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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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Thermal & Rheological Characterization Of Two High Density Polyethylene Grades
Phat T. Vu, Azizeh-Mitra Yousefi, June 2022

Presently, polymers such as high density polyethylene(HDPE) are utilized for an extensive array of applications because of their low weight, economical production, and exceptional physical and chemical properties. Thermal analysis and rheological measurements are the ideal techniques for characterizing the material properties of polymers. This paper employs thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and capillary rheometry to collate the contrasting nature of two HDPE resins. These resins will be referred to as HDPE A and HDPE C and are similar to two resins (Sample A and Sample C) included in a previous publication [1] that focused on blow molding parison sag and swell. TGA was used to investigate the thermal stability of these polymeric materials, as they were ultimately decomposed inside a furnace. DSC was conducted to examine the thermal transition behaviors of the polymers. Capillary rheometry was run to construct shear viscosity and extrudate swell versus shear rate data through single and twin bore configurations under varying temperatures. These measurements were conducted under testing conditions that are representative of industrial processes, such as extrusion blow molding. HDPE C was found to exhibit greater extrudate swell than HDPE A, as measured by capillary rheology measurements, and these data correspond to the earlier published results that Sample C exhibited greater parison diameter, thickness, and weight swell than Sample A as measured with a lab scale extruder.

Effect Of Plasticizer Content In EPDM On Ex-Situ Wear Test After High Pressure Hydrogen Exposure
Byeonglyul Choi, Byoung-Ho Choi, Un Bong Baek, June 2022

In high pressure hydrogen environment, elastomeric seals undergo degradation of mechanical properties and wear problems. Especially, wear of elastomeric seals causes failure of sealing system. Therefore, developing the material with good mechanical properties and wear resistance is important. In this study, five ethylenepropylene-diene-monomer (EPDM) with different content of plasticizer were prepared to investigate the effect of plasticizer on their tribological properties after the specimens were exposed to high pressure hydrogen.

Stress Corrosion Crack Growth Of High Density Polyethylene With Cracked Round Bar Specimen In Chlorine Medium
Jung-Wook Wee, Alexander Chudnovsky, Byoung-Ho Choi, June 2022

In this study, the stress corrosion crack (SCC) growth model for the cracked round bar (CRB) specimen was developed. The axisymmetric crack layer (CL) theory for simulating the slow crack growth (SCG) behavior of CRB specimen was modified to consider the chemical degradation due to diffused aggressive environment. The diffusion of oxidative fluid into the process zone (PZ) in radial direction is considered. Also, the chemical degradation kinetics of PZ materials due to the oxidation were modeled. The proposed model was shown that the discontinuous SCG behavior and the deteriorative effect from the chemicals were successfully simulated.

Diffusion-Softening Of Cellulose Nanocrystal And Thermoplastic Polyurethane Composites
Cailean Q. Pritchard, Jacob J. Fallon, Jeffrey Shelton, Michael J. Bortner, Cody Weyhrich, Katherine Heifferon, Boer Liu, Timothy E. Long, E. Johan Foster, June 2022

Smart materials that can adapt their mechanical response in the presence of an external stimuli are popular for their applications in 4D printing. Such printing methods exploit a smart material’s capability to interact with these stimuli to impart controlled material deformation tailored to specific applications. A modified percolation model was formulated to predict the dynamic transition exhibited in polymer composites containing cellulose nano-crystals (CNCs) which undergo mechanical softening in the presence of water. Coupling the effects water diffusion to the degree of CNC connectivity provided a method to capture the dynamic softening of CNC-based, water responsive smart materials as a function of filler loading. This modeling approach can be implemented to develop humidity sensing actuators and water-sensitive shape memory devices.

Enhanced Compost Rate With Simultaneous Toughening By Multifunctional Particle Additives In Poly(Lactic Acid)
Caroline R. Multari, Raymond A. Pearson, June 2022

A particle additive is reported that simultaneously improves ductility and biodegradation behavior of poly(lactic acid) (PLA). Our approach explores the use of encapsulation technology to create degradation-promoting additives while limiting any breakdown of the matrix during melt extrusion and service life. In addition to promoting biodegradation such encapsulated particles are designed to enhance toughness of the matrix. Such dual use particles have the potential to broaden the uses of PLA. In this work, particle properties are examined and the accompanying tensile behavior and compostability of the composite investigated. Particles were dispersed within the PLA matrix by extrusion to 3D printer filament. Elongation at break was improved over neat PLA with limited loss of yield strength. Degradation rate in compost is accelerated and decoupled from environmental conditions by embedding a degradant material into the PLA matrix itself, aided by encapsulation technology that isolates and protects the degradant. The additive has been found to improve mechanical properties while accelerating the biodegradation of parts produced by extrusion-based methods.

Characterization Of Vibration Welded Pine, Maple, And Bamboo
Curtis Covelli, Dr. David Grewell, Shichen Yuan, Klaus Schmidt-Rohr, June 2022

This study investigates the factors affecting the welding of pine, maple, and bamboo pulp-board. This research used a Branson Mini II vibration welder traditionally used for welding plastics. The effects of weld pressure, amplitude, and weld time were varied to determine their effects on lap-shear weld strength. Strength testing was performed with a universal testing machine. The morphology of the weld zone was also analyzed to gain insight into the welding mechanics. The highest strength of pine samples was 8.4 MPa, while maple was approximately 35% stronger and had a smaller standard error. It was observed that bamboo pulp board weld strength was primarily dependent on weld pressure. Also, pulp-board seemed to weld in a similar fashion to wood.

GLIM: Glas Fabric Insert Molding - Polymer Back-Injection Of Glass Fabrics To Increase Strength
Christian Rust, June 2022

Hybrid materials nowadays are achieving increasing market dominance in the technical segment due to their outstanding mechanical properties. One such hybrid material that is increasingly coming into focus, especially in mobility branch, are fiber-reinforced plastics. They offer the advantage of low weight and high strength. As a rule, generally glass or carbon fibers are embedded in the matrix material. Over the last few years, the demand for fiber-reinforced plastics has increased continuously. Considering the recent changes in the automotive industry, it is expected that this trend will not change in the near future, especially with regard to the weight reduction of means of vehicles.

Effect Of Talc And Carbodiimide On The Hydrolytic Resistance Of A Poly(L-Lactic Acid) Compound
Nishant Singh, Celina Alvarado, Carlos A. Diaz, Baxter Lansing, Christopher L. Lewis, June 2022

In this work we examine the influence of talc and a polymeric carbodiimide on the hydrolytic degradation resistance of a commercially available Poly(L-Lactic acid) PLLA. Here, polymer blends containing 0-4wt% talc, a crystal nucleating agent and 0-1 wt% of a polymeric carbodiimide (CDI), an anti-hydrolysis agent, were melt blended and compression molded into plaques. Samples were then submerged in a phosphate buffer solution (PBS) at 50°C for up to 60 days. Results indicate that the presence of talc as the sole ingredient in the formulation increases the crystallization rate and this translates to an increase in the degree of crystallinity of compression molded plaques and a modest improvement in hydrolytic degradation resistance as compared to unfilled PLLA. The presence of CDI retards PLLA crystallization. In spite of this, compounds containing CDI exhibited much greater hydrolytic degradation resistance than PLA with the effect being more pronounced with increasing CDI concentration. Under DSC conditions, the addition of 1wt% talc to CDI containing compounds improved the non-isothermal crystallization rate at 5°C/min but this effect diminished as cooling rate increased and this explains the low crystallinity of compression molded samples. However, compounds containing both talc and CDI showed an improved hydrolysis resistance as compared to compounds containing only CDI implying that talc's role in reducing the rate of hydrolysis is caused by the hydrophobic characteristic of the material. It is envisioned that this work will help pave the way for the usage of PLA in durable applications where long-term resistance to humidity is anticipated.

Effect Of Plasma Treatment On Degradation Of Biodegradable Mulch Film
Swapnil Bhattacharya, Harshal J. Kansara, Celina E. Alvarado, Carlos A. Diaz, Jeffrey Lodge, Christopher L. Lewis, June 2022

Mulch films modify soil conditions thus improving crop output, hence are widely used across the world. Traditional PE (polyethylene) films do not degrade and must be disposed of afterwards. Biodegradable mulch films (BMFs) provide a much better alternative and are meant to be tilled with the soil after harvest. But most BMFs degrade slowly and accumulate in soil, harming the soil productivity. In this investigation we evaluate the effect of gliding arc plasma treatment on the behavior of a commercially available biodegradable mulch film based on polybutylene adipate co-terephthalate (PBAT) and polylactic acid (PLA). Following plasma treatment an initial increase in the hydrophilicity of the films is observed and this is attributed to an increase in oxygen containing species on the surface. Moreover, hydrophobic recovery is slow as indicated by contact angle measurements taken over a 30-day time. Thermal analysis results indicate no significant difference indicating that treatment is confined primarily to the surface. A treated film showed enhanced disintegration as compared to an untreated film following 65 days of composting in an aerated static pile compost. These results indicate that plasma treatment may aid the biodegradation of plastic mulch films and therefore eliminate their accumulation in soil.

Investigation Of Orotic Acid Effects On The Crystallinity Development Of Poly-Lactic Acid
Faisal J. Alzahrani, Peng Gao, Alaauldeen Duhduh, John P. Coulter, June 2022

This research investigated the effect of the addition of Orotic Acid (OA) on the crystallization kinetics of Polylactic Acid (PLA) in quiescent and non-quiescent conditions. A differential scanning calorimetry (DSC) study was used to investigate and understand the effect of the addition of orotic acid on 2500 HP PLA under quiescent conditions. DSC technique was utilized to capture the crystallinity, melting point, and other thermal parameters of PLA-OA blends. Conventional injection molding (CIM) was used to investigate the influence of adding OA into PLA under non-quiescent conditions. Two concentrations of orotic acid, 0.3 wt% and 0.7wt% were mixed with neat PLA and then investigated. It was observed that the 0.3 wt.% orotic acid provided significant improvement in crystallization kinetics by increasing the crystallinity and reducing the incubation time. Both blends under quiescent conditions showed almost the same crystallinity in which the maximum crystallinity that was observed was around 63% in the blend of the PLA/0.7OA at 85°C. For 2500HP PLA, Orotic acid (OA) showed to be an effective nucleating agent. A small amount (0.3 wt%) was sufficient to achieve 61% of crystallinity in injection molding at 80°C mold temperature.

Automated Optimization Of A Block-Head-Mixer With An Innovative Algorithm
Felix Vorjohann, Lucas Schulz, Mirco Janßen, Reinhard Schiffers, June 2022

CFD-Simulations are a common tool to design and optimize mixing elements. The manual evaluation and experience-based derivation of an optimized geometry is still an iterative process which is time consuming. In this paper an automated algorithm is developed and tested for a mainly distributive Block-Head-Mixer. To automatically evaluate the flow field of each geometry variant, quality criteria are introduced which enable the assessment of the mixing capability. The investigation showed that the quality criteria are suitable to evaluate the flow field and an optimized candidate compared to a starting geometry could be found automatically.

Curing Behavior Simulator For Robotic 3D Printing Of Uvcurable Thermoset Polymers
Luke Weger, Luis Velazquez, Corina Barbalata, Debaroty Roy, Genevieve Palardy, June 2022

Robotic 3D printing systems utilizing photopolymers can enable free-standing structures, large-scale printing, extensive mobility, and increased part complexity. However, to better estimate robotic printing parameters and eliminate expensive trial-and-error approaches, a simulation framework for curing behavior is needed. In this work, an autocatalytic curing model, considering printing speed, UV light intensity, spotlight diameter, and filament thickness, was used to create a MATLAB simulation to study the effect of different printing parameters. The printed filament was discretized into a set number of elements over its length and thickness. UV light exposure time above each element was derived based on spot diameter and printing speed. This simulation framework, combined with experimental data (real-time ATR-FTIR), can better inform decisions regarding printing parameters selection. Overall, it was estimated that a speed ≤ 3 mm/s with a filament thickness ≤ 2 mm would produce acceptable ranges of degrees of cure at different UV light intensities and spot diameters. Finally, control of printing parameters (robotic arm movement and UV light intensity) to obtain a specific degree of cure (DoC) ensuring structural rigidity is demonstrated for a two-degree-of-freedom manipulator, showing both the desired endeffector position and the desired DoC are achieved in four seconds.

Injection Molidng Of Microporous Ultra-High Molecular Weight Polyethylene
Huaguang Yang, Lih-Sheng Turng, June 2022

Microporous ultra-high molecular weight polyethylene (UHMWPE) parts were produced by microcellular injection molding (MIM) technology, which enabled higher production efficiency and lower part cost compared to the traditional powder sintering method. The microstructure could be tuned by adjusting the shot size to produce either sandwiched solid-skin – porous-core – solid-skin parts or open porous parts. The pore morphology, average pore size, pore size distribution, and pore density were characterized, and the water contact angle (WCA) and degree of oil-water separation were determined. The part weight reduction of open-porous UHMWPE and sandwiched UHMWPE parts were 16.5 wt% and 11.8 wt%, respectively. The WCA results showed that the porous surface transformed molded UHMWPE samples from being hydrophilic (34.5°) to hydrophobic (124.6°). Furthermore, the open-porous structure exhibited good oil water separation capacity. Tensile tests were carried out to study the effect of morphology on the mechanical performances of the molded UHMWPE parts. The characterization shows that a possible application for the sandwiched UHMWPE parts could be as a bone replacement material because of its high mechanical performance, and an application for the open-porous UHMWPE is as a functional filter material due to the fine pore size and high pore density.

From Petroleum To Biobased Crude: A Thermoplastic Polyurethane From Lignin-Oil Without Isocyanates
James Sternberg, Srikanth Pilla, David G. Brandner, Reagan J. Dreiling, Arik Ringsby, Jacob S. Kruger, Gregg T. Beckham, June 2022

The movement to transfer from petroleum-based products and materials to renewables does not necessarily have to bypass the use of oil. A new type of “black-gold” is readily abundant from the earth’s most abundant source of aromatic carbon: lignin. While fractionation of petroleum yields fuels and chemicals for a diverse set of industries, lignin fractionation using targeted catalysts has demonstrated the ability to generate monomers and oligomers rich in functional groups for polymer synthesis. This study explores the use of lignin-oil, generated from reductive catalytic fractionation of popular wood, to a hydroxyl-rich mixture of aromatics that is used to synthesize a thermoplastic non-isocyanate polyurethane. The lignin-oil is first converted to a cyclocarbonated derivative using a benign synthetic sequence and further polymerized with a diamine to yield the non-isocyanate TPU. While more work is underway to optimize the reaction conditions and meet typical mechanical properties of commercial materials, initial analysis shows thermoplastic behavior and flexible properties consistent with traditional thermoplastic polyurethanes.

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.

Development Of An Inline-Measurement System Of The Surface Temperature Of Square Hollow Profiles
Jonas Köllermeier, Volker Schöppner, June 2022

In polymer extrusion, the die temperature is normally set to the recommended temperature in order to reach a homogeneous melt. Nevertheless, the measurement of the melt and surface temperature of the product leaving the die is not state of the art due to the difficulty of an inline - measurement. As a consequence, the product temperature leaving the die is assumed as the set die temperature. Therefore, this article aims to engineer an inline-measurement system of the surface temperature of square hollow profiles immediately after leaving the die. First, two objective quality criteria to define the thermal melt homogeneity, named weighted melt temperature and radial temperature, are introduced. After that, experimental investigations are carried out for two different types of polyolefin polymers with the variation of several process parameters such as the screw speed and the die temperature. In order not to distort the product, the developed construction is based on a contactless measurement system using infrared pyrometers to measure the average surface temperature on each side of the profile. After all, rules of behavior are derived from the process and correlations between the investigated process parameters and the melt quality as well as the surface temperature are identified.

Deformation Mechanisms Of Toughened Poly(Lactic Acid) Using Novel Additives
Jordan Greenland, Caroline Multari, Raymond A. Pearson, June 2022

Poly(lactic acid) (PLA) is certified biodegradable under specific composting conditions, but its inherent brittleness limits usefulness in commercial applications. In this study, novel additives were supplied by TRuCapSol for twin-screw melt compounding and injection molding with general purpose PLA resin. These additives were received in powder form and investigated for their ability to improve the tensile toughness. We compared our blends to several commercially available toughened PLA blends. The inherent micro-deformations of PLA were amplified by the novel additive and resulted in improved ductility. Therefore, the potential for the development of blends that enhances the toughness and increase the rate of biodegradation of PLA has been demonstrated.

Pressure-Controlled Injection Molding Of Recycled Polyolefins
Joshua Krantz, Peng Gao, Zarek Nieduzak, Elizabeth Kazmer, Olvia Ferki, Margaret Sobkowicz-Kline, Davide Masato, June 2022

The importance of utilizing recycled materials to manufacture plastic products has been a topic of great interest due to the environmental repercussions. Processing issues arise from the usage of these resins due to the variation in their molecular weight and rheology. In this work, pressure-controlled injection molding is evaluated and compared against conventional velocity-controlled injection molding. The effects of injection velocity, mold temperature, and pressure on part shrinkage and mechanical properties of injection molded parts fabricated with post-consumer film-grade polyethylene were evaluated. The experimental results show that the different processing techniques significantly affect the mechanical properties and part shrinkage for both materials. Additionally, different levels of injection pressure and velocity significantly affect the shrinkage of the plastic parts. Moreover, it was seen that parts fabricated using pressure-controlled injection molding had preferable overall quality.

Potential Of Five-Axis Kinematic Systems For Additive Manufacturing Using Fused Deposition Modelling (FDM)
Joshua Voll, Jonathan Baier, Rene Brunotte, Stefan Roth, June 2022

Fused Deposition Modelling (FDM) technology is a widely used additive manufacturing processes. In this process, a plastic filament is fed to a nozzle, melted there and deposited in the X, Y direction based on an imported geometry. Afterwards the print bed moves one layer in the Z direction and starts depositing the plastic again in the X, Y-direction. These steps are repeated until the component is completely built up. In a recently developed system by one of the authors, the degrees of freedom in movement of the print head are extended to five axes: X, Y, Z-movement in translational direction plus an additional degree of rotation of the print bed and the possibility to tilt the print head with respect to the printed surface. Thereby, the surface quality and the geometric accuracy for rotationally symmetrical parts are intended to be improved. This paper investigates the potential of the additional motion axes with respect to part quality. To determine the accuracy, surface quality and the ability to print overhangs, tests have been carried out and compared to conventional manufactured FDM parts (X, Y, Z-kinematics). In a further step, the printing of the parts after model preparation in polar coordinates is compared to printing in Cartesian coordinates. To investigate the influence of the print head adjustment on part quality, namely surface roughness, test runs were performed with print head adjusted at different angles to the surface. Suitable demonstrators were developed for this purpose and evaluated in comparison with manufactured FDM parts using commercially available printers limited to X, Y, Z-movement only. The tests show that the recently developed 5-axis printer has a lot of potential. It’s comparable in performance to a commercially available FDM printer from the mid-price segment. The possibility of tilting the print head is the biggest advantage of the system. This has significantly improved part quality when printing overhangs and angled surfaces. The comparison between polar and Cartesian coordinates showed an improvement in surface quality for cylindrical parts printed by polar coordinates.

Investigating The Optical And Mechanical Properties Of Stimuli Responsive Electrosterically Stabilized Nanocellulose Crystals In Thermoplastic Polyurethane
Justin Anderson, Tyler Sequine, Mica Pitcher, Amir Sheikhi, Michael J. Bortner, June 2022

A new type of nano-cellulose crystal (CNC) has been gaining interest for its unique morphology combined with its as-produced carboxylate functionality: electrosterically stabilized nano-crystalline cellulose (ENCC). When ENCCs are added to thermoplastic polyurethane (TPU) composites and submerged in water they display a unique increase in opacity. Using UV-VIS and DMA, the optical and mechanical properties of these composites can be studied at differing ENCC concentrations.

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