Application of shear thickening fluid in ultra high molecular weight polyethylene fabric

An advanced stab‐resistant material composed of shear thickening fluid (STF) and ultra high molecular weight polyethylene (UHMWPE) fabric was investigated. STF was prepared by dispersing nanosilica (SiO₂) into ethylene glycol. The shear thickening behavior of STF with the increase of the shear rate was observed by PhysicaMCR301. STF/UHMWPE composite fabric was synthesized by impregnating UHMWPE fabric in STF dilution. Stab resistant experiment was conducted on a self‐made stab test machine with knife and spike as stab tool. The results demonstrate that the stab resistant property of the UHMWPE fabric is greatly improved by impregnating STF. The stab resistant property is greatly increased with the increase of mass fraction of silica in STF. Especially, when the mass fraction of SiO₂ in STF is 38%, the stab resistance force and energy absorption of STF/UHMWPE are optimal for knife and spike threats. With the same stab resistant properties, the flexibility of UHMWPE fabric impregnated with STF is higher than that of the neat fabric. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The rheological properties of shear thickening fluid reinforced with ZnO of different friction characteristics

The viscosity of shear thickening fluid (STF) changes significantly with low concentrations of additives. However, existing research has suggested that there has not been any consistent enhancement mechanism of additives. The possible reason for this research gap is that existing research has focused on the effect of the shape and content of additives on shear thickening (ST) performance, whereas the friction characteristics of additives on ST performance have not been considered. Accordingly, nanoparticle-enhanced STF with various friction characteristics of ZnO was synthesized in this study to investigate the enhancement mechanism of additives. The aspect ratio of ZnO with different shapes was obtained through SEM analysis. The friction characteristics of ZnO were examined. Lastly, the rheological behavior of reinforced STFs was evaluated. The results indicated that ST performance was enhanced compared with that of neat STF, which was significantly dependent on the friction characteristics of ZnO.     

Improving mechanical properties of poly(vinyl chloride) by doping with organically functionalized reactive nanosilica

Nanosilica particles are functionalized by in situ surface‐modification with trimethyl silane and vinyl silane. Resultant reactive nanosilica (coded as RNS) contains double bonds and possesses good compatibility with vinyl chloride (VC) and polyvinyl chloride (PVC). This makes it feasible for RNS to copolymerize with VC generating RNS/PVC composites via in situ suspension polymerization. As‐prepared RNS/PVC composite resins are analyzed by means of FTIR. The tensile strength and impact strength of compression‐molded RNS/PVC composites are measured and compared with that of compression‐molded PVC composites doped with dispersible nano‐SiO₂ particles (abridged as DNS) surface‐modified with trimethyl silane alone. Moreover, the thermal stability of compression‐molded RNS/PVC and DNS/PVC composites is evaluated by thermogravimetric analysis. It has been found that RNS/PVC composites possess greatly increased impact strength and tensile strength than PVC matrix, while DNS/PVC composites possess higher impact strength than PVC matrix but almost the same tensile strength as the PVC matrix. This implies that DNS is less effective than RNS in improving the mechanical strength of PVC matrix. Particularly, RNS/PVC composites prepared by in situ suspension polymerization have much higher mechanical strength than RNS/PVC composites prepared by melt‐blending, even when their nanosilica content is only 1/10 of that of the melt‐blended ones. Besides, in situ polymerized RNS/PVC and DNS/PVC composites have better thermal stability than melt‐blended nanosilica/PVC composites. Hopefully, this strategy, may be extended to fabricating various novel high‐performance polymer‐matrix composites doped with organically functionalized nanoparticles like RNS. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhanced tribological performance of hybrid polytetrafluoroethylene/Kevlar fabric composite filled with milled pitch‐based carbon fibers

As self‐lubricating bearing liner materials, tribological properties of milled pitch‐based carbon fibers (CFs) modified polytetrafluoroethylene (PTFE)/Kevlar fabric composites were investigated, and the microscopic morphology of worn surface was studied. The results show that the appropriate incorporation of CFs can obviously reduce the wear rate of the fabric composite with almost unchanging friction coefficient. The wear rates of 5 wt % CF‐filled PTFE/Kevlar fabric composites are decreased by 30% and 48% for two kinds of composites made with fibers from different producers compared with unfilled fabric composites. Scanning electron microscopy observations show that the appropriate incorporation of CFs obviously improves the interfacial bonding and reduces pull‐out and fracture of Kevlar fiber. Meanwhile, the introduction of CFs at proper fraction is helpful to form smooth and continuous transfer film on the surface of metal counterpart. The improving mechanism of the CF is attributed to increasing mechanical strength, thermal conductivity and self‐lubricating effects. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46269.     

Effects of silica morphology on the shear-thickening behavior of shear thickening fluids and stabbing resistance of fabric composites

Shear-thickening fluid (STF) refers to a system where nonaggregating solid particles are suspended in a specific fluid. Due to its unique viscosity variation, STFs have attracted a lot of attention as soft body armor materials for impact protection. In this work, two kinds of STFs were designed using polyethylene glycol (PEG) and spherical or irregularly shaped silica particles. Rheological results showed that shear thickening can even occur at lower shear rates in the irregularly shaped silica-based STF; however, the thickening range of the spherical silica-based STF was broader. Meanwhile, the composites prepared with STFs and aramid fabrics exhibited better antistab properties than neat fabrics. Compared to composite prepared with irregularly shaped silica-based STF, spherical silica-based STF/aramid composite had better stabbing resistance. In addition to the binding effect of silica particles to the fiber bundle, it was considered that when the fabric composite was subjected to impact, spherical particles were easier to slide so that the STF was more likely to be thickened to achieve a greater viscosity, resulting in the better stabbing resistance performance. Our studies will provide guidance for the design of the high-performance soft body armor equipment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48809.     

Effect of nanoparticle localization on the rheology,morphology and toughness of nanocomposites based on poly(lactic acid)/natural rubber/nanosilica

In this study, poly(lactic acid)/natural rubber blends and their nanocomposites with silica nanoparticles were prepared via the melt mixing process. The rheology, morphology and impact resistance of the prepared samples were examined depending on the silica content (0–7 phr) and its localization. The results obtained showed that the incorporation of silica below its percolation threshold led to its selective localization in the matrix and mostly near the interface. This was in agreement with the results obtained by calculation of the wetting parameter. At a high content of silica, the silica nanoparticles could also be located in the dispersed phase. Energy dispersive spectroscopy and compositional mapping of oxygen and silicon atoms proved the presence of nanoparticles at the interface. The formation of a silica nanolayer with a thickness of 55–70 nm at the interface was shown by AFM. An optimum amount of nanosilica in the blend, through its interfacial localization and reduction of the natural rubber droplet size (confirmed by SEM test), caused a significant improvement in the impact strength, which was nearly 26 times that of neat poly(lactic acid). © 2019 Society of Chemical Industry     

黏弹性流体基纳米流体流变学特性

黏弹性流体基纳米流体（viscoelastic fluid based nanofluid,VFBN）是一种具有湍流减阻和对流换热相对强化特性的新型换热工质,其湍流减阻机理与流变学特性关系密切。通过对以2.5×10^-3、5×10^-3、1×10^-2三种质量分数的十六烷基三甲基氯化铵/水杨酸钠水溶液为基液,粒子体积分数为0.1%、0.25%、0.5%、1.0%的铜纳米流体的剪切黏度、零剪切黏度以及松弛时间的测量,实验结果表明VFBN有明显的剪切稀变特性,同时纳米粒子的添加增大了基液的零剪切黏度,并导致基液黏弹性增强。以Giesekus本构模型为理论基础,利用实验参数得到了描述VFBN剪切黏度的实验关联式。     

Influence of the dispersion of Nanoclays on the cellular structure of foams based on polystyrene

In the present work blends of polystyrene (PS) with sepiolites have been produced using a melt extrusion process. The dispersion degree of the sepiolites in the PS has been analyzed by dynamic shear rheology and X-ray micro-computed tomography. Sepiolites treated with quaternary ammonium salts (O-QASEP) are better dispersed in the PS matrix than natural sepiolites (N-SEP) or sepiolites organo-modified with silane groups (O-SGSEP). A percolated network is obtained when using 6.0 wt% of O-QASEP, 8.0 wt% of N-SEP and 10.0 wt% of O-SGSEP. It has been shown that multiple extrusion processes have a negative effect on the polymer architecture. They produce a reduction in the length of the polymeric chains, and they do not lead to a better dispersion of the particles in the polymer matrix. Foams have been produced using a gas dissolution foaming process, where a strong effect of the dispersion degree on the cellular structure of the different foams was found. The effects on the cellular structure obtained by using different types of sepiolites, different contents of sepiolites and different extrusion conditions have been analyzed. The foams produced with the formulations containing O-QASEP present the lowest cell size and the most homogeneous cellular structures.     

Enhanced thermal conductivity of PLA‐based nanocomposites by incorporation of graphite nanoplatelets functionalized by tannic acid

Enhancing thermal conductivity of polymeric nanocomposites remains a great challenge because of the poor compatibility between nanofillers and the polymeric matrix and the aggregation effect of nanofillers. We report the enhanced thermal conductivity of poly(lactic acid) (PLA)‐based nanocomposites by incorporation of graphite nanoplatelets functionalized by tannic acid. Graphite nanoplatelets (GNPs) were noncovalently functionalized with tannic acid (TA) by van der Waals forces and π–π interaction without perturbing the conjugated sp² network, thus preserving the high thermal conductivity of GNPs. PLA‐based nanocomposites with different contents of TA‐functionalized GNPs (TA‐GNPs) were prepared and characterized, and the influences of TA‐GNPs content on the morphologies, mechanical properties, and thermal properties of the composites were investigated in detail. TA‐GNPs remarkably improved the thermal conductivity of PLA up to 0.77 W/(m K), showing its high potential as a thermally conductive filler for polymer‐based nanocomposites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46397.     

Effect of layering pattern on the water absorption behavior of banana glass hybrid composites

Hybridization of Banana fibers with glass fibers has been found to reduce the water absorption behavior of the composites in an earlier work by us. Banana fibers were hybridized with glass and different layering patterns were followed in the preparation of the composites. The effect of the various layering patterns on the water absorption of the composites was studied. It was found that water diffusion occurs in the composite depending on the layering pattern as well as the temperature. In all the experiments, it has been found that composites with an intimate mixture of glass and banana show the maximum water uptake except for temperature of 90°C. At 90°C the maximum water uptake is found to be for composites where there is one layer of banana and another layer of glass. The water uptake follows the same trend as that in all other temperatures till a time span of 4900 min is reached. The kinetics of diffusion was found to be Fickian in nature. The various thermodynamic parameters like sorption coefficient, diffusion coefficient. Enthalpy change, entropy change, and activation energy of the various composites were calculated. From all the calculations it has been concluded that layering pattern is an important parameter which controls the water absorption of the composites. The layering pattern Cg‐b‐g was found to have the lowest water uptake. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Modeling and numerical analysis of nanoliquid (titanium oxide,graphene oxide) flow viscous fluid with second order velocity slip and entropy generation

The prime objective of the present communication is to examine the entropy-optimized second order velocity slip Darcy–Forchheimer hybrid nanofluid flow of viscous material between two rotating disks.Electrical conducting flow is considered and saturated through Darcy–Forchheimer relation. Both the disks are rotating with different angular frequencies and stretches with different rates. Here graphene oxide and titanium dioxide are considered for hybrid nanoparticles and water as a continuous phase liquid. Joule heating, heat generation/absorption and viscous dissipation effects are incorporated in the mathematical modeling of energy expression. Furthermore, binary chemical reaction with activation energy is considered. The total entropy rate is calculated in the presence of heat transfer irreversibility, fluid friction irreversibility,Joule heating irreversibility, porosity irreversibility and chemical reaction irreversibility through thermodynamics second law. The nonlinear governing equations are first converted into ordinary differential equations through implementation of appropriate similarity transformations and then numerical solutions are calculated through Built-in-Shooting method. Characteristics of sundry flow variables on the entropy generation rate, velocity, concentration, Bejan number, temperature are discussed graphically for both graphene oxide and titanium dioxide hybrid nanoparticles. The engineering interest like skin friction coefficient and Nusselt number are computed numerically and presented through tables. It is noticed from the obtained results that entropy generation rate and Bejan number have similar effects versus diffusion parameter. Also entropy generation rate is more against the higher Brinkman number.