Volume 36, Issue 2

Nowadays, sustainable and eco-friendly products are gaining more attention in various engineering industries owing to their considerable strength-to-weight ratio, abundant availability, and recyclability. The properties of biofibers depend on the cultivation method, environmental conditions, and extraction method. Biofibers are hauled out by dew retting, water retting, and mechanical decortication methods. The properties of natural fiber–reinforced composites can be enhanced by proper physical and chemical treatments. The aim of this study is to propose a complete evaluation of the different extraction methods applied on natural fibers. Various physical and chemical treatment methods were used to ascertain the properties of optimized natural fiber-reinforced composites for various industrial applications. The key findings derived from various existing data and the chemical treatment results of the biofiber-reinforced composite are specifically highlighted with critical assessment. The properties and use of natural fiber-reinforced composites in the various fields of applications have made them candidates of choice over synthetic petroleum–based fibers.

In precision optical applications, plastics thick-walled optical lenses are increasing. Dimensional stability and optical performance are the critical issues that should be addressed for plastic thick-walled lenses. A novel multi-layer counter-pressure injection molding process is proposed in this study. The experimental prism mold with moveable pistons was developed to investigate the effects of layering methods, counter-pressure and their combination on thick-walled optical lenses. The experimental results reveal that counter-pressure injection molding is effective in improving shrinkage, transmittance and refractive index of the thick-walled optical prism. Counter-pressure of the piston provided lower melt velocity and shorter flow path of melt to improve polymer molecules orientation, and also offered continuous holding pressure during the filling stage to eliminate defects such as shrinkage or short shots. The combination of counter-pressure and multi-layer injection molding technology further improved the dimension stability and optical performance of the thick-walled optical lens. Much thinner layers than the final wall thickness of prism ensures shrinkage reduction during the cooling stages. A thick-walled optical prism was fabricated successfully upon applying a multi-layer counter-pressure injection molding process.

This paper aims to describe the thermal, mechanical, and surface properties of a PVA/HPP blend whereby the film was prepared using a solution casting method. The improvements in thermal and mechanical properties of HPP-based PVA composites were investigated. The characterization of pure PVA and PVA composite films included tensile tests, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results of TGA and DSC indicated that the addition of HPP increased the thermal decomposition temperature of the composites. Mechanical properties are significantly improved in PVA/HPP composites. The thermal stability of the PVA composite increased with the increase of HPP filler content. The tensile strength increased from 15.74 ± 0.72 MPa to 27.54 ± 0.45 MPa and the Young’s modulus increased from 282.51 ± 20.56 MPa to 988.69 ± 42.64 MPa for the 12 wt% HPP doped sample. Dynamic mechanical analysis (DMA) revealed that at elevated temperatures, enhanced mechanical properties because of the presence of HPP was even more noticeable. Morphological observations displayed no signs of agglomeration of HPP fillers even in composites with high HPP loading.

The connecting rod, as an important part in internal combustion engines, has been most widely used in automotive industry, and its main function is to transfer the reciprocating motion of the piston into the rotatory motion of the crankshaft. In this study, fatigue analysis of the connecting rod is performed numerically for different engine speeds. With this aim, it is attempted to reduce the weight of the connecting rod by choosing the low density and high strength of GFRP and CFRP composite materials instead of structural steel. In this way, it is possible to improve the engine efficiency with saving unnecessary balancing weights as well as reducing the cost of the connecting rod. In the current study, the connecting rod was modeled using Solidworks software, and its CAD model was transferred to the ANSYS/Workbench software for Finite Element Analyses (FEA). In FEA, fatigue analyses were performed to determine fatigue parameters such as alternating stress, deformation, fatigue life and safety factor according to Soderberg’s fatigue model. Results from this study showed that alternating stress and safety factor reached a critical value between piston pin end and crank end near to the piston pin end. Alternating stress values of the GFRP and CFRP connecting rods were much lower than those of structural steel rod. In contrast to reduction of the weight by 1/5, fatigue life of the connecting rod with structural steel material was much greater than those of GFRP and CFRP providing a higher safety factor compared with composite materials.

In this work, thermoplastic elastomers (TPE) are produced by melt mixing of recycled high-density polyethylene (RHD) with two types of off-the-road (OTR) ground tire rubber (GTR). Non-regenerated (NR) and regenerated (RR) rubbers are used to investigate the effect of GTR concentration and regeneration on the blends properties containing up to 90 wt.% GTR. The blend morphology is studied by scanning electron microscopy (SEM) to show incompatibility and low interfacial adhesion between RHD and GTR (NR and RR) especially above 40 wt.% RR. This behavior is attributed to the GTR regeneration process and agglomeration of RR particles with lower surface area and affinity toward RHD compared with NR. In all the compounds, the mechanical properties in tension of RR blends were lower than for NR blends, which is attributed to the degradation of the GTR backbone chains lowering the molecular weight (MW) during the regeneration process. Also, NR has a more important effect on impact strength improvement due to its higher crosslinked structure making the particles more deformable/elastic to absorb the mechanical energy before crack initiation. The experimental results also show that 80 wt.% GTR is the optimum concentration for the production of low cost and eco-friendly TPE based on recycled materials.

Novel kinds of magnetism-driven poly N,N-dimethylacrylamide bilayer intelligent hydrogels with various nanofibrillated cellulose (NFC) contents were prepared successfully via one-step insitu free radical polymerization. The bilayer hydrogels possessed high mechanical strength, efficient swelling and steady magnetic response. With the increase of nanofibrillated cellulose content, the crosslinking density of the hydrogels increased, leading to the decrease of swelling rate and increase of mechanical strength and swelling bending degree of hydrogel actuators, respectively. Fe 3 O 4 particles existed tightly on the micropore surfaces of the hydrogels, which built the function base of magnetic response of hydrogel actuators. The addition of Fe 3 O 4 was irrelevant to the variation of crosslinking density. The bilayer structure exhibited high bonding strength. Based on intelligent responsive properties, bilayer hydrogels were designed as soft magnetism-driven actuators, realizing capture and transportation properties and provided material candidates for soft robots.

A polyphosphonate (PDPA) flame retardant that contains phenyl phosphonic dichloride and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide groups, has been synthesized. The flame retardant was introduced into epoxy resins (EP) and cured by 4,4’-diamino diphenylmethane. The vertical burning, limited-oxygen index and cone calorimeter tests reveal that the PDPA can enhance the flame-retardant properties of the EP significantly. With only a 4 wt% PDPA loading, the EP composites achieved a limited-oxygen index value of 33.4% and a V-0 rating in the vertical burning test, and the peak heat release rate and total heat release were decreased by 40.9% and 24.6%, respectively. The thermal properties and gas pyrolysis products of the EP composites were evaluated by thermogravimetric analysis and thermogravimetric analysis-Fourier transform infrared spectroscopy, and the morphology and structure of residual char were characterized by scanning electron microscopy, Flourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. To explain the combined effects of the condensed and gas phases, modes of the flame-retardant action are proposed.

Basic equations describing steady, two-directional, isothermal and fully developed drag-pressure flow of generalized Newtonian fluid between parallel plates assumed as the appropriate flow model in flat, shallow screw channel, are given. It is shown that the flow output for any generalized Newtonian fluid in the two-directional case can be described by a simple expression with a few parameters depending in a complicated way on pressure gradient, channel geometry and constants of the constitutive model. The expression is also valid for unidirectional flow as the limiting case of the two-directional flow. The parameters must be determined as a rule with numerical methods. To simplify the practical calculations, a few (semi)analytical methods of parameters determination for unidirectional power law flow are discussed first. These methods make possible to calculate analytically the pressure gradient for known output that is typical of screw flow characterization. The results obtained for the unidirectional flow 1-D were generalized to describe the two-directional flow 2-D, which takes into account both longitudinal and transverse velocity components. The generalization is based on translation and dilation of the 1-D flow characteristics by introducing a few additional parameters, which are only dependent on the helix angle and power law exponent. It was found a very good agreement between exact numerical and approximate ( semi)analytical characteristics for both flows.

The current study deals with the effect of basalt fiber hybridization on the compressive properties of composite pipes reinforced with glass fiber and carbon fiber. Hybrid and non-hybrid fiber reinforced pipes (FRPs) were fabricated through wet filament winding technique. Intraply fiber winding structure in which different fiber types were simultaneously wound at the layer was employed for the hybridization. The FRP samples wound by different fiber winding angles (± (40°), ± (55°), ± (70°)) were prepared in order to gain a better insight on the influence of basalt intraply fiber hybridization. The compression properties of FRP samples were experimentally determined by quasi-static compression tests using external parallel-plates for both the axial and radial directions. The non-hybrid carbon FRP pipes showed the maximum axial compression strength in parallel to the highest strength and lowest ductility of carbon fibers, while the minimum axial compression strength was obtained for the non-hybrid pipes reinforced with basalt fibers that, in comparison, exhibit much less strength and higher ductility. The pipes submitted to the axial compression tests predominantly failed due to the development of cracks and buckling along the fiber direction. While the inclusion of basalt fiber reduced the axial compression behavior of the non-hybrid carbon and glass FRP samples, it improved that behavior in the radial compression tests. Delamination was determined as the major failure mode for the damaged FRPs under radial compression. It is found that the incorporation of basalt fiber provides improvements in radial compression properties as opposed to axial compression properties and in the same manner the increment in fiber winding angle makes a positive contribution to radial compression properties.

To harness the inherent advantages of both synthetic and natural reinforcements, mercerized bagasse fibers (BF) and particulate calcium carbonate (CaCO 3 ) were utilized as a complementing reinforcement for the fabrication of bagasse fiber/calcium carbonate (BF/CaCO 3 ) polypropylene composites. Two sets of composites were produced – one with mercerized BF/CaCO 3 and the other with unmercerized BF/ CaCO 3 . The effect of reinforcement loading on the impact energy, wear behavior, thermal resistance and water absorption properties of the composites were studied. Results showed that the mercerized BF/CaCO 3 hybrid reinforced polypropylene composites exhibited significant increase in impact energy and offered better resistance to weight loss during wear test. Similarly, the thermal resistance of the mercerized composites was higher than their corresponding unmercerized composites. Additionally, water absorption in mercerized composites was highly resisted than in unmercerized samples. These results indicated that mercerization treatment and reinforcement hybridization improved the impact energy, wear, thermal resistance and water ingress resistance of hybrid fiber/ particulate reinforced polypropylene composites.

In this study, the strain rate sensitivity of a discontinuous short fiber reinforced composite and the strain rate effect on the damage evolution are investigated. The studied material is a polymeric composite with a polyamide 6.6 matrix reinforced with oriented randomly short glass fibers at a 50% weigh ratio (PA6.6GF50). Tensile tests at low and high strain rate are conducted. In addition, interrupted tensile tests are carried out to quantify the damage at specific stress levels and strain rates. To perform the interrupted tensile tests, an intermediate fixture is realized via double notched mechanical fuses with different widths designed to break at suitable stress levels. The damage is estimated by the fraction of debonded fibers and matrix fractures. Based on the experimental observations, it is concluded that the ultimate stress and strain, and the damage threshold are mainly governed by the strain rate. Furthermore, it is established that the considered composite has a non-linear dynamic behavior with a viscous damage nature.

Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT)-based nanocomposites filled with 1 vol.% silicon dioxide nanoparticles (nano-SiO 2 ) were prepared using a co-rotating twin-screw extruder and injection molding. The nanocomposites with various blending sequences were investigated using PLA-based and PBAT-based nanocomposite masterbatches. Morphology of the PLA/PBAT/SiO 2 nanocomposites was examined using a scanning electron microscope (SEM) and a focused ion beam (FIB) SEM. It is found that the nano-SiO 2 locates in the original polymer phase, in which it is firstly incorporated in the masterbatch process, as well as at the interface between the two polymers. However, as the residence time in the extrusion process increases, the nanoparticles migrate from the original phase to the interface, governed by the thermodynamic driving force. The best optimization of mechanical properties is achieved by using the PBAT-based masterbatches with a one-step process or short residence time. The processing history, therefore, has a tremendous impact on the final properties of the resulting materials.