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Conference Proceedings

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.

Integration of Polycarbonate Thermoplastic in LED Lighting
Nicolas J. Sunderland | Jim Lorenzo, May 2021

Thermally conductive (TC) polycarbonate was utilized as aluminum metal replacement in LED lighting luminaires, along with transparent, diffusion, and reflective polycarbonate thermoplastics in order to describe a light weight, design-friendly, cost efficient part. To assess suitability of the TC polycarbonate, the part was subjected to thermal testing. Results showed very similar thermal characteristics as aluminum.

Designing for Six Sigma (DFSS) - A Systematic Approach to Robust Plastic Part Design
Vikram Bhargava, May 2021

Designing for Six Sigma (DFSS) - A Systematic Approach to Robust Plastic Part Design To design and manufacture today's complex plastic components, product designers are under tremendous pressure to produce robust designs at a minimum cost and in the fastest possible time. Leading author David Wright wrote in his book titled “Failure of Plastics and Rubber Products” that design issues account for almost 20% of product failures. The fact is that many errors that manifest themselves as material, tooling or processing can also be attributed to design issues. Conventional plastic flow simulation does not necessarily help diagnose and avoid common design issues. Decisions made at the design stage impacts manufacturing quality, product cost, and delivery lead times. Taking a proactive approach by including Six Sigma philosophy upfront into the early design stage can help develop high quality, profitable products eventually bringing sustained value to customers and markets. The Paper will discuss the Design for Six Sigma (DFSS) philosophy and best practices and tools for its incorporation into new plastic product development. This will include: • Understanding the DFSS concept and popular methodologies such as DMAIC and DMADV • Learning how to use DFSS Methodology in early part of plastic product design lifecycle • Applying DFSS techniques and available simulation and DFM tools for successful implementation

Analysis of the State of the Art of Technical Drawings of Plastic Molded Parts Regarding Tolerances
Anja Falke | Friedrich-Alexander | Martin Bohn | Tim A. Osswald, May 2021

The plastic-specific material properties are often not taken into account in the specification of technical drawings of injection molded parts. As a result, tolerance requirements are specified, that are too tight and sometimes even impossible to manufacture, which result in high production expenses. To avoid this, it is necessary to coordinate the functionally required accuracies of plastic components with the technical possibilities available for injection molding production.
In this paper a systematic analysis of drawings from practice is used, to show the current state of the art regarding geometric product specification and tolerance assignment of plastic molded parts. In addition to the quantification of the number of specified features, the unambiguousness of the product specification is assessed. Beyond that, the degree of accuracy of the tolerance requirements is quantified and the manufacturing feasibility is checked in accordance with ISO 20457 in order to then determine the resulting production expense that is necessary to achieve the required tolerances. It is proven that for almost a fifth of the plastic parts tolerance requirements are specified that are not feasible to be produced in the injection molding process. Additionally, it is found that all drawings examined do contain ambiguously specified features, that do not allow for an unambiguous verification.

Three Trends in Healthcare Adhesives
Joanne Moody, May 2021

With an aging global population growing, the demand for new healthcare products and telehealth systems will increase. The FDA aims to advance innovation and development in digital health while ensuring patient safety and effectiveness. Adhesives are critical in the new remote monitoring products, such as the small wearable devices that stick to skin. In addition, surgical adhesives are replacing stitches, and robotic surgical systems are rising. With healthcare adhesives, there are additional challenges in safety, performance, biocompatibility ISO 10993, and cost requirements. This paper reviews three healthcare adhesive trends: (1) topical skin adhesive patches, (2) tissue adhesives, and (3) medical device assembly and equipment adhesives.

Adhesion of Overmolded TPE to FR-PC/ABS: Effect of TPE Properties and Substrate Color Recipe
Pierre Moulinié | Godwin Suen, May 2021

Various grades of Thermoplastic Elastomer (TPE) were overmolded onto a FR-PC/ABS blend prepared with several different color recipes and tested for adhesion. All combinations prepared exhibited adhesive failure with a standardized peel test, yet showed relatively high average peak peel forces that ranged from 3.74-4.07 N/mm, which agreed well with literature values. Different color recipes for the substrate had no discernable effect on peel forces. Two-step overmolding of TPE using pre-molded (and therefore conditioned) substrates gave no significant difference to those prepared with direct 2-shot overmolding.

The Most Frequent Design Flaw That Leads to Part Failure
Paul J. Gramann, Ph.D., P.E., May 2021

The topic presented in this paper is not new. There are numerous reasons why sharp transitions should not be present in a plastic part. However, the number of failures that are occurring at sharp transitions is still very common. In most cases, they can easily be avoided by simply removing metal from the mold to make a smooth transition. This paper will review where most of these transitions are being found, and why they are common in critical parts. A tensile testing study was performed to better understand the effect of geometric transitions. Two cases studies are given showing why the sharp corners can significantly reduce the lifetime of a plastic part.

Effect of Molding Parameters on Orientation and Tensile Properties of Polycarbonate
Pierre Moulinié | Isaac Platte | Ravishankar Ayyar | Kyle Kulwicki | Louis Somlai, May 2021

The tensile properties of two different molecular weight polycarbonates were examined in relation to injection-molding conditions, such as low and high temperatures & speeds (affecting injection pressures), that were beyond those recommended by the supplier. We found conditions that prompted higher injection pressures led to decreases in tensile elongation-at-break, with more significant decreases for higher molecular weight (and high viscosity) PC. Examination of molded samples under polarized light suggested higher degrees of molded-in stress along the flow length as an important contributor to the changes in elongation at break. Additionally, corresponding to the elongation at break, the onset of strain hardening decreased under injection molding conditions that produced higher injection pressures.

Effect of Rubber Surface Treatment on the Properties of Rotomolded Thermoplastic Elastomers
Roberto C. Vázquez-Fletes and Denis Rodrigue | Gustavo Gallardo-Paniagua | Erick O. Cisneros-López | Pedro Ortega-Gudiño | Rubén González-Núñez, May 2021

Thermoplastic elastomers (TPE) are a combination of a rubber and a thermoplastic to create a recyclable blend combining the properties of both resins. The objective of this work is to produce and characterize rotomolded parts based on polyamide 6 (PA6) as the matrix and recycled ground tire rubber (GTR) as the dispersed phase. In order to improve the adhesion between PA6 and GTR, and consequently the mechanical properties of the resulting TPE, a treatment with formic acid was used on the GTR surface. All the samples were initially mixed via dry-blending using 5 and 10% wt. of GTR and then rotomolded. For these concentrations, successful rotomolded parts were produced to report on their morphological and mechanical properties. The results show that increasing the GTR content led to lower tensile modulus and tensile strength, but higher elongation at break and impact strength compared to the neat matrix.

Polypropylene/Ground Tire Rubber (PP/GTR) Composites Produced Via Rotational Molding
Y. Dou | D. Rodrigue, May 2021

In this work, polypropylene (PP) was dry-blended with ground tire rubber (GTR) to produce composites by rotational molding. In particular, the effect of GTR content was investigated to modify the mechanical properties of the PP matrix. Each compound was characterized via morphology, density and mechanical properties (tensile, flexural and impact). As expected, the results showed that all the mechanical properties decreased with increasing GTR concentration due to its low modulus and strength. Also, the crosslinked structure of the GTR particles is believed to limit the interfacial PP-GTR interaction, thus also limiting mechanical stress transfer.

Self-reinforced Polylactide Composites Manufactured by Melt Spunbond Technology
Amirjalal Jalali | Anthony Tuccitto | Sandra Romero-Diez | Patrick C. Lee | Chul B. Park, May 2021

A series of stereocomplex polylactide (SC-PLA) blends (PLLA 95 wt%/PDLA 5 wt%) were prepared by spunbond technology. For this, the compounds of linear PLLA, and low and high molecular weight as well as branched PDLAs were spun at two different temperatures. They were spun at 190 °C, which was below the melting temperature of the stereocomplex crystals. And, they were melt-spun at 230 °C, which was above the melting temperature of the stereocomplex crystals. Morphological observation of the etched samples showed that the samples spun at 190 °C demonstrated tiny spherical crystals exhibiting diameters in the range of 100–200 nm; however, the samples spun at 230 °C showed thin fibers in the size range of 60–70 nm. The obtained results were supported by shear and elongational rheological measurements. Moreover, crystallization kinetics of the samples was also enhanced after spinning and was largely dependent on the spinning temperature. Tensile modulus and strength of the spun samples was also significantly improved. The spun samples also presented a considerable decrease in boiling water and hot air shrinkage.

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