The effect of maleated polylactic acid (PLA) as an interfacial modifier in PLA‐talc composites

Polylactic acid (PLA)‐talc composites were reactively compatibilized using maleic anhydride‐functionalized PLA (MAPLA) as an interfacial additive. The effect of MAPLA was investigated based on evaluation of composite properties and examination of the microstructure using scanning electron microscopy. The incorporation of MAPLA contributed to an increase in the crystallinity of PLA in the composites, and when added in an optimal concentration, showed improved tensile strength. Thermo–mechanical measurements indicated the reinforcement effect of the talc and the coupling effect of the MAPLA inclusion. Microscopic studies revealed the composite microstructures along with the corresponding modes of failure which were in accordance with the mechanical behavior. Overall, this investigation provided experimental evidence of enhanced adhesion at the interface, which is believed to be due to the MAPLA addition. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A Spectroscopic Method for Hydroxyl Value Determination of Polyols

A relatively simple method is described for routine determination of hydroxyl values for a wide range of hydroxyl containing compounds including soybean oil polyols, polyols derived from soy meal, polyether polyols and ethylene glycol as well as their blends. This method is based on reacting the hydroxyl compound with hexamethyldisilazane (HMDS) and determining the FTIR peak area of the silylated product at 1,251 cm^?1. The method is simple, accurate and reproducible. It is not limited to a specific family of polyol compounds. It does not require any special equipment, hazardous chemicals and can be carried out by non‐technical staff as a rapid and convenient method for quantitative determination of hydroxyl values. An excellent linear correlation was obtained between this spectroscopic method and conventional titration methods for different polyols over a wide range of hydroxyl values. Furthermore, unlike the titration methods the current method is not affected by the presence of acid, base or small amounts of water in the test sample.     

Using electrochemical impedance to determine airflow rates

This paper proposes the use of electrochemical impedance spectroscopy (EIS) to estimate the cathode flow rate in a fuel cell system. Through experimental testing of an eight-cell, hydrogen-fueled polymer electrolyte stack, it shows that the ac impedance measurements are highly sensitive to the airflow rates at varying current densities. The ac impedance magnitude at 0.1 Hz allows the distinction of airflow rates (stoichiometry of 1.5–3.0) at current densities as low as 0.1 A/cm². Using experimental data and regression analysis, a simple algebraic equation that estimates the airflow rate using impedance measurements at a frequency of 0.1 Hz is developed. The derivation of this equation is based on the operating cell voltage equation that accounts for all the irreversibilities.     

Influence of gamma irradiation on the formation of methanol induced micro-cracks in polycarbonate

The effects of -irradiation on the methanol diffusion behaviour in polycarbonate have been investigated by UV-visible, Fourier Transform Infra-red (FTIR) Spectroscopy, Positron Annihilation Lifetime Spectroscopy (PALS), Differential Scanning Calorimetry (DSC), Sorption, and Optical Microscopy. Positron results show that the free volume size and its content decreases after -irradiation which is due to cross-linking of chains. The cross-linking process is further confirmed by DSC measurements, which indicate an increase in glass transition temperature (T _g) after -irradiation. Sorption results reveal that methanol diffuses faster in virgin polycarbonate as compared to cross-linked polycarbonate (after gamma irradiation) in agreement with the results of supplementary techniques. Interestingly, the optical microscopic examination of the sample surfaces provides clear evidence of decreased micro-crack formation in -irradiated polycarbonate as compared to the virgin sample. This decrease in crack formation can be related to the decrease in the rate of methanol diffusion.     

Site-specific gene delivery in vivo through engineered Sendai viral envelopes

Inspite of several stimulating developments in gene therapy, the formulation of a targeted gene delivery "vector" is still far from ideal. We have demonstrated the potential of reconstituted Sendai viral envelopes containing only the fusion glycoprotein (F-virosomes) in targeted delivery of reporter genes to liver cells of BALB/c mouse in vivo. The membrane fusion-mediated high efficiency of gene transfer to liver cells was ascertained following a critical evaluation of the level of the DNA, mRNA, and relevant proteins. Furthermore, the involvement of viral glycoprotein both as a unique natural ligand and as a membrane fusogen could lead to preferential transfection of parenchymal cell types of liver. The integration of transgenes in the mouse chromosomal DNA and its stable expression up to 4 mo after single i.v. administration of this gene carrier has bolstered its efficiency and novelty. Moreover, the F-virosomes did not elicit significant humoral immune response against the fusion protein in the injected animal. The findings reported here open up the possibility for considering "F-virosomes" as a promising "vehicle" for site-specific DNA delivery in gene therapy.     

Multi-material topology optimization with strength constraints

A heuristic approach to handle strength constraints based on material failure criteria in multi-material topology optimization is presented. This is particularly advantageous if different materials have different failure criteria. The change in the material failure function in an element due to a contemplated material change is estimated without the need for expensive matrix factorizations. This change is used along with the changes to the objective and deflection-based constraint functions, computed using pseudo-sensitivities, to determine a single aggregated ranking parameter for the element. Elements are ranked on the basis of their ranking parameters and this rank is used to modify the material ID-s of a few top-ranked elements during an optimization iteration. The working of the algorithm is demonstrated on a few example problems showing its effectiveness and utility in deriving optimal topologies with multiple materials in the presence of stress and strain-based failure criteria, in addition to the conventional stiffness-based constraints.     

A pseudo-sensitivity based discrete-variable approach to structural topology optimization with multiple materials

An algorithm has been developed which uses material as a discrete variable in multi-material topology optimization and thus provides an alternative to traditional methods using material interpolation and level-set approaches. The algorithm computes ‘pseudo-sensitivities’ of the objective and constraint functions to discrete material changes. These are used to rank elements, based on which a fraction of elements are selected for material ID modification during the optimization iteration. The algorithm is of general applicability and avoids frequent matrix factorizations so that it is applicable to large structural problems. In addition to the conventionally used evolutionary and morphogenesis approaches for iteration, a new iteration scheme of ‘resubstitution’ which combines the two approaches is presented. The application and functioning of the algorithm is demonstrated through case studies and comparisons with a few benchmark problems, showing its capability in providing mass-optimal topologies under stiffness constraints for various structural problems where multiple materials are considered.     

Influence of strain on the thermal behaviour of poly(chlorotrifluoroethylene)

The effects of uniaxial drawing on the free volume of poly(chlorotrifluoroethylene) have been investigated using the positron annihilation lifetime technique. Annealing measurements were made both in unstrained and maximum strained conditions of the polymer to understand the influence of residual stress on the thermal behaviour. The results indicate uncoiling of the molecular chains upon stretching accompanied by orientation of the polymeric chains. The results further indicate an increase of the glass transition temperature of the drawn film and a negative thermal expansion beyond the glass transition temperature, supported by an increase in activation energy for the strained polymer. © 1999 Society of Chemical Industry     

Free‐volume microprobe study of iodine diffusion in polymers

The effect of iodine sorption on the free‐volume of three polymers, namely, acrylonitrile–butadiene–styrene, poly(ethylene terephthalate) and polycarbonate have been investigated by the positron annihilation lifetime technique. Diffusion coefficients have been evaluated from the sorption curves using Crank's solution for Fick's second law of diffusion. The positron results are explained in terms of iodine filling the free‐volume holes, swelling and conformational changes. It has also been found that the diffusion process in acrylonitrile–butadiene–styrene and poly(ethylene terephthalate) deviates from Fick's law of diffusion whereas in polycarbonate, the diffusion process obeys Fick's law. Further, for polymers in which diffusion deviates from Fick's law, the sorption process has been separated into diffusion‐controlled (Fickian) and relaxation‐controlled (non‐Fickian) parts using the dual‐mode sorption model. Interestingly, the present results show that the polymers which deviate from Fickian diffusion also deviate from Fujita's free‐volume theory of diffusion and vice versa. The positron results also indicate that sorbed iodine in the polymer acts as an inhibitor of ortho‐positronium. © 2001 Society of Chemical Industry