Thermal and shape memory properties of cyanate/polybutadiene epoxy/polysebacic polyanhydride copolymer

A novel thermal‐induced shape memory polymer was synthesized by copolymerization of a new kind of epoxy resin‐polybutadiene epoxy (PBEP), bisphenol A‐type cyanate ester (BACE), and polysebacic polyanhydride (PSPA) with different mass ratios. Fourier transform infrared spectroscopy (FTIR), bending test, dynamic mechanical analysis (DMA), and shape memory property were investigated systematically. It was found that the PSPA significantly enhanced the bending strength and flexural modulus. The DMA results showed that the glass transition temperature reduced with increasing content of PSPA. Furthermore, the shape memory tests proved that the copolymer possessed excellent shape memory properties. The shape recovery time decreased with increasing content of PSPA and temperature. The shape memory rate increased as the PSPA content increased. The shape recovery ratio decreased with increasing cycle times. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42045.     

Dependency of the shape memory properties of a polyurethane upon thermomechanical cyclic conditions

The relationship between the shape memory properties and thermomechanical cyclic conditions was investigated with a type of shape memory polyurethane (SMPU). The thermal and dynamic mechanical properties of the polyurethane were examined by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). It was found that the SMPU exhibited good shape memory effects (SMEs) at deformation temperatures ranging from T_g to T_g + 25 °C. The strain recovery ratios increased with the increase of deformation speed and with the decrease in maximum strain. The recovery ratios also increased with increasing fixing speed. Therefore, in practical applications, in order to obtain better SMEs, the SMPU should be cooled to its frozen state as soon as possible after being deformed at a high temperature. The ‘fixity’ dramatically increased with the decrease in fixing temperature. To obtain optimal SMEs, the polymer has to be reheated up to the temperature at which the polymer deformed. In addition, the recovery ratios of the SMPU could increase slightly with the increase of recovery time. Copyright © 2004 Society of Chemical Industry     

Polymer Ion-Exchangers Modified with Zirconium Hydrophosphate for Removal of Cd2+ Ions from Diluted Solutions

Hybrid ion-exchangers have been synthesized by modification of strongly acidic cation-exchange resin with zirconium hydrophosphate. The samples were investigated with scanning and transmission electron microscopy and standard contact porosimetry. Single nanoparticles and their aggregates have been found in the polymer. The nanoparticles in transport pores increase the electrical conductivity of ion-exchanger from 0.21 to 0.65 Ohm^?1 m^?1. The diffusion coefficient of Cd²⁺ ions reaches 2.43 × 10^?11 m² s^?1 for initial resin and (2.50–4.34) × 10^?11 m² s^?1 for nanocomposites. The inorganic constituent improves Cd²⁺ recovery from a solution, which contains also Ca²⁺ and Mg²⁺. The degree of Cd²⁺ removal is 18% for non-modified resin and 99% for the sample containing 38 mass% zirconium phosphate.     

Bio-based shape memory epoxy resin synthesized from rosin acid

A bio-based shape memory epoxy resin (DGEAPA) was synthesized from rosin to achieve the sustainability of shape memory epoxy resin, and its chemical structure was determined by FTIR and ¹H NMR. For comparison, a petroleum-based epoxy, diglycidyl ester of terephthalic acid (DGT) having one benzene ring, was also synthesized. The properties, including thermal and mechanical properties, as well as shape memory properties of the epoxy resins cured with poly(propylene glycol)-bis (2-aminopropyl ether) (D230), were studied by differential scanning calorimeter, dynamic mechanical analysis, thermogravimetric analysis, tensile test, and U-type shape memory test. The effect of the stoichiometric ratio n_DGEAPA/n_DGT on the properties was studied as well. The thermal and mechanical properties, including thermal stability, glass transition temperature, tensile strength, and modulus of the cured epoxy systems, were found to be increased with DGEAPA incremental content, and the cured neat rosin-based epoxy system exhibited the highest properties. Both the cured rosin-based epoxy and the cured DGEAPA showed significant shape memory performance. Meanwhile, the rosin ring structure made the cured rosin-based epoxy systems display excellent shape recovery fixity, while small lower shape recovery and shape recovery rate relative to the cured neat DGT system. Therefore, the rosin-based epoxy resin has a great potential in the shape memory material applications.     

Effect of SBA-15 on the energy absorption characteristics of epoxy resin for blast mitigation applications

The energy absorption characteristics of silica-filled epoxy composites, for potential application as a blast mitigating retrofitting polymer coating has been explored. Mesoporous silica (SBA-15) with controlled pore size of 5.4 nm was synthesized by the hydrolysis of tetraethyl orthosilicate in the presence of amphiphilic copolymer (PEO-PPO-PEO) which was characterized by nitrogen physisorption studies at 77 K. The porous siliceous rods were homogeneously dispersed in the epoxy resin by ultrasonication (0.5–7 wt%) and subsequently cured using triethylene tetra-amine hardener to prepare silica reinforced composites. Structural, thermal and mechanical properties of the composites were evaluated under dynamic as well as quasi-static conditions which revealed that introduction of SBA-15 at low loadings (1 wt%) led to an increase in the toughness of the base resin but macroporous silica led to deterioration in the properties. The results clearly revealed that the mesoporous nature of silica plays a major role towards improving the dispersion of the filler which in turn resulted in improved properties. Neat epoxy samples fractured in a brittle fashion, but in the presence of SBA-15, the sample exhibited ductile failure, which was explained on the basis of a crack pinning mechanism. High strain rate studies (~10³ s^?1) of selected compositions were performed on a Split Hopkinson pressure bar and the effect of addition of mesoporous silica on the energy absorption characteristics were established. Finite element analysis was used to predict the behavior of concrete slabs on exposure to dynamic loadings resulting from TNT explosions, both in the presence and absence of the epoxy layer, which revealed the role of the retrofit as a fragment arrestor.     

A novel shape memory polynorbornene functionalized with poly(?-caprolactone) side chain and cyano group through ring-opening metathesis polymerization

A novel functionalized norbornene-based copolymer with long poly(?-caprolactone) side chain and cyano group was synthesized in the combination of ring-opening polymerization and ring-opening metathesis polymerization, which was characterized by means of ¹H NMR, gel permeation chromatography, thermogravimetry, differential scanning calorimetry, wide-angle X-ray diffraction, and stress-strain measurements. The shape memory effect of the copolymer was evaluated by dynamical mechanical analysis, shape recovery ability, and shape recovery speed. Having the properties of the good shape fixity and the large shape recovery, the functionalized polynorbornene copolymer is expected to use as a potential shape memory material.     

Synthesis and properties of magnetic sensitive shape memory Fe3O4/poly(ε‐caprolactone)‐polyurethane nanocomposites

Fe₃O₄/poly (ε‐caprolactone)‐polyurethane (PCLU) shape memory nanocomposites were prepared by an in situ polymerization method. The thermal properties, magnetic properties, and shape memory properties of the nanocomposites were investigated systematically. The results showed that the Fe₃O₄ nanoparticles were homogeneously dispersed in the PCLU matrix, which ensured good shape memory properties of nanocomposites in both hot water and an alternating magnetic field (f = 45 kHz, H = 29.7 kA m^?1/36.7 kA m^?1). The nanocomposites started to recover near 40°C, which is slightly higher than body temperature. Thus, they would not change their deformed shape during the implanting process into the human body. Considering potential clinical applications, 45°C was chosen as shape recovery temperature which is slightly higher than 37°C, and the nanocomposites had high shape recovery rate at this temperature. With increasing content of Fe₃O₄ nanoparticles, the shape memory properties of the nanocomposites in an alternating magnetic field increased and the best recovery rate reached 97%, which proves that this kind of nanocomposites might be used as potential magnetic sensitive shape memory materials for biomedical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Hyperbranched polyurethane/Fe3O4 thermosetting nanocomposites as shape memory materials

Nanocomposites of hyperbranched polyurethane were prepared by the in situ pre-polymerization technique with Fe₃O₄ nanoparticles. The synthesized Fe₃O₄ nanoparticles were characterized by the Fourier transform infrared spectroscopy and the X-ray diffraction study. The transmission electron microscopic study indicates the homogeneous distribution of Fe₃O₄ nanoparticles in the polymer matrix. The mechanical, thermal and shape memory behaviors of the nanocomposites were studied as a function of nanomaterial content. The glycidyl bisphenol-A based epoxy cured thermosetting nanocomposites exhibited significant improvement of tensile strength (5.7–18 MPa), scratch hardness (3.0–6.5 kg) and thermal stability (241–275 °C) with the increase of the content of Fe₃O₄. The nanocomposites possess excellent shape fixity over the repeated cycles of test. They also showed good shape recovery under the application of microwave energy. The shape recovery speed found to increase with the increase of the loading of Fe₃O₄ in the nanocomposites. Thus, the prepared nanocomposites might be utilized as advanced shape memory materials in their potential fields.     

ENZYME-MEDIATED PRODUCTION OF SUGARS FROM SAGO STARCH: STATISTICAL PROCESS OPTIMIZATION

Glucoamylase (γ-amylase, EC 3.2.1.3) from Aspergillus niger was used to hydrolyze the soluble sago starch to reducing sugars without any major pretreatment of the substrate. A 2 L stirred tank reactor was used for the hydrolysis. The effects of pH, temperature, agitation speed, substrate concentration, and enzyme concentration on the reaction were investigated in order to maximize both the initial reaction velocity v and the final product yield Y_p/s. A response surface methodology central composite design was used for the optimization. A maximum Y_p/s of 0.58 g · g^?1 and a high v of 0.50 mmoles · L^?1 · min^?1 were predicted by the response surface at the identified optimal conditions (61°C, a substrate concentration of 0.1% (w/v, g/100 mL), an enzyme concentration of 0.2 U · mL^?1). The pH and agitation speed did not significantly affect the production of sugars. The subsequent validation experiments under the above-specified optimal conditions confirmed a maximum conversion rate and yield combination of 0.51 ± 0.07 mmoles · L^?1 · min^?1 and 0.60 ± 0.08 g · g^?1.     

High strain rate compressive behavior of PMMA

Polymethylmethacrylate (PMMA) materials are extensively used for diverse applications e.g., protective vehicular windows to eye protection devices. However, the high strain rate deformation and fracture mechanisms of PMMA are far from well understood. Therefore, controlled split Hopkinson pressure bar (SHPB) experiments that could lead to deformation with and without fracture were conducted on PMMA samples at strain rates of ~4 × 10⁰ to 1.3 × 10³ s^?1. With increase in strain rate, the maximum compressive yield strength of PMMA is enhanced by about 25 %. Absence of global failure characterized the deformation at relatively lower strain rates (e.g., ~4.75 × 10² to 6.75 × 10² s^?1), while its marked presence characterized the same at comparatively higher strain rates (e.g., ~7.69 × 10² to 9.31 × 10² s^?1). Attempts were made to explain these observations by the subtle changes in failure mechanisms as revealed from the fractographic examinations of the PMMA samples deformed with and without failures. The implications of the test-condition induced restrictions on the degrees of freedom locally available to the polymeric chains were discussed in the perspective of the relative strain rate dependencies of the yield behaviors of the present PMMA samples.     

Thermomechanical properties and deformation behavior of a unidirectional carbon-fiber-reinforced shape memory polymer composite laminate

A shape memory polymer (SMP) demonstrates large reversible deformation functionality upon exposure to heating stimuli. In this study, the thermomechanical properties and deformation behavior of a unidirectional carbon-fiber-reinforced SMP composite (SMPC) laminate were studied. The findings can be used as a basis to design angle-ply laminated plates, woven laminated plates, or special laminated structures used for space deployment. The fundamental static and dynamic mechanical properties of SMP and SMPC were characterized. The fiber-reinforced SMPC exhibited local postmicrobuckling behavior and obtained a high-reversible macroscale strain of 9.6%, which enabled the high-reversible deformation to be used for foldable structures in space. The state of critical failure of bending deformation was determined through microscale morphology observations and provided the upper limit in the design of SMPC structures. The evolution of the key shape memory properties (e.g., recovery speed and recovery ratio) during deformation cycles was characterized, and it offered the general recovery performance of a space deployable structure. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48532.     

Graphite-Filled Polyethylene/Epoxy Blend for High-Conductivity Applications: The Immiscibility Edge

ABSTRACT

Polyethylene (PE)/epoxy blends filled with graphite were prepared and studied in this work. The in-plane and through-plane conductivities of the composites increased from 11.68 Scm^?1 to 73.11 Scm^?1 and 0.20 Scm^?1 to 4.12 Scm^?1, respectively, as graphite content increased from 30 to 80 wt%. Phase bonding effect of the compatibilizer and reinforcing effect of the filler enhanced the flexural modulus and strength of the composites up to 70 wt% filler content. The electrical conductivities attained by these composites being significantly higher than comparable composite formulations in literature show the edge of immiscible PE/epoxy blend for achieving high-conductivity polymer composites.     

Phthalonitrile end-capped sulfonated polyarylene ether nitriles for low-swelling proton exchange membranes

A series of phthalonitrile end-capped sulfonated polyarylene ether nitriles are synthesized via K₂CO₃ mediated nucleophilic aromatic substitution reaction at various molar ratios. The as-prepared polymer structures are confirmed by ¹H NMR and FTIR spectroscopy. The properties of membranes cast from the corresponding polymers are investigated with respect to their structures. The membranes exhibit good thermal and mechanical properties, low methanol permeability (0.01?×?10^?6–0.58?×?10^?6 cm²·s^?1 at 20 °C), and high proton conductivity (0.021–0.088 S·cm^?1 at 20 °C). The introduction of phthalonitrile is proved to increase intermolecular interaction, mainly contributing to the reduction in water uptake, swelling ratio, and methanol permeability. More importantly, its introduction does not decrease the proton conductivity, but there is a slight increase. Furthermore, the selectivity of SPEN-CN-50 can reach 4.11?×?10⁵ S·s·cm^?3, which is about nine times higher than that of Nafion 117. All the data show that the as-prepared membranes may be potential proton exchange membrane for DMFCs applications.     

ELECTRO-DEIONIZATION OF Cr (VI)-CONTAINING SOLUTION. PART I: CHROMIUM TRANSPORT THROUGH GRANULATED INORGANIC ION-EXCHANGER

Kinetics of Cr (VI) → OH^? exchange on both hydrogel and xerogel of hydrated zirconium dioxide was investigated. Self-diffusion coefficient of Cr (VI) species has been determined by analysis of kinetic curves. Transport of Cr (VI) anions through the inorganic ion exchangers under the influence of applied voltage was also researched. In the case of hydrogel, the ions are transported mainly through the solid phase. Diffusion coefficient of chromate anions through this material was estimated as 9.00 × 10^?12 m² s^?1. This is in agreement with self-diffusion coefficient of Cr (VI) obtained from kinetic measurements (1.60 × 10^?12–9.92 × 10^?12 m² s^?1). Owing to the rather high mobility of Cr (VI) through hydrogel of hydrated zirconium dioxide, this material was recommended for electro-deionization processes. On the other hand, the use of polymer anion-exchange membrane must be excluded to prevent poisoning of the inorganic ion exchanger with Cr (III) cations to be formed during chemical interaction of Cr (VI) with organic materials.     

Convective Drying of Wastewater Sludge: Introduction of Shrinkage Effect in Mathematical Modeling

Drying of two kinds of wastewater sludge was studied. The first part was an experimental work done in a discontinuous cross-flow convective dryer using 1 kg of wet material extruded in 12-mm-diameter cylinders. The results show the influence of drying air temperature for both sludges. The second part consisted of developing a drying model in order to identify the internal diffusion coefficient and the convective mass transfer coefficient from the experimental data. A comparison between fitted drying curves, well represented by Newton's model, and the analytical solutions of the equation of diffusion, applied to a finite cylinder, was made. Variations in the physical parameters, such as the mass, density, and volume of the dried product, were calculated. This allowed us to confirm that shrinkage, which is an important parameter during wastewater sludge drying, must be taken into account. The results showed that both the internal diffusion coefficient and convective mass transfer coefficient were affected by the air temperature and the origin of the sludge. The values of the diffusion coefficient changed from 42.35 × 10^?9 m² · s^?1 at 160°C to 32.49 × 10^?9 m² · s^?1 at 122°C for sludge A and from 33.40 × 10^?9 m² · s^?1 at 140°C to 28.45 × 10^?9 m² · s^?1 at 120°C for sludge B. The convective mass transfer coefficient changed from 4.52 × 10^?7 m · s^?1 at 158°C to 3.33 × 10^?7 m · s^?1 at 122°C for sludge A and from 3.44 × 10^?7 m · s^?1 at 140°C to 2.84 × 10^?7 m² · s^?1 at 120°C for sludge B. The temperature dependency of the two coefficients was expressed using an Arrhenius-type equation and related parameters were deduced. Finally, the study showed that neglecting shrinkage phenomena resulted in an overestimation that can attain and exceed 30% for the two coefficients.     

Hyperbranched‐modified epoxy thermosets: Enhancement of thermomechanical and shape‐memory performances

In this study a complete characterization of the thermomechanical and shape‐memory properties of epoxy shape‐memory polymers modified with hyperbranched polymer and aliphatic diamine was performed. Focusing on the mechanical properties that are highly desirable for shape‐memory polymers, tensile behavior until break was analyzed at different temperatures and microhardness and impact strength were determined at room temperature. As regards shape memory performance, the materials were fully characterized at different programming temperatures to study how this influenced the recovery ratio, fixity ratio, shape‐recovery velocity, and switching temperature. Tensile testing revealed a peak in deformability and in the stored energy density at the onset of the glass transition temperature, demonstrating that this is the best programming temperature for obtaining the best shape‐memory performances. The Young's moduli revealed more rigid structures in formulations with higher hyperbranched polymer content, while microhardness showed higher values with increasing hyperbranched polymer content due to the increased crosslinking density. Impact strength was greatly improved as the aliphatic diamine content increases due to the energy dissipation capability of its flexible structure. As regards the shape‐memory properties, increasing the programming temperature has a minor effect on formulations with a lower hyperbranched polymer content and worsens these properties when the hyperbranched polymer content is increased. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44623.     

Strain rate-dependent deformation behaviors of multi-layer carbon fiber reinforced polymer laminates

This paper focuses on the contributions of diversities of strain rate and orientations for aggravating the diversities of micro failure behaviors on carbon fiber reinforced polymer (CFRP) laminates. A miniature horizontal type tensile tester is employed to conduct experiments with strain rate ranging from 2.6 × 10⁻⁶ s⁻¹ to 2.6 × 10⁻³ s⁻¹. The CFRP laminates are obtained based upon a thermoset toughened epoxy matrix (termed CF/Epoxy) with ply orientations of (0°/0°) and (0°/90°). Significant differences in deformation behaviors of CFRP laminates are determined through tests. The study clearly reveals the strain rate-dependent deformation modes of CFRP laminates, involving pure fiber fracture, epoxy crack with stepped surface and interface failure with residual voids, determines the “low-high-low” variation tendency of Young's modulus and strength as a function of strain rate. Ply orientation-dependent differences in deformation behaviors are also investigated via severe interfacial shearing effect. A unified model consisted of four deformation modes to is clarified to analyze the complexity of CFRP laminates failure mechanism.     

UV curable micro-structured shape memory epoxy with tunable performance

Micro-structured shape memory polymer (SMP) surfaces are indispensable in various applications. Epoxy polymer emerged as an ideal candidate for SMP surfaces due to its low curing shrinkage and superior thermo-mechanical properties. In this study, we develop a UV curable epoxy system with tunable glass transition temperature and superior shape memory performance. The glass transition temperatures can widely range from 49 to 164°C by simply tuning the ratio of two comonomers. All samples possess excellent shape fixity, shape recovery ratios, and cycling stability. The synergy of the moldable liquid epoxy precursors and the spatiotemporal UV light allows shape memory epoxy with both surface microstructures and complex macro-geometries. We anticipate this UV curable epoxy will expand the scopes of surface shape memory applications.     

A novel heteropolyacid-doped carbon nanotubes/Nafion nanocomposite membrane for high performance proton-exchange methanol fuel cell applications

A novel proton-exchange polymer composite membrane was synthesized using Nafion^®, tetraethoxysilane-modified carbon nanotubes (CNTs) and phosphotungstic acid-modified carbon nanotubes with the aim of using direct methanol fuel cells (DMFCs). Physicochemical properties of the modified CNTs and fabricated composite membranes were investigated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, water uptake, thermogravimetric analysis, ion exchange capacity, proton conductivity and methanol permeability tests. It was demonstrated that chemical surface modification of CNTs and introduction of the phosphotungstic acid (PWA) groups effectively improved the performance of DMFC. It was found that the presence of PWA groups on the surface of CNTs led to the formation of strong electrostatic interactions between the PWA groups and clusters of sulfonic acid in Nafion^® macromolecules. Hence, the incorporation of inorganic phosphotungstic super-acid-doped silicon oxide-covered carbon nanotubes (CNT@SiO₂-PWA) into Nafion^® matrices enhanced the proton conductivity of the prepared membranes. Moreover, the methanol permeability was reduced to 2.63 × 10^?7 cm² s^?1 in comparison with the recast Nafion^® membrane (2.25 × 10^?6 cm² s^?1). Enhancing the proton conductivity and reducing the methanol permeability, the selectivity of the prepared nanocomposite membranes was enhanced to a greater value of 330,700 S s cm^?3 as compared to the value of 38,222 S s cm^?3 for recast Nafion^®.     

Highly Efficient Supported Diimine Ni(II) and Iminopyridyl Fe(II) Catalysts for Ethylene Polymerizations

A facile and user friendly technique to immobilize late transition metal complexes on nonporous silica has been developed. Among the supported diimine Ni(II) and iminopyridyl Fe(II) catalysts, former showed high activities exceeding 10⁵ g-PE mol-metal^?1 h^?1 bar^?1 combined with ethylaluminum sesquichloride. The obtained polymer morphology was tunable from spherical to fibrous shape.