Polyvinyl alcohol-borate

Polysorbates or sorbitan esters, acacia, and tragacanth Aluminum magnesium silicate, bentonite, carbomers, cellulose derivatives, gelatin, pectin, polyvinyl alcohol, alginates, starch, and xanthan gum Borates, citrates, acetates, and phosphates... 

Lopez Garcia et al. [2] have described a rapid and sensitive spectrophotometric method for the determination of boron complex anions in plant extracts and waters which is based on the formation of a blue complex at pH 1 - 2 between the anionic complex of boric acid with 2,6-dihydroxybenzoic acid and crystal violet. The colour is stabilised with polyvinyl alcohol. At 600 nm the calibration graph is linear in the range 0.3-4.5 xg boron per 25 ml of final solution, with a relative standard deviation of 2.6% for xg/l of boron. In this procedure to determine borate in plant tissues, the dried tissue is treated with calcium hydroxide, then ashed at 400 °C. The ash is digested with 1N sulfuric acid and heated to 80 °C, neutralized with cadmium hydroxide and then treated with acidic 2,6-dihydroxybenzoic acid and crystal violet, and the colour evaluated spectrophotometrically at 600 nm. Most of the ions present in natural waters or plant extracts do not interfere in the determination of boron complex anions by this procedure. Recoveries of boron from water samples and plant extracts were in the range of 97 -102%. 

SCHEME 9.1 Polyvinyl alcohol cross-linked by borate. 

Bulmus et al. (1997) demonstrated the modified PMMA mono-size microbeads for glucose oxidase immobilization, in which PMMA substrate was washed with 10% (w/v) NaOH followed by 50% (v/v) ethanol. Freshly cleaned PMMA was then immersed in a solution of 1 g/L polyvinyl alcohol for 20 min, followed by oxidation reaction with a solution of 1% NaI04 for 1 h at room temperature. The amino functionality was then added by using a solution of 10% (w/v) hexamethylene diamine in 100 mM borate buffer pH 11.5, for 2 h (123) (shown in scheme 8.5). 

Highly polymerized polysaccharides with adjacent OH-groups in cis position, or even 1,3-diols, such as in polyvinyl alcohol react with borax (77, 78, 55, 77). The reaction was studied by measuring the increase in viscosity of the respective polymer. For the molecular structure a cross linkage of the borate tetrahedron to the polysaccharides has been suggested (77) (Fig. 12). 

Alginic acid s-Amyl acetate Bayberry (Myrica cerifera) wax Beeswax s-Butyl acetate C12-18 acid triglyceride Carboxymethylcellulose sodium Casein Cellulose acetate Ethylene/MA copolymer Milk protein Perchloroethylene Polyvinyl alcohol Sodium silicate Starch Styrene/MA copolymer Tristearin sizing compounds Calcium bromide Sodium borate sizing ingredient, paper Dodecenylsuccinic anhydride Rosin Sodium stearate Stearic acid sizing paper Dextrin... 

Polyvinyl alcohol is a water-soluble polymer which can be cross-linked into a gel by sodium borate (Na2B40v). This is shown in Fig. 11.6. Fibers made from PVAl can be made insoluble in water by cross-linking with formaldehyde, shown in Fig. 11.7. Such fibers are excellent substitutes for cotton because they absorb moisture (sweat) readily. 

An interesting and separate application proposed for borate is as a component of a cement fluid loss additive. Cements require a minimum amount of water for proper hydration and setting and if water from the cement filters into the formation, the setting process can be compromised. Cements therefore contain fluid loss additives. A dried, preformed borate cross-linked polyvinyl alcohol (PVA)-sorbitol complex has been proposed for use as a fluid cement fluid loss additive [100]. This may have wider application in other oil well fluids. 

Plasticizers, solvents, tackified (borated) and untackified polyvinyl alcohol, and certain polyvinyl emulsions impart wet tack to polyvinyl acetate emulsions. Those additives specifically designated as tackifiers are listed in Table 11. 

Because it is a hydrophilic polymer, polyvinyl alcohol functions as a humectant to retard the loss of water from the formulation and prolong open time of the adhesive film. Wet tack is increased and can be enhanced further by adding tackified (borated) polyvinyl alcohols. 

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