Few-layer graphene aqueous suspensions for polyurethane composite coatings
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Few-layer graphene aqueous suspensions for polyurethane composite coatings Eunice Cunha1, Fernando Duarte1, M. Fernanda Proença2 and M. Conceição Paiva1 1 Instituto de Polímeros e Compósitos/i3N, Universidade do Minho, Campus de Azurém, 4808533 Guimarães, Portugal 2 Centro de Química, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal ABSTRACT Graphite nanoplates (GnP) have recently attracted attention as an economically viable alternative for the development of functional and structural nanocomposites. The incorporation of GnP into waterborne polyurethane (WPU) with loadings from 0.1 to 10 wt.% was studied. The mechanical properties of the composite films were assessed by tensile testing showing an increase of the Young’s modulus up to 48%. The electrical conductivity increased by 9 orders of magnitude and the water vapor permeability of the composite films decreased 57% for composites containing 5.0 wt.% of GnP. INTRODUCTION Graphite nanoplates (GnP), a thin form of graphite flakes with thickness ranging from that of few-layer graphene to approximately 100 nm, have recently attracted attention as an economically viable alternative for the development of functional and structural nanocomposites. [1] Normally these materials are obtained by expansion process, using heat or microwave irradiation, resulting in GnP or expanded graphite (EG) with an interlayer spacing similar or higher than that of graphite (0.335 nm). [2-4] Polyurethane (PU) is a versatile polymer which has been extensively used as paints, adhesives and coatings in a wide variety of applications in the field of construction, textiles, foot wear, furniture, packaging, electronics, automotive and aerospace, among others. [5-8] The synthetic methods for PU production can be differentiated as: solvent free, in organic solvents, and in water. The latter is denominated as waterborne polyurethane (WPU) and has been presented as an eco-friendly alternative to other solvent-borne PU since only water is evolved during the drying stage. [9] WPU typically presents excellent elasticity, abrasion resistance and flexibility. Some of the properties of WPU such as water resistance, thermostability and mechanical properties are inferior to those of solvent-borne PU. [5,9] The incorporation of carbon based reinforcing materials such as carbon black, carbon nanotubes, GnP and graphene (graphene oxide and reduced graphene oxide) in the WPU matrix has been used to improve the mechanical, thermal, electrical and barrier properties of the composites, relative to WPU. [10-15] The present work reports the production of thin films of WPU/GnP with loadings from 0.1 to 10 wt.%. The mechanical properties of the composite films were measured by tensile testing showing an increase of the Young’s modulus up to 48%. The electrical properties increased by 9 orders of magnitude and the water vapor permeability of the composite film decreased 57% for 5.0 wt.% of GnP content.
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