Material Selection
Chemtainer.com 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, enables 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. BPA-Free Material.
A) 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 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. BPA-Free Material.
B) 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 thermoses 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.
2) 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.
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 discolorations, embrittlement
and eventual cracking. Fluorescent lighting has a similar effect. Elevated
temperatures can accelerate the embrittling process. Chem-Tainer 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- (see our chemical compatibility Chart on pages 46
- 49.) 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.
Chemtainer.com tanks are molded visually 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 fillings, bands, tie
down lugs, etc.
Characteristics and Physical Properties
