Reinforcing materials, defined

In this chapter we have reviewed some of the most important characteristics of cellulose and cellulose based blends, composites and nanocomposites. The intrinsic properties of cellulose such as its remarkable mechanical properties have promoted its use as a reinforcement material for different composites. It has been showed that cellulose is a material with a defined hierarchy that tends to form fibrillar elements such as elementary fibrils, micro fibrils, and macro fibers. Physical and chemical processes allow us to obtain different scale cellulose reinforcements. Macro fibers, such as lignocellulosic fibers of sisal, jute, cabuya, etc. are used for the production of composites, whereas nano-sized fibers, such as whiskers or bacterial cellulose fibers are used to produce nanocomposites. Given that cellulose can be used to obtain macro- and nano-reinforcements, it can be used as raw material for the production of several composites and nanocomposites with many different applications. The understanding of the characteristics and properties of cellulose is important for the development of novel composites and nanocomposites with new applications. 

There is considerable overlap within this category of additives. A particular material, such as glass, may be employed in one application and be considered a reinforcement, but in another application it is called a filler. However, most commonly, a reinforcement is defined as an additive that improves the mechanical properties (e.g., strength) of the polymer system. A filler is defined as an additive that takes up space in the system, generally to reduce cost. A few of the most important additives within this category are described here. 

Hybrid composites may be defined as systems in which one kind of reinforcing material is incorporated into a mixture of different matrices (blends) [18], or when two or more reinforcing/filling materials are present in a single matrix [19,20], or also if both approaches are combined [12]. 

Laminates can be defined as combinations of liquid thermosetting resins with reinforcing materials that are bonded together by the application of heat and pressure, forming an infusible matrix. Plywood is a good example of a thermosetting laminate with the phenolic resin... 

The bond coefficient between the reinforcing material and soil may be generally defined as ... 

Carbon (sometimes referred to as graphite) fibre is the reinforcement material of choice for advanced composites. Carbon fibres have a higher fatigue resistance than glass or aramid. Carbon fibre properties depend on the structure of the carbon used and are typically defined as standard, intermediate and high modulus fibres. Several thousand fibres are twisted together to form a yarn which may be used by itself or woven into a fabric. The yarn or fabric is combined with a resin, usually epoxy, and wound or moulded to shape to form a wide variety of products. 

By means of the described technology properties, both processes are suitable for mass production. Nevertheless, there is a preferred field of application for both technologies. Unidirectional reinforcement fibers are best suited for the pultrusion process. In contrast, the CCM process is independent of the fiber orientation, thus it doesn t matter if unidirectional or multidirectional reinforcement materials are used. The assessment of the rates of production (= process speed) against the circumferences of the profiles, which are in contact with the tools surface (see Fig. 8.34), defines relevant process parameters and emphasizes the preferred field of application. Thus the circumference characterizes the profile shape. 

Nanocomposites are usually defined as a combination of two or more components or phases in which the reinforcement material has one dimension in the nanometer range (1-100 nm) [22,80,81]. The terminology usually refers to a polymer (thermoplastic or thermosetting) matrix that represents the continuum phase, while reinforcements are able to induce enhanced performances (e.g., mechanical, thermal, etc.) from the composite. In biodegradable nanocomposites, also called bionanocomposites, matrices may... 

Laminates contain different reinforcement materials (woven/non-woven glass/organic fibers, expanded PTFE, etc.), resin types (phenolic, epoxy, cyanate ester, polyimide, BT, etc.), resin formulations (blended, functionality, etc.), hardeners (dicyanodiamide [dicy],phenol-novolak, cresol-novolak, p-aminophenol, isocyanurate, etc.), and sometimes fUler particles (ceramic or organic). The ratio of aU of these individual components can vary widely.To define a test strategy for laminates, it is important to understand the different main components of the materials as well as the conditions during manufacturing, as these wiU have a large influence on their properties and quality. 

The material properties for structural steel, steel reinforcement and concrete to be considered in such evaluations should represent the realistic ductility of the materials (defined by test) and should also include strain rate effects if the impact velocity is compatible with the selected scenario. Safety factors could be increased for direct impact on safety related structures and lowered for impact on sacrificial shielding structures. 

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