure, viscous binder, and hardening binder are the typical process that might take place in the bridge material. (c) Mechanical Interlocking
A new method to characterize sludge stickiness during drying: Effects of sludge temperature and calcium oxide (CaO) on stickiness
Published in Drying Technology, 2020
Wenyi Deng, Jiamin Xiao, Zhicheng Lai, Yaxin Su
The effect of temperature on the evolution of tensile stress can also be clearly observed in Figure 4. Both for SL1 and SL2, the increase of the temperature led to a marked decrease of the tensile stress. As discussed above, the tensile stress reflected the adhesion force between the sludge and the probe, which can be divided into intermolecular/electrostatic force, solid bridge, liquid bridge and mechanical interlocking.[32] The solid bridge usually originates from melting, crystallization or evaporation of liquid binder.[11] In our previous research, it has been reported that the solid bridge was an important force when sludge was in contact with a hot surface, due to the evaporation of liquid binder between sludge and the hot surface.[5] In this study, the probe was not a heat source; thus, there was no moisture evaporation between sludge and the probe, and the solid bridge can be neglected. Consequently, the adhesion force between the sludge and the probe should be mainly originated from intermolecular/electrostatic force, liquid force, and mechanical interlocking. The liquid bridge can be estimated by the following Equation [33]: where τl is the liquid bridge, Pa; σ is liquid surface tension, N m−1; φ is porosity (dimensionless) of the agglomerate; k is a constant (k = 2.8 in pendular state, k = 8.0 in funicular and capillary states); d is the particle diameter, m. Equation(6) indicates that the liquid bridge is proportional to the liquid surface tension. It is well known that the surface tension of water decreases with the increase of temperature.[33] The surface tension of water drops from 71.17 mN m−1 at 30 °C to 64.44 mN m−1 at 70 °C. Therefore, the increase of temperature will lead to the decrease of the liquid bridge, which should be an important reason for the decrease of the tensile stress. Mechanical interlocking is a type of physical force in which two components of distinct interfaces are held together.[34] Sewage sludge is mainly composed of EPS in a shape of polymer networks.[36] The mechanical interlocking could be formed during the tight contact of the polymer networks with the upper surface of the probe, and the strength of the mechanical interlocking should be correlated with the rigidity of the polymer networks. It is well known that organic materials can be softened by increasing temperature. Thus, with the increase of sludge temperature, the rigidity of EPS polymer networks could be lowered, leading to the decrease of mechanical interlocking. Additionally, it can be found that all forces (intermolecular/electrostatic force, liquid force and mechanical interlocking) were negligible when the sludges were fully dried (at moisture content of 0.10 kg H2O kg−1 DS).