Partially miscible poly(lactic acid)‐ blend‐poly(propylene carbonate) filled with carbon black as conductive polymer composite

BACKGROUND: Conductive polymer composites (CPCs) can be obtained by filling polymer matrices with electrically conductive particles, and have a wide variety of potential applications. In the work reported, the biodegradable polymer poly(lactic acid) (PLA) as a partially miscible blend with poly(propylene carbonate) (PPC) was used as a polymer matrix. Carbon black (CB) was used as the conducting filler. RESULTS: Fourier transform infrared spectroscopy revealed interactions between matrix and CB filler; this interaction was stronger in PPC‐blend‐CB than in PLA‐blend‐CB composites. A rheology study showed that low‐viscosity PPC could improve the fluidity of the CPCs, but decrease that of CB. With increasing CB content, the enforcement effect, storage modulus and glass transition temperature increased, but the elongation at break decreased. CPCs exhibited the lowest electrical percolation thresholds of 1.39 vol.% CB when the content of PPC in PLA‐blend‐PPC was 40 wt%. The conductivity of CPCs containing 5.33 vol.% CB and 40 wt% PPC reached 1.57 S cm^?1. Scanning electron microscopy revealed that CB exhibits a preference for dispersion in the low‐viscosity phase (PPC) of the multiphase matrix. CONCLUSION: In the presence of CB, partially miscible PLA‐blend‐PPC could form multi‐percolation CPCs. Moreover, the combination of PLA and PPC with CB broadens novel application of both renewable polymers and CPCs. Copyright © 2008 Society of Chemical Industry     

Novel fire-protecting mortars formulated with magnesium by-products

Several kinds of sprayable mortars are commonly used as passive fire protection of building structures. Several authors have reported the effect of different kinds of aggregates (e.g. vermiculite, fly ashes) in the thermal behaviour of fire-protecting mortars. In this study, the use of magnesium by-products as aggregates in fire-protecting mortars has been evaluated. These by-products were obtained during the calcination process of natural magnesite. Endothermic decompositions of the different aggregates have been determined and analysed by means of thermal techniques. Mortars with different mixtures of these by-products have been prepared. Mechanical properties and temperature behaviour tests have been performed to evaluate the suitability of these substances as aggregates in fire-protecting mortars. During the endothermic decomposition of the studied aggregates the advance of temperature inside the mortar is delayed. Mortar with a mixture of 50% of both magnesium by-products shows a good agreement between mechanical properties and temperature behaviour.     

Simultaneous lower and upper critical solution temperature‐type co‐nonsolvency behaviour exhibited in water–dioxane mixtures by linear copolymers and hydrogels containing N‐isopropylacrylamide and N,N‐dimethylacrylamide

The co‐nonsolvency behaviour in water–dioxane mixtures of linear copolymers and hydrogels consisting of N‐isopropylacrylamide (NIPAM) and N,N‐dimethylacrylamide (DMAM) was studied as a function of solvent composition and temperature. The composition of the copolymers, P(NIPAM‐co‐DMAMx), in DMAM units, x, varies from x = 0 up to x = 100%. It is shown that the copolymers combine the lower critical solution temperature (LCST)‐type co‐nonsolvency behaviour of poly‐NIPAM with the upper critical solution temperature (UCST)‐type co‐nonsolvency behaviour of poly‐DMAM. Depending on x, both the LCST‐ and UCST‐type co‐nonsolvency behaviour may be simultaneously observed in water‐rich and dioxane‐rich solvent mixtures, respectively. Due to this complex phase separation behaviour, the variation of the reduced viscosity of the linear copolymers, as well as the swelling–deswelling behaviour of the respective hydrogels, are shown to be temperature‐ and solvent‐sensitive. Copyright © 2006 Society of Chemical Industry     

Anisotropic multilayer conductive networks in carbon nanotubes filled polyethylene/polypropylene blends obtained through high speed thin wall injection molding

To prepare composites with anisotropic conductive networks, electrical conductive polymer composites (CPCs) consisting of polypropylene (PP) and carbon nanotubes (CNTs) filled polyethylene (PE) are fabricated through high speed thin-wall injection molding. Morphological study demonstrates that CNTs are localized in PE phase while the alternating multilayer structure with different polymer phases elongated as well as conductive network oriented parallel to flow direction is observed. To form such alternating layered structure, the dispersed phases are firstly deformed into discontinuous layers, and finally further deformed into wide and regular continuous alternating layers. In term of the mechanism behind this, the good viscosity match, low interfacial tension between different polymer components, short relaxation time and high shear rate are thought as important issues. The anisotropic conductive behavior of these CPCs, i.e. conductive in longitudinal (parallel to flow direction) and transverse (perpendicular to flow direction) direction but non-conductive in thickness direction, is contributed by the insulating PP layer which cuts off the conductive networks in the core layer. More importantly, much better electromagnetic interference (EMI) shielding ability is obtained for these CPCs with alternating multilayer conductive networks comparing with the same polymer blends with isotropic conductive networks, despite of the fact that much lower resistivity is obtained for the later. This indicates great potential of these anisotropic CPCs for electronic applications. Moreover, this study has shed some light on the potential use of such alternating multi-layered structure to prepare a range of multi-functional materials.     

Conductive polymer tape containing highly oriented carbon nanofillers

The effect of the orientation of carbon fillers with different aspect ratios on the resistivity and morphology of conductive polymer composites (CPCs) based on polypropylene was investigated in this study. Multiwall carbon nanotubes (MWNTs) and carbon black (CB) were used as conductive fillers. The CPCs were made by melt compounding, hot pressing, and solid‐state drawing. The alignment of the filler was observed after solid‐state drawing. The resistivity of the composites increased with the draw ratio at relatively low carbon filler loadings (<20 wt %), whereas it remained unchanged at a high filler loading (20 wt % CB). Orientation‐promoted anisotropy of the conductive network was observed in both the morphology and resistivity. MWNTs were found to be better at maintaining a percolating network under large deformations than CB because of their larger aspect ratio and their entangled network structure. The experimentally obtained resistivity was analyzed with percolation theory, and this indicated that the initial three‐dimensional conductive network was deformed into a two‐dimensional network after solid‐state drawing for the composites containing CB. The three‐dimensional network was found in isotropic CPCs containing MWNTs with the same analysis. Theoretical analysis using excluded volume theory was in good agreement with results obtained experimentally. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Enhancement in the osteogenesis and angiogenesis of calcium phosphate cement by incorporating magnesium-containing silicates

Based on the good osteogenic and angiogenic effects of silicon and magnesium elements, three types of micro-nano magnesium-containing silicates (MS), including akermanite (Ake, Ca₂MgSi₂O₇), diopside (Dio, CaMgSi₂O₆) and forsterite (For, Mg₂SiO₄), were incorporated into calcium phosphate cement (CPC) to improve its osteogenic and angiogenic performances for clinical application. In this present work, the physicochemical properties, osteogenesis and angiogenesis of MS/CPCs (Ake/CPCs, Dio/CPCs and For/CPCs) were investigated systematically and comparatively. The results showed that all MS/CPCs had good biomineralization and significantly stimulated the osteogenic differentiation of mBMSCs and angiogenic differentiation of HUVECs, respectively. Besides, the stimulating effects were related to not only the category of MS, but also the content of MS. The For/CPCs had a good angiogenic property but their initial setting times were beyond 60 min. The Dio/CPCs showed the lowest biological performance among the three groups of MS/CPCs due to the lower ion release (Si and Mg). The Ake was the ideal modifier that could provide CPC with appropriate physicochemical properties, better osteogenesis and angiogenesis. Simultaneously, a higher addition (10 wt%) of akermanite resulted in the best potential to bone regeneration. Taken together, this research provides an effective approach to improve the overall performance of CPC, and 10Ake/CPC is of great promising prospect in bone repair.     

Dependence of CPC cut-off diameter on particle morphology and other factors

In this investigation, we summarize performance parameters of 24 TSI CPCs model 3772 and 9 TSI CPCs model 3790 determined at the World Calibration Aerosol Centre Physics hosted by the Leibniz Institute for Tropospheric Research. Model 3790 CPCs are basically identical to model 3772 laminar continuous flow type butanol-based CPCs with a modified temperature difference between saturator and condenser. The average 50% detection efficiency for silver particles for 3772 and 3790 instruments was found to be 7.52 ± 0.04 nm and 24.34 ± 0.29 nm (average mobility diameter ± standard deviation), respectively. Small changes of the temperature difference between saturator and condenser cause larger shifts of the 50% detection efficiencies of 3790 CPCs compared to 3772 CPCs. In addition to the known calibration material dependence of the 50% detection efficiencies of 3790 CPCs, we found a dependence on the morphology of the particles used for calibration. In our experiments more spherical particles shifted the 50% detection efficiencies towards larger mobility diameters.

Copyright © 2016 American Association for Aerosol Research     

Synthesis and characterization of radio‐opaque thermosensitive poly[N‐isopropylacrylamide‐2,2′‐(ethylenedioxy)bis(ethylamine)‐2,3,5‐triiodobenzamide]

BACKGROUND: In situ gelling polymers, like poly(N‐isopropylacrylamide) (poly(NIPAAm)), have many potential medical applications due to their biocompatibility and thermosensitivity. RESULTS: Radio‐opaque thermosensitive poly(NIPAAm) grafted with 10.7 wt% 2,2′‐(ethylenedioxy)bis(ethylamine)‐2,3,5‐triiodobenzamide was successfully synthesized and characterized. The conjugated polymer showed good visibility with X‐ray fluoroscopy. The polymer had a lower critical solution temperature of 30 °C after conjugation with triiodobenzamide as determined by cloud point determination and a transition peak temperature of 33.3 ± 0.57 °C as determined by differential scanning calorimetry. CONCLUSION: The polymer synthesized was highly visible under X‐rays, based upon the percentage incorporation of triiodobenzamide. After conjugation of the NIPAAm to the triiodobenzamide through a bis(ethylamine) linkage, the resultant polymer retained lower critical solution temperature characteristics in a temperature region that makes it physiologically useful. Copyright © 2009 Society of Chemical Industry     

Polymer/carbon nanotube composites for liquid sensing: Model for electrical response characteristics

Electrically conductive polymer composites (CPCs) based on carbon nanotubes (CNTs) and polycarbonate were investigated regarding their electrical resistance change in different solvents like tetrahydrofuran, acetone, and ethyl acetate. CPCs containing 0.086 to 2.778 vol.% CNT were melt mixed using a twin-screw extruder under optimised conditions and subsequently compression-moulded.All sensing experiments revealed a resistance increase of CPCs having a U-shaped sample geometry during solvent immersion. Light microscopy investigations have shown that the diffusion of solvents into CPCs can be monitored in terms of a pronounced diffusion front, separating a swollen skin from the dry core. Based on this observed skin-core morphology, a model allowing the calculation of the time depending relative resistance change has been proposed considering several factors like diffusion parameters, composite characteristics, and geometrical values.Simulated response curves based on the model were compared with experimental data obtained on the CPCs and very good agreement was observed. Using this model the influence of CNT content and kind of solvent could be described exactly.     

The effect of gamma irradiation on the pressure dependence of the room temperature transition in PTFE

Some of the effect of gamma irradiation on the pneumatic pressure dependence of the well established room temperature transition (ca. 19 °C) in polytetra(fluoroethylene) are described. The experiments, conducted up to a maximum gamma dosage of 60 Mrad and a superimposed nitrogen pressure of 48.3 MPa indicate a significant reduction in the room temperature transition as well as its pressure dependence with the increasing of the gamma dosage. These data, combined with the observed and reported reduction in the free volume (actually net volume) are consistent with the proposition that irradiation process results in a reduction in the ‘effective internal pressure’ due to extensive bond scission. The latter process is manifested in an observed dramatic decrease in the molecular weight. Data on the compressibility and coefficient of thermal expansion, accompanied by thermodynamic arguments, indicate that the room temperature transition more closely resembles a second order transition as gamma dosage increases. This is consistent with a change in system behaviour progressing from a viscoelastic to that of a brittle glassy polymer as confirmed by monitoring the polymer creep behaviour following rapid pressurisation. Data for the ‘freshly’ irradiated specimens indicate highly transient post-irradiation induced changes in the polymer morphology.     

Functionalized silk promotes cell migration into calcium phosphate cements by providing macropores and cell adhesion motifs

Calcium phosphate cements (CPCs) are attractive synthetic bone grafts as they possess osteoconductive and osteoinductive properties. Their biomimetic synthesis grants them an intrinsic nano- and microporosity that resembles natural bone and is paramount for biological processes such as protein adhesion, which can later enhance cell adhesion. However, a main limitation of CPCs is the lack of macroporosity, which is crucial to allow cell colonization throughout the scaffold. Moreover, CPCs lack specific motifs to guide cell interactions through their membrane proteins. In this study, we explore a strategy targeting simultaneously both macroporosity and cell binding motifs within CPCs by the use of recombinant silk. A silk protein functionalized with the cell binding motif RGD serves as foaming template of CPCs to achieve biomimetic hydroxyapatite (HA) scaffolds with multiscale porosity. The synergies of RGD-motifs in the silk macroporous template and the biomimetic features of HA are explored for their potential to enhance mesenchymal stem cell adhesion, proliferation, migration and differentiation. Macroporous Silk-HA scaffolds improve initial cell adhesion compared to a macroporous HA in the absence of silk, and importantly, the presence of silk greatly enhances cell migration into the scaffold. Additionally, cell proliferation and osteogenic differentiation are achieved in the scaffolds.     

Photonics based on carbon nanotubes

Among direct-bandgap semiconducting nanomaterials, single-walled carbon nanotubes (SWCNT) exhibit strong quasi-one-dimensional excitonic optical properties, which confer them a great potential for their integration in future photonics devices as an alternative solution to conventional inorganic semiconductors. In this paper, we will highlight SWCNT optical properties for passive as well as active applications in future optical networking. For passive applications, we directly compare the efficiency and power consumption of saturable absorbers (SAs) based on SWCNT with SA based on conventional multiple quantum wells. For active applications, exceptional photoluminescence properties of SWCNT, such as excellent light-emission stabilities with temperature and excitation power, hold these nanometer-scale materials as prime candidates for future active photonics devices with superior performances.     

Structural methacrylate/epoxy based adhesives for aluminIum joints

The aim of this work was to investigate the influence of elastomer and monomer concentration on the properties of methacrylate/epoxy based adhesive formulations using a Plackett-Burman experimental design. The adhesive formulations were developed in order to bond non-treated aluminium panels. Their chemical structure was analysed by Fourier transformed infrared spectroscopy (FTIR) and the thermal behaviour by thermogravimetry (TGA) and differential scanning calorimetry (DSC) in comparison to a commercial adhesive. After room temperature mixing, time and temperature of the curing reaction were measured. Further, non-treated aluminium single-lap joints were adhesively bonded and their shear strengths were evaluated. The formulations showed chemical structure similar to a commercial adhesive but the thermal behaviour was quite distinct. The commercial adhesive cured slower than the developed adhesive formulations which can directly affect the bonding quality. However, some formulations showed higher shear strengths than the commercial one, but all with adhesive failure mode. The adhesive formulations with elastomers in methacrylate part showed the highest shear strengths.     

Anomalous luminescence phenomena of indium-doped ZnO nanostructures grown on Si substrates by the hydrothermal method

In recent years, zinc oxide (ZnO) has become one of the most popular research materials due to its unique properties and various applications. ZnO is an intrinsic semiconductor, with a wide bandgap (3.37 eV) and large exciton binding energy (60 meV) making it suitable for many optical applications. In this experiment, the simple hydrothermal method is used to grow indium-doped ZnO nanostructures on a silicon wafer, which are then annealed at different temperatures (400°C to 1,000°C) in an abundant oxygen atmosphere. This study discusses the surface structure and optical characteristic of ZnO nanomaterials. The structure of the ZnO nanostructures is analyzed by X-ray diffraction, the superficial state by scanning electron microscopy, and the optical measurements which are carried out using the temperature-dependent photoluminescence (PL) spectra. In this study, we discuss the broad peak energy of the yellow-orange emission which shows tendency towards a blueshift with the temperature increase in the PL spectra. This differs from other common semiconductors which have an increase in their peak energy of deep-level emission along with measurement temperature.     

以聚乳酸为基体的导电高分子复合材料研究进展

概括了导电填料种类、结构及成型方法、工艺条件等因素对单相聚乳酸(PLA)基导电高分子复合材料(CPCs)电学性能的影响,介绍了PLA基多相CPCs中导电填料选择性分布机制和较低逾渗值的机理,总结了PLA基CPCs在有机溶剂中的响应行为,并对材料的应用前景进行了展望。     

Setting properties,mechanical strength and in vivo evaluation of calcium phosphate-based bone cements

Calcium phosphate cement (CPC) is a promising material for use in minimally invasive surgery for bone defect repair due to its similarity to the mineral phase of bone, biocompatibility, bioactivity, self-setting characteristics, low setting temperature, adequate stiffness and ease of shaping in complicated geometrics. In this study, we systematically investigate the influence of preparation variables on the final properties of CPCs. We determined the effects of CPC composition, accelerators, seed hydroxyapatite and reaction temperatures on the setting times and compressive strength of CPCs based on tetracalcium phosphate (TTCP), dicalcium phosphate dehydrate (DCPD), dicalcium phosphate anhydrous (DCPA), and α-tricalcium phosphate (α-TCP). The three types of CPCs (TTCP/DCPD, TTCP/DCPA, and TTCP/α-TCP-based bone cements) were prepared by varying the amounts of seed hydroxyapatite and citric acid used as a hardening accelerator. After 24 h of incubation, all three types of bone cements exhibited the characteristic peaks attributable to hydroxyapatite (HA) without characteristic peaks of unreacted raw materials. These results indicated that the bone cements were completely converted to HA. TTCP/DCPD-based bone cements showed faster setting times than TTCP/DCPA and TTCP/α-TCP-based bone cements. As citric acid concentrations in the liquid phase increased, the setting times of all three types of bone cements gradually decreased. However, the concentrations of seed HA in the cements were not related to significant changes in setting time. The compressive strengths of CPCs were significantly influenced by composition and reaction temperature. We also studied the effects of immersion time in physiological solution on the properties of the various CPCs. In the results of in vivo tests, subjects with bone defects implanted with CPCs exhibited more bone formation than control subjects that did not receive implantations of CPCs.     

Flexible poly(styrene-ethylene-butadiene-styrene) hybrid nanofibers for bioengineering and water filtration applications

Among the thermoplastic elastomers that play important roles in the polymer industry due to their superior properties, styrene-based species and polyurethane block copolymers are of great interest. Poly(styrene-ethylene-butadiene-styrene) (SEBS) as a triblock copolymer seems to have the potential to meet many demands in different applications due to various industrial requirements where durability, biocompatibility, breaking elongation, and interfacial adhesion are important. In this study, the SEBS triblock copolymer was functionalized with natural (Satureja hortensis, SH) and synthetic (nanopowder, TiO₂) agents to obtain composite nanofibers by electrospinning and electrospraying methods for use in biomedical and water filtration applications. The results were compared with thermoplastic polyurethane (TPU) composite nanofibers, which are commonly used in these fields. Here, functionalized SEBS nanofibers exhibited antibacterial effect while at the same time improving cell viability. In addition, because of successful water filtration by using the SEBS composite nanofibers, the material may have a good potential to be used comparably to TPU for the application.     

Progress on the morphological control of conductive network in conductive polymer composites and the use as electroactive multifunctional materials

Since the emergence of large aspect ratio and multifunctional conductive fillers, such as carbon nanotubes, graphene nanoplates, etc., conductive polymer composites (CPCs) have attracted increasing attention. Although the morphological control of conductive networks in CPCs has been extensively investigated as an important issue for the preparation of high performance CPCs, recent extensive progress has not been systematically addressed in any review. It has been observed that the morphological control of conductive networks during the preparation of CPCs has crucial influence on the electrical properties of these composites. Several methods have been shown to be able to control the network structure, and thus, tune the electrical properties of CPCs, including the use of shear, polymer blends, thermal annealing, mixed filler, latex particle etc. Moreover, many novel and exciting applications have been extensively investigated for CPCs, such as stretchable conductor, electroactive sensors, shape memory materials and thermoelectric materials, etc. Therefore, the morphological control of conductive network in CPCs is reviewed here. Issues regarding morphology characterization methods, morphological control methods, resulted network morphology and electrical properties are discussed. Furthermore, the use of CPCs as electroactive multifunctional materials is also reviewed.     

CPCs在应力场下的性能演变及机理研究进展

综述了导电高分子复合材料(CPCs)在压缩应力场、拉伸应力场及应力-应变循环力场中电阻率随应力、应变、循环次数及时间等的变化规律,分析了CPCs在上述应力场中电阻率变化与其微观结构演变之间的关系,结合导电粒子在高分子基体中的位置改变及导电粒子与高分子基体间相互作用,归纳了CPCs电性能在上述外力场中的演变机制。针对目前该复合材料在上述循环应力场中出现的磁滞效应和可重复性差等问题,归纳了相应的改善方法。简要概括了CPCs的工业应用。     

高分子基导电复合材料研究进展

高分子基导电复合材料凭借其导电性、稳定性、加工性等方面的明显优势,成为导电材料研究的热点。系统地介绍了复合型导电高分子材料的导电机理、制备方法并对导电复合材料的应用进行了总结,并展望了导电高分子复合材料的发展趋势。