Water absorption,biodegradation, thermal and morphological properties of Spartium junceum fiber-reinforced polyvinylchloride composites: effects of fibers content and surface modification

In this study, we want to investigate the effects of fibers content and surface modification of Spartium junceum (SJ) fibers on the water absorption characteristics, thermal degradation, and morphological properties of SJ-reinforced poly (vinyl chloride) (PVC) composites. In addition, the change in mechanical proprieties of the composites after biodegradation test was evaluated by tensile strength. In order to improve the interfacial interactions between the PVC matrix and the SJ fibers, SJ fibers were modified by sodium hydroxide (NaOH), vinyltrimethoxysilane (VTMS) and treated with sodium hydroxide solution followed by VTMS (NaOH+VTMS). The results show that the water uptake of PVC/SJ fibers composites increases with the increase in the fibers’ content. However, the surface modification reduces water uptake. Moreover, the results indicate that the kinetics of water absorption of the PVC/SJ fibers composites approaches the Fickian diffusion mechanism. Also, the results indicate that the tensile strength of the composites is affected by the biodegradation test and chemical treatments. The atomic force microscope pictures of the composites illustrate the reduction of roughness via surface treatments of fibers.     

A New Active Micro-Mixing Strategy

An active micro-mixing strategy through forcing the flow by synthetic wall jets is proposed. It is based on the interaction of induced streamwise vortices in a specific way. There is a spanwise shift between two quasi-streamwise vortices in such a way that one of them compresses the wall normal vorticity layer created by the other, leading to the generation of new wall normal vortical structures. The latter are subsequently tilted by the shear to give birth to new small-scale longitudinal active structures that are efficient in mixing. The feasibility of this strategy is shown through direct numerical simulations of high spatial and temporal resolution.     

Characterization of a stable intermediate trapped during reversible refolding of Bacillus subtilis alpha-amylase

Bacillus subtilis exocellular alpha-amylase is reversibly refolded after denaturation by guanidine hydrochloride at pH 7 and 37 degrees C. The unfolding-folding transition monitored by intrinsic fluorescence changes and resistance to proteolysis was resolved into a two-state transition. The first step (t1/2 < 1 s) led from D, the totally unfolded state, to C, a stable partially structured state of the protein. This folding intermediate was devoid of any enzyme activity and partially resistant to protease degradation. Calcium was required for the transition from C to N, the native state. This metal did not remain associated with the native form and could be replaced by barium or strontium, but not by magnesium. We discuss the hypothesis that C, the folding intermediate whose further transformation is under kinetic control, is the competent state involved in the secretion process of alpha-amylase.     

Effects of surface functionalized partially reduced graphene oxide and different compatibilizers on the properties and structure of PP/EPR nanocomposites

In this study polypropylene/ethylene-propylene rubber (PP/EPR) and different amounts of partially reduced graphene oxide (prGO) and its derivatives were investigated. The nanocomposites were also compatibilized with EPR containing diethyl maleate (DEM), glycidyl methacrylate (GMA) and maleic anhydride (MAH) functionality as a means of controlling their ultimate mechanical behaviour and their structural morphology. Mechanical tests show that the addition of pristine prGO to PP/EPR blend promotes tensile strength and Young’s modulus, while reducing elongation at break and impact strength. A significant improvement of these properties was achieved by the presence of functionalized prGO and EPR-g-DEM. TGA analysis showed that the nanocomposites exhibit a higher thermal stability than that of the matrix alone. XRD analysis revealed that the polymer chains have been successfully intercalated into prGO layers. SEM has been used to verify the dispersion of the prGO particles in the matrix and to reveal the developed morphology of PP/EPR, in the presence of compatibilizers and functionalized prGO.     

Viscoelastic,thermo-mechanical and environmental properties of composites based on polypropylene/poly(lactic acid) blend and copper modified nanoclay

Poly(lactic acid) (PLA)/polypropylene (PP) blends composites were prepared by incorporating 3 wt.% of copper modified montmorillonite (MMT-Cu²⁺), obtained using cation exchange in a CuSO₄ solution, and 10 wt.% of polypropylene-graft-maleic anhydride (PP-g-MA) as a compatibilizer then varying the PLA content until 50 wt.%. These materials were subjected to several investigations such as X-rays diffraction, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and tensile and environmental tests. The DMTA analysis showed that the glassy PLA high stiffness and the PP crystalline phase compensate the decrease in the storage modulus occurring during the PP and PLA glass transitions, respectively. The variations of tan δ revealed no changes on the PP and PLA phases glass transitions temperatures which indicate the immiscibility of the two polymers, as supported by DSC analysis. Blends composites SEM micrographs stated the immiscibility of the system resulting in the poor adhesion of the PLA droplets to the PP matrix. Also, the blends composites exhibited intermediate tensile properties between those of PP and PLA. The incorporation of MMT-Cu²⁺ to the (50/50) PP/PLA blend accentuated its aptitude to water absorption and ensured an efficient antimicrobial activity over a satisfactorily long period of around six months.     

Effect of graphene oxide on the properties of compatibilized polypropylene/ethylene-propylene-rubber blend

In this work, the effect of graphene oxide (GO) and its derivatives on the mechanical, thermal and morphological properties of nanocomposites based on polypropylene/ethylene-propylene rubber (PP/EPR) were investigated. In order to achieve a better dispersion of the nanofiller and to enhance its interaction with the polymer matrix, amine and alcohol grafted polypropylene were used as compatibilizers. These compatibilizers were synthesized by the reaction of polypropylene-grafted anhydride maleic (PP-g-MAH) with 1,12-dodecanediamine and 1,12-dodecanediol, respectively in the presence of dicumyl peroxide (DCP) by melt mixing. The nanocomposites were prepared via melt blending masterbatch process using Brabender mixer. The addition of functionalized GO and compatibilizers improved the tensile strength and Young’s modulus of PP/EPR nanocomposite. While the elongation and Izod impact strength were adversely affected. Furthermore, the TGA analysis showed that the incorporation of GO and compatibilizers improve significantly the thermal stability. SEM micrographs of the fractured surfaces of the nanocomposites revealed a good dispersion of functionalized GO in the polymer matrix.     

Tree distributions approximation model for robust discrete speech recognition

This paper proposes a new discrete speech recognition method which investigates the capability of graphical models based on tree distributions that are widely used in many optimization areas. A novel spanning tree structure that utilizes the temporal nature of speech signal is proposed. The proposed tree structure significantly reduces complexity in so far that can reflect simply a few essential relationships rather than all possible structures of trees. The application of this model is illustrated with different isolated word databases. Experimentally it has been shown that, the proposed approaches compared to the conventional discrete hidden Markov model (DHMM) yield reduced error rates of 2.54?%–12?% and improve recognition speed minimum 3-fold. In addition, an impressive gain in learning time is observed. The overall recognition accuracy was 93.09?%–95.34?%, thereby confirming the effectiveness of the proposed methods.     

A new approach to the determination of optical constants and thickness of thin dielectric transparent films

A new calculating method to deduce optical constants n, k and thickness d from the fringe pattern of the transmission spectrum is proposed. In this method the optical parameters are determined using only one curve of the transmission spectra even for thin films where nd < /4. The method is demonstrated by experimental data obtained using evaporated vacuum deposited TiO₂ thin film on a glass substrate. The experimental values are in very good agreement with those calculated using the above described technique.