Filler Mineral flour

Typical fillers wood flour, glass fiber, carbon fiber, mica, wollastonite, mineral wool, talc, magnesium hydroxide, graphite, molybdenum sulfide, carbon black, cashew shell particles, alumina, chromium oxide, brass and copper powder, iron particles, steel fiber, ceramic powder, rubber particles, aramid, wollastonite, cellulosic fiber, lignin... 

Fillers and other additives are used to make molded objects from phenolic resins to reduce shrinkage during cure, improve strength, and provide flow control. Representative materials added are mineral flour, wood flour, nutshell flour, pressed olive stones, lignite, and natural rubber. Crosslinked phenolics containing inorganic or organic fillers are schematically illustrated in Scheme 35. 

Kaolin is used only in small quantities in PR The anisotropic particle geometry of wollastonite and mica reinforces the pol)uner. The latter is applied more extensively in USA and Canada due to the closer location of mining facilities. Barite-filled PP has excellent vibration damping properties due to the high density of this filler. Wood flour filled PP is occasionally applied in the automotive industry for the preparation of door panels. Water absorption of this filler creates problems in processing and application. The most important characteristics of mineral fillers are collected in Table 2. 

Fillers. Fillers used in molding compounds are glass fibers, aromatic polyamide fibers (like Kevlar and Arenka), mineral flour (mica, silica, wollastonite, talcum, and calcium carbonate), wood flour, cellulose, and caibon fibers. Fillers reduce shrinkage during cure, give higher compressive strength and stiffness, and improve thermal resistance, electrical properties, and flame retardancy. 

Another tanning method is mineral tanning, which involves soaking a skin in a solution of alum and salt. This is called tawing. The products of this process are white and open-pored, and become stiff and hard when dried. Due to its open-pored texture, tawed leather is often treated with additives that fill in some of the irregularities and add to the skin s strength. Historically, these fillers have included flour, grease, egg yolks, and fat. 

Shellac was in use by 1856. It is another natural polymer and is based on a secretion from an insect, Laccifer lacca - the lac insect - which is a plant parasite. To produce shellac, the secretion and the insects are scraped off plants and filtered, resulting in a hard, brittle thermoplastic material. It is mixed with wood flour or a mineral filler, pressed, and steamed, dyed, and rolled into sheets to be moulded. 

The common availability of silica is not the sole reason for its extensive use. Probably, it is the chemical inertness and durability of silica which determined its popularity. The fillers discussed here include not only natural minerals but also a variety of synthetic products. Natural products can be divided into crystalline and amorphous. Crystalline silica fillers include sands, ground silica (or silica flour), and a form of quartz - tripoli, whereas the amorphous types include diatomaceous earth. 

Most composite decking manufacturers utilize high-density polyethylene, (HDPE), polypropylene, or polyvinylchloride (PVC) as polymer matrix, and wood flour or rice hulls as the principal filler for their products. Some manufacturers also add mineral fillers, such as talc. These and other changes in compositions make composite materials to vary in their appearance, shape, strength, deflection, moisture absorption, fade resistance, microbial resistance, slip resistance, flammability, and other properties, which will be discussed later in this book. 

Table 3.1 lists WPC deck boards (and one railing system), commercially available and registered by the ICC in 2006 or before (with two exceptions). Most of the materials contain wood flour (or wood hber ), typically in 50-60% amount by weight. Only four products contain rice hulls as a cellulosic filler. One product—GeoDeck—contains delignified cellulose fiber as a part of its principal filler Biodac (which in turn contains about 50% delignified cellulose and 50% minerals). 

However, only few wood-plastic composites (WPCs) use mineral fillers along with cellulose fiber. Table 4.1 lists these composites. Some of them contain minerals only because they employ rice hulls as a principal filler, as rice hulls typically contain 19 1% of silicates. Hence, 50% of rice hulls (by weight) in WPG results in about 9.5% of minerals. In comparison, wood flour typically contains about 0.25% of minerals by weight, and 50% of wood filler would result in only 0.125% (w/w) of minerals in WPG. 

COMPOSITION OF WOOD-PLASTIC COMPOSITES MINERAL FILLERS TABLE 4.3 Effect of inorganic fillers and wood flour on flexural strength and flexural modulus of polypropylene (homopolymer) [2] ... 

Effect of talc on the coefficient of linear thermal expansion-contraction was not pronounced (Table 4.10) and was actually superimposed with that of wood flour. In other words, the principal effect was just a displacement of plastic with a filler, regardless whether it was wood flour or talc. It certainly makes sense because both wood and mineral fillers have their own coefficients of thermal expansion-contraction by an order of magnitude lower than that of HDPE (see Chapter 10). 

Despite beneficial properties of mineral fillers, only few commercially available WPC deck boards include them along with cellulosic liber, such as wood flour and/or rice hulls. As a result, many commercial deck boards can be installed at a span only less than 16 in. on center due to their high deflection under the code-prescribed load (low flexural modulus). This property of deck boards is analyzed in Chapter 7. 

Mineral fillers used are calcium carbonate (CaCOj), China Clay (Al/0H [Si.,0 J), miea especially muscovite (KAyOHjFlJAlSijOj J), silica flour (SiO ), talc (Mg, (OH)j[Si Oj J), and wollastonite (CaSiOj). Parameters that need to be considered during inorganic filler selection are basicity, filler impurities that may influence the resin euring proeess, and filler hardness that eauses abrasion of the mold [1]. Mica filled phenolics are used in electrical parts because mica adds outstanding dielectric properties, high thermal and chemical resistance and low water absorption [1]. 

The lignocellulosic materials mostly used as fillers in thermoplastic composites include wood flour, starch, rice husk and a wide variety of vegetable fibers available such as jute, sisal, flax, hemp, coir, banana, pineapple, among others. And whenever vegetable fiber reinforced thermoplastic composites with higher properties are needed, possible solutions include improved adhesion, better fiber orientation, and filler hybridization with synthetic fibers or mineral fillers. The latter solution is an intermediate alternative regarding environmental friendliness, cost, weight and performance compared to an all synthetic composite [12,26]. 

Reinforcements. Both the resole and novolac compounds use a broad array of reinforcements to meet the demands of the market place wood flour, cotton flock, minerals, chopped fabric. Teflon, glass fibers (long and short), nylon, rubber, and kevlar. Asbestos, which had been a widely used filler in many thermosetting compotmds, has been replaced over the past 20 years with glass fiber-reinforced phenolic compounds in many applications. 

Calcium and magnesium carbonates and wollastonite are all attacked by dilute mineral acids so, when used as fillers, they reduee the acid resistance of the product. Carbon black increases the eleetrical conduetivity, although rather high loadings are needed. Wood flour increases the... 

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