Effects of Combining Graphene Nanoplatelet and Phosphorous Flame Retardant as Additives on Mechanical Properties and Flame Retardancy of Epoxy Nanocomposite.

Woranan Netkueakul,Jing Wang,Milijana Jovic,Sabyasachi Gaan,Peter Jacob,Christian Walder,Beatrice Fischer,Frank Nüesch,Marcel Rees

doi:10.3390/polym12102349

Woranan Netkueakul, Jing Wang + Show 7 more

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https://doi.org/10.3390/polym12102349

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Abstract

The effects of combining 0.1–5 wt % graphene nanoplatelet (GNP) and 3–30 wt % phosphorous flame retardant, 9,10- dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as fillers in epoxy polymer on the mechanical, flame retardancy, and electrical properties of the epoxy nanocomposites was investigated. GNP was homogeneously dispersed into the epoxy matrix using a solvent-free three-roll milling process, while DOPO was incorporated into the epoxy resin by mechanical stirring at elevated temperature. The incorporation of DOPO reduced the crosslinking density of the epoxy resin. When using polyetheramine as a hardener, the structural rigidity effect of DOPO overshadowed the crosslinking effect and governed the flexural moduli of epoxy/DOPO resins. The flexural moduli of the nanocomposites were improved by adding GNP up to 5 wt % and DOPO up to 30 wt %, whereas the flexural strengths deteriorated when the GNP and DOPO loading were higher than 1 wt % and 10 wt %, respectively. Limited by the adverse effects on mechanical property, the loading combinations of GNP and DOPO within the range of 0–1 wt % and 0–10 wt %, respectively, in epoxy resin were further studied. Flame retardancy index (FRI), which depended on three parameters obtained from cone calorimetry, was considered to evaluate the flame retardancy of the epoxy composites. DOPO showed better performance than GNP as the flame retardant additive, while combining DOPO and GNP could further improve FRI to some extent. With the combination of 0.5 wt % GNP and 10 wt % DOPO, improvement in both mechanical properties and flame retardant efficiency of the nanocomposite was observed. Such a combination did not affect the electrical conductivity of the nanocomposites since the percolation threshold was at 1.6 wt % GNP. Our results enhance the understanding of the structure–property relationship of additive-filled epoxy resin composites and serve as a property constraining guidance for the composite manufacturing.

Highlights

Epoxy resin is a thermoset polymer that has been extensively used for composite manufacturing due to its chemical and thermal resistance, excellent adhesion, and ease of processing [1].Despite its attractive properties, the main disadvantages of epoxy resin are flammability [2], poor thermal conductivity, and brittleness
The linear structure of polyetheramine, which was the hardener used in this study, allowed the rigidity of grafted DOPO to dominate the flexural modulus of the composites; the flexural modulus increased continuously as the DOPO loading increased, the crosslinking density decreased when DOPO was incorporated
Higher DOPO and graphene nanoplatelet (GNP) contents could cause difficulty in composite manufacturing due to an increase in viscosity, which resulted in poorer dispersion of GNP and poorer flexural strength of the composites

Summary

Introduction

Epoxy resin (denoted as EP) is a thermoset polymer that has been extensively used for composite manufacturing due to its chemical and thermal resistance, excellent adhesion, and ease of processing [1].Despite its attractive properties, the main disadvantages of epoxy resin are flammability [2], poor thermal conductivity, and brittleness. Epoxy resin (denoted as EP) is a thermoset polymer that has been extensively used for composite manufacturing due to its chemical and thermal resistance, excellent adhesion, and ease of processing [1]. The chemical structure of amines, i.e., aliphatic, cycloaliphatic and aromatic play important roles in the mechanical properties and thermal properties of the cured epoxy resin [3,4]. Polyetheramine, an aliphatic amine, has been used for surface coatings, adhesives and castings for artistic purposes since aliphatic amines usually are colorless after curing. Aromatic amines such as 4,4’-diaminodiphenyl sulfone (DDS)

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