Cohesive Mechanical Properties

Tensile strength and flexural modulus are generally increased and ultimate elongation is reduced in proportion to the amount of filler, when tested at room temperature. The reverse is generally true when the cured epoxy is tested at elevated temperatures. Impact strength is generally adversely affected by particulate fillers. 

The addition of particulate fillers generally decreases compression fatigue, but increases ultimate compressive modulus and compressive yield strength, because of a stiffening effect. Compressive strength as a function of filler loading is shown for a cured epoxy formulation in Fig. 9.7. 

The reinforcement of adhesives has typically been achieved through the use of fibrous and flake fillers. Asbestos historically has been one of the most widely used reinforcing fibers in adhesive systems due to its needlelike shape. However, it is now seldom used because of health concerns. 

One material that has been used to replace asbestos in certain applications is wollas-tonite or calcium metasilicate. This is also a fibrous mineral filler but with a lower aspect ratio than asbestos. Surface-treated versions are available to improve adhesion to the epoxy matrix. It can be applied at relatively high loading levels to provide for high strength and improvements in moisture resistance.25 

Talc or hydrated magnesium silicate is another mineral that is used to reinforce epoxy adhesives. It has a platelike structure that provides good stiffness and creep resistance at elevated temperatures. It also provides good electrical and chemical resistance characteristics.26 It is relatively inexpensive and disperses well in the resin. 

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Reinforcing fillers (active) Fumed Silica (Si02) precipitated calcium carbonate (CaCOi) carbon black Thixotropic reinforcing agents (non-slump), adjustment of mechanical properties (cohesion) provide toughness to the elastomer as opposed to brittle materials. 

An EB-curable struetural adhesive formulation usually eonsists of one or more crosslinkable oligomeric resins or prepolymers, along with such additives as reactive diluents, plasticizers, and wetting agents. The oligomer is an important component in terms of the development of mechanical properties. The adhesive and cohesive properties depend on the crosslink density, chemical group substitution, and molecular organization within the polymer matrix. Adhesion is achieved... 

Polymer. The polymer determines the properties of the hot melt variations are possible in molar mass distribution and in the chemical composition (copolymers). The polymer is the main component and backbone of hot-melt adhesive blend it gives strength, cohesion and mechanical properties (filmability, flexibility). The most common polymers in the woodworking area are EVA and APAO. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

The mechanical properties of a material play an important role in powder flow and compaction by influencing particle-particle interaction and cohesion, that is to say, by influencing the true area of contact between particles. For example, Hertz [26] demonstrated that both the size and shape of the zone of contact followed simply from the elastic properties of a material. Clearly then, the true area of contact is affected by elastic properties. From the laws of elasticity, one can predict the area of contact between two elastic bodies. More recent work has demonstrated, however, that additional factors must be taken... 

Indices are dimensionless parameters derived from various mechanical and physical properties of the tablet blend and resulting compacts. Mechanical properties typically measured include indentation hardness (kinetic and static), elastic modulus, and tensile strength (10,11). Physical properties include particle size, shape, and size distribution, density (true, bulk, and tapped), flow properties and cohesive properties. 

Binders increase cohesion between the particles of fuel and oxidizer, facilitating better consolidation and resulting in better mechanical properties of the end products. In addition, an equally important function is to coat and protect metallic or non-metallic fuels (such as metal or non-metal powders) which may otherwise react with moisture and oxygen. They also modify the burning rate and hence the performance, and at the same time reduce sensitivity to impact or friction. A comprehensive list of binders, natural to synthetic resins used for pyrotechnic formulations follows. 

As for linear polymers, the low-strain mechanical properties of thermosets in the glassy state are essentially under the influence of two factors cohesion and segmental mobility. 

The epidermis plays a role in skin mechanics. Thereby, hydrophilic as well as hydrophobic substances affect mechanical properties of the skin. Changes in skin mechanics can be the result of either a direct influence of a substance on the intercellular matrix, or an epiphenomenona, for example, a physiological shift of water between the tissues aimed to maintain physiological homeostasis, 50 The hydration level of the SC affects its mechanical properties. Increased hydration of the SC influences its extensibility and elasticity.51-54 Examples from human diseases such as ichthyotic and xerotic disorders indicate that thickening of the SC due to hyperkeratosis and increased corneocyte cohesion is responsible for a marked decrease in the flexibility of the entire SC.55... 

The physical and mechanical properties of excipients were important variables in achieving performance of the final products as well. The preferred formulation strategy for a low-dose product using dry granulation is to design a cohesive blend to... 

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