Properties of a semi-crystalline and an amorphous thermotropic liquid crystalline polymer

The physical properties, thermal stability, rheology and tensile properties of a commercial semi-crystalline and an amorphous thermotropic liquid crystalline polymer (TLCP) have been investigated. Analysis by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) confirm the presence of a small melting endotherm and a glass transition in the former material. The as-received amorphous TLCP exhibits no obvious melting endotherm and a strong glass transition is detected. The flow and tensile properties of the semicrystalline polymer are dominated by the presence of the crystalline to nematic transition temperature. The properties of the amorphous TLCP appear to be governed by increasing mobility afforded by increasing temperature. Based on flow behaviour and further DSC analysis it has been shown that under appropriate annealing conditions the as-received amorphous TLCP can develop solid crystalline order.     

The modulus of the amorphous component in polyethylenes

Various approaches to representing the modulus of a semicrystalline polymer as a composite crystal-amorphous material are applied to the extensive data of Illers on the shear modulus of linear and branched polyethylenes as a function of crystallinity and temperature. It is found that the modulus of linear polyethylene is fit very well over the range of 47-96 percent crystallinity from ? 180 to 100°C by the Tsai-Halpin equation with a single value of the contiguity factor, ζ, and crystallinityindependent phase moduli. A value of ζ ? 1(near lower bound behavior) is found. In branched polyethylene the behavior below the β relaxation (T < T_β) is similar to linear polyethylene, but above T_β, the behavior indicates that the amorphous modulus is crystallinity dependent. The amorphous component modulus as a function of temperature for linear polyethylene extracted from the fitting process is discussed in terms of various interpretations of the relaxations (α, β, γ) in polyethylene.     

Electro-mechanical deformation of amorphous and semi-crystalline polymeric films

In our previous study, electrically induced mechanical stress was produced on monolithic polycarbonate (PC) films under a DC voltage using a needle-plane electrode setup. This study investigated other materials with various structures and dielectric constants, in order to further understand the deformation mechanism. It was found that the elastic behavior occurred at electric fields intensities below that initiating measurable surface deformation. The amorphous materials, PS, and the semi-crystalline materials, HDPE and PP, having dielectric constants all around 2.5, exhibited a similar observable deformation onset electric field at 200 MV/m. While PVDF, having a dielectric constant of 10.0–12.0, showed an onset at only 30 MV/m. The data was also compared to our previous study on PC. The depth and diameter of the deformation for all materials increased relative to the applied electric field up to film breakdown. Thermal annealing of the deformed films revealed a recoverable “delayed elastic” component and an irreversible “plastic” component. A three-stage electrically induced mechanical deformation mechanism was proposed for amorphous materials, while a two-stage mechanism was proposed for the semi-crystalline materials. The difference on the energy loss versus deformed volume for amorphous and semi-crystalline polymers was also determined and discussed.     

Carbon black network contribution to the dynamic modulus of a tire stock

Summary The dynamic mechanical measurements reported here were made to get a measure of the carbon black network contribution to the mechanical properties of a tire stock. The results indicate directly that independent, carbon black networks can contribute greatly to the rigidity of a vulcanized tire stock.     

A re-examination of the elastic modulus dependence on crystallinity in semi-crystalline polymers

The elastic modulus versus crystallinity linear relationship in Polyethylene (PE) is re-examined via meticulous measurements over a wide set of PE. First, large discrepancies to linearity are observed; moreover, Raman spectroscopy revealed that the content of the so-called interphase exhibits considerable variations over the set of PE. Therefore a novel strategy based on DMA is developed for a better identification of the modulus of each phase along the temperature.On the one hand, below the α and β relaxations, the young modulus proved to be linearly dependant on the sum of the crystal and interphase content. On the other hand, between the α and β relaxations, the interphase appears surprisingly as stiff as the crystal. In addition, the quenched samples exhibit a particular behavior. A simple model has lead to the conclusion that their mechanical coupling and/or amorphous modulus are significantly different as compared with all others materials.     

The contribution of neutron scattering to polymer science

The contribution of neutron scattering to polymer science is reviewed. A summary is given of the theory of neutron scattering followed by a review of the literature. Particular emphasis is placed on the use of small angle neutron scattering to observe the conformation of polymer chains in bulk polymers and concentrated polymer solutions and on quasi elastic neutron scattering to measure the dynamics of polymer chains.     

The elastic modulus of filled polymer composites

The elastic modulus of polyepichlorohydrin (PECH) filled with glass beads and wollastonite was studied. It was found that the elastic modulus of the composites depends not only on the volume fraction of the fillers but also on their size. Percolation theory was used to explain the experimental results. © 1993 John Wiley & Sons, Inc.     

Photo-DSC I: A new tool to study the semi-crystalline polymer accelerated photo-ageing

Photo-DSC was used, to study, in situ, the photo-ageing of polycyclo-octene which is a semi-crystalline elastomer. The ‘crystallizability’, which is the ability of the polymer to crystallize, was tightly dependent on the exposure time and was used to follow the photo-ageing.The irradiation system of photo-DSC was also compared with a usual accelerating device and no difference was detected in the chemical alteration of the polymeric matrix. Meanwhile, with photo-DSC, the photo-ageing was accelerated compared to a usual accelerating device. By using photo-DSC, atmosphere, exposure time, light intensity and ageing temperature were accurately controlled.     

Recent developments in the formation, characterization, and simulation of micron and nano-scale droplets of amorphous polymer blends and semi-crystalline polymers

Polymer micro- and nano-particles are fundamental to a number of modern technological applications, including polymer blends or alloys, biomaterials for drug delivery systems, electro-optic and luminescent devices, coatings, polymer powder impregnation of inorganic fibers in composites, and are also critical in polymer-supported heterogeneous catalysis. In this article, we review some of our recent progress in experimental and simulation methods for generating, characterizing, and modeling polymer micro- and nano-particles in a number of polymer and polymer blend systems. By using instrumentation developed for probing single fluorescent molecules in micron-sized liquid droplets, we have shown that polymer particles of nearly arbitrary size and composition can be made with a size dispersion that is ultimately limited by the chain length and number distribution within the droplets. Depending on the time scale for solvent evaporation—a tunable parameter in our experiments—phase separation of otherwise immiscible polymers can be avoided by confinement effects, producing homogeneous polymer blend micro- or nano-particles. These particles have tunable properties that can be controlled simply by adjusting the size of the particle, or the relative mass fractions of the polymer components in solution. Physical, optical, and mechanical properties of a variety of micro and nano-particles, differing in size and composition, have been examined using extensive classical molecular dynamics calculations in conjunction with experiments to gain deeper insights into fundamental nature of their structure, dynamics, and properties.     

Temperature dependence of some thermodynamic functions for amorphous and semi-crystalline polymers

The temperature dependence of some heat-capacity related functions is evaluated on the basis of experimental data, and a further elaboration is given for polyethylene.     

The steady flow shear modulus of polymer melts

Relaxation times of polyethylene melts have been measured by Aloisio, Matsuoka, and Maxwell. One implication regarding their observations is that the elastic properties of polymer melts must be time-dependent. In particular, the steady-flow shear modulus depends on the strain rate. Some interpretations of data in the literature have been based on concepts in rubber elasticity where the steady-flow modulus is an equilibrium value, independent of strain rate. We have used Pao's theory for viscoelastic flow together with measurements of relaxation times to discuss the strain rate dependence of the steady-flow shear modulus of melts. The existence of a strain rate-dependent shear modulus leads naturally to a nonlinear relation between shear stress and recoverable shear strain. The conclusions regarding the molecular weight dependence of the modulus also differ from interpretations based on rubber elasticity.     

Tensile modulus of polymer nanocomposites

Based on Takayanagi's two‐phase model, a three‐phase model including the matrix, interfacial region, and fillers is proposed to calculate the tensile modulus of polymer nanocomposites (E_c). In this model, fillers (sphere‐, cylinder‐ or plateshape) are randomly distributed in a matrix. If the particulate size is in the range of nanometers, the interfacial region will play an important role in the modulus of the composites. Important system parameters include the dispersed particle size (t), shape, thickness of the interfacial region (τ), particulate‐to‐matrix modulus ratio (E_d/E_m), and a parameter (k) describing a linear gradient change in modulus between the matrix and the surface of particle on the modulus of nanocomposites (E_c). The effects of these parameters are discussed using theoretical calculation and nylon 6/montmorillonite nanocomposite experiments. The former three factors exhibit dominant influence on E_c. At a fixed volume fraction of the dispersed phase, smaller particles provide an increasing modulus for the resulting composite, as compared to the larger one because the interfacial region greatly affects E_c. Moreover, since the size of fillers is in the scale of micrometers, the influence of interfacial region is neglected and the deduced equation is reduced to Takayanagi's model. The curves predicted by the three‐phase model are in good agreement with experimental results. The percolation concept and theory are also applied to analyze and interpret the experimental results.     

A comparative study to predict the interphase modulus in polymer nanocomposites

In this study, the interphase modulus (E_i) in polymer nanocomposites is calculated by two methods and the calculated results are compared at different conditions. In the first method, the experimental moduli of samples are applied to Ji model and suitable “E_i” is calculated. In the second method, a multilayered interphase is considered, in which the Young's moduli of layers (E_k) depend to the distance between the nanoparticle surface and the polymer matrix by power function of “Y” parameter. The “E_i” is calculated for multilayered interphase assuming the same and different layer thicknesses (t_k) by Parallel and Series models. Finally, the “E_i” values calculated by the explained methods are compared for two reported samples. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44076.     

Elastic modulus of linear polymer crystals

A method based on energy balance over the repeat unit is used for the calculation of the elastic modulus of linear polymer crystals. The result for polyethylene agrees with that of Treloar who used a statical analysis over the whole molecule. Both methods are much simpler than those of Shimanouchi and Miyazawa, the latter being based on the complete potential function for the polymer. Using force constants based on a Urey Bradley force field, the following values of modulus were found (all syndiotactic except PE) in GN/m²: PE, 299; PVC, 153; PVF, 212; PVA, 142; PAN, 236; PMMA, 63.     

Mobile amorphous phase fragility in semi-crystalline polymers: Comparison of PET and PLLA

PET and PLLA were cold crystallised at various times and the two polymers were studied by differential scanning calorimetry (DSC), dielectric spectroscopy (DS) and thermally stimulated depolarisation currents (TSDC). The crystalline, the amorphous and the rigid amorphous fraction were quantified. The percentage of rigid amorphous fraction is very large in semi-crystalline PET and very low in semi-crystalline PLLA. From DSC, DS and TSDC data, the values of the relaxation times of four samples were obtained above and below the glass transition. The “strong-fragile” glass former liquid concept was used and the fragility of polymers was obtained. The presence of the crystalline phase and of a rigid amorphous fraction does not significantly modify PLLA fragility parameters and the polymer remains “fragile”, while for PET the semi-crystalline material goes towards a “strong character”. The coupling between phases is much weaker in PLLA than in PET.     

Application of the group contribution lattice-fluid EOS to polymer solutions

A new group contribution lattice-fluid equation of state (GCLF-EOS) is described that can accurately predict the activities of solvents in polymer solutions. This equation of state is a modification of the equation of state derived by Panayioutou and Vera (1982), which is based on the lattice statistics developments of Guggenheim (1952). The group contribution modification permits the prediction of solvent activity, given only the structure of the polymer and solvent involved. The GCLF-EOS can accurately predict solvent activities in polystyrene, polyethylene, poly(ethylene oxide), poly(ethylene glycol), poly(propylene oxide), and poly(vinyl chloride). The model does not perform as well for solvent activities in polyisobutylene due to the inaccurate group contribution values for the quaternary carbon group.     

Visualisation of the structure transfer between an oriented polymer melt and the semi-crystalline state

Structure evolution of highly oriented polyethylene during cautious melting and crystallization is investigated with both high time resolution and high signal-to-noise ratio by means of small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The two-dimensional SAXS patterns are transformed to the multidimensional chord distribution function (CDF) in physical space. The results are continuous and smooth movies of the nanostructure, which elucidate the mechanisms of the evolution of semicrystalline structure.We find that in our material crystallization is preceeded by a rather diffuse mesomorphic nanostructure. Based on its variation in relation to other observed features like row nuclei and crystalline lamellae, we propose to associate it to phase separated regions of entangled and disentangled chain segments, respectively. The movies show that the mesophase structure holds the key for the understanding of crystallite orientation and arrangement in the fibre.     

A contribution to the interpretation of polymer viscoelasticity in DMTA testing

Some ideas relevant to the prevailing viscoelasticity interpretations of dynamic mechanical thermal analysis (DMTA) experiments are presented. The main aspect is the inclusion of kinetic energy and inertia as variables, seeing the relaxing mass constantly increasing during strain, assigning inertial variation and not viscosity to energy dissipation. The equations developed make it possible to obtain the values of important viscoelastic properties, under in any experimental condition, with the data taken from previous experiments.     

Solution spinning of a semirigid chain polymer forming ultrahigh modulus fibers

Single filaments of the polyterephthalamide of p-aminobenzylhydrazide (X-500) were prepared by spinning X-500 solutions in dimethyl sulfoxide (DMSO) using water as a coagulating agent. The polymer is known for its ability to develop ultrahigh modulus fibers and for having a semirigid chain conformation with a persistence length of ～50 Å in DMSO. In the latter solvent, molecular rigidity appears to be just below that required for spontaneous formation of a nematic phase. The orientation of the fibers was performed in three different stages: during coagulation (I), in the washing bath following coagulation (II), and during postspinning treatments (III). Corresponding mechanical properties were determined. The results indicate that high elastic modulus (15 GPa) already appears during step I at very moderate pulloff ratios. Therefore, considerable orientation had already occurred in the flowing solution. Further increase of fiber orientation yields a large increase of modulus (from 22 to 67 GPa) during solid-state deformation (step III). The orientation of the flowing solution was monitored by viscosity and birefringence measurements. The results are discussed in terms of orientation due to elongational and shear flow and, possibly, a flow-induced transition to a nematic phase in the concentrated solution in which chain entanglement is shown to occur.