Band 18, Heft 1 - Special Issue: Polymers and Composite Materials (PCM 2017) / Guest Editor: Esteban Broitman

Facile methods to improve the dissolution rate of poorly water-soluble drugs are highly sought after. In this study, a modified coaxial electrospinning process was exploited to create medicated amorphous nanocomposites, an approach characterized by the application of a Teflon-coated coaxial spinneret. The hydrophilic polymer hydroxypropyl methylcellulose and the active ingredient tamoxifen citrate (TAM) were selected as the drug carrier and model drug, respectively. Their electrospun nanocomposites showed linear morphology with the drug presented in an amorphous state. The loaded cargoes could be released from the nanocomposites simultaneously when they were placed in the dissolution media, showing faster dissolution rates than their counterparts (physical mixtures). Based on the reasonable application of the polymeric carrier, the reported protocols not only provided an approach to enhance the dissolution of poorly water-soluble drugs, but also exhibited a method to facilitate the implementation of coaxial electrospinning.

In this article, three composites were prepared by filling the composition of hydrophobically modified pearlite with polyvinyl alcohol (PVA), urea-formaldehyde resin (UF), and melamine urea formaldehyde resin (MUF). Properties including combustion time, smoke density, oxygen index, and thermal conductivity, as well as the effects of component ratio on the combustion performance were determined for each of the three composites. The results indicated improved flame retardancy of all composite samples as a result of synergistic effects of the hydrophobically modified pearlite and the three binding agents. The PVA-based composite showed advantages in density, thermal decomposition, and smoke density, whereas UF-based and MUF-based ones showed good flame retardancy. Specially, the oxygen index of MUF-based composite material reached 52.5% (Level B1 flame retardancy).

Key thermophysical properties of the thermosetting resin, including density, conductivity coefficient and specific heat that evolve with resin curing, are related to temperature and curing degree fields of the fiber/resin composite material. However, their effects on heat transfer inside composite materials, consequently on the curing non-uniformity in thick-section laminates, are not well understood. The focus of this study is on the effects of key thermophysical properties of resin on the curing uniformity of AS4/3501-6 composite by means of the coupled thermochemical analysis with the method of numerical simulation. The results clearly indicate that the conductivity coefficient and specific heat of resin have obvious influence on curing uniformity, especially for thick laminates, while the density of resin has no noticeable effect on the curing uniformity. The simulation results can help to guide the material preparation of industrial production.

Carbon fiber reinforced plastics (CFRPs) are advanced composite materials that have been used as lightweight structural materials for vehicles. Unlike general isotropic materials, the structural characteristics of composite materials are strongly influenced by the stacking directions and sequences of the composite laminates. In this study, finite element analysis was used to predict the material properties of the carbon fibers and the resin composing a CFRP in cases of laminated carbon fibers and modified external angles. The results verify the approach’s reliability by comparing the simulation results and the real test results related to the material properties of the carbon fibers and the resin. The results of the finite element analysis and the experimental results were compared with the load-displacement curves and the maximum load. The [0 2 /90 2 ] S , [90 2 /0 2 ] 2 , and [0/90] 2S specimens showed a maximum error rate of 8.6%, whereas the [90 2 /0 2 ] S , [0 2 /90 2 ] 2 , and [90/0] 2S specimens showed a maximum error rate of approximately 12.93%. By applying CFRP static collapse analysis of fiber properties and resin properties through basic experiments and basic theory, we predicted the properties of CFRPs through finite element analysis; an error rate of approximately 10% indicated that our approach is effective.

In this study, an ultrasonic-assisted impregnation method was employed to deposit carboxyl multiwalled carbon nanotubes (MWCNTs) onto the E-glass fiber fabric (GFf) for the preparation of the MWCNT-GFf reinforcer. The effects of ultrasonic power, duration and temperature on the dispersion of MWCNTs onto GFf were investigated, and the mechanical properties, interlaminar adhesion, and dynamic viscoelasticity of the resulting MWCNT-GFf-reinforced composites (MGCs) were evaluated. The results indicated that an effective dispersion of MWCNTs onto GFf without obvious breakage of the MWCNTs was achieved under an ultrasonic power of 600 W, duration of 6 min, and processing temperature of about 0°C. Compared with the GFf-reinforced composite, the tensile strength, flexural strength and interlaminar shear strength of the MGCs exhibited maximum increments of 38.4%, 34.6% and 47.1%, respectively. Moreover, the storage moduli and glass-transition temperatures of the MGCs were significantly enhanced. The ultrasonic parameters were of key importance for dispersing MWCNTs onto GFf and improving the interfacial properties of the composites.

Space charge accumulation within insulating material poses a threat to the reliability in the operation of DC power cables. To investigate the influence of carbon black (CB) on the space charge accumulation of low density polyethylene (LDPE), both conductive carbon black (C-CB) and insulating carbon black (I-CB) were employed as filler particles. The space charge distributions of LDPE and CB/LDPE nanocomposites were obtained by the pulsed electro-acoustic (PEA) method. Additionally, dynamic mechanical analysis (DMA) and thermally stimulated current (TSC) spectroscopy were applied to explore the mechanism of improving space charge performance. Both the C-CB/LDPE and I-CB/LDPE nanocomposites can effectively suppress space charge accumulation. It was concluded that the improvement in space charge characteristics of CB/LDPE nanocomposites was attributable to the interaction between the CB particles and the LDPE, which reduces the number of defects formed from molecules participating in α relaxation and decreases the density of traps within the LDPE.

Polymers modified by graphene have become an attractive method to enhance the matrix properties, wherein the dispersion of graphene in the matrix and the interfacial interactions between graphene and matrix are critical to influence the final performance. In the present work, graphene nanosheet (GNS)-modified hydrogenated nitrile butadiene rubber (GNS/HNBR) composites were prepared via solution-mixing and mechanical-blending methods. The curing performance, mechanical properties and heat resistance of the prepared composites were studied. The results showed that when the content was 0.2 wt%, the tensile strength and modulus at 300% elongation of the GNS/HNBR composite prepared via solution-mixing method reached 19.36 and 3.62 MPa, which increased by 32% and 18% compared with those of pure HNBR, respectively. In addition, the swelling index of the composite in cyclohexane was decreased from 413% to 337%. On the other hand, the tensile property of GNS/HNBR composite prepared by mechanical-mixing method became poor. SEM observation showed that GNS was well dispersed and incorporated into HNBR via the solution-mixing method, resulting in a significant reinforcing effect.

The poly(butylene terephthalate) (PBT)/ethylene-vinyl acetate copolymer (EVA) blends with different contents of EVA were prepared by an vane extruder. From the observation of morphologies, impact strength and dynamic mechanical analysis (DMA), the EVA particles were well dispersed in the PBT matrix and improved the impact strength of PBT. Differential scanning calorimetry measurements demonstrate that there is little diversification in the crystal structure and type. Thermogravimetric analysis reveals that as the weight fraction of EVA increases, the thermal stability of composite is enhanced. The rheological analyses indicate that the PBT/EVA blends follow a non-Newtonian behavior and viscosities of the blends are drastically lower than that of pure PBT at higher frequencies. The storage modulus (G′) and loss modulus (G″) of the blends monotonously increase as the frequency rises. This work provides a novel method to develop blends with excellent performance.

Nanocomposites of waterborne polyurethane (WPU) containing graphene oxide sheets (GO) were prepared by an in-situ polymerization method at low temperature. The morphology and interface structure were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Without undergoing complicated functionalization processes, GO can be finely embed into a WPU matrix and present high degree of orientation at high GO contents, due to the formation of chemical bonds and hydrogen bonding. From the Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) results, incorporation of GO exists in two ways and shows inverse effects. At a content of 2.0 wt.% GO loading, the tensile elastic modulus of the GO-WPU film increased by 193% to neat WPU. The nanocomposites also displayed 30°C higher thermal stability than WPU in thermogravimetric (TG) curves. This environment-friendly method may pave the way to design graphene-based polymer composites.

Epoxy resin (ER)/micron-aluminum particles (MP) composites with different filling concentration of spherical particles were fabricated. The nonlinear conductive behavior of ER/MP composites under increasing applied voltage using the improved V-I method was investigated. Under sufficient high intensity applied constant voltage, the obvious conductive switching behavior of samples with volume fraction 12.7%, 16.9% and 18.9% was found. The conductivity of ER/MP composites increase up to 3–4 orders of magnitude when the conductor-insulator transition occurs. The switching threshold voltage decreases with the increase of volume fraction of MP in the composites. The results show that the ER/MP composites with conductive switching properties are of great potential application in electromagnetic protection of electron devices and systems.

This paper introduces a feasible method to improve the color value of bio-based polyamide 56 (PA56) fiber. Three types of whitening modifiers were introduced into the bio-based PA56 fibers by the in-situ polymerization method and melt blending method in order to improve the fiber color. The color values and mechanical properties of PA56 fibers were tested and analyzed and the optimum additive ratio and process conditions were discussed. The results show that the improved color value of bio-based PA56 fibers can be achieved by the melt blending method of fluorescent whitening masterbatch and reasonable spinning condition control. When the additive amount of fluorescent whitening agent is 0.3%, the index of lightness (L) increased from 84 to 90, while the yellow index (YI) reduced from 16.8 to 12.6. Moreover, PA56 fibers show high breaking strength about 4.27 cN/dtex and good yellowing resistance and durability.

Using the melt polycondensation method, a polyesteramide was prepared based on poly(L-lactic acid) prepolymer and poly(ε-caprolactam) prepolymer and was characterized by Fourier transform infrared spectroscopy and 1 H-NMR. Isothermal crystallization behavior at different temperatures and non-isothermal crystallization kinetics at different cooling rates were investigated by differential scanning calorimetry, and non-isothermal crystallization kinetics parameters were obtained using the Mo, Ozawa and Jeziorny methods. It was found that the increased cooling rates led to the broadening of the polyesteramide crystallization peaks and their shift toward lower temperatures. Mo and Jeziorny methods were found to be more suitable than the Ozawa method for the analysis of this system, as shown by the comparison these non-isothermal crystallization analysis methods. In addition, the values of activation energy of non-isothermal crystallization for polyesteramide obtained by the Kissinger and Takhor methods were −155.96 and −149.12 kJ/mol, respectively.