The On-Line Measurement of Water in Polymers

Abstract

Water is a common contaminant of many products. Most natural products such as grain and flour, tobacco, wood and paper contain a high proportion of water in their normal states and can be too wet or too dry. Many synthetic materials such as polymers manufactured from petroleum are hydrophobic in nature, and give the most satisfactory performance during processes such as extrusion, moulding and spinning when they are completely dry. Polypropylene and polyvinyl chloride come into this category. Both these polymers, however, exist in a finely divided state during manufacture and tend to retain significant quantities of water upon the large surfaces they present. This water may then cause trouble during fabrication such as surface imperfections on injection mouldings, filament breakages during spinning and voids in extruded sections. Routine analysis for moisture content is therefore an important control on the manufacturing process, and there are many advantages in a semi-continuous on-line analyser for this purpose. On-line analysis avoids the necessity for product storage pending laboratory analysis for moisture by giving early warning of a change in the drier performance and enables the drier to be run at the lowest possible temperature. Material packed for despatch must have a water content not exceeding 0.03% w/w so that equipment capable of detecting 0.003% water is required. This paper describes a fully automatic analyser for this duty.