Modification of graphene oxide to induce beta crystals in isotactic polypropylene

Graphene oxide (GO) was functionalized with pimelic acid (PA) on its surface to produce a β-crystal nucleating agent. The functionalization was characterized by Fourier transform infrared spectroscopy, showing the presence of new bands at 1570 and 1406 cm⁻¹ indicating a bridging bidentate link of the PA on the GO surface through the Ca used during the functionalization. These observations were concomitant with the Raman spectroscopy results where the D–G intensity ratio increased, suggesting that the disorder in GO structure increased when the PA molecules are attached on the GO surface. The modified graphene oxide (GO-PA) showed high thermal stability, making it attractive for melt blending composites. These results were observed by thermal differential scanning calorimetry (DSC) and thermogravimetric analysis. The DSC and wide-angle X-ray diffraction (WAXD) results demonstrated that the modified GO is an excellent β-nucleating promoter even at low percentages (0.05 GO-PA % w/w) in contrast to the unmodified GO. The content of β-crystals under isothermal crystallization conditions reached a value as high as 92% by DSC while the extrudes prepared by compression and analyzed by WAXD showed a kβ = 0.78 by Turner-Jones method at the same percentage of modified filler. The storage modulus for the iPP composites (GO/iPP and GO-PA/iPP) was in all cases higher than that for the raw iPP sample because of the presence of GO in the polymer matrix. However, a decrease in the storage modulus can be observed for the GO-PA/iPP composites because of the presence of high percentages of β-crystal.