Fillers also

Another advantage of the addition of inorganic filler is the significant increase in density of the silicone, which helps the dispensing process. The use of fillers also reduces the total cost of the product, as the expensive high performance silicone does not require 100% volume occupancy to fulfil its function. 

In dispersed systems the nature of the filler also plays a controlling role in the way the crystallization proceeds. Examples are reported in [105], whose authors have used X-ray analysis to estimate the degree of crystallinity of polyisobutylene filled with different concentrations of a number of filler materials, after 100 cycles of 50% stretching. Polyisobutylene crystallizes as a result of such treatment. The results are given in Table 1. 

Except for a lew thermoset materials, most plastics soften at some temperatures, At the softening or heat distortion temperature, plastics become easily deformahle and tend to lose their shape and deform quickly under a Load. Above the heat distortion temperature, rigid amorphous plastics become useless as structural materials. Thus the heat distortion test, which defines The approximate upper temperature at which the material can be Safely used, is an important test (4,5.7.24). As expected, lor amorphous materials the heat distortion temperature is closely related to the glass transition temperature, hut tor highly crystalline polymers the heat distortion temperature is generally considerably higher than the glass transition temperature. Fillers also often raise the heat distortion test well above... 

A rubber compound containing elastomer, curatives and the minimum of fillers. Also called a pure gum compound. 

Silica fillers also react with the rubber causing an increase in viscosity and dry and unmanageable processing behaviour. Filler activators need to be added to silica-reinforced compounds to overcome these problems. The usual filler activators used are diethylene glycol, polyethylene glycol and amines such as triethanolamine. Some of these activators not only overcome the problems of processing and accelerator absorption, but depending on the cure system used, will also act as vulcanisation activators. 

Pulp type is also important and, in general, unbleached pulps are easier to size than bleached pulps. Pulps with a high cellulose content are extremely difficult to size and require as much as 10 times the amount of reacted AKD to produce similar levels of sizing to those of Kraft pulps. This effect is not easily understood and cannot be explained in terms of surface area. The presence of fillers also increases the amount of size required, and sizing efficiency has... 

A minimum shrinkage of 5% or less, more typically 1% or less, has been specified in order to maintain excellent seal transference in the cured mass. This requirement has been met through much experimentation involving various levels of filler. Fillers typically result in lower shrinkage with lower bulk viscosity. Fillers also present difficulty in this application due to the inherent problem presented by a fibrous mass with its high surface area. The present formulation has avoided the use of fillers. 

Translucent plastics may be produced by the addition of fillers such as alumina trihydrate (ATH) which have n values similar to that of the polymer. Such fillers also serve as flatting agents in paints. 

Addition of fillers such as alumina trihydrate, antimony trioxide, molybdenum oxide [315], zinc borate and zinc borate complex [316] leads to increase in TS but decrease in elongation and NG migration/absorption. Addition of inorganic fillers also leads to increase in flame retardance. 

These in situ generated silica fillers also give increased resistance to creep or compression set in cyclic deformations, as is illustrated in Figure 8.6.43 The in situ filled PDMS samples are seen to show very little compression set. They can also provide increased thermal stability, as demonstrated by the results presented in Figure 8.7. 44... 

Solid-state 13C NMR spectra of carbon black filled, uncured and sulfur-vulcanised HR were recorded at 22.6 MHz. The line broadening of the filled polymer relative to the unfilled polymer is attributed to incomplete motional narrowing of the NMR lines [53, 54] Incorporation of filler also results in a decrease in the signal-to-noise ratios in the spectra, but fundamentally it does not obscure the qualitative and quantitative nature of the spectra for the moderately cured elastomer systems. 

There is evidence to show that the particle size of the filler also plays a significant role in flammability resistance. For example, below a certain particle size (about 1-2 pm), in many tests, including oxygen index, aluminum hydroxide shows enhanced fire-retarding performance,34 which may be associated with the rate of filler decomposition and/or with the formation of a more stable ash. However, it has been found that the particle size effect is absent, or less evident, in the cone calorimeter test.35 Similarly, particle size reduction has been shown to enhance fire retardancy in magnesium hydroxide-filled PP in this case, samples were characterized by the UL94 test.36 This raises the question as to whether further reductions in particle size to the nanoscale will lead to an additional increase in flammability performance, and perhaps enable filler overall levels to be significantly reduced. This aspect is considered in a later section. 

It is well known that freshly formed oxides have high surface areas and in addition, can be cata-lytically active,52 thereby promoting both carbon deposition and subsequent oxidation processes.53 The reduced combustion rate arising from the effects of the fire-retardant filler also contributes to lowering the rate of smoke evolution and, by improving oxygen to fuel ratios, further limits levels of smoke density.1... 

A more sophisticated pressure filler also is used in the industry. This filler vacuumizes the empty bottle before pressurizing with gas. There is less air enclosed in the bottle with this type than with the other. 

We first encountered fillers in Chapter 1. Fillers also called extenders) are used to reduce cost and sometimes also to improve the strength of a polymer. 

Elastic adhesives deform when exposed to such internal stress and are less affected by shrinkage. Fillers also reduce the rate of shrinkage by bulk displacement of the resin in the adhesive formulation. This results in an increase in the inherent bond strength of the adhesive. Fillers may improve operational bond strength by 50 to 100 percent although all of this improvement is not due to reduced shrinkage (see Sec. 9.3.11). ... 

Aluminum powder, in particular, is frequently employed at relatively high concentrations in high-temperature epoxy adhesive formulations. The filler provides improvement in both tensile strength and heat resistance, and it increases the thermal conductivity of the adhesive. Aluminum powder fillers also reduce undercut corrosion and, hence, improve adhesion and durability of epoxy adhesive between bare steel substrates. It is believed that this is accomplished by the aluminum filler providing a sacrificial electrochemical mechanism.27... 

Many mineral fillers are also commercially available with an organofunctional silane surface treatment. Suppliers of treated mineral fillers are shown in Table 10.2. These fillers are used in a variety of applications having critical property requirements that must be protected from moisture. Surface treatment of the mineral fillers also provides the formulator with a tool to reduce the viscosity of highly filled systems. 

Stresses caused by items 1 and 2 above are magnified by the mismatch in thermal expansion coefficients between the adhesive and the substrate. Incorporating fillers into the adhesive formulation can often reduce these stresses. Fillers also reduce the thermal shrinkage during aging by bulk displacement of the polymeric resin. 

Fillers offer a variety of benefits increased strength and stiffness, reduced cost, shrinkage reduction, exothermic heat reduction, thermal expansion coefficient reduction, improved heat resistance, slightly improved heat conductivity, improved surface appearance, reduced porosity, improved wet strength, reduced crazing, improved fabrication mobility, increased viscosity, improved abrasion resistance, and/or impact strength. Fillers also can have disadvantages. They may limit the method of fabrication, inhibit cure of certain resins, and shorten pot life of the resin. 

Chalk fillers also have extensive use in PVC-P applications where the particle size restriction is not so essential. Higher addition levels can also be accommodated. They have extensive use in wire and cable where they assist, in combination with other additives to reduce HC1 generation in a fire situation. 

Calcium carbonate and lithium carbonate fillers also act as HC1 absorbers and the effect on HC1 generation during the combustion of PVC-P has been shown to be effective, particularly when used in combination (15). 

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