Wood Based Substrates

SEMI-STERILE AND STERILE WOOD BASED SUBSTRATES 

Commercial growers of lignicolous mushrooms are turning increasingly to sawdust based substrates. Such substrates have been developed in Japan for growing Pleurotus, Flammulina and 

Auricularia. They are also being utilized with some modifications by commercial shiitake growers in the United States. The development of these mushroom specific substrates follows certain well defined guidelines. 

The basic raw material is cellulose, a major constituent of sawdust, straw, cardboard or paper wastes, wood chips, or other natural plant fibers. Any of these materials should be chopped or shredded, but never so finely as to eliminate their inherent structural qualities. This cellulosic base comprises approximately 80% of the total substrate mixture. 

Japanese growers of Flammulina velutipes. Auricularia auricula and allies, and Pleurotus ostreatus have a standard substrate formula consisting of 4 parts sawdust and 1 part bran. The saw- 

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Epoxy resins are also used in special appHcations, such as an overlaying procedure requiring a durable, heat-resistant bond of a difficult-to-bond overlay on a wood-base panel substrate. Metal sheets used as overlays, for example, often require an epoxy adhesive. 

Molasses, fruit juice, corns, bagasse, Jerusalem artichockes, cassava, whey, sulfite liquor, saw dust and other wood by-products are used as substrates for alcohol and glycerin production. Starch-based substrates should be first saccharified by amylases prepared from barley, fungi or bacteria. Cellulosic materials must also be chemically or enzymatically hydrolyzed before being used as substrates for alcohol production. Clostridium species contain amylases and are able to convert starch and cellulose directly16). 

It has already been mentioned that a large number of components are used for the construction of wood-based furniture. In addition to the compounds described earlier, a large spectrum of volatile organics can be found in emission studies (Salthammer, 1997b). The main sources for formaldehyde (which is not considered here), phenol and acetic acid are substrates such as particle board and MDF. BHT is a common antioxidant. Volatile plasticizers include dimethyl phthalate (DMP), dibutyl phthalate (DBP), as well as esters of adipic acid and sebacic acid. Further important compound groups are amines, siloxanes, carboxylic acids and naphthalenes. The identification of special substances does not only require suitable analytical equipment. Both experience and detailed knowledge of the chemical composition of furniture are also necessary. 

Wood and wood-based furniture are potential sources of a variety of organic compounds in the indoor environment. Most emitted compounds are typical solvents, but monomers and reaction products are also of importance. The source strength of a product will strongly depend on the substrate, the type of coating and the quality of the manufacturing process. It seems that one main reason for frequent complaints about VOC emissions from furniture is the common practice of tight wrapping in non-permeable foil immediately after manufacture and fast delivery to the customer. VOC residuals are reabsorbed in the interior of cabinets and problems such as a sudden release and contamination of textiles may arise. 

Nystrom G, Mihranyan A, Razaq A et al (2010) A nanocellulose polypyrrole composite based on microfibrillated cellulose from wood. J Phys Chem B 114 4178-4182 Okahisa Y, Yoshida A, Miyaguchi S et al (2009) Optically transparent wood-cellulose nanocomposite as a base substrate for flexible mganic light-emitting diode displays. Compos Sci Technol 69 1958-1961... 

The authors of this chapter conducted a recent study, which evaluated the efficacy of plasma treatment on a model wood substrate. In order to imderstand the effect of plasma treatment on wood-based fibers, clear pine wood veneers with an identical chemical composition was used as a model substrate. Plasma treatment was conducted using a custom built 13.56MHz inductively coupled plasma chamber in continuous wave mode (CW) and continuous wave mode plus pulse plasma mode [60]. During continuous wave mode the plasma is always on , so the formation of functional groups is accompanied by their destruction due to the continuous ion bombardment or surface ablation. During the pulse mode, the plasma source is on for a specific period and the plasma generated is similar to the continuous wave mode, where the plasma reactive species interact with the surface of the wood substrate. During the period when the... 

While PVOH and the vinyl acetate (co)polymers would not typically be considered to be compatible, the grafting achieved during polymerization and the resultant morphology yields useful and compatible compositions. The presence of PVOH yields good adhesion to cellulosic based substrates for wood glue, non-woven binder, and paper based packaging applications. The miscibility of PVOH with cellulose has been demonstrated, providing a rationale for the excellent adhesion [30]. 

By varying molecular weight and functionaUty of the castor polyols and the type of isocyanate, a variety of clear and pigmented urethane coatings can be prepared. Copolymers of vinyl and castor-based urethane have also been reported for use as exterior coatings for plywood and flexible substrates (90) and for appHcation over steel, concrete, and wood substrates (91). 

Amino resms are probably the mos important modifiers for alkyd resins. Many industrial baking enamels, such as those for appliances, coil coatings, and automotive finishes (especially refinishing enamels), are based on alkyd-amino resin blends. Some of the so-called catalyzed lacquers for finishing wood substrate require very low bake or no bake at all. 

To be able to predict the release of SVOCs from a material to the indoor environment it is important to understand the fundamental mechanisms in order to mathematically model the emissions. The emission behavior of DEHP from PVC in the FLEC and CLIMPAQ experiments (Clausen et al., 2004) have now been successfully modeled (Xu and Little, 2006). Fluid building materials such as paints (Clausen, 1993 Xu and Little, 2006) and wood oil (Clausen, 1997) may also emit SVOCs and are usually used on large indoor surfaces such as walls, ceilings and floors. Such wet materials may be applied on substrates like wood or plaster board. The emission of for example, Texanol from water-based paint was found likely to be limited by gas phase mass transport (Clausen, 1993) similar to the DEHP emission from PVC (Clausen et al., 2004). 

Vinyl Acetate-Ethylene. Materials based on copolymers of vinyl acetate and ethylene exhibit a good balance of properties. As the ratio of vinyl acetate to ethylene is increased the copolymers become softer, more hydrophilic, and offer enhanced adhesion. However, at the highest levels of vinyl acetate the films become hard again, showing good adhesion to substrates such as wood and paper but with resistance to water somewhat inferior to that of the intermediate copolymers. 

The objective of bleaching is to produce a white pulp of stable color obtained at reasonable cost and a minimum deleterious effect on the physical and chemical properties of the pulp. Inasmuch as the major chromophoric substances in wood pulps are derived from the lignin substrate, it must be chemically changed to colorless configurations in a stable form, or it must be oxidized, reduced, or hydrolyzed, rendering it soluble in aqueous solutions and so removable from the pulp. The two major methods of bleaching are based on these principles (23,24). 

Chemical modification reactions continue to play a dominant role in improving the overall utilization of lignocellulosic materials [1,2]. The nature of modification may vary from mild pretreatment of wood with alkali or sulfite as used in the production of mechanical pulp fibers [3] to a variety of etherification, esterification, or copolymerization processes applied in the preparation of wood- [4], cellulose- [5] or lignin- [6] based materials. Since the modification of wood polymers is generally conducted in a heterogeneous system, the apparent reactivity would be influenced by both the chemical and the physical nature of the substrate as well as of the reactant molecules involved. 

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