Nitrocellulose molecular weight

Nitrocellulose lacquers were used very early as automobile topcoats. They produced very attractive high-gloss finishes. Since the nitrocellulose molecular weight is high, a very high level of solvent was needed to reach spray viscosity. This resulted in the need for many coats to reach adequate film thickness. Both the high solvent levels and the use of multiple coats contributed to extremely high volatile losses from nitrocellulose lacquers. 

Figure 8.9 is a plot of osmotic pressure data for a nitrocellulose sample in three different solvents analyzed according to Eq. (8.87). As required by Eq. (8.88), all show a common intercept corresponding to a molecular weight of 1.11 X 10 the various systems show different deviations from ideality, however, as evidenced by the range of slopes in Fig. 8.9. 

Commodity Phthalate Esters. The family of phthalate esters are by far the most abundandy produced woddwide. Both orthophthaUc and terephthahc acid and anhydrides are manufactured. The plasticizer esters are produced from these materials by reaction with an appropriate alcohol (eq. 1) terephthalate esterification for plasticizers is performed more abundandy in the United States. Phthalate esters are manufactured from methanol (C ) up to Qyj alcohols, although phthalate use as PVC plasticizers is generally in the range to The lower molecular weight phthalates find use in nitrocellulose the higher phthalates as synthetic lubricants for the automotive industries. 

The problem of solvent selection is most difficult for high molecular-weight polymers such as thermoplastic acryHcs and nitrocellulose in lacquers. As molecular weight decreases, the range of solvents in which resins are soluble broadens. Even though solubihty parameters are inadequate for predicting ah. solubhities, they can be useful in performing computer calculations to determine possible solvent mixtures as replacements for a solvent mixture that is known to be satisfactory for a formulation. 

Nitrocellulose, of the resins used in these end uses and in car refinishing, is the nitrate ester of cellulose. The structure is linear and a wide range of (high) molecular weights is available as well as various degrees of nitration ... 

These opposing tendencies may defeat the purpose of the fractional precipitation process. The fractional precipitation of crystalline polymers such as nitrocellulose, cellulose acetate, high-melting polyamides, and polyvinylidene chloride consequently is notoriously inefficient, unless conditions are so chosen as to avoid the separation of the polymer in semicrystalline form. Intermediate fractions removed in the course of fractional precipitation may even exceed in molecular weight those removed earlier. Separation by fractional extraction should be more appropriate for crystalline polymers inasmuch as both equilibrium solubility and rate of solution favor dissolution of the components of lowest molecular weight remaining in the sample. 

Deposition of the analyte on nitrocellulose films instead of metal foils allows the removal of alkali ion contaminations by washing of the sample layer which results in better PD spectra. [163] Further improvements can be achieved by adsorption of the analyte molecules on top of an organic low-molecular weight matrix layer. [164,165]... 

DNA adsorption properties were first studied using a variety of solid supports for classical analysis methods including Southern and Northern transfers, dot-blotting, colony hybridization and plaque-lifts [31,32]. Studies of the interactions between nucleic acids and nitrocellulose revealed that molecular weight, finite macromolecular conformation, ionic forces and weaker forces of attraction all play a role. DNA is retained on nitrocellulose only in... 

After developing the film, overlay the film and nitrocellulose membrane to confirm the molecular weight of the band with the aid of a protein ladder (Fig. 3). Identify the target band according to the molecular weight of the protein. 

Figure 3.5b shows data for a sample of nitrocellulose in three different solvents. All show the same intercept corresponding to a single molecular weight as required. Note, however, that the slopes are different, including even a negative slope, indicating that wide variations in B are possible. We examine the factors that determine B in Section 3.4. 

Solutions of cellulose derivatives, such as nitrocellulose, passed through a fine porous filter demonstrate neither the Tyndall effect, nor the presence of particles visible in the ultra-microscope. This is one more piece of evidence that the properties of these solutions are the same as those of substances with low molecular weight. The same holds for cellulose in ammoniacal solutions of cupric oxide ( cupr-ammonium ). 

Nitrocellulose with a decreased molecular weight may be obtained as the result of depolymerization (degradation) of the cellulose before nitration, e.g. by keeping it at a temperature of 150-170°C or by treating it with acids. The resultant hydrocellulose, which usually possesses a lower molecular weight than cellulose, is then subjected to nitration to produce a more soluble substance as compared with the nitration product of a non-depolymerized raw material. 

Water content of nitrating acid % Nitrogen content of nitrocellulose /o Solubility % Molecular weight of nitrocellulose (from viscosity measurements)... 

Ultrasonic waves also bring about a reduction in the viscosity of nitrocellulose. The effect is more marked the higher the initial viscosity, and thus the longer the nitrocellulose chains (Sollner [93] Schmidt and Rommel [94]). For instance, nitrocellulose with a molecular weight of 123,000, estimated by means of Staudinger s viscosity equation, subjected in solution form to the action of ultrasonic waves suffered a degradation to a molecular weight of 70,000-80,000. 

More recently Staudinger and Dreher [96] have confirmed these observations, by determining the effect of the time of pulping nitrocellulose in a colloid mill on its molecular weight as determined by viscosity measurement. They further established that owing to intensive milling a partial denitration of nitrocellulose took also place, as seen in Table 56. 

Fig. 108. Chromatographic separation of nitrocellulose fractions (quantity of fractions in mg/g and their molecular weight Af Claesson [116]).

Gloor and Spurlin [33] are of the opinion that compounds are formed between the nitrocellulose and the powdered metal by means of the secondary valencies. They have demonstrated that the higher the molecular weight of the nitrocotton, the smaller the quantity of metal powder necessary to cause the gel to coagulate. 

Using the ultracentrifuge sedimenting method, Gralen and Svedberg [40] have determined the molecular weight of nitrocellulose prepared from various types of cellulose. The nitration was carried out at 0°C by means of a mixture composed of 40% of nitric acid, 40% of phosphoric acid, and 20% of phosphorus pentoxide. The results are collected in Table 79. 

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