Detection of Migration of Chemical Constituents from Polyurethane Waterproof Coatings into PPR Pipes by TD-GC-MS

Three brands of PPR pipes used in water conveying and 3 brands of polyurethane waterproof coatings were selected as testing samples for the migration study. Procedures for preparation of specimen and for manipulation of the migration test were proposed. The test were carried out in a oven through a period of 14 d and at various temperature. At the end of the 14th day, 0.5 mL each of gas sample of EG and IG were taken and used for GC-MS analysis. The adsorption tube, which was placed preliminarily in the PPR pipe was taken out instantly in due succession and used for TD-MS analysis. The PPR pipe was then washed thoroughly with 20 mL of ethylacetate, which was collected and submitted for GC-MS analysis. And finally, the PPR pipe was cut into 2 pieces at its center along the inner diameter, and then the 2 pieces of the PPR pipe were cleaned inside and out with ethanol and acetone in succession, after which the PPR pipe pieces were cultivated for 1 d in the environmental cabin, and sample of gases in the cabin was collected and analyzed by TD-MS. In either of the above analysis, 3 toluenes (i.e., 3-ethyltoluene, 2-ethyltoluene and 1,3,5-trimethylbenzene) in polyurethane waterproof coatings were selected as reference compounds of the migration (MRPU) to be detected, because these 3 toluenes could be migrated at a relatively low temperature of 50 ℃ and these compounds gave high peak areas and showed well separation. It was found that ① testing temperature is the decisive influential factor to the migration of chemical components among the chemical materials. As shown by the results of this study, under temperature conditions of ≥50 ℃, chemical components in polyurethane coatings, happened to migrate to PPR pipes, while under temperatures ≤40 ℃, no such migration was observed. Hence, the critical migration temperature for the migration of chemical components from polyurethane is confined in 40 ℃ to 50 ℃. ② Same migration results were found among the 3 brands of PPR pipes under same testing temperature. Hence, it is recognized that PPR material itself gives only slight influence to the migration process or that the influence given by PPR material is much less those given by temperature. ③ If the PPR pipe was coated with protective layer preliminarily, the migration of chemical components from polyurethane coating to PPR pipes was completely blocked.