Mesoporous silica aerogel reinforced dental composite: Effects of microstructure and surface modification.

A mesoporous silica aerogel (SiA) with a high specific surface area was synthesized through the sol-gel process and subsequently modified with two different silane-based modifiers to reveals the effect of microstructure and surface modification on the fracture mechanics of a dental composite. The synthesized and modified aerogel were characterized using field-emission scanning electron microscopy (FESEM), nitrogen adsorption-desorption, and Fourier-transform infrared spectroscopy (FTIR). The prepared aerogels were then incorporated within methacrylate-based dental composites with the filler content of 0-35 wt%. Flexural modulus (FM) and Flexural strength (FS) were evaluated by the three-point bending test. The fracture toughness (FT) of the composites was evaluated by single edge V-notched beam (SEVNB) flexure test, while FESEM was employed to investigate the fracture surface morphology of the composites. Furthermore, the wettability of the composites was assessed according to the sessile drop method. The characterization of synthesized aerogels revealed the formation of SiA with a surface area of 550-560 m2/g and porosity of 77%, while FTIR results confirmed the successful modification. Statistical analysis (ANOVA, p≤0.05, and n = 5) revealed that FM significantly enhanced (from 1.43 GPa to 2.66 GPa) as filler content increased over 0-30 wt%, and FS improved (from 80 to 95 MPa) as filler content increased over 0-15 wt%. Furthermore, the modification of aerogels improved both fracture characteristics and the wettability of the composites. The FT evaluations and fractography analysis revealed that the mesoporous structure of the fillers mainly dominated the filler-matrix adhesion strength at the same filler content.

Improved performance of Bis-GMA dental composites reinforced with surface-modified PAN nanofibers.

In the present work, polyacrylonitrile (PAN) nanofibers reinforced dental composites were investigated to achieve the improved interfacial adhesion between the PAN nanofiber and resin matrix using surface modification of nanofibers. PAN nanofibers mat were prepared by electrospinning and then, surface treated with the activated bisphenol A glycidyl methacrylate (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA) (50/50 mass ratio) dental resin followed by photo-curing. Also, the treated nanofibers mat was milled into a powder to achieve the uniform distribution of nanofibers in the matrix resin. The reinforced dental composite were prepared by mixing the various mass fraction of the powder (0.5-15 wt%) with the Bis-GMA/TEGDMA dental monomers. The effect of weight ratio of surface-modified nanofibers to blend resin on the chemical structure, morphology, compression and flexural properties, color and polymerization shrinkage of dental composites was evaluated. The results showed that using surface-treated nanofibers with content of 5 wt% enhanced the compression strength, flexural strength, flexural modulus and work of rupture of the resultant dental composite by factors of 23%, 7%, 80%, and 145%, respectively, comparing to the unreinforced neat resin. Also, the polymerization shrinkage reduces by 37%. These significant improved properties of the dental composite could be due to the semi-interpenetration network formation between surface-modified nanofibers and resin matrix and well distribution of nanofibers in the dental resin. Further increasing the nanofiber content led to poor mechanical properties of obtained dental composites. The results also, revealed that the color of resin composite could be whiter using modified PAN nanofibers as the filler.

Pentiptycene-Based Polyurethane with Enhanced Mechanical Properties and CO2-Plasticization Resistance for Thin Film Gas Separation Membranes.

The development of thin film composite (TFC) membranes offers an opportunity to achieve the permeability/selectivity requirements for optimum CO2 separation performance. However, the durability and performance of thin film gas separation membranes are mostly challenged by weak mechanical properties and high CO2 plasticization. Here, we designed new polyurethane (PU) structures with bulky aromatic chain extenders that afford preferred mechanical properties for ultra-thin-film formation. An improvement of about 1500% in Young's modulus and 600% in hardness was observed for pentiptycene-based PUs compared to the typical PU membranes. Single (CO2, H2, CH4, and N2) and mixed (CO2/N2 and CO2/CH4) gas permeability tests were performed on the PU membranes. The resulting TFC membranes showed a high CO2 permeance up to 1400 GPU (10-6 cm3(STP) cm-2 s-1 cmHg-1) and the CO2/N2 and CO2/H2 selectivities of about 22 and 2.1, respectively. The enhanced mechanical properties of pentiptycene-based PUs result in high-performance thin membranes with the similar selectivity of the bulk polymer. The thin film membranes prepared from pentiptycene-based PUs also showed a twofold enhanced plasticization resistance compared to non-pentiptycene-containing PU membranes.

Development of electrospun poly (vinyl alcohol)-based bionanocomposite scaffolds for bone tissue engineering.

The article is focused on the role of nanohydroxy apatite (nHAp) and cellulose nanofibers (CNFs) as fillers in the electrospun poly (vinyl alcohol) (ES-PVA) nanofibers for bone tissue engineering (TE). Fibrous scaffolds of PVA, PVA/nHAp (10 wt.%), and PVA/nHAp(10 wt.%)/CNF(3 wt.%) were successfully fabricated and characterized. Tensile test on electrospun PVA/nHAp10 and PVA/nHAp10/CNF3 revealed a three-fold and seven-fold increase in modulus compared with pure ES-PVA (45.45 ± 4.77). Although, nanofiller loading slightly reduced the porosity percentage, all scaffolds had porosity higher than 70%. In addition, contact angle test proved the great hydrophilicity of scaffolds. The presence of fillers reduced in vitro biodegradation rate in PBS while accelerates biomineralization in simulated body fluid (SBF). Furthermore, cell viability, cell attachment, and functional activity of osteoblast MG-63 cells were studied on scaffolds showing higher cellular activity for scaffolds with nanofillers. Generally, the obtained results confirm that the 3-componemnt fibrous scaffold of PVA/nHAp/CNF has promising potential in hard TE. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1111-1120, 2018.

Effect of nanoclay on the properties of low density polyethylene/linear low density polyethylene/thermoplastic starch blend films.

The aim of this work is to study effect of nanoclay (Cloisite(®)15A) on morphology and properties of low-density polyethylene/linear low-density polyethylene/thermoplastic starch (LDPE/LLDPE/TPS) blend films. LDPE/LLDPE blend (70/30wt/wt) containing 15wt.% TPS in the presence of PE-grafted maleic anhydride (PE-g-MA, 3wt.%) with 1, 3 and 5phr of nanoclay are compounded in a twin-screw extruder and then film blown using a blowing machine. Nanocomposites with intercalated structures are obtained, based on the X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. However, some exfoliated single platelets in the samples are also observable. Scanning electron microscopic (SEM) images confirm the ability of both exfoliated nanoclay and PE-g-MA to reduce the size of TPS domains and deform their particles within the PE matrices. As the nanoclay content increases from 1 to 5phr, the tensile strength, tear resistance and impact strength of the films increase, whereas a slight decrease in the elongation at break is observed. The film samples with 5phr nanoclay possess the required packaging properties, as specified by ASTM D4635. These films provide desired optical transparency and surface roughness which are more attractive for packaging applications.

Study on ternary low density polyethylene/linear low density polyethylene/thermoplastic starch blend films.

In this work, low-density polyethylene/linear low-density polyethylene/thermoplastic starch (LDPE/LLDPE/TPS) films are prepared with the aim of obtaining environmentally friendly materials containing high TPS content with required packaging properties. Blending of LDPE/LLDPE (70/30 wt/wt) with 5-20 wt% of TPS and 3 wt% of PE-grafted maleic anhydride (PE-g-MA) is performed in a twin-screw extruder, followed by the blowing process. Differential scanning calorimetric results indicate starch has more pronounced effect on crystallization of LLDPE than LDPE. Scanning electron micrograph shows a fairly good dispersion of TPS in PE matrices. Fourier transfer infrared spectra confirm compatibility between polymers using PE-g-MA as the compatibilizer. Storage modulus, loss modulus and complex viscosity increase with incorporation of starch. Tensile strength and elongation-at-break decrease from 18 to 10.5 MPa and 340 to 200%, respectively when TPS increases from 5 to 20%. However, the required mechanical properties for packaging applications are attained when 15 wt% starch is added, as specified in ASTM D4635. Finally 12% increase in water uptake is achieved with inclusion of 15 wt% starch.