Manufacturing gluing

Four other groups of synthetic adhesives find uses in secondary processing, ie, overlaying, assembly gluing, etc, and in furniture and cabinet manufacture. Poly(vinyl acetate) (PVA) adhesives are widely used in appHcation of veneers and other overlays to panel substrates and in some unit-assembly operations. PVA adhesives are an emulsion of polyvinyl acetate in water and cure by loss of water. The PVA adhesives are somewhat... 

These adhesives are essentially for gluing wood. Urea—formaldehyde adhesives are used in the manufacture of plywood, in the fortification of starch... 

Truax, T.R., Gluing Practice at Aircraft Manufacturing Plants and Repair Stations. Technical Note No. 291, National Advisory Committee for Aeronautics, Washington, DC, 1928. 

A small rupture disc failed to operate it was then found that the manufacturer had inadvertently supplied two discs that nested one on top of the other and appeared to be one. Most discs are individually boxed, but some are supplied stacked and should be carefully checked. Some small discs are supplied with gaskets already glued to them, and these are particularly likely to stick together. 

Developments in glued laminated structures and panel products such as plywood and chipboard raises the question of the durability of adhesives as well as wood. Urea-formaldehyde adhesives are most commonly used for indoor components. For exterior use, resorcinol adhesives are used for assembly work, whilst phenolic, tannin and melamine/urea adhesives are used for manufactured wood products. Urea and casein adhesives can give good outdoor service if protected with well-maintained surface finishes. Assembly failures of adhesives caused by exudates from some timber species can be avoided by freshly sanding the surfaces before glue application. 

Most of the benzene used in chemical applications ends up in the manufacturing processes for styrene (covered in Chapter 8), cumene (covered in Chapter 7), and cyclohexane (covered in Chapter 4), Polymers and all sorts of plastics are produced from styrene. Cumene is the precursor to phenol, which ultimately ends up in resins and adhesives, mostly for gluing plywood together. The production of styrene and phenol account for. about 70% of the benzene produced. Cyclohexane, used to make Nylon 6 and Nylon 66, is the next biggest application of benzene. 

Reconstituted Wood Products. This category includes three general varieties wood flake board, particle board, and wood fiberboard. The manufacturing processes are similar for all these products except for the size of the wood particles that are glued together. 

After the veneer has been properly unitized and dried, it is transported to the gluing operation. It is here that the greatest proportion of chemicals other than water are involved in the plywood process. To better understand the adhesive resins involved, perhaps it is best to review the quantities of softwood and hardwood plywood manufactured in relation to the adhesive needs required. The 1972 - 1973 era were years of peak production in the United States for plywood. Data will be extracted from various reports for presentation purposes. Hardwood and softwood plywood production is normally reported in different manners and it is difficult to compare. While the values reported are not intended to be exactly accurate, they will give some comparison, relatively speaking, and should give some concept of the volume of plywood produced and in turn the volume of adhesives used. 

In the April, 1975, issue of Plywood Panel magazine, we find reported square feet, quarter inch basis, domestic hardwood plywood manufactured in this country was approximately 3.5 billion and softwood plywood was 27.5 billion. This means 89 percent of the total plywood produced was softwood plywood, and 97 percent of this production was glued with phenol-formaldehyde resin adhesives, according to the American Plywood Association. This leaves 11 percent domestic hardwood plywood which was 95 percent glued with urea-formaldehyde resin adhesives,... 

The traditional method of starch production involves alkali solubilization of the glu-telin which constitutes approximately 80% of the protein in rice. This method has been described by Hogan,21 and is utilized in some form by almost every rice starch manufacturer (with the exception described below). It produces a starch containing <1% protein. The protein by-product of this process, while good-quality protein, has a distinct aftertaste (alkali, salt and amino acid), making it not easily acceptable as a food ingredient. 

---