Cheng Zhu Liao

Novel polypropylene biocomposites reinforced with carbon nanotubes and hydroxyapatite nanorods for bone replacements

Multi-walled carbon nanotubes (MWNTs) of 0.1 and 0.3 wt.% and hydoxyapatite nanorods (nHAs) of 8-20 wt.% were incorporated into polypropylene (PP) to form biocomposites using melt-compounding and injection molding techniques. The structural, mechanical, thermal and in vitro cell responses of the PP/MWNT-nHA hybrids were investigated. Tensile and impact tests demonstrated that the MWNT additions are beneficial in enhancing the stiffness, tensile strength and impact toughness of the PP/nHA nanocomposites. According to thermal analysis, the nHA and MWNT fillers were found to be very effective to improve dimensional and thermal stability of PP. The results of osteoblast cell cultivation and dimethyl thiazolyl diphenyl tetrazolium (MTT) tests showed that the PP/MWNT-nHA nanocomposites are biocompatible. Such novel PP/MWNT-nHA hybrids are considered to be potential biomaterials for making orthopedic bone implants.

The development, fabrication, and material characterization of polypropylene composites reinforced with carbon nanofiber and hydroxyapatite nanorod hybrid fillers

This study focuses on the design, fabrication, microstructural and property characterization, and biocompatibility evaluation of polypropylene (PP) reinforced with carbon nanofiber (CNF) and hydroxyapatite nanorod (HANR) fillers. The purpose is to develop advanced PP/CNF–HANR hybrids with good mechanical behavior, thermal stability, and excellent biocompatibility for use as craniofacial implants in orthopedics. Several material-examination techniques, including X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, tensile tests, and impact measurement are used to characterize the microstructural, mechanical, and thermal properties of the hybrids. Furthermore, osteoblastic cell cultivation and colorimetric assay are also employed for assessing their viability on the composites. The CNF and HANR filler hybridization yields an improvement in Young’s modulus, impact strength, thermal stability, and biocompatibility of PP. The PP/2% CNF–20% HANR hybrid composite is found to exhibit the highest elastic modulus, tensile strength, thermal stability, and biocompatibility.

Mechanical and fracture behaviors of elastomer-rich thermoplastic polyolefin/SiCp nanocomposites

Elastomer-rich thermoplastic polyolefin (ETPO) resin containing 70wt% maleated styrene-ethylene-butadiene-styrene (SEBSg-MA) and 30wt% polypropylene and its nanocomposites filled with 1-5wt% SiC nanoparticles (SiCp) were fabricated using extrusion and injection molding techniques. The mechanical and thermal behaviors of ETPO and its nanocomposites were investigated. Tensile measurements showed that the SiCp additions lead to reductions in both tensile stiffness and strength of ETPO. However, Izod impact and EWF measurements indicated that the impact strength and fracture toughness of ETPO improve substantially with increasing SiCp content. This demonstrated that SiC nanoparticles toughen the ETPO blend effectively. Furthermore, SiCp additions were found to improve the thermal resistance of ETPO blend considerably.

Preparation of polyetheretherketone composites with nanohydroxyapatite rods and carbon nanofibers having high strength, good biocompatibility and excellent thermal stability

In recent years, research in the development of polymeric materials for orthopedic implants has become ever more important because the global demand of biocompatible implants has been steadily increasing. Bioinert polyetheretherketone (PEEK) is typically reinforced with bioactive hydroxyapatite microparticles. However, the tensile strength of conventional PEEK/hydroxyapatite microcomposites falls sharply with increasing filler loading. To address low strength and high filler loading issues, nanohydroxyapatite rods (nHA) and carbon nanofibers (CNF) were employed to reinforce PEEK. In this study, molded-grade PEEK pellets, nHA and CNF fillers were melt-mixed and injection molded to form PEEK/nHA and hybrid PEEK/nHA–CNF nanocomposites. The tensile and thermal properties, as well as the bioactivity and biocompatibility of such nanocomposites, were investigated. Tensile test results showed that elastic modulus of PEEK/nHA nanocomposites increases with increasing nHA content. The PEEK/9.3 vol% nHA nanocomposite exhibited higher tensile strength than that of a conventional HAPEX microcomposite. Thermogravimetric measurements indicated that the nHA addition improves the thermal stability of PEEK. Thus, the PEEK/9.3 vol% nHA nanocomposite that had good mechanical, thermal and biological performances was an attractive biomaterial for use in maxillofacial surgery. Furthermore, the tensile property of the PEEK/15 vol% nHA–1.9 vol% nHA nanocomposite compared favorably with that of human cortical bones. The results of biomineralization, alkaline phosphatase (ALP), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1) assays also showed that the PEEK/15 vol% nHA and PEEK/15 vol% nHA–1.9 vol% CNF nanocomposites exhibited excellent bioactivity and biocompatibility. The ALP assay showed good activity of osteoblast cells on the composite specimens with high nHA content. Moreover, CNF addition further increased the ALP activity of PEEK/15 vol% nHA nanocomposites. The PEEK/15 vol% nHA–1.9 vol% CNF composite, with enhanced tensile strength and excellent biocompatibility, shows large potential for load-bearing implant applications.

Mechanical and Thermal Performance of High-Density Polyethylene/Alumina Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with pristine and vinyltrimethoxysilane (VTMS)-treated alumina nanoparticles of 2, 4, and 6 wt% were melt-compounded in a twin-screw extruder followed by injection molding. Their structure, thermal and mechanical behaviors were studied. Fourier transform infrared (FTIR) spectra showed that VTMS was successfully covalently grafted to the alumina nanoparticles. The X-ray diffraction (XRD) patterns indicated that the alumina nanoparticle additions broadened the characteristic peak width of HDPE, indicating that they reduced the crystallite size of HDPE. The heat deflection temperature and thermogravimetric analyses demonstrated that the dimensional and thermal stability of HDPE were enhanced markedly by adding pristine and silane-treated alumina nanoparticles. The alumina nanoparticle additions were also beneficial in enhancing Youngs modulus and yield strength of HDPE. The reinforcing effect was particularly apparent in the silane-treated nanocomposites due to improved filler–matrix interactions.

Effect of Silicon Carbide Nanoparticle Additions on Microstructure and Mechanical Behavior of Maleic Anhydride Compatibilized High Density Polyethylene Composites

Maleated high density polyethylene (mPE) loaded with 2, 4, 6 and 8 wt% SiC nanoparticles (SiCnp) were prepared by injection molding. The effect of SiCnp additions on the microstructure and mechanical properties of mPE were studied using X-ray diffraction (XRD), polarizing optical microscopy (POM), heat deflection temperature (HDT), tensile and Izod impact measurements. XRD and POM results showed that the SiCnp additions reduce the crystallite thickness and spherulite size of mPE. HDT measurements revealed that SiCnp additions enhance the thermal stability of mPE considerably. Tensile test showed that the addition of 2 wt% SiCnp improves the Youngs modulus and yield strength of mPE at the expenses of elongation at break and impact strength. SEM fractography was used to reveal the failure deformation of nanocomposites after impact test. The low impact strength of mPE/SiCnp nanocomposites was related to the absence of particle cavitation and matrix fibrillation. The impact fracture deformation of such nanocomposites is discussed.

Polyetheretherketone Hybrid Composites with Bioactive Nanohydroxyapatite and Multiwalled Carbon Nanotube Fillers

Polyetheretherketone (PEEK) hybrid composites reinforced with inorganic nanohydroxyapatite (nHA) and multiwalled carbon nanotube (MWNT) were prepared by melt-compounding and injection molding processes. The additions of nHA and MWNT to PEEK were aimed to increase its elastic modulus, tensile strength, and biocompatibility, rendering the hybrids suitable for load-bearing implant applications. The structural behavior, mechanical property, wettability, osteoblastic cell adhesion, proliferation, differentiation, and mineralization of the PEEK/nHA-MWNT hybrids were studied. X-ray diffraction and SEM observation showed that both nHA and MWNT fillers are incorporated into the polymer matrix of PEEK-based hybrids. Tensile tests indicated that the elastic modulus of PEEK can be increased from 3.87 to 7.13 GPa by adding 15 vol % nHA and 1.88 vol % MWNT fillers. The tensile strength and elongation at break of the PEEK/(15% nHA)-(1.88% MWNT) hybrid were 64.48 MPa and 1.74%, respectively. Thus the tensile properties of this hybrid were superior to those of human cortical bones. Water contact angle measurements revealed that the PEEK/(15% nHA)-(1.88% MWNT) hybrid is hydrophilic due to the presence of nHA. Accordingly, hydrophilic PEEK/(15% nHA)-(1.88% MWNT) hybrid promoted the adhesion, proliferation, differentiation, and mineralization of murine MC3T3-E1 osteoblasts on its surface effectively on the basis of cell culture, fluorescence microscopy, MTT assay, WST-1 assay, alkaline phosphatase activity, and Alizarin red staining tests. Thus the PEEK/(15% nHA)-(1.88% MWNT) hybrid has the potential to be used for fabricating load-bearing bone implants.

Fracture Toughness of Polyamide 6/ Maleated Styrene-Ethylene-Butylene-Styrene/Silicon Carbide Nanocomposites

Polyamide 6 (PA6) based nanocomposites toughened with 20 wt% maleated styrene-ethylene-butylene-stryrene (mSEBS) reinforced with 1-7 wt% silicon carbide nanoparticles (SiCp) were fabricated via melt blending followed by injection molding. Tensile results showed that SiCp additions improve the Young’s modulus and tensile strength of PA6/mSEBS blends but decrease their tensile ductility and impact strength. EWF test revealed that the SiCp additions reduce both the specific essential work of fracture and specific non-essential plastic work of fracture. Thus SiCp additions are detrimental to the fracture toughness of PA6/mSEBS blend.

Fabrication, mechanical properties and fracture toughness of thermoplastic polyolefin filled with carbon nanofibers

Thermoplastic polyolefin (TPO) blends consisting of polypropylene (PP) and maleated styrene-ethylene-butadiene-styrene (SEBS-g-MA) were reinforced with 0.2–2.5wt% carbon nanofibers (CNFs). Such nanocomposites were fabricated by melt-blending followed by injection molding. The structure, mechanical behavior and fracture toughness of TPO blends and their nanocomposites were studied. Tensile tests showed that the Youngs modulus and tensile strength of nanocomposites increase with increasing CNF content. The Izod impact and essential work of fracture (EWF) test results indicated that CNF additions improve the impact strength and fracture toughness of TPO blends.

Essential work of fracture study on thermoplastic polyolefin filled with silicon carbide nanoparticles

Abstract Thermoplastic polyolefin (TPO) containing 70 wt% polypropylene and 30 wt% styrene-ethylene-butadiene-styrene grafted maleic anhydride and its nanocomposites filled with 1-5wt% silicon carbide nanoparticles (SiCp) were prepared by melt processing followed by injection molding. Tensile tests show that both Young’s modulus and tensile strength increase with increasing SiCp loading. Essential work of fracture (EWF) method was used to evaluate the fracture toughness of resulting nanocomposites. EWF test demonstrates that the fracture toughness of TPO blend generally decreases with increasing SiCp content. Shield yielding and fibrillation are the main fracture mechanisms for TPO blend and composites. SiCp are found to improve the heat deflection temperature of the TPO blend.