Effects of temperature, repeated exposure, and aging on polybutylene permeation by organic chemicals

Abstract

SYNOPSISThe permeation parameters, partition coefficient and diffusion coefficient, were obtained for polybutylene (PB) with toluene using a gravimetric method. A PB sample was repeatedly exposed and desorbed, and the partition coefficient and diffusion coefficient were measured. Permeation parameters were also measured at different temperatures. The results were compared with those obtained from a 12-year-old PB pipe sample, which had experienced structural failure. Tests at an elevated temperature of 45°C failed to simulate the effect of polymer aging, whereas repeated sorption/desorption tests produced permeation parameters compatible with those of a 12-year-old PB pipe in service. I NTRODU CTlO NThe major thermoplastic materials used for potable water transport and plumbing applications include poly ( vinyl chloride) ( PVC ) , chlorinated poly ( vinyl chloride) (CPVC) , polyethylene ( P E ) , polybutylene ( PB ) , and acrylonitrile-butadiene-styrene ( ABS ) .Advantages claimed for plastic pipes include immunity to corrosion, ease of use, ductility, and durability. During the last decade, however, it has been found that plastic piping and gasket materials are susceptible to attack and/or permeation by certain organic chemicals.'s2Polymers are permeated by organic chemicals through a combination of partitioning (solubility) and diffusion phenomena. Prediction of a partition coefficient and diffusion coefficient has been attempted by other ~esearchers.~'~ For aromatic organic chemicals, the vapor-phase partition coefficient was predicted from a logarithmic correlation with the saturation vapor concentration for PB and styrene butadiene rubber (SBR) .' Also, the diffusion coefficient was estimated from the relationship between the molecular diameter and the logarithm of the diffusion coefficient for PVC, PB, and SBR.' During service, polymers may change their physical properties including strength, stiffness, strain at failure, and permeability. Attempts have been made to evaluate the changes of original properties over a long period of time. One method adopted by EPA is to raise the temperature to 5OoC to test chemical ~ompatibilities.~ It is not clear whether a test at an elevated temperature can produce permeation parameters comparable to those of samples exposed to organic chemicals for a long time. A technique should be developed to assess the effects the aging of a polymer has on its permeability. In other words, how does the performance of a polymer change when it is exposed to organic chemicals for a long service time.The objective of this paper is to evaluate permeability of PB to toluene after long-term use. The results from 12-year-old specimens, repeated sorption-desorption tests, and various temperature conditions are compared. MATERIALS AND METHODS MaterialsPB, trade name for poly ( 1-butene) , is a member of the polyolefin group of polymers made of straightchain hydrocarbons. PB is partially crystalline and 2989

Mass flux of organic chemicals through polyethylene geomembranes

“…Percent weight gain was calculated by the following expression (Berens, 1985, andPark et al, 1991): Where v1= volume of the organic chemical sorbed per unit volume of M∞/p l the geomembrane at equilibrium = M∞/p 1 M∞/p1+M s /p 2 P1 = density of the organic chemical, g/cm 3 ; and p 2 = density of the geomembrane, g/cm 3 . The organic chemical partition coefficient for a polymer has been found to have a logarithmic relationship with the octanolwater partition coefficient .…”

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