An experimental study on foaming of linear low-density polyethylene/high-density polyethylene blends. (January 2017)

• Record Type: Journal Article
• Authors: Shahi, Peyman; Behravesh, Amir Hossein; Haghtalab, Ali; Rizvi, Ghaus; Goharpei, Fatemeh
• Is Part Of: Journal of cellular plastics. Volume 53:Number 1(2017)
• Page Start: 83
• Page End: 105
• Publication Date: 2017-01
• Subjects: Polyethylene blends -- batch foaming process -- rheology -- DSC -- 3D X-ray scanning; Plastic foams -- Periodicals; 668.493
• DOI: 10.1177/0021955X16639033
• Languages: English
• ISSNs: 0021-955X

Abstract

In this research work, foaming behavior of selected polyethylene blends was studied in a solid-state batch process, using CO2 as the blowing agent. Special emphasis was paid towards finding a relationship between foamability and thermal and rheological properties of blends. Pure high-density polyethylene, linear low-density polyethylene, and their blends with two weight fraction levels of high-density polyethylene (10 and 25%wt.) were examined. The dry blended batches were mixed using an internal mixer in a molten state, and then the disk-shaped specimens, 1.8 mm in thickness, were produced for foaming purposes. The foaming step was conducted over a wide range of temperatures (120–170℃), and the overall expansion and cellular morphology were evaluated via density measurements and captured SEM micrographs, respectively. Three-dimensional structural images were also captured using a high resolution X-ray micro CT for different foamed samples and were compared. Rheological and DSC tests for the virgin and blends were also performed to seek for a possible correlation with the formability. Based on the results, blended polyethylene foams exhibited remarkable expansion and highly enhanced cell structure compared to pure polymers. Bulk density, as low as 0.33 g/cm 3, was obtained for blends, while for the virgin high-density polyethylene and linear low-density polyethylene, bulk density lower than 0.5 g/cm 3 was not attainable. The lowest density was observed at a foaming temperature of 10–20℃ above the melting (peak) temperature obtained via DSC test. Rheological characteristics, including storage modulus and cross-over frequency value, were also found to be the indicators for the materials foaming behavior. Moreover, blends with 25% wt. of high-density polyethylene exhibited the highest expansion values over a wider range of temperature compared with 90% linear low-density polyethylene/10% high-density polyethylene.