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AssigneeCorrugatedd Polyethylene Pipe Ltd.
InventorJoseph M. Starita
Estimating the term…
Melt blended HDPE compositions for single and dual wall corrugated HDPE pipe and associated fabricated and molded fittings and accessories with enhanced physical properties and processing and environmental stress crack resistance (ESCR) characteristics and associated blend methods are disclosed in which virgin or recycled homopolymer and/or copolymer HDPE resin components are blended. The invention discloses methods for 1) selecting and determining the relative weight fractions of the HDPE blending components that provide specific physical properties and processability of HDPE blended compositions associated with density and melt index respectively and specific values of environmental stress crack resistance (ESCR) associated with specific molecular parameters and 2) for determining from molecular parameters, the ESCR of linear polyethylene resins and blended compositions within a class having similar densities. The invention reduces the cost of raw materials to corrugated HDPE pipe manufacturers by enabling the use of virgin prime commodity HDPE resins and/or wide and off specification prime HDPE resins in place of single stream specialty HDPE resins and favorably impacts the environment by providing the capability of utilizing recycled HDPE resins in place of prime HDPE resins in the manufacture of corrugated HDPE pipe.
A blend composition of HDPE resin components having a number average molecular weight (Mn) greater than about 20,000 grams/mole and a polydispersity index (PI), defined as a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), from about 5 to about 12, resulting in a melt blend having a density of about 0.945 to about 0.955 grams per cubic centimeter, MI in the range of about 0.15 grams up to about less than 0.40 grams per 10 minutes, a flexural modulus of at least 110,000 pounds per square inch, and ESCR greater than about 24 hours.
A method of determining ESCR of linear polyethylene resin and blend compositions by applying the formula ESCR=EMnF to polyethylene resin and blend compositions having similar density values wherein:
A method of determining ESCR in linear polyethylene resin and blend compositions by applying the formula log ESCR=Glog(Mn)+H to polyethylene resin and blend compositions having similar densities, plus or minus 0.005 grams per cubic centimeter, wherein Mn=number average molecular weight and G is the slope and H is the intercept of a straight line.
Dependencies are inferred from the claim text.