Applikasjoner

Hydroxyl is an important functional group and knowledge of its content is required in many intermediate and end-use products such as polyols, resins, lacquer raw materials and fats (petroleum industry). The test method to be described determines primary and secondary hydroxyl groups. The hydroxyl number is defined as the mg of KOH equivalent to the hydroxyl content of 1 g of sample.The most frequently described method for determining the hydroxyl number is the conversion with acetic anhydride in pyridine with subsequent titration of the acetic acid released: H3C-CO-O-CO-CH3 + R-OH -> R-O-CO-CH3 + CH3COOH. However, this method suffers from the following drawbacks: - The sample must be boiled under reflux for 1 h (long reaction time and laborious, expensive sample handling) - The method cannot be automated - Small hydroxyl numbers cannot be determined exactly - Pyridine has to be used, which is both toxic and foul-smellingBoth standards, ASTM E1899-08 and DIN 53240-2, offer alternative methods that do not require manual sample preparation and therefore can be fully automated: The method suggested in ASTM E1899-08 is based on the reaction of the hydroxyl groups attached to primary and secondary carbon atoms with excess toluene-4-sulfonyl-isocyanate (TSI) to form an acidic carbamate. The latter can then be titrated in a non-aqueous medium with the strong base tetrabutyl- ammonium hydroxide (TBAOH). The method suggested in DIN 53240-2 is based on the catalyzed acetylation of the hydroxyl group. After hydrolysis of the intermediate, the remaining acetic acid is titrated in a non-aqueous medium with alcoholic KOH solution. The present work demonstrates and discusses an easy way to determine the hydroxyl number according to ASTM E1899-08 or DIN 53240-2 with a fully automated titrimetric system for a great variety of industrial oil samples.

This Application Bulletin describes a simple polarographic method to determine monomeric styrene in polymers. The limit of determination lies at 5 mg/L. Before the determination, styrene is converted to the electrochemically active pseudonitrosite using sodium nitrite.

The present Application Bulletin elucidates several applications for the polymer industry that can be carried out with the aid of NIR instruments. This Bulletin contains analyses of a wide range of parameters in a very large array of samples. The hydroxyl number is one of the best-known of the parameters that can be determined rapidly using near-infrared spectroscopy. The determination of the hydroxyl number in different areas and in different polyol types is also a part of this Bulletin. Each application describes the sample and the instrument that was originally used for the analysis, as well as the recommended instruments and the results.

This method is applicable to all samples containing glycerin in the absence of other triols or other compounds that react with periodate to produce acidic products. Glycerin may be determined in the presence of glycols. A periodate solution reacts slowly with diols and triols in acidic aqueous media at room temperature. A quantitative amount of formic acid is generated from the reaction with glycerin (a triol). The reaction with diols produces neutral aldehydes. The amount of formic acid generated by this reaction is determined by titration against sodium hydroxide.

This Application Note describes a fast, nondestructive, and reliable NIRS method for the determination of the hydroxyl number in polyols. Results are available in real-time for which reason NIRS is highly suited for in-process quality control. Second-derivative spectra and linear least-squares regression provide results that match very well with those obtained by titration.

During polymerization, real-time determination of hydroxyl and acid numbers of polyols provide important information about molecular weight and the reaction end point. This Application Note sheds light on the practical aspects of process monitoring in a polyol batch process using NIRS methodology. Real-time process monitoring with NIRS is the key to lower production costs and better product quality.

Determination of the vinyl content of silicone rubber is a lengthy and challenging process. First, the vinyl groups must be converted to ethylene by reacting with an acid, followed by the determination of the produced ethylene with gas chromatography (GC).This application note demonstrates that Vis-NIR (visible near-infrared) spectroscopy provides a cost-efficient and fast solution for the determination of vinyl content in silicone rubbers. With the DS2500 Solid Analyzer it is possible to obtain results in less than a minute without sample preparation or any chemical reagents.

Raman spectroscopy can easily monitor polymerization by tracking monomer consumption and polymer formation, providing a valuable tool for polymer manufacturers.

Aromatic dicarboxylic acids, e.g., terephthalate, isophthalate and 5-sulfoisophthalate, are important monomers in the manufacture of polyesters and alkyd resins. The monomer ratio of the dicarboxylic acids has an enormous influence on polymerization. The separation of the late-eluting components is completed within 15 minutes if a short Metrosep A Supp 15 - 50/4.0 type column is used together with high eluent concentrations and flow rates.

The epoxy content of epoxy resins has a strong influence on the reactivity of the resins as well as on the properties of the coating obtained from the resin curing process. The epoxy content is thus an important quality control parameter for manufacturers as well as consumers. This analysis is based on the reaction of hydrogen bromide with the epoxy groups of the sample. Hydrogen bromide in turn is produced by the reaction of tetraethylammonium bromide (TEABr) with standardized perchloric acid. The standards EN ISO 3001 and ASTM D1652 describe the determination of the epoxy content expressed as epoxy equivalent weight (EEW) by titration. The use of a Titrando and Solvotrode easyClean instead of manual titration greatly increases the reproducibility and repeatability of the determination.

Determination of styrene monomers in polystyrene. Free styrene is converted to a polarographically active pseudonitrosite.

Chemical manufacturing such as polyurethane production is characterized by a cost intensive production process combined with a negative ecological impact. These adverse effects can be significantly improved by using vibrational spectroscopy. This analytical technique can assist the operator of the plant to reduce costs and minimize the impact onthe environment as is demonstrated in the present white paper.