Chemical Compatibility

Lind explained that it is the responsibility of the company filling the container or offering it for shipment to determine and certify its chemical compatibility with the contents. Sounds like there are references to indicate what materials can go in different types of containers and when additional precautions are needed? I think saying to would make the quote clearer. They must determine the appropriate hazard classifications and the packing group as well as any special provisions that may apply.

Then, they must determine the suitability of the packaging; namely its compliance with lading requirements and that it has the proper U.N. rating. Finally, Lind noted, they must ensure that the container is closed according to the packaging manufacturers instructions, and that it meets stowage and load securement requirements.

The European Union and the United States have slightly different approaches to ensuring the chemical compatibility of shipping containers. In the EU, container testing is performed in accordance with the European Agreement Concerning the International Carriage of Dangerous Goods by Road/Rail (ADR/ RID) issued by the United Nations Economic Commission for Europe (UNECE). In the test protocol, plastic packages are filled with so-called model liquids to simulate actual ladings, said Lind. They are then stored for 6 months at ambient temperature [23 degrees C] and checked for damage.

To avoid having to test for each individual chemical, the ADR/RID has what is known as an assimilation list in which six standard liquids – water, 55 percent nitric acid, white spirits, acetic acid, wetting solution and N-butyl acetate in wetting solution – can be used to simulate the effects of more than 408 chemicals. Lind noted that the EU test does not assess synergies of mixtures, high-temperature effects or organic peroxides. It also does not require performance-oriented packaging (POP) tests that simulate the stresses of transportation.

In contrast, Lind said, U.S. Department of Transportation testing employs 250 to 1,000 milliliter sample bottles made from the same plastic as the proposed packaging and containing the actual chemical to be transported. The bottles are stored for 6 months at ambient temperature. Alternately, the bottles can be stored for 28 days at 50 C or 14 days at 60 C.

At the end of storage, plastic degradation is measured in terms of tensile strength change, elongation and high load melt index. In addition, POP tests are performed.

Because the U.S. protocol uses the actual product, the testing assesses synergies of mixtures – whether a mixture of two or more chemicals has different compatibility characteristics than the individual chemicals themselves. Also, the small volumes involved allow testing of experimental products because less product has to be disposed, added Lind. It also provides faster results in high-temperature tests and assesses possible performance issues.

The testing does not assess the effect of the chemical on gaskets and other components. Also, while compatibility databases are available, no assimilation lists have been developed.

Containers that Crack

Lind stated that environmental stress cracking is a major cause of packaging failure. It is a function of time, temperature, stress and the environment. It causes catastrophic failures because there usually are no warning signs of an impending failure.

A few things we know about environmental stress cracking is that it takes time for it to occur and that it accelerates at higher temperatures. Every seven degrees rise in temperature doubles the potential for stress cracking, Lind said.

Stress cracking generally arises at molded-in stress points and areas of externally applied stress caused by point loads, poor stacking or spots where drums overhang pallets. Point loading can double or triple stress on a drum, said Lind. In addition, a chemical such as a surfactant or wetting agent usually provides the ideal environment for cracking.

Hot Filling

While a container may be perfectly chemical resistant when the contents are at ambient temperature, filling when the fluid is hot can radically alter the containers properties. Lind noted that a variety of online resources rate the temperature effects of high-temperature fluid.

For example, Chembest (published by Brkle GmbH) rates the chemical resistance for 12 thermoplastics, five fluoroplastics, four elastomers (EPDM, FKM, NBR, silicone rubber) and three metals commonly used in shipping containers. The database rates the temperature effects of 1,158 chemicals from 20 to 50 degrees C, Lind said, ranking materials as Resistant, Practically Resistant, Partially Resistant and Not Resistant. The database showed 64 cases of Resistant materials becoming Not Resistant, 249 cases of Practically Resistant materials becoming Partially Resistant and 59 cases of Practically Resistant materials becoming Not Resistant.

This leads to 378 opportunities for failure due only to temperature effects. Too often, no one gets hot fill or hot storage guidance and supporting chemical composition data. Therefore, when investigating any quality issues, whether leaking valves or plugs, stacking failures or paneling, stress cracking, etc., its important to check the MSDS and verify fill and storage temperature guidelines, Lind said.

Chembest is one of more than 10 databases that Mauser uses regularly. In addition, we have 40-plus years of data and incident reports for more than 1,200 formulations and pure chemicals, Lind said. We also have gasket compatibility charts, steel coating charts, information from resin suppliers and online data.

Choosing Container Linings

First, its important to remember that lined drums are shipping containers and not long-term storage vessels, because drum linings are likely to deteriorate over time, Lind said. To determine the most appropriate liner material, Mauser first checks an end users packaging history to determine if past experience provides any guidance. They may advise a customer to run laboratory exposure tests, and they take into account any special filling and handling concerns.

Lind explained that phenolic linings were developed in the 1930s from resin technology initially used in electrical insulation. Phenolics are very hard, durable resins that are extremely resistant to solvent and acid. They have poor flexibility and are not suitable for highly alkaline products with a pH of 9 or higher. Phenolics can be used with strong acids and solvents, agricultural chemicals, insecticides and corrosive chemicals. They are not recommended for aqueous materials.

Epoxy phenolics were developed during World War II to seal cockpits. They are more elastic resins that have excellent water resistance and high alkali resistance. Epoxy phenolic linings have good impact and caustic resistance. Their resistance to solvents and strong acids is not as effective as that of phenolics, but they have fair resistance to mild solvents and weak acids.

A typical epoxy phenolic consists of 65 percent epoxy and 35 percent phenolic. These resins can be used with mild acids, highly alkaline products, water-based products, food products, medium strength solvents and detergents.

Modified phenolics were developed in the 1960s and have chemical resistance close to that of phenolic but with better impact resistance. They are called modified phenolics because the phenolic content is higher (typically 65 percent) than in epoxy phenolics. These linings do not have the impact resistance of epoxy phenolics or the acid resistance of phenolics. They can be used with alkalines, acids, strong solvents and water-based products.

Besides the container liner, Lind said, its also important to check gasket compatibility. The wrong gasket can leak and degrade the product.

Guarding Against Permeability

Plastics are not as solid as we think, and several chemicals readily permeate through plastics. In doing so, they soften the plastic causing paneling and possible collapse of a stack of drums. Permeation can also create a hazardous atmosphere in warehouses and transport vehicles.

Lind explained that permeation can be predicted based on chemical structure and is measured by a plastics weight loss or gain. It can be reduced or eliminated by using other plastics such as Teflon, steel drums, fluorination and barrier layers such as polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH) and nanosilicates. Maintaining cool storage conditions and adequate ventilation also are important.

Lind noted, however, that some alternate approaches have drawbacks. For example, Teflon is expensive, cannot be co-extruded because of its high melting temperature and is hard to recycle. Steel is subject to dents and rust, while stainless steel is expensive.

PVOH and EVOH barrier layers are widely used in fuel tanks and consumer packaging. However, they make drum recycling more difficult and hinder reuse. Nanosilicates are more effective barrier layers that do not impact recycling and reuse. In the same way, fluorination is widely used and does not impact recycling and reuse.

Both the U.N. and U.S. Department of Transportation have published permeability limits. The U.N evaluation is run for 28 days at 23 C and has a maximum limit of 0.008 grams per liter per hour for flammable liquids. The U.S. evaluation is run under one of the following three test conditions: 180 days at 18 C, 28 days at 50 C or 14 days at 60 C. It has a maximum limit of 2 percent (poisons are limited to 0.5 percent).

Stacking Safely

Compatibility needs to be assessed accurately to avoid catastrophic failure, said Lind. Also, stacking and storage conditions are critical to avoid cracking and collapsing drums. Even steel develops stress cracks and can panel. Also, he noted, the most impermeable drum with perfect compatibility is of little value if the load is not secured properly. Improper stacking can multiply the force on the bottom drums by four to five times.

Another issue is that the filler is responsible for closing drums properly. You can be fined if you cannot verify that a plug is installed correctly.

Finally, all global regulations require that a load be secured from movement in every direction. And up is a direction, Lind emphasized. Most transport damage is caused by mishandling, careless towmotor and forklift operators, failure to secure a load against vertical forces, and poor stacking.

The bottom line, Lind concluded, is that IBCs [intermediate bulk containers] and drums need to be restrained from movement in every direction. Not just nose to tail, but side-to-side and up-and-down.