Volume 37, Issue 7

The physical characteristics of cell culture materials, such as their elasticity, affect stem cell fate with respect to cell proliferation and differentiation. We systematically investigated the morphologies and characteristics of several stem cell types, including human amniotic-derived stem cells, human hematopoietic stem cells, human induced pluripotent stem (iPS) cells, and embryonic stem (ES) cells on poly(vinyl alcohol) (PVA) hydrogels immobilized with and without extracellular matrix-derived oligopeptide. Human ES cells did not adhere well to soft PVA hydrogels immobilized with oligovitronectin, whereas they did adhere well to PVA hydrogel dishes with elasticities greater than 15 kPa. These results indicate that biomaterials such as PVA hydrogels should be designed to possess minimum elasticity to facilitate human ES cell attachment. PVA hydrogels immobilized with and without extracellular matrix-derived oligopeptides are excellent candidates of cell culture biomaterials for investigations into how cell culture biomaterial elasticity affects stem cell culture and differentiation.

In this study, polyvinyl chloride (PVC)/rice straw (RS)/graphene oxide (GO) sustainable nanocomposite was prepared using the direct compounding method. Structural, morphological and mechanical properties of fabricated sustainable nanocomposites were compared with unfilled and RS-filled PVC compounds. Mechanical characteristics of PVC decreased with loading RS fibers. The main reason for the mechanical failure of PVC/RS composite is the incompatibility between PVC and RS fibers. GO nanosheets are used here to improve the compatibility between RS fibers and PVC macromolecules. Compared to the neat PVC, maximum strength of the RS/GO-loaded PVC composite increased up to 31%, with incorporating only 1 wt% of GO nanosheets. This enhancement in the mechanical characteristics of PVC/RS/GO nanocomposite can only be due to the role of GO nanosheets as a compatibilizer, as 1 wt% GO loading can only increase the mechanical strength of PVC compounds up to 9%. Fourier transform infrared spectroscopy results are used here to study the nature of these behaviors. It is suggested that the non-covalent and physical interactions between cellulose/hemicellulose portions of RS fibers and GO functional groups result in the enhancement of mechanical characteristics. Consequently, GO can be considered as a new compatibilizer for fabricating high performance PVC-based sustainable nanocomposites.

Ethylene propylene diene monomer (EPDM) and silicone rubber (SiR) are well-known polymers for high-voltage (HV) outdoor applications. In this research work, the effect of hybrid SiO 2 (a mixture of 15% microsized and 5% nanosized silica) has been investigated on the mechanical, thermal, and electrical properties of EPDM and SiR composites. Using the ASTM standard procedure, the EPDM and SiR composites filled with hybrid silica were compounded by two roll mill and simple blending techniques, respectively. It was observed that with the addition of hybrid SiO 2 , the composites exhibited improved tensile strength of ~2500 kPa, reduced elongation at break, and enhanced hardness. The samples filled with SiR hybrid silica showed higher thermal stability and volume/surface resistivities relative to EPDM hybrid composites. However, EPDM hybrid composites showed higher dielectric strength of ~23.4 kV/mm as compared with SiR composites. From these characterization results, it can be suggested that SiR hybrid composites are more suitable for outdoor HV insulation applications.

Polytetrafluoroethylene (PTFE) and its composite coating with various poly-p-oxybenzoyl (POB) proportions was prepared by spray suspensions. The friction and wear behavior were evaluated against a GCr15 steel ball on a ball-on-disc tribometer under dry sliding. The effect of the content of POB on the hydrophobic, mechanical and tribological properties of the PTFE-based coatings and the performances of the corresponding ultrasonic motors (USMs) were studied. Experimental results showed that the optimal content of POB not only increased the hardness, adhesion force and contact angle (CA), but also increased the coefficient of friction and wear resistance of the PTFE coatings. Especially, the wear rate of PTFE coating filled with 15 wt.% POB (3.42×10 −4 mm 3 /N·m) was only a quarter of pure PTFE. The morphologies of the worn surfaces of the PTFE coatings were observed by scanning electron microscopy to discuss the wear mechanism. The mechanical output properties of USMs were the best with filling of 10 wt.% POB into PTFE matrix.

The mechanical properties, thermal properties, antibacterial activity, and fabrication of three-dimensional (3D) printing strips of composite materials containing polyhydroxyalkanoate (PHA) and wood flour (WF) were evaluated. Maleic anhydride (MA)-grafted PHA (PHA-g-MA) and WF were used to enhance the desired characteristics of these composites. The PHA-g-MA/WF composites had better mechanical properties than the PHA/WF composites did. This effect was attributed to a greater compatibility between the grafted polyester and WF. Additionally, the PHA-g-MA/WF composites provided higher quality 3D printing strips and were more easily processed because of ester formation. The water resistance of the PHA-g-MA/WF composite was greater than that of PHA/WF. Moreover, WF enhanced the antibacterial activity of the composites. Composites of PHA-g-MA or PHA containing WF had better antibacterial activity.

The anisotropic mechanical properties of parts that are fabricated using acrylonitrile butadiene styrene (ABS) polymer relative to part-built orientation employing the fused deposition modelling process are reported in this work. ABS plus -P430 polymer was used to investigate the effects of infill orientation on the parts’ mechanical properties under tensile and compression loading. Results revealed that infill orientation strongly affected the tensile properties of fabricated ABS samples. Specifically, the values for Young’s modulus ranged from ~1.5 to ~2.1 GPa, ultimate tensile strength from ~12.0 to ~22.0 MPa, yield strength from ~1.0 to ~21.0 MPa, and elongation-at-break from ~0.2 to ~4.8% for different infill orientations. Samples with infill orientation aligned to the vertical (i.e. Z -) axis displayed the highest values relative to all other infill orientations investigated. Mechanical properties anisotropy was lower for parts under compressive loading, such that the Young’s modulus, ultimate compressive and yield strength were weakly correlated with infill orientation apart from samples whose built orientation was aligned at 45° to the vertical Z -axis. The latter samples displayed inferior mechanical properties under all compressive tests. The effects of sample gauge thickness on tensile properties and ABS sample micro- and bulk- hardness with respect to infill orientation are also discussed.

The morphology, dynamic mechanical properties and infrared spectra of polycarbonate (PC)/polypropylene (PP) blends were investigated. As expected, PC and PP were immiscible when blended together; however partial miscibility developed following annealing. The miscibility of one polymer in the other was examined using the modified Fox equation and the values of the Flory-Huggins polymer-polymer interaction parameter ( χ 12 ) were also calculated following the Kim and Burns approach. Moreover, the possible causes for partial miscibility in the annealed PC/PP blends were explored by infrared spectroscopy. It was concluded that annealing caused degradation of PP, leading to the formation of polar groups which were then able to interact with PC generating regions of partial miscibility.

This research designed a series of novel approaches aiming to tackle a long-standing problem that is the brittleness of polypropylene (PP) random copolymer (PPR) at low temperature. By introducing polyolefin elastomer (POE), the toughness of PPR was improved; talc improved the stiffness of PPR, low density polyethylene (LDPE) or high density PE (HDPE) improved the low temperature toughness of PPR, and annealing treatment also improved the low temperature toughness of PPR significantly. The addition of dicumyl peroxide (DCP) and triallyl isocyanurate (TAIC) increased its stiffness through the formation of cross-linking networks. Also, the crystallization behavior and morphology were investigated in detail. Differential scanning calorimetry (DSC) results indicated that the adoption of annealing treatment can improve the crystallinity of PPR, while a polarizing microscope revealed that the incorporation of foreign matter can facilitate the crystallization process of the matrix. X-ray diffraction (XRD) tests showed an unchanged polymorphic composition of PPR after introducing different additives, and scanning electron microscopy (SEM) indicated that annealing treatment can enhance interfacial interactions between the matrix and fillers.

Modern optical fibers require a double-layer coating on the glass fiber in order to provide protection from signal attenuation and mechanical damage. The most important plastic resins used in wires and optical fibers are plastic polyvinyl chloride, low- and high-density polyethylene, nylon, and polysulfone. One of the most important things that affect the final product after processing is the design of the coating die. In the present study, double-layer optical fiber coating is performed using melt polymer satisfying the Phan-Thien-Tanner (PTT) fluid model in a pressure-type die. The fluid is electrically conducted in the presence of applied magnetic field. Wet-on-wet coating process is applied for double-layer optical fiber coating. The assumption of fully developed flow of PTT fluid model, two-layer liquid flows of an immiscible fluid, is modeled in an annular die of length L, where the fiber is dragged at a higher speed. The equations characterizing the flow ad heat transfer phenomena are solved exactly and the effects of emerging parameters are shown with the help of graphs. It is interesting to remark that an increase in the non-Newtonian parameters increases the velocity in the absence or presence of slip parameters, which coincides with the results reported earlier. Also, the effect of important parameters such as Deborah numbers, slip parameters, magnetic parameter, characteristic velocity, radii ratio, and Brinkman numbers on the axial velocity, flow rate, thickness of coated fiber optics, and temperature distribution are investigated. Furthermore, the results were compared with the experimental results already published. To the best of our knowledge, no such analysis of the double-layer coating flows of PTT fluid using slip conditions is available in the literature. At the end, the result of the present work is also compared with the experimental results already published by taking λ → 0 (non-Newtonian parameter).