Reinforcement Surface

The value of the epoxy resins lies in their reactivity with a variety of chemical groups. This enhanced reactivity also means that the surface chemistry of the reinforcement which the epoxies are cured against, can alter the local structure in the interphase regionJl). The most common reinforcement surfaces cured in contact with the epoxies are carbon/graphite fibers, glass fibers, aramid fibers and metal oxides. The surface chemistry of these reinforcement surfaces is quite diverse and in many cases can be the reason for alteration of the interphase epoxy structure as compared to the bulk. 

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The end result of the surface chemistry of the reinforcement, the adsorbed material, topographical features, and epoxy composition is in the formation of the polymerized epoxy on the reinforcement surface. In order for this to happen, the fluid epoxy mixture must be brought into contact with the reinforcement surface, wetting must take place and energy added to aid the polymerization. The wetting of the reinforcement by the epoxy is a necessary criterion for optimum mechanical properties. 

However, the chemical bonding theory cannot account for the increase in adhesion experienced between non-reactive matrices such as polyolefins and inorganic reinforcements in which chemical bonds will not be formed [4], This observation, among others, leads to an alternative proposal that an interphase composed of various constituents forms surrounding the reinforcement. This third phase in the composite is possibly formed through interdiffusion of physisorbed silane and matrix molecules in the interphase and perhaps via preferential adsorption of both matrix components as well as silane coupling agents on the reinforcement surface [5],... 

A more vital application is to discern how reinforcement surface treatments improve adhesion to thermoplastic matrices. Since the nonreactive nature of thermoplastics normally precludes interfacial covalent bond formation, secondary bonding forces, such as London dispersion interactions and Lewis add/base interactions, may play a major role in these drcumstances. These secondary binding forces are subject to surface energetics analysis. 

Improved control of and/or improved latitude in ink/water balance at the printing plate by this mechanism is accomplished best with isopropanol because of its bulk-reinforced surface activity. Limited-solubility additives, such as 2-ethyl-l, 3-hexanediol, function similarly but are slightly less effective. Commercial fountain concentrates using soluble, low-surface- tension additives provide some of this improved control but remain more dependent on printing format, ink and additive variables. Commercial concentrates having high surface tension provide none of this enhanced control and with no fountain solution additives the system is virtually inoperable. 

The metalworking nature of the process leads to the plunge and rehll FSSW methods, with properties comparable to riveted and resistance spot-welded joints. The use of FSP to locally modify the microstructure of arc welds and castings has shown to increase strength, improve fatigue life, and remove defects. Using FSP to stir particulate materials into the surface has shown increased wear resistance and creates particulate-reinforced surface layers. Friction stir reaction processing can be used to create new materials and alloy combinations on part surfaces. 

Circulating current is thus mainly carried by hydroxyl ions, so that most of the alkahnity produced by the cathodic reaction is removed from the reinforcement surface. On the other hand, the fraction of current carried by chlorides is modest... 

Figure 20.3c shows the effect of application of cathodic protection on carbonated concrete. The applied cathodic current density, even if it brings about only a small lowering of the steel potential, can produce enough alkalinity to restore the pH to values higher than 12 on the reinforcement surface and thus promote passivation. The effectiveness of cathodic protection in carbonated concrete was studied with specimens with alkaline concrete, carbonated concrete and carbonated concrete with 0.4% chloride by cement mass that were tested at current densities of 10, 5, and 2 mA/m (of steel surface) [45]. Carbonated concrete specimens polarised at 10 mA/m showed that, although initially protection was not achieved since the four-hour decay was slightly lower than 100 mV, after about four months of polarization, the protection criterion was fulfilled and higher values, in the range 200-300 mV of the four-hour potential decay were measured (Figure 20.6). The same results were obtained on carbonated and slightly chloride-contaminated concrete.

Similar studies were made on polypropylene [44], both with and without glass fibre reinforcement. Surface effects were again seen with both materials but UV penetration was considerably reduced by the presence of glass. 

Relative Typical specific reinforcement surface area, (HAF = 100) mVg... 

Qiemical bonds can maintain bonding even in the presence of small hydrophilic molecules such as water and alcohol which compete for the hydrophilic reinforcement surface with the silane. Physical bonds including van der Waals force, ionic bonds, and acid-base interactions are quite adequate to provide good dry strength but these effects can yield misleading results if the wet strength is also of interest... 

Head lamp bezel reinforced Mineral-reinforced Surface finish, heat resistance... 

Hair dryer/steam Glass-reinforced/ Surface finish, temperature... 

In their activity, stabilizers normally are consumed other losses may occur through migration into elastomer inclusions or to the surface as well as through fixation to filler/reinforcement surfaces (adsorption). Under low loading levels, chemical aging will definitely determine the lifetime of a PP part. Not only does it create discolorations and aesthetic failure of the surface, but also cracks are induced which increase the stress sensitivity dramatically. 

The main problem in using glass-ceramics with reinforced surfaces, however, is the high risk of damaging the surface. If the relatively thin, warped surface layer were damaged or destroyed, the glass-ceramic could break even if a small amount of force were exerted upon it. 

Mechano-activated modification uses a mechanical method, such as crushing, grinding, and friction, to change the lattice structure and crystal structure of the packing, increase system internal energy and temperature, promote particle melting and thermal decomposition, produce free radicals or ions, reinforce surface activity of fillers, promote chemical reactions between packing and other material or attachment... 

Nanocomposite describes a two-phase material where one of the phases has at least one dimension in the nanometer range (1-100 nm). They differ from conventional composites by the exceptionally high surface-to-volume ratio of the reinforcing phase and/ or its exceptionally high aspect ratio. The reinforcing material can be made up of particles (e.g., minerals), sheets (e.g., exfoliated clay stacks) or fibers (e.g., carbon nanotubes, electrospun fibers or cellulose nanofibers). Large reinforcement surface area means that a relatively small amount of nanoscale reinforcement can have an observable effect on the macroscale properties of the composite. There has been enormous interest in the commercialization of nanocomposites for a variety of applications, and a number of... 

To improve adhesion of binders to fibres, including carbon fibers, methods of surface treatment by cold plasma were developed. In the course of such treatment, the removal of a weak border layer of the fiber proceeds and the contact between the surface and a binder is improved. At the same time, the number of active centers capable of chemical interaction with a binder increases and the wetting becomes better. It may be expected that pol5mierization under plasma action may also serve as a tool adhesion improvement at the phase border. In spite of the existence of many ways of surface treatment of the reinforcement surface, no model of interaction was proposed which is effective in predicting the t5T)e of reinforcement by surface treatment of a given filler-matrix combination. According to Drzal, the major reason for this lack of theoretical developments is in the over-simplification of the composition and nature of the filler-matrix interface. 

If the carbonated front penetrates deeply into concrete and reaches the reinforcement surface. 

Details of the above reactions are given in Chapter 2. The films do not remain protective any more if the pH falls due to carbonation. They do not remain adherent to the reinforcement any longer and loose their passivity causing the reinforcement surface to be exposed to corrosive species. The ingress of CO2 is a major factor which breaks down the passivity and dissolves the protective oxide layer on the reinforcement surface. 

Passivity The formation of a thin layer of y-FeOOH (iron oxide) on the reinforcement virhich acts as a barrier between die reinforcement and the environment and makes the reinforcement surface inert to corrosion. This phenomena is called passivity. See Pourbaix diagram, high pH zone. 

Matrix molecules can be anchored to the reinforcement surface by chemical reactions or adsorption, which determines the strength of interfacial adhesion. In certain cases, the interface may be composed of an additional constituent such as a bonding agent or an interlayer between the two components of the composite. The choice of a matrix depends on several factors like application, compatibility between the components, technique of processing, and costs. 

The enhancement of adhesion provided by asymmetric organotitanates and zirconates in reinforced composites appears to be a consequence of the interaction of multiple mechanisms, including ligand-specific interfacial wetting enhancement, primary chemical bond formation between the substrate particulate and resin matrix, and, in many instances, matrix repolymerization and reinforcement surface modification. The particular mechanism which is dominant in a specific application appears to... 

Zircoaluminate coupling agents are analogous to the silanes. Each of their product line has organic functionality and an inorganic backbone, so that one end can interact with the matrix resin and the inorganic component will have an affinity for the filler or reinforcement surface. 

Sihcone elastomers have relatively weak mechanical properties and require fillers to provide reinforcement. Surface-treated sihca fillers with small particle size and, therefore, with high surface area, are commonly used. Facial prosthe-ses are normally cleaned in water and, therefore, the incorporation of hydrophobic sihca filler into the base polymer is a good choice for medical-grade materials. 

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