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HDPE is known for its high strength-to-density ratio. [4] The density of HDPE ranges from 930 to 970 kg/m 3. [5] Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength (38 MPa versus 21 MPa) than LDPE. [6]
Ambient Temperature: A change in ambient temperature to less than 50 °F (10 °C) or greater than 125 °F (52 °C) (XXVI–4412(b)). (10) Interfacial Pressure: A change in interfacial pressure to a value beyond the range tested (XXVI–2321). (11) Decrease in Melt Bead Width: A decrease in melt bead size from that qualified. (12)
The high-temperature properties of the polymer are improved, its flow is reduced, and its chemical resistance is enhanced. PEX is used in some potable-water plumbing systems because tubes made of the material can be expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water-tight connection.
LDPE is defined by a density range of 917–930 kg/m 3. [6] At room temperature it is not reactive, except to strong oxidizers; some solvents cause it to swell. It can withstand temperatures of 65 °C (149 °F) continuously [6] and 90 °C (194 °F) for a short time.
The Properties of Polyethylene Crystallized Under the Orientation and Pressure Effects of a Pressure Capillary Viscometer, Journal of Applied Polymer Science vol. 14, pp. 2305–2317 (1970). Kanamoto, On Ultra-High Tensile by Drawing Single Crystal Mats of High Molecular Weight Polyethylene, Polymer Journal vol. 15, No. 4, pp. 327–329 (1983).
Further improvements can be achieved through substitution of aliphatic by aromatic units. Operating temperatures up to 130 °C are reached in this way. Thermosets (which do not belong to the high-performance plastics, see above) have a similar temperature stability with up to 150 °C.
With hot wedge welding, the speed of travel is an added parameter as the wedge unit is self-propelled by the rollers. The typical temperature range when welding high-density polyethylene (HDPE) is 220 to 400 °C (428 to 752 °F); the travel speed is typically 0.7 to 4 metres per second (2.3 to 13.1 ft/s). [5]
Particular grades of PPS can be used in injection and compression molding at temperatures (300 to 370 °C) at which PPS particles soften and undergo apparent crosslinking. Principal applications of injection and compression molded PPS include cookware, bearings, and pump parts for service in various corrosive environments.
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