Investigating the impact of Cloisite® 15A nanoclays on the diffusivity of Irganox 1035 antioxidant in high-density polyethylene nanocomposite

Knowing the diffusion coefficients of antioxidants in packaging materials is essential to assess their effectiveness in protecting materials against oxidation, but also to prevent their eventual migration to food. In this work, the diffusion of a commercial phenolic antioxidant (Irganox 1035) was measured experimentally in pristine high-density polyethylene (HDPE) and in HDPE nanocomposite filled with 3 wt% of nanoclays (Cloisite® 15A). Diffusion experiments were performed using the Roe's method between 60 and 100°C. The local concentration of Irganox1035 in each film was measured by UV–Vis spectroscopy from the UV absorbance at 282 nm. The adjustment of the experimental data by Fick's second law allowed us to deduce the values of the diffusion coefficient of Irganox1035 at each temperature and to show that the temperature dependence of this coefficient obeys an Arrhenius' law. It is shown that the incorporation of 3 wt% of Cloisite®15A into HDPE significantly hinders the diffusion of Irganox 1035 and increases its activation energy. Several mechanistic assumptions could explain this result, first the increase in the tortuosity of diffusion paths, but also the possible establishment of strong intermolecular interactions between the antioxidant and some chemical groups on the nanofiller surface, or even the formation of an interphase with reduced molecular mobility around the nanofillers.     

Solving Fixed Final Time Fractional Optimal Control Problems Using the Parametric Optimization Method

In this paper, the parametric optimization method is used to find optimal control laws for fractional systems. The proposed approach is based on the use for the fractional variational iteration method to convert the original optimal control problem into a nonlinear optimization one. The control variable is parameterized by unknown parameters to be determined, then its expression is substituted into the system state‐space model. The resulting fractional ordinary differential equations are solved by the fractional variational iteration method, which provides an approximate analytical expression of the closed‐form solution of the state equations. This solution is a function of time and the unknown parameters of the control law. By substituting this solution into the performance index, the original fractional optimal control problem reduces to a nonlinear optimization problem where the unknown parameters, introduced in the parameterization procedure, are the optimization variables. To solve the nonlinear optimization problem and find the optimal values of the control parameters, the Alienor global optimization method is used to achieve the global optimal values of the control law parameters. The proposed approach is illustrated by two application examples taken from the literature.     

Characterization of an Am-Be PGNAA set-up developed for in situ liquid analysis: Application to domestic waste water and industrial liquid effluents analysis

A prompt gamma neutron activation analysis (PGNAA) set-up with an Am-Be source developed for in situ analysis of liquid samples is described. The linearity of its response was tested for chlorine and cadmium dissolved in water. Prompt gamma efficiency of the system has been determined experimentally using prompt gamma of chlorine dissolved in water and detection limits for different elements have been derived for domestic waste water. A methodology to analyze any kind of liquid is then proposed. This methodology consists mainly on using standards with water as bulk or in the case of absolute method, to use gamma efficiency determined with prompt gammas emitted by chlorine dissolved in water. To take into account the thermal neutron flux variations inside the samples, flux monitoring was carried out using a He-3 neutron detector placed at the external sample container surface. Finally, to correct for the differences in gamma attenuation, average gamma attenuations factors were calculated using MCNP5 code. This method was then checked successfully by determining cadmium in industrial phosphoric acid and our result was in good agreement with that obtained with inductively coupled plasma (ICP) method.     

Thermal Stability of Gamma Irradiated Low Density Polyethylene Films Containing Hindered Amine Stabilizers

Summary: The thermal stability of gamma irradiated low density polyethylene (LDPE) films in presence of various structures of hindered amine stabilizers (HAS) was investigated by the oxygen uptake method under constant temperature of 180 °C and normal pressure conditions. The thermo‐oxidation was run using air environment. The sigmoidal dependency of oxygen uptake allows the calculation of the main kinetic parameters: oxidation induction time and oxidation rate on the propagation step. The various steps involved in the thermal degradation process were detected by the derivative procedure applied to the dependencies of oxygen uptake on time. It was found that the kinetic parameters of the thermal degradation process, determined by oxygen uptake, revealed the antioxidant role of HAS in γ‐irradiated LDPE films by providing better stability, when compared with the unstabilized samples. Moreover, the results indicated that the dependencies of oxygen uptake on thermal degradation time involved two degradation stages: the former occurring in the ungrafted moiety and the latter taking place after the antioxidant depletion is achieved. The stabilization efficiency of these oxidation inhibitors provides satisfactory thermal resistance to LDPE films, especially those based on an alkoxyamine structure.

Dependencies of oxygen uptake on time at the thermal degradation of LDPE irradiated at 812 kGy. (‐□‐) free of additive; (‐○‐) Tinuvin 123; (‐?‐) Sanduvor PR 31; (‐?‐) Uvasil 299.     

Investigating the diffusional behaviour of Irganox®1076 antioxidant in HDPE/Cloisite®15A nanocomposite‐based food contact packaging films: Effect of nanoclay loading

In this research work, the prediction of the diffusion coefficient (D_p) of Irganox ® 1076 (Ir‐76) antioxidant in HDPE‐based food contact packaging films was carried out. The diffusion of this additive was studied both, in neat HDPE film and in HDPE nanocomposites films made of HDPE matrix filled with 1, 3, and 5 wt% of a commercially available organoclay (Cloisite ® 15A). The diffusion experiments were carried out by using the Roe's method on films consisting of a stack of several polymer films having a total nominal thickness of 120 ± 01 μm. Diffusion coefficients were determined in the temperature range 80°C to 100°C according to the second Fick's law by measuring the evolution of the Ir‐76 concentration in the films by means of Fourier transform infrared (FTIR) spectroscopy analysis. The results indicated that the diffusion coefficient of Ir‐76 in HDPE films decreased with the addition of the organoclay, and a maximum reduction of 78% (at 23°C) in the diffusion rate of the Ir‐76 was observed at an optimum filler content of 3 wt%, thus making these films attractive for the plastic packaging industry.     

Kinetic Study of Hindered Amine Light Stabilizer Photografting in Poly(propylene) Films under Natural Weathering and Accelerated UV Conditions: Effect of Additive Concentration

Full Paper: The objective of this work is aimed at determining the kinetics of HALS photografting in PP films as a function of the additive concentration under both natural weathering and accelerated UV conditions. The stabilizer studied had a single structure that combined HALS and a UV absorbing unit detectable at 308 nm in the UV spectrum of PP, capable of inducing a photoreaction with the polymer matrix. The kinetics of HALS photografting on PP films at various additive concentrations was determined by direct spectroscopic measurements on film samples through the absorption band of the stabilizer positioned at 308 nm in the UV spectra, which was attributed to the highly conjugated methylenic double bond. The content of free HALS was determined as a function of exposure time by UV spectroscopy for all the additive concentration ratios used. It is shown that the kinetics of HALS photografting increase with a decrease in the additive concentration ratio. The whole grafting process under conditions of natural weathering occurred in the PP film after almost 350 h of exposure, while approximately 20 h were necessary under accelerated UV conditions. Moreover, these kinetics are well described by a third order polynomial model, validated by a maximum value of the coefficient of correlation close to unity. This was also confirmed by a comparison of the time values measured at 50% of the total grafting calculated from the model with those observed experimentally. This finding was consistent with the data obtained on the free HALS content determined by UV spectroscopy.

The percentage of HALS photografting in PP films as a function of time under natural weathering, determined by UV spectroscopy.     

Speaker-independent ASR for Modern Standard Arabic: effect of regional accents

This paper deals with speaker-independent Automatic Speech Recognition (ASR) system for continuous speech. This ASR system has been developed for Modern Standard Arabic (MSA) using recordings of six regions taken from ALGerian Arabic Speech Database (ALGASD), and has been designed by using Hidden Markov Models. The main purpose of this study is to investigate the effect of regional accent on speech recognition rates. First, the experiment assessed the general performance of the model for the data speech of six regions, details of the recognition results are performed to observe the deterioration of the performance of the ASR according to the regional variation included in the speech material. The results have shown that the ASR performance is clearly impacted by the regional accents of the speakers.     

Finite element analysis of linear plates buckling under in-plane patch loading

The elastic buckling load is physically important in design because it is actually the critical step in the changing plate configuration that will eventually lead to complete failure. The present work investigates the problem of linear buckling of simply supported thin plates subjected to patch compression. In order to satisfy the boundary conditions in a rigorous way, the authors chose the finite element method using the exact stress distribution throughout the plate.In the present paper, the stability problem treated using the total energy is briefly outlined. The plate modelling is made by means of an eight noded rectangular element and a reduction of variable strategy is applied to estimate the number of degrees of freedom leading to little or no loss in seeking solution accuracy.The buckling coefficient is determined for different load cases applied to a range of plate with various edge ratios. The achieved results are summarised through different graphs representing variation of the buckling coefficient against the plate ratio for each load case treated. A comparison with previous works is made. Finally, it is shown that the resolution of the plate buckling problem using true stress distribution with the finite element method leads to a good agreement with results previously obtained by means of analytical methods using an exact stress distribution.