SPE Library

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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Investigating The Processing Of Stimuli-Responsive Cellulose Nanocrystal Polymer Composites In Graded 3D Printing
Yimin Yao, Michael J. Bortner, June 2022

Functionally gradient 3d printing is of great importance for polymer composites to be applied in soft robotics or smart electronic devices. Imparting mechanical gradients within the design of new materials would help to prevent premature failure of devices and could reduce strain mismatches. In this work, we first focus on investigating the mechanical gradients and water responsive behavior of cellulose nanocrystal (CNC) / thermoplastic polyurethane (TPU) films by changing the concentration of CNCs. After generating masterbatched feedstocks, CNC/TPU films were extruded with a single screw extruder to obtain 3D printable filaments. The thermal and rheological behavior of the nanocomposite system is characterized to evaluate the mechanical property gradient of CNC/TPU filaments as a function of CNC concentration within a 3D printed geometry.

Deformation Analysis Of Mold Cavity With Sla Conformal Cooling Channel Insert
Olumide Aladesiun, Kyehwan Lee, Yooseob Song, Younggil Park, June 2022

Injection molding is the process of injection molten plastic into a mold to form desired shape of part and it’s widely used process for mass production of plastics over the world. This process is not complete without the mold as it is the most critical part of the process. The cost of producing mold is huge due to manufacturing process and technique, tool material and cost of labor. The more effective the mold, the more efficient the process and the more profitable to the business. A critical factor is the cooling time, and a well-designed mold can achieve even cooling in the shortest period, which leads to increased productivity and higher quality of molded parts. In this research, an alternative core design was employed, to achieve these goals during the molding process. The core has 2 parts: the core and core insert. The core insert was produced using SLA technology to achieve the conformal cooling while the core was machined, and the deflection was studied using finite element analysis.

A Semi-Genetic Process For Fitting Polymer Viscosities And Selecting Best Models
Paul Van Huffel, June 2022

This paper presents a process for fitting corrected viscosity data to constituent and temperature dependent data to a range of two-equation models. The process tests different models to determine the best fit model for each. Rheometer data for polymer melts, after corrections for shear rate and entrance pressure losses, may fit one model better than another, and as such the following constituent models are reviewed in the form as they are commonly applied in commercial software today: 1) Cross Model, 2) Modified Cross Model, and 3) Carreau-Yasuda. Once the constituent model is fit, the following temperature dependent models are compared: 1) WLF, Exponential, Arrhenius, and Masuko-Magill. The differences between the models are presented in order to highlight the need to compare different models to obtain a best fit. Lastly, a solution is presented to the problem of convergent viscosities with respect to shear rate as compared across a range of temperatures as no existing model in common use today can capture this specific behavior.

An Explicit Non-Newtonian Fluid Model For Polymeric Flow With Finite Stretch
Donggang Yao, June 2022

After nearly 80 years of research in constitutive modeling of polymeric fluids, simple yet capable models are still sought after today. In this work, we provide an explicit constitutive equation where the extra stress tensor is an explicit function of the objective velocity gradient while finite stretch of polymer chains are considered. With this model, the basic rheological functions in uniaxial extensional, planar extension and simple shear can all be obtained as closed-form analytical solutions with only elementary mathematical functions involved. The new model demonstrates excellent fitting to some sear and extensional data in the literature, and is able to simultaneously predict the major rheological functions in steady-state shear and extension.

Chemorheological Analysis Of Slow Reacting Polyurethanes
John Reynolds, Michael Bortner, June 2022

Tracking the cure progress of slow reacting, uncatalyzed polyurethane systems is a tedious, time consuming process that has been largely neglected due to the availability of catalysts. The use of catalysts has enabled quick, nonisothermal studies to dominate the field of research, but when catalysis is not an option, these methods become impractical. In this context, we can use chemorheology to correlate viscoelastic data to several previously developed cure models. The models presented here examine viscosity buildup, reaction rate progress, and thermodynamic behavior, while emphasizing the importance of interpretation during data analysis. These chemorheological techniques focus on the development of thermally curing networks during subjection to flow fields, and apply to a vast array of thermosetting polymeric materials.

Complex Viscosity Of Star-Branched Macromolecules From Analytical General Rigid Bead-Rod Theory
S.J. Coombs, M.A. Kanso, K.E. Haddad, A.J. Giacomin, June 2022

The complex viscosity of planar star-branched polymers has been derived from general rigid bead-rod theory, but only for singly-beaded arms. Here, we explore the respective roles of branch functionality, arm length of non-planar arrangements, analytically from general rigid bead-rod theory. For non-planar, we include polyhedral, both regular and irregular. We fit the theory to complex viscosity measurements on polybutadiene solutions, one quadrafunctional star-branched, the other unbranched, of the same molecular weight. We learn that when general rigid bead-rod theory is applied to quadrafunctional polybutadiene, a slightly irregular center-beaded tetrahedron of interior angle 134º is required (with 1,360,000 g/gmol per bead) to describe its complex viscosity behaviour.

Development Of A Micro-Capillary Rheometer For High Solids Content Rheology
Michael C. Coco, Michael J. Bortner Ph.D., June 2022

Rheological testing of new material formulations can require significant quantities, specifically when considering development of new chemistries at the laboratory scale. In order to minimize the quantity of material required for evaluation, we are developing approaches suitable for characterization of high solids content formulations using micro-capillary rheometry. The goal of this investigation is to design and produce a micro-capillary rheometer capable of characterizing basic rheological properties, such as viscosity and shear-thinning behavior, while requiring the least amount of sample possible. In our current design, we implement a micro-dispensing approach combined with calibrated force transducers. With this approach we can further elucidate an understanding of the differences between typical capillary rheometry and behavior at reduced dimension flow fields. Issues such as pressure relaxation and free volume compaction can therefore be studied through readily modified geometries and testing rates. This design will lead to a better understanding of micro-capillary rheometer design and enable a unique approach for rheology measurements for new chemistries and formulations, including high solids content formulations (up to 60+ vol%). Additionally, this framework will facilitate the study of a variety of flow geometries applicable to a wide range of applications including precision dispensing of adhesives and sealants, and direct ink write additive manufacturing.

Fabrication Of Expandable Filaments Towards In-Situ Foam 3D Printing Of Microcellular Poly(Lactic Acid)
Karun Kalia, Benjamin Francoeur, Alireza Amirkhizi, Amir Ameli, June 2022

The purpose of this study was to investigate the feasibility of in-situ foaming in fused filament fabrication (FFF) process. Development of unexpanded filaments loaded with thermally expandable microspheres, TEM is reported as a feedstock for in-situ foam printing. Four different material compositions, i.e., two grades of polylactic acid, PLA, and two plasticizers (polyethylene glycol, PEG, and triethyl citrate, TEC) were examined. PLA, TEM and plasticizer were dry blended and fed into the extruder. The filaments were then extruded at the lowest possible barrel temperatures, collected by a filament winder, and used for FFF printing process. The results showed that PLA Ingeo 4043D (MFR=6 g/10min) provides a more favorable temperature window for the suppression of TEM expansion during extrusion process, compared to PLA Ingeo 3052D (MFR=14 g/10min). TEC plasticizer was also found to effectively lower the process temperatures without adversely interacting with the TEM particles. Consequently, unexpanded filaments of PLA4043D/TEM5%/TEC2% was successfully fabricated with a density value of 1.16 g/cm3, which is only ~4.5% lower than the theoretical density value. The in-situ foaming in FFF process was then successfully demonstrated. The printed foams revealed a uniform cellular structure, reproducible dimensions, as well as less print marks on the surface, compared to the solid counterparts.

Fitting Of Tait Coefficients For Molding Simulation
Paul Van Huffel, June 2022

For several decades, the Tait model has been used in simulation software to describe the volumetric mechanical behavior of thermoplastic polymers as they cool. It is used to compute the residual strains and stresses of the polymer as it solidifies, but there is a problem. Many data sets have coefficients where there exists a discontinuity at the transition between the molten and solid domains. This paper outlines some basic checks that can be done to detect this problem and a procedure to fit the coefficients to data so that this problem does not arise.

High Shear Rate Rheology Of Cellulose Nanofibrils
Aliya J. Kaplan, Bradley P. Sutliff, Michael J. Bortner, June 2022

Nanofibrillated cellulose (NFC) has properties ideal for applications in the packaging and medical industries. To understand if cellulose-based polymers could become a replacement for synthetic polymers in these fields, NFC suspensions were repeatedly exposed to elevated shear stresses to simulate industrial processing procedures and allow for observation of changes in material properties. A capillary rheometer was used to run aqueous NFC suspensions of 10 wt% at room temperature at shear rates beyond 30,000 s-1. Due to repeated shear rate exposure, a decrease in volume resulting from unavoidable water loss informed the observable increase in apparent viscosity and suggested that this increasing trend was not caused by a change in material morphology. Noisy data as a result of flocs was detrimental to the analysis of material behavior during rheological testing. Once preprocessing procedures are successfully designed to reduce noise in the data, material behavior at high shear rates will be further defined.

High Shear Viscosity Measurement Of A Natural Rubber And Synthetic Rubber Materials Using The Rubber Screw Rheometer
Myung-Ho Kim, JaeSik Hyun, InSu Seol , Sunwoong Choi, June 2022

The shear rate-dependent viscosity of natural rubber and three types of synthetic rubber was measured using the Rubber Screw Rheometer. Viscosity values with Mooney viscometer, which has traditionally measured rubber viscosity, have a high correlation with the values of RSR shear rate 10 [1/s]. Thus the Mooney Viscosity value can be estimated using the RSR shear viscosity measurement. Also, in the case of virgin rubber, the accuracy of the measured value increases when it has a pre-shear history. It was confirmed that the viscosity measurement value was a measurement value having a deviation within +3% when comparing the three times repeated measurements. The measured value was correlated to Mooney Viscosity successfully with a first- order equation.

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.

Compounding and Characterization of Polylactic Acid-Sawdust Deep Eutectic Solvent Extracted Lignin
Saurabh Pawale | Karun Kalia | Dylan Cronin | Xiao Zhang | Amir Ameli, August 2021

There is an ever increasing need for sustainable and biobased materials. Plant-based feedstock such as cellulose and lignin can potentially become competitive resources as alternatives to fossil-based materials. Lignin as an inexpensive feedstock has been examined toward preparing polymer composites. It however faces some challenges including its detrimental impact on the mechanical and thermal properties of the resultant composites. This work reports the fabrication and characterization of polylactic acid/lignin composites with the incorporation of a new type of lignin, called deep eutectic solvent (DES) extracted lignin. White fir sawdust was used as feedstock to extract DES lignin. For comparison, commercial alkali lignin (CAL) was also used as a benchmark. PLA/lignin composites containing 0-15 wt.% lignin were fabricated using twin screw extrusion process followed by compression molding. Composites characterization were conducted using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing. The results revealed that the mechanical and thermal behaviors of DES lignin composites significantly outperformed their CAL counterparts. For composites with 15 wt.% DES, the tensile strength, Young’s modulus, and elongation at break dropped by ~33, 7 and 45%, respectively, compared to those of neat PLA. However, the composites with 15 wt.% CAL showed 90, 45 and 86% drop in the strength, modulus, and elongation, respectively. The initial thermal degradation temperature of PLA dropped by ~ 8-27 °C with the incorporation of 5-15 wt.% DES lignin. On the other hand, the introduction of CAL to PLA lowered the degradation temperature by ~89-124 °C. DSC also showed a drop in the glass transition temperature (Tg) and melt temperature (Tm) for both the composites but the drop was less significant for DES lignin composites. The good performance of PLA/DES lignin composites may be associated with the DES lignin’s high purity, low heterogeneity, low molecular weight, fine particle size as well as its homogenous dispersion and compatibility with PLA matrix.

3D Chemical Foaming Simulation For Transfer Molding Process
Li-Yang Chang, May 2020

This study presents the recent development of three-dimensional prediction of cross-linked ethylene propylene diene monomer rubber (EPDM) with chemical blowing agent azodicarbonamide (ADCA) in transfer molding process. Plunger retraction is applied after transfer process is completed. The reaction kinetics model, density model, and viscosity model are applied to describe the complex foamed rubber system in the simulation study. The experimental investigation of material properties into EPDM/ADCA system are studied to make physical parameters in simulation model more realistic. The flow front behavior, the density of foamed rubber, the reaction behavior in foaming and curing conversion are examined to understand the dynamic behavior of the rubber material in both transfer and foaming stages. Furthermore, we study the effect of foaming and plunger retraction. Simulation results show that foaming effect make clamp force larger, however, plunger retraction effect make the back flow occur from cavity to pot to avoid high pressure in the cavity and therefore eliminate the mold clamp force. This study is of great relevance to light weighting application and should reduce the product-to-market cycle time by eliminating the need for the traditional trial-error method.

3D Printed Hybrid Composite Structures - Design and Optimization of A Bike Saddle
Alec Redmann, May 2020

As designers and engineers continue to push the boundaries of high performance and lightweight design, the use of complex geometries and composite materials is growing. However, traditional composite manufacturing often requires the use of additional tooling and molds which can significantly increase the cost. In this study, a carbon fiber reinforced composite bike saddle is designed and manufactured to demonstrate a newly developed hybrid composite manufacturing process. Using a 3D printed epoxy to print the final part geometry and co-cure pre-impregnated carbon fiber reinforcement, the bike saddle can be optimized, designed and manufactured in less than 24 hours.

A Review of Impact Modification Technologies for Different Thermoplastics using Ethylene Copolymers
Jeff Munro, May 2020

Thermoplastics have been blended with reactor-based and grafted-ethylene copolymers for over 50 years to improve room temperature and low temperature ductilityfor many applications, including those in the automotive, appliance, sporting goods industries. The compatibilityof the modifier with the thermoplastic matrix and the rheology of the blend components are key factors in controlling blend morphology. The amount of modifier used and the morphology obtainedaffect the balance of critical properties, including stiffness,impact toughness, and flow. Compatibility of the modifiers with the thermoplastic matrix can be controlled by composition of the modifier produced in-reactor, use of additional compatibilizers (such as diblock copolymers), and by in-situcompatibilization achieved through reactive blending. This paper reviews commercially practiced technologies for impact modification of various thermoplastics based on ethylene copolymers.

A Valid Design Prediction Approach of 3D Metal-Printed Mold Manufacturing
Yann-Jiun Chen, May 2020

In plastic part production, 3D metal printing is a leading manufacturing method for fast, waste-less, and high-accuracy way for making molds with conformal cooling channels. In this automotive power supply test-seat assembly case, the development process combines injection molding simulation, 3D metal printing technology and real experiments to demonstrate an effective mold development approach. Simulation-driven conformal cooling design minimizes the mold temperature difference and significantly reduces part deformation from the traditional straight-line cooling design. Through 6 sets of distance detection, the product dimensions are optimized and can improve the fitting of the three assemblies.

Advanced Simulation Methods for Prediction of Multi-Layer Non-Matching Fiber-Mat Applications In Resin Transfer Molding Process
Fred Yang, May 2020

The objective of this study is to use a simulation tool of resin transfer molding (RTM) process to get a comprehensive understanding of the permeabiliy measuring process. In order to varify the simulation tool’s capibility to simulate oil flow in non-matching fabric we build the mesh model of the measuring instrument cavity with the non-matching meshes in this study. This varifaciton case focuses on two properties of the RTM process, the arriving time and local pressure increasing trend in filling process. By using the simulation tools, we can observe the resin flow within the mold. The comparison between simulation and experiment result shows the reliability of simulation result. We expect that this study will help to clarify relevant issues and then reduce the trial-and-error time and materials.

Blending Scholarly Knowledge and Practioner Know-How To Successfully Injection Mold A Complex Part
Jeremy Dworshak, May 2020

A complex piece of sporting equipment was molded to customer satisfaction, meeting critical dimensions despite complicated tooling and the use of a crystalline resin. Combining modern simulation techniques and industry expertise proved to be a winning strategy in solving this challenge. The use of post-molding, warp controlling fixtures was completely eliminated from the legacy production process, leading to improved part performance and plant efficiency.

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