Polymers2015, 7(5), 963-984; doi:10.3390/polym7050963 (registering DOI) - published 22 May 2015 Show/Hide Abstract
Abstract: In the current research work, an attempt is made to increase the seismic capacity of unreinforced masonry (URM) structures by proposing a new composite material which can improve shear strength and deformation capacity of URM wall systems. Fiber Reinforced Polymer (FRP) having high tensile and shear stiffness can significantly increase in-plane and out-of-plane strength of masonry walls, but, inherently, FRP strengthened wall systems exhibit brittle failure under extreme seismic loading. Polypropylene (PP-band) is a low cost material with sufficient ductility and deformation capacity. Keeping in view the behavior of FRP and PP-band, a composite of FRP and PP-band is proposed for retrofitting of URM walls. Mechanical behavior of the proposed composite material is assessed by carrying out an in-plane diagonal compression test and an out-of-plane bending test on twenty-five 1/4-scaled masonry wall panels. Experimental plan for each panel, URM, PP-band retrofitted, FRP retrofitted and FRP + PP-band retrofitted masonry, is diagonal compression test and three-point bending test. Experimental results have determined that FRP + PP-band composite increased, not only the initial peak strength, but also the ductility, deformation capacity and residual strength of URM wall systems.
Abstract: This study was dedicated to the blown film extrusion of poly(lactic acid), which mainly presents poor shear and elongation viscosities, and its blends. In order to enhance its melt strength, two main routes were selected (i) a structural modification through chain extension and branching mechanisms by adding a reactive multifunctional epoxide (named Joncryl) and (ii) blending with poly(butylene adipate-co-terephtalate), named PBAT in presence (or not) of Joncryl. The effects of the reactive agent on the shear and elongation rheology, morphological, and interfacial properties of the blends were systematically investigated. A decrease of the interfacial tension has been also demonstrated according to the deformed drop retraction method (DDRM). Hence, the role of Joncryl as a compatibilizer was highlighted. Consequently, finer morphology of the dispersed phase was obtained. Furthermore, the impact of the two modification routes on the blown film extrusion ability of PLA has been studied. Based on the improved shear and elongational rheological properties, a great enlargement of the blowing processing window of PLA modified with Joncryl was demonstrated. Indeed, with the addition of Joncryl into PLA–PBAT blends, a reduction of the instability defects has been detected. Finally, the induced crystalline structure and the thermo-mechanical properties of blown films were shown to be improved.
Abstract: Star polymers are one example of three-dimensional macromolecules containing several arms with similar molecular weight connected to a central core. Due to their compact structure and their enhanced segment density in comparison to linear polymers of the same molecular weight, they have attracted significant attention during recent years. The preparation of block-arm star copolymers with a permanently hydrophilic block and an “environmentally” sensitive block, which can change its nature from hydrophilic to hydrophobic, leads to nanometer-sized responsive materials with unique properties. These polymers are able to undergo a conformational change or phase transition as a reply to an external stimulus resulting in the formation of core–shell nanoparticles, which further tend to aggregate. Star-shaped copolymers with different cores were synthesized via atom transfer radical polymerization (ATRP). The core-first method chosen as synthetic strategy allows good control over the polymer architecture. First of all the multifunctional initiators were prepared by esterification reaction of the hydroxyl groups with 2-chloropropionyl chloride. Using β-cyclodextrin as core molecules, which possess a well-defined number of functional groups up to 21, allows defining the number of arms per star polymer. In order to prepare stimuli-responsive multi-arm copolymers, containing a stimuli-responsive (poly(N-isopropylacrylamide) (PNIPAAm)) and a non-responsive block (poly(N,N-dimethylacrylamide) (PDMAAm)), consecutive ATRP was carried out. The polymers were characterized intensively using NMR spectroscopy and size exclusion chromatography (SEC), whereas the temperature-depending aggregation behavior in aqueous solution was determined via turbidimetry and differential scanning calorimetry (DSC).
Abstract: We tuned the lower critical solution temperature (LCST) of amphiphilic poly(N-isopropylacrylamide) (PNIPAAm) via copolymerization with a hydrophilic comonomer of N-hydroxymethyl acrylamide (NHMAAm). A series of copolymers P(NIPAAm-co-NHMAAm) were synthesized by atom transfer radical polymerization (ATRP) using CuBr/(N,N,N',N',N''-Pentamethyldiethylenetriamine) (PMDETA) as a catalyst system and 2-bromo ethyl isobutyrate (EBiB) as an initiator. The copolymers were well characterized by Fourier transform infrared spectroscopy (FT-IR), 1H Nuclear magnetic resonance (NMR), and Thermogravimetric analysis (TGA). The copolymers followed a simple rule in their thermosensitive behaviors and have a linear increase in the LCST as a function of NHMAAm mol%. The thermosensitive properties of the copolymer films were investigated and demonstrated hydrophilic-hydrophobic transitions. Finally, the copolymer was grafted onto cotton fabrics using citric acid (CA) as a crosslinking agent and sodium hypophosphite (SHP) as a catalyst following a two dipping, two padding process. The large number of hydroxyl groups in the copolymer makes grafting convenient and firm. The grafted cotton fabrics show obvious thermosensitive behaviors. The results demonstrate that the cotton fabrics become more hydrophobic when the temperature is higher than the LCST. This study presents a valuable route towards temperature-responsive smart textiles and their potential applications.
Abstract: A new functionalized fullerene-glycidyl azide polymer (C60-GAP) was synthesized for the first time using a modified Bingel reaction of fullerene (C60) and bromomalonic acid glycidyl azide polymer ester (BM-GAP). The product was characterized by Fourier transform infrared (FTIR), ultraviolet-visible (UV-Vis), and nuclear magnetic resonance spectroscopy (NMR) analyses. Results confirmed the successful preparation of C60-GAP. Moreover, the thermal decomposition of C60-GAP was analyzed by differential scanning calorimetry (DSC), thermogravimetric analysis coupled with infrared spectroscopy (TGA-IR), and in situ FTIR. C60-GAP decomposition showed a three-step thermal process. The first step was due to the reaction of the azide group and fullerene at approximately 150 °C. The second step was ascribed to the remainder decomposition of the GAP main chain and N-heterocyclic at approximately 240 °C. The final step was attributed to the burning decomposition of amorphous carbon and carbon cage at around 600 °C.
Abstract: The fire performance of protected concrete-filled fiber reinforced polymer (FRP) tube (CFFT) and conventional reinforced concrete (RC) bridge columns is studied through two phases of experimental research comprised of fire exposure and residual axial capacity tests. Two one-fifth scale CFFT columns and two one-fifth scale conventional RC columns having similar axial and flexural capacities were subjected to two durations of extreme temperature exposure. The CFFT columns were protected by the Tyfo® CFP fire protection system during the experiments. Subsequently, the post-fire robustness of the columns was quantified by measuring the residual axial capacity characteristics of each column. The protected CFFT columns exhibited superior axial strength and stiffness retention compared to the RC columns after fire exposure.