Abstract An experimental study of film formation and structure development of polybutylene terephthalate (PBT) in single and double bubble tubular film extrusion processes is presented. PBT was found largely stable in the first stage. In the second stage, the bubble was unstable and biaxial inflation was achieved only with a blow-up ratio of one. The sources of second bubble instabilities were related to the crystalline nature of the first bubble being inflated in the second stage. The structure and properties in the films varied substantially with processing conditions. While the first bubble had poorly ordered α-structure, the double bubble possessed oriented polymorphic texture. The second deformation that induced high film-line stress favored the formation of a stable β phase. The mechanical behavior of the films reflected the crystal perfection as well as orientation in the films.

The levels in biaxial orientations and mechanical properties of stretched extrusion cast polyamide 12 films were investigated with birefringence, wide angle X-ray diffraction (WAXD) pole figure and mechanical testing. Introduction of a pseudo-orthogonal crystalline symmetry enabled the calculation of White-Spruiell biaxial orientation factors using WAXD pole figure data. The orientation was uniaxial or biaxial depending on the stretch ratios along two principal stretching directions that are the machine direction (MD) and the transverse direction (TD). According to the WAXD pole figure patterns, planar alignments of hydrogen bonded layers were formed with respect to the film surface from most of the stretched films. Balanced stretching at higher stretch ratios enhanced the planarity. It was found that the mechanical properties (tensile strength and elongation at break) of the films had a close correlation with the out-of-plane birefringences.

An experimental study of the distribution of material and internal flow patterns in the cold feed screw injection molding machine for rubber compounds is presented. Experimental studies are carried out by vulcanizing rubber compounds in the screw of the plasticating unit at various positions in the molding cycle. The screw is then removed and the rubber strip unwound from the flights. It is found that transverse flow patterns begin at the feed port and proceed down the channel. Various kinds of starvation behavior are observed especially at low back pressures and with narrow feed strips.

A composite model of solids conveying, melting and melt flow in a closely intermeshing counter-rotating twin-screw extruder of modular design has been developed. This is based on combining melt conveying models with new melting and solids conveying models. Computations are made for axial fill factor pressure, temperature and melting profiles. The results are compared with experiment.

Abstract A generalized representation of second moment orientation in polymer systems is presented. Orientation is expressed through the asymmetry of the polarizability tensor. The formulation presumes that local symmetry directions differ from macroscopic machine and transverse directions. The formulation leads to a set of biaxial orientation factors (equivalent to those of White and Spruiell) defined relative to symmetry axes I, II, III and a set of angles ϑI1,ϑII2 and ϑIII3 ${{\vartheta }_{I1}},{{\vartheta }_{II2}}\text{ }\!\!~\!\!\text{ and }\!\!~\!\!\text{ }{{\vartheta }_{III3}}$representing the directions of the axes relative to the laboratory axes (1,2, 3) such as the machine (1), transverse (2) and thickness (normal) directions (3). Any two of these angles eγ, Θ11 ${{\Theta }_{11}}$and ΘII2 are sufficient. The formulation is applied to interpret orientation developed in simple shear.

AbstractWe describe an experimental and theoretical study of the mechanisms of flow of rubber compounds in a screw extruder. Two compounds, a typical synthetic rubber (butadiene-styrene copolymer-cis-1, 4 polybutadiene) based passenger tire tread (PTT) and a natural rubber based truck tire tread (TTT), were investigated in a 112${}^{1}/{}_{2}$inch NRM cold feed screw extruder using a screw with a constant channel depth and constant channel pitch along the whole screw length. The rubber was cured in place and the screw removed. The screw exhibited starvation behavior except near the die. The length of the rubber strip in the screw is proportional to the pressure developed at the die. Marker studies showed transverse circulating flows beginning in the region immediately downstream from the hopper. These observations indicate that cold feed extruders exhibit a metering region flow, albeit sometimes starved, from entry port to die. Under these conditions the extruder is independent of the pressure developed in the screw channel. A simple non-Newtonian isothermal mathematical model for the metering zone is described. The rubber compound is considered as a pseudoplastic material with a yield value. A comparison of theory and experiment shows that a one dimensional isothermal model quite accurately predicts the flow rate pressure development of the rubber compound in our screw (with a shallow prismatic channel) when starvation is considered. The yield value of the rubber compound influences screw characteristic curves only for very high values of the dimensionless pressure gradient.

Filling ratio is an important process parameter related to the residence time distribution and thermal history of resin in a twin-screw extruder. This study presents a theoretical method of filling ratio distribution calculated by our newly developed 2.5 D Hele–Shaw flow model and finite element method. The calculated filling ratio distribution of a full-flight screw was validated by on-line measurement of resin volume with the laser light section method. The calculation and measurement results were in good agreement.

Extensive experimental studies on silica agglomerate breakup during compounding with polymermelts of various viscosities and polarities in amodular corotating twin-screw extruder were conducted. To avoid a subjectivity of the result, due to small size particles involved, silica agglomerates were characterized by measuring their mass average values. Increasing the screw speed, melt viscosity, and silica concentration were found to increase the silica agglomerate breakup. The effect of these parameters on agglomerate breakup was ranked as follows: silica concentration > polymer viscosity approximate to screw revolutions perminute (rpm). A good correlation between silica agglomerate breakage and power input was also found. Based on the experimental data and dispersion process, a compositemodular kinetic model for evaluating silica agglomerate breakup during compounding in a corotating twin-screw extruder was tested. The kinetic constants of breakup and reagglomeration of silica agglomerates were calculated based on the stresses applied to the agglomerates and their cohesive strength. These constants for silica agglomerates were found to be not significantly different at high concentrations. The latter was in contrast to experimental data from available literature on compounding of calcium carbonate with polypropylene where the high reagglomeration kinetic constants of calcium carbonate in comparison with those of breakup played a major role in the agglomerate breakup. Comparison of the experimental and calculated results on the silica agglomerate size evolution during compounding with polymer melts indicated a reasonable agreement between them at high rotational speeds.

One polypropylene (PP) was mixed with two ethylene butene copolymers (EBM). EBM1 had 12.5 mol % of butene and was immiscible with the PP. EBM2 had 51.6 mol % of butene and was miscible with the PP. The dispersed PP in EBM1 showed fractionalized crystallization behavior with a crystallization temperature at around 45°C and a much slower isothermal crystallization rate comparing to the neat PP. The PP did not exhibit fractionalized crystallization behavior in EBM2. EBM1 did not decrease both the crystallization and melting temperatures of the continuous PP. However, EBM2 could decrease both the two temperatures. It was found that EBM2 could largely suppress the epitaxial lamellar branching of the PP. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The damage of glass fibers at various conditions was investigated in a corotating twin screw extruder by varying viscosity, screw speed, and screw configuration. Increasing the screw speed and melt matrix viscosity were found to increase the extent of fiber breakage. Based on the experimental data and Euler buckling theory, a composite modular kinetic model to describe glass fiber breakage was developed. Regions of the major and minor fiber breakage in a corotating twin screw extruder were found. The simulation program based on the experimental data and kinetic constants was developed for fiber breakage along the screw length. Comparisons were made between simulated results and experimental data indicating a reasonable quantitative agreement between them. Predictions of the model are also in general qualitative agreement with many published data on fiber breakage in twin screw extruders. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

This article details uniaxial and biaxial orientation processes in films, fibers and moldings.

Humankind has been mixing together different materials since the dawn of written history to produce products with improved engineering properties. The compounds are more uniform have superior mechanical properties and much shorter residence times. The major continuous mixers used commercially in 2009 for compounding and blending are modular co-rotating self-wiping twin-screw extruders. Blends of the natural rubber and the new synthetic elastomers must have been studied by the IG Farbenindustrie and various German rubber fabricators such as Continental Gummi-Werke in the 1930s. Perhaps the first widely used synthetic polymer blend was the NBR-poly (vinyl chloride) system. NBR was widely used in under the hood applications in automobiles. The phase morphology of polymer blends shows significant variations in polymer melt processing. One of the most striking observations is the formation of mini-fibers in melt spun blends, where the blend experiences uniaxial elongational flow.

We describe the development of phase morphology in polypropylene (PP)/ethylene–butene copolymer (EBM) blends in both extrusion through dies and in subsequent melt spinning to form filaments. This immiscible blend has a very low interfacial tension around 0.69 dynes/cm. In the die extrusion process, at low extrusion rates, the dispersed PP phase was sheared into fibrils; at higher extrusion rates, the PP fibrils formed an encapsulation layer near the die wall first, then it broke into droplets because of both interfacial tension and long residence time. These droplets agglomerated together to form a network. In melt spinning, the dispersed phase was also drawn down into fibrils, which coalesced into a continuous layer on the outer surface of the filaments at higher drawdown rates. POLYM. ENG. SCI., 50:1969–1977, 2010. © 2010 Society of Plastics Engineers

Polypropylene (PP)/ethylene butene copolymer (EBM) blends were melt-spun into fibers. The fiber orientation was determined by wide angle diffraction (WAXS) and birefringence. The birefringence of the blend fibers was much lower than that of the pure PP or EBM filaments spun at the same stresses. WAXS study showed that the PP phase had the same orientation versus stress relationship in its blends and in its pure state. However, EBM phase demonstrated much lower birefringence in its blends than in its pure state. The mechanism was explained as following. In melt spinning of the blends, the PP phase crystallized first. Before the PP phase crystallized, both PP and EBM phase had comparable modulus leading uniform stress distribution. After the PP phase crystallized, the modulus of PP phase became much larger than that of the EBM melt. Thus it would take most of the stress if it was the continuous phase leaving the EBM phase crystallizing at much lower stresses. This led to a large birefringence suppression of the EBM phase. In melt spinning of the blends with only 1 to 10 wt.% of PP, the dispersed PP phase could coalesce into a continuous surface layer. Thus small amount of PP could largely decrease the birefringence of EBM fibers.

A composite model has been developed to simulate the extrusion process for intermeshing counter-rotating twin-screw extruders. An experimentally based inciting model, solids conveying model, and new improved metering model, were combined to develop this formulation. The procedure for global design of a flood feed intermeshing counter-rotating twin screw extruder is presented. Illustrative calculations are made for polyvinyl chloride and high density polyethylene in this type of machines with different screw designs. Computations are made for axial variation of the fill factor, pressure, temperature and melting profiles. Simulations were found to match with experimental results well. The model was also applied to scale-up.

Intermeshing counter-rotating twin screw extruders play an important role in polymer processing, especially for the extrusion of profiles and pipe, largely from polyvinyl chloride There has been little effort on flow modeling of these machines and most of this has involved representing the machine as a "leaky" positive displacement pump and estimating leakages In recent years, M H Hong and the authors have developed more general methods of simulation of flow in this machine and both applied and experimentally verified it for a few designs Here we extend these efforts to a broader range of screw designs, especially with deeper screw channels where transverse shearing induced by the flights is important Calculations are done for isothermal power law fluids The results are compared with experiment POLYM ENG SCI, 51 37-42, 2011 (C) 2010 Society of Plastics Engineers

During the last quarter of the 20(th) century, there was a transition from batch to continuous mixing in the polymer and food industries. We present and summarize experimental studies of flows in both internal and continuous mixers. Simulation of flow in these machines is also described. It is argued that the primary reason for this transition was that continuous mixers produce more uniform and better quality mixes, and that this is inherent in their different fluid mechanics. Batch mixers are always starved and largely unpressurized. Their complex fluid mechanics produce non-uniform mixing in the various portions of the compound material. Continuous mixers set up a steady state hydrodynamic flow field generally consisting of alternating regions of pressurized fully filled flow and starved flow. All of the compounds must pass through these regions to reach the die exit and thus possess uniform mixing histories. This uniform deformation history which includes pressurized mixing regions produces superior uniform products.

A comprehensive computer model for counter-rotating twin-screw extrusion has been verified on the base of experimental and simulation studies for closely intermeshing strave fed extrusion (Fig. 3). Melting behavior of the polymer, pressure and temperature profiles as well as fill factor were evaluated at various flow rates and screw speeds (Fig. 4-9). The agreement of predictions and observations was satisfactory (Fig. 10-12).