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Applied Rheology

SPE Library content related to rheology
Mechanical, Thermal And Rheological Properties Of E-Beam Crosslinked Ethylene Octene Copolymer
Rajesh Theravalappil, Petr Svoboda, June 2022

Ethylene-octane copolymer (EOC) with high octane content (45 wt.%) was cross-linked via electron beam irradiation at different dosages (30, 60, 90, and 120 kGy). Effect of irradiation dosage on thermal and mechanical properties was studied. When compared to low density polyethylene, EOC exhibited higher degree of cross-linking reflected in increased gel content, higher elastic modulus (G’), and lower tan obtained by rheology measurement at 150 °C. Cross-linking caused improvement in high temperature creep and also in elastic properties at room and elevated temperatures. Differential scanning calorimetry revealed that e-beam irradiation has caused a gradual reduction in crystallinity and a presence of a fraction with higher melting temperature. In the case of EOC, as the extent of cross-linking increased, stress at break showed an increasing trend whereas irradiation dosage had an inverse effect on elongation at break which could be aroused from the formation of crosslink networks. Radiation dosage has positive effect on thermal stability estimated by thermogravimetric analysis. After 30 min of thermal degradation at 220 °C, slightly higher C=O peak for cross-linked sample was found by Fourier transform infrared spectroscopy while for room temperature samples no C=O peak was detected.

Temperature-Dependent Anomalous Rheological Behavior Of TPU Nanocomposites With Carbon Nanofillers
Li-Min Yu, Han-Xiong Huang, June 2022

Multi-wall carbon nanotubes (MWCNTs), graphene nanoplates (GNPs), and hybrid fillers (MWCNTs/GNPs) filled thermoplastic polyurethane (TPU) nanocomposites are prepared via melt mixing. The effects of filler (contents of 1, 2, and 3 wt%) and temperature are investigated on the rheological behavior of the TPU nanocomposites. The results demonstrate that the TPU/MWCNT nanocomposites exhibit stronger polymer-filler and filler-filler interactions than TPU/GNP and TPU/GNP/MWCNT nanocomposites. It is found that the nanocomposites with 2 and 3 wt% MWCNTs (2CNT and 3CNT) and 3 wt% MWCNTs/GNPs (3Hybrid) exhibit anomalous rheological behavior. As rising the temperature from 180 to 190 ℃, the complex viscosity values slightly increase in the low frequency region (< 0.4 rad/s) for the 2CNT and 3Hybrid samples, and more significantly increases over a wider frequency range (up to about 10 rad/s) for the 3CNT sample. The Fourier transform infrared spectroscopy spectra demonstrate that the anomalous rheological behavior is not caused by hydrogen bonding in the TPU nanocomposites. The results of scanning electron microscopy observation, time sweep tests, and volume electrical conductivity measurements reveal that the anomalous rheological behavior is attributed to physical contact of the MWCNTs under low shear.

Acrylic Impact Modifiers for PVC: Core-shell modifier chemistry and performance
Raber Inoubli, July 2021

Part 2 of the All Things PVC Workshop series. The speaker will review the basics of core-shell chemistry focusing on acrylic technology and its advantages for mechanical property improvement and weatherability in PVC formulating. Core principles of mechanical property improvement via stress concentrators for PVC matrices and formulations will be presented. In addition to rheology and mechanical property enhancement via acrylic chemistry, the presentation will also provide perspective on choosing the best impact modifier based on specific formulation needs or application types where standards vary based on the final needs of the vinyl building product, for example. The talk will follow-up on the principles covered in the introduction to PVC Gelation and Formulation.

Acrylic Additive for Thermoplastics Melt Flow Enhancement
Hailan Guo | Morris Wills | John Kohn | Felix Zhang | Mubashir Ansari | Kurt Koppi | Eric Marchbanks | Ted Price, May 2021

Acrylic compositions (Type 1 and Type 2) with branched chain structure were synthesized, and evaluated as melt flow enhancement additives in flexible acrylic resin, which were produced using proprietary sequential multistage polymerization process, and polycarbonate (PC) compounds. In this article, it was demonstrated that at up to 15% loading level, Type 1 additive could effectively enhance the melt flow index (MFI), and spiral flow length without negatively impact on flexible acrylic resin 21308XP’s optical properties. Analytical characterizations including DMA, frequency sweep validated that Type 1 additive effectively reduced 21308XP melt viscosity without altering the thermal-mechanical property of the resin. It was further demonstrated that Type 1 additive could effectively improve 21308XP thin gauge injection molding process. Similar melt flow enhancement performance was demonstrated for Type 2 additive in PC matrix.

Rheokinetics of Thermal-Induced Gelation of Liquid Polybutadiene Resin
Samy A. Madbouly, May 2021

Liquid polybutadiene with high unsaturation of pendant vinyl groups are very sensitive for crosslinking reaction compared to other polymer systems. The curing kinetics of LPB over a wide range of angular frequencies at different constant temperatures (130 to 160 °C) have been investigated rheologically using small amplitude oscillatory shear flow experiments. The elastic storage modulus, G′, at a constant temperature in the vicinity of the gel point increases abruptly, and the magnitude of the elevation in G′ was found to be temperature dependent. Similar behaviors have been observed for complex viscosity and loss modulus at identical conditions. The gel temperature (Tgel) and gel time (tgel) were evaluated from the crossover point of G′ and G′′ or more accurately from the temperature at which tanδ is angular frequency independent (i.e., all curves of tanδ at different constant angular frequencies coincided and became no longer frequency dependent).

Understanding the Effect of Long Chain Branching on the Flame Properties in Polycarbonate Resins
Shankar Kollengodu Subramanian | Tianran Chen | Himanshu Asthana, May 2021

It is known from literature [1, 2] that the rheological properties of polymer melts are influenced by the degree of long chain branching (LCB). Therefore, it is very important to understand the influence of LCB on the solid-state properties to help improve material design for unique applications. The objective of the present study is to demonstrate the role of long chain branched polycarbonate in enhancing the FR performance pertaining to dripping. References 1. Liu, C., et al. 2004. "Influence of long-chain branching on linear viscoelastic flow properties and dielectric relaxation of polycarbonates." Polymer 45(8): 2803-2812 2. Han, X., et al. 2016. "Preparation and characterization of long chain branched polycarbonates with significantly enhanced environmental stress cracking behavior through gamma radiation with addition of di functional monomer." Polymer Chemistry 7(21): 3551-3561

WLF Parameters and their Connection to Viscosity and Physical State
Paul Van Huffel, May 2021

For many years, the injection molding simulation market has used the Williams-Landel-Ferry (WLF) equation for time-temperature superposition of viscosity data, and one specific parameter is almost ubiquitously fixed at 51.6. This paper reviews this practice and its origins, and then examines a reliable fitting process that can be used to fit data to this model with a given transition temperature, and then delves into the selection of an appropriate transition temperature. There are two goals in this paper. The first is to demonstrate that regardless of transition temperature, fitting the same 3 temperatures and viscosities will produce the exact same temperature dependent curve, more broadly than in the original paper. The second is to show that by tying the transition temperature to the state data, we can add pressure dependence to the viscosity from characterization data that we may or should already have from other testing.

Characterization of Polycarbonate Blends: Executive (FT-IR) Compared To Rheology
J. Al Sadi | A.Hawari, May 2021

This work was mainly focused on examining the viscosity and FT-IR for the same samples at the same temperatures. The characterizations were run in three stages. The first stage: The polycarbonate resins were melt-blended using (Coperion) a Co-rotating twin-screw extruder (SB). In the second stage, the same material was included; the same compositions were blended in steps of eleven in a Thermo Haake Mini Lab II twin-screw micro compounder (ML). The steps (%PC1/%PC2) were (100%/0%), (90%/10%), (80%, 20%)… (0%/100%) which resulted in eleven batches. In the third stage, the same polycarbonate blends samples were characterized by Fourier transform infrared spectroscopy (FT-IR) spectra analysis. The research aims to identify a comparative characterization study for the viscosity and FTIR. The results have a significant fundamental science by steering a systematic effect on viscosity and dispersion. This technique is particularly useful since it allows identification and localization of compounds to study and identify chemical groups or chemical compounds when the sample absorbs infrared radiation. The focus was extended to the polymer grade to extract the impact of the rheological characteristic, FTIR and to study their correlations in the viscosity data and their bearing effects on color output

Evaluation of High Flow Poly Ether Imide Resins Using Structure-Property-Process Relationships
Manojkumar Chellamuthu | Mark Sanner, May 2021

Melt stability of polyetherimide based resins were evaluated as a function of time and temperature to determine their respective processing temperature ranges for injection molding applications. The study identified temperature ranges where four experimental materials demonstrated equivalent (or nearly) thermal stability as commercial polyetherimide. Additionally, the entanglement density of the experimental materials was determined using van Gurp-Palmen plots to understand rheology and impact properties. The material with the lowest entanglement density showed the least thermal stability with reduction in toughness properties

Nonlinear Rheological Behavior Carbon Nanotube-Filled Polypropylene Nanocomposites: Modeling and EXP
Sandeep S. Pole | Avraam I. Isayev | Jing Zhong, May 2021

The rheological behavior of multi-walled carbon nanotube (MWCNT)-filled polypropylene (PP) nanocomposites with different filler loadings was experimentally studied and simulated using constitutive modeling. Rheological behavior was characterized in small amplitude oscillatory shear (SAOS) flow, large amplitude oscillatory shear (LAOS) flow, startup of shear flow, steady shear flow, and stress relaxation after the imposition of a step shear strain. Virgin PP and PP with CNT loadings of 1, 3, and 5 wt% were used. The formation of a rheological percolation network was observed at these loadings. The Leonov and Simhambhatla-Leonov (SL) models were used to simulate the rheological behavior. In the linear region, the simulations provided good predictions of the experimental data for both the unfilled and filled PP. In the nonlinear region, the simulations also provided good results for the virgin PP and satisfactory results for the PP/1wt%CNT nanocomposite under most flow conditions. However, for the other two nanocomposites the model showed mixed results.

Viscous Heating Correction for Polymer Melts in Capillary Viscometry
Yu-Ho Wen | Chen-Chieh Wang | Chia-Hsiang Hsu | Rong-Yeu Chang, May 2021

Viscous heating in polymer melts can be a disturbing factor in high-shear-rate viscosity measurements. The present study employs an iterative algorithm that we recently developed to improve the accuracy of the shear viscosity from a capillary rheometer [1]. A generalized Newtonian fluid, along with the Cross-WLF model for shear viscosity, was used to simulate the contraction flow in the capillary rheometer by Moldex3D flow solver. According to the proposed algorithm, the simulated temperature rise and shear rate were used to iteratively correct the corresponding nominal data, so as to obtain the optimized parameters in the Cross-WLF model. The predicted pressure drops based on the proposed methodology were shown to be in better agreement with the capillary experiments, with an average relative error reduced by ~20% for the melts studied.

Melting and Crystallization Behaviors of Polyphenylene Sulfide Blended With Thermoplastics: A Review
Guowei Chen | Mary Hedrick | Manjusri Misra | Amar K. Mohanty, April 2021

Recent research about the melting and crystallization behaviors of Polyphenylene sulfide (PPS) blended with thermoplastics are reviewed in this paper. Thermoplastics discussed herein are mainly polyamide (PA) and Liquid Crystal Polymer (LCPs). Other thermoplastics including high-density polyethylene (HDPE), polycarbonate (PC), polyethylene terephthalate (PET), polyetherketone (PEK), polyether ether ketone (PEEK), polysulfone (PSF), polystyrene (PS), and polyvinylidene fluoride (PVDF), etc. are also discussed. The recent literature shows that by blending with certain content of thermoplastic polymer, the crystallization rate and crystallinity of PPS can be improved.

Superhydrophobic Encapsulants for FHE Devices
A. Bar | K. Jaju | E. Keaney | S. Kenig | H. Dodiuk#, J. Mead | B. Budhlall | C. Stoessel | A. Kumar | S.Gonya, April 2021

Flexible Hybrid Electronics (FHE) offer benefits for a wide range of applications, such as healthcare wearables, smart layer-based integrated sensor networks, soft robotics, and digital microcontroller circuits. It is critical to developing flexible and stretchable encapsulants for FHE devices to protect them from environmental conditions. Encapsulants for advanced FHE devices require innovative materials and processes to ensure the microchips' physical/chemical protection without compromising the stretch or flex characteristics. Consequently, this work is focused on developing a superhydrophobic (SH) coating that can be spray-coated on FHE device for encapsulation. The SH coating is based on commercial conformal acrylic resin with alkyl treated SiO2 nanoparticles that provide both the roughness and hydrophobic chemistry to be applied to alumina and treated polyimide. The resulted coatings possess low surface energy due to the formation of a micro/nano tailored hierarchical structure and hydrophobic moieties. The study investigates the durability of the superhydrophobic coatings using the Peel Test, Flexibility Test, Scratch Test, and Hardness Test on the two substrates. Experimental results indicated that the mechanical durability was improved when applying two coating layers with a mixing time of 1 hour first and then ½ hour withstanding more than 8 peels. Furthermore, the aluminum and polyimide substrates' Scratching indicates that the coating peels off completely with ˜0.5 [N] and˜4 [N], respectively. The Pencil hardness test results suggest that the polyimide substrate starts to fail at '5H' hardness, and the Alumina coating starts to fail at ‘H’ hardness. The final coatings show good durability overall and long shelflife stability.

Capillary Rheometry: Application to Extrusion
Olivier Catherine, April 2021

In this webinar, we will explore the advantages of capillary rheometers for extrusion application through specific processing and equipment design examples. While some materials like polyolefins can have straightforward flow behaviors, other more complex materials and compounds involved in the extrusion of film and sheet products can exhibit non-typical flow behaviors for which capillary rheometry is a critical characterization tool. We will review the advantages of capillary rheometry over other rheological characterization techniques, and we will also discuss some of the challenges and limitations of the capillary measurements.

Extrusion Technologies for Low Temperature Compounding
Travis Menapace, May 2020

For many applications the ability to continuously compound at low temperatures can be extremely beneficial. However, many challenges prevent traditional setups from being functional, particularly for applications requiring a high degree of mixing with extreme cooling or simultaneous temperature control. This paper addresses and experimentally validates four different technologies for compounding materials at low temperatures.

High Temperature Extensional Rheology Measurements to Understand Anti-Drip Properties
Manojkumar Chellamuthu, May 2020

We have used a novel custom-built capillary break up rheometer to understand the polymer decomposition mechanisms and effects of FR salts on the polycarbonates. The objective of the present study is to optimize the concentration of FR salts on the polycarbonate resins to improve dripping properties under flame.

Comparison of Additive and Conventional Tooling on Injection Molded Part Properties
Maria Camila Montoya, May 2020

Additive tooling can make injection molding viable for low volume production, reducing tooling cost and lead-time. This studycomparesthe final properties of injection-molded samples manufactured with a steel mold and two sets of 3D printed polymerinserts using material jetting (Digital ABSfrom Stratasys) and stereolithography(Toughfrom Formlabs). Results show thatthe Digital ABS insertsfailed after100 cycles, while the Tough insertsfailed after15 cycles. Parts producedwith steelmold and Tough and Digital ABS inserts exhibited a shrinkage of approximately3%, 6% and 9% respectively. The shrinkage and ultimate tensile strength was directly proportional to the degree of crystallinity measured using differential scanning calorimetry(DSC).

Finite Element Modeling on Barrel Mar Behavior of Amorphous Polymers
Shuoran Du, May 2020

Mar damage on polymer surfaces has become a significant concern over a wide range of engineering applications. To gain insight into the strategies for improving mar damage resistance of polymers, it is necessary to learn about why and how mar damage is formed and how it is related to constitutive parameters such as Young’s modulus and yield stress, etc. In this study, three model amorphous polymers, i.e., PMMA, PC, and PS, were investigated using a well-established ASTM/ISO scratch testing in combination with the finite element method (FEM) parametric study to gain the fundamental structure-property relationships to furtherly understand mar damage. It is found that the total plastic energy dissipation during mar process correlates well with mar damage formation and can possibly be chosen as the criterion for mar damage formation. Three-dimensional FEM parametric study was further performed based on the verified mar damage criterion.

Minimizing Interfacial Orientation During Processing of Immiscible Blends
Donggang Yao, May 2020

An interface between two immiscible polymer phases represents a material weakness due to reduced cohesive adhesion. For a co-continuous polymer blend, this interface can be viewed as an elastic membrane. From continuum mechanics, we show that the deformation of this interface during normal melt processing is largely affine, involving a slow relaxation process as compared with the relaxation process of the polymer chain. Accordingly we propose a processing strategy to minimize the development of the unwanted interfacial orientation and yet promote the development of molecular orientation so that a strong blend material can be fabricated. Some experimental results are provided and discussed.

Modern Rheological Techniques for Polymer Analysis: Capillary Rheometer, Screw Rheometer, and Melt Strength Tester
Myung-Ho Kim, May 2020

As a result of measuring the shear viscosity on a capillary rheometer and the screw rheometer, a viscosity function corresponding to 6 decades of shear rate of 0.1 to 10,000 [1 / s] was obtained. We have identified a new method for identifying crossover point with a single temperature measurement without performing complex ‘Time-Temperature-Superposition’. Also shear viscosity and melt strength functions were compared for eight LDPE grades. It was found that the melt strength showed a completely different behavior for similar melt index materials.

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