Carl Klason

The Efficiency of Cellulosic Fillers in Common Thermoplastics. Part II. Filling with Processing Aids and Coupling Agents

Abstract This paper reports on the effect of additives on the properties of injection moulded composites based on polypropylene (PP) and high density polyethylene (HDPE) filled with wood and cellulose flour. Three types of additives were studied: dispersion aids, elastomeric additives, and adhesion promoting agents. Some of the dispersion aids were found to improve the filler dispersion and the impact strength. The modulus remained relatively unaffected while the strength was lowered. The high molecular weight elastomeric additives increased the impact strength and ductility, while the stiffness was reduced. An adhesion promotor based on a maleic anhydride modified polypropylene was found to behave as a true coupling agent, i.e. the strength and ductility increased, the melt strength was improved, and also the hot water resistance was raised. The experimentally determined composite moduli are found to agree relatively well with theoretical predictions. The effect of processing on the shape and size of the...

Prehydrolyzed Cellulose as Reinforcing Filler for Thermoplastics

Abstract This paper presents the results of an experimental study of the mechanical properties of composites consisting of prehydrolyzed cellulose and thermoplastic matrices. The main feature of prehydrolyzed cellulose fibres is a high degree of brittleness, permitting the fibres to be finely comminuted in the shear field of normal compounding and processing machinery. Such an effect can be anticipated to improve the homogeneity and the mechanical parameters of the moulded samples. In the present work, this has been demonstrated with PP, HDPE and PS containing varying amounts of prehydrolyzed cellulose of different origin (bleached pulps). The tests were done on injection moulded samples. The compounding method (Buss-Kneader vs. twin-screw extruder) had only minor influence on the results. Theoretical assessment of the modulus values using the Tsai–Halpin equation gave somewhat lower values than those recorded on experimental samples. This was interpreted in terms of the disintegration of the cellulose co...

Electrical properties of polyaniline suspensions

Abstract The ordering of electrically conducting polyaniline particles dispersed in a non-conducting liquid, 1,2,4-trichlorobenzene, in a weak electric field (of the order V mm −1 ) has been studied. The time needed for the formation of conducting chains, depending on the applied voltage, the polyaniline concentration and the viscosity of the suspension medium, was used to calculate the effective relative electric permittivity for polyaniline, ɛ p = 4.8, responsible for the dipole-dipole interaction leading to the structure formation. Nonlinear limit current-voltage characteristics typical of electrorheological suspensions were observed. The formation of the conducting chains could be followed in an optical microscope.

The conductivity distribution in injection moulded LDPE and HDPE filled with carbon black

Abstract This study of the distribution of conductivity in injection-moulded compositions (test bars) of LDPE and HDPE containing carbon black (20% Vulcan XC-72, 10% Ketjenblack EC) showed that the skin and shear zones have substantially higher resistivity levels than the core. In general, the resistivity increased with the degree of orientation, as determined by thermal shrinkage measurements. There was, however, no simple relation between resistivity and shrinkage. Regions with increased resistivity showed a pronounced frequency dependence, the resistivity decreasing with increasing frequency; in annealed samples or samples taken from the core, the resistivity was frequency independent. Annealing restored the high conductivity of isotropic samples. The results are in qualitative agreement with the assumption of a conducting CB-network changing its connectivity upon deformation and flow, and recovering when the sample is annealed.

The imbedded disk retraction method for measurement of interfacial tension between polymer melts

A method for measuring interfacial tension of high viscosity polymer melts at elevated temperatures is described. The method involves the tracking of the shape evolution of a disk of one material imbedded in a second one. This makes it possible to determine the interfacial tension over a relatively short time period. The technique of preparing the samples makes it possible to measure on practically any combination of polymer melts without restrictions on viscosities and melting temperature, as long as one of the materials is transparent in the molten state.The retraction of the disk is observed by using a microscope with a high resolution video camera. The camera is connected to a video frame grabber in a personal computer which is programmed to collect images with preselected time intervals. Data of the retraction is acquired by using an image analysis software, measuring the average radius of the disk.The driving force for the shape evolution is interfacial tension and it is balanced by viscous forces. The analysis of the retraction process is done analytically with a simplified one-dimensional model. The model has been compared to experiments with the system PS/PMMA at 210 °C, covering viscosity ratios over a range of six decades and five different molecular weight values of PS. It is shown that interfacial tension can be determined over the whole range and a value of 1.1±0.2 mN/m was obtained for all samples.

Multi-component polymeric composites

Abstract New types of composite systems based on polymeric matrices (polystyrene, polyethylene) containing conductive (Pd, Ag, Ag alloys) and dielectric (ferroelectric) components such as as BaTiO 3 or piezosonic powder were developed and investigated in bulk and as thick films. The latter were prepared using a screen-printing technique applying the composite paste on alumina, thermoset, enamelled steel and ceramic-coated Cu substrates. In samples with a spatially homogeneous distribution of the metal particles, as was the case with Pd, incorporation of the dielectric component caused a marked decrease of the percolation threshold. The opposite was true when the particles were inhomogeneously distributed (Ag), namely, in thick films. Dielectric measurements showed that the real part of the complex permittivity increased substantially with the content of both the dielectric additive and the metal component, especially at high resistivity levels. Thick films are interesting because the constant positive temperature coefficient of resistance can be used to make temperature sensors screen-printed on various substrates, for instance, on insulated metal.

Excess thermal noise generated during Poiseuille flow of certain polymer solutions

The previously reported results concerning the generation of excess thermal noise induced by capillary flow of aqueous solutions of poly(ethylene oxide) (PEO) are supplemented by measurements on the following solutions: PEO/DMF, PEO/i-PrOH, PS/THF, PVAC/cyclohexanone, and poly(acrylamide)/water. Similarly to the previous findings, a noise level increasing with the flow rate is recorded, the noise exhibiting a l/fα-frequency spectrum. Within a certain flow range, distinct peaks are recorded in the spectrum (harmonics of a fundamental frequency,f0). Thef0-values of the various solutions under varying flow conditions arrange themselves along a commonf0-shear rate curve. They appear to be associated with transversal oscillations of the solution upstream the capillary entrance.

Excess thermal noise and low‐frequency oscillations in capillary flow of non‐Newtonian aqueous polymer solutions exhibiting elasticity

Results of thermal noise measurements (frequency range 0.01–1000 Hz) on aqueous solutions of poly(ethylene oxide) and maltose/poly(acrylamide) during capillary flow are reported. The flow of these solutions, both being of the pseudoplastic (shear thinning) type, gave rise to an excess thermal noise exhibiting a 1/fα‐frequency distribution. The excess noise level increased with the flow rate. At a critical value of this rate, the noise showed a pulsating character. The corresponding frequency spectra contained a number of sharp peaks, all being multiples of a fundamental frequency of the order of 1 Hz. Increasing the flow rate still higher caused the pulsations to disappear, the excess noise regaining its 1/fα character. The pulsations appear to be associated with the elasticity of the solutions used. Solutions with comparable shear thinning properties but lacking elasticity did not produce such effects. No excess thermal noise was observed with Newtonian solutions of comparable viscosity.

Influence of Anisotropy on the PTC Effect in Injection Moulded Samples of CB-filled Polyethylene and Polystyrene

Abstract This paper reports on measurements of the temperature dependence of resistivity, ρ, in injection moulded samples of LDPE, HDPE, and PS filled with two grades of carbon black (CB). The CB concentration was adjusted to give a relatively small PTC-effect in isotropic (annealed) samples. It was found that the orientation of the matrix polymer that occurred during the injection moulding process highly enhanced the PTC-efficiency of all the compounds used. The magnitude of this effect and the level of RT resistivity were orientation dependent. Upon annealing (second heating run) the behaviour of the isotropic samples was recovered. In general, ρ increased with the degree of orientation in a fashion similar to the effects associated with lowering the CB content. One of the effects observed in highly oriented samples was a pronounced frequency-dependence of the resistivity (ρ decreasing at higher frequencies), and a non-ohmic I-V-behaviour. The ρ-data relate to d.c. and 1 kHz. Samples with higher and low...

Magnetically Textured Composite Materials as Elements of Electromagnetic Wave Absorbers

This article treats absorption of electromagnetic waves by thin multilayer magnetogyrotropic structures. Two types of structures with uniaxial magnetic anistropy in each layer are proposed. In structure I, easy magnetization axes in layers are normal to the layers plane. In structure II, easy magnetization axes are parallel to one of the coordinate axes, lying in the layers plane. Structure I is made as glass-fiber-reinforced plastic, with each layer containing a set of tiles, made from textured hexaferrites. This structure can also be made from multilayer fabrics of ultrahigh molecular weight polyethylene fibers, filled with magnetically uniaxial hexaferrites, having natural ferromagnetic resonance frequencies from 14 to 40 GHz. Structure II is made as multilayer fabrics from ultrahigh molecular weight polyethylene fibers, filled with hexaferrites, having a plane or cone of magnetization and natural ferromagnetic resonance frequencies 1 to 20 GHz.This article treats absorption of electromagnetic waves by thin multilayer magnetogyrotropic structures. Two types of structures with uniaxial magnetic anistropy in each layer are proposed. In structure I, easy magnetization axes in layers are normal to the layers plane. In structure II, easy magnetization axes are parallel to one of the coordinate axes, lying in the layers plane. Structure I is made as glass-fiber-reinforced plastic, with each layer containing a set of tiles, made from textured hexaferrites. This structure can also be made from multilayer fabrics of ultrahigh molecular weight polyethylene fibers, filled with magnetically uniaxial hexaferrites, having natural ferromagnetic resonance frequencies from 14 to 40 GHz. Structure II is made as multilayer fabrics from ultrahigh molecular weight polyethylene fibers, filled with hexaferrites, having a plane or cone of magnetization and natural ferromagnetic resonance frequencies 1 to 20 GHz.