5 research outputs found
Derivation of a qualitative model for the spatial characteristic wavelength of extrusion flow instabilities: Investigation of a polybutadiene rubber through capillary, slit and complex geometry extrusion dies
The extrusion flow instabilities of a commercial polybutadiene (PBD) are investigated as a function of different extrusion die geometries, such as round capillary, slit, and complex cross-section profile slit dies via capillary rheology. Qualitative models are used to fit the experimental data for the spatial characteristic wavelength (λ) of the appearing extrusion flow instabilities. A new qualitative model for the slit die geometry, rectangular cross-section, is derived based on the theoretical concept of the âtwo layersâ extrudate and the force balance at the die exit region. The proposed qualitative model for the slit die geometry is used to predict the spatial characteristic wavelength (λ) for extrudates obtained by complex cross-section profile slit die geometries similar to industrial manufacturing. Correlation between the ratio of the extensional ( ) and shear ( ) stress at the die exit area and the characteristic dimension, height H for slit dies and diameter D for round capillary dies, is presented. Moreover, a geometry-dependent model is used to predict the spatial characteristic wavelength (λ) of the extrusion flow instabilities from a round capillary die to a slit die and vice versa
Detection of Meltflow Instabilities in the Extrusion of Polymer Melts- The Sharkskin Die vs. the Advanced Image Analysis
Detection of Meltflow Instabilities in the Extrusion of Polymer Melts- The Sharkskin Die vs. the Advanced Image Analysis
High sensitivity measurements of normal force under large amplitude oscillatory shear
The two aims of this publication are to introduce a new and rheometer-independent rheometric tool for measuring the axial normal force in oscillatory shear rheology and to study the normal forces of polyolefin melts under large amplitude oscillatory shear (LAOS). A new plate geometry with an incorporated highly sensitive piezoelectric normal force sensor was designed for a rotational rheometer. The new geometry was used to investigate normal forces of polyethylene (PE) melts under LAOS. The resulting stress and normal force data was compared with the data from measurements in commercial high performance rotational rheometers. The stress and the normal force response were Fourier-transformed and their resulting spectra were analysed. The non-linear contributions to the FT-magnitude spectra (i.e. the intensities of the higher harmonics) were analysed using the framework of the Q-parameter, for both the stress spectrum and the normal force spectrum, resulting in the strain-dependent and , respectively. The newly designed normal force geometry had a sensitivity in the measurement starting from N up to 20 N, and respectively a signal-to-noise ratio (SNR) of 16.000, which is about a factor of 1.8 times better than the best performing commercial rheometers. The new geometry was used to determine and , to characterize the shear rheological behaviour of the PE melts. Even rather simple rheometers, those without normal force detection, can be extended utilizing the here presented tools for high sensitive FT-rheology analysing the normal forces
An Intriguing Array of Extrudate Patterns in LongâChain Branched Polymers During Extrusion
Abstract The present study highlights a range of surface and volume extrudate patterns that can be detected during the extrusion flow of longâchain branched polymers. Thus, four linear lowâdensity polyethylenes (LDPEs) have been extruded using a singleâscrew extruder coupled to an inline optical imaging system. The selected LDPEs are selected to outline the influence of molecular weight and longâchain branching on the types of melt flow extrusion instabilities (MFEI). Through the inline imaging system, spaceâtime diagrams are constructed and analyzed via Fourierâtransformation using a custom moving window procedure. Based on the number of characteristic frequencies, peak broadness, and whether they are surface or volume distortions, three main MFEI types, distinct from those typically observed in linear and shortâchain branched polymers, are identified. The higher molecular weight, low longâchain branching LDPEs exhibited all three instability types, including a special type volume instability. Independently of the molecular weight, higher longâchain branching appeared to have a stabilizing effect on the transition sequences by suppressing volume extrudate distortions or limiting surface patters to a form of weak intensity type