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Recently, fiber-reinforced, epoxy-based, optically transparent composites were successfully produced using resin transfer molding (RTM) techniques. Generally, the production of structural, optically transparent composites is challenging since it requires the combination of a very smooth mold surface with a sufficient control of resin flow that leads to no visible voids. Furthermore, it requires a minimum deviation of the refractive indices (RIs) of the matrix polymer and the reinforcement fibers. Here, a new mold design is described and three plates of optically transparent glass fiber-reinforced polymers (tGFRP) with reproducible properties as well as high fiber volume fractions were produced using the RTM process and in situ polymerization of an epoxy resin system enclosing E-glass fiber textiles. Their mechanical (flexural), microstructural (fiber volume fraction, surface roughness, etc.), thermal (DSC, TGA, etc.), and optical (dispersion curves of glass fibers and polymer as well as transmission over visible spectra curves of the tGFRP at varying tempering states) properties were evaluated. The research showed improved surface quality and good transmission data for samples manufactured by a new Optical-RTM setup compared to a standard RTM mold. The maximum transmission was reported to be ≈74%. In addition, no detectable voids were found in these samples. Furthermore, a flexural modulus of 23.49 ± 0.64 GPa was achieved for the Optical-RTM samples having a fiber volume fraction of ≈42%., Bundesministerium für Wirtschaft und Klimaschutz

This study investigates the effect of washing fabrics (nylon 6.6 powernet knitted fabrics with 30% spandex) treated with chitosan on their moisture management and air permeability. The knitted fabrics were treated with three different solutions of chitosan and dimethylol dihydroxyethylene urea (DMDHEU); in addition to chitosan and DMDHEU, one solution contained the complexing agent ethylenediaminetetraacetic acid (EDTA) and the other contained the nonionic surfactant and penetration agent octylphenol ethoxylate. The three solutions were compared in terms of their effect on moisture management and air permeability properties. Nylon fabrics treated and washed with these solutions were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Nylon fabrics treated with chitosan and DMDHEU showed the potential to transfer liquid moisture to the lower layer and keep the layer next to the skin dry after 20 washes.

The production of optically transparent glass-fiber-reinforced composites based on a thermoset resin using both vacuum-assisted resin infiltration (L-RTM) and resin transfer molding (RTM) was successfully accomplished. The composites have been characterized in terms of infiltration quality, degree of transparency, mechanical and thermal properties. A good match in the RIs, smooth composite surfaces, and high infiltration quality have been achieved. The key to success was the low viscosity of the resin-hardener mixture. The good surface quality was accomplished via polymerization in a glass cavity of the L-RTM setup. The mechanical properties of the composites containing 5- or 10-layers of the glass fabric correlate with a heterogeneous distribution of these fabrics. By contrast, composites containing 29-layers, corresponding to 44 v. % of fiber, possess strongly enhanced mechanical properties. By matching the RIs of the materials at 589 nm, almost unchanged optical properties were obtained in this wavelength region for the 5- and 10-layer samples. Furthermore, compared to 86% of the pure polymer matrix, up to 75% transmittance was accomplished with the composite containing 29 layers of fabric, both prepared by L-RTM. A tensile strength of 435 MPa and a modulus of 24.3 GPa were achieved for the same composite, compared to 67 MPa strength and 3.6 GPa modulus of the polymer matrix, both prepared by RTM. Manual process control of the presented LCM manufacturing methods is challenging, particularly with regard to controlling sample thickness i.e., fiber v. %. Also, the flow front propagation requires better mold design, resin volume flow, and injection pressure control. For a homogeneous distribution of the textiles within the cavity, a new mold design combining the good surface quality of the L-RTM and the capability of the RTM setups to produce large-sized parts is required. Considering that commercially available resin systems and textiles were used in this study, the major limitation of the technology outlined here is related to upscaling and equipment. To satisfy these needs, a new RTM mold design and development is required that can provide an industry-scale, low porosity, and smooth surface production.

The profound stereosequence dependence of the glass transition temperature (Tg) of poly(methyl methacrylate)s (PMMAs) offers the possibility to evaluate any conformational contributions to their gl...

This research focused on understanding the microbe killing mechanism of the antimicrobial properties of highly elastic conductive poly(ethylene terephthalate) (PET)/multi-walled carbon nanotube (MWCNT) powernet fabrics with the help of electric fields and highly elastic structure. In this study, PET/MWCNT fabrics containing three different percentages of MWCNT were knitted and characterized with antimicrobial activity, cytotoxicity, electromagnetic shielding properties, DSC analyses, stiffness tests, and pressure measurements using wireless pressure sensors. Results show that MWCNT has a statistically significant effect on antibacterial activity, cytotoxicity, electromagnetic shielding, stiffness, and exerted pressures. PET/MWCNT fabrics showed excellent antibacterial activity against tested germs; S. aureus and E. coli. A statistically significant increase in percentage reduction of bacteria was observed with the increase in carbon nanotube nanoparticle concentration, accompanied by a good laudering durability even after 20 washing cycle. In terms of cytotoxicity tests, all PET/MWCNT samples were found to have over 70% average relative cell viability, indicating that they are noncytotoxic without interrupting the cell line and primary cell growth in vitro. The materials have provided longer conductive networks and formed electromagnetic shielding at the range of 22.79 dB-25.77 dB at the frequency of 0–1.30 GHz. Moreover, MWCNT concentration did not lead to considerable changes in physical properties like stiffness and exerted pressure properties. Characterization analyses confirmed the changes in the chemical structure of the PET/MWCNT.

Antimony tin alloy (SnSb) has been regarded as a promising anode material for sodium-ion batteries due to its high capacity. However, the rapid capacity decay of SnSb anodes caused by volume changes during repeated cycles must be solved before they can be used in practical batteries. Here, we introduce centrifugally-spun SnSb@rGO@CMF composite anode for sodium-ion batteries, which not only has high sodium storage capability but also maintains its structural integrity after repetitive cycles. SnSb@rGO@CMF composite was prepared by high-speed and cost-effective centrifugal spinning and subsequent heat treatment processes. Electrochemical performance results demonstrated that SnSb@rGO@CMF composite anode had excellent initial reversible capacity (350.3 mAh g−1), outstanding initial Coulombic efficiency (68.2%), and superior capacity retention (91.1%) over 200 cycles at 50 mA g−1. Therefore, centrifugally-spun SnSb@rGO@CMF composite has great application prospect as an anode material for sodium-ion batteries.

Polymer-urea inclusion compounds (P-U-ICs) were formed using a series of linear aliphatic polyesters with varying crystallizabilities: from highly crystalline to wholly amorphous. The traditional hexagonal P-U-ICs were obtained irrespective of the crystallinities of the neat guest polyesters. Two distinct co-crystallization mechanisms were evident based on the observation of the change in thermal stabilities of the ICs using DSC and the crystal morphologies by SEM; one involves polymer chain folding back and forth in a lamella-like crystal structure and the other grows much like short chain molecule U-ICs absent of chain reentering different channels. For polymers with sufficient chain length, their inherent flexibility is the key factor determining the co-crystallization mechanism while their crystallizability affects the kinetics, the consequences of which are more pronounced during recrystallization from melt. The amorphicity induced by random ester group placement is an interchain property, which does...

Potential sampling errors (regional variation) on an electrospun mat were explored and person-to-person (analyst affect) variation in image analysis of the fiber diameter were investigated via detailed statistical analyses. Scanning electron microscope (SEM) samples were prepared from the vertical midline of a single non-woven mat of electrospun polyethylene oxide. Thirteen analysts with identical training and instructions measured the diameters of the nanofibers from the six SEM images and statistical analyses were performed on the resulting data. The fiber diameters were significantly different in the lower region than the upper and center regions. Furthermore, the fiber diameters in the lower region—from micrographs taken only millimeters apart—were statistically different demonstrating a statistically significant regional variation in the sample. Furthermore, statistically significant variation between the analysts also was observed, with the average fiber diameter ranging from 166 nm to 276 nm.

A series of wholly amorphous linear aliphatic co- and tetra-polyesters were synthesized via bulk melt step-growth polymerization. Their glass transition temperatures were determined using DSC and were essentially unaffected by crystallinity. The glass transition temperatures of the polyesters increase linearly with the ratio of ester groups per methylene group. Extrapolations of the ratio to zero ester group content gave a reliable value for the Tg of amorphous polyethylene (PE). The experimental Tgs manifest a steeper slope on the Tg vs. ester group content plot compared to those calculated using Van Krevelen's group contribution method. The intramolecular equilibrium flexibilities were evaluated through the calculation of conformational entropies of individual polymer chains approximated by considering solely the short-range interactions between neighboring groups, as embodied in their RIS conformational models. Their calculated conformational entropies, Sconf, decrease linearly with increasing ester group content, leading to the observation that Sconf ∝ 1/Tg.

Nanocomposites prepared by incorporating functionalized polyhedral oligomeric silsesquioxane (POSS) into polymer matrices afford a wide range of versatile hybrid materials for use in technologies ranging from cosmetics and pharmaceuticals to sensors and batteries. Here, we investigate the phase behavior of nanocomposites composed of poly(ethylene oxide) (PEO) and monosubstituted isobutyl POSS (iPOSS) modified with different functional moieties. Microscopic analyses of blends containing these iPOSS variants reveal the existence of different macroscopic morphologies and surface topologies. In the presence of octa-iPOSS, a POSS-rich surface cell motif reminiscent of breath patterns develops, whereas addition of allyl-iPOSS promotes the formation of surface plates. While aminopropyl-iPOSS forms dispersed aggregates, maleamic acid-iPOSS disperses in PEO with little effect on PEO crystal morphology. We perform rotational isomeric state Monte Carlo simulations to discern the effect of monosubstitution on the interaction energy between iPOSS and PEO, and establish the molecular-level origin for these observed differences in phase behavior.

Pyriproxyfen is a pyridine based pesticide which is effective against mosquito larvae. Here we report the inclusion complexes (ICs) between guest pyriproxyfen and host β and γ cyclodextrins, but not with α cyclodextrin, based on WAXD, DSC, FTIR, and TGA characterization results. We show that one pyriproxyfen molecule is covered with between one and two β or γ cyclodextrin molecules when it forms columnar ICs upon precipitation from aqueous solution.

Melt-spun fibers were made from poly(ε-caprolactone) (PCL) coalesced from stoichiometric inclusion complex crystals formed with host urea. Melting and crystallization behaviors, mechanical properties, and the birefringence of undrawn and cold-drawn fibers were investigated. Undrawn coalesced PCL fibers were observed to have 500-600% higher moduli than undrawn as-received (asr) PCL fibers and a modulus comparable to drawn asr PCL fibers. Drawn coalesced PCL fibers have the highest crystallinity, orientation, and 65% higher moduli than drawn asr PCL fibers. Drawn coalesced PCL fibers have only a 5% higher crystallinity than drawn asr PCL fibers, yet they have 65% higher moduli and lower elongation at break values. Clearly, the intrinsic alignment of the coalesced polymers is the reason for their higher moduli and lower elongation, as confirmed by the birefringence observed in drawn coalesced and asr-PCL fibers. The improved mechanical properties of coalesced PCL fibers make them a better candidate for use in tissue engineering as scaffolds.

A poly(ethylene terephthalate) (PET)/allylisobutyl polyhedral oligomeric silsesquioxanes (a-POSS) nanocomposite is prepared by a solvent-casting method and as-received PET (asr-PET) is modified by a precipitation method to yield precipitated PET (p-PET). Their crystallization behaviors have been studied, and both modification methods improved the crystallization temperatures and crystallinities of PET. They were subsequently used to further nucleate asr-PET at 1 and 5 wt% levels to form self-nucleated PETs, with higher crystallization temperatures and higher crystallinities. Thermogravimetric analyses (TGA) show their thermal stabilities have been improved, and both self-nucleated PETs have superior mechanical properties.

During the past several years, we have been utilizing cyclodextrins (CDs) to nanostructure polymers into bulk samples whose chain organizations, properties, and behaviors are quite distinct from neat bulk samples obtained from their solutions and melts. We first form non-covalently bonded inclusion complexes (ICs) between CD hosts and guest polymers, where the guest chains are highly extended and separately occupy the narrow channels (~0.5–1.0 nm in diameter) formed by the columnar arrangement of CDs in the IC crystals. Careful removal of the host crystalline CD lattice from the polymer-CD-IC crystals leads to coalescence of the guest polymer chains into bulk samples, which we have repeatedly observed to behave distinctly from those produced from their solutions or melts. While amorphous polymers coalesced from their CD-ICs evidence significantly higher glass-transition temperatures, Tgs, polymers that crystallize generally show higher melting and crystallization temperatures (Tms, Tcs), and some-times different crystalline polymorphs, when they are coalesced from their CD-ICs. Formation of CD-ICs containing two or more guest homopolymers or with block copolymers can result in coalesced samples which exhibit intimate mixing between their common homopolymer chains or between the blocks of the copolymer. On a more practically relevant level, the distinct organizations and behaviors observed for polymer samples coalesced from their CD-ICs are found to be stable to extended annealing at temperatures above their Tgs and Tms. We believe this is a consequence of the structural organization of the crystalline polymer-CD-ICs, where the guest polymer chains included in host-IC crystals are separated and confined to occupy the narrow channels formed by the host CDs during IC crystallization. Substantial degrees of the extended and un-entangled natures of the IC-included chains are apparently retained upon coalescence, and are resistant to high temperature annealing. Following the careful removal of the host CD lattice from each randomly oriented IC crystal, the guest polymer chains now occupying a much-reduced volume may be somewhat “nematically” oriented, resulting in a collection of randomly oriented “nematic” regions of largely extended and un-entangled coalesced guest chains. The suggested randomly oriented nematic domain organization of guest polymers might explain why even at high temperatures their transformation to randomly-coiling, interpenetrated, and entangled melts might be difficult. In addition, the behaviors and uses of polymers coalesced from their CD-ICs are briefly described and summarized here, and we attempted to draw conclusions from and relationships between their behaviors and the unique chain organizations and conformations achieved upon coalescence.

Recently Ting et al. [ACS Macro Lett. 2013, 2, 770−774] described the syntheses of acrylic tetrapolymers with controlled molecular weights and tetramonomer compositions. Relative reactivity ratios of all monomer pairs were determined and used in the Walling–Briggs terminal copolymerization model along with Skeist’s equations to address the expected compositional drift in the monomer feed ratios. The anticipated control of monomer incorporation based on this approach was verified experimentally on several tetrapolyacrylates synthesized by RAFT polymerization, which additionally controlled their molecular weights. Their “new and simple paradigm combining both predictive models provides complementary synthetic and predictive tools for designing macromolecular chemical architectures with hierarchical control over spatially dependent structure–property relationships for complex applications” is extended here to the derivation of expected monad compositions, and diad, triad, and tetrad monomer sequence distribu...