Materials preparation

1 Manipulation of Surface Properties PLA-based materials have relatively low hydrophihcity that can reduce the affinity of human body cells for such materials. As stated above, surface treatment involving alkaline or enzymatic surface hydrolytic degradation can enhance hydrophilicity 

FIGURE 21.19 Scanning electron photomicrographs of PLLA films containing spherulites after alkaline hydrolytic degradation for 30 days (a) and 150 days (b) [49]. 

FIGURE 21.20 Polarized optical photomicrographs of PLLA films containing spherulites before (a) and after (b) NHD [30]. 

FIGURE 21.21 Schematic representation of alkaline treatment and graft polymerization of biodegradable polyester film [56]. 

Tsuji et al. [68] prepared block copolymers by ringopening polymerization of DLLA coinitiated with PLLA crystalline residues (or extended-chain crystallites) prepared by NHD of crystallized PLLA films. Extended-chain crystallites can act as a macrocoinitiator because they have many hydroxyl groups as terminal groups on their surface. In spite of the activity as the coinitiator, the chains inside the extended-chain crystallites are inert and expected to be protected from intersegmental transesterification between block chains synthesized in the first step (L-lactide chains) and the second step (DL-lactide chains) due to the rigidity of the crystalline lattice. 

---

The sohd can be contacted with the solvent in a number of different ways but traditionally that part of the solvent retained by the sohd is referred to as the underflow or holdup, whereas the sohd-free solute-laden solvent separated from the sohd after extraction is called the overflow. The holdup of bound hquor plays a vital role in the estimation of separation performance. In practice both static and dynamic holdup are measured in a process study, other parameters of importance being the relationship of holdup to drainage time and percolation rate. The results of such studies permit conclusions to be drawn about the feasibihty of extraction by percolation, the holdup of different bed heights of material prepared for extraction, and the relationship between solute content of the hquor and holdup. If the percolation rate is very low (in the case of oilseeds a minimum percolation rate of 3 x 10 m/s is normally required), extraction by immersion may be more effective. Percolation rate measurements and the methods of utilizing the data have been reported (8,9) these indicate that the effect of solute concentration on holdup plays an important part in determining the solute concentration in the hquor leaving the extractor. 

Nitrates. Iron(II) nitrate hexahydrate [14013-86-6], Fe(N03)2 6H20, is a green crystalline material prepared by dissolving iron in cold nitric acid that has a specific gravity of less than 1.034 g/cm. Use of denser, more concentrated acid leads to oxidation to iron(III). An alternative method of preparation is the reaction of iron(II) sulfate and barium or lead nitrate. The compound is very soluble in water. Crystallisation at temperatures below — 12°C affords an nonahydrate. Iron(II) nitrate is a useful reagent for the synthesis of other iron-containing compounds and is used as a catalyst for reduction reactions. 

Reverse osmosis membrane separations are governed by the properties of the membrane used in the process. These properties depend on the chemical nature of the membrane material, which is almost always a polymer, as well as its physical stmcture. Properties for the ideal RO membrane include low cost, resistance to chemical and microbial attack, mechanical and stmctural stabiHty over long operating periods and wide temperature ranges, and the desired separation characteristics for each particular system. However, few membranes satisfy all these criteria and so compromises must be made to select the best RO membrane available for each appHcation. Excellent discussions of RO membrane materials, preparation methods, and stmctures are available (8,13,16-21). 

TSR 5. Within the Malaysian scheme SMR 5 is restricted to mbber derived from sheet material prepared by conventional processes, ie, ribbed smoked sheet (RSS), air-dried sheet (ADS), and unsmoked sheet (USS) and presented in small bale form. Other countries may source different raw materials, eg, Indonesia produces SIR 5 from thin latex coagulum (14). SMR 5 prepared by pressing dry-sheet material into standard bales must be identified by the type of sheet material, eg, SMR 5RSS, on the test certificate as well as on the wrapping. 

K. Bauer, in D. Garbe, ed.. Common Fragrance and Flavor Materials Preparation, Properties and Uses, VCH, Weioheim, Germany, 1985. 

The cerium concentrate derived from bastnasite is an excellent polish base, and the oxide derived direcdy from the natural ratio rare-earth chloride, as long as the cerium oxide content is near or above 50 wt %, provides an adequate glass poHsh. The polishing activity of the latter is better than the Ce02 Ln0 ratio suggests. Materials prepared prior to any Ln purification steps are sources for the lowest cost poHshes available used to treat TV face plates, mirrors, and the like. For precision optical polishing the higher purity materials are preferred. 

Materials prepared at Teclinical University Munchen, Germany by U. GriguU and S. Marek. For a table as a function of temperature, see Grigull, U. and S. Marek, Waime u. Staff., 30 (1994) 1-8. 

Example. The Pechini method for fuel cell electrode preparation. La, Ba, Mn niU ates - - CgHgO — citrate complex - - C2FI6O2 — gel. Metal nitrates are complexed with citric acid, and then heated with ethylene glycol to form a transparent gel. This is then heated to 600 K to decompose the organic content and then to temperatures between 1000 and 1300K to produce tire oxide powder. The oxide materials prepared from the liquid metal-organic procedures usually have a more uniform particle size, and under the best circumstances, this can be less than one micron. Hence these particles are much more easily sintered at lower temperatures than for the powders produced by tire other methods. 

A system of guidelines for air concentrations of toxic materials prepared by the American Industrial Hygiene Association. An ERPG is the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour with the following results ... 

Ammonium chloroplatinate often can be used to advantage in place of chloroplatim c acid in the preparation of Adams catalyst. A mixture of 3 g. of ammonium chloroplatinate and 30 g. of sodium nitrate in a casserole or Pyrex beaker is heated gently at first until the rapid evolution of gas slackens and then more strongly until a temperature of 500° is reached. This operation requires about fifteen minutes and there is no spattering. The temperature is held at 500-520° for one-half hour and the mixture is then allowed to cool. The platinum oxide catalyst, collected in the usual way by extracting the soluble salts with water, weighs 1.5 g. and it is comparable in appearance and in activity to the material prepared from chloroplatinic acid. 

Besides the MBS materials, related terpolymers have been prepared. These include materials prepared by terpolymerising methyl methacrylate, acrylonitrile and styrene in the presence of polybutadiene (Toyolac, Hamano 500) methyl methacrylate, acrylonitrile and styrene in the presence of a butadiene-methyl methacrylate copolymer (XT Resin), and methylacrylate, styrene and acrylonitrile on to a butadiene-styrene copolymer. 

Ohki, Y., New Tc-electron materials preparation and properties. In Supercarbon, Synthesis, Properties and Applications, ed. S. Yoshimura and R. P. H. Chang. Springer-Verlag, Heidelberg, 1998, pp. 149 166. 

These types of reactions have been used extensively to pTspaicJluorotelomers For example, Zonyl products, manufactured by E I du Pont de Nemours Co, Inc, are based on materials prepared from perfluoroethyl iodide and tetrafluoroethylene [2] (equation 1)... 

Cobaltocene, [Co ()7 -C5H5)2], is a dark-purple air-sensitive material, prepared by the reactions of sodium cyclopentadiene and anhydrous C0CI2... 

Accuracy and reproducibility are of vital importance to industry. Quite apart from the effect of these factors on the final product, several plant items are frequently links in a continuous chain of production processes. A sizing error in one machine, for example, could overstress and damage the succeeding machinery. Similarly, an error in a press may increase stress on the tool and could necessitate an additional operation to remove excessive flash . Wear in a material preparation unit could allow oversize material to be passed to a molding machine, creating an overload situation with consequent damage. 

F rom 5-deoxy-5-iodo-1,2-0-isopropylidene-/ -l-arabinofura-nose (37). Anhydrous silver fluoride (600 mg.) was added to a solution of 300 mg. of 37 in pyridine (4.0 ml.), and the mixture was shaken at room temperature for 24 hours. Ether (4 ml.) was added, and the mixture was passed through a column of silica gel (1.5 X 12 cm.). The column was washed with ether/pyridine, 1 1 v/v. (10 ml.), and the effluent, which contained 5-deoxy-l,2-0-isopropylidene-/ -L-threo-pent-4-enofuranose (33), was concentrated to 4 ml. Acetic anhydride (0.2 ml.) was added, and the reaction mixture was kept at room temperature for 16 hours. Concentration afforded a sirup from which the last traces of solvent were removed by storage in high vacuum at 20°C. The sirup was distilled at 90°C. (bath) at 2.5 X HHmm. The distillate (110 mg., 51%), which crystallized on standing, had physical constants which were identical to material prepared as above. 

From 1,2-0-isopropylidene-3,5-di-0-tosyl-/ -d-xylofuranose (21) (29). Treating 29 with silver fluoride in pyridine and isolating as described above for the l-arabino isomer gave a 40% yield of 32 after a reaction time of 48 hours. The product had [ ]D25 — 14.9° and had an infrared spectrum identical with material prepared as above. 

From 5-deoxy-5-iodo-1,2-0-isopropylidene- -d-xylofuranose (30). A solution of 1.14 grams of 30 in pyridine (8.0 ml.) was shaken at room temperature with silver fluoride (2.0 grams). The reaction was slower than with the corresponding 5-tosylate (22) and was complete after 72 hours. The reaction mixture was processed as described above to give a pale yellow sirup which contained, in addition to 28, three minor components. Distillation afforded pure material (0.4 grams, 75%) identical with material prepared as above. 

The material, prepared as above, is usually transferred to a weighing bottle which is stoppered and stored in a desiccator. Samples of appropriate size are withdrawn from the weighing bottle as required, the bottle being weighed before and after the withdrawal, so that the weight of substance is obtained by difference. 

Analysed at Materials Preparation Center, Ames Laboratory, Ames, IA, USA... 

---