Thermographic analysis of monomers in the production of threads from aromatic polyamides

Abstract

OAO Kamenskvolokno is a domestic industrial manufacturer of aramid threads. Specialists of the firm pay special attention to analytical production control at all stages, from starting material analysis, at intermediate synthetic steps of the aromatic copolyamide, to release of the final product, in order to improve the production process. Special attention is paid to the purity of the diamines and aromatic acid anhydrides. The monomers for manufacture of aramid threads are aromatic diamines [1] 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI) and p-phenylenediamine (PPDA), terephthalylchloride (TPC), isophthalylchloride (IPC), and pyromellitic acid dianhydride (PAD). As a rule, these are crystalline compounds.Herein the analysis of these monomers by differential scanning calorimetry (DSC) methods is examined. This method allows quantitative values of thermodynamic parameters such as melting point and enthalpy of aggregate transitions to be obtained. Measurement of these values enables the degree of purity and the crystallinity of the monomers to be estimated. DSC measures heat fluxes carried to the sample and a reference compound according to a certain program. A temperature difference is measured and used to determine the values of thermal effects corresponding to transitions from the crystal to the liquid state (endoeffect) or upon crystallization from the melt (exoeffect). The uncertainty of the temperature observed at the maximum of thermal effects is less than fractions of a degree in modern DSC instruments.At present, DSC in addition to spectroscopic, chromatographic, and x-ray methods are promoted as basic methods for studying and monitoring materials. Results from DSC studies are represented as the dependence of differential enthalpy on temperature, ΔH/ΔT.The measurement process is usually organized so that the sample and reference receive those portions of heat at which their temperatures would be equal (isothermal regime). This is carried out using two thermoelectric heating elements placed in a paired calorimeter. The temperature is measured alternately in both its measurement cells. If the temperatures of the cells differ, the heating rate is automatically changed so that the temperatures even out.DSC can not only determine the composition of compounds but also measure their thermal characteristics. The sphere of application of the method is very broad, from checking the purity of chemicals to studying crystallization processes of polymers, because chemical reactions are usually accompanied by significant enthalpy changes.

Inhibitory Effect of Epigallocatechin Gallate, Epigallocatechin, and Gallic Acid on the Formation of N‐Nitrosodiethylamine In Vitro

“…It has been reported that tea polyphenols are able to scavenge nitrite and JFDS-2019-0460 Submitted 3/30/2019, Accepted 6/24/2019 inhibit the N-nitrosation of secondary amines effectively both in vitro and in vivo (Nakamura & Kawabata, 2010;Ohsawa et al, 2003;Tanaka, Hayatsu, Negishi, & Hayatsu, 1998). Recently, catechins, the active bio-compounds rich in polyphenols, showed significant capacities to reduce residual nitrite content in cured meats, thus blocking N-nitrosamine formation (Moawad, Abozeid, & Nadir, 2012;Wang et al, 2015). The observed blocking effects may be ascribed to the mechanisms that polyphenols could scavenge the nitrosating agent by reacting with nitrite to form phenol derivatives, ultimately inhibiting the N-nitrosation of amines (Lu, Dong, Li, & He, 2016;Panzella, Manini, Napolitano, & D'Ischia, 2005;Vermeer, Moonen, Dallinga, Kleinjans, & Maanen, 1999).…”