Title

Analysis of contaminants in oxygen from PVC tubing used in respiratory therapy, chromatographic components in electrochemical sensors, and a model for degradation of electrical cable insulation

Date of Completion

January 1997

Keywords

Chemistry, Analytical|Chemistry, Polymer|Environmental Sciences

Degree

Ph.D.

Abstract

Results from three projects involving current and prospective performance for polymeric materials are described. These questions were addressed: Can polymerized microemulsions be used as chromatographic components in electrochemical devices? What is the exposure level to plasticizers and other components in PVC tubing used in respiratory therapy? Does polyethylene cable insulation degrade via a proposed electrochemical mechanism?^ Polymerized microemulsions (PME) containing styrene, divinylbenzene, water and Aerosol-OT, were prepared by thermal and photochemical polymerization, and characterized using electroanalytical techniques. Although the surfaces of these materials appeared smooth macroscopically, electron microscopy showed a porous polymer with micropore sizes from 6-9 $\mu$m. Characterization of surface modified electrodes by voltammetry showed PMEs bind cations not anions. A robust, porous, ion-exchanging material is easily fabricated for many applications.^ Plasticizers improve PVC tubing flexibility for applications in respiratory therapy. Plasticizers are not chemically bound to PVC which increases the likelihood of human exposure. The amount of plasticizers migrating from PVC tubing was determined using direct dynamic thermal desorption gas chromatography-mass spectrometry. Air passed through PVC tubing and custom-made devices containing Tenax, a commercial adsorbant for GC. Plasticizers and other compounds volatilized from the tubing into air were preconcentrated on the Tenax for GC/MS analysis. Specific compounds identified in both air and PVC itself were the antioxidants, BHT and p-nonylphenol, and the plasticizers, diethyl phthalate and di(2-ethylhexyl) phthalate above the detection limit of 0.2 $\mu$g/mL.^ Mechanisms for degradation of polyethylene insulation in electrical cables are unclear but include long-term exposure to the electric field and water in the cable. A proposed electrochemical mechanism for cable insulation degradation was investigated. LDPE was electrolyzed under high-voltage ac and low-voltage dc electric fields in the presence of air and water containing sodium hydroxide. In one experiment, benzoic acid was observed from ac electrolysis of LDPE. Changes in voltammetric and contact angle measurements may suggest physical changes occurred. No evidence suggested that oxidation of the polyethylene occurred above the detection limit of 1.0 $\mu$g/mL. ^