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Chemical Compatibility of Plastics Packagings

This article covers chemical compatibility of plastics packagings manufactured from polyethylene. Due to recent interest in compatibility, especially the possibility of permeation through plastics packagings creating a potentially hazardous situation, Mr. Lind discusses the UN, the U.S. DOT, and the ADR/RID provisions, and concludes that compatibility of plastics packagings and IBCs is an important factor to consider in safe storage and transportation of hazardous liquids and that permeation is a critical consideration in the packaging selection process.

Summary: This article covers chemical compatibility of plastics packagings manufactured from polyethylene, a widely employed primary raw material for packagings used in the transportation of hazardous materials. Much of this information has appeared in past articles published several years ago1. These articles covered the areas of permeation and environmental stress cracking in polyethylene packagings. Due to recent interest in compatibility, especially the possibility of permeation through plastics packagings creating a potentially hazardous situation, this subject is well worth re-visiting at this time. Coincidentally, it was addressed in a UN Information (INF) paper presented in December 20072 by Germany, at the 32nd session of the UN Sub-Committee of Experts (SCOE) on the Transport of Dangerous Goods. It is fully expected that the German delegation will introduce a formal paper on this subject at the July UN Subcommittee on the Transport of Dangerous Goods meeting.

Introduction
Knowledge of the chemical resistance of plastics to chemicals is essential in the selection of packagings for safely handling and transporting chemicals through typical distribution systems. While this information is needed for all types of materials going through the distribution system it is required knowledge when the materials being transported are hazardous materials or dangerous goods, as they are called internationally. When we speak here of “hazardous materials in the transportation environment”, for the most part we are referring to chemicals in polyethylene packagings, with High Density Polyethylene (HDPE) being the predominant material used in the construction of these packagings. And when we speak of plastics packagings larger than 5 U.S. gallons (20 liters) capacity, High Molecular Weight High Density Polyethylene (HMWHDPE) is the major plastic resin utilized. In this paper I will cover hazardous liquids, and hazardous solids that are likely to become liquid under the conditions of transport. First, I will point out the sections in various regulations that relate to compatibility issues such as permeation and chemical attack such as failure by stress cracking (ESC).

UN Provisions
There are references to permeation in the UN Recommendations on the Transport of Dangerous Goods – Model Regulations3 for rigid plastic IBCs, e.g. 31H1 and composite IBCs with plastic inner receptacles, e.g., 31HA1, sections 6.5.5.3.2… “Any permeation of the substance contained shall not constitute a danger under normal conditions of transport”, and 6.5.5.4.6… “Any permeation of the substance contained shall not constitute a danger under normal conditions of transport”, respectively.

In the case of plastics drums and jerricans there is no reference to permeation, however there is a suggested procedure to determine compatibility set forth in section 6.1.5.2.4:

“Additional steps shall be taken to ascertain that the plastics material used in the manufacture of plastics drums, plastics jerricans and composite packagings (plastics material) intended to contain liquids complies with the requirements in 6.1.1.2, 6.1.4.8.1 and 6.1.4.8.3. This may be done, for example, by submitting sample receptacles or packagings to a preliminary test extending over a long period, for example six months, during which the samples would remain filled with the substances they are intended to contain, and after which the samples shall be submitted to the applicable tests listed in 6.1.5.3, 6.1.5.4, 6.1.5.5 and 6.1.5.6. For substances which may cause stress-cracking or weakening in plastics drums or jerricans, the sample, filled with the substance or another substance that is known to have at least as severe a stress cracking influence on the plastics material in question, shall be subjected to a superimposed load equivalent to the total mass of identical packages which might be stacked on it during transport. The minimum height of the stack including the test sample shall be 3 metres”.

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