Wood flour extenders

In thermosetting adhesives, wood flour has been used for several functions. As an extender, it is added to reduce cost while retaining bulk for uniform spreading. Unfortunately, wood flour extenders generally also reduce durability of a given resin. As filler, it is added to thermoset adhesives to control penetration when bonding wood and to improve characteristics of the hardened film [31]. 

By far the preponderance of the 3400 kt of current worldwide phenolic resin production is in the form of phenol-formaldehyde (PF) reaction products. Phenol and formaldehyde are currently two of the most available monomers on earth. About 6000 kt of phenol and 10,000 kt of formaldehyde (100% basis) were produced in 1998 [55,56]. The organic raw materials for synthesis of phenol and formaldehyde are cumene (derived from benzene and propylene) and methanol, respectively. These materials are, in turn, obtained from petroleum and natural gas at relatively low cost ([57], pp. 10-26 [58], pp. 1-30). Cost is one of the most important advantages of phenolics in most applications. It is critical to the acceptance of phenolics for wood panel manufacture. With the exception of urea-formaldehyde resins, PF resins are the lowest cost thermosetting resins available. In addition to its synthesis from low cost monomers, phenolic resin costs are often further reduced by extension with fillers such as clays, chalk, rags, wood flours, nutshell flours, grain flours, starches, lignins, tannins, and various other low eost materials. Often these fillers and extenders improve the performance of the phenolic for a particular use while reducing cost. 

Fillers are relatively nonadhesive substances added to the adhesive formulation to improve its working properties, strength, permanence, or other qualities. The improvements resulting from the use of fillers are listed in Table 1.8. Fillers are also used to reduce material cost. By selective use of fillers, the properties of an adhesive can be changed significantly. Thermal expansion, electrical and thermal conduction, shrinkage, viscosity, and thermal resistance are only a few properties that can be modified by the use of fillers. Common fillers are wood flour, silica, alumina, titanium oxide, metal powders, china clay and earth, slate dust, and glass fibers. Some fillers may act as extenders. 

Organic Extenders. Organic extenders are primarily of two types (1) fillers derived from organic materials and (2) low-cost, naturally occurring or synthetic resins. Of the first type, wood flour, shell flour, and other cellulosic fillers are the most common. They also provide a margin of mechanical property reinforcement because of their relatively high aspect ratio. Of the resinous types these are petroleum-based derivatives as well as soluble lignin and scrap synthetic resins. 

The casein content of the dry adhesive varies from 30% to 70% depending on its use. Extenders and fillers such as soy and wood flours are added to obtain an economical adhesive. One or more alkalis such as sodium hydroxide, lime,... 

These recycling techniques aside, it is also possible to extend the lifetime of plastics dnring their nsage. It has been shown by certain studies that wood flour/poly(ethyIene) composites used to build public benches could have a more favorable balance than wood itself, which is because of the non-biodegradabihty of PE [HOL 04]. Other authors have observed that the introduction of a certain quantity of wood flour into poly(propylene) helped increase its durabihty and improve its mechanical properties [LAM 08]. 

Diatomaceous earth Magnesium oxide Pyrophyllite Quartz Silica, hydrated Sodium silicate Sodium silicoaluminate Terpene resin Wollastonite Xanthan gum extender, paints/coatings Calcium carbonate Kaolin extender, paper Calcium sulfate dihydrate extender, paper coatings Wollastonite extender, paper sizing Kaolin Xanthan gum extender, paperboard Wood flour... 

The ureas are a group of chemical compounds that are generally compounded with wood flour as their chief reinforcement, providing a free-flowing granular compound that can be preformed, preheated, or preplasticated. These compounds can be readily molded with both compression and transfer molding methods, however they require special formulations when they are processed with screw injection equipment due to the need to extend their flow life at the higher barrel temperatures. 

Examples of inert or extender fillers include china clay (kaolin), talc, and calcium carbonate. Calcinm carbonate is an important filler, with a particle size of about 1 pm. It is a natural product from sedimentary rocks and is separated into chalk, limestone, and marble. In some cases, the calcium carbonate may be treated to improve interaction with the thermoplastic. Glass spheres are also used as thermoplastic fillers. They may be either solid or hollow, depending on the particular application. Talc is a filler with a lamellar particle shape. It is a namral, hydrated magnesium silicate with good slip properties. Kaolin and mica are also natural materials with lamellar structures. Other fillers include woUastonite, silica, barium sulfate, and metal powders. Carbon black is used as a filler primarily in the rnbber industry, but it also finds application in thermoplastics for conductivity, for UV protection, and as a pigment. Fillers in fiber form are often used in thermoplastics. Types of fibers inclnde cotton, wood flour, fiberglass, and carbon. Table 1.3 shows the fillers and their forms. An overview of some typical fillers and their effect on properties is shown in Table 1.4. Considerable research interest exists for the incorporation of nanoscale fillers into polymers. This aspect will be discussed in later chapters. 

Wood flour has been produced commercially since 1906 [2] and has been used in many and varied products including soil amendments, extenders for glues, and absorbents for explosives. One of its earliest uses in plastics was in a phenol-formaldehyde and wood flour composite called Bakelite. Its first commercial product was reportedly a gearshift knob for Rolls Royce in 1916 [3], Though once quite prevalent as filler for thermosets, its use has diminished over the years. 

Lignin lig-n9n (1822) n. The major noncarbohydrate constituent of wood and woody plants, functioning in nature as a binder to hold the matrix of cellulose fibers together. Lignins are obtained commercially from by-products of coniferous woods, for example, by treating wood flour with a derivative of lignosulfonic acid. They are used as extenders in phenolic resins, and sometimes as reactants in the production of phenol-formaldehyde resins. Hoadley RB (2000) Understanding wood. The Taunton Press, Newtown, CT. 

Wood flour 40-325 mesh Extender for thermosets Moisture content can be up... 

The term wood-plastic composites (WPG) covers an extremely wide range of composite materials using plastics ranging from polypropylene (PP) to polyvinyl chloride (PVC) and binders/fillers ranging from wood flour to flax. These new materials extend the current concept of wood composites from the traditional compressed materials such as... 

Organic fillers Extenders/fillers (wood flour, nutshell, corncobs, rice, peanut hulls)... 

The typical sodium salts include sodium fluoride, trisodium phosphate, soda ash, sodium bicarbonate, sodium sulfite, and others. The lime and sodium fluoride are essential for ready liquefaction of the glue. Casein may be dissolved with only lime, but this type of adhesive remains fluid only a short time before gelling. Additives, including defoamers and zinc compounds, and extenders, such as clays, wood flour, and shell flour, are frequently used. 

Fillers. Fillers are particulate materials whose major ftmction often is simply to extend the polymer and thereby reduce the cost of the plastic compound. One of the earliest examples of a filler is the wood flour (fime sawdust) long used in phenolics and other thermosets. Calcium carbonate is used in a variety of plastics and polypropylene is often filled with talc. Even water has been used to extend polyester casting compounds. 

In gluing, the adhesive must not saturate veneers or wood chips, but must remain in the glue line on the surface of the chips or between the pHes. The adhesives are generally of high viscosity so that they remain in the glue line. Thickeners and extenders, such as powdered pecan shells and wheat flour, are often used. 

EXTENDER. A low-graxily material used in paint, ink. plastic, and rubber formulations chiefly to reduce cost per unit volume by increasing bulk, Extenders include dialomaccou.s earth, wood flock, mineral rubber, liquid asphalt, etc. Microscopic droplets of water fixed permanently in a plastic matrix are an efficient extender tor polyester resins. In the food industry, the term refers to certain extruded proteins, especially those derived from soybeans, which are used in meat products to provide equivalent nutrient values at lower cost. Made from defatted soy flour, they are often called textured proteins. 

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