The test method covers the determination of the isocyanate group (NCO) content of a urethane intermediate or prepolymer.
NCO may refer to: 1  NCO Group, an international corporation that provides customer service contracting. 2  Net capital outflow, an economic metric measuring the amount of money from a country holding assets elsewhere. 3  NetCDF Operators, a suite of programs for manipulating NetCDF files. 1 NCO Group, an international corporation that provides customer service contracting. 2  Net capital outflow, an economic metric measuring the amount of money from a country holding assets elsewhere. Usually, they have a free isocyanate (NCO) content comprised between 1 and 15 wt%. Urethane prepolymers containing higher free isocyanate contents, between 15 and 30 wt%, are known as isocyanate quasi-prepolymers [13] . In the presence of the isocyanate excess, biurets and allophanates can also be formed [7] . This fact is due to the higher content in free NCO for prepolymer P400-MDI. The reactive NCO groups of the prepolymer react with soap –OH groups for several months after grease manufacture. As expected, the rheological response is satisfactorily modified during grease ageing, as will be discussed later (see Fig. 10) This fact can be explained taking into account the decrease in free isocyanate content for the same amount of additive (3% w/w), associated to a significantly higher molecular weight (Table 5). Similarly, the free NCO absorption band at 2273 cm −1 is not detected in greases with branched prepolymers (Fig. 4 d). This fact is due to the higher content in free NCO for prepolymer P400-MDI. The reactive NCO groups of the prepolymer react with soap –OH groups for several months after grease manufacture. As expected, the rheological response is satisfactorily modified during grease ageing, as will be discussed later (see Fig. 10 The percent NCO is used to establish unit ratios for stoichiometric reactions with co-reactants. 1. Scope. 1.1 This test method covers the determination of the isocyanate group (NCO) content of a urethane intermediate or prepolymer. 1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard The free isocyanate content can easily be measured by titration of the free isocyanate with an amine and back-titration of the unreacted amine. R-NCO +R'-NH2 R-NHC=ONH-R' urea formation. Weigh approximately 5 g of prepolymer accurately weight into a dried flask. Run a blank and use the calculation below. In the blank all the materials are charged as shown above, but no sample is charged. %NCO = 4.2 x [(ml HCl blank) - (ml HCl sample)]/sample weight. Bromophenol indicator: 0.1 g bromophenol blue add 1.5 ml of 1 N sodium hydroxide and dilute to 1000 ml with distilled water. Isocyanate is the functional group with the formula R–N=C=O. Organic compounds that contain an isocyanate group are referred to as isocyanates. An isocyanate that has two isocyanate groups is known as a di-isocyanate. Di-isocyanates are manufactured for reactions with polyols in the production of polyurethanes, a class of polymers. The global market for diisocyanates in the year 2000 was 4.4 million tonnes, of which 61.3% was methylene diphenyl diisocyanate (MDI), 34.1% was toluene diisocyanate (TDI), 3.4% was the total for hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI), and 1.2% was the total for various others. Application date: 20.06.2013 page 1 from 10 Determination of isocyanate (NCO-) content. Application date: 20.06.2013 page 2 from 10 Use This method is applicable for material containing reactive isocyanate groups. The isocyanate is reacted with di-n-butyl amine to form a urea. Unreacted(excess) amine is determined by backtitration with hydrochloric acid.
https://en.wikipedia.org/wiki/NCO http://www.sciencedirect.com/science/article/pii/S0014305708002103 http://www.sciencedirect.com/science/article/pii/S0014305708002103 http://www.astm.org/Standards/D2572.htm http://www.wernerblank.com/polyur/testmethods/ncotitrat.htm https://en.wikipedia.org/wiki/Isocyanate http://www.si-analytics.com/fileadmin/upload/Publ/Titration/Anwendung/UK/NCO-isocyanate-content_260KB_English-PDF.pdf
what is nco content