Preparation of mixed matrix composite membrane for hydrogen purification by incorporating ZIF-8 nanoparticles modified with tannic acid

The incompatibility between nanofillers and polymer, caused by the agglomeration of nanoparticles and their weak interaction with each other, is still a challenge to develop mixed matrix composite membrane. Herein, we introduced the ZIF-8-TA nanoparticles synthesized by in situ hydrophilic modification into the hydrophilic poly(vinylamine) (PVAm) matrix to prepare composite membranes for H₂ purification. The dispersion of ZIF-8 in water was improved by tannic acid modification, and the compatibility between ZIF-8 particles and PVAm matrix was enhanced by chemical crosslinking between the quinone groups in oxidized tannic acid (TA) and the amino groups in PVAm. Moreover, the compatibility between hydrophobic polydimethylsiloxane (PDMS) gutter layer and hydrophilic separation layer was achieved by the adhesion of TA-Fe³⁺ complex to the surface of PDMS layer during membrane preparation. The interlayer hydrophilic modification and the formation of separation layer were accomplished in one step, which simplified the preparation process. The experimental results indicated that when the TA addition used for modification was 0.5 g and the ZIF-8-TA_0.5 content in membrane was 12 wt%, the prepared membrane showed the best separation performance with the CO₂ permeance of 987 GPU and the CO₂/H₂ selectivity of 31, under the feed gas pressure of 0.12 MPa.     

Homogenization with uncertainty in Poisson ratio for polymers with rubber particles

The main aim of this work is dual computer analysis of probabilistic coefficients for the homogenized tensor of the polymer filled with the rubber particles having randomized Poisson ratios of both constituents. The major issue is to verify an influence of a randomness in rubber Poisson ratio close to the compressibility limit on the uncertainty of the effective tensor probabilistic characteristics. Probabilistic analysis presented here is carried out using mainly the stochastic perturbation technique provided by the common application of the traditional FEM commercial code ABAQUS and the symbolic computations package MAPLE. This FEM-based technique employs polynomial response function of the optimum order recovered from the weighted least squares method and following a set of deterministic solutions obtained for various values of the randomized input parameter. Optimization procedure is released entirely into a symbolic environment, where maximization of the correlation factor together with minimization of the fitting variance and approximation error are applied. Homogenization technique consists in equating of deformation energies for the real composite and the artificial one characterized by the effective elasticity tensor with uncertainty.     

Dynamic mechanical analysis and thermal properties of LLDPE/EVA/modified silica nanocomposites

The effect of hexamethylene disilazane modified nanosilica on the dynamic mechanical analysis (DMA), crystallization, melting and thermal degradation behavior of linear low density polyethylene/ethylene vinyl acetate copolymer (LLDPE/EVA) blends are explored.Detailed DMA analysis is carried out in order to investigate the reinforcing behavior of nanosilica adopting Kerner–Nielson model. Oxidative degradation and thermal stabilities of samples are also studied by the thermogravimetery analysis. The high content of nanosilica particles results in significant shift of degradation temperature to higher temperatures in the oxygen atmosphere. This behavior might be attributed to the barrier properties of nanoparticles against oxygen and gaseous degradation products. However, incorporation of modified nanosilica into LLDPE/EVA blend is decreased the onset of degradation temperature of the unfilled system. In nitrogen atmosphere, no changes are observed in the thermal degradation range and only a reduction is documented in the onset of degradation temperature. Considering important role of onset of degradation temperature, activation energy of starting of degradation temperature is calculated utilizing Kissinger-Ozawa model in both oxygen and nitrogen atmospheres. Results showed that activation energy of degradation reaction is decreased by ∼ 20 kJ/mol. This decrease is owing to the release of modifiers from the nanoparticles.     

Impact behavior and fractographic study of carbon nanotubes grafted carbon fiber-reinforced epoxy matrix multi-scale hybrid composites

Carbon nanotubes are the most promising reinforcement for high performance composites. Multiwall carbon nanotubes were directly grown onto the carbon fiber surface by catalytic thermal chemical vapor deposition technique. Multi-scale hybrid composites were fabricated using the carbon nanotubes grown fibers with epoxy matrix. Morphology of the grown carbon nanotubes was investigated using field emission scanning electron microscopy and transmission electron microscopy. The fabricated composites were subjected to impact tests which showed 48.7% and 42.2% higher energy absorption in Charpy and Izod impact tests respectively. Fractographic analysis of the impact tested specimens revealed the presence of carbon nanotubes both at the fiber surface and within the matrix which explained the reason for improved energy absorption capability of these composites. Carbon nanotubes presence at various cracks formed during loading provided a direct evidence of micro crack bridging. Thus the enhanced fracture strength of these composites is attributed to stronger fiber–matrix interfacial bonding and simultaneous matrix strengthening due to the grown carbon nanotubes.     

Characteristics and formation mechanism of porosities in CFRP during laser joining of CFRP and steel

An experimental investigation on the mechanism of porosity formation during the laser joining of carbon fiber reinforced polymer (CFRP) and steel is presented. The porosity morphology and distribution were characterized by optical and scanning electron microscopy, and the thermal pyrolysis behaviors were investigated by thermal analysis and designed back-side cooling experiments. The results show that there are two types of porosities in CFRP. Porosity I only appears when the heat input is more than 77.8 J/mm. It has a smooth inner wall and distributes near the bonding interface between CFRP and steel at the central area of melted zone, which is caused by gaseous products such as CO₂, NH₃, H₂O, and hydrocarbons produced by the pyrolysis of CFRP. Porosity II can be seen under all joining conditions. It has a rough inner wall and distributes far away from the bonding interface, concentrating at the final solidification locations. Porosity II is caused by the shrinkage of melted CFRP during solidification stage.     

Microwave assisted-in situ synthesis of porous titanium/calcium phosphate composites and their in vitro apatite-forming capability

Microwave irradiation has been proven to be an effective heating source in synthetic chemistry, and can accelerate the reaction rate, provide more uniform heating and help in developing better synthetic routes for the fabrication of bone-grafting implant materials. In this study, a new technique, which comprises microwave heating and powder metallurgy for in situ synthesis of Ti/CaP composites by using Ti powders, calcium carbonate (CaCO₃) powders and dicalcium phosphate dihydrate (CaHPO₄·2H₂O) powders, has been developed. Three different compositions of Ti:CaCO₃:CaHPO₄·2H₂O powdered mixture were employed to investigate the effect of the starting atomic ratio of the CaCO₃ to CaHPO₄·2H₂O on the phase, microstructural formation and compressive properties of the microwave synthesized composites. When the starting atomic ratio reaches 1.67, composites containing mainly alpha-titanium (α-Ti), hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP) and calcium titanate (CaTiO₃) with porosity of 26%, pore size up to 152 μm, compressive strength of 212 MPa and compressive modulus of 12 GPa were formed. The in vitro apatite-forming capability of the composite was evaluated by immersing the composite into a simulated body fluid (SBF) for up to 14 days. The results showed that biodissolution occurred, followed by apatite precipitation after immersion in the SBF, suggesting that the composites are suitable for bone implant applications as apatite is an essential intermediate layer for bone cells attachment. The quantity and size of the apatite globules increased over the immersion time. After 14 days of immersion, the composite surface was fully covered by an apatite layer with a Ca/P atomic ratio approximately of 1.68, which is similar to the bone-like apatite appearing in human hard tissue. The results suggested that the microwave assisted-in situ synthesis technique can be used as an alternative to traditional powder metallurgy for the fabrication of Ti/CaP biocomposites.     

High strain rate visco-damageable behavior of Advanced Sheet Molding Compound (A-SMC) under tension

Advanced Sheet Molding Compound (A-SMC) is a serious composite material candidate for structural automotive parts. It has a thermoset matrix and consists of high weight content of glass fibers (50% in mass) compared to standard SMC with less than 30% weight fiber content. During crash events, structural parts are heavily exposed to high rates of loading and straining. This work is concerned with the development of an advanced experimental approach devoted to the micro and macroscopic characterization of A-SMC mechanical behavior under high-speed tension. High speed tensile tests are achieved using servo-hydraulic test equipment in order to get required high strain rates up to 100 s⁻¹. Local deformation is measured through a contactless technique using a high speed camera. Numerical computations have led to an optimal design of the specimen geometry and the experimental damping systems have been optimized in terms of thickness and material properties. These simulations were achieved using ABAQUS explicit finite element code. The developed experimental methodology is applied for two types of A-SMC: Randomly Oriented (RO) and Highly Oriented (HO) plates. In the case of HO samples, two tensile directions were chosen: HO-0° (parallel to the Mold Flow Direction (MFD)) and HO-90° (perpendicular to the MFD). High speed tensile tests results show that A-SMC behavior is strongly strain-rate dependent although the Young's modulus remains constant with increasing strain rate. In the case of HO-0°, the stress damage threshold is shown an increase of 63%, when the strain rate varies from quasi-static (0.001 s⁻¹) to 100 s⁻¹. The experimental methodology was coupled to microscopic observations using SEM. Damage mechanisms investigation of HO and RO specimens showed a competition between two mechanisms: fiber-matrix interface debonding and pseudo-delamination between neighboring bundles of fibers. It is shown that pseudo-delamination cannot be neglected. In fact, this mechanism can greatly participate to energy absorption during crash. Moreover, the influence of fiber orientation and imposed velocity is studied. It is shown that high strain rate and oriented fiber in the tensile direction favor the pseudo-delamination.     

Development of Cu particles and Cu core-shell particles reinforced Al composite

Copper particles were incorporated and retained in elemental state in an aluminium matrix by friction stir processing thereby producing a non-equilibrium particulate composite. The processed Al–Cu_p composite exhibited improved strength with significantly high ductility. The composite was stable up to a temperature of more than 300°C. Thermal exposure at 350°C for more than 10 min led to diffusion of Cu atoms into the Al matrix forming a core-shell type structure in the Cu particles and thus producing an Al–Cu core-shell composite. The shell consists of multiple layers, the thickness of which was controllable.     

Mechanical damage characterization of glass fiber-reinforced polymer laminates by ultrasonic maps

A method for simultaneous measurement of the thickness and density for Glass Fiber-Reinforced Polymer (GFRP) laminate plates with ultrasonic waves in C-Scan mode is presented in the form of maps. The method uses three different signals in immersion pulse-echo C-Scan mode. The maps obtained based on the density show the heterogeneity of the material at high resolution at the pixel level (1 × 1 mm²) and therefore they represent an efficient tool to assess and evaluate the damage of the composite structures after manufacturing and after an applied mechanical loading.     

Recovery of residual nutrients from agri-food byproducts using a combination of solid-state fermentation and insect rearing

The present research develops an innovative nutrient recovery strategy for capturing of un-utilised nutrients from agri-food byproducts using a combination of solid state fermentation (SSF) and insect rearing. SSF of borage and flaxseed meals were performed using GRAS organisms to release indigenous nutrients and to produce additional nutrients. Proximate analysis of the SSF-meals showed increases in both lipid and protein contents. Black soldier fly larvae (BSFL) were then grown on these SSF-meals for 12 day. The meals fermented singularly with Lactobacillus plantarum or Aspergillus niger displayed up to 30% enhancement in BSFL biomass, and dual fermentation with L. plantarum and Aspergillus oryzae resulted in an additional 10% enhancement. These examinations showed SFL use over-90% of proteins and lipids in SSF-meals. The results indicate that fermentation of these low-value meals can boost the efficacy of larval growth and the recovery of nutrients from agricultural byproducts as larval biomass.