Popular fillers

To meet fabricated dimensional tolerances different approaches are used. They include use of specific fillers and reinforcements and process control (Chapter 3). Popular filler used is short glass fibers (Chapter 15). Over 50wt% of all types of glass fibers used with different plastics and by different processes are used in injection molding compounds. Table 2.2 shows the shrinkage of different unreinforced plastics ad glass fiber reinforced plastics based on ASTM testing procedures. 

The most popular fillers are soft materials in the hardness range of 1 -3. Silica fillers are hard and frequently abrasive. Most grades of silicas have a hardness in the range 6-7. 

Fillers are used in these products to improve mechanical properties or impart flammability resistance. Fillers are frequently silane-treated to further improve mechanical properties. Fillers must have a low moisture (below 0.1%), a low absorption of resin, and are expected to impart thixotropic properties. There are special cases. For example, if peroxyketals are used as initiators, basic fillers have to be used because acidic fillers interfere with cure times and the shelf-life of the composition. Shape and particle size distribution must be considered in filler selection to impart the desired rheological properties. Calcium carbonate is the most popular filler but aluminum trihydrate, anhydrous calcium sulfate, and silica are also frequently used. Barite is well suited to this application, especially if acid... 

Apart from being a popular filler for elastomeric materials, soot is an excellent black pigment. Several properties make it downright ideal for printing purposes it is light-fast and insoluble in almost any common solvent as well as it exhibits low particle size and great color depth and strength. Yet more than 90% of the... 

Montrorillonite (MMT) is the most popular filler used for developing thermoplastic starch (TPS)/clay nanocomposites. Nanocomposites showed a significant improvement in tensile properties compared to the pure matrix [231]. 

Nanocomposites refer to the combination of nanosized fillers (10 m diameter) with polymers, rather than the combination of polymer matrix (filled with nanoparticles) and fiber reinforcement The most popular fillers used as fire retardants are layered silicates. Loading of 10% or less (by weight) of such fillers significantly reduces peak heat release rates and facilitates greater char production [7]. The char layer provides a shielding effect for the composites below and the creation of char also reduces the toxicity of the combustion products, as less carbon is available to form the CO and CO2. 

The thermal conductivity, or X factor (mW/m-k), for some of the most popular filler materials is shown in Figure 4.1 as a function of pressure (Pa). The thermal conductivity of cyclopentane (CP) blown closed cell PU foam is also given for comparison. 

Milled wood flour is becoming a popular filler for thermoplastics today. It is inexpensive and imparts to the polymer some of the properties of natural wood, for example. 

Asbestos. Asbestos is a low-cost magnesium silicate mineral that occurs as very short, fine fibers of high modulus, strength, and thermal and chemical resistance. It was a popular filler until it was noticed that it collected in the lungs and caused serious health problems. Its use has been discontinued except in critical applications such as brake linings. Since then, a number of other promising short, fine fibers have been abandoned for fear that they may cause similar problems. 

A popular filler in the SMPC world is Cloisite 30B. In the MMT clay manufactured by Southern Clay Products, the particle size distribution is such that 90% of the particles (dry weight) are of less than 13 pm diameter, while 50% of the particles are less than 6 pm and 10% are less than 2 pm [68], This breakdown makes Cloisite in some sense a nanoclay, but in reality still a microclay. TEM images presented by Schulz et al. [68] did indicate 500 nm particles in Cloisite 30B. Cloisite 30B is, however, comprised of platelets that are approximately 120 nm in diameter and as small as 3 nm thick [69]. Under the correct pre-processing conditions, these platelets can be incorporated into polymer networks to varying degrees of uniformity and success at very different size scales. 

Carbon, silica, or combinations of the two are the most popular fillers used. Carbon is the most inert of the fillers and therefore is the one most often selected. The most popular resin systems, both organic and inorganic, will be discussed, starting with the organic systems, many of which are also used as monolithic surfacings. 

Nerve guidance conduit can be hollow or filled with matrix to support axonal elongation. A popular filler choice is natural polymeric gel. Ideally, the... 

For many electronic and electrical appHcations, electrically conductive resias are required. Most polymeric resias exhibit high levels of electrical resistivity. Conductivity can be improved, however, by the judicious use of fillers eg, in epoxy, silver (in either flake or powdered form) is used as a filler. Sometimes other fillers such as copper are also used, but result in reduced efficiency. The popularity of silver is due to the absence of the oxide layer formation, which imparts electrical insulating characteristics. Consequently, metallic fibers such as aluminum are rarely considered for this appHcation. 

Clays. Clay, which is generally considered a mild reinforcing filler, is used sparingly in tires. It is most often used in white sidewalls or in low performance tires. Clay toimage in tires worldwide is estimated at 36,000 t annually. Clay can also be coupled to mbber with silanes, and this is the more popular version used in tires. Even with silane coupling, clays are still a weak reinforcing filler compared to both carbon black and siUca. 

Rheological methods of measuring the interphase thickness have become very popular in science [50, 62-71]. Usually they use the viscosity versus concentration relationships in the form proposed by Einstein for the purpose [62-66], The factor K0 in Einstein s equation typical of particles of a given shape is evaluated from measurements of dispersion of the filler in question in a low-molecular liquid [61, 62], e.g., in transformer oil [61], Then the viscosity of a suspension of the same filler in a polymer melt or solution is determined, the value of Keff is obtained, and the adsorbed layer thickness is calculated by this formula [61,63,64] ... 

There are different techniques that have been used for over a century to increase the modulus of elasticity of plastics. Orientation or the use of fillers and/or reinforcements such as RPs can modify the plastic. There is also the popular and extensively used approach of using geometrical design shapes that makes the best use of materials to improve stiffness even though it has a low modulus. Structural shapes that are applicable to all materials include shells, sandwich structures, and folded plate structures (Fig. 3-8). These widely used shapes employed include other shapes such as dimple sheet surfaces. They improve the flexural stiffness in one or more directions. 

Certain inorganic salts are also used as fillers. Some common examples are listed in Table 7 together with their comparative properties. Among the most popular... 

Unsaturated polyesters are relatively brittle and about 70% are used with fillers, of which glass fiber is easily the most popular. Glass fiber-reinforced polyester for small boat hulls consumes one quarter of unsaturated polyesters. Automobiles, furniture, and construction also make use of this thermoset resin. 

One popular misconception concerns the counter-pressure filler. It is often stated that the overpressure of gas in the filler bowl pushes the product into the container, but this is not the case. Once the valve is open the pressures in the bottle and the filler bowl equilibrate and product is filled by gravity. (Note a counter-pressure filler is usually used for carbonated beverages but it can successfully fill still products with an inert overpressure.)... 

There are different types of plastics that are usually identified by their composition and/or performance. As an example there are virgin plastics. They are plastic materials that have not been subjected to any fabricating process. NEAT polymers identify plastics with Nothing Else Added To. They are true virgin polymers since they do not contain additives, fillers, etc. They are very rarely used. Plastic materials to be processed are in the form of pellets, granules, flakes, powders, flocks, liquids, etc. Of the 35,000 types available worldwide there are about 200 basic types or families that are commercially recognized with less than 20 that are popularly used. Examples of these plastics are shown in Table 1.1. 

---