Wood-plastic combinations

In industry, radiation is applied both as an initiator and as a control mechanism on one hand, and as a sustainer of reactions on the other. Among the many industrial uses of radiation, one may mention food preservation, curing of paints, manufacture of wood-plastic combinations, syntheses of ethyl bromide, of ion exchange materials, of various graft copolymers, and of materials for textile finishing. In addition, there are important uses of tracers in various process industries and in mining and metallurgy. 

How does our research stand in rendering wood fire retardant What is the effect of fire-retardant treatments on the fire performance properties of wood and on the physical and mechanical properties of wood that are important to its utility Discussion will be limited to fire retardancy obtained by pressure impregnation, which is currently the most effective method. Fire-retardant coatings, wood-plastic combinations, and chemical modifications of wood will not be considered. 

Kent, J. A., Winston, A., and Boyle, W. R., "Preparation of Wood - Plastic Combinations using Gamma Radiation to Induce Polymerization", U. S. Atomic Energy Commission Report 0. R. 0. - 600 and 612 (1962). 

Terpolymers, prepared from various methacrylate-MA pairs, copolymerization with glycidyl methacrylate and acrylonitrile have been examined in water-soluble films and coatings " and wood-plastic combinations. 

The thermosetting coatings exhibited excellent protective and decorative properties. Wood-plastic combinations prepared by this procedure exhibited excellent dimensional stability and other properties, due to significant condensation reaction of the anhydride groups with cellulosic hydroxyl residues. 

With only 90 elements, one might assume that there could be only about 90 different substances possible, but everyday experience shows that there are millions of different substances, such as water, brick, wood, plastics, etc. Indeed, elements can combine with each other, and the complexity of these possible combinations gives rise to the myriad substances found naturally or produced artificially. These combinations of elemental atoms are called compounds. Since atoms of an element can combine with themselves or with those of other elements to form molecules, there is a wide diversity of possible combinations to make all of the known substances, naturally or synthetically. Therefore, atoms are the simplest chemical building blocks. However, to understand atoms, it is necessary to examine the structure of a typical atom or, in other words, to examine the building blocks of the atoms themselves. The building blocks of atoms are called electrons, protons, and neutrons (Figure 46.1). 

U.S. Pat. No. 6,958,185 [59] (by Crane Plastics Co., TimbeiTech) describes a wood-plastic composition comprised of a layer of a first composition that is secured to a layer of a second composition, with the resulting multilayer component having an improved combination of appearance, strength, durability, weight, weatherability, and other characteristics. 

New developments give options in the form of hybrid materials combining wood with conventional plastics (e.g. Wood Plastic Composites, WPC) (Section 9.4.4) or as solid wood improved by heat treatment or chemical modification, e.g. acetylation, oil treatment etc. (Section 9.4.5). 

EPI adhesives have very good adhesion properties to the wood surface and thus can glue different wood species very well. Since this adhesive type also has very good adhesion to materials like metals, plastics and foams, it is very well suited for gluing composite materials where wood is combined with other materials [2,4, 5]. The excellent adhesion of EPI adhesives to metals has to be taken into account in the production process since the glued pieces may adhere to the press plates if no surface treatment of the press plates is used. Release agents are available and are in use. 

Styrene, MA, peroxides, and sawdust may be combined and polymerized to obtain useful wood-plastic composites.In the effort, the hydroxyl groups on the cellulose react to some extent with the anhydride residues to give a three-dimensional structure, with very good moisture resistance. This concept could possibly be useful for improving the physical properties of many soft woods. 

X The results imply that wood-plastic composites with properties similar to solid wood could be manufactured by tailoring the formulation, i.e., combining nanoclay, rigid PVC, wood flour, and coupling agent. 

Phenol—formaldehyde (PF) was the first of the synthetic adhesives developed. By combining phenol with formaldehyde, which has exceptional cross-linking abiHties with many chemicals and materials, and a small amount of sodium hydroxide, a resin was obtained. The first resins soHdified as they cooled, and it was discovered that if it was ground to a powder with a small amount of additional formaldehyde and the appHcation of more heat, the mixture would Hquify and then convert to a permanently hard material. Upon combination of the powdered resin mixture with a filler material such as wood flour, the result then being placed in a mold and pressed under heat and pressure, a hard, durable, black plastic material was found to result. For many years these resulting products were called BakeHte, the trade name of the inventor. BakeHte products are still produced today, but this use accounts for only a small portion of the PF resins used. 

The polymers of the 2-cyanoacryhc esters, more commonly known as the alkyl 2-cyaiioacrylates, are hard glassy resins that exhibit excellent adhesion to a wide variety of materials. The polymers are spontaneously formed when their Hquid precursors or monomers are placed between two closely fitting surfaces. The spontaneous polymerisation of these very reactive Hquids and the excellent adhesion properties of the cured resins combine to make these compounds a unique class of single-component, ambient-temperature-curing adhesives of great versatiUty. The materials that can be bonded mn the gamut from metals, plastics, most elastomers, fabrics, and woods to many ceramics. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

A rather impressive Hst of materials and products are made from renewable resources. For example, per capita consumption of wood is twice that of all metals combined. The ceUulosic fibers, rayon and cellulose acetate, are among the oldest and stiU relatively popular textile fibers and plastics. Soy and other oilseeds, including the cereals, are refined into important commodities such as starch, protein, oil, and their derivatives. The naval stores, turpentine, pine oil, and resin, are stiU important although their sources are changing from the traditional gum and pine stumps to tall oil recovered from pulping. 

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