Microfoams based on castor oil polyurethanes and vegetable fibers

This work was focused on the production and characterization of microcellular polyurethane (PU) composites reinforced with pine wood‐fibers or with hemp, which can be applied to the manufacture of car interior panels, or acoustic insulation panels for the construction industry. The polymers selected for the study were crosslinked PUs, synthesized from a castor oil‐based polyol, with the formulations adjusted to obtain different foaming levels. Microfoamed composites with preferential orientation were prepared from long hemp fibers. Also, samples with random arrangement of short hemp and wood fibers were obtained. The morphology of the composites was analyzed by scanning electron microscopy. The mechanical performance of the reinforced foams was studied through three point bending and dynamic mechanical tests. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Shape memory segmented polyurethanes: dependence of behavior on nanocellulose addition and testing conditions

The response of synthesized shape memory segmented polyurethanes (PUs) was affected by the addition of cellulose nanocrystals, as well as by the various conditions selected to carry out thermomechanical cyclic tests. The PUs were synthesized from an α‐hydro‐ω‐hydroxy‐poly(ethylene oxide), tolylene‐2,4‐diisocyanate and 1,4‐butanediol as chain extender. Nanocomposites were prepared by mixing a suspension of cellulose nanocrystals in N,N‐dimethylformamide with the thermoplastic PU dissolved in the same organic solvent. The thermal properties of the neat PU and resulting composites were examined using differential scanning calorimetry. It was found that cellulose addition increases the PU soft segment melting and crystallization temperatures and the degree of crystallinity of this phase. Shape memory behavior was studied using cyclic thermal tensile tests. Both neat PU and composites exhibit shape memory properties, with fixity and recovery values that depend on heating temperature, imposed deformation, deformation rate and nanofiller addition. Copyright © 2011 Society of Chemical Industry     

Rapeseed oil‐based polyurethane foams modified with glycerol and cellulose micro/nanocrystals

A rapeseed oil‐based polyol (ROPO) was synthesized using chemical modification of the rapeseed oil (RO) by epoxidation reaction followed by oxirane ring‐opening with diethylene glycol. The ROPO was used in the formulation of low‐density green polyurethane (PU) foams. The use of glycerol as hydroxyl component, water as a reactive blowing agent and micro/nanocellulose (MNC) as a reinforcement increases the content of natural components in the formulations with important effects on the final foam properties. The ROPO and their intermediate products are characterized by analytical techniques and FTIR spectroscopy, while the final PU foams are characterized by morphological and mechanical analysis. The results show that the addition of glycerol increases the modulus and yield stress. The incorporation of MNC in small amounts is enough to increase the modulus at low temperatures. Both modifiers cause an increase in water absorption and the fragility of the cell walls, reflected in the micrographs of the foams. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41602.     

Exposure to radiofrequency radiation induces oxidative stress in duckweed Lemna minor L

Widespread use of radiofrequency radiation emitting devices increased the exposure to electromagnetic fields (EMFs) from 300 MHz to 300 GHz. Various biological effects of exposure to these fields have been documented so far, but very little work has been carried out on plants. The aim of the present work was to investigate the physiological responses of the plant Lemna minor after exposure to radiofrequency EMFs, and in particular, to clarify the possible role of oxidative stress in the observed effects. Duckweed was exposed for 2 h to EMFs of 400 and 900 MHz at field strengths of 10, 23, 41 and 120 V m(-1). The effect of a longer exposure time (4 h) and modulation was also investigated. After exposure, parameters of oxidative stress, such as lipid peroxidation, H(2)O(2) content, activities and isoenzyme pattern of antioxidative enzymes as well as HSP70 expression were evaluated. At 400 MHz, lipid peroxidation and H(2)O(2) content were significantly enhanced in duckweed exposed to EMFs of 23 and 120 V m(-1) while other exposure treatments did not have an effect. Compared to the controls, the activities of antioxidative enzymes showed different behaviour: catalase (CAT) activity increased after most exposure treatments while pyrogallol (PPX) and ascorbate peroxidase (APX) activities were not changed. Exceptions were reduced PPX and APX activity after longer exposure at 23 V m(-1) and increased PPX activity after exposures at 10 and 120 V m(-1). By contrast, at 900 MHz almost all exposure treatments significantly increased level of lipid peroxidation and H(2)O(2) content but mostly decreased PPX activity and did not affect CAT activity. Exceptions were exposures to a modulated field and to the field of 120 V m(-1) which increased PPX and CAT activity. At this frequency APX activity was significantly decreased after exposure at 10 V m(-1) and longer exposure at 23 V m(-1) but it increased after a shorter exposure at 23 V m(-1). At both frequencies no differences in isoenzyme patterns of antioxidative enzymes or HSP70 level were found between control and exposed plants. Our results showed that non-thermal exposure to investigated radiofrequency fields induced oxidative stress in duckweed as well as unspecific stress responses, especially of antioxidative enzymes. However, the observed effects markedly depended on the field frequencies applied as well as on other exposure parameters (strength, modulation and exposure time). Enhanced lipid peroxidation and H(2)O(2) content accompanied by diminished antioxidative enzymes activity caused by exposure to investigated EMFs, especially at 900 MHz, indicate that oxidative stress could partly be due to changed activities of antioxidative enzymes.     

Reactivity ratios and copolymer composition evolution during styrene/dimethacrylate free‐radical crosslinking copolymerization

In this article, experimental and simulated results are presented for the evolution of the copolymer composition as unsaturations are consumed in the free‐radical cross‐linking copolymerization of Styrene(St) and BisphenolA glycerolate dimethacrylate (BDMA). Real time FTIR measurements were performed to monitor the depletion of each comonomer double bond during the isothermal curing reaction at 80°C. From the experimental data corresponding to different feed compositions, the initial reactivity ratios and their evolution with conversion were determined via a nonlinear least squares optimization of the integrated form of the copolymerization equation. The reactivity ratio of St increases continuously and exponentially with the overall reaction conversion, while that of BDMA decreases linearly. A modified terminal copolymerization model including the dependence of the reactivity ratios with the overall conversion was proposed. The application of this model provides a consistent fitting for the conversion of each comonomer during all reaction stages, even at high conversion values where large diffusion and topological restrictions for chain movements are present. Simulations show that the concentration of styrene units added to the copolymer increases with the overall reaction conversion, while that for the BDMA double bonds diminishes. Structures rich in homopolymerized styrene are predicted at later stages of the reaction.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Caseinate films modified with tung oil

Sodium caseinate/tung oil composite films were prepared through emulsification in order to reduce the water affinity of the protein-based film. Addition of lipid leads to milky films, resulting in a sharp increase in opacity. Uneven lipid distribution was evidenced by SEM in films prepared with 15% tung oil, which most likely arose from the limited dispersion capability of the lipids. Tung oil content also affects the film mechanical response, increasing tensile strength and elastic modulus but decreasing deformability. Contact angle measurements, besides water absorption tests, confirm lower hydrophilicity of the samples. However, tung oil incorporation into the caseinate matrix did not affect significantly the WVP at any of the three levels used, probably due to pore formation. The advantages of cross-linking composite films using heat were also addressed.     

Identification of extrinsic proteins in boneless cooked ham by SDS-PAGE: detection level in model systems

Protein extraction and separation in polyacrylamide slab gel electrophoresis with Laemmli system (SDS-PAGE) were used to establish the detection level of protein raw materials in mixtures with porcine meat in boneless cooked ham. Model systems of boneless cooked ham with soy protein isolates, caseinate, skim powdered milk, bovine plasma, porcine plasma and whey proteins were studied. The quantification level of this method was 0.5% for soy protein isolates, caseinate and bovine plasma and 1.0% for porcine plasma, milk powder and whey proteins in boneless cooked ham. The electrophoretic method proved to be useful to identify some proteinic raw materials in porcine meat products and verify compliance with Argentine legislation. It may be used as a control methodology.     

Dependence of the mechanical properties of woodflour–polymer composites on the moisture content

Woodflour of Eucaliptus saligna with two different chemical treatments (mercerization and esterification with maleic anhydride) was used as filler of an unsaturated polyester matrix. Woodflour was treated to increase the interfacial adhesion with the matrix, to improve the dispersion of the particles, and to decrease the water sorption properties of the final composite. The objective of this study was to determine the influence of the moisture content and the woodflour chemical modification on the physical and mechanical properties of the different composites. Results indicated that mechanical properties (compression and bending tests) were severely affected by moisture and chemical modifications. In wet conditions, the composites made from treated woodflour had the lowest flexural modulus and ultimate stress. It was found that this was a reversible effect, because the original values of the compression properties were recovered after drying. Temperature scans in dynamic mechanical tests showed that an irreversible change occurred during exposure to humid environments, probably due to the hydrolysis of the polyester matrix. Essentially, the same behavior was observed for matrix and composites; however, a wood-related transition overlapped the main transition in the case of wet composites. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2069–2076, 1998     

Cupric tannate: A low copper content antifouling pigment

Fouling organisms attached to man-made surfaces submerged in seawater constitute a major worldwide technical and economical problem. Protection against biofouling is essential for efficient service of boats and ships. Due to recent and imminent restrictions of the use of traditional toxic antifouling paints, there is a growing need for new alternative compounds that ensure a good performance without polluting the marine ecosystem.

The aim of this work is to develop a new antifouling formulation using compounds of natural origin, i.e. tannates, in combination with a minimum concentration of a known bioactive pigment, i.e. copper.

Laboratory assays have shown that cupric tannate has a narcotic effect on biofouling larvae. In the field, after 12 months of immersion in Mar del Plata harbor (Argentine), none of the tested painted panels showed macrofouling organisms. This result was obtained with a large decrease in copper content in the order of 40 times relative to conventional cuprous oxide based paints.

Because copper tannate is not lethal at low concentrations, this pigment has an excellent potential as an antifouling agent.     

Surfactant-aided dispersion of polystyrene-functionalized carbon nanotubes in a nanostructured poly(styrene-b-isoprene-b-styrene) block copolymer

The synergistic effect of using polystyrene-grafted multi-walled carbon nanotubes (PSgMWCNT) and a surfactant in the dispersion of MWCNT in a self-assembled poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer is reported. The functionalization of MWCNT with polystyrene achieved by the grafting-from approach is not enough to disperse them in the SIS block copolymer. However, a high dispersion of PSgMWCNT in SIS is achieved when dodecanethiol (DT) was added through composite preparation, without affecting the SIS capacity to self-assemble in ordered cylinders. Suspensions of PSgMWCNT without DT and not functionalized MWCNT with DT presented low stability forming aggregates in less than 10 min. On the contrary, the stability of PSgMWCNT suspension in the presence of DT was dramatically enhanced to more than two weeks. This synergistic effect is due to interactions between PSgMWCNT and DT molecules, as proved by UV-Vis spectroscopy.