Disruption of self-assembly and altered mechanical behavior in polyurethane/zinc oxide nanocomposites

The addition of less than 1 vol%, 33 nm zinc oxide nanoparticles into a polyurethane matrix resulted in approximately 40% decrease in the Young's modulus, 80% decrease in strain at fracture, and 50% decrease in the storage modulus, but at the same time resulted in an ∼11 °C increase in the glass transition temperature of the polymer. These results appear to contradict the general principle observed for many polymeric systems, where higher glass transition temperature generally means higher elastic modulus. Detailed experiments with FTIR, DMTA, FE-SEM, and AFM indicated that the addition of ZnO nanoparticles disrupts the phase separation in the polymer, resulting in weaker mechanical properties. The special interaction between the particles and polymer possibly constrains the mobility of polymer chains, which increases the glass transition temperature. The most likely reason for the disruption and the nature of the interaction is the reaction between the surface hydroxyl groups of the zinc oxide nanoparticles and the isocyanate groups of the polyurethane pre-polymer.     

Synthesis of chain-extended organifier and properties of polyurethane/clay nanocomposites

Clay organifier with hydroxyl end-group and relatively high molecular weight was synthesized. The clay treated with the organifier was suspended in DMF and the dispersibility of organoclay in polyurethane matrix was enhanced by applying the sonication to the suspension of organoclay in DMF. The d-spacing of organoclay was found to be 2.29 nm compared to 1.18 nm of pristine montmorillonite. The polyurethane/clay nanocomposites formed an intercalated structure with some disorder and their d-spacings were about 2.6-2.7 nm. The barrier property, thermal stability and tensile properties significantly increased with increasing the dispersibility of organoclay. A 2.9-fold increase in tensile strength with 1 wt% of well-dispersed organoclay, a 41% decrease in oxygen permeability and a 1.7-fold increase in Young's modulus at 5 wt% of well-dispersed organoclay were achieved.     

Characteristics of polyurethanes incorporating starch granules

Polyurethanes containing different starch contents were synthesized in a one-step reaction by suspending starch granules in polycaprolactone diol, MDI and 1,4 butane diol in a bulk phase at 175 °C. The products were characterized by FTIR spectroscopy, SEM, DSC, and swelling behavior. Their mechanical properties, e.g. tensile strength and elongation, were measured for different starch contents. The starch dispersed well as a grafted state in the polyurethane phase. The grafted percentage of polyurethane to starch granules increased with the starch content to a maximum point (about 20 wt%) and then decreased due to gapping between the two phases and probably the homo-polymerization tendency of the polyurethane. The DSC indicated that T_g increased with the starch content due to the decreased average molecular weight of the homo-polyurethane. Three endothermic transitions at 60-70 °C (I), ∼150 °C (II), 190-210 °C (III) were observed. Transition I was not changed by the starch content, whereas transition II appeared only for the psb2m3 series (32-48 wt% hard segment) at the lower range of 26 wt% of starch content. The temperature of transition III, which is related to the melting point of the hard segments, increased with the starch content despite a decrease in the molecular weight of the homo-polyurethane. The tensile strength and the elongation of the polymers slightly increased or were constant up to about 20 wt% of starch, and then decreased rapidly because of phase separation (gapping) between the starch granules and the polyurethane phase and division of the starch granules.     

The use of nanoclay in preparation of epoxy anticorrosive coatings

Epoxy/clay nanocomposites (NC) have become a very interesting topic among researchers in the past two decades because nanoclays have a positive effect on the mechanical, thermal and especially barrier and anticorrosive performances of the polymers. In this study epoxy NCs and NC-based epoxy coatings were prepared by the solution intercalation method using Cloisite 30B as nanoclay. WAXD and SEM analyses revealed that a mainly exfoliated structure was obtained in epoxy NC with 1 wt% clay content, while higher clay loadings reduced the number of exfoliated clay nanolayers and produced a mainly intercalated structure. EIS, TGA and DMA analyses showed that epoxy NCs with clay content below 5 wt% exhibited increased corrosion stability, thermal stability, glass transition temperature (T_g) and storage modulus (G′), in both glassy and rubbery states due to the nanoscale dispersion of Cloisite 30B and the barrier effect of individual nanolayers. Enhanced mechanical properties were also noticed at higher clay loadings, but the rate of improvement was lower. The highest extent of exfoliation and the most homogeneous macromolecular network was found for NC with 1 wt% of clay, leading to the highest improvement of thermal and anticorrosive properties. The salt spray test results showed that anticorrosive properties of epoxy coatings in the presence of 3 wt% and especially 1 wt% of Cloisite 30B were significantly better, thus indicating that nanoclay efficiently modifies the commercial epoxy coatings.     

Preparation, characterization and mechanical properties of epoxidized soybean oil/clay nanocomposites

New epoxidized soybean oil (ESO)/clay nanocomposites have been prepared with triethylenetetramine (TETA) as a curing agent. The dispersion of the clay layers is investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM data reveal the intercalated structure of ESO/clay nanocomposites has been developed. The thermogravimetric analysis exhibits that the ESO/clay nanocomposites are thermally stable at temperatures lower than 180 °C, with the maximum weight loss rate after 325 °C. The glass transition temperature, T_g, about 7.5 °C measured by differential scanning calorimetry (DSC) and T_g about 20 °C measured by dynamic mechanical study have been obtained. The difference in the T_g between DSC and dynamic measurements may be caused by different heating rate. The nanocomposites with 5-10 wt% clay content possess storage modulus ranging from 2.0×10⁶ to 2.70×10⁶ Pa at 30 °C. The Young's modulus (E) of these materials varies from 1.20 to 3.64 MPa with clay content ranging from 0 to 10 wt%. The ratio of epoxy (ESO) to hydrogen (amino group of TETA) greatly affects dynamic and tensile mechanical properties. At higher amount of TETA, the nanocomposites exhibit stronger tensile and dynamic properties.     

UV-cured clay/based nanocomposite topcoats for wood furniture. Part II: Dynamic viscoelastic behavior and effect of relative humidity on the mechanical properties

Topcoat constituting multi-layer coatings for wood furniture used in high humidity environments, like bathrooms, must have not only good barrier properties, but also good mechanical properties. Three different types of commercial organoclays, namely Cloisite 10A (C10A), Cloisite 15A (C15A) and Cloisite 30B (C30B), were chosen in this study as reinforcing agents. These nanoparticles were dispersed (1 and 3 wt% into the formulation) into a commercial epoxy acrylate oligomer by means of a three roll mill. Samples obtained from free standing UV-cured coatings were used for mechanical assessments. Mechanical tests were performed in both dynamic and static mode in order to investigate the viscoelastic behavior and tensile properties of coatings. Results from dynamic mechanical analysis have shown that all nanocomposite coatings have higher (72–75 °C) glass transition temperature compared to that observed (71 °C) in unreinforced coatings. The restriction of polymer chains mobility, due to the presence of layered silicate nanoparticles, has been used to explain the increase of glass transition temperature related to the decrease of the free volume. The storage modulus for nanocomposites containing 3 wt% of C10A, C15A and C30B was found to be slightly higher than that observed in pure coatings. The analysis of tensile stress–strain curves has revealed that tensile properties are affected by relative humidity (RH) due to the plasticization effect of humidity. In fact, results have shown that regardless of the organoclay type, the increase of RH decreases both Young's modulus and tensile strength while increasing maximum strain. We believe that low interfaces between photocrosslinked polymer chains and organoclays explain the lack of any effect of organoclays on both storage and Young's moduli. Among samples from each type of UV-cured coating tested at 0, 20 and 80% of RH, regardless of the organoclay type and content, only samples tested (tensile tests in static mode) at RH = 80% were broken. SEM images obtained from the fractured surface of these samples have shown that unreinforced UV-cured coatings and nanocomposite coatings are respectively characterized by smooth and rough fracture surface.     

Synthesis and characterization of novel UV-curable polyurethane–clay nanohybrid: Influence of organically modified layered silicates on the properties of polyurethane

Nanohybrids based on UV-curable polyurethane acrylate (PU) and cloisite 20B (C-20B) have been synthesized by solution blending method using different loading levels of C-20B. The structures of PU/C-20B nanohybrids were confirmed by Fourier transform infrared spectroscopy (FTIR) while X-ray diffraction and transmission electron microscopy (TEM) showed the intercalation of PU into layer silicates. The thermal properties of PU and PU/C-20B nanohybrids were investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetric (DSC). TGA tests revealed that the thermal decomposition temperature (T_d10%) of the nanohybrid containing 5 wt% of C-20B increased significantly, being 61 °C higher than that of pure PU while DSC measurements indicated that the introduction of 5 wt% of clay increased the glass transition temperature from 89.7 to 101 °C. Accordingly, the mechanical and anti-water absorption properties proved also to be enhanced greatly as evidenced by nanoindentation anylsis and water absorptions data in which the nanohybrid containing 5 wt% of clay have highest elastic modulus (4.508 GPa), hardness (0.230 GPa) and lowest water absorption capacity. Thus the formations of nanohybrids manifests through the enhancement of thermal, mechanical and anti-water absorption properties as compared with neat PU due to the nanometer-sized dispersion of layered silicate in polymer matrix.     

Transparent and thermally stable improved poly (vinyl alcohol)/Cloisite Na/ZnO hybrid nanocomposite films: Fabrication,morphology and surface properties

A series of poly(vinyl alcohol)/Cloisite Na⁺-Tyrosine/Zinc oxide (PVA/Cloisite Na⁺-Tyr/ZnO) bionanocomposites were prepared by dispersing ZnO nanoparticles in solution containing mixture of the PVA and modified Cloisite Na⁺. Structure of nanocomposite coatings was investigated by X-ray diffraction and Fourier-transform infrared spectroscopy. The thermal stability and optical properties of bionanocomposite were characterized by thermogravimetric analysis and UV–vis spectroscopy, respectively. The introduction of ZnO nanoparticles into PVA/Cloisite Na⁺-Tyr mixed solutions significantly increased the thermal stability of the obtained films. The results revealed that the high UV-shielding efficiency of the composites: for a film containing 6.0 wt% of ZnO nanocrystals, over 92% of UV light at wavelengths of 368 nm was absorbed while the optical transparency in the visible region was slightly below that of a PVA/Cloisite Na⁺-Tyr film.     

Ionene segmented block copolymers containing imidazolium cations: Structure-property relationships as a function of hard segment content

Imidazolium ionene segmented block copolymers were synthesized from 1,1′-(1,4-butanediyl)bis(imidazole) and 1,12-dibromododecane hard segments and 2000 g/mol PTMO dibromide soft segments. The polymeric structures were confirmed using ¹H NMR spectroscopy, and resonances associated with methylene spacers from 1,12-dibromododecane became more apparent as the hard segment content increased. TGA revealed thermal stabilities ≥250 °C for all imidazolium ionene segmented block copolymers. These ionene segmented block copolymers containing imidazolium cations showed evidence of microphase separation when the hard segment was 6-38 wt%. The thermal transitions found by DSC and DMA analysis found that the T_g and T_m of the PTMO segments were comparable to PTMO polymers, namely approximately −80 °C and 22 °C, respectively. In the absence of PTMO soft segments the T_g increased to 27 °C The crystallinity of the PTMO segments was further evidence of microphase separation and was particularly evident at 6, 9 and 20 wt% hard segment, as indicated in X-ray scattering. The periodicity of the microphase separation was well-defined at 20 and 38 wt% hard segment and found to be approximately 10.5 and 13.0 nm, respectively, for these ionenes wherein the PTMO soft segment is 2000 g/mol. Finally, the 38 and 100 wt% hard segment ionenes exhibited scattering from correlations within the hard segment on a length scale of approximately 2-2.3 nm. These new materials present structure on a variety of length scales and thereby provide various routes to controlling mechanical and transport properties.     

Phase separation and phase inversion of polyurethane networks

A series of polyurethane networks were prepared from MDI (4,4¹-diphenyl methane diisocyanate), ethylene glycol and a polyoxyethylene-tipped polyoxypropylene triol. The phase separation and phase inversion phenomena of these polyurethane networks were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and measurement of their tensile properties. The DSC and DMA data indicate that the segmented copolyurethanes possess a two-phase morphology comprising soft and hard segments. It can be found from DSC data that the polyether soft segments exhibit a T_g (glass transition temperature) of –60 °C, and the aromatic hard segments display a T_g of about 128 °C. Two T_gs corresponding to the comprised segments can also be found by DMA for some segmented polyurethanes. Varying the content of aromatic hard segments over the range from 0 to 80 wt% changes the material behavior from a soft rubber through a highly extensible elastomer to a brittle semi-ductile glassy material. Based on the property-composition plots, phase inversion appears to occur at a hard segment content of about 50 wt%.     

Nanostructure and dynamic mechanical properties of silane-functionalized montmorillonite/epoxy nanocomposites

In this work sodium montmorillonite (Na-MMT) was functionalized with N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane and the corresponding silylated clay was used to modify epoxy matrix cured with triethylenetetramine. The grafting/intercalation of the aminosilane inside the clay galleries were followed by infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and ²⁹Si cross-polarization magic-angle-spinning nuclear magnetic-resonance (CP/MAS NMR) spectroscopy. Epoxy-based nanocomposites were prepared with different amounts of silylated clay or commercial organoclay, Cloisite 30B, whose intercalating agent consists of a methyl, tallow, bis-2-hydroxyethyl quaternary ammonium salt. The degree of intercalation/exfoliation was estimated by X-ray diffraction experiments and confirmed by small angle X-ray scattering. Nanocomposites prepared with silylated clay displayed no peak in both XRD and SAXS curves whereas those prepared with Cloisite 30B exhibited a clear interference peak corresponding to an interlayer spacing d₀₀₁ of 4.1 nm. The former also presented a better dispersion, with a high proportion of tactoids smaller than 2 nm, as estimated by SAXS. From the results of dynamic mechanical analysis it was observed that most of the nanocomposites display higher storage modulus mainly at temperatures above the glass transition temperature. The glass transition temperature is similar or higher than the neat epoxy network for nanocomposites containing 1 wt.% of silylated clay or higher.     

Miscibility and viscoelastic properties of acrylic polyhedral oligomeric silsesquioxane-poly(methyl methacrylate) blends

We investigate the miscibility of acrylic polyhedral oligomeric silsesquioxanes (POSS) [characteristic size d≈2 nm] and poly(methyl methacrylate)(PMMA) in order to determine the effect of well-dispersed POSS nanoparticles on the thermomechanical properties of PMMA. Two different acrylic POSS species (unmodified and hydrogenated) were blended separately with PMMA at volume fractions up to ?=0.30. Both POSS species have a plasticizing effect on PMMA by lowering the glass transition temperature T_g and decreasing the melt-state linear viscoelastic moduli measured in small amplitude oscillatory shear flow. The unmodified acrylic-POSS has better miscibility with PMMA than the hydrogenated form, approaching complete miscibility for loadings ?<0.10. At a loading ?=0.05, the unmodified acrylic POSS induces a 4.9 °C decrease in the T_g of PMMA, far less than the 17.4 °C decrease in the glass transition temperature observed in a blend of 5 vol% dioctyl phthalate (DOP) in PMMA; however, the decrease in the glass transition temperature per added plasticizer molecule is nearly the same in the unmodified acrylic-POSS-PMMA blend compared with the DOP-PMMA blend. Time-temperature superposition (TTS) was applied successfully to the storage and loss moduli data and the resulting shift factors were correlated with a significant increase in free volume of the blends. The fractional free volume f₀=0.046 for PMMA at T₀=170 °C while for a blend of 5 vol% unmodified acrylic-POSS in PMMA f₀=0.057, which corresponds to an addition of 0.47 nm³ per added POSS molecule at ?=0.05. The degree of dispersion was characterized using both wide-angle X-ray diffraction (WAXD) and dynamic mechanical analysis (DMA). Diffraction patterns for both blend systems show clear evidence of phase separation at ?=0.20 and higher, but no significant phase separation is evident at ?=0.10 and lower. The storage modulus measured in DMA indicates appreciable phase separation for unmodified acrylic POSS loadings ?≥0.10, while no evidence of phase separation is present in the ?=0.05 blend in DMA.     

Effects of bismuth oxide on the sinterability of hydroxyapatite

The sinterability of Bi₂O₃-doped hydroxyapatite (HA) has been studied and compared with the undoped HA. Varying amounts of Bi₂O₃ ranging from 0.05 wt% to 1.0 wt% were mixed with the HA. The study revealed that most sintered samples composed of the HA phase except for compacts containing 0.3, 0.5 and 1.0 wt% Bi₂O₃ and when sintered above 1100 °C, 1000 °C and 950 °C, respectively. In general, the addition of 0.5 wt% Bi₂O₃ was identified as the optimum amount to promote densification as well as to improve the mechanical properties of sintered HA at low temperature of 1000 °C. Throughout the sintering regime, the highest value of relative bulk density of 98.7% was obtained for 0.5 wt% Bi₂O₃-doped HA when sintered at 1000 °C. A maximum Young's modulus of 119.2 GPa was measured for 0.1 wt% Bi₂O₃-doped HA when sintered at 1150 °C. Additionally, the ceramic was able to achieve highest hardness of 6.08 GPa and fracture toughness of 1.21 MPa m^1/2 at sintering temperature of 1000 °C.     

Fabrication and characterization of ZnO modified bioactive glass nanoparticles

Bioactive glass nanoparticles in the system (SiO₂-CaO-P₂O₅-ZnO) were synthesized following the sol-gel technique. The prepared glass nanoparticles of 1, 3 and 5 wt% of ZnO (coded: GZ1, GZ3 and GZ5, respectively) were characterized by TEM, FTIR, XRF, TGA and DSC. All glass powders had particle sizes less than 100 nm. Textural analysis revealed that for GZ1, GZ3 and GZ5, the average pore diameters, measured by the high-speed gas sorption analyzer, were 15.9, 15.4 and 15.2 nm, respectively, while the average pore diameters measured by the mercury intrusion porosimetry were 47, 50 and 63 nm, respectively. All glass powders were highly porous (75, 76 and 75%) with surface areas of 233, 94 and 118 m²/g for GZ1, GZ3 and GZ5, respectively. All glass powders induced an apatite layer on their surfaces upon immersion in simulated body fluid (SBF) as verified by SEM and TF-XRD.     

Effect of hydrogen bonding on the rheology of polycarbonate/organoclay nanocomposites

The linear dynamic viscoelastic properties and non-linear transient rheology of polycarbonate (PC)/clay nanocomposites were investigated at temperatures ranging from 240 to 280 °C. For the study, nanocomposites of PC and natural montmorillonite (Cloisite Na⁺) or chemically modified clay (Cloisite 30B) were prepared by melt blending in a twin-screw extruder. Cloisite 30B is a natural montmorillonite modified with methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium chloride (MT2EtOH). In both PC/Cloisite Na⁺ and PC/Cloisite 30B nanocomposites the concentration of clay was varied from 2.3 to 4.3 wt%. In situ Fourier transform infrared (FTIR) spectroscopy results show that at temperatures ranging from 30 to 280 °C the carbonyl groups in PC and the hydroxyl groups in MT2EtOH of Cloisite 30B in PC/Cloisite 30B nanocomposites formed hydrogen bonds, while no evidence of hydrogen bonding was observed in the PC/Cloisite Na⁺ nanocomposites. There are no discernible sharp reflections in the X-ray diffraction (XRD) patterns of PC/Cloisite 30B nanocomposites, after Cloisite 30B having the d₀₀₁ spacing of 1.85 nm was mixed with PC, whereas the d₀₀₁ spacing changes little (1.17 nm) before and after the mixing of Cloisite Na⁺ to PC. Transmission electron microcopy (TEM) images show that organoclay platelets are well dispersed in PC/Cloisite 30B nanocomposites, while the untreated clay platelets are poorly dispersed in PC/Cloisite Na⁺ nanocomposites. The observed differences in XRD patterns and TEM images between the two nanocomposite systems are explained by in situ FTIR spectroscopy. The results of rheological measurements (linear dynamic viscoelasticity, non-linear transient shear flow, and steady-state shear flow) support the conclusions drawn from the results of XRD, TEM, and FTIR spectroscopy.     

Preparation and properties of starch thermoplastics modified with waterborne polyurethane from renewable resources

A waterborne polyurethane (PU) aqueous dispersion was synthesized from castor oil, and blended with thermoplastic starch (TPS) to obtain a novel biodegradable plastic with improved physical properties. The effect of PU content on the morphology, miscibility and physical properties of the resulting blends was well investigated by scanning electron microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis and measurements of mechanical properties and water sensitivity. The research results show that the blends exhibit a higher miscibility when PU content is lower than 15 wt% due to the hydrogen bonding interaction between urethane groups and hydroxyl groups on starch, whereas obviously phase separation occurs in the blends with more than 15 wt% PU. Incorporating PU of 4-20 wt% in TPS results in the blends with improved Young's modulus (40-75 MPa), tensile strength (3.4-5.1 MPa), elongation at break (116-176%). Further, PU also plays an important role in improving the surface- and bulk-hydrophobicity and water resistance of the resulting blends.     

High improvement in the properties of exfoliated PU/clay nanocomposites by the alternative swelling process

In this work, a stable de-aggregated solvent-swollen organic modified clay, ALA-MMT, suspension is prepared by an efficient solvent swelling process using a home-made shaking mixer. It is found that the estimated average size of the as-prepared organoclay particles in the suspension is reduced to about 155 nm, which has not been reported before. The X-ray diffraction (XRD) patterns confirm that the d-spacing of the silicate layers of the solvent-swollen ALA-MMT expands from 1.4 nm to about 2.1 nm. The de-aggregated solvent-swollen ALA-MMT suspension is then used with polyurethane (PU) to prepare a series of highly exfoliated and high-organoclay-loading nanocomposites, PU/ALA-MMT. Both the XRD patterns and the TEM photographs of the as-prepared PU/ALA-MMT nanocomposites indicate that the organoclay is uniformly dispersed in the PU matrix with a highly exfoliated morphology structure of up to 7 wt% loading. Meanwhile, the TEM photographs give the first report for PU/clay nanocomposites which are almost completely exfoliated, and ∼1-nm thin silicate nanolayers are homogeneously dispersed in the polymer matrix with a high aspect ratio of 30-100. The thermal, mechanical, and anti-corrosion properties are all tremendously enhanced for the as-prepared nanocomposites. The results obtained for the PU nanocomposite with 7 wt% ALA-MMT loading (PUC7) reveal a 19 °C increment in T_g, a 48 °C increment in T_5%, a 248% increase in the tensile strength, and a 123% increase in the elongation. The stainless steel disk (SSD) coated with PUC7 shows the lowest corrosion rate of 2.01 × 10⁻⁶ mm/year, which is 469% lower than that of the SSD coated with pure PU. The reinforcements are much greater than the previously reported PU/clay nanocomposites with comparable clay loadings ascribed to the exceptional homogeneity of as-prepared nanocomposites, which are accredited largely to the stable de-aggregated solvent-swollen organoclay suspension generated by the efficient solvent swelling process.     

Thermal stability,surface wettability and mechanical behavior of highly ordered ZnO-doped thermoplastic polyurethane films with hierarchically porous structures

In this paper, the effect of ZnO nanoparticle on thermal, microstructure, mechanical behavior, superhydrophobicity of thermoplastic polyurethane (TPU), ZnO/TPU composite materials with doped-ZnO nanoparticles were obtained via a solution blending method. The results show that the melting temperature region in soft segments of ZnO/TPU composite materials was the transition temperature region. The added ZnO slightly enhances the crystalline slipped of ZnO/TPU composite materials, and effectively hinder the transfer of high temperature small gas molecules. Due to the added ZnO nanoparticles, the microphase separation and ordered structures in TPU are reduced. In TPU, and between TPU and ZnO nanoparticles, there are variations in electron density at hard phase and soft phase interfaces. The good ZnO/TPU composites exhibit high water repellence with water contact angle of ~157°. The prepared ZnO/TPU nanocomposites show mechanical properties that are superior to those of pristine TPU. Tensile strength and storage modulus increase by 47.1% and 39.8% at ZnO loading values of 10 wt%. The results indicate that thermal behavior, microstructure, superhydrophobicity and the mechanical behavior of TPU composite materials can be enhanced by the doped ZnO.     

Bone-like forming ability of apatite-wollastonite glass ceramic

This research describes the preparation, characterisation and in vitro behavior of a bioactive glass ceramic containing 44.8 wt% apatite, 28.0 wt% wollastonite-2 M and 27.2 wt% of amorphous phase. The biomaterial was obtained by a specific thermal cycle process that caused the devitrification of the Ca₃(PO₄)₂-CaSiO₃ binary system's stoichiometric eutectic composition. Overall, the material combines the properties of a resorbable Si-Ca-rich glass, in addition to bioactive properties of wollastonite and apatite phases. The bioactivity of this material was studied by soaking the samples in a simulated body fluid (SFB) for 3, 7, 14 and 21 days at 36.5 °C. During the soaking, the amorphous phase and also wollastonite-2 M phase underwent steady dissolution by releasing Si and Ca ions into the SBF medium. After 7 days, a porous hydroxy-carbonate apatite (HCA) layer was formed at the SBF-glass ceramic interface. The micro-nanostructured apatite-wollastonite-2 M glass ceramics with improved mechanical properties, in comparison with the parent glass, could serve as a promising platform for hard tissue regeneration.     

The thermal and mechanical properties of a polyurethane/multi-walled carbon nanotube composite

A polyurethane/multi-walled carbon nanotube elastomer composite was synthesized. The microstructure of the composite was examined by field-emission scanning electron microscopy and transmission electron microscopy. The thermal and mechanical properties of the composite were characterized by dynamic mechanical thermal analysis, thermogravimetric analysis and tensile testing. The chemical linkage of carbon nanotubes with polyurethane matrix was confirmed by Fourier transform infrared spectra. The study on the structure of the composite showed that carbon nanotubes could be dispersed in the polymer matrix well apart from a few of clusters. The results from thermal analysis indicated that the glass transition temperature of the composite was increased by about 10 °C and its thermal stability was obviously improved, in comparison with pure polyurethane. The investigation on the mechanical properties showed that the modulus and tensile strength could be obviously increased by adding 2 wt% (by weight) CNT to the matrix.