Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Phenol-carbohydrate , adhesive formulation

Carbohydrate-phenolic-based resins have shown promise for partial replacement of phenol and formaldehyde in exterior plywood adhesives (7,2). Such resins are produced in a two-stage reaction sequence. First, the carbohydrate is reacted with phenol, and sometimes urea, under acid catalysis at elevated temperatures (up to 150 °C), to produce an acid-stage resin. The acid-stage resin is then made basic, formaldehyde added, and the reaction continued at lower temperatures to produce a resol-type resin. Adhesives formulated from these resins have curing speeds consistent with present-day plywood production needs in the western United States, veneers are typically dried to 0 to 7% moisture content and the adhesive cured by hot pressing the panels at approximately 140 to 150 °C and 1.2 MPa. [Pg.384]

Soybean flour can be used as the main component in adhesive formulations, but it is commonly added as extender for phenolic systems, or blended with casein or other adhesives. They are packaged as dry powders that contain both proteins and carbohydrates. The flour is dispersed in aqueous sodium hydroxide for preparing the adhesive, and also calcium hydroxide is added to extend the open time and to improve water resistance. Soybean glues have a limited water resistance, but recover their strength on drying. They are also susceptible to mold growth, and some fungicides need to be included in the commercial formulations. Fillers are used to reduce cost, but they also lower the performance of the adhesive. Some commonly used fillers are wood and walnut-shell flours, and also clay. [Pg.1392]

Figure 1 illustrates the fact that resins and adhesives formed by the possible combinations of a phenolic compound, a nitrogenous compound, an aldehyde compound, and a carbohydrate have been reported in the literature. The exact conditions used to formulate the resins and adhesives represented in Figure 1 vary considerably. For example, additional circles representing acidic, basic, and neutral reaction conditions could be added. In most instances, the exact chemistry that occurs during the formulation of resins at each intersection is not known. Indeed, in many cases, the component actually reacting into the resin or adhesive system may not be the original carbohydrate added at the start. In this and other respects, these formulations will overlap with those discussed in the next section. [Pg.274]

Table III lists a number of selected references that describe the formulation of resins or adhesives at each intersection in Figure 1. PF, UF, UF modified with phenolics, and PF modified with nitrogenous compounds (e.g., urea) have not been included, because they do not contain carbohydrates and because they are in common use. The resin and adhesive systems that have been investigated most recently are those formed by the combination of carbohydrates with PF, both with and without the addition of a nitrogenous compound. Our attempts at the Forest Products Laboratory to use carbohydrate modified PF to bond wood are discussed in Chapter 25. Table III lists a number of selected references that describe the formulation of resins or adhesives at each intersection in Figure 1. PF, UF, UF modified with phenolics, and PF modified with nitrogenous compounds (e.g., urea) have not been included, because they do not contain carbohydrates and because they are in common use. The resin and adhesive systems that have been investigated most recently are those formed by the combination of carbohydrates with PF, both with and without the addition of a nitrogenous compound. Our attempts at the Forest Products Laboratory to use carbohydrate modified PF to bond wood are discussed in Chapter 25.

See other pages where Phenol-carbohydrate , adhesive formulation is mentioned: [Pg.166]    [Pg.382]    [Pg.1182]    [Pg.276]    [Pg.368]    [Pg.384]    [Pg.390]   
See also in sourсe #XX -- [ Pg.279 ]




SEARCH



Adhesive formulation

Phenol-carbohydrate

© 2024 chempedia.info