Production of high melt strength polypropylene by gamma irradiation

High melt strength polypropylene (HMS-PP) has been recently developed and introduced in the market by the major international producers of polypropylene. Therefore, BRASKEM, the leading Brazilian PP producer, together with EMBRARAD, the leading Brazilian gamma irradiator, and the IPEN (Institute of Nuclear Energy and Research) worked to develop a national technology for the production of HMS-PP. One of the effective approaches to improve melt strength and extensibility is to add chain branches onto polypropylene backbone using gamma radiation. Branching and grafting result from the radical combinations during irradiation process. Crosslinking and main chain scission in the polymer structure are also obtained during this process. In this work, gamma irradiation technique was used to induce chemical changes in commercial polypropylene with two different monomers, Tri-allyl-isocyanurate (TAIC) and Tri-methylolpropane-trimethacrylate (TMPTMA), with concentration ranging from 1.5 to 5.0 mmol/100 g of polypropylene. These samples were irradiated with a ⁶⁰Co source at dose of 20 kGy. It used two different methods of HMS-PP processing. The crosslinking of modified polymers was studied by measuring gel content melt flow rate and rheological properties like melt strength and drawability. It was observed that the reaction method and the monomer type have influenced the properties. However, the concentration variation of monomer has no effect.     

In situ estimation of crack concentration in hard rock

Results of a 2004 field experiment aimed at determining the quadratic nonlinearity parameter in granite that forms the shore of the Ladoga lake are presented. The measurements were based on the observation of the nonlinear interaction between monochromatic waves excited by two hydroacoustic radiators of 1 kW each positioned near the shore. The initial level of nonlinear distortions was much lower than the level of the received difference-frequency signal. The quadratic nonlinearity parameter proved to be higher than that reported in the majority of publications. An assumption was put forward that the high nonlinearity of granite is caused by the high concentration of cracks in it. Pieces of rock were taken from the measurement site, and rectangular samples were prepared from them. The samples were studied by the acoustic spectroscopy method in laboratory conditions. As a result, estimates of crack concentration were obtained, which proved to be consistent with the field measurements of the quadratic nonlinearity parameter. Thus, the possibility of estimating the crack concentration in situ from the measurements of the quadratic nonlinearity parameter was demonstrated.     

Source detection in mechanoacoustic systems by the wave front inversion and time reversal methods

A combined experimental and theoretical method is proposed for finding the vibration sources in mechanoacoustic systems. The method is similar to the wave front inversion and time reversal focusing methods used in optics and acoustics. The method performs coherent measurements of the vibration field at a set of points and employs the reciprocity principle in its theoretical part. To enhance the stability of the method, modifications are proposed that perform nonlinear processing of vibration fields calculated by the finite element method. Possibilities of using the method in self-testing vibrating systems are discussed.     

On the free‐edge effect in piezoelectric laminated plates

The present paper considers the effect of electromechanical coupling on the interlaminar stresses and the electric field strengths at free edges of laminated plates with piezoelectric material properties. The results of coupled and uncoupled piezoelectric analyses performed by use of the finite element method are compared. Exemplarily, a symmetric cross‐ply and a symmetric angle‐ply laminate are investigated under uniaxial tension and without any electrical loading. It is shown that the interlaminar stresses at the free edge are significantly higher in the coupled case for the symmetric cross‐ply laminate, whereas the coupling effect for the symmetric angle‐ply laminate is of minor significance. In addition, the occurrence of electric field strengths with singular character is revealed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Numerical simulation of acoustic emission using acoustic contact elements

A new method is described for nonconformal finite-element simulation of the region of interaction between an acoustic fluid and deformed solid bodies. The method is based on the use of special contact finite elements simulating the interpolation coupling between the acoustic pressure in the fluid and displacements of a two-phase surface. The test results of the method demonstrate a significant acceleration of grid convergence of computations. The numerical method is verified by the problem of predicting noise emission by a thin-wall inhomogeneous shell.     

Analysis of free-edge effects by boundary finite element method

The scaled boundary finite element method is a novel semi-analytical analysis technique that combines the advantages of the finite element method and the boundary element method. Only a part of the boundary of the considered domain has to be discretized but nevertheless the method is solely finite element based. The governing equations are solved in the so-called scaling direction analytically, whereas a finite element approximation of the solution is performed in the circumferential directions, which form the boundary of the considered domain. Thus, the numerical effort can be reduced considerably when handling stress concentration problems such as e.g. the free-edge effect in laminated plates. In order to analyze the free-edge effect in a semi-infinite half plane, some kinematic coupling equations have to be introduced, that not only couple the degrees of freedom on the boundary, but also within the non-discretized domain. The implementation of kinematic coupling equations within the method is presented. Finally, the efficiency of the new approach is shown in some benchmark examples. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Review on the production process and uses of controlled rheology polypropylene—Gamma radiation versus electron beam processing

Controlled rheology polypropylene grades are established commodities in the polymer processing market. However, new types, mainly the so-called high melt strength polypropylene (HMSPP) grades, are being introduced in the last two decades and radiation processing has played an important role. The melt strength properties of a polymer increases with molecular weight and with long-chain branching due to the increase in the entanglement level. As polypropylene (PP) is a linear polymer, the way to improve its elongational viscosity is by the production of a bi-modal polymer. Basell's patents claim the production of long-chain branching on PP by irradiating with electrons under oxygen free atmosphere, followed by two heating steps to allow radical recombination and annihilation reaction. Some other companies have issued patents using electron beam processing, but so far there is no actual production other than the Basell one. As a result of a research joint effort, IPEN, BRASKEM (the biggest Brazilian polymer producer) and EMBRARAD (the major Brazilian radiation processing center) developed a new process to produce HMSPP based on gamma processing. This paper will address some characteristics of each technology and the main industrial opportunities.     

Seismoacoustic survey of artificial inhomogeneities in the ground

The results of processing the field test data obtained for the seismoacoustic system designed at the Institute of Applied Physics of the Russian Academy of Sciences for the visualization of underground engineering structures are presented. The described experiment is the first demonstration of the use of a high-power, high-stability transmitting-receiving system for producing a coherent insonification with a frequency of 195 Hz. The receiving element of the system is a synthetic aperture array. With the use of focusing as a method of the final signal processing, an image of a tunnel lying at a depth of 30 m is obtained in three spatial cross-sections, which demonstrates the possibility of a three-dimensional, coherent, high-frequency seismic survey of engineering structures.     

Focusing of a sound beam in an underwater waveguide using a vertical antenna

We propose a method for calculating the amplitude-phase distributions of signals on the elements of an emitting antenna for generating narrow wave beams and field focusing at given points of the waveguide. The efficiency of the method is confirmed by the data of a field experiment conducted in Lake Ladoga.     

Verification of the Numerical Model in the Problem of Studying Directional Characteristics of Sound Radiation from Inhomogeneous Shells

Results of verifying the levels and directional characteristics of sound radiation are presented for a finite-element numerical model of a submerged inhomogeneous shell. The error in numerical modeling of directional characteristics is determined for sound radiation from shell parts with one-layer (shell–liquid) and multilayer (shell–liquid–shell–liquid) structures.