Layered Clay-Graphene Oxide Nanohybrids for the Reinforcement and Fire-Retardant Properties of Polyurea Matrix.

Mădălina Ioana Necolau,Celina Maria Damian,Radu Claudiu Fierăscu,George Mihail Vlăsceanu,Eugeniu Vasile,Anita-Laura Chiriac,Horia Iovu

doi:10.3390/polym14010066

Abstract

Nanostructures are more and more evolved through extensive research on their functionalities; thus, the aim of this study was to obtain layered clay–graphene oxide nanohybrids with application as reinforcing agents in polyurea nanocomposites with enhanced thermal–mechanical and fire-retardant properties. Montmorillonite (MMT) was combined with graphene oxide (GO) and amine functionalized graphene oxide (GOD) through a new cation exchange method; the complex nanostructures were analyzed through FTIR and XPS to assess ionic interactions between clay layers and GO sheets by C1s deconvolution and specific C sp3, respective/ly, C-O secondary peaks appearance. The thermal decomposition of nanohybrids showed a great influence of MMT layers in TGA, while the XRD patterns highlighted mutual MMT and GO sheets crystalline-structure disruption by the d (002) shift 2θ = 6.29° to lower values. Furthermore, the nanohybrids were embedded in the polyurea matrix, and the thermo-mechanical analysis gave information about the stiffness of MMT–GO nanocomposites, while GOD insertion within the MMT layers resulted in a 30 °C improvement in the Tg of hard domains, as shown in the DSC study. The micro CT analysis show good dispersion of inorganic structures within the polyurea, while the SEM fracture images revealed smooth surfaces. Cone calorimetry was used to evaluate fire-retardant properties through limiting the oxygen index, and MMT–GOD based nanocomposites showed a 35.4% value.

Highlights

Polyurea is a synthetic versatile elastomer used for high-strength coatings to protect different substrates from corrosion, temperature and weathering conditions
Polyureas, synthesized by rapid step-growth polymerization of isocyanates and polyether amines, have proved to be microphase-separated block copolymers with hard high-Tg domains represented by the rigid aromatic moieties embedded in relatively soft low-Tg matrix that come from the aliphatic polyamine [1,2,3]
Qiao et al concluded in their study that the dynamic mechanical properties of polyurea can be enhanced by controlling the size, properties and distribution of hard domains [2]

Summary

Introduction

Polyurea is a synthetic versatile elastomer used for high-strength coatings to protect different substrates from corrosion, temperature and weathering conditions. Polyureas, synthesized by rapid step-growth polymerization of isocyanates and polyether amines, have proved to be microphase-separated block copolymers with hard high-Tg domains represented by the rigid aromatic moieties embedded in relatively soft low-Tg matrix that come from the aliphatic polyamine [1,2,3]. The viscoelastic character of polyurea is a determining parameter and represents the topic of numerous studies in order to determine and understand their behavior and performances. A very important particularity for this material comes from the hard domains. Qiao et al concluded in their study that the dynamic mechanical properties of polyurea can be enhanced by controlling the size, properties and distribution of hard domains [2]. Polymers 2022, 14, 66 can be enhanced by controlling the size, properties and distribution of hard domains [2]

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Methods

Results