Melt transformation coextrusion of polypropylene and polyethylene
The melt transformation coextrusion process was studied in this investigation. The main focus of this investigation was to utilize the melt transformation coextrusion process by using a twin screw plasticating extruder to obtain higher die pressures, similar to the pressures used in the melt transformation extrusion process, so coextruded polymer samples with enhanced thermal and mechanical properties could be produced at higher production rates. A multimanifold die, with variable draw ratio inserts, was used. A single screw plasticating extruder was used for processing the polyethylene shell polymer while a twin screw counterrotating plasticating extruder was used to process the polypropylene core polymer. The extrudate was coextruded downward into a water bath and then through a take-up device. The results of this investigation showed that coextrusion did dramatically increase the production rate, from a few centimeters per minute up to 45 feet per minute, of the melt transformation extrusion process. The samples produced had oriented polypropylene cores which had melting points elevated by as much as 5°C when tested by differential scanning calorimetry (DSC). When tested, the mechanical properties showed increased elastic modulus, yield strength, and ultimate tensile strength. When the samples, cooled in liquid nitrogen, were fractured the cores displayed layered surfaces when viewed by a scanning electron microscope. The polyethylene shell layers exhibited depressed melting points, lowered by as much as 2.7°C, when tested by DSC. The shell layer gave the coextruded samples properties that enabled them to be greatly elongated, up to 990%, before failure when tensile tested. It was also found that the die pressure and the length of the melt conditioning pipe were important factors in determining the degree of orientation of the samples.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:melt transformation coextrusion differential scanning calorimetry polyethylene
Date of Publication:01/01/1984