Otávio Bianchi

Crosslinking Kinetics of Blends of Ethylene Vinyl Acetate and Ground Tire Rubber

The copolymer ethylene vinyl acetate (EVA) and blends of EVA and ground tire rubber (GTR) with different compositions are prepared in the presence and absence of dicumyl peroxide (DCP) as a crosslinking agent. The crosslinking kinetics is investigated through oscillatory disc rheometry (ODR) and differential scanning calorimetry (DSC). The crosslinking kinetics is found to be dependent on the amount of GTR in the EVA/GTR blends; the partially crosslinked GTR phase acts as a physical barrier, slowing down the EVA crosslinking rate. Furthermore, activation energies (Ea) and reaction order (n) values suggest that the crosslinking reactions are not restricted to the EVA bulk, but can also occur to some extent at the EVA/GTR interface.

Morphological and structural characterization of PHBV/organoclay nanocomposites by small angle X-ray scattering.

In this work, the morphological and structural behaviors of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposites were investigated using small angle X-ray scattering (SAXS), wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). The nanocomposites with 1, 3 and 5 wt.% of organically modified montmorillonite Cloisite® 30B (OMMT) were prepared by melt processing in a twin screw extruder using two different processing conditions (low and high shear intensity). The lamellar long period of the polymer was lower for the nanocomposites, with high polydispersity values. However, the crystalline thickness increased with the clay content and was independent of the processing conditions. This behavior resulted in a high linear crystallinity of the nanocomposites with 3 and 5 wt.% OMMT. The disruption factor (β) was in agreement with the WAXD and TEM findings, indicating a good dispersion of the nanoparticles in the PHBV matrix with 3 wt.% of OMMT during the high shear intensity of melt processing.

Avaliação da degradação não-isotérmica de madeira através de termogravimetria-TGA

The thermal stability of wood and cellulosic materials is an important factor for applications of these natural renewable materials as fillers for reinforcing polymeric matrices. However, these materials have low thermal stability caused mainly by species that ignite at low temperatures. These characteristics contribute significantly to limit their use in situations where higher temperatures are required. In this work, the thermal degradation of two kinds of wood (Pinus and Garapeira) was evaluated using thermogravimetric measurements under nitrogen atmosphere. The parameters of thermal decomposition kinetics were estimated using the Flynn-Wall-Ozawa (FWO) method. The Garapeira wood showed lower activation energy at reaction degrees below 0.5, probably due to the presence of volatiles compounds, such as oil and wax. The Pinus wood had different characteristics in the initial reaction degree (up to 0.4). After this point, however, Garapeira becomes more stable than Pinus due to the formation of more thermally stable species and because of the higher amount of lignin. Besides, the thermal degradation processes of both woods were found to be mainly controlled by diffusion (Dn) of volatile species at reaction degrees up to 0.8, achieving a third order (F3) mechanism afterwards.

Effect of dynamic cross-linking on phase morphology and dynamic mechanical properties of polyamide 12/ethylene vinyl acetate copolymer blends

Dynamic cross-linking of polyamide 12 (PA12) and ethylene vinyl acetate copolymer (EVA) blends in the mixing chamber of a torque rheometer was investigated. EVA was selectively cross-linked within the PA12 phase through free radical reactions using dicumyl peroxide. The torque level and temperature in the torque rheometer chamber were monitored to follow the evolution of the EVA cross-linking during the dynamic cross-linking process. The degree of cross-linking of EVA in the PA12/EVA materials was estimated based on the gel content (insoluble EVA fraction). The PA12/EVA phase morphology was investigated by scanning electron microscopy. The solid viscoelastic properties were investigated by dynamic mechanical thermal analysis (DMTA). The morphology, interfacial tension and viscoelastic results showed the immiscible nature of this system. The morphology of the blends was observed and the results revealed a two-phase system. The PA12/EVA 70/30 showed disperse-phase morphology, however a co-continuous phase was observed in blend ratios of 50/50 and 60/40. The dynamic cross-linking process resulted in a more stable EVA phase morphology with disperse and interconnected structures in the thermoplastic PA12 domains.

Characterization of EVA residues from the shoe industry and post-consumer urban-waste polyethylenes

This paper presents a characterization of a crosslinked EVA residue (EVA-c) from expanded sheets used in the shoe industry and post-consumer urban-waste polyethylenes regarding their molecular (FTIR), mechanical (tensile and impact tests), morphological (SEM), thermal (DSC, TGA) and dynamic-mechanical (DMTA) properties. For comparison, the properties of the EVA-c and recycled polyethylenes are compared to respective virgin polymers. The recycled polyethylenes generally presented similar properties to the virgin ones. On the other hand, some EVA-c properties differed from virgin ones since it has a high degree of crosslinking and it therefore has a higher tensile modulus and lower elongation at break, notched Izod impact strength and hardness. Additionally, crosslinking was also found to modify the thermal properties (TGA and DSC) of EVA-c.

Caracterização viscosimétrica de nanocompósitos híbridos PS/POSS

Polystyrene (PS) and polyhedral oligomeric silsesquioxanes (POSS) hybrid nanocomposites with different compositions were obtained by reactive melt processing using dicumyl peroxide (DCP) as initiator in the presence or absence of styrene as radical transfer agent. The materials were characterized by viscosimetry by means of gel permeation chromatography (GPC) using triple-detector: light scattering, viscometer and refractive index. PS/POSS samples processed with styrene showed higher weight average molecular weights (Mw) and lower polydispersity indexes (Mw/Mn), as a result of higher PS-POSS conversion (28-40%) and lower PS degradation, as compared to the PS/POSS samples processed without styrene in which the degree of conversion was lower (24-28%). For the PS/POSS solutions in THF, the parameters of the Mark-Houwink-Sakurada equation, α ≅ 0.7 and log K ≅ -3.5 to -3.9, and the values of polymer-solvent interaction parameter, χij ≅ 0.49, were not changed with respect to changes in molecular size. On the other hand, these changes were characterized by a cumulative function of the mass fraction of chains as a function of the root mean square end to end distance ( 01/2).

Dynamic Vulcanization of HDPE/EVA Blend Using Silane

Dynamic vulcanization of high-density polyethylene and ethylene vinyl acetate (HDPE/EVA) blends (50/50 wt%) in the mixing chamber of a torque rheometer was investigated. EVA was selectively cross-linked within the HDPE phase by transesterification reaction between ester groups of the EVA and alkoxysilane groups of tetrapropoxysilane, catalyzed by dibutyl tin oxide. Torque level and temperature in the torque rheometer chamber were monitored to follow the evolution of the EVA cross-linking during dynamic vulcanization. The degree of cross-linking of EVA in the HDPE/EVA materials was estimated by the gel content (insoluble EVA fraction). The changes in the HDPE/EVA phase morphology caused by different degrees of EVA cross-linking were investigated by scanning electron microscopy. Melt-state linear viscoelastic properties of the materials were investigated by small amplitude oscillatory shear rheometry. For the composition and processing conditions adopted in this study, the HDPE/EVA showed a coarse co-continuous phase morphology, with large EVA domains interconnected with HDPE domains. Following the dynamic vulcanization, this changed to a more refined co-continuous morphology. The linear viscoelastic relaxation behavior of dynamically vulcanized HDPE/EVA materials suggests the existence of a percolated network structure of high viscous and elastic EVA domains interconnected with thermoplastic HDPE domains.

Influence of composition and crosslinking on mechanical and thermal properties of recycled polyethylene/EVA mixtures

This study aims to investigate a recycling alternative for a crosslinked ethylene-vinyl acetate (EVA-c) copolymer (75 wt% of gel content) from the shoe industry through mixing with virgin and recycled polyethylenes. The Drais equipment, an ultra-high-speed thermo-kinetic mixing and compounding system specifically developed for very difficult compounding, mixing and dispersion applications, was chosen for processing highly loaded EVA-c (60-90 wt%) compounds. PE/ EVA-c mixtures presented additive or synergistic mechanical properties, which reveals good compatibility between the polymers. The addition of dicumyl peroxide (DCP) as a crosslinking agent was also evaluated. The PE/EVA-c/DCP mechanical properties were found to be influenced by the degree of crosslinking; significant softening was observed for mixtures with DCP contents higher than 2 phr, that is, with maximum gel content. It is proposed here that the softening caused by DCP addition was related to a decrease in the degree of crystallinity; although the crosslinking process itself make polymeric materials more rigid, for semicrystalline polymers it causes defects in their crystalline arrangement, increasing the volume of amorphous phase, i.e., the crosslinking process induces a decrease in the degree of crystallinity of PE/EVA-c mixture, presenting a rubber-like behavior. Therefore, the use of the recycling procedure developed in this work represents an alternative for crosslinked EVA-c and PE re-use through a low-cost and easy-to-handle batch mixer (Drais), making it possible to prepare materials with a range of mechanical properties suitable for technological applications.

Effects of POSS addition on Non-isothermal crystallization and morphology of PVDF

The influence of polyhedral oligomericsilsesquioxane (POSS) content on the rheological behavior, non-isothermal crystallization behavior, and on crystal morphology of the poly(vinylidene fluoride) nanocomposites prepared through melt blending were investigated in this work. Rheological analysis showed that the POSS additiondecreased viscosity as compared to pure PVDF and induced a deviation in the liquid-like behavior predict by Einstein Suspension Sphere Law. The addition of POSS into PVDF promoted chances in the crystallization behavior. The crystallization was slower in the nanocomposite with higher POSS content due to the diluent effect of POSS in this system. Small angle X-ray scattering (SAXS) patterns showed a small increasing in the lamellar region of PVDF. The amorphous region increases significantly with POSS addition. The interface between the crystalline and amorphous region remains practically unchanged.

Mistura polipropileno/poliestireno: um exemplo da relação processamento-estrutura-propriedade no ensino de polímeros

Polymer blends remain an important research topic in different areas, in spite of innumerous studies over the years. In particular, mixtures of polypropylene and polystyrene are among the most studied, mainly owing to their low cost and technological relevance. In this work, the students enrolled in the discipline Polymer Processing I (PG24) in the Materials Science Graduate Program (PGCIMAT-UFRGS) produced blends of polypropylene and polystyrene, where all polymer processing steps were performed during lab classes. Then, each student undertook a characterization procedure with a specific technique, which included samples preparation, the analysis itself and discussion of the results. Subsequently, the results were confronted in the classroom, where we sought the correlations. Finally, all students reviewed this article, including suggestions and criticisms. As expected, the mixture of polystyrene and polypropylene formed an immiscible blend. Furthermore, the processing affected the characteristics of the polymers, leading to a reduction in molecular weight, and as a result a drop in its physical properties. In the PP/PS mixtures, phase separation produced PS domains with micrometers in size, and low adhesion to the PP matrix, which explains the loss of mechanical properties.