Volume 3, Issue 2

A fundamental investigation of the influence of fibre loading, fibre length and matrix properties on shear viscosity, complex viscosity and the first normal stress coefficient of filled polyethylene melts prepared by different compounding techniques was carried out. Carbon fibre was compounded into two different types of low-density polyethylene (PEA and PEB) at concentrations up to about 20% by volume using different compounding techniques: a single screw extruder, and a twin screw extruder. The main difference in flow behaviours for the two kinds of carbon fibre-filled systems (CF/PEA and CF/PEB) is not due to differences between the matrix polymers, but due to the difference in fibre length or its distribution caused by the difference in compounding technique. Increasing fibre loading and fibre length increases the shear viscosity and the normal stress coefficient, with the highest increase observed at low shear rates. Especially for longer fibre-filled melts (CF/PEA series) one can estimate the yield stress in the very low shear rate region from the steady shear and dynamic flow data. In the moderate and high shear rate regions the viscosity and normal stress coefficient are influenced greatly by shear flow. Data on the relative viscosities η r , the relative complex viscosities |η*| r and the relative normal stress coefficients ψ r of the two filled systems in the moderate and high shear rate regions were compared with the empirical equation derived previously for η r for short fibre filled polymer melts. It was found that a form of the expression similar to that obtained previously could describe η r , |η*| r , and ψ r for relatively long carbon fibre filled systems.

In order to gain an idea of the flow processes in an internal mixer coloured mixtures were produced. Using these the randomness with which the distribution of the flow properties in the mixing chamber occurs could be shown. The thermal boundary conditions were found to have a strong effect on the flow processes in several regions of the chamber. Further experiments showed that the feeding behaviour of the mixture between the rotors and the time required for the incorporation both depend highly on the wall temperatures. In practice, fluctuating wall temperatures are caused by start-up effects, because mixing is a discontinuous process. A model was developed with which the variation of the internal wall temperatures can be calculated. This forms a basis for estimating the conditions to adjust heating systems in order to minimize temperature fluctuations.

We present a basic characterization methods and parameters for poly-p-phenylene sulfide (PPS) which are necessary to interpret experimental studies on fabricated parts. In particular (i) we determined the heat of crystallization of 100% crystalline PPS from density and DSC data, this allows the use of DSC to determine the percent crystallinity (ii) devised a method of calculation of crystalline orientation factors from Wide-Angle X-ray diffraction experiments. The latter problem is non-trivial because of WAXS peak overlap. The methods and parameters developed were applied to uniaxially stretched and annealed PPS films. (iii) We theoretically computed the intrinsic birefringence Δ° from first principles, this allows interpretation of birefringence data.

In practical rubber processing the compounds will be subjected to high shear rates. Hence in order to optimize processing conditions and also to guarantee a constant quality of the compounds it's a must to test processibility of rubber compounds in the shear rate range of practical processing. Processibility of rubber compounds is predominantly determined by its viscosity that's balanced by two effects; viscosity of these materials decreases drastically with increasing shear rate (pseudoplasticity) but increases markedly with the onset and development of curing. The rheovulkameter has been developped especially to take care of these effects and allowing to measure easily and fast processibility of rubber compounds under conditions of practical processing. It can be used like a capillary rheometer but like an injection molding tester as well. Rheovulkameter tests given information about both: flowing (Rheo-) and curing (Vulkameter) of rubber compounds and other curing systems, too.

Wide angle X-ray diffraction technique was used to characterize a series of post-neck drawn high density polyethylene filaments which were stretched by a two-stage drawing process. The first stage of this drawing process utilizes 100%/min draw rate until the natural draw ratio of 8–10 × ist attained. In the second stage, the fully necked filament is re-clamped and further stretched at lower stretch rate (1%/min) upto the desired stretch ratio. Wide angle X-ray diffraction data were analyzed using the Warren-Averbach fourier technique. This analysis showed that number average crystallite size increase with increasing draw ratio. In addition, the root mean square strains (∊ 2 ) ½ in the crystals decreased with increasing draw ratio upto the draw ratio of 25 then showed an increase with further increase of draw ratio.

It is observed that preoriented yarn (POY) begins orientating crystallization near the area of sharp structural change through the measurements of stress, optical birefringence and density at the speed of 3600 m/min. The investigated relationship between optical birefringence (Δn) and stress (σ) of spinning line proposed by Hamana is, to some extent, deviated from our observation. This paper gives an empirical formulation as Δn = 13.18 × 10 −3 + 6.32 × 10 −10 σ with a deviation within 4%. It also provides a predicting method for controlling the change of PET structure of spinning line. Our tests have shown that the less the denier of POY single yarn, the greater the stress and crystallinity during the fiber formation, and that stress induced effect of the crystallization kinetics of PET high speed spinning is greater than that of the cooling rate.

A basic study of fibrillation and void development during drawing of melt spun polypropylene filaments is presented. The filaments are characterized by small angle x-ray scattering (SAXS), density, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), wide angle x-ray diffraction (WAXS), and birefringence. The latter two methods were used to characterize the molecular orientation produced by processing while SEM studies of peeled filaments revealed, qualitatively, the development of the fibrillated internal superstructure. The volume fraction of microvoids was computed from the intensity of SAXS and from a combination of DSC and density measurements. The microvoid fractions determined by these two techniques were in good agreement. The volume per cent of microvoids varied from 0.04 to 2.8%. It was found that the fibrillation observed qualitatively by SEM and the measured volume fraction and number density of microvoids increased with (i) increase in draw ratio, (ii) decrease in draw temperature, (iii) increased orientation of melt spun filaments, and (iv) increased molecular weight of the polypropylene. Using Guinier analysis of the SAXS data it was found that the voids had dimensions of 25–40 nm, parallel to the fiber axis and of order 15 to 30 nm perpendicular to the fiber axis. As the drawing temperature increased the SAXS void size increased and void number density decreased. The longitudinal mechanical properties of the fibers were found to be mainly a function of the orientation and were not very much affected by changes in fibrillation or void structure per se.

The speckle photography method is used for measurement of the viscosity changes during curing of polymer composites. Subject of considerations are the changes in the reflective ability of the composite during the hardening, in the degree of polymerization and of the properties. A new relation for a time dependence of viscosity is proposed on the basis of the obtained specklegrams.