When choosing a container for any substance, compatibility of the contents with the material forming the container is crucial. Testing is necessary to ensure safe transportation and storage. Hazardous materials (corrosive, flammable, etc.) bear a legal responsibility for chemical compatibility.
A popular material for packaging based on wide general compatibility is polyethylene. It has exceptional chemical resistance as well as mechanical strength. Laboratory results and a long history of field experience indicate acceptability of many liquid chemicals for use with polyethylene packaging. There are many published listings which show general compatibility of common chemicals with polyethylene and other resins. ThermoFisher Scientific provides a particularly thorough listing. Testing is still always recommended.
Before shipping, there are a variety of tests that can be conducted to prove good chemical compatibility. Test strips molded from the polyethylene used to manufacture the containers can be exposed to the liquid in question and a ‘before and after’ comparison can be made of key properties such as tensile strength, elongation, and impact resistance (ASTM D-638). However, since the container design and the molding process can influence performance of the container, a test involving the container itself is recommended. This involves holding the liquid in the container under conditions which duplicate or exceed the proposed storage time and severity of storage conditions (stacked height, temperature, internal pressure, etc.).
If the storage time is unacceptable, the test can be “accelerated” by raising the storage temperature. Reduction of storage time by a factor of 2.5 for 10°C increase in storage temperature is used as an approximation. For example, a proposed application involving a one-year shelf life at an average temperature of 25°C would be held for 21 weeks at 35°C or eight weeks at 45°C to obtain equivalent results. A specific test procedure for hazardous material compatibility testing is specified in Appendix B of Part 173, Title 49, Code of Federal Regulations.
There are many indications of incompatibility. A few include:
- A chemical attack is indicated by the weakening wall structure of the polyethylene container. Drop testing the filled samples after the storage period will provide an approximate determination.
- Softening/Swelling is evident with the storage of permeating hydrocarbons. If the container is being used for a single use for a short duration, this is not necessarily a problem if you ensure that the degree of softening or swelling is small.
- Permeation to the outside manifests as weight loss in the container. Unless the product is a poison, 2% loss during testing is acceptable. If it is a poison, a rate of ½% is allowed. Naphtha, benzene, gasoline and carbon tetrachloride are known to excessively permeate polyethylene containers.
- Pressure build-up can occur from vapor pressure of liquid contents, accentuated by elevated temperature or by reaction of permeating oxygen with liquid contents. It can exert stress at seams and other areas, making the container more susceptible to environmental stress cracking.
- Discoloration of contents can occur from reaction of the product with permeating oxygen or by reaction of the product with polyethylene. For example, concentrated sulfuric acid darkens when stored in contact with polyethylene, although it does not reduce the efficiency of the acid.
Zacros America is responsible for manufacturing containers in accordance with applicable construction and physical (not chemical) performance standards, codes and regulations, without production defects. The shipper is responsible for deciding to ship (or not to ship) a given chemical in a given container. Based on extensive history of field experience and comprehensive testing, Zacros America aids in determining fitness of an application. Any opinions are given in good faith with the understanding that the responsibility for container choice belongs to the shipper of the substance. Testing is always recommended.