Polymer Strands Research Articles

GFRP composite bars for splicing prestressed precast concrete piles: Design and experimental investigation

Glass Fiber Reinforced Polymer (GFRP) composite bars were investigated in this study as a corrosion-resistant dowel for splicing prestressed precast concrete piles (PPCPs). In addition to their durability and good mechanical performance, GFRP bars show cost advantage when compared to other corrosion-resistant material. Using available design guides for FRP-reinforced concrete sections, a typical epoxy bonded dowel splice using GFRP bars was designed for an 18 × 18 in (457 × 457 mm) PPCP. In order to validate the adopted design procedure and to investigate the effectiveness of GFRP reinforcing bars as bonded dowels for pile splice design, 10 full-scale PPCP specimens of 18 × 18 in (457 × 457 mm) cross-section with a total length of 28 ft (8.5 m) were designed, fabricated, and tested at the Florida Department of Transportation (FDOT) Structures Research Center. In these specimens, three different materials for dowels; GFRP reinforcing bars, Carbon Fiber Reinforced Polymer (CFRP) strand, and traditional carbon-steel reinforcing bars were used in combination with CFRP and steel prestressing strands for PPCPs for both unforeseen and preplanned drivable splicing cases. The focus of this study was on the flexural performance at the splice. The experimental results show that the proposed epoxy GFRP dowel pile splice can match the required design flexural resistance for a preplanned PPCP carbon-steel pile splice. The laboratory tests performed in this research validates the new design procedure for the GFRP dowel splice. The design flexural resistance for the GFRP dowel splice calculated by the new procedure provides 68 % of 245 kip-ft (332.2 kNm), the flexural resistance required by the FDOT design specifications for mechanical preplanned splices. This research will help to improve the standard designs and construction specifications.

Synergistic influence of tetraethyl orthosilicate crosslinker on mixed matrix hydrogels

Hydrogel is a 3D framework of hydrophilic polymeric material that quickly absorbs and retains a huge amount of water (or other fluid) and offers versatile functionality. A series of unique carboxymethyl cellulose/Xanthan gum/polyvinyl alcohol (CXP) blended hydrogels, containing both the natural and synthetic polymers, were prepared by following the blending and casting approach. The polymers were incorporated through chemical crosslinking by tetraethyl orthosilicate (TEOS). The fabricated hydrogels showed all required features: non-toxicity, biocompatibility, and improved mechanical strength. The addition and variation in TEOS (crosslinker) significantly impacted the key characteristics of CXP hydrogel. The scanning electron microscopy (SEM) images showed the porous structure and indicated that the pore's size and intensity were reduced with the surge in TEOS content. Fourier transform infrared spectroscopy (FTIR) results confirmed the successful incorporation of various polymeric strands through crosslinking by TEOS. The thermogravimetric analysis (TGA) highlighted the greater stability of all the hydrogels over high temperatures. The crosslinked hydrogel displayed higher thermal resilience than the uncross-linked one. The differential thermal analysis (DTA) also confirmed that the addition of TEOS content drastically enhanced the thermal endurance of crosslinked hydrogels in comparison with the neat hydrogel. All the specimens exhibited good swelling ability in distilled water during the swelling studies. This study also reflected that the addition of crosslinker in a limited amount (50 µL) has significantly enhanced the swelling but further increase in concentration hindered the water uptake. The swelling response of blends towards pH revealed low swelling of films in acidic and basic pH, but maximal swelling in neutral media. This unique pH response of hydrogels at neutral pH along with the biocompatibility made them suitable for injectable managed drug carrier.

Stress‐free two‐way shape memory property and microstructure evolution of single‐phase polymer networks

AbstractIn this work, single‐phase polymer networks with excellent stress‐free two‐way shape memory effect (2W‐SME) were successfully fabricated based on poly(ethylene‐co‐vinyl acetate) (EVA) and dicumyl peroxide. The microstructural evolution during actuation was repeatable and reversible, as demonstrated by the in situ wide‐angle X‐ray scattering. During multiple heating and cooling cycles, the (110) and (200) reflections of EVA appeared with increasing intensity, and the orientation degree was high at the low temperature point (10°C), suggesting that the oriented crystallites are present throughout the entire sample and hold extended conformation of the polymer strands in the amorphous phase. When heating to a high temperature (Thigh = 70°C), partial melting of crystallites leads to the contraction of the material, and the intensity of the (110) and (200) reflections and the orientation became smaller, indicating that the residual oriented crystallites could still provide an anisotropic skeleton for the oriented recrystallization of the amorphous molecular chain. Moreover, the reversible actuation strain showed a maximum value of 15.6% at a Thigh of 72°C and was present even at a Thigh of 80°C when the polymer had a very small crystalline fraction (2.2%). Considering the remarkable stress‐free 2W‐SME, EVA may have potential applications in smart grippers, actuators, and sensors.

Recent advances in melt electro writing for tissue engineering for 3D printing of microporous scaffolds for tissue engineering

Melt electro writing (MEW) is a high-resolution 3D printing technique that combines elements of electro-hydrodynamic fiber attraction and melts extrusion. The ability to precisely deposit micro- to nanometer strands of biocompatible polymers in a layer-by-layer fashion makes MEW a promising scaffold fabrication method for all kinds of tissue engineering applications. This review describes possibilities to optimize multi-parametric MEW processes for precise fiber deposition over multiple layers and prevent printing defects. Printing protocols for nonlinear scaffolds structures, concrete MEW scaffold pore geometries and printable biocompatible materials for MEW are introduced. The review discusses approaches to combining MEW with other fabrication techniques with the purpose to generate advanced scaffolds structures. The outlined MEW printer modifications enable customizable collector shapes or sacrificial materials for non-planar fiber deposition and nozzle adjustments allow redesigned fiber properties for specific applications. Altogether, MEW opens a new chapter of scaffold design by 3D printing.

Polyacrylamide hydrogels. V. Some strands in a polymer network bear loads, but all strands contribute to swelling

When a polymer network is stretched, some polymer strands do not bear loads. Examples include looped strands, dangling strands, and extremely long strands. When the polymer network is submerged in a solvent, however, all strands mix with solvent molecules. This distinction between strands that bear loads and strands that do not leads us to modify the Flory-Rehner model. The modified model has three parameters: the density of load-bearing strands, N, the density of all strands, M, and the interaction parameter, χ. For a polymer network submerged in a reservoir of solvent and bearing triaxial stresses, the modified model provides equations of state, relating the stresses to stretches, as well as the chemical potential of solvent molecules and temperature in the reservoir. We synthesize polyacrylamide hydrogels using precursors of various concentrations of monomer, crosslinker, and transfer agent. We determine the three parameters N, M, and χ by fitting the modified model to several experiments, including free swelling, fast tension, and stress relaxation. In all samples tested, M is several times N, whereas χ is nearly constant. This work demonstrates the consequences of the notion that some polymer strands in a polymer network bear loads, but all strands contribute to swelling.

Conformation Dynamics of Single Polymer Strands in Solution.

Conformational changes in macromolecules significantly affect their functions and assembly into high-level structures. Despite advances in theoretical and experimental studies, investigations into the intrinsic conformational variations and dynamic motions of single macromolecules remain challenging. Here, liquid-phase transmission electron microscopy enables the real-time tracking of single-chain polymers. Imaging linear polymers, synthetically dendronized with conjugated aromatic groups, in organic solvent confined within graphene liquid cells, directly exhibits chain-resolved conformational dynamics of individual semiflexible polymers. These experimental and theoretical analyses reveal that the dynamic conformational transitions of the single-chain polymer originate from the degree of intrachain interactions. In situ observations also show that such dynamics of the single-chain polymer are significantly affected by environmental factors, including surfaces and interfaces.

Tight junction channel regulation by interclaudin interference

Tight junctions form selectively permeable seals across the paracellular space. Both barrier function and selective permeability have been attributed to members of the claudin protein family, which can be categorized as pore-forming or barrier-forming. Here, we show that claudin-4, a prototypic barrier-forming claudin, reduces paracellular permeability by a previously unrecognized mechanism. Claudin-4 knockout or overexpression has minimal effects on tight junction permeability in the absence of pore-forming claudins. However, claudin-4 selectively inhibits flux across cation channels formed by claudins 2 or 15. Claudin-4-induced loss of claudin channel function is accompanied by reduced anchoring and subsequent endocytosis of pore-forming claudins. Analyses in nonepithelial cells show that claudin-4, which is incapable of independent polymerization, disrupts polymeric strands and higher order meshworks formed by claudins 2, 7, 15, and 19. This process of interclaudin interference, in which one claudin disrupts higher order structures and channels formed by a different claudin, represents a previously unrecognized mechanism of barrier regulation.

Superstretchable Elastomer from Cross-linked Ring Polymers.

The stretchability of polymeric materials is critical to many applications such as flexible electronics and soft robotics, yet the stretchability of conventional cross-linked linear polymers is limited by the entanglements between polymer chains. We show using molecular dynamics simulations that cross-linked ring polymers are significantly more stretchable than cross-linked linear polymers. Compared to linear polymers, the entanglements between ring polymers do not act as effective cross-links. As a result, the stretchability of cross-linked ring polymers is determined by the maximum extension of polymer strands between cross-links, rather than between trapped entanglements as in cross-linked linear polymers. The more compact conformation of ring polymers before deformation also contributes to the increase in stretchability.

Differentiated transmittance of vortex beams in helical polymer media

Light beam with helical wavefront, also called optical vortex, carries quantized orbital angular momentum, and as such have many potential photonic applications. In this study, the interaction of a fluorene-based helical polymer thin film with vortex beams was studied. The helicity of the polymeric strands was greatly enhanced by thermal annealing. A liquid crystal phase plate was used to convert TEM00 laser beams into a helical wavefront beam with a phase singularity at its axis. A relatively high absorption dissymmetry was observed in a longer wavelength range, compared with the linear optical absorption of the annealed film sample. The left- and right-handed vortices had different transmittances. The absorption asymmetry of the annealed fluorene film in the case of vortex beams is mainly attributed to quadrupole interactions.

Interfacial Reinitiation of Free Radicals Enables the Regeneration of Broken Polymeric Hydrogel Actuators

Interfacial Reinitiation of Free Radicals Enables the Regeneration of Broken Polymeric Hydrogel Actuators

Stereocomplexation of Stereoregular Aliphatic Polyesters: Change from Amorphous to Semicrystalline Polymers with Single Stereocenter Inversion.

Stereocomplexation is a useful strategy for the enhancement of polymer properties by the co-crystallization of polymer strands with opposed chirality. Yet, with the exception of PLA, stereocomplexes of biodegradable polyesters are relatively underexplored and the relationship between polymer microstructure and stereocomplexation remains to be delineated, especially for copolymers comprising two different chiral monomers. In this work, we resolved the two enantiomers of a non-symmetric chiral anhydride (CPCA) and prepared a series of polyesters from different combinations of racemic and enantiopure epoxides and anhydrides, via metal-catalyzed ring-opening copolymerization (ROCOP). Intriguingly, we found that only specific chiral combinations between the epoxide and anhydride building blocks result in the formation of semicrystalline polymers, with a single stereocenter inversion inducing a change from amorphous to semicrystalline copolymers. Stereocomplexes of the latter were prepared by mixing an equimolar amount of the two enantiomeric copolymers, yielding materials with increased melting temperatures (ca. 20 °C higher) compared to their enantiopure constituents. Following polymer structure optimization, the stereocomplex of one specific copolymer combination exhibits a particularly high melting temperature (Tm = 238 °C).

Novel High‐Speed Elongation Rheometer

AbstractThe elongational viscosity of polymers can be determined by utilizing different devices such as extensional rheometer after Sentmanat (SER), oil bath rheometer after Meissner or tensile rheometer after Münstedt (MTR), with strain rates up to 10 s–1. Although these investigations are already complex, they do not depict real fiber spinning processes where higher elongation strain rates occur. Therefore, a novel method is developed to calculate the elongational viscosity of polymers during the fiber spinning process. To reduce the complexity of the system, two polymethylmethacrylates (PMMAs) with different molar masses are investigated using a capillary rheometer to exclude crystallization effects. The diameter of the polymeric strand is determined via a high‐speed camera from the die exit to the aspirator. In addition, simulations are carried out to describe the temperature profile of the polymeric strand along the spinline. It is possible to determine the elongational viscosity of the polymers in dependence of temperature and strain rates up to 100 s–1, by calibration of the force in an aerodynamic stretching device (aspirator).

Coordination polymers of d- and f-elements with (1,4-phenylene)dithiazole dicarboxylic acid

The new ditopic ligand [2,2′-(1,4-phenylene)bithiazole]-5,5′-dicarboxylic acid (H2TzPhTz) was synthesized in ∼ 70% yield through a classical Hantzsch synthesis. Isolation of the dimethyl ester intermediate Me2TzPhTz as the trifluoroacetic acid adduct Me2TzPhTz·2CF3CO2H allowed its crystal structure determination, revealing that the constituting molecules are interconnected through an extended hydrogen-bond network. Reaction of H2TzPhTz with suitable ZnII and UVI salts yielded the 1-D coordination polymers [Zn(TzPhTz)(H2O)2] (Zn_TzPhTz) and [UO2(TzPhTz)(DMF)]·DMF (U_TzPhTz). The former is characterized by zig-zag chains with cis-{Zn(OCOO)4(OH2O)2} nodes and μ-η2:η2-TzPhTz2- spacers, while in the latter TzPhTz-bridged {UO2(TzPhTz)(DMF)}2 dimeric units form polymeric strands. In the solid state, both H2TzPhTz and Zn_TzPhTz emit in the blue-green visible region (λem = 474 and 477 nm, respectively). The two coordination polymers witness the versatility of H2TzPhTz as a linker toward d and f metal ions, and they should be considered as the preliminary step toward the preparation of TzPhTz-based metal–organic frameworks for practical applications in the field of luminescence sensing.

Investigating the effect of cooling rate on strength of Fused Filament Fabrication parts using differential scanning calorimetry technique

Desired mechanical properties are major area of interest within the field of Additive Manufacturing (AM) technologies. Fused Filament Fabrication (FFF) is an extrusion-based AM technique. In FFF process, the primary concern of strength is bonding between strands,and it is greatly influenced by the heat transfer during the manufacturing process. The extent of bonding not only influences the strength, but also the structural integrity of the part. To study the bonding between the extruded polymer strands of FFF process, investigation must be done to understand the influence of rate of cooling during FFF process. The present study focuses on investigation of cooling rate effects on FFF-ABS (Acrylonitrile Butadiene Styrene) parts over their tensile strength. Since glass transition temperature plays a key role in understanding the history of the thermal behavior, it is hence important to estimate its value for various extrusion temperatures. To understand this, glass transition temperature is estimated through Differential Scanning Calorimetry (DSC) experimentation technique as it records the thermal history of the polymer and hence this test is applied at different cooling rate. Additionally, to support the DSC graphs, tensile testing of FFF made parts is done on the parts manufactured at two extreme extruder temperatures namely 230° C and 250° C. Better bond formation between the strands contributes to higher strength and hence neck growth is estimated by capturing the scanning electron microscope graphs. The higher strength (as obtained for higher neck growth)is due to higher or proper cooling process. The results also show that the parts cooled at higher cooling rate have better bonding in terms of neck growth which proves a good agreement among the cooling rate, strength, and neck growth. The novelty of this work lies in polymer characterization to provide more insights in FFF layer deposition process (effect of different cooling rate on FFF process) using DSC and mechanical testing/analysis.

Correlation between Scratch Behavior and Tensile Properties in Injection Molded and Extruded Polymers.

This study investigates the validity and applicability of the correlation between scratch and tensile properties for extruded polymer strands. The mechanical properties could be predicted for extruded samples, which allows skipping the step of injection molding and therefore enables a faster material development. Extruded polymer strands and tensile test specimens out of PMMA, PS, POM, PP and PE have been investigated. A correlation of the Young’s modulus and the elastic deformation as well as a correlation of the yield stress and the plastic deformation during scratching is given for both flat molded and cylindrical extruded specimens. SEM images of the scratch grooves are used to analyze the scratch deformation mechanism. The deformation mechanism correlates well to the variation coefficient of the indentation depth. Polarized light microscopy of thin cross sections of both types of specimens provides information about skin layer thickness and morphology. However, the optical analysis could not provide an explanation for the different levels of the indentation depth in the two specimen types. Further investigations should include a study of differences in process induced morphology and the effect of two layers with different mechanical properties, i.e., skin and center, on the stress and strain fields underneath the scratch.

The Effect of 5-Fluorouracil on the Adhesion Process in Patients Operated on for Colorectal Cancer

Objective:The aim of this study was to improve the direct results of reconstructive surgery in patients operated on for complicated forms of colorectal cancer, by using 5-fluorouracil in the postoperative period. Methods:The study involved 126 patients (they were divided into 2 groups) with colorectal cancer, who underwent reconstructive surgery. They underwent a standard clinical examination and a mandatory examination program. Results:The use of 5-fluorouracil in adjuvant treatment in patients with colorectal cancer significantly reduces the number of subjective clinical manifestations (positional tests) in the main group – 17%, and in the control group – 54.3%, as well as objective clinical manifestations (instrumental research methods) in Group I – 13%, and Group II – 89.5%, respectively. The study shows that in re-operated patients with colorectal cancer who received 5-fluorouracil, abdominal adhesions are characterized by a low content of collagen and fibroblasts, low vascularization and a high content of polymerized fibrin strands. It was also found that re-operated patients with colorectal cancer who did not receive 5-fluorouracil, abdominal adhesions are characterized by a high collagen content, a large number of fibroblasts, and severe angiogenesis. Conclusion:It was found that the prolonged administration of 5-fluorouracil statistically significantly reduces the risk of adhesions, thereby showing the effectiveness of preventing adhesive disease of the abdominal organs. It was shown that the prolonged administration of 5-fluorouracil significantly reduces the number of subjective and objective signs of adhesive disease of the abdominal organs, as well as significantly decreases intraoperative and postoperative complications, the duration of the operation, and the amount of blood loss. In the postoperative period, it reduces the length of hospital stay and improves the quality of life of patients.

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Computer simulations of melts of ring polymers with nonconserved topology: A dynamic Monte Carlo lattice model.

We present computer simulations of a dynamic Monte Carlo algorithm for polymer chains on a fcc lattice which explicitly takes into account the possibility to overcome topological constraints by controlling the rate at which nearby polymer strands may cross through each other. By applying the method to systems of interacting ring polymers at melt conditions, we characterize their structure and dynamics by measuring, in particular, the amounts of knots and links which are formed during the relaxation process. In comparison with standard melts of unknotted and unconcatenated rings, our simulations demonstrate that the mechanism of strand crossing makes polymer dynamics faster provided the characteristic timescale of the process is smaller than the typical timescale for chain relaxation in the unperturbed state, in agreement with recent experiments employing solutions of DNA rings in the presence of the type II topoisomerase enzyme. In the opposite case of slow rates the melt is shown to become slower, and this prediction may be easily validated experimentally.

Measuring packing length in simulations for different polymer architectures

The packing length p figures prominently in scaling predictions of the entanglement length and bulk modulus for polymer melts and solutions. p has been argued to scale as the ratio of chain displaced volume V and mean square end-to-end distance R2. This scaling works for several cases; however, it is not obvious how to apply it to chains with side groups, and the scaling must fail for sufficiently thin, stiff chains. In this work, we measure the packing length in simulations, without making any scaling assumptions, as the typical distance of closest approach of two polymer strands in a simulated bead-spring melt. We use the intermolecular correlation function to measure the distance up to which a given polymer strand dominates the local volume fraction. Using our measured packing length, we find good agreement of entanglement properties with Lin–Noolandi scaling for flexible polymers of different architectures.

Wearable membranes from zirconium-oxo clusters cross-linked polymer networks for ultrafast chemical warfare agents decontamination

The urgent need for immediate personal protection against chemical warfare agents (CWAs) spurs the requirement on robust and highly efficient catalytic systems that can be conveniently integrated to wearable devices. Herein, as a new concept for CWA decontamination catalyst design, sub-nanoscale, catalytically active zirconium-oxo molecular clusters are covalently integrated in flexible polymer network as crosslinkers for the full exposure of catalytic sites as well as robust framework structures. The obtained membrane catalysts exhibit high swelling ratio with aqueous content as 84 wt% and therefore, demonstrate quasi-homogeneous catalytic activity toward the rapid hydrolysis of both CWA, soman (GD) (t1/2 = 5.0 min) and CWA simulant, methyl paraoxon (DMNP) (t1/2 = 8.9 min). Meanwhile, due to the covalent nature of cross-linkages and the high flexibility of polymer strands, the membranes possess promising mechanical strength and toughness that can stand the impact of high gas pressures and show high permeation for both CO2 and O2, enabling their extended applications in the field of collective/personal protective materials with body comfort.