Graphene Nanoplatelet-Reinforced Poly(propylene): Nanofiller Characteristics Influence on the Properties of Nanocomposites ^†

Graphene is a 2D single layer of hybridized sp² carbon atoms covalent bond in a hexagonal structure (honeycomb type). Due to their unique mechanical properties, such as Young’s modulus of 1.0 TPa and tensile strength of 130 GPa, graphene has become an attractive candidate as a structural reinforcement for polymer nanocomposites [1,2]. However, the production of pure graphene is quite challenging, and its industrial applications in nanocomposites are very limited at this stage. On the other hand, graphene nanoplatelets (GnPs) can combine large-scale production and low costs for the development of advanced materials with remarkable properties [3]. Nowadays, GnPs are supplied by several companies, which makes a detailed analysis of these materials an important requirement, namely when comparative studies are envisaged for nanocomposites properties containing GnPs of different sources.

Herein, we report the properties of poly(propylene) (PP, melt flow index of 47 g/10 min)–based nanocomposites reinforced with GnPs of different origins. Some characteristics of GnPs have been assessed by structural and microscopic analysis. PP nanocomposites reinforced with 1 wt.% of GnPs were compounded by melt blending technique, using a Brabender type internal mixer. A mini-injection moulding machine was used to obtain specimens for mechanical tests. The influence of GnPs physicochemical characteristics on the structural, thermal, and mechanical properties of nanocomposites was evaluated.

Overall, our results have shown that different commercial GnPs can present distinct structural and morphological characteristics. The presence of GnPs caused a marginal influence on nanocomposites’ melt temperature. Moreover, the GnPs promoted an increase in the crystallization temperature and degree of crystallinity, suggesting a nucleation effect due to their presence. Regarding the nanocomposites’ mechanical properties, the GnPs presence promoted an improvement in the tensile strength as compared to neat PP. Furthermore, the results suggested an improved adhesion between components for fillers having the smallest lateral average size, highest specific surface area, and most functional groups in their structure. The results highlighted the importance of pre-screening the properties of commercial GnPs before their application in polymer-based nanocomposites.