R. D. Maksimov

Creep and stress relaxation in a longitudinal polymer liquid crystal: Prediction of the temperature shift factor

The polymer liquid crystal PLC is the PET/0.6PHB copolymer; PET=poly(ethyleneu200aterephthalate), PHB=ρ-hydroxybenzoic acid (LC): 0.6=the mole fraction of PHB. This is a multiphase system with PHB-rich islands in a PET-rich matrix. Tensile creep compliance was measured isothermally from 20u200a°C to 160u200a°C in 10u200a°C intervals. Master curves were determined using the time–temperature superposition for 20u200a°C and for the glass transition temperature of the PET-rich phase TgPET=62u200a°C. Experimental values of the temperature shift factor aT as a function of temperature T agree in the entire T range with those from Eq. (7) relating aT to the reduced volume ṽ and the Hartmann equation of state Eq. (10). Values of aT(T) calculated from the Williams–Landel–Ferry (WLF) formula give very large errors below Tg. A control 14 months creep experiment agrees with the theoretical predictions from Eq. (7). Stress relaxation experiments were performed under the constant strain of 0.5% from 20u200a°C to 120u200a°C, again master curves were de...

Creep and stress relaxation

Thermotropic polymer liquid crystals (PLCs) are a relatively new class of materials; they are under extensive investigation which is still growing in scope. Many studies have been reported concerning their rheological, dielectric, thermal and mechanical properties, and processing and morphology [1-14]. New areas of their potential applications continue to emerge. The PLCs have good physical and mechanical properties as well as better dimensional stability and chemical resistance than flexible polymers. They show ease of processing due to their low melt viscosity. Their properties are highly anisotropic in fabricated products; this is associated with the sensitivity of the stiff molecules to the flow fields causing a molecular orientation in the flow direction.

Time and temperature dependent deformation of poly(ether ether ketone) (PEEK)

The stress-strain behavior in tension and the effect of temperature on the creep of poly(ether ether ketone) (PEEK) have been studied. At room temperature, ∼130° below the glass-transition temperature, the material does not become brittle, and the specimens show necking in tension over a wide range of elongation rates. The stress and strain at yield and the strain at break are almost linear functions of the logarithmic elongation rate. The values of stress and strain at yield increase slightly with increasing elongation rate, while the strain at break decreases markedly. The short-term creep tests were conducted at temperatures extending from 20 to 200°C. The glass-transition temperature was found to be about 155°C. The creep of PEEK is greatest at temperatures above 130°C. In the glass region the time dependence of the deformation is much weaker. It has been found that the time-temperature relation for PEEK corresponds well with its thermorheological simplicity in the temperature range investigated. The data on the temperature shift factor below and above the glass-transition temperature may be fitted separately to the Arrhenius and Williams-Landel-Ferry (WLF) equations, respectively. The long-term creep tests show that PEEK has excellent creep resistance at room temperature. After 14-month tests at a stress level of 30 MPa the total strain exceeds the instantaneous elastic strain only by a factor of 1.15.

Prediction of the deformation properties of a polymeric composite with a granular-fibrous filler

ConclusionA variant of calculation of the characteristics of the deformation properties of a hybrid composite containing a complex disperse filler in the form of granular particles and short fibers was proposed. The effect of aggregation of the granular filler, the statistical distributions of the fibers by lengths and orientation in the material, and the anisotropy of the fibers are taken into consideration in the calculation. The statistical distribution of the orientation of the fibers is given by a function proportional to the distance from the center to the surface of a triaxial ellipsoid in the corresponding direction. The uniform random distribution of the fibers in bulk and in the plane is a special case of this distribution. The results of the analysis of the effect of the parameters of the statistical distributions of the length and orientation of short fibers on the elasticity characteristics of a composite are reported. The dependence of the creep of the composite on the ratio of the concentration of the components of the complex filler was determined, and the efficiency of partial replacement of a granular filler by a short-fiber filler to inhibit creep of the composite was demonstrated. The possibilities of predicting the long-term creep were experimentally confirmed on the example of LDPE filled with ground limestone and short glass fibers.

Effect of temperature on the creep of a thermotropic liquid crystalline polymer

Thermotropic liquid crystalline polymers (LCP) are a relatively new class of materials; they are currently being intensively investigated. Many articles have been published concerning their rheological, dielectric, thermal, and mechanical properties, processing, and morphology. New areas of their potential applications continue to emerge. The LCP have good physical and mechanical properties as well as a satisfactory dimensional stability and chemical resistance. They show ease of processing thanks to their low melt viscosity. In fabricated products, these properties are highly anisotropic which is associated with the sensitivity of stiff molecules to flow fields causing a molecular orientation in the longitudinal direction.

Effect of parameters of the distribution of the length and orientation of short fibers on characteristics of the dynamic viscoelasticity of a polymer composite

ConclusionAn algorithm for calculating the dynamic viscoelastic characteristics of a composite reinforced with short fibers was developed and realized in the form of a computer program. An analysis was made of the dependence of the characteristics of the composite on the volume content and length of its fibers, as well as on statistical distributions of fiber length and orientation in the material. It was shown that a change in the parameters of the statistical distributions has a significant effect on both the elastic and the dissi-pative properties of the composite. It was found that ignoring the statistical fiber-length distribution might lead to overestimation of the real component of the complex modulus and underestimation of the mechanical loss tangent.

Reclamation of post-consumer plastics for development of polycarbonate and acrylonitrile butadiene styrene based nanocomposites with nanoclay

Suitability of recycled acrylonitrile-butadiene-styrene (R-ABS) and recycled polycarbonate (R-PC) for the development of polymer matrix nanocomposites with organically modified nanoclay (OMMT) is evaluated in comparison to virgin polymers (V-ABS and V-PC) based systems. The influence of OMMT content on the structure as well as calorimetric, mechanical and thermal properties of virgin and recycled polymers containing systems is revealed. Increase in stiffness and strength of virgin and recycled polymers based systems is observed along with rising nanoclay content. However, it is observed that reinforcing efficiency of clays on the R-ABS containing systems is reduced to certain extent in comparison to those, based on virgin polymers. It is shown, that in the presence of OMMT approximation of glass transition temperatures of both polymeric components is observed, which can testify about certain improvement of compatibility between PC and ABS. Increment of the modulus of elasticity and yield strength of the n...