Processing and mechanical properties of hydroxyapatite–polysulfone laminated composites

Designing biocomposites that mimic bone with specific mechanical properties of toughness and elastic modulus is a long-standing challenge in the biomaterials field. Traditional biocomposites comprise polymer matrices reinforced with ceramic particles. Laminated composites are structures also found in nature that can offer improved mechanical properties such as strength, elastic modulus and toughness. Hydroxyapatite/polysulfone laminated composites were fabricated to develop biologically compatible, toughened composites that would match the elastic modulus of bone. Multilayered composites were successfully designed with improved toughness measured by the work of fracture. Toughness measurements were more than an order of magnitude greater than monolithic hydroxyapatite. The toughness and modulus values of hydroxyapatite/polysulfone were within the range of cortical bone.     

cBN–TiN,cBN–TiC composites: chemical equilibria,microstructure and hardness mechanical investigations

This paper summarizes theoretical and experimental studies of cBN–TiN and cBN–TiC of cBN:TiN/TiC molar ratio 1:1 and 2:1. Theoretical calculations show that, at temperatures between 1000 and 1400°C, TiN reacts with BN forming one new phase, TiB₂, and that TiC reacts with cBN forming two new phases, TiB₂ and TiC_0.8N_0.2.. Experimental cBN–TiC/TiN composites were prepared by high pressure hot pressing and the samples were subsequently heat treated.After heat treatment, sinters of cBN–TiN/TiC were characterized using transmission electron microscopy and X-ray diffraction. The samples exhibited a dense polycrystalline structure, and a thin layer of fine TiB₂ was visible at the BN–binder interface. It was found that hardness decreased significantly after heat treatment.     

Adsorption mechanism of copper ions in aqueous solution by chitosan–carboxymethyl starch composites

Based on the structural characteristics of chitosan (CTS) and carboxymethyl starch (CMS), CTS–CMS composites were prepared by crosslinking. The composites had a plurality of reactive functional groups such as  NH₂,  NH₃⁺,  COOH, and  OH and are applied to the adsorption of Cu²⁺ in aqueous solution. The adsorption capacity and stability in acidic solution of the composites were preferable to that of raw material. The effects of temperature, contact time, initial concentration, and pH on the adsorption of Cu²⁺ were investigated. Infrared spectroscopy, scanning electron microscope–energy dispersive spectrometer, X-ray diffraction, and X-ray photoelectron spectroscopy were used to explore the adsorption mechanism. The experiment showed that chemisorption and physisorption coexisted in the adsorption process. It is promising to apply this adsorbent to remove the metal ions in wastewater. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48636.     

Fractal dimension analysis of interface and impact strength in core–shell structural bamboo plastic composites

To analyze quantitatively the interface of core–shell structural bamboo plastic composites (BPCs) surface, the relationship between the microstructure of composite surface and the macroscopic impact performance was investigated. The effect of shell layer on the interface and impact strength of the core–shell BPCs was studied by scanning electron microscope (SEM) images, computer image processing technique and fractal theory. The fractal dimensions of the core–shell BPCs were calculated and the relationship between the measured impact strength and the fractal dimensions of the core–shell BPCs fracture surface was discussed. The results showed that the fractal dimensions of the interface and fracture surface were within the range of about 2.1725 to 2.1970 and 2.2075 to 2.2204, respectively. All the correlative coefficients were higher than 0.99, therefore, the strong linear correlation indicated that the fractal characterization of the interface and impact fracture surface for the BPCs was possible, and also proved that the interface could be analyzed quantitatively depending on the feature parameters of the fractal dimension. The relationship between the fractal dimension and the measured impact strength was linear. The bigger the fractal dimension of surface, the bigger the impact strength and stronger the interfacial bond were. Thus, using the fractal dimensions the surface morphology of core–shell structural BPCs can be described and it may provide a new approach to investigate the inherent rules of fractal characteristics and Charpy impact strength of the BPCs with core–shell structure.     

Effect of nanosized reinforcement particles on mechanical properties of high density polyethylene–hydroxyapatite composites

Abstract

The effect of nanoscaled hydroxyapatite (HA) filler particles on the mechanical properties of the high density polyethylene–hydroxyapatite (HDPE–HA) composite samples has been investigated. Nanosized HA particles with an average size in the range of 40–50 nm were synthesised by mechanical milling method. The composite samples with various amounts of nanoscaled HA particles were produced by mixing the ceramic and high density polyethylene particles using a single screw extrusion system. The results of the mechanical testing on the composite samples showed an increase in the fracture strength and the young's modulus values with increasing volume fraction of HA content in the composite samples. At the same time, there were decreases in both the fracture strain and toughness values with increasing volume fraction of the ceramic filler particles. In addition the comparison of the results obtained in this study with the mechanical properties of the commercially available composite samples (HAPEX) shows that similar mechanical properties can be reached at a much lower ceramic content, if nanoscaled HA particles are used in the fabrication of these composite biomaterials.     

Sintering and mechanical properties of tricalcium phosphate–fluorapatite composites

Tricalcium phosphate and synthesized fluorapatite powder were mixed in order to elaborate biphasic ceramics composites. The effect of fluorapatite addition on the densification and the mechanical properties of tricalcium phosphate were measured with the change in composition and microstructure of the bioceramic. The Brazilian test was used to measure the mechanical resistance of the tricalcium phosphate–26.52 wt% fluorapatite composites. The densification and rupture strength increase versus sintering temperature. The composites have a good sinterability and rupture strength in temperature ranging between 1300 and 1400 °C. Thus, the densification ultimate was obtained at 1350 °C and the mechanical resistance optimum reached 9.6 MPa at 1400 °C. Above 1400 °C, the densification and the mechanical properties were hindered by the allotropic transformation of tricalcium phosphate, grain growth and the formation of both intragranular porosity and many cracks. The ³¹P magic angle spinning nuclear magnetic resonance analysis of composites reveals the presence of tetrahedral P sites.     

Poly(lactic acid)–thermoplastic starch–cotton composites: Starch-compatibilizing effects and composite biodegradability

Poly(lactic acid) (PLA) is a biodegradable, brittle, and high-cost polymer, which can be applied over structural components and green packaging. In this study, we reinforced PLA with natural cotton (10 wt %) and thermoplastic starch (TPS; 3 wt %) to obtain a biodegradable and lower cost composite. TPS was incorporated in three distinct ways: it was blended, coated, and blended and coated. In this study, we investigated the compatibilization of TPS in the improvement of matrix-reinforcement adhesion and increase in the tensile behavior without a compromise in biodegradation. The samples were investigated with thermal analysis, dynamic mechanical thermal analysis, tensile testing, scanning electron microscopy, confocal laser scanning microscopy, and hydrolytic degradation. The results show that the coupling effect was more pronounced in the PLA_TPS–cotton_TPS (hybrid system with PLA and cotton) hybrid system. This formulation presented a higher glass-transition temperature, thermal stability, storage modulus, wettability, and ductility. The TPS addition improved the adhesion between the matrix and starched cotton fiber and retarded abiotic biodegradation. These properties will allow for green applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47490.     

Sintering behavior and growth mechanism of β-TCP in nanocrystalline hydroxyapatite synthesized by mechanical alloying

Nanocrystalline carbonated HAp powder has been synthesized successfully within 2 h by mechanical alloying the stoichiometric mixture of CaCO₃, CaHPO₄·2H₂O at room temperature under open air. To observe the sintering behavior of HAp the as-milled sample is sintered at different temperatures. The amorphous HAp phase (~14 vol%) in as-synthesized sample transforms completely to crystalline HAp after sintering at 700 °C and after sintering the sample at 800 °C, the crystalline HAp partially transforms to β-TCP phase. Presence of low content of β-TCP phase in HAp powder could be useful in artificial hard tissue applications. Increase in sintering temperature up to 1000 °C results in enhancement of decomposition rate of HAp into β-TCP phase. Microstructure characterization in terms of lattice imperfections and relative phase abundances in non-sintered and all sintered samples are made both by analyzing the respective XRD patterns using Rietveld's structure refinement method as well as TEM images. The growth mechanism of β-TCP from crystalline HAp phase has been proposed based on structure and microstructure characterizations of sintered samples.     

In situ synthesis,physical and mechanical properties of ZrB2–ZrC–WB composites

In this study, two composition ZrB₂–ZrC–WB composites were synthesized by reactive hot-pressing of Zr + B₄C + WC powder mixtures at 1900 °C. The microstructure of the resulting composites was characterized by a combination of scanning electron microscopy and X-ray diffraction. It is seen that highly-dense ZrB₂–ZrC–WB composites with a homogenous fine-microstructure were obtained after the sintering. The mechanical behavior of the composites was evaluated using by testing under four-point bend testing at room and high temperatures. The results show that the high-temperature strength of the ZrB₂–ZrC–WB composites was substantially improved, compared to ZrB₂–ZrC-based composites without WB. In addition, the elastic properties, electrical conductivity, hardness and fracture toughness of the composites were measured at room temperature. The results reveal that these properties were comparable to those of ZrB₂–ZrC-based composites without WB.     

Synergized poly(lactic acid)–hydroxyapatite composites: Biocompatibility study

In vitro biocompatibility of impact modified composites produced from poly(lactic acid) (PLA) and hydroxyapatite (HA) is reported in this study. Surface modification was previously used to facilitate the dispersion of HA in PLA, whereas impact property of the PLA-HA composites was deliberately enhanced as it was necessary. Herein, osteoblast cell culture assay was used to assess the possible effects of HA surface modification and impact modification on the cell behavior in physiological media. Furthermore, antimicrobial properties of the HA were assessed. Evidence of HA modification was confirmed through elemental and spectroscopic analysis. Incorporation of HA offered better cell attachment and proliferation to the PLA matrix, with significant increase in the cell viability (%). Also, modification of HA did not present obvious cytotoxicity to the PLA-HA composite. Conversely, incorporation of impact modifier slowed down the rate of cell proliferation on the composite surface but facilitates increased wettability. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47400.     

Thermal,mechanical and structural investigation of copolyimide–silica hybrids containing phosphine oxide

In this study, a novel hybrid copolyimide was synthesized from copolyamic acid solutions (PAAs) obtained by the reaction between bis(3-aminophenoxy-4-phenyl)phenylphosphine oxide (m-BAPPO), 3,3′-diaminodiphenyl sulfone (DDS) and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), followed by thermal imidization. Hybrid materials containing 5% SiO₂ were synthesized by sol–gel technique. The polyimide–silica hybrids were characterized by Fourier Transform Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Thermogravimetric analysis showed that the weight loss of hybrids is shifted to the higher temperature compared to the neat copolyimide. The contact angle measurements confirmed the hydrophobic surface of hybrids. Moreover, the gas permeability measurements were also done to take a step for forthcoming gas separation studies. The tensile modulus and strength of the copolyimides are good.     

Microstructure and ablation mechanism of C/C–SiC composites

C/C–SiC composites were prepared by molten infiltration of silicon powders, using porous C/C composites as frameworks. The porosities of the C/C–SiC composites were about 0.89–2.8 vol%, which is denser than traditional C/C composites. The ablation properties were tested using an oxyacetylene torch. Three annular regions were present on the ablation surface. With increasing pyrocarbon fraction, a white ceramic oxide layer formed from the boundary to the center of the surface. The ablation experimental results also showed that the linear and mass ablation rates of the composites decreased with increasing carbon fraction. Linear SiO₂ whiskers of diameter 800 nm and length approximately 3 μm were formed near the boundaries of the ablation surfaces of the C/C–SiC composites produced with low-porosity C/C frameworks. The ablation mechanism of the C/C–SiC composites is discussed, based on a heterogeneous ablation reaction model and a supersaturation assumption.     

Antibacterial properties,in vitro bioactivity and cell proliferation of titania–wollastonite composites

Titania–wollastonite materials that show high in vitro bioactivity, appropriate cell proliferation and antibacterial behavior have been developed. Titania–wollastonite compounds were synthesized by two different routes: (i) solid state reaction and (ii) sol–gel. The in vitro bioactivity assessment was performed by immersing samples in a simulated body fluid (SBF). The materials characterization, before and after immersion in SBF, was performed by SEM and EDS. Cytotoxicity was assessed by estimating cell proliferation and the antibacterial properties were evaluated by performing a kinetic study of a bacterium growth (Burkhoderia cepacia). In order to evaluate the band gap value UV–vis spectroscopy was performed. A faster apatite layer formation was observed on the samples processed by sol–gel. However, these agglomerates were smaller than those formed on the solid state reaction substrates. The highest inhibition of the bacteria growth and the highest cell proliferation were observed on the samples synthesized by solid state reaction.     

A study of the structural and morphological properties of Ni–ferrite,Zn–ferrite and Ni–Zn–ferrites functionalized with starch

Zinc–ferrite, nickel–ferrite and mixed nickel–zinc ferrites were successfully synthesized via the thermal decomposition method from acetylacetonate complexes. To control the particle size and enhance dispersibility in an aqueous medium, starch, a natural and biocompatible compound, was used for the first time for coating such magnetic powders. X-ray powder diffraction (XRPD) was performed to study the structural properties of all samples. The presence of a single-phase spinel structure as well as the cation distribution in both sites of all investigated magnetic powders was confirmed. The values of unit cell parameters obtained from the results of the Rietveld analysis decreased, while the average crystallite size increased with increasing Ni²⁺ content. The average microstrain parameters unambiguously showed a change in the spinel structure with cation distribution. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) analyses were also utilized to characterize the synthesized materials, corroborating the XRPD data. The obtained results indicated that functionalization by starch was successfully achieved.     

Microstructural and mechanical investigation of hydroxyapatite–zirconia nanocomposites prepared by spark plasma sintering

Nano hydroxyapatite (nHA)–zirconia (ZrO₂) composites have been produced by spark plasma sintering (SPS). During the SPS process low temperatures (600–950 °C) and short dwelling time (5 min) have been applied to avoid the decomposition of nHA as well as the reaction between nHA and ZrO₂. The grain size of the sintered composites was between 200 and 1000 nm. Carbon diffusion was induced from the graphite die and layered composite structure was formed. These observations might be related to the spark plasma sintering side effects. The microstructure and mechanical properties of high hydroxyapatite content zirconia composites have been found to be influenced and strongly correlated with the specialties of SPS method.     

New hydroxyapatite–hydrotalcite composites II. microwave irradiation effect on structure and texture

Acid-basic materials are often used to catalyse organic reactions. Hydroxyapatite is acidic and hydrotalcite presents basic properties. The association of both compounds in a single material should present a rather unique catalytic behavior. Three preparations of hydroxyapatite impregnated with hydrotalcite are presented. The effect of microwave irradiation, at different preparation levels, is discussed. A homogeneous distribution of hydrotalcite on hydroxyapatite surface is obtained when hydrotalcite is precipitated over a previously microwave irradiated hydroxyapatite. Instead, if the hydrotalcite mixture is incorporated to the hydroxyapatite precursor gel and the resulting mixture microwave irradiated, hydrotalcite is preferentially deposited in the hydroxyapatite interparticle spaces. When both hydroxyapatite and hydrotalcite solutions are irradiated, mixed and irradiated again, the composite behaves as the addition of the two components.     

Morphological characteristics and thermal,rheological, and mechanical properties of cellulose nanocrystals-containing biodegradable poly(lactic acid)/poly(ε-caprolactone) blend composites

This work investigates the effect of cellulose nanocrystal (CN) loading on the properties of polylactide / poly(ε-caprolactone) (PLA/PCL) (70/30) blend processed in a twin-screw extruder as a potential material that can be utilized in various applications where biodegradation is highly desired. The morphological analysis revealed a reduction in droplet size of dispersed PCL phase upon addition of CN at low concentrations (1 and 2 wt %) with maximum reduction at 2 wt % which led to maximum improvement in mechanical properties. The reinforcing effect of CN in increasing the DMA storage modulus of the prepared systems was noticed when CN concentration was increased. Further, CN enhanced the crystallization of PCL, whereas the cold crystallization of PLA remained the same with CN addition. Both melt strength and viscosity of PLA improved with the incorporation of PCL and CN. In general, a green composite material with improved properties was successfully prepared using an environmentally friendly filler material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48665.     

Preparation,mechanical properties and long-term ablation resistance of Cf/SiBCN–ZrB2 composites

The C_f/SiBCN–ZrB₂ composites were prepared by dipping and winding combined with reactive hot pressing. The flexural strength and fracture toughness reached 261 MPa and 11.96 MPa • m^1/2, respectively, through continuous carbon fibers debonding, pulling and bridging mechanisms. Excellent mechanical properties ensured that the C_f/SiBCN–ZrB₂ composites remained intact after exposure to a plasma flame with a heat flux of 9.37 MW/m² for 300 s, with the mass and linear ablation rates of 1.78 mg/s, 1.01 μm/s, respectively. The excellent ablation resistance was due to the formation of dense oxide layers separating the matrix from the plasma flame. The SiO₂ formed in the low-temperature areas away from the center was the main ablation-resistant barrier, while the ZrO₂/SiO₂ double oxide layer formed in the high-temperature region at the center was the major ablation-resistant barrier.     

Effects of different silane coupling agents on structure and properties of starch–chitosan–kaolin composites

Effects of different silane coupling agents on clay surface modification were studied. Herein, functionalized superfine kaolin was compounded with starch–chitosan (SCS) to prepare starch–chitosan-functionalized superfine kaolin composite. The characterization results showed that kaolin (K) was successfully modified; the composite formed a dense intercalated structure. The glass-transition temperature (T _g) was measured by differential scanning calorimetry and dynamic mechanical analysis. It decreased by 60 °C which attested the crystallinity of SCS. The results of thermogravimetric analysis showed that the fastest weight-loss temperature (T_max) was elevated by over 50 °C for composites. Mechanical properties of the composites were explored by electronic universal testing machine. Tensile strength and elongation of composites were improved by 4.7 and 10.9 times. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48050.