Dynamically vulcanized PP/EPDM blends: Influence of curing agents on the morphology evolution

Thermoplastic vulcanizates (TPE‐Vs) are a special class of thermoplastic elastomers (TPEs), where the rubber phase is dynamically crosslinked in the presence of a thermoplastic matrix. The goal of this work is to compare the behavior of two curing agents systems, conventional peroxide named Peroximon and bismaleimide/dicumyl peroxide, in TPE‐Vs based on PP/EPDM 35/65 w/w. It was also investigated the TPE‐Vs morphological evolution and samples was collected at different times during the mixture and dynamic crosslinking. The materials were characterized by some techniques, which allowed investigating mechanical, morphological, hardness, and swelling properties. Considering the used curing agents contents, the TPE‐Vs obtained by using Peroximon presented lower tensile strength, lower swelling degree, and remarkable lower deformation than those obtained with BMI/DCP system. The hardness properties were not significantly affected by the content of the curing agent, showing only a slight decrease when the Peroximon content was increased. The study of the evolution of morphology showed the rubber phase undergoes crosslinking after adding the curing agent. It could be observed by the increase of the torque and by the appearance of domains in the micrographs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of Dielectric Particles by Impedance Spectroscopy (Part I)

Impedance spectroscopy is an effective method to investigate physical properties of multicomponent systems so that contributions of individual components can be extracted from different sections of the spectra, which is frequency dependent. Slurries can be considered as 0–3 mixed systems containing a host liquid and dispersed particles. It was shown that low-frequency part of impedance spectra is sensitive to dielectric properties of dispersed particles. Applicability of this technique was extended using various dielectric powders dispersed in appropriate liquids. Characterization of slurries by impedance spectroscopy through applying of equivalent circuit models allows a reliable measurement of dielectric constant of particulate materials and liquids.     

Processability of revulcanizable SBR compositions

The problem of vulcanized rubber scraps is of high importance nowadays, and the revulcanization of these scraps is an alternative to reutilize them. This work concerns the investigation of the processability of new compositions made from revulcanizable rubber scraps, through data from the Haake torque rheometer and the Rubber Process Analyzer (RPA). By varying cure system and oil addition, powdered butadiene-styrene rubber compositions (SBR-r) scraps were used in the preparation of six formulations. A control composition of identical formulation as the scraps was supplied by the industry and analyzed in all situations. Data reveal that new products can be produced by the reutilization of these industrial scraps.     

Molecular mass characteristics of polyethylene produced with supported vanadium‐magnesium catalysts

Highly active supported vanadium‐magnesium catalysts (VMC) produce polyethylene (PE) with broad and bimodal molecular mass distribution (MMD) in comparison with the famous titanium‐magnesium catalysts (TMC). The effect of hydrogen as an efficient chain‐transfer agent on the MMD of PE has been studied. Increasing hydrogen concentration causes a considerable broadening of MMD of PE due to the shift of the low molecular weight peak on the MMD curve. At the same time, the high molecular weight shoulder stays at the same position even at high hydrogen concentration. This means that VMC contain two types of active centre. One type is very reactive in the chain‐transfer reaction with hydrogen. These centres produce low molecular weight PE in polymerization in the presence of hydrogen. The other type of active centre is not active in chain transfer with hydrogen. These centres produce high molecular weight PE ((1–3) × 10⁶) and hydrogen does not affect the position of the high molecular weight shoulder. MMD data were used to analyze the kinetics of the chain‐transfer reaction with hydrogen and to calculate the rate constants of this reaction. Copyright © 2005 Society of Chemical Industry     

Some factors affecting pore size in the synthesis of rigid polymer monoliths: Theory and its applicability

Macroporous monoliths represent now widely used materials whose successful application strongly depends on their characteristics. Among those the average pore size is one of the key parameters. In this paper, we consider the applicability of theoretical calculations for the selection of appropriate porogens to generate the materials with required average pore size. A set of macroporous poly(meth)acrylate monoliths was synthesized via thermo- and photo-initiated free radical polymerization and characterized in regards to their average pore size. Additionally, the difference in solubility parameters as well as Hansen's solubility parameter distance between monomers and porogens were calculated for each polymerization mixture using Hildebrand's and Hansen's solubility theories. The theoretical predications and experimental data were compared and analyzed to establish the applicability of theoretical calculations to previse average pore size for different systems. It was found that Hildebrand's theory seems to be poorly appropriate as universal tool, while Hansen's theoretical approach explained better the efficiency of solvents as porogens. The application of oligomers and polymer solutions due to the increase of viscosity as well as the variation of crosslinker amount in the monomer system can be singled out as Hansen's theory limitations at the prediction of the average pore size.     

Optimization problem with normally distributed uncertain parameters

The issue of chemical process optimization when at the operation stage the design specification should be met with some probability and the control variables can be changed has been considered. A common approach for solving the broad class of optimization problems with normally distributed uncertain parameters were developed. This class includes the one‐stage and two‐stage optimization problems with chance constraints. This approach is based on approximate transformation of chance constraints into deterministic ones. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2471–2484, 2013     

Wine industry residue as antioxidant in cooked chicken meat

The effectiveness of grape extracts as food ingredient has been tested in various systems. The objective of this study was to evaluate the efficiency of four concentrations of residues of the wine industry in delaying lipid oxidation in processed chicken meat stored under refrigeration. The development of oxidation during the 14‐day storage was evaluated through the thiobarbituric acid reactive substances method (TBAS). The analyses of phenolic compounds and antioxidant activity were performed in grape residue extracts through DPPH (1,1‐difenil‐2‐picrilidrazil) method, lipid peroxidation inhibition and Rancimat. The profile of polyphenols was determined using reversed‐phase high‐performance liquid chromatography. Isabel grape extract (IGE) and Niagara grape extract (NGE) showed significant content of phenolic compounds. NGE and IGE had high antioxidant activity. The addition of grape extracts significantly increased the oxidative stability of processed and cooked chicken meat during the storage time. The extracts from both grape varieties when applied in concentrations of 40 and 60 mg of GAE, presented results similar to that of Butyl hydroxy toluene (BHT).