Melting of immiscible physical and compatibilized polymer blends in single screw extruders (original) (raw)
Related papers
Melting of PP/PA6 Polymer Blends in Single Screw Extruders – An Experimental Study
Materials Science Forum, 2008
A prototype modular single screw extruder fitted with a screw extracting device is used to monitor melting of an immiscible polymer blend (PP/PA6, with different weight ratios) in this popular type of processing equipment. As anticipated, the observed phenomena are much more complex than those involved in extruding PP or PA6, when the well known Maddock/Tadmor mechanism is valid. Consequently a hybrid melting mechanism, involving Maddock/Tadmor and Dispersive melting sequences, is proposed.
Melting of polymer blends in single-screw extrusion - An experimental study
International Journal of Material Forming, 2009
Melting is a major step in plasticating single screw extrusion, but most of the existing phenomenological know how was gathered by performing Maddock-type experiments with homopolymers. Given the current widespread industrial use of polymer blends, it is worth determining whether the same mechanisms and mathematical models apply, or whether different sequences develop. This work reports the results of Maddock-type experiments using a PA6/PP blend, both in its immiscible and compatibilized varieties. A melting mechanism combining the features of the classical Tadmor mechanism and of the dispersed melting mechanism, also previously reported in the literature, was observed.
Chemical and morphological evolution of PA-6/Epm/Epm-g-MA blends in a twin screw extruder
Journal of Polymer Science Part A: Polymer Chemistry, 1999
Chemical conversion and morphological evolution of PA-6/EPM/EPM-g-MA blends along a twin screw extruder were monitored by quickly collecting small samples from the melt at specific barrel locations. The results show that the MA content of all blends decreases drastically in the first zone of the extruder, i.e., upon melting of the blend components. Significant changes in morphology are also observed at this stage. A correlation between chemistry and morphology could thus be established.
Morphological Parameters of PP/PA6 Blend Measured In‐Line During Extrusion
Macromolecular Symposia, 2006
An optical detector, assembled at a slit die at the exit of a twin screw extruder was used to quantify in‐line the extrusion of a PP/PA6 immiscible blend. During the extrusion the detector respond according to the changes in concentration and particle size of the polyamide 6 phase. The influence of dispersed phase concentration was evaluated varying its concentration from 0 to 5% (w/w). Reduction in the PA6 particle size was followed adding different amounts of polypropylene grafted with acrylic acid (PP‐g‐AA), which acts as a compatibilizer. The normalized detector signal intensity increases with an increase in PA6 concentration, due to an increase in the number of scattering particles in the medium, and with a decrease in its particle size. Plots of detector signal as a function of particle concentration and size enabled the calculation of the extinction cross sections of the PA6 segregated particles.
In-line assessment of the melting behaviour during polymer extrusion
The in-line melting behaviour of a polyamide blended in polypropylene has been investigated in-line using a turbid-meter, an optical detector fitted at the die exit of an extruder. During the flow the PA-6 particulate second phase scatters light producing a turbid melt. The intensity of the detector signal is dependent of the type of the second phase (scattering cross-section), its concentration and particle size. Operating the extruder at low temperature the course particulate PA-6 phase (200 microns) passes through the extruder and detector without melting, which does not scatter light and so be undetected by the turbid-meter. Upon raising the temperature the solid course particulate PA-6 phase starts to melt, induced by the higher temperature and the shear level found in the extruder. The detector signal is sensitive to the turbidity, generated by the reduction in the PA-6 particle size (down to ~1 micron), due to its melting. From the overall signal behaviour is possible to measure an average reduction of 10 ~ 15ºC comparing with values obtained by the standard DSC thermogram. This technique can be extended in order to quantify the shear level and heat built-up inside an extruder, due for instance, the kneading blocks added in the screw configuration.
Melt temperature consistency during polymer extrusion
A thermocouple mesh technique measured melt temperature radially across polymer flows, precisely profiling the relationship between melt behavior and processing parameters in polymer extrusion. In polymer extrusion, a homogenous melt output is required to achieve a uniform extruded product. Temperature variations in the melt may cause non-uniformity of the optical, mechanical, or chemical properties of the extruded parts, or lead to extrudate containing un-molten or gelled particles. Process problems can also occur due to the variability of feedstock materials, machine geometry, or set process conditions. Here we measured the consistency of the polymer melt temperature in the die of a single screw extruder in order to understand the individual and combined effects of extruder screw geometry and barrel set temperature for a selection of materials. The measurements were carried out in the die zone of a highly instrumented 63.5mm diameter single screw extruder (see Figure 1). We generated 2D temperature maps of melt temperature with data from a thermocouple mesh technique. 1 The melt temperature was measured at a number of radial positions across the melt flow. Our experimental work focused on identifying the effects of screw geometry , material, and set barrel temperature on the melt temperature across the flow, considering both spatial and temporal variations. Four commercial grade polymers were used (see Table 1). The materials included a virgin high density polyethylene (HDPE), a recycled extru-sion grade high density polyethylene (RHDPE), a virgin low density polyethylene (LDPE), and a virgin polypropylene (PP). Three different screw geometries were used, gradual compression (GC), rapid compression (RC), and barrier flighted with spiral Maddock mixer (BF) at five discrete screw rotation speeds, selected to cover the full operating range of the extruder. We tested three temperature settings, low (A), medium (B), and high (C). During extrusion of HDPE, the 2D thermal profiles clearly showed that spatial melt temperature homogeneity deteriorated as screw rotation speed increased. At low flow rates, the temperature was relatively consistent across the flow. However, as flow rate increased, regions of higher temperature became apparent, both in the center of the flow and Figure 1. Arrangement and dimensions of the apparatus. in regions between the wall and the center. Screw geometry was significant. The BF screw showed the flattest melt temperature profiles, and the smallest variation in temperature with increasing speed. We attribute this to the separation of melt and solid due to the barrier flight, and the spiral Maddock mixer at the end of the screw. 2 The highest variations were observed for the GC screw at high flow rates. Surface temperature of the screw is known to affect the melting process but was not measured here. 3 The rate of mass throughput (i.e. melting capacity), the level of material mixing, and the heat transfer along the material in the barrel depend on the screw geometry. 4, 5 We processed LDPE, HDPE and PP to observe the effects of polymer type on the thermal homogeneity at a medium set temperature. Melt temperature in the center of the flow increased with screw speed for all polymer types investigated. For similar screw speed values, differences in maximum melt temperature between the different materials were evident. As the same screw and barrel set temperatures were used to process all the materials, the significance of differences in the rheo-logical and thermal properties of each material were easily recognized. Resin form and shape/size can also affect melt temperature and process thermal behavior. 6, 7 All the materials we used in this study were in pellet form, although they differed slightly in their shape and size. The nature of the melt temperature profiles differed depending on the material , validating observations from previous work. 8, 9 We used the GC screw to process RHDPE under three different barrel set temperature conditions. Higher set barrel temperature resulted Continued on next page
2015
In this paper, the preparation and compare of some mechanical and physical properties of two groups of polymer blends consisting of polyvinyl chloride with polypropylene (PP-PVC) and poly-vinyl chloride with high-density polyethylene (HDPE-PVC). Using a twin-screw extruder, three weight percentages of PP and HDPE (5, 10 and 15%) were used to prepare the polymer blends. Experimental investigation was carried out for analyzing the mechanical properties like tensile strength, flexural strength, compression, impact, and hardness and physical properties (thermal characteristics and melt flow index) for the polymer blend samples. The results show that the polymer blend (HDPE-PVC) get higher values than polymer blend (PP-PVC) in fracture strength, young´s modulus, elongation, flexural strength, creep resistant and maximum shear stress and thermal characteristics, whereas the polymer blends (PP-PVC) get higher values in impact strength, fracture toughness, hardness and compression and melt ...
Materials Science Forum, 2008
This investigation aims at establishing the relationships between the thermomechanical conditions and the mechanical properties of a direct injection moulded polypropylene/polycarbonate blend (70/30wt composition). Rectangular plates (2 mm thick) were injection moulded by systematic variations of the processing conditions. The moulding programme was based on a design of experiments (DOE) approach, being considered variations in two levels of the melt (240 and 280ºC) and the mould (5 and 80ºC) temperatures and the injection flow rate (3.8 and 38 cm 3 /s). For comparison purposes, neat polypropylene was also moulded under the same set of processing conditions. In both cases the thermomechanical environment was characterised by computer simulations of the mould filling phase using commercially available codes (Moldflow). Tensile specimens were cut from the injected plates. The microstructure of the mouldings was characterized by polarized light microscopy, PLM. The mechanical characterization encompass the assessment of the tensile (at 5 mm/min at 23 ºC) and impact toughness (unnotched Charpy test). The results are analysed by ANOVA. The presence of PC particles affects the crystallization of PP, this being revealed on the mouldings microstructures observed by PLM that are distinct for the neat and PP/PC blends. The mechanical properties are determined differently by the processing variables.