Tensile deformation of electrospun nylon‐6,6 nanofibers

Nylon‐6,6 nanofibers were electrospun at an elongation rate of the order of 1000 s^?1 and a cross‐sectional area reduction of the order of 0.33 × 10⁵. The influence of these process peculiarities on the intrinsic structure and mechanical properties of the electrospun nanofibers is studied in the present work. Individual electrospun nanofibers with an average diameter of 550 nm were collected at take‐up velocities of 5 and 20 m/s and subsequently tested to assess their overall stress–strain characteristics; the testing included an evaluation of Young's modulus and the nanofibers' mechanical strength. The results for the as‐spun nanofibers were compared to the stress–strain characteristics of the melt‐extruded microfibers, which underwent postprocessing. For the nanofibers that were collected at 5 m/s the average elongation‐at‐break was 66%, the mechanical strength was 110 MPa, and Young's modulus was 453 MPa, for take‐up velocity of 20 m/s—61%, 150 and 950 MPa, respectively. The nanofibers displayed α‐crystalline phase (with triclinic cell structure). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1482–1489, 2006     

The influence of grafted cellulose nanofibers and postextrusion annealing treatment on selected properties of poly(lactic acid) filaments for 3D printing

l ‐lactide monomers were grafted onto cellulose nanofibers (CNFs) via ring‐opening polymerization, forming poly(lactic acid) grafted cellulose nanofibers (PLA‐g‐CNFs). PLA‐g‐CNFs and pristine PLA were then blended in chloroform and dried to prepare a master batch. PLA‐g‐CNFs/PLA composite filaments targeted for 3D printing were produced by compounding the master batch in PLA matrix and melt extrusion. The as‐extruded composite filaments were subsequently thermal annealed in a conventional oven, and their morphological, thermal, and mechanical properties were evaluated. PLA was successfully grafted on the surface of CNFs as demonstrated by elemental analysis, and the concentration of grafted PLA was estimated to be 33 wt %. The grafted PLA were highly crystallized, contributing to the growth of crystalline regions of PLA matrix. The incorporation of PLA‐g‐CNFs improved storage modulus of the composite filaments in both low temperature glassy state and high temperature rubbery state. Postextrusion annealing treatment led to 28 and 63% increases for tensile modulus and strength of the filaments, respectively. Simulated Young's moduli from the Halpin‐Tsai and Krenchel models were found comparable with the experimental values. The formed composite filaments are suitable for use in 3D printing. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 847–855     

Comparing the mechanical response of di‐, tri‐, and tetra‐functional resin epoxies with reactive molecular dynamics

The influence of monomer functionality on the mechanical properties of epoxies is studied using molecular dynamics (MD) with the Reax Force Field (ReaxFF). From deformation simulations, the Young's modulus, yield point, and Poisson's ratio are calculated and analyzed. Comparison between the network structures of distinct epoxies is further advanced by the monomeric degree index (MDI). Experimental validation demonstrates the MD results correctly predict the relationship in Young's moduli. Therefore, ReaxFF is confirmed to be a useful tool for studying the mechanical behavior of epoxies. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 255–264     

Exploring thiol‐yne based monomers as low cytotoxic building blocks for radical photopolymerization

The last decade has seen a remarkable interest in the development of biocompatible monomers for the realization of patient specific medical devices by means of UV‐based additive manufacturing technologies. This contribution deals with the synthesis and investigation of novel thiol‐yne based monomers with a focus on their biocompatibility and also the mechanical properties in their cured state. It could be successfully shown that propargyl and but‐1‐yne‐4‐yl ether derivatives have a significant lower cytotoxicity than the corresponding (meth)acrylates with similar backbones. Together with appropriate thiol monomers, these compounds show reactivities in the range of (meth)acrylates and almost quantitative triple bond conversions. A particular highlight is the investigation of the network properties of photo cured alkynyl ether/thiol resins by means of low field solid state nuclear magnetic resonance spectroscopy. Additionally, dynamic mechanical analysis of those polymers revealed that monomers containing rigid backbones lead to moduli and glass transition temperatures (T_g's), sufficiently high for the fabrication of medical devices by UV based additive manufacturing methods. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3484–3494     

Mechanical properties of the novel organometallic polymer poly(ferrocenyldimethylsilane)

A study of the mechanical properties of poly(ferrocenyldimethylsilane) [Fe(η‐C₅H₄)₂SiMe₂]_n, 3 , a novel organometallic polymer, has been performed on thin films of this material. The Young's modulus and Poisson's ratio of film samples (15 × 1 × 1 mm) of 3 were measured in quasi‐static tension using a video extensometer. For 3 , the values of the Young's moduli (E) and Poisson's ratios (ν) were similar between axes in the plane and independent of the splicing direction used during sample preparation. The mean and standard deviation of the Young's modulus and Poisson's ratio were 0.78 ± 0.08 GPa and 0.37 ± 0.06 GPa, respectively. Thermomechanical analysis of 3 revealed a steady decrease of E from a room temperature value of approximately 0.70 GPa. Additionally, it was found that at 150 °C, 3 was unable to support even small stresses, consistent with the onset of a melt transition (ca. 135 °C). A mathematical model based on molecular geometry is developed to describe the results. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2280–2288, 2005     

Mechanical properties of anion exchange membranes by combination of tensile stress–strain tests and dynamic mechanical analysis

The thermomechanical properties of anion exchange polymers based on polysulfone (PSU) quaternized with trimethylamine (TMA) or 1,4‐diazabicyclo[2.2.2]octane (DABCO) and containing hydroxide or chloride anions by tensile stress–strain tests and dynamic mechanical analysis (DMA) have been determined. The reported mechanical properties included the Young's modulus, tensile strength, and elongation at break from tensile tests and the storage and loss modulus and glass transition temperature from DMA. The anion exchange membranes behaved as stiff polymers with Young's modulus in the order of 1 GPa, relatively with high strength (about 30 MPa) and low elongation at break (around 10%) was observed. Tensile tests were also made with membranes exchanged with hydrogen‐carbonate and carbonate anions to control the absence of important carbonation of the OH form. The glass transition temperatures were of the order of 150 °C (PSU‐TMA) or 200 °C (PSU‐DABCO) for the hydroxide form, confirmed by differential scanning calorimetry; they increase further by about 50 K, when hydroxide ions are replaced by chloride. This result and the increase of the storage modulus could be interpreted by the higher hydration of hydroxide ions and the plasticizing effect of water, which reduced the Van der Waals interactions between the macromolecular chains. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1180–1187     

Mechanical properties and characterization of slowly cooled isotactic polypropylene/high‐density polyethylene blends

In previous studies, we found that Young's moduli of quenched isotactic polypropylene/high‐density polyethylene (iPP/HDPE) exceeded the upper bound, calculated from the Voigt model, with the moduli of the quenched homopolymers as those of the two components. We suggested that this might be due to crystallization, as the components crystallized at higher temperatures in the blend than on their own. We repeated the same set of measurements, this time on iPP/HDPE blends that were cooled slowly. We also examined crystallization at various rates of cooling with differential scanning calorimetry. At slow cooling rates, the HDPE and iPP components in the blends crystallize at lower temperatures than in the pure homopolymers, suggesting that the presence of one component inhibits rather than promotes the crystallization of the other. Electron microscopy of slowly cooled blends revealed very different interfacial morphologies depending on whether the HDPE or the iPP crystallizes first. Young's moduli of most of the blends lie on the upper bound; however, some blends with co‐continuous morphologies fall well below the lower bound. The mechanical properties are discussed in terms of the interfacial morphology, the crystallization behavior, and the large‐scale phase separation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1384–1392, 2003     

Segmented block copolyesters using click chemistry

Copper(I) catalyzed azide‐alkyne 1,3‐Huisgen cycloaddition reaction afforded the synthesis of triazole‐containing polyesters and segmented block copolyesters at moderate temperatures. Triazole‐containing homopolyesters exhibited significantly increased (～40 °C) glass transition temperatures (T_g) relative to high temperature, melt synthesis of polyesters with analogous structures. Quantitative synthesis of azido‐terminated poly(propylene glycol) (PPG) allowed for the preparation of segmented polyesters, which exhibited increased solubility and mechanical ductility relative to triazole‐containing homopolyesters. Differential scanning calorimetry demonstrated a soft segment (SS) T_g near ?60 °C for the segmented polyesters, consistent with microphase separation. Tensile testing revealed Young's moduli ranging from 7 to 133 MPa as a function of hard segment (HS) content, and stress at break values approached 10 MPa for 50 wt % HS segmented click polyesters. Dynamic mechanical analysis demonstrated an increased rubbery plateau modulus with increased HS content, and the T_g's of both the SS and HS did not vary with composition, confirming microphase separation. Atomic force microscopy also indicated microphase separated and semicrystalline morphologies for the segmented click polyesters. This is the first report detailing the preparation of segmented copolyesters using click chemistry for the formation of ductile membranes with excellent thermomechanical response. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Pressure‐sensitive adhesive utilizing molecular interactions between thymine and adenine

A simple pressure‐sensitive adhesion (PSA) system incorporating noncovalent interaction between thymine and adenine is presented. A copolymer having thymine moieties is combined with a low‐molecular‐weight bifunctional adenine cross‐linker. Molecular interactions caused by multiple hydrogen bonds between the thymine and adenine units are evaluated by FT‐IR spectral measurement. Mechanical properties of the PSA are examined by stress–strain curves and dynamic mechanical analysis. As the number of adenine cross‐linkers increases, Young's modulus increases from 0.24 to 3.0 MPa, and the glass transition temperature increases. Furthermore, it is found that the PSAs have adequate adhesive property from their shear strength test. Heat treatment at 80 °C is effective for reinforcement because of interchange of the hydrogen bonds. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1332‐1338     

Young's modulus and loss tangent measurement of polydimethylsiloxane using an optical lever

In this article, the Young's modulus and the loss tangent of polydimethylsiloxane (PDMS) is obtained in the frequency range between 10 and 1500 Hz using an optical technique. The first three mechanical modes of vibrating PDMS beams are detected by measuring the tip rotational displacement using an optical lever. The experiments are carried out for 10:1 and 20:1 volume mixing ratios between the polymer base and the curing agent. The experimental results show that the Young's modulus varies between 1 and 2.6 MPa for 10:1 while its values are between 0.6 and 1.1 MPa for 20:1. The loss tangent is between 0.2 and 0.4 for 10:1 and 0.2 and 0.5 for 20:1. However, the measured values of the loss tangent are greater than the values reported in ref. 13. We also found that if the PDMS is not cured properly, its mechanical properties are time dependent. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 747–751     

Relationships between molecular structure and thermomechanical properties of bio‐based thermosetting polymers

Molecular dynamics simulations are used to study highly cross‐linked epoxy networks comprised of furanyl epoxy monomer, 2,5‐bis[(2‐oxiranylmethoxy)methyl]‐furan (BOF), that is cross‐linked by two furanyl amine hardeners, 5,5'‐methylenedifurfurylamine (DFDA) and 5,5'‐ethylidenedifurfirylamine (CH₃‐DFDA). Important properties of these fully furan‐based systems, including room temperature density, glass transition temperature, and Young's modulus are found to agree with previous experimental results. We also compare the simulated and experimental values of four fully furan‐based thermosetting materials to those using the conventional resin diglycidyl ether of bisphenol A (DGEBA) cured with the two furanyl hardeners. Our simulation results predict a slight decrease in density and Young's modulus, but no impact on the glass transition temperature, upon adding the methyl group in DFDA. Detailed analyses of the MD trajectories reveal the underlying mechanisms responsible for the observed structure/property relations, which center on the lack of collinear covalent bonds in the BOF molecular structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 285–292     

Effects of humidity on Young's modulus in poly(methyl methacrylate)

Tensile tests on poly (methyl methacrylate) (PMMA) were conducted to clarify the effects of humidity and strain rate on tensile properties, particularly Young's modulus. Prior to the tensile tests, specimens were kept under various humidity conditions at 293 K, which were the same as the test conditions, for a few months to adjust the sorbed water content in the specimens. The tensile tests were performed under each humidity condition at three different strain rates (approximately 1.4 × 10^?3, 1.4 × 10^?4, and 1.4 × 10^?5 s^?1). Stress‐strain curves changed with humidity and strain rate. Young's moduli were also measured at small applied stresses (below 6.7 MPa) under various humidity conditions at 293 K. Young's modulus decreases linearly with increasing humidity and a decreasing logarithm of strain rate. These results suggest that Young's modulus of PMMA can be expressed as a function of two independent parameters that are humidity and strain rate. A constitutive equation for Young's modulus of PMMA was proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 460–465, 2002; DOI 10.1002/polb.10107     

Effect of the comonomer content on the mechanical parameters and microhardness values in poly(ethylene‐co‐1‐octadecene) synthesized by a metallocene catalyst

Stress–strain and microhardness measurements were carried out on a series of copolymers of ethylene and 1‐octadecene with different comonomer contents in the corresponding homopolymer of ethylene, synthesized with a metallocene catalyst. The different mechanical properties, deduced from the stress–strain curves (Young's modulus, yield stress, deformation at break, and energy to break) are interpreted in terms of the crystallinity and molecular weight of the samples because these two characteristics show considerable variations with the comonomer content. The microhardness values are explained in terms of these properties, and they are also correlated with Young's moduli and yield stresses deduced from the stress–strain curves. Linear relations are found between microhardness and yield stress and between the logarithm of the microhardness and the logarithm of the elastic modulus. The properties deduced from these lines are compared with literature values. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 277–285, 2001     

Nanostructural evidence of mechanical aging and performance loss in ballistic fibers

It is understood that the ballistic resistance of aromatic polyamide fibers is related to the fiber's ultimate tensile strength, strain‐to‐failure, and Young's modulus. Ideal high‐performance ballistic materials maximize these properties while minimizing material density. Equally important is long‐term mechanical and chemical stability: the fibers should not exhibit performance loss over their lifetime. However, less is known quantitatively about their modes of degradation, and experimental methods to quantify the aging and degradation in these fibers are critical. Multiple variations of next generation high‐performance fibers have been investigated under chemical and mechanical accelerated aging conditions. Performance losses have been empirically correlated to chemical degradation of the polymer chain and nanostructural changes in the fiber morphology through X‐ray photoelectron spectroscopy (XPS). Here, we introduce positron annihilation lifetime spectroscopy measurements as a sensitive method to quantify the early onset of damage in the flexed fibers as quantified through changes in the nanoscale void structure in the material. Published 2017.^? J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1711–1717     

Synthesis and characterization of poly(arylene ether sulfone)s with trans‐1,4‐cyclohexylene ring containing ester linkages

trans‐1,4‐Cyclohexylene ring containing acid chloride monomers were incorporated into poly(arylene ether sulfone) (PAES) backbones to study their effect on mechanical and thermal properties. The trans‐1,4‐cyclohexylene ring containing acid chloride monomers were synthesized and characterized by NMR and high‐resolution mass spectrum. trans‐1,4‐Cyclohexylene containing PAESs were synthesized from the acid chloride monomers and hydroxyl terminated polysulfone oligomers with a pseudo‐interfacial method and a solution method. These PAESs, with trans‐1,4‐cyclohexylene ring containing ester linkages, were fully characterized by NMR, thermogravimetric analysis, differential scanning calorimetry (DSC), size exclusion chromatography, and dynamic mechanical analysis (DMA). The tensile properties were also evaluated. The polymers made with the pseudo‐interfacial method had relatively low molecular weights when compared to the solution method where much higher molecular weight polymers were obtained. Crystallinity was promoted in the low molecular weight biphenol‐based PAES samples with the pseudo‐interfacial method. The crystallinity was confirmed by both the DSC and the wide angle X‐ray diffraction results. The tensile test results of the high molecular weight polymers suggested that incorporation of the trans‐1,4‐cyclohexylene ring containing linkage slightly improved the ultimate elongations while maintaining the Young's moduli. The trans‐1,4‐cyclohexylene ring containing PAESs also showed higher sub‐T_g relaxations in DMA when compared with their terephthaloyl containing analog. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Apparent depth‐dependent modulus and hardness of polymers by nanoindentation: Investigation of surface detection error and pressure effects

Nanoindentation is a widely used technique to characterize the mechanical properties of polymeric materials at the nanoscale. Extreme surface stiffening has been reported for soft polymers such as poly(dimethylsiloxane) (PDMS) rubber. Our recent work [J. Polym. Sci. Part B Polym. Phys. 2017 , 55, 30–38] provided a quantitative model which demonstrates such extreme stiffening can be associated with experimental artifacts, for example, error in surface detection. In this work, we have further investigated the effect of surface detection error on the determination of mechanical properties by varying the sample modulus, instrument surface detection criterion, and probe geometry. We have examined materials having Young's moduli from ∼2 MPa (PDMS) to 3 GPa (polystyrene) using two different nanoindentation instruments (G200 and TI 950) which implement different surface detection methods. The results show that surface detection error can lead to apparent large stiffening. The errors are lower for the stiffer materials, but can still be significant if care is not taken to establish the range of the surface detection error in a particular experimental situation. We have also examined the effect of pressure beneath the probe on the nanoindentation‐determined modulus of polystyrene with different probe geometries. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 414–428     

Synthesis and mechanical properties of para‐aramid nanofibers

Scalable, bottom‐up chemical synthesis and electrospinning of novel Cl‐substituted poly(para‐phenylene terephthalamide) (PPTA) nanofibers are herein reported. To achieve Cl‐PPTA nanofibers, the chemical reaction between the monomers was precisely controlled, and dissolution of the polymer into solvent was tailored to enable anisotropic solution formation and sufficient entanglement molecular weight. Electrospinning processing parameters were studied to understand their effects on fiber formation and mat morphology and then optimized to yield consistently high quality fibers. Importantly, the control of relative humidity during the fiber formation process was found to be critical, likely because water promotes hydrogen bond formation between the PPTA chains. The fiber and mat morphologies resulting from different combinations of chemistry and spinning conditions were observed using scanning electron microscopy, and observations were used as inputs to the optimization process. Tensile properties of single Cl‐PPTA nanofibers were characterized for the first time using a nanomanipulator mounted inside a scanning electron microscope (SEM), and fiber moduli measuring up to 70 GPa, and strengths exceeding 1 GPa were achieved. Given the excellent mechanical properties measured for the nanofibers, this chemical synthesis procedure and electrospinning protocol appear to be a promising route for producing a new class of nanofibers with ultrahigh strength and stiffness. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 563–573     

Amine–quinone polyimides

Two dianiline monomers were prepared by the reaction of either 4,4′‐methylenedianiline or 4,4′‐oxydianiline with 1,4‐benzoquinone. These monomers were used to synthesize a series of amine–quinone polyimides by condensation with either 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride or 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride to make the corresponding polyamic acid. The polyamic acids were converted to the polyimides by thermal imidization at 290 °C. The amine–quinone polyimides gave freestanding films with tensile strengths in the range of 90 to 150 MPa and Young's moduli of 0.9 to 1.5 GPa. The thermal decomposition temperature under nitrogen was 440 to 480 °C and the glass‐transition temperature was in the range of 280 to 310 °C. The amine–quinone polyimides had the excellent thermal and mechanical properties that one expects for polyimides. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4044–4049, 2001     

In situ measurement of the thermal expansion behavior of benzocyclobutene films

In situ measurement techniques suitable for determination of the coefficient of thermal expansion (CTE) in thin, spin‐cast polymer films in both the in‐plane and through‐plane directions are presented. An examination of the thermal expansion behavior of cyclotene thin films has been performed. In particular, the effect of film thickness on the in‐plane and through‐plane CTE and in‐plane Young's modulus of spin‐coated cyclotene films was examined. It is shown that the mechanical response of in situ cyclotene films can be adequately described by isotropic film properties. It was also demonstrated that there is no thickness dependence on the free‐standing mechanical properties or on the resulting through‐plane thermal strain in an in situ film. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 311–321, 1999     

Effects of Na‐sulfopropyl groups on the mechanical properties and morphology of polystyrene‐co‐methacrylate ionomers

The dynamic mechanical properties and morphology of poly(styrene‐co?3‐sulfopropyl sodium‐methacrylate) SSPMANa ionomers were investigated. It was found the increasing rate of ionic moduli of the SSPMANa ionomer was very low, and the cluster T_g of the ionomers remained more or less constant with increasing ion content. A well‐developed SAXS peak was seen for low ion content SSPMANa ionomers and the peak position changed slightly with ion content. Thus, it was suggested that the presence of the alkyl ester side chains made the ion pairs form multiplets more easily at their prevalent distances, and the small‐agglomerated multiplets were dispersed in the polymer matrix relatively evenly. The interpretation of ionic moduli using a number of theories implied that the multiplets and clusters acted as effective crosslinks and filler particles, respectively, and the size and shape of the clusters were irregular. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1043–1053