Adhesives, starch

Polymers. AH nitro alcohols are sources of formaldehyde for cross-linking in polymers of urea, melamine, phenols, resorcinol, etc (see Amino RESINS AND PLASTICS). Nitrodiols and 2-hydroxymethyl-2-nitro-l,3-propanediol can be used as polyols to form polyester or polyurethane products (see Polyesters Urethane polymers). 2-Methyl-2-nitro-l-propanol is used in tires to promote the adhesion of mbber to tire cord (qv). Nitro alcohols are used as hardening agents in photographic processes, and 2-hydroxymethyl-2-nitro-l,3-propanediol is a cross-linking agent for starch adhesives, polyamides, urea resins, or wool, and in tanning operations (17—25). Wrinkle-resistant fabric with reduced free formaldehyde content is obtained by treatment with... 

In this method thin layers of adsorbents(such as silica gel, A1 oxide, etc) are bound to glass plates(usually 20x20cm or 20x5cm) by a suitable binding agent(such as starch adhesive). These adsorption plates are often called chromatoplates or chromatostrips. By means of a micropipet, a small drop of sample soln is placed ca 20mm from side and bottom of the plate with other drops placed 10mm apart. 

Even if pigments are completely stable to wet treatments, there is the potential for starch adhesive joins and fills adhered with starch to give way. In addition, delaminations between layers may also occur, or increase if already present. It has also been observed that tapa may decrease in strength while wet, and can be stretched and distorted if not carefully supported. 

The hemicellulose adhesives were evaluated on 50- by 100-mm2 A-flute corrugated board samples. Commercial single-faced board (125 to 160 g/m2) bonded with a maize starch adhesive and liner (160 g/m2) was obtained. The liner and fluting material were prepared from virgin kraft pulp and were not surface-sized with starch. The single-faced material was cut into samples (50 x 100 m2) with the flutes in the 50-mm direction. Liner samples were cut in 60- by 110-m2 samples. 

The hemicellulose adhesive used consisted of one-sixth of the hemicellulose in the dissolved (cooked) state and the remainder in a suspended (raw) state. This preparation was subsequently compared with a hemicellulose adhesive with all the powder dissolved (70 °C treatment) and with a preparation with all the hemicelullose powder suspended (raw). The same amounts of borax and NaOH were used in each case. A starch adhesive prepared according to the Steinhall procedure 13) was used as control. 

The viscosities of the three hemicellulose adhesives and the starch control are given in Figure 4. The viscosity of the suspended hemicellulose adhesive was lower when compared at different solids contents than that of the starch control. It was, on the other hand, much higher than the viscosity of a raw starch suspension (30 cP at 35% solids). The higher viscosity of the raw hemicellulose adhesive is probably caused by the gel-like outer layer of the raw hemicellulose-suspended particles. The suspended starch particles showed no such surface gel effect, but remained totally undissolved. The viscosities of the cooked and raw-cooked hemicellulose adhesive were similar to those of the starch adhesive (Figure 4). 

Kroeschell, W. O. Preparation of Starch Adhesives, in Preparation of Corrugating Adhesives, TAPPI Press, Florida, USA. 1977, Chapter 2, 5-17. 

In polymeric terms, a main distinction between starch and cellulose is that the former contains highly branched molecules whereas the latter contains linear molecules. The branching means that crystalline sequences are shorter in starch and fibres do not form. Accordingly, native starch is more readily destructuned than native cellulose. Such destructuring is, of course, the basis of much food preparation and, hence, the processing of starch dates back several millennia into human history. In addition, starch adhesives were known by 3500 BC. 

Starch adhesive Aqueous adhesive based on natural starch. 

Additional information on starch ethers has been reported by Pringsheim,1264 Hjermstad1265 as well as Banks and coworkers,1266 and Mishler1267 [only (hydrox-yethyl)starch], Omae and coworkers1268 [only (hydroxypropyl)starch adhesives], Hjermstad,1269 Mehltretter,1270 Moser1271 [(hydroxyethyl)starch], Tuschhoff1272 [(hydroxypropyl)starch], and Wurzburg1273 (crosslinked starches). 

Adhesives. Adhesives can be considered as coatings between two surfaces. The classic adhesives were water-susceptible animal and vegetable glues obtained from hides, blood, and starch. Adhesion may be defined as the process that occurs when a solid and movable material (usually in a liquid or solid form) are brought together to form an interface, and the surface energies of the two substances are transformed into the energy of the interface. 

Ketac. [Am. Cyanamid] Acetone-formaldehyde for waterproofing starch adhesives. 

In his book The Technology of Adhesives [6], John Dehnonte tells us that the first commercial glue plant was founded in Holland in 1690, that casein glues appear to have been manufactured in Germany and Switzerland in the early nineteenth century, and that the first U.S. patent (number 183,024) on a casein glue was issued in 1876. He mentions that starch adhesives were used on postage stamps when they were first issued in 1840, and that the first U.S. patent (number 61,991) on a dextrin adhesive was issued in 1867. 

Corrugated board is produced by the adhesion of a fluted layer of paper to a flat layer. A two-phase starch adhesive is commonly used to join the two layers. The liquid phase, a gelled mixture of starch and sodium hydroxide in water, is called the carrier. The solid phase of ungelled starch and borax is suspended in the carrier phase. The mixture is applied to a warm fluted sheet, which is then placed into contact with a hot flat sheet. The ungelled starch gels from the heat of the sheets. Table 2 shows a recipe for a typical corrugating adhesive [13]. 

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