The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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SPE Library content related to rheology
Effects Of Sample Shape And Adhesive Type On Rheology Of Unidirectional Carbon Fiber Prepregs
The viscoelastic properties of carbon fiber reinforced thermoset composites are of utmost importance during processing such materials using composite forming. The quality of the manufactured parts is largely dependent on intelligent process parameter selection based on the viscoelastic and flow properties of the polymer resin. Viscoelastic properties such as the complex viscosity (η*), storage modulus (G’), loss modulus (G’’), and loss tangent (tanδ) are used to determine the critical transition events (such as gelation) during curing. An understanding of the changes in viscoelastic properties as a function of processing temperature and degree of cure provides insight to establish a suitable processing range for compression forming of prepreg systems. However, tracking viscoelastic properties as a function of cure during the forming process is a challenging task. In this current work, we have investigated the effect of sample size and adhesive type on the rheological properties of a commercially available carbon fiber prepreg material. Specifically, determining the linear viscoelastic region (LVE) as a function of sample configuration and different adhesive chemistries were explored. The results suggest that the square-shaped sample geometries coupled with cyanoacrylate based adhesive are optimum for conducting rheological characterization on the carbon fiber prepreg system.
Acrylic Impact Modifiers for PVC: Core-shell modifier chemistry and performance
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
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
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
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
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
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
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
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
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 . 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
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
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 ¬Ω hour withstanding more than 8 peels. Furthermore, the aluminum and polyimide substrates' Scratching indicates that the coating peels off completely with Àú0.5 [N] andÀú4 [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 ‚ÄòH‚Äô hardness. The final coatings show good durability overall and long shelflife stability.
Capillary Rheometry: Application to Extrusion
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
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
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
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
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
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
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.
Screw Design for Ultra-High-Speed, Quad-Screw Extrusion
The effect of screw programming on the performance of an ultra-high-speed, 15 mm quad-screw extruder was investigated by processing low-density polyethylene with four screw programs, no active barrel cooling (to evaluate viscous dissipation), and screw speeds of 500-2000 rpm. Observations indicated that kneading blocks were needed for timely melting of polymer pellets. Large increases in barrel temperature occurred with mixing, rather than melting, kneading blocks. Kneading block design had limited effects on power consumption but significantly affected residence time, melt temperature, and drive torque. All designs produced significant reductions in the viscosity of the extrudate, which previously has improved mixing.
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