Confinement and Complex Viscosity

Steacy Coombs, March 2023

Whereas much is known about the complex viscosity of polymeric liquids, far less is understood about the behaviour of this material function when macromolecules are confined. By confined, we mean that the gap along the velocity gradient is small enough to reorient the polymers. We examine classical analytical solutions [Park and Fuller, JNNFM, 18, 111 (1985)] for a confined rigid dumbbell suspension in small-amplitude oscillatory shear flow. We test these analytical solutions against the measured effects of confinement on both parts of the complex viscosity of a carbopol suspension and three polystyrene solutions. From these comparisons, we find that both parts of the complex viscosity decrease with confinement, and that macromolecular orientation explains this. We find the persistence length of macromolecular confinement, ?? , to be independent of both ?? ?? and?? ?? 0.

Effect of Shear of and Pressure on Structure for Binary Blends of Bisphenol — A Polycarbonate and Poly(methyl Methacryslate)

Masayuki Yamaguchi, March 2023

The effect of applied shear flow and pressure on the miscibility and structure for the binary blends of bisphenol-A polycarbonate (PC) and low-molecular-weight poly(methyl methacrylate) (PMMA) was studied using a conventional capillary rheometer. The lower critical solution temperatures (LCSTs) of PC/PMMA (70/30) and PC/PMMA (80/20) were found to be 260 and 270°C, respectively, without flow field under atmospheric pressure. During capillary extrusion at/below 250°C, however, shear induced demixing was detected. Moreover, pressure induced demixing was also detected at high pressure. Finally, surface segregation of PMMA fraction was observed without phase separation for PC/PMMA (90/10).

Experimental Characterization and Modelling of the Pressure Dependence of the Viscosity for Injection Molding Simulations

Steffen Verwaayen, March 2023

The pressure dependence of melt viscosity of thermoplastic materials is difficult to measure and is therefore often neglected, although it can have a major influence on the results of an injection molding simulation. Current viscosity models provide the ability to model this dependence. Therefore, the viscosity is measured in a high- pressure capillary rheometer and the pressure dependence of the viscosity is determined in an online rheometer for a polypropylene. The generated experimental data is used as input to fit the Carreau-WLF model. The accuracy of the models varies depending on the input data chosen. In particular, the pressure dependence of the viscosity could not be correctly represented while maintaining good viscosity representation. A correction of the neglected pressure during the high-pressure capillary rheometer measurement improved the modeling of the pressure dependence of the viscosity slightly.

Exploiting Structure-Process Property Relationships of Branched Polycarbonates for Industrial Applications

Manojkumar Chellamuthu, Ph.D., March 2023

Current electrification market needs materials with good balance of Flow, Flame Property and Mechanical Performance. In this talk, we will discuss the rheological features of three commercially available linear, branched and hyper-branched polycarbonates (PCs) using comprehensive investigations. Applications of rheological properties to enhance Z-strength in Large Format Additive Manufacturing (LFAM) will also be discussed. Additionally, high temperature extensional Rheometer (CaBER) was used to understand the evolution of microstructure at high temperatures. The experiments were performed at temperatures ranging from T = 250 to 370 °C to a maximum Hencky strain of ten. At lower end of the temperature range, no significant degradation of the linear and branched Polycarbonate (PC) was observed either in the shear or extensional measurements. Beyond, T > 300 °C branched PC showed a dramatic increase in extensional viscosity which helps in Flame performance (anti-drip) better than its linear counterpart.

Introducing a Differentiable, Shear-Thinning Viscosity Model

Paul Van Huffel, March 2023

A differentiable model for non-Newtonian, shear- thinning viscosity is presented as derived by integrating the log-log domain derivative function of the Carreau-Yasuda viscosity model. This work starts with the discovery of the log-log domain derivative function as this is the foundation for the statement of the new viscosity model. Potential uses for this work include development of explicit or hybrid flow solvers for polymer flows and possibly extending into the incorporation of effects based on the rate of change of the spherical (i.e. expansion/compression) and deviatoric parts of the rate-of-strain tensor, although this model specifically deals with the deviatoric part. A fitting experiment of rheometer data that was initially fit for each temperature curve as part of another work is used to demonstrate the flexibility of having a variable curve shape parameter as opposed to a fixed value, and a simulation of a conical section is used to compare the apparent wall shear rate in a converging channel versus the numerically obtained shear rate by a finite element analysis of the same conical channel.

Steady State and Dynamic Oscillatory Shear Properties of Carbon Black Filled Elastomers

Avraam Isayev, Ph.D., March 2023

A correlation between the steady shear viscosity and complex dynamic viscosity of carbon black (CB) filled rubbers was found by evaluating the Cox-Merz rule and an alternative approach originally proposed by Philippoff for dilute polymer solutions, but since applied to amorphous polymers and concentrated suspensions. This was done by measuring the rheological properties of 16 industrially important rubber mixes containing CB N660 at concentrations of 20 and 35 % by volume. A capillary rheometer at various shear rates and a dynamic oscillatory shear rheometer at small and large amplitude oscillatory shear (SAOS and LAOS) were used. The apparent viscosity, storage and loss moduli, complex dynamic viscosity and Fourier transform harmonics were measured. Generally, the shear stress, storage and loss moduli increased with increasing CB loading. Also, the ratio of 3rd and 5th stress harmonics to 1st harmonics increased with increasing strain amplitude and filler loading. Viscous Lissajou figures (shear stress versus shear rate) at a strain amplitude of 14% showed a nearly linear response for compounds containing CB at 20% by volume. All other shear stress responses demonstrated a strong nonlinearity. The stress waveforms at a strain amplitude of 140% for compounds containing 35% CB by volume displayed a backwards tilted shape expected for highly filled compounds. The stress waveforms at a strain amplitude of 1,000% tended toward a rectangular shape expected for pure polymer. Generally, the nonlinear response of the compounds appeared to be dominated by the filler at strain amplitudes of 14% and 140% and by the rubber matrix at a strain amplitude of 1,000%. The Cox-Merz rule was not applicable for any of the compounds with their complex dynamic viscosity being greater than the apparent viscosity. However, a modification of the approach proposed by Philippoff provided reasonable agreement between the apparent viscosity and complex dynamic viscosity.

Using Thermal and Rheological Techniques to Help Guide Recycled PET Extrusion Processing

Tianhong Chen, Ph.D., March 2023

Polyethylene terephthalate (PET) is one of the most commonly used plastics in our daily life. It is completely recyclable and is the most recycled plastic in the U.S and worldwide. However, recycled PET from different sources may have large variabilities, such as reduced molecular weight, broader molecular weight distribution, different crystallinity, and containing different impurity contents, all of which can affect their processing and application. This presentation will discuss of using thermal and rheological techniques to fingerprint the feedstock resins and help guide extrusion processing. Specifically, we will discuss using differential scanning calorimetry (DSC) to identify the type of impurities, monitor the effect of thermal history on the crystallinity and crystal melting. We will also discuss using rheological techniques to estimate the molecular architecture, measure melt stability, melt viscosity, and help optimize extrusion conditions.

Time, Temperature & Applied Rheology in Wire & Cable

Scott Wasserman, March 2023

Many years ago, Union Carbide Corporation (UCC) had established a well-equipped melt rheology lab designed to accomplish large-scale melt testing to simulate high shear conditions and small-scale dynamic and steady shear capabilities to both predict low deformation phenomena and delineate key features of molecular structure. UCC later initiated an aggressive metallocene catalyst development program to develop polyethylenes (PEs) with unique molecular structures. In an effort to fully characterize the key features of molecular structure that was manifested in the observed viscoelastic properties, we calculated the melt relaxation spectra for the new PEs and in comparing them to incumbent PEs, we found the new PEs to be differentiated. This led to a family of patent applications [1] to protect the technology, and a new parameter, called the “relaxation spectrum index” or “RSI” to quantify the breath of the relaxation time distribution reflecting the novel molecular structures. The RSI proved to be a useful parameter to use to not only delineate interesting features of molecular structure, but also to predict large-scale processing behavior, such as motor load and amperage in extrusion of layers and components for wire and cable applications [2]. This presentation will illustrate the power found in calculating and characterizing the relaxation spectrum with dynamic oscillatory shear experiments. As an illustration, a case study will be presented in which a new compound was to be developed for high-speed thin-walled chemical-foamed telecommunications wire insulation. Many key rheological phenomena needed to be simultaneously considered to design the next-generation product, and the RSI proved to be instrumental in allowing the necessary differentiation between inventive and comparative materials. This led to the development of a powerful set of patent claims [3] to protect the strategic space for UCC (now Dow). The power of this rheology-based approach to intellectual property is that the invention is not limited to a particular composition – instead, the patent claims would be a potential challenge to any composition that meets the critical rheological profile. References 1. G. N. Foster, T. Chen, S. H. Wasserman, D.C. Lee, S. J. Kurtz, L. H. Gross, R. H. Vogel, U.S. Patent 5,798,427 (1998). 2. Wasserman, SH & Adams, JL. “Rheology and Crystallization in Fiber Optic Cable Jacket and Conduit Extrusion,” ANTEC 1997, Toronto, CA April 27-May 2, 1997. 3. S. Maki, G. D. Brown, S. H. Wasserman, D. J. Frankowski, V. Y. He, U.S. Patent 6,455,602 (2002).

3-D Printing of Thermoplastic Polyurethane Foams using Thermally Expandable Microspheres

Nikith Lalwani, Karun Kalia, Amir Ameli, March 2023

Thermoplastic polyurethane (TPU) foams have a wide range of applications due to their high elasticity, good flexibility, low density, and high resistance to impact forces. They are used as cushioning for a variety of consumer and commercial products, including furniture, automotive interiors, helmets, and packaging. 3D printing of TPU foams would enable increased product design freedom and graded structures for novel and enhanced applications. To this end, unexpanded TPU filaments loaded with 0.0%, 7.5%, and 15.0wt.% thermally expandable microspheres (TEM) were prepared using a single screw extrusion system. TEM was incorporated using a masterbatch with 50wt.% ethylene-vinyl acetate carrier. The extrusion process parameters were set to achieve the lowest possible melt temperatures to prevent the foaming during filament fabrication. Foam samples were then in-situ printed using fused filament fabrication (FFF) process. 3-D printing parameters such as flow rate, print speed, and nozzle temperature were varied to achieve a wide range of foam density. Scanning electron microscopy and quasi-static compression tests were performed to characterize the cellular morphology and mechanical performance of the printed samples. Foams with good printability and dimensional accuracy were successfully achieved with densities as low as 0.15 g/cm3. The ability to 3-D print TPU foams with different densities provides higher design flexibility and allows to create more complex and optimized structures for a number of applications.

Conducting a Plastic Failure Analysis

Jeffrey A. Jansen, March 2023

Agenda

• Defining Failure
• Plastic Part Performance Factors
• Understanding Failure Rate in Plastic Components
• Plastic Failure Mechanisms
• Failure Analysis Methodology
• Failure Analysis Testing
• Case Illustrations

Study On Machine Identification And Its Effect On The Rsm Optimization In Injection Molding

Rui-Ting Xu, Tsung-Han Wang, Chao-Tsai (CT) Huang, Po-Hsuan Chen, Wen-Ren Jong, Shia-Chung Chen, David Hsu, Rong-Yeu Chang, June 2022

Preliminary Investigation Of Oxygen Pressurized Chambers For Accelerated UV Weathering

Henry K. Hardcastle III, June 2022

This paper presents results of a preliminary proof-of-concept investigation into the effect of pressurized oxygen on UV photodegradation rates of a polystyrene standard reference material. Exposures under UVA and UVB revealed significant and important acceleration effects using pressurized oxygen compared with ambient air.

Novel Nanocellulose Based Supports For PHBV Composites - Synthesis And Properties

Kavan Sheth, Ting Zheng, James Sternberg, Craig Clemons, Srikanth Pilla, June 2022

Novel nano-cellulose based nano-structures modified with hyper-branched polymers were prepared by using isocyanate linking chemistry. The chemistry was investigated using FTIR spectroscopy. The composites were homogenized utilizing solvent casting followed by injection molding of the samples. The thermal properties of the prepared samples were investigated using DSC and TGA.

Melting Performance Analysis Of A Single-Screw Extruder With A NSB Screw

Xiaofei Sun, Ryan A. Pratt, Mark A. Spalding, Jeffery A. Myers, Robert A. Barr, Aaron F. Spalding, June 2022

A recent design of a new screw referred to as the No Solid Bed (NSB) screw was introduced and the initial operation was presented [1]. This new screw has channels in the transition section that do not allow a compacted solid bed to form. The data presented here compliments the data that was previously published.

Simulation Of Polymer Imprinting And Embossing Using Smoothed Dissipative Particle Dynamics

James St Julien, Donggang Yao, June 2022

A simulation of an imprinting process using Smoothed Dissipative Particle Dynamics is shown. Cavity filling modes and their dependence on die parameters is demonstrated for single and multicavity die, showing results consistent with FEM simulations and experimental data. Particle-based simulation methods can allow for modeling of more complex fluid behaviors.

Development Of A Gas-Based Temperature Control System For Injection Molds - Gasmold

Alexander Paskowski, Ruben Schlutter, June 2022

The paper describes the development of a variothermal process, which increases the mold surface temperature during the injection molding process without significantly extending the cycle time and minimizes unintentionally heated mold areas. To this end, the possibility of achieving the desired effects by direct introduction of heated gases into the mold cavity is being investigated. By addressing central issues such as gas distribution geometry, injection possibilities, required gas temperatures or the possibility of process implementation in a demonstrator mold, it was possible to develop a process with which it is possible to achieve temperature optimization for visually appealing parts within seconds. This means that weld lines, streaks or uneven mold impressions can be concealed even on flat parts.

Discover The Physical Mechanism Of The Interface Formation In Co-Injection Molding Using Rheological Behavior

You-Ti Rao, Kuan-Yu Ko, Chao-Tsai Huang, Chih-Chung Hsu, You-Sheng Zhou, David Hsu, Rong-Yue Chang, Shi-Chang Tseng, June 2022

Co-injection molding has been introduced into industrial application for several decades. However, due to the formation of the interface between skin and core materials is very difficult to be observed, and controlled, a good quality of co-injection product can not be obtained effectively. The reason is that the formation of that interface in co-injection molding is very sensitive to various factors. In this study, the formation of the interfacial morphology and its physical mechanism in coinjection molding have been studied based on the ASTM D638 TYPE V system by using both numerical simulation and experimental observation. Results showed that the critical skin/core material ratio to generate the skin breakthrough is identified. The reason to cause the breakthrough is due to the flow front of core material catches up with the melt front of skin, and the skin is stop at a fixed distance. This mechanism is similar with that of literature. However, when the higher core material ratio is selected, the mechanism of the interfacial morphology is different. Specifically, after core melt front catches the skin melt front, the broken skin material can move forward with the inner core material to generate special core-skin-core structure. It could be due to different forces balance inside the skin and core melts, but needs to do more study in the future.

Quality Prediction In Injection Molding Based On Thermal Images With Convolutional Neural Networks

Dimitri Kvaktun, Yannick Elsinghorst, Reinhard Schiffers, June 2022

Precise predictive models are required for the use of machine learning methods for quality control in injection molding. Thermal images offer the advantage of containing information in the data that is not available in machine and process data. Currently, convolutional neural networks (CNN) have numerous applications in image recognition. Therefore, the objective of this work was to investigate the application of convolutional neural networks to thermal images of injection molded parts. For this purpose, 751 injection molding cycles from a central composite design were used. The goal was to predict the weight, height, and width of the injection molded part. The results were also compared with classical machine learning methods. Depending on the quality parameters, the networks were able to achieve an R² of up to 0.91 and were thus among the three best methods.

Changes In Polyamide 11 Microstructure And Chemistry During Selective Laser Sintering

Gabrielle Esposito, Raymond A. Pearson,, June 2022

A polyamide 11/carbon black (PA11/CB) SLS nanocomposite printing powder was characterized throughout a laser area energy density range (express by using Andrew’s numbers, AN) to elucidate significant changes to the PA11 microstructure and chemistry during the SLS printing process. We will show that there are specific microstructural changes that occur in PA11, some gradual and others more striking, between the as received PA11/CB powder and printed parts. The melting temperature (Tm), percent crystallinity (Xc), lamellae thickness (lc) and dhkl spacing of PA11 were all shown to change significantly upon printing, whereas the molecular weight was shown to have a rather gradual increase as a function of AN. These results imply that the printing conditions used result in an irreversible change in PA11 polymer microstructure and chemistry, and correlate well to the measured mechanical behavior of parts print with corresponding AN. The use of DSC, XRD, and molecular weight analysis provides a more complete picture of the changes due to the SLS printing process and can help optimize the printing parameters to create high-quality printed parts.

Twin Screw Melting Model Prediction Of Experimental Study Of LDPE Melting In A Twin Screw Extruder

Gregory A. Campbell, Mark D. Wetzel, Paul Andersen, Joseph Golba, June 2022

The melting of polymers in a twin-screw (T/S) extruder is an important operation in many industrial processes. Research by Shih, Gogos, Geng and others has identified the physical phenomena that take place during the melting phase transition. This paper describes a new approach for modeling the melting in a twin-screw extruder and the model predictions are compared with an experimental study of Low-Density Polyethylene (LDPE) melting in a co-rotating, intermeshing T/S extruder using on-line visualization and axial scanning of pressure and temperature techniques. This paper focuses on the physics and engineering concepts that are inherent in the melting mechanism in the extruder, and viscous energy dissipation in the melt with un-melted solids. The effects of throughput, Q, and at a constant rotation speed, N, is examined. Low and high Q/N ratios have significantly different axial pressure profiles.