| Material Selection Chem-Tainer
Industries offers you a selection of materials that are by far the best suited for molded
tanks and containers for use with aggressive corrosive chemicals as well as food products.
Our 35 plus years of experience in rotational molding, combined with our professional
staff of chemical, mechanical and plastics engineers, enable us to provide you with the
highest quality rotationally molded tanks and containers available in the industry.
The following is a brief description of these materials:
Polyethylene
A high quality thermoplastic that has outstanding resistance to both physical
and chemical attack. The overall general toughness and excellent chemical resistance to a
wide array of wet and dry industrial chemicals and food products make polyethylene ideally
suited for storage tanks and containers.
Polyethylene is translucent and its natural color ranges from slightly off white
to creamy yellow, depending on wall thickness and type. Ultraviolet light stabilizers are
added for use in outdoor applications. Colors are available on request for a nominal up
charge.
Linear Polyethylene
Linear Polyethylene is available as low, medium and high density. Most products
offered in this catalog are molded of linear medium density polyethylene (LMDPE) and
linear high-density polyethylene (LHDPE). They have superior mechanical properties, high
stiffness, excellent low temperature impact strength and excellent environmental stress
crack resistance. The linear polyethylene used by Chem-Tainer Industries meets
specifications contained in FDA regulation 21CFR177.1520 (c) 3.1 and 3.2 and so may be
used as an article or a component of articles intended for use in contact with food,
subject to any limitations in the regulations. Maximum operating temperature for linear
polyethylene is 140° F.
Crosslinkable Polyethylene
Crosslinkable polyethylene is a high-density polyethylene that contains a
crosslinking agent, which reacts with the polyethylene during molding, forming a
crosslinked molecule similar to a thermoset plastic. This reaction improves toughness and
environmental stress crack resistance. Crosslinked Polyethylene (XLPE) is not weldable and
does not meet FDA requirement 21CFR177.1520. Maximum operating temperature of crosslinked
polyethylene is 150° F.
Polypropylene
Polypropylene is a rigid plastic that has a higher operating temperature limit
than polyethylene: 212° F. It offers good chemical resistance,
has a high resistance to stress crack, and is autoclavable. Polypropylene (PP) is not
recommended for applications in sub-freezing temperature or where high impact strength is
needed. A rough, irregular interior surface is common characteristic of molded
polypropylene.
Material Selection - Considerations to Material Selection
Elevated Temperatures
Continued or prolonged service with contents at elevated temperatures can
shorten the life of a tank. The effects of the temperature will depend on the chemical
content and its specific gravity, tank size and configuration, material of construction,
wall thickness and if there are any external supports on the tank.
Exposure to Ultraviolet Light
Unprotected thermoplastics exposed to sunlight for an extended period of time
absorb ultraviolet (UV) light, which can cause discoloration, embrittlement and eventual
cracking. Fluorescent lighting has a similar effect. Elevated temperatures can accelerate
the embrittlement process. Chem-Tainer Industries products are molded from materials
utilizing the latest technology for UV stabilizers, which greatly reduce the harmful
effects of UV, light. For greater protection, keep tanks out of direct sunlight or order
dark colored tanks, which will further retard the effect of UV light.
Environmental Stress Cracking
Certain surface active materials, although they have no chemical effect on
polyethylene, can accelerate its cracking when under stress, such as liquid detergents and
ultra pure water. Elevated temperatures tend to accelerate the cracking. Although all
polyethylenes are subject to stress cracking, some are more resistant to it than others.
The degree of stress on the plastic has a direct bearing on its resistance, therefore a
tank and system should be designed to minimize stress. Chem-Tainer Industries tanks are
molded virtually stress free, employing materials that are highly resistant to
environmental stress cracking and hence are less prone to cracking than fabricated tanks.
Stress cracking agents are surface-active materials. Proper care should be taken to reduce
stress at fittings, bands, tie down lugs, etc. |