Influence of processing methods on the mechanical and barrier properties of HDPE-GNP nanocomposites
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ORIGINAL RESEARCH
Influence of processing methods on the mechanical and barrier properties of HDPE-GNP nanocomposites K. Honaker 1 & F. Vautard 1 & L. T. Drzal 1 Received: 19 May 2020 / Revised: 9 August 2020 / Accepted: 18 September 2020 # Springer Nature Switzerland AG 2020
Abstract In order to improve the barrier properties of Graphene nanoPlatelets (GnP)–High-Density PolyEthylene (HDPE) composites made by melt mixing, extra processing steps were investigated (solution mixing prior to melt mixing, cryomilling of the HDPE pellets into a fine powder, coating of the GnP with low molecular weight wax or with a thermoplastic elastomer, and microlayer co-extrusion). The associated mechanical properties were characterized by a flexural test and a notched Izod impact test. The barrier properties were evaluated by the permeation to oxygen. Each method resulted in a different state of dispersion and alignment of the graphene nanoplatelets, leading to a specific evolution of the barrier and mechanical properties. Microlayer co-extrusion led to a better relative improvement of the barrier properties versus neat HDPE. Solution mixing did result in an improvement of the barrier properties only if the composite was not further processed by melt mixing and extrusion. Starting with a fine HDPE powder did improve the barrier properties but affected the flexural properties. Lastly, a coating of the GnP with a thermoplastic elastomer enhanced the resistance to impact and barrier properties, but a coating with wax did not show any improvement. Keywords Graphene nanoplatelets . High-density polyethylene . Barrier properties . Oxygen permeation
1 Introduction In a previous study, melt mixing process was used to manufacture Graphene nanoPlatelets (GnP)–HighDensity PolyEthylene (HDPE) composites, and their potential for a use in fuel tanks and fuel lines was investigated [1]. The concept was to exploit the enhancement of the HDPE barrier properties by addition of a platy filler in order to replace the current HDPE/Ethylene Vinyl alcOHol (EVOH)/HDPE sandwich structure by a plain HDPE-based composite, thus simplifying the production process. A clear decrease in fuel permeation
* K. Honaker [email protected] 1
Composite Materials and Structures Center, Chemical Engineering and Materials Science Department, Michigan State University, 2100 Engineering Building, East Lansing, MI 48824, USA
was obtained (− 75% with a GnP concentration of 15 wt.%), but the barrier properties were still inferior to the ones obtained with EVOH. Also, the resistance to impact, as measured by a notched Izod test, was significantly affected. Melt mixing followed by injection molding is the most simple and cost-effective process to produce thermoplastic-based composites [2, 3], but it may not be the most efficient at dispersing the filler efficiently, and both the mechanical and barrier properties are directly impacted by the quality of filler dispersion. This work aims at exploring alternative mixing processes to achieve better GnP dispersion. The dispersion
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