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Rigidity and tensile strength of the HDPE resins are considerably higher than
those properties in the low and medium density materials.
Impact strength is slightly lower, as is to be expected in a stiffer
material, but values are high, especially at low temperatures, compared to those
of many other thermoplastics.
HDPE resins are available with broad, intermediate, and
narrow molecular-weight distribution, which provides a selection to the
processor to meet specific performance requirements. As with the other polyethylene grades, very high molecular
weight copolymers of HDPE resins are available with improved resistance to
stress cracking.
Applications of HDPE range from film products to large, blow-molded
industrial containers. The largest
market area is in blow-molded containers for packaging milk, fruit juices,
water, detergents and various household and industrial liquid products.
Other major uses include high-quality, injection-molded housewares,
industrial pails, food containers and tote boxes; extruded water and
gas-distribution pipe, wire insulation and structural-foam housings.
Mechanically ground HDPE resins are used to rotationally mold
large, complex shaped products such as fuel tanks, trash containers, dump carts,
pallets, agricultural tanks, highway barriers and water and waste tanks for
RV’s.
A specific category of HDPE known as high-molecular-weight
HDPE (HMW-HDPE) offers outstanding toughness and durability.
These characteristics result from a unique combination of high average
molecular weight (250,000 to 500,000) a broad molecular weight distribution and
generally, a distribution that is bimodally shaped.
In blow-molding applications, HMW-HDPE allows drum
manufacturers to meet DOT and OSHA specifications. The primary market, however, for HMW-HDPE is in film
applications, where its toughness allows down gauging in merchandise bags and
trash bags. The material is also
suited for use in T-shirt-type grocery sacks where high handle strength is
required. HMW-HDPE has the
potential for significant paper and metal replacement on the basis of both cost
and performance.