Rafael S. Araújo

Poly(lactic acid)/Cellulose Composites Obtained from Modified Cotton Fibers by Successive Acid Hydrolysis

This work is focused on the hydrolysis of cotton fibers from waste textiles to obtain micro and nanofibers to be used as reinforcements in polymer composites. To promote their compatibility with polymeric matrix, hydrolyzed cotton fibers were surface modified with various silane compounds. Thus, these fibers were mixed with commercial poly(lactic acid) (PLA) at 5% w/w loading by melt compounding. Acid treatments caused a decrease of the crystallinity index whereas the thermal stability was significantly improved, especially for cellulose fibers hydrolyzed in two steps. Morphological analysis revealed a reduction of the fibers diameter and a decrease of their length as a consequence of the hydrolysis. NMR analysis confirmed the silanization of the fibers by reaction with the silane agent. Tensile tests revealed that silanization treatments were able to increase the composite Young’s modulus and the stress at break with respect to the neat matrix, indicating that silanization improved the polymer/fiber compatibility interfacial adhesion. The overall results demonstrated that applying suitable surface modification strategies, waste cotton textiles can be effectively recycled as fillers in polymer based composites.

Synthesis of Nanocomposites of Polypropylene with Graphite Nanosheets by In Situ Polymerization Using a Fourth Generation Ziegler-Natta Catalyst

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.