Wood cellulose fibers

The surface energy of fibers is closely related to the hydrophilicity of the fiber [38]. Some investigations are concerned with methods to decrease hydrophilicity. The modification, of wood cellulose fibers with stearic acid [43] hydrophobizes those fibers and improves their dispersion in polypropylene. As can be observed in jute-reinforced unsaturated polyester resin composites, treatment with polyvinylacetate increases the mechanical properties [24] and moisture repellency. 

Enzymatic methods show the biggest promise for conversion of waste paper from municipal waste into glucose for ethanol production. Because paper is composed primarily of wood cellulose fibers, the enzyme inhibition due to lack of accessibility with whole wood is partially alleviated. As mentioned previously, waste paper can represent up to 50 percent of typical municipal waste. Currently the separated paper from the waste is burned for its fuel value. 

It is practically impossible to make industrial WPC boards without any porosity, hence, without any decrease in density compared to its theoretical value. Even traces of moisture in wood/cellulose fiber create steam at hot melt tempera-tnres, hence, porosity. Plastic decomposition during processing prodnces volatile organic compound (VOC), hence, porosity. Wood extractives decomposition prodnces VOC, hence, porosity. Wood fibers lignin decomposition at plastic hot... 

For wood-cellulose fiber composite materials, flex strength is measured typically in thousands of psi (pounds per square inch), whereas flex modulus is measured in hundreds of thousands of psi. 

The physical macroscopic notion of porosity or pores in a solid and the phenomenon of absorption of a fluid in a porous object are both quite familiar to all of us. Further, wide varieties of natural or synthetic solids, compounds, species, and materials are known to be of porous nature, for example, minerals, wood, cellulose fibers, seashells. 

Polymer Blends Incorporating PHA. The mechanical properties, morphology, biodegradability, and thermal and crystallization behavior of PHAs melt-blended or solvent-cast with nonbiodegradable pol5uners [such as poly(vinyl acetate)] and with biodegradable materials [such as wood cellulose fibers (21) and starch] have been reviewed (22). PHB blends with poly(ethylene oxide), poly(vinyl alcohol), poly (L-lactide), poly(D,L-lactide), poly( -caprolactone), poly(3-butyrolactone), P(HB-co-HV), and cellulose and starch derivatives have been... 

As such wood flour, used as a filler in thermoplastic composites, offers only modest, if any, reinforcement, but wood fibers can lead to superior composite properties and act more as reinforcing filler. Commercial wood flour is a by-product of the wood industry, often mechanically processed from waste materials such as planer shavings, chips, and sawdust, which are reduced to fine powders, with various grades available depending upon the particle size and the wood species. Wood (cellulose) fibers are produced through more or less complex defibrillation techniques, using raw materials from both virgin and recycled resources, and are different from natural fibers, such as jute, hemp, or sisal. 

Other fibrous and porous materials used for sound-absorbing treatments include wood, cellulose, and metal fibers foamed gypsum or Pordand cement combined with other materials and sintered metals. Wood fibers can be combined with binders and dame-retardent chemicals. Metal fibers and sintered metals can be manufactured with finely controlled physical properties. They usually are made for appHcations involving severe chemical or physical environments, although some sintered metal materials have found their way into architectural appHcations. Prior to concerns regarding its carcinogenic properties, asbestos fiber had been used extensively in spray-on acoustical treatments. 

A commercial bacterial cellulose product (CeUulon) was recently introduced by Weyerhaeuser (12). The fiber is produced by an aerobic fermentation of glucose from com symp in an agitated fermentor (13,14). Because of a small particle diameter (10 P-m), it has a surface area 300 times greater than normal wood cellulose, and gives a smooth mouthfeel to formulations in which it is included. CeUulon has an unusual level of water binding and works with other viscosity builders to improve their effectiveness. It is anticipated that it wiU achieve GRAS status, and is neutral in sensory quaUty microcrystaUine ceUulose has similar attributes. 

The modem interest in composite materials can be traced to the development of BakeHte, or phenoHc resin, in 1906. BakeHte was a hard, brittle material that had few if any mechanical appHcations on its own. However, the addition of a filler— the eadiest appHcations used short cellulose fibers (2)—yielded BakeHte mol ding compounds that were strong and tough and found eady appHcations in mass-produced automobile components. The wood dour additive improved BakeHte s processibiHty and physical, chemical, and electrical properties, as weU as reducing its cost (3,4). 

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

The cellulose fiber in paper is attacked and weakened by sulfur dioxide. Paper made before about 1750 is not significantly affected by sulfur dioxide (11). At about that time, the manufacture of paper changed to a chemical treatment process that broke down the wood fiber more rapidly. It is thought that this process introduces trace quantities of metals, which catalyze the conversion of sulfur dioxide to sulfuric add. Sulfuric acid causes the paper to become brittle and more subject to cracking and tearing. New papers have become available to minimize the interaction with SO2. 

Electric discharge (corona, cold plasma) is another method of physical treatment. Corona treatment is one of the most interesting techniques for surface oxidation activation. This process changes the surface energy of the cellulose fibers [28]. In the case of wood surface activation it increases the amount of aldehyde groups [291. 

The mechanical properties of composites reinforced with wood fibers and PVC or PS as resin can be improved by an isocyanate treatment of those cellulose fibers [41,50] or the polymer matrix [50]. Polymethylene-polyphenyl-isocianate (PMPPIC) in pure state or solution in plasticizer can be used. PMPPIC is chemically linked to the cellulose matrix through strong covalent bonds (Fig. 8). 

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

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