Relations between morphology and crystallization behavior of poly (l-lactide) / poly (butylene succinate) bioblend nanocomposites with graphene oxide nano-sheets

S. Fenni1, D. Cavallo2, and N. Haddaoui1

1LPCHP, Faculty of Technology, University of Setif -1, Algeria.
2DCCI, University of Genova, Italy.

Bio-based blend nanocomposites of poly(L-lactic acid) (PLA) and poly(butylene succinate) (PBS) [1] with different concentration (from 0.1 wt% to 0.5 wt%) of Graphene Oxide nano-sheets (GOs) were prepared by melt blending. The resulting morphology is investigated with scanning and transmission electron microscopy (FE-SEM and TEM). FE-SEM of fracture surfaces revealed that the addition of GO to the bio-based PBS/PLA blend improves the adhesion between the two polymers, indicating that GOs nanosheets locate at the interface.[2] TEM analysis showed that the nanofillers are preferentially found in the PBS phase (minority component). The grapheme oxide nanosheets act as nucleting agents for both semicrystalline polymers. The nucleating effect of the added particle is compared to the one of own self-nuclei for each polymer, to define a convenient nucleating efficiency (NE) scale. A value of around 80% is determined for GO towards PBS, among the highest nucleating efficiencies ever reported for this polymer. On the other hand, the efficiency in nucleating PLA is equal to a modest 15%, due to the uneven distribution of the filler in the two polymers. A close relationship between the nanocompostie complex morphology and crystallization behavior of the two different polymers is thus established.

References
[1] Wang, R. et al. Polym. Eng & Scie. 49:1, 26–33. 2009. (link)
[2] Cao, Y. et al. ACS Nano. 5:7, 5920-5927. 2011. (link)

Tailoring Properties of Polypropylene through Crystallization in the Presence of Polymeric Nucleating Agents

C. De Rosa, F. Auriemma, O. Tarallo, C. Santillo, M. Scoti

Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Complesso di Monte S.Angelo, Via Cintia, I-80126 Napoli.

In this communication, we present a strategy for the addition of polymeric nucleating agents for the crystallization of isotactic polypropylene (iPP) that guarantees a perfect fine dispersion of nucleating particles within the entire mass of the polymer, with consequent their high efficiency even at very low concentrations. The Ziegler-Natta catalyst particles are coated by a thin skin of poly(trimethylallylsilane) (PTMAS) or poly(vinylcyclohexane) (PVCH) that will act as nucleating agents, by prepolymerization of the corresponding monomers. PVCH shows higher nucleation efficiency than PTMAS with greater increase of crystallization temperature by standard cooling from the melt. Both polymeric nucleating agents affect the crystal morphology greatly reducing the size of shperulites. This in turn affects the mechanical properties improving ductility and flexibility. The presence of the nucleating agent accelerates the crystallization of iPP and affords crystallization of the α form even upon fast crystallization by quenching the melt, condition that generally produces crystallization of the mesomorphic form of iPP (1). Crystals of α form so obtained show a nodular morphology and absence of spherulitic superstructure. This novel iPP material is characterized by outstanding and unexpected properties of high mechanical strength and modulus and contemporarily high ductility, flexibility and good transparency due to the nodular morphology of α form (2).

References
[1] C. De Rosa; F. Auriemma Ang. Chem. Int. Ed. 51, 1207 (2012). (link)
[2] C. De Rosa, F. Auriemma, O. Tarallo et al. Polym Chem. 8, 655 (2017). (link)