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Applied Rheology

SPE Library content related to rheology
Study of the Preparation and Superiority Properties of the Novel Propylene-Based Elastic HMAs
Chang Hefei, Ma Yi, Liang Wenbin, May 2016

The novel propylene-based elastic hot melt adhesives (HMAs) with improved adhesive and elasticity were first reported and prepared by styrene-assisted melt free-radical grafting of maleic anhydride. The changes in chemical composition, thermal property, melt viscosity, and adhesive performance were measured by FTIR, GPC, TREF, rheology, TEM, melt flow indexer, and Intron universal testing machine, respectively. Compared to the commercial HMAs, the propylene-based elastic HMAs with special continuous phase distribution exhibited 20% increasing in peel strength, and doubled 100% tensile deformation recovery rate, which achieved a consistent of high degree of adhesion and elasticity. Meanwhile, the weather resistance test results also indicated that the propylene-based elastic HMAs had excellent resistance with high and low temperature shock, which alleviated the interface delamination caused by the different thermal shrinkage between the steel interface and plastic interface, further benefitting and extending the service life of steel composite pipe.

Development of a Predictive Power Law Relationship for Concentrated Slurries, Part 2: Experiment and Processing Implications
Mark D. Wetzel, D. Ray Pettitt, Jr., Gregory A. Campbell, May 2016

It is well established that the addition of solid particles into polymers can increase the melt viscosity significantly by perturbing the flow field and through particle-particle interactions or particle network formation [1-3]. Highly-filled polymer compounds can present processing challenges, including high screw shaft torque, energy consumption, pressure and melt temperature. This paper describes an evaluation of the effects of filler concentration on melt processing. The experimental results using a batch mixer are linked to the theoretical treatment of the rheology as a particulate percolating system with power-law behavior [4]. The implications of the increase in viscosity with filler concentration on polymer processing will be discussed from a practical engineering perspective.

Rheology as a Tool to Evaluate Polymer/Active Pharmaceutical Ingredient (API) Solid Dispersions
Fengyuan Yang, Chad D. Brown, Lawrence A. Rosen, May 2016

Despite significant advances have been achieved in applying amorphous solid dispersion to enhance bioavailability of poorly soluble active pharmaceutical ingredients (APIs), there remain challenges in characterizing the microstructures of solid dispersions and correlating their performance with microstructures. This study focused on utilizing rheology as a tool to investigate and evaluate several model polymer/API solid dispersions prepared by various techniques with different mixing capabilities. Rheological responses of different model solid dispersions displayed a strong correlation between microstructures and viscoelastic properties. For the currently studied system, storage modulus and viscosities versus frequency of different solid dispersions indicated that the incorporation of API imparted a plasticizing effect to the polymer matrix. In comparison, crystalline/aggregated forms of the API exhibited a more elastic response than its amorphous/dispersed counterparts. In addition, a temperature ramp interrogation of a physical mixture of polymer and API captured a critical temperature, at which a transition in slope observed in the damping factor was attributed to the dissolution of crystalline API into the polymer.

Rheology Optimized Processing Temperature for Preparation of Amorphous Solid Dispersions via Hot Melt Extrusion (HME)
Fengyuan Yang, Chad D. Brown, May 2016

The production of amorphous solid dispersions via hot melt extrusion (HME) relies on elevated temperature, applied mechanical force and prolonged residence time, which can result in potential degradation and decomposition of thermally-sensitive components. In this study, the rheological properties of a physical mixture of polymer/active pharmaceutical ingredient (API) were utilized to guide HME processing temperature. A critical temperature, which is substantially lower (~13°C) than the melting point of crystalline API, was captured during a temperature ramp examination and regarded as the critical point at which the API molecularly dissolves into the polymer. After identification, solid dispersions were prepared by HME processing below, on, or above the recognized critical temperature and characterized by scanning electron microscopy, hot stage microscopy, Xray diffraction, differential scanning calorimetry and rheology. Physicochemical properties of resultant solid dispersions indicated that the obtained critical temperature is sufficient for the polymer/API system to reach a molecular-level mixing, manifested by the transparent and smooth appearance of extrudates, absence of API crystalline diffraction and melting peaks, and dramatically decreased complex viscosity. Once the critical temperature is achieved, further raising temperature only results in limited improvement of the dispersion, reflected by slightly reduced storage modulus and complex viscosity.

Influence of Filler Dispersion on Electrical and Rheological Properties of Pc/San Blends with Graphite Nanoplates or Expanded Graphite
Marco Liebscher, Petra Pötschke, Gert Heinrich, May 2016

The effect of Graphite Nanoplates (GnPs) and Expanded Graphite (EG) on electrical and rheological properties was investigated in co-continuous melt-mixed polycarbonate (PC) /poly(styrene-acrylonitrile) = 60/40 wt% prepared using micro-compounder in two steps. Mixing conditions in premixing the fillers into PC were varied. Similar to carbon nanotubes (CNTs), GnPs and EG tend to localize in PC. Improved filler dispersion for samples exposed to higher mixing energy in the premixing step resulted in larger increase of complex viscosity and storage modulus. However, electrical resistivity was lower in samples which experienced lower mixing energy. Comparing EG and GnP, the effects are quite similar. EG showed a slightly better electrical performance.

Improvement of the Extrusion Foaming Properties of Externally Plasticized Cellulose Acetate by Reactive Melt Mixing Using a Multifunctional Reactive Oligomer
Christian Hopmann, Sven Hendriks, Stefan Zepnik, May 2016

Externally plasticized cellulose acetate was modified by reactive melt mixing with a multi-functional oligomer (chain extender). The modified compound was characterized in terms of molecular properties and viscosity. The reactive modification was applied in an extrusion foaming process using 1,3,3,3-tetra-fluoropropene (HFO-1234ze) as blowing agent. The reactive modification in the foam extrusion process can be used to affect the rheology and thereby foaming properties of the cellulose acetate compound to optimize the cell morphology of the resulting foam sheets or boards.

Dynamic Rheological Measurements of Aqueous Polyester Dispersion in Batch Reactor and Twin Screw Extruder
Ali Goger, Michael R. Thompson, John L. Pawlak, David J.W. Lawton, May 2016

This paper reports on inline measurement techniques for the rheological behavior of aqueous polyester dispersion in batch reactor and twin screw extruder (TSE). Since the preparation of latex without hazardous solvent is a relatively new technique, very little has been reported to understand the kinetic aspects of the process for both batch reactor and TSE. A sudden viscosity drop is observed in a batch reactor whereas the viscosity tends to oscillate in TSE during the addition of water when surface tension is low enough. The viscosity changes during the addition of water are thought to be related to the morphological changes during the process since surfactant must be present else no change occurs. In this paper, different surfactant and NaOH concentrations have been studied for their influence on the viscosity so that emulsification may become a predictable process in a TSE.

Evaluating Rigid and Semi-Flexible Fiber Orientation Evolution Models in Simple Flows
Gregory M. Lambert, Donald G. Baird, May 2016

As American vehicle fuel efficiency requirements have become more stringent due to the CAFE standards, the auto industry has turned to thermoplastic-fiber composites as replacements for metal parts to reduce weight while simultaneously maintaining established safety standards. Furthermore, these composites may be easily processed using established techniques such as injection molding and compression molding. The mechanical properties of these composites are dependent on, among other variables, the orientation of the fibers within the part. Several models have been proposed to correlate fiber orientation with the kinematics of the polymer matrix during processing, each using various strategies to account for fiber interactions and fiber flexing. However, these all require the use of empirical fitting parameters. Previous work has obtained these parameters by fitting to orientation data at a specific location in an injectionmolded part. This ties the parameters to the specific mold design used. Obtaining empirical parameters is not a trivial undertaking and adds significant time to the entire mold design process. Considering that new parameters must be obtained any time some aspect of the part or mold is changed, an alternative technique that obtains model parameters independent of the mold design could be advantageous. This paper continues work looking to obtain empirical parameters from rheological tests. During processing, the fiber-polymer suspension is subjected to a complex flow with both shear and extensional behavior. Rather than use a complex flow, this study seeks to evaluate and compare the effects of shear and extension on two orientation models independently. To this end, simple shear and planar extension are employed and the evolution of orientation from a planar random initial condition is tracked as a function of strain. Simple shear was imparted using a sliding plate rheometer designed and fabricated in-house, and a novel rheometer tool was developed

Preparation and Characterization of Biodegradable Polylactide/Ethylene Methyl Acrylate Copolymer Blends
Lin-Qiong Xu, Yong-Qing Zhao, Xiang-Fang Peng, May 2016

The poly(lactic acid)/ethylene methyl acrylate copolymer (PLA/EMA) blends were melt blended with by a twin-screw extruder. The phase morphologies, mechanical, and rheological properties of the PLA/EMA blends with three weight ratios were investigated. The results showed that the addition of EMA improves the toughness of PLA at the expense of the tensile strength to a certain degree. All the PLA/EMA blends display typical droplet-matrix morphology, and different characteristic linear viscoelastic properties in the low frequency region, which were investigated in terms of their complex viscosity, storage modulus, and Cole-Cole plots. The interfacial tension between the PLA and EMA is calculated using the Palierne model conducted on the 80/20 PLA/EMA blend, and the calculated result is 3.3 mN/m.

Optimizing Process Condition of Compression Molding: from Material Properties Characterization to Numerical Simulation
C-W. Wang, W-C. Tsai, S-B. Sun, C-H. Hsu, R-Y. Chang, May 2016

Herein, we present the recent development in viscosity measurement by squeeze flow method. We applied this technique to investigate to fiber reinforced plastic (FRP) systems including, polypropylene-based glass mat thermoplastic (PP-GMT), and thermosetting sheet molding compound (SMC). The effects of compression rate, temperature and curing time are systematically studied. In both cases, the squeeze flow data deviate from simple power law model, and is analyzed by the approach proposed by Laun et al (J. Rheol. 1992, 36, 743) [1]. The results demonstrate the promising potential of viscosity measurement by squeeze flow method, and great relevance to industrially important process such as compression molding. The measured rheological material properties are then used in process simulation to obtain optimal process conditions of compression molding.

Simulation of an Industrial High Capacity Blown Film Extrusion Process
Benedikt Neubert, Johannes Wortberg, May 2016

One of the most important production processes for manufacturing plastic films is the blown film extrusion. The conventional way to improve the output of a production line can be achieved by a substitution or a modification of the limiting air cooling ring. In order to verify an output intensification, typically the trial and error method is being used. For reducing the experimental costs, a numerical procedure called Process Model has been developed for simulating the formation of the bubble with regard to changing process conditions and rheological behavior. The applicability of the Process Model has been proven for small production lines with a maximum output of approximately 100 kg/h (LDPE).
According to industrial concerns, the Process Model has to be verified for higher mass flow rates (> 750 kg/h). Therefore, the numerical procedure has to be adapted. Besides a modification of the simulation domain and the integration of an internal bubble cooling device (IBC), an adaption of the material model has to be done. For the consideration of the material behavior from each layer of the multilayer film, a specific approach has been developed and used. In this paper, the simulation results of the first application of the Process Model for an industrial blown film line including an internal bubble cooling system will be presented. This device intensifies the heat exchange and enhances the bubble stability with regard to higher air volume flow rates [1]. The resulting heat exchange and the flow phenomena will be discussed.

Evaluation of Liquid Crystal Polymers (LCP) as an Additive for Polybutylene Terephthalate (PBT) to Improve Melt Processing and Properties
Anshuman Shrivastava, Litsa Rubino, Zach Richmond, May 2016

Liquid Crystal Polymers (LCP) are partially crystalline aromatic polymers based on p-hydroxybenzoic acid and related monomers. LCP’s offer numerous benefits such as higher melt flow during molding, low warpage, good dimensional stability, better moldability, superior mechanical and thermal properties, excellent chemical resistance, flame resistance, and weatherability and are used in thin walled and optical applications. This paper evaluates the use of LCP as an additive to improve the properties and performance of Polybutylene Terephthalate (PBT). Unfilled PBT formulations with different loadings of LCP (0.25wt% to 5wt%) were compounded and tested. Rheological analysis was performed using a capillary rheometer to quantify the influence of LCP in melt flow of unfilled PBT. Thermal analysis through DSC was performed to measure the influence of LCP on crystallization phenomenon of PBT. Mechanical properties and heat deflection temperature were measured to estimate the differences in performance between the various formulations.

Evaluation of Branched Polypropylene Degradation by Using Different Constitutive Equations
Martin Zatloukal, Jiri Drabek, May 2016

In this work, virgin as well as thermally degraded branched polypropylenes were investigated by using rotational and Sentmanat extensional rheometers. Based on the shear and extensional rheology data it was deduced that both chain scission and chain branching takes place during thermal degradation of the tested polypropylene. It was found that simple constitutive equations such as Generalized Newtonian law, modified White-Metzner model and Yao model can be used to describe the measured steady state shear and uniaxial extensional viscosity data. It was revealed that Yao and Generalized Newtonian models have capability to quantify level of extensional strain hardening (i.e. the maximum steady state uniaxial extensional viscosity divided by 3 times Newtonian viscosity) as a function of degradation time via their parameters not only quantitatively but also qualitatively.

Thermal and Time-Dependent Rheological Stability Behavior of Polyacrylonitrile with Various Plasticizers
Jianger Yu, Jianhua Huang, Donald G Baird, Gregory C Miller, Judy S Riffle, May 2016

The feasibility of melt spinning polyacrylonitrile (PAN) with plasticizers has been investigated for decades but it is still not been commercialized yet. In this paper, the thermal and time-dependent rheological stability behavior of PAN with various plasticizers is reported. The thermal behavior experiments show that the plasticizers are able to sufficiently decrease the melt temperature of PAN which make the melt spinning process feasible. The timedependent rheological stability experiments show that PAN could hold its viscosity stable without significant degradation and crosslinking for a sufficient period of time below 180?.

Applied Rheology for Understanding Flow Instabilities in Polymer Processing
Martin Zatloukal, May 2016

Due to the fact that polymer melts behaves as non- Newtonian viscoelastic fluids, their flow behavior is rather complex and leads to number of flow phenomena which have negative impact on their processing and final product properties [1-19]. The polymer melt elasticity, high shear viscosity, extensional viscosity and its tendency to slip at the solid surfaces causes the flow destabilization. Typical flow instabilities occurring during polymer melt flows are die drool [1-2, 11-12, 15-18], neck-in [3, 5, 7, 15, 17], film blowing instabilities [3, 5, 14, 15-17] and interfacial instabilities in coextrusion [4, 5, 6, 10, 15, 17]. In this work, it is demonstrated how the polymer melt rheology and modeling of polymer processing can be used to understand and minimize the above mentioned flow instabilities occuring in extrusion and coextrusion technologies.

Improving the Mechanical Properties and Flame Retardancy of Multilayered PP Foam/Films via the Introduction of Flame Retardants
Sangjin Lee, João Maia, Alex B. Morgan, May 2016

In this work we improve the mechanical properbities and flame retardancy of polypropylene (PP) foam/films produced by continuous multi-layered co-extrusion.Two different types of PP were used and named as PP1 and PP2. The nitrogen/phosphorous based flame retardant (FR) particles play the dual role of nucleating agent and flame retardant. FR particles were used to fabricate PP-FR composites. To investigate the effect of FR on PP crystallization and rheology, DSC thermograms, small amplitude oscillatory shear (SAOS), transient extensional viscosity were measured on both PP1 and PP2 system. FR particles played role of a nucleating agent for both PP1 and PP2 system. PP2 system has a 4x higher zero shear viscosity than PP1, while PP1 system showed much stronger strain-hardening than PP2. PP1 foam/ PP2 film structures were fabricated with different FR content. Both neat PP1 foam/PP2 film and PP1 foam/PP2 film-20%FR have good 16 layered film/foam structures and well-defined ellipsoidal shape bubble cells. The compressive modulus of PP1 foam/ PP2 film samples is 5-6 times higher than that of PP1 foam samples. Compressive strain of PP1 foam/ PP2 film samples is 2-3 times higher than one of PP1 foam samples. PP1 foam/ PP2 films showed excellent flame retardancy.

Extensional Mixing Elements for Twin-Screw Extrusion: Effectiveness at Dispersive Mixing Operations in Composites
Sidney O. Carson, João M. Maia, May 2016

The extensional mixing element for twin-screw extrusion was applied to the melt mixing of two different polypropylene/carbon nanofiller systems and compared to a standard shear kneading block in an effort to improve the state of dispersive mixing of the operation. It was concluded that there was a qualitative and quantitative difference in microscale dispersion for both carbon nanotubes and graphene nanosheets when implementing the extensional mixing element, as evidenced by the optical microscopy images and subsequent image analysis. However, the composites exhibited minimal differences in rheological or electrical percolation, indicating that the reducing the initial agglomerate size is only a small part of effective composite production.

A Process for Generating Composites of Acrylonitrile-Butadiene-Styrene Reinforced with a Thermotropic Liquid Crystalline Polymer for Use in Fused Filament Fabrication
Mubashir Q. Ansari, Craig D. Mansfield, Donald G. Baird, May 2016

In this paper, processing conditions were determined to blend Thermotropic Liquid Crystalline Polymers (TLCP’s) with acrylonitrile butadiene styrene (ABS) for use in Fused Filament Fabrication. Differences between the available TLCP’s based on rheology were also determined for generation of longer fibrils in the ABS matrix. Rheological tests on the matrix polymer (ABS) and TLCP’s of various melting points were carried out to find the temperature ranges where viscosity of the TLCP is lower than that of ABS, which leads to successful generation of longer fibrils when processed using a novel blending technology referred to as the dual extrusion system. All the TLCP’s tested viz. HX3000, HX6000 and HX8000, supplied by DuPont, are composed of various ratios of terephthalic acid, 4-hydroxybenzoic acid (HBA), hydroquinone, and hydroquinone derivatives. Only HX8000 had its complex viscosity below that of ABS in the stable temperature range of ABS. Moreover, only HX8000 had a long overlap of temperature with ABS for favorable conditions leading to longer fibril generation.

Recycling of PP/LDPE Blend: Miscibility, Thermal Properties, Rheological Behavior and Crystal Structure
Chuanchom Aumnate, Claudia Spicker, Raphael Kiesel, Majid Samadi, Natalie Rudolph, May 2016

Blending of plastics used in packaging is an interesting approach for recycling or upcycling. Therefore, this study focused on the effects of processing on the properties of recycled PP and PP/LDPE blends. MFI measurements, Differential Scanning Calorimetry (DSC) and hot-stage polarized optical microscopy techniques were used to investigate the miscibility of PP/LDPE blends based on the thermal properties, degree of crystallinity, crystallization and morphology development in the blends. The MFI indicates, that PP and PP/LDPE blends are marginally sensitive to degradation at common processing conditions. The degree of crystallinity of the blends decreases with an increase of the LDPE content. Furthermore, the spherulite growth rate and crystal size of PP decrease with an increase of LDPE content.
The shifts of crystallization temperatures from the DSC measurement, in conjunction with the crystallization kinetics, indicate that PP/LDPE (25 wt% LDPE) is partially miscible.

The Effects of Nano-Clay on the Rheological Properties of Polylactic Acid
Jinghua Chen, Wei Zheng, May 2016

The rheological properties of polylactic acid (PLA) and its nano-composites with 3% and 6% montmorillonite (clay) are investigated using parallel plate rheometry. Frequency sweep experiments are performed at temperatures ranging from 160 to 185 ?. For all of the samples, as expected, both the storage modulus G' and the loss modulus G' decrease with increasing temperature. Master curves of G' and G' are successfully constructed for the neat PLA and its nano-composites, indicating the validity of the time-temperature superposition for these systems. Adding the clay filler increases the G' especially in the long term region as well as the dynamic viscosity, exhibiting reinforcement effects. This is consistent with the discrete relaxation spectra determined based on the dynamic shear data. Long chain modes are present in the composites, presumably coming from the interaction between the clay and the surrounding polymer chains.

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