Fabio R. Passador

Estado de mistura e dispersão da fase borrachosa em blendas PVC/NBR

Thermoplastics modified with elastomers have attracted great interest of researchers and industries due to the low cost/benefit relationship and the possibility of significant increase in the toughness of brittle polymers through the incorporation of a dispersed rubber phase. This article shows the relationship between the interaction between phases and rubber phase dispersion in poly (vinyl chloride)/nitrile rubber blends. The interaction between components in polymer blends is an important factor to be considered in the development of this kind of materials because it determines the level of the mixture at the molecular level. The particulate nature of PVC and the degree of nitrile groups in the NBR are responsible to the PVC/NBR blends morphologies leading to an optimization of the mechanical properties when the rubber particles form a pseudo-network morphology with the rubber particles randomly dispersed in between the PVC primary particles.

Thermoplastic Elastomers Based on Natural Rubber/Polypropylene Blends: Effect of Blend Ratios and Dynamic Vulcanization on Rheological, Thermal, Mechanical, and Morphological Properties

Thermoplastic elastomers (TPEs) based on natural rubber (NR)/polypropylene (PP) with different blend ratios were prepared and studied. The TPEs were obtained by dynamic vulcanization of NR/PP using a sulfur (S)/N-tert-butyl-2-benzothiazolesulphenamide (TBBS) and tetramethylthiuram disulphide (TMTD) curative system during processing in the melt state in an internal mixer equipped with cam rotors. Rheological, thermal, mechanical, dynamic, and morphological properties of the TPEs prepared were investigated. Based on this study a mechanism for the NR crosslinking was proposed where the sulfur vulcanization occurs through radical substitution in the forms of polysulfide bridges. The dynamic vulcanization process increases the stiffness of the NR phase in the TPEs and modifies the rheological and thermal behavior of the system compared to the behavior of the basic material PP. The crosslinked NR particles restrict the spherulitic growth and the regular arrangement of the spherulites of PP phase, decreasing the crystallinity degree. On the other hand, a reduction of mobility of the chain segments was also observed and, consequently, an increase of the Tg values. NR/PP TPEs with high content of NR showed superior mechanical performance compared to the uncrosslinked NR/PP blends in terms of tensile strength, Youngs modulus and hardness. An increase of approximately 320% in Youngs modulus values was obtained for the NR70/PP30 TPE compared to NR70/PP30. Morphological studies revealed the formation of large aggregates of NR domains in NR/PP TPEs which increased in size with an increase of the rubber content.

Blendas PVC/NBR por processamento reativo I: desenvolvimento do processo de vulcanização Dinâmica in situ

Dynamic vulcanization is a process of vulcanization of an elastomer during melt mixing with a thermoplastic wich results in material called thermoplastic vulcanizates or TPVs. In this study, a new kind of TPV was obtained by in situ dynamic curing of poly(vinyl chloride) (PVC)/nitrile rubber (NBR) blends. The crosslinking of PVC/NBR blends was accomplished using sulphur (S)/tetramethylthiuram disulphide (TMTD) and mercaptobenzthiazyl disulphide (MBTS) curative system during the reactive processing. The blends of PVC/NBR at the ratio of 90/10; 80/20 and 70/30 wt. (%) were melt mixed using a Haake Rheomix 600 at 160 °C and rotor speed of 60 rpm. The curing behavior of NBR was investigated by a Monsanto Rheometer and the degree of cure was calculated using differential scanning calorimetry (DSC) for different mixing times. It was observed that the degree of cure increases with the mixing time and the crosslinking system used in this work was considered efficient.

In Situ Dynamic Vulcanization of Poly(Vinyl Chloride)/Acrylonitrile-butadiene Rubber Blends

Poly(vinyl chloride) (PVC)/acrylonitrile-butadiene rubber (NBR) blends can be obtained through a dynamic vulcanization process as a melt-processible thermoplastic elastomer which produces parts that look, feel and perform like vulcanized rubber with the advantage of being processible as a thermoplastic material. In this study, a vulcanized thermoplastic was obtained by in situ dynamic vulcanization of PVC/NBR blends using a sulphur/ tetramethylthiuram disulphide (TMTD) and mercaptobenzothiazyl disulphide (MBTS) curative system during processing at the melt state. The blends were melt-mixed using a Haake Rheomix 600. The curing behavior of NBR was then investigated by a Monsanto rheometer. The thermal analyses were performed and the cross-linking at different mixing times was calculated using DSC. FT-IR was also performed for characterization of the blends. The cross-link densities of the samples were measured by a swelling method. The degree of cure increases with the mixing time. The cross-linking formation was verified through the formation of C─ S bonds in the blends.

Blendas PVC/NBR por processamento reativo II: caracterização físico-mecânica e morfológica

Dynamic vulcanization is a process of vulcanization of an elastomer during melt mixing with a thermoplastic. This process increases the mechanical resistance of elastomers through the increase of elastic modulus, hardness and abrasion/fatigue resistance. In this study, it was evaluated the physical-mechanical and morphological behaviors of the PVC/NBR blends obtained by reactive processing. The dynamic vulcanized blends have a better performance compared to the similar conventional ones. It was observed an increase of 205% in the elastic modulus to the dynamic vulcanized blend PVC/NBR (90/10) compared with the conventional blends. The morphology of the blends examined by scanning electron microscopy evidenced the crosslinking formation only in the elastomeric phase. The vulcanized rubber particles are responsible by the increase of stiffness and consequently displayed better mechanical properties.

Influência do tipo de agente de partição da borracha nitrílica na obtenção de blendas PVC/NBR

Nitrile rubbers used in mixture with PVC resin are supplied in powder. This kind of nitrile rubber has a partitioning agent to avoid agglomeration in the particles during the transport and storage. In this study, the influence of the partitioning agent on the preparation of PVC/NBR blends was investigated. The mechanical properties of the blends were evaluated by tensile properties, tear strength and hardness. The PVC/NBR blends with partitioning agent of PVC showed an increase in the tensile stress and Youngs modulus compared to the PVC/NBR blends with partitioning agent of CaCO3. The morphology of the blends examined by scanning electron microscopy demonstrated the influence of the partitioning agent.

Characterization of nanocomposites for hydrogen storage

The use of hydrogen as an energy carrier suitable to replace gasoline and other fossil fuels has been widely discussed as a way to sustainably fuel our civilization. However, hydrogen storage is a major barrier in the establishment of infrastructure for hydrogen technology. The incorporation of nanoparticles to the polymer matrix may be an alternative to obtain materials with promising properties for hydrogen storage. In this work, polyetherimide-based Nanocomposites were prepared using carbon nanotubes doped with sodium alanate (NaAlH4) as filler. The sodium alanate content was fixed at 30 wt% and were studied three carbon nanotubes concentrations: 5, 10 and 20 wt%. The nanocomposites were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Hydrogen sorption measurements.The use of hydrogen as an energy carrier suitable to replace gasoline and other fossil fuels has been widely discussed as a way to sustainably fuel our civilization. However, hydrogen storage is a major barrier in the establishment of infrastructure for hydrogen technology. The incorporation of nanoparticles to the polymer matrix may be an alternative to obtain materials with promising properties for hydrogen storage. In this work, polyetherimide-based Nanocomposites were prepared using carbon nanotubes doped with sodium alanate (NaAlH4) as filler. The sodium alanate content was fixed at 30 wt% and were studied three carbon nanotubes concentrations: 5, 10 and 20 wt%. The nanocomposites were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Hydrogen sorption measurements.

Polymer nanocomposites for hydrogen storage

Hydrogen is considered to be a clean, economical and safe renewable energy source that would be ideal to replace fossil fuels, because it is light, highly abundant and its oxidation product (water) is environmentally benign. However, hydrogen is easy to burn (the chemical energy per mass of hydrogen is at least three times larger than that of other chemical fuels), which has the risk of fire and explosion. The problems of transportation and storage restrict the application of hydrogen energy, which has become a key factor in the development and utilization of hydrogen energy. This gas adsorbs at solid surfaces depending on the applied pressure and temperature. For storage purposes in mobile applications, the adsorption of hydrogen has been studied mainly on carbon species, but light and reasonably cheap materials of high surface area should prove to be attractive as well. Porous material is a very promising hydrogen storage material, which stores the gas in the form of molecules at low temperatures and co...

Sulfonated poly(ether imide)/aluminium nanocomposites for hydrogen storage

Mobility is a socioeconomic reality that increases every year and it should be safe, economic and reasonably clean. Little energy needs to be expended to overcome potential energy changes, but a great deal is lost through friction and low-efficiency energy conversion. Hydrogen would be ideal as a synthetic fuel because it is lightweight, highly abundant and its oxidation product (water) is environmentally benign, but storage remains a problem. The clean way to produce hydrogen from water is to use sunlight in combination with photovoltaic cells and water electrolysis, although other forms of primary energy and other water-splitting processes are generally used. The chemical energy per mass of hydrogen is at least three times larger than that of other chemical fuels. Hydrogen adsorbs at solid surfaces depending on the applied pressure and temperature. The variation of attractive surface forces as a function of distance from the surface decides whether van der Waals-type weak physisorption of molecular hydr...

Effect of Molecular Weight of Polyamide 6 in Rheological Properties of Nanocomposites with Brazilian Organoclay

Polyamide 6 (PA6)/Brazilian organoclay nanocomposites were obtained by melt intercalation and the structural and rheological properties were studied. The nanoclay was treated with quaternary ammonium salt (Cetremide) and characterized using infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results indicated the effective organophilization of nanoclay. The nanocomposites were obtained by melt intercalation using a twin screw corrotacional extruder in two steps. Firstly, a masterbatch of PA6 / nanoclay (1: 1) was prepared. In the second step the masterbatch was diluted in PA6 to obtain 3 and 5 wt% of nanoclay in the nanocomposites. The specimens were injection molded and analyzed using capillary rheometry, X-ray diffraction and transmission electron microscopy (TEM). The results of capillary rheometry showed that the presence of the organoclay in PA6 increased the viscosity of the systems. Structural characterization showed that the nanocomposites were predominant in exfoliated structure.