Poly(propylene) is one the polymers with the widest range of commercial applications, though as all polymers, it is susceptible to degradation reactions. The addition of antioxidants to polymers is the main way to prevent or retard the degradation process. Extrusion is the most used industrial process to mix additives to the polymer, but this technique involves processing under high temperatures and shear, which causes polypropylene to degrade. Therefore, a Ziegler‐Natta catalyst system based on MgCl2/TiCl4 was prepared with morphology control and the antioxidant was added directly in the polymerization medium, thereby producing spherical and stabilized PP.

In the present study, a new polypropylene (PP)/multi-walled carbon nanotube (MWCNT) masterbatch is synthesized by in situ polymerization and compared with a masterbatch obtained by melt mixing. Both masterbatches are used for the realization of PP/MWCNT nanocomposites by mixing with a commercial PP in a laboratory extruder. It is shown that the use of masterbatch synthesized in situ allows providing additional enhanced thermal stability and mechanical properties. Samples are characterized according to their thermo dynamicmechanical properties, thermal stability, and degree of crystallinity, as well as by scanning electron microscopy. DMA analysis shows that there is a sharp increase in both storage and loss moduli of materials even with very low CNT content, in comparison with the neat PP. By means of thermogravimetric analysis, it is found that the thermal stability of nanocomposites is also increased. Furthermore, the degree of crystallinity of the materials containing CNTs is increased to higher value than that of neat PP, suggesting that the carbon nanotubes act as nucleating agent. A sharper increase of X c is observed in the composites with low CNT content prepared in the method using meltmasterbatch, suggesting that there are more agglomerations of CNTs in this material.

Summary In the present study, masterbatch of polypropylene and graphene nanocomposite was obtained by in situ polymerization. Afterwards, this masterbatch was diluted in commercial PP matrix previously treated with dicumyl peroxide (DCP) and vinyl trimethoxysilane (VTMS), originating grafted and reinforced filaments. Then, this material was crosslinked in water at 90 °C through condensation of hydroxyl groups derived from grafted PP chains. These materials were evaluated according to their thermal, mechanical and rheological properties. The results showed that it was possible to graft and crosslink PP, however, crosslinking was hindered by the presence of graphene sheets in the polymer matrix. In non‐reinforced crosslinked polymer, an increase in complex viscosity was observed, showing that actually occurred crosslinking. Furthermore, the grafted sample has lower molecular weight compared to the commercial PP. The crosslinked sample reduced its Newtonian plateau.

Polypropylene nanocomposites with expanded graphite nanosheets (xGN) were synthesized by In Situ polymerization employing a Ziegler-Natta catalyst supported on particles of MgCl2 containing xGN (mass ratio 1:1) and internal electron donor to control isotacticity, and their properties were compared with those of neat polypropylene obtained using a prepared standard Ziegler-Natta catalyst. SEM micrographs showed an alteration in the morphology of the catalyst with nanoparticles when compared with the standard one. It was noted that the catalyst containing xGN was more reactive for propylene polymerization than the standard one. By thermogravimetric analyses, it was detected that the PP/xGN nanocomposites showed higher thermal stability than PP. Differential scanning calorimetry (DSC) showed that the nanocomposites presented higher crystallinity degree, indicating that the nanofillers acted as nucleating agent. Scanning (SEM) and transmission (TEM) electron microscopies showed that the nanofillers were well dispersed into the PP matrix. By dynamic-mechanical analyses (DMA) it was observed an increase in glass transition temperature and the nanocomposites moduli.

Blends of polypropylene (PP), polyamide 6 (PA6), and biodegradable polymers (BPs) such as poly(D,L-lactic acid) (PDLLA), poly(lactic acid-co-ε-caprolactone) (poly[LA-co-ε-CL]) and poly(ε-caprolactone) (PCL) were prepared using a twin-screw mini-extruder. The composition of the blend PP/PA6 was fixed at a mass proportion of 70/30, and the compatibilized blends contain 5 wt% of each BP. The morphology observed through scanning electronic microscopy, the dynamic mechanical thermal properties (DMTA), and the biodegradation test after composting and performing optical microscopy (OM) of the blends were investigated. The blend PP/PA6 compatibilized with polypropylene grafted with maleic anhydride (PPMA) was also obtained and used as a reference. The results showed that the PP/PA6/PPMA revealed a more homogeneous morphology and resulted in higher modulus; nevertheless, the sample obtained with the lower molar mass PDLLA as an alternative for PPMA showed a storage modulus behavior close to the reference material. Poly(LAco-ε-CL) and PCL also showed changes in the morphology of the PA6 dispersed phase. Positive results were observed in the biodegradation test examined by OM for all samples containing BPs. The novelty of this work was to employ BPs as compatibilizing agents of the blends comprising PP/PA6, producing ternary blends with superior mechanical properties due to the better dispersion of the phases.