Hygroscopic Behavior of Polypropylene Nanocomposites Filled with Graphene Functionalized by Alkylated Chains

Abstract

Owing to stringent international environmental and fuel efficiency requirements for lightweight automotive systems, polymer composites have attracted widespread attention. Polypropylene (PP) is a widely employed commercial polymer because of its lightweight and low cost. In this study, PP nanocomposites were fabricated to reduce the moisture absorption of PP composites in automotive headlamp housings. Alkylated chemically modified graphene (CMG-R) was synthesized to reduce the surface hydrophilicity of graphene and increase compatibility with the PP matrix. Fourier transform-infrared spectroscopy and scanning electron microscopy were performed to analyze the nanofillers. X-ray diffraction was performed to determine the interlayer spacing of the nanofiller resulting from surface treatment. Differential scanning calorimetry was used to analyze the crystallinity of the nanocomposites. The results indicated that the improved hydrophobicity of the nanofiller due to alkylation reduced the maximum moisture absorption of the PP nanocomposites by 15% compared to PP composites. The findings of this study are useful for reducing fogging in automotive headlamps.

Reducing Moisture Absorption in Polypropylene Nanocomposites for Automotive Headlamps Using Hydrophobicity-Modified Graphene/Montmorillonite

“…The surface of MMT-Ca 2+ is hydrophilic because of its structure (as discussed earlier), and as illustrated in Figure 6, owing to the hydrophilic properties of MMT-Ca 2+ , a substantially low contact angle (12.0 • ) was obtained. As previously reported by our research group [17], the surface of GO is hydrophilic because of the hydroxyl and carboxyl groups and exhibits a low water contact angle (53.5 • ). However, CMG + is hydrophobic, which can be attributed to the reduction in the number of hydrophilic functional groups (hydroxyl and carboxyl groups) and the increase in the crystallinity of graphene.…”

“…In contrast, for polymers with low moisture-absorbing ability, such as PP, the hydrophilic properties of the clay filler are expected to have a significant impact. In our previous study [17], we demonstrated the hygroscopic behavior of PP nanocomposites prepared with alkylated graphene. However, the mechanical properties of the chemically modified PP/alkylated graphene nanocomposites were poor and, therefore, require improvement.…”

“…Second, positively charged graphene (CMG + ) capable of forming chemical interactions with the cationic nitrogen (N + ) of organo-MMT was produced. For CMG + , GO was prepared using an improved method [18] reported previously [17,19]. Subsequently, a CMG + colloid with high dispersibility was prepared with 4,4-oxidianiline.…”

“…The surface of MMT-Ca 2+ is hydrophilic because of its struc- Figure 5 shows the XRD patterns of samples with different degrees of MMT functionalization used to investigate the interlayer structure of the MMT-based nanofiller. The distance between the layers of nanofiller was calculated using Bragg's law [17,26]. As shown in Figure 5a, the d-spacing of organo-MMT was determined to be 2.49 nm, indicating an increase from that of MMT-Ca 2+ (1.23 nm).…”