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Thermoplastic Elastomers

Generation of Tough, Stiff Polycarbonate Nanocomposites Through the In-Situ Nanofibrillation of Rubber Network
Hamidreza Akrami, March 2023

In this study, we introduce the concept of in-situ nanofibrillation as an efficient, low-cost, and environmentally friendly tailored technique for the enhancement of polycarbonate (PC) properties. PC/ Ethylene Propylene Diene Monomer Rubber (EPDM)-fibril composites are prepared by a twin-screw extruder. Taking advantage of the crosslinked rubber phase as well as nanofibrillation processing play the main role in properties improvement. Modifications of the mechanical and rheological properties of PC via fiber-spinning of PC/EPDM are distinguished by elongation and crosslinked network of the second phase (EPDM) properly in the main matrix (PC). Morphological observations showed the well-dispersed fibrillar phase of EPDM with a high aspect ratio in the PC matrix. PC with nanofibrillated EPDM also improved the mechanical properties, especially the ductility and the toughness, while increasing the stiffness, in comparison with neat PC. The change in the tensile, Izod Impact and flexural properties was governed by the draw ratio. Hence, having stretched fibrils is an effective way to enhance the mechanical and rheological properties. Rheological investigations proved that PC with nanofibrillated EPDM has dramatically improved melt elasticity compared with neat PC. Linear viscoelastic behavior of small amplitude oscillatory shear measurements showed a strain-hardening, solid-like, behavior in the fiber-spun PC/EPDM, which was not observed in the neat PC or the melt-blended PC/EPDM.

Smart Foams Generated via Supercritical Carbon Dioxide
John Daguerre-Bradford, March 2023

Natural and synthetic polymeric foams display a variety of open and closed pores with diverse shapes, sizes, and degrees of anisotropy. In state-of-the-art foaming processes, microcellular anisotropy is generated by releasing confinement in one or more directions during the expansion of an initially isotropic melt or resin. As a result, the entire monolith foamed in this way exhibits cells aligned in the direction dictated by the confinement. This, in turn, results in a uniform deformational response that is dictated by the loading condition relative to the microcellular orientation. In this work, investigation was performed into generating a foamed morphology within an anisotropic medium (e.g. film or fiber) to understand how molecular orientation affects the resulting anisotropy in the microcellular structure. Additionally further investigation into the use of this strategy to generate complex microcellular hierarchical constructs was performed by using fibers and or films as templates to understand their effect on the corresponding deformation. Herein, results are presented to show how assemblies of fibers are woven or twisted with a bias or helical structure and then foamed using superheated water (shH2O) and/or supercritical carbon dioxide (scCO2) to manufacture complex microcellular structures. In addition, results from mechanical tests also show how the imposed bias in the foams result in complex deformation imposed by the bias. That is, foams generated to create a helical bias are shown to undergo torsional deformation commensurate wit h uniaxial deformation when compressed uniaxially. These concepts propose a technology to manufacture “smart foams” by assembling templates (films and/or fibers) that have locally different molecular orientations that ultimately create locally changing anisotropic microcellular patterns that govern complex deformational behavior under applied loads.

Micro/Nano-layer Structured Foams With Tunable Foam Morphology and Properties
Patrick Lee, Ph.D., March 2023

In the frame of polar, deep water, and exoplanet exploration, lightweight multifunctional materials with durability targeting extreme environments are highly sought. Specifically, mechanical strength and a high degree of thermal insulation are among the most critical properties of structural materials in these applications. Mechanical strength imparts the structural integrity needed to minimize damage to sensitive electronic components, while thermal insulation is needed to protect equipment in extreme temperature conditions. Herein, this work uses micro/nano-layered technology to fabricate film/foam alternating structures for an advanced structural architecture that combines the mechanical performance of multilayered materials with the thermal insulation properties characteristic of polymer foams. We used PC as the film layer, PMMA as the foam layer, and CO2 as the foaming agent. With respect to foam structure, our work demonstrates that due to the confinement effect of the film layers, samples expand only in the thickness direction with no noticeable expansion along the in-plane direction. The apparent expansion ratio in the thickness direction increases with increasing layer numbers (up to 513 layers), ranging from 2.3 to 11 times expansion. With respect to cell morphology, there is a clear decrease in cell size with increasing layer numbers, with a concomitant increase in cell density. Specifically, we obtain the highest cell nucleation density and smallest cell size, around 1.1×1013 cells/cm3 and 400 nm, respectively, from the 513-layer sample foam, when treated at 70 C and 20 MPa. This micro/nano-layered film/foam alternating system offers an outstanding combination of tensile strength (~33 MPa) and low thermal conductivity (~0.0297 W/m·K), in comparison to foams or aerogels with similar thermal conductivity and tensile strength of less than 1 MPa. The balanced tensile performance and insulation properties offered by this multi-tiered structure open the door for use in applications including the exterior layer of vehicles operating in extreme conditions.

Novel Approach to Improve the Performance of TPV via Self-Nano Reinforced Network Structure
Guralp Ozkoc, Ph.D., March 2023

Thermoplastic vulcanizates (TPVs) are highperformance polymeric materials classified as thermoplastic elastomers, and contain a continuous thermoplastic matrix with crosslinked elastomers as a dispersed phase. TPVs combine the high elasticity of crosslinked elastomers and the easy processability and recyclability of thermoplastics. The most widely produced TPV type is polypropylene (PP)/ethylene propylene diene monomer (EPDM), which is the focus of this study. In this study, polyhedral oligomeric silsesquioxane nanoparticles containing reactive side groups were used as coagents for PP/EPDM TPV system for the first time in the literature. The peroxide crosslinked PP/EPDM/POSS system was dynamically vulcanized in a lab-scale micro-compounder. The mechanical properties of samples were determined by tensile, hardness, and compression set analyses. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to evaluate the phase morphology. The results showed that nano-reinforced network structure improved the performance of the TPV materials.

In-Situ Rubber Nanofibrillation of Compatibilized High-Density Polyethylene/Thermoplastic Polyester Ether Elastomer With Superior Melt Strength and Foamability
Chul Park, Ph.D., March 2023

High-density polyethylene (HDPE) exhibits poor melt strength which limits its widespread application especially where it is exposed to an elongational deformation flow in processes such as film blowing, melt spinning, and foaming. In this study, by taking advantage of in-situ nanofibrillation of thermoplastic polyester ether elastomer (TPEE) in HDPE matrix, we improved the rheological properties as well as the foamability of HDPE. TPEE consists of a hard crystalline segment of polybutylene terephthalate (PBT) and a soft amorphous segment of polyether. The polarity of these two groups causes TPEE to be thermodynamically incompatible with non-polar HDPE. Therefore, styrene/ethylene-butylene/styrene copolymer grafted maleic anhydride (SEBS-g-MA) as a compatibilizer was used for reducing the interfacial tension between two blend components. In the first step, a 10% masterbatch of HDPE/TPEE with and without compatibilizer was prepared employing a twin screw extruder. Next, to fabricate fiber-in-fiber composites, the 10% masterbatch was diluted and processed by spunbonding. Scanning electron microscopy (SEM) revealed that not only the spherical size of HDPE/TPEE decreased significantly after SEBS-g-Ma inclusion, but also a much smaller TPEE nanofiber size (60-70nm for 5%TPEE) was achieved. Moreover, the extensional rheological results showed strain-hardening behavior for both compatibilized and non-compatibilized stretched samples at earlier times, at a given extensional rate, compared to the unstretched counterparts. It is worth mentioning that the improvement of extensional rheological properties was more pronounced for compatibilized samples compared to the non-compatibilized ones. This can be attributed to smaller nanofiber size and consequently higher aspect ratio as well as a more robust 3D fibrillated network. Finally, batch foaming was conducted to investigate the foamability of fibrillated nanocomposites.

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.

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.

A Hansen Compatibility Approach in Understanding Solvent Bonding Between Acrylic Copolymers
Pooja Bajaj | Kay Bernhard | Dirk Heyl | Maurice Biagini, April 2021

Flexible PVC is the tubing of choice used in infusion therapy applications as well as other medical devices applications. But the health risk awareness for the plasticizer (Diethylhexylphthalate) DEHP in flexible PVC is gearing the industry to seek alternative tubing materials. Solvent bonding between two materials is a common joining technique that relies on compatibility between the substrate polymers to the tubing material for fabricating medical assemblies. Solvent is the integral component to swell the joining components and allow intermingling, diffusing and sealing the joint. In this study, we present solvent bonding as a versatile fabrication technique for joining various plastic materials to medical tubing. Acrylic copolymers, (specifically CYROLITE® GS-90 manufactured by Roehm America LLC) are tested for bond strength against four different tubing materials, namely non-DEHP-PVC, TPU, Polybutene, and Silicone, using solvent bonding. A variety of industrially accepted solvents such as Acetone, Methylethylketone (MEK) and Cyclohexanone/MEK were tested. These solvents demonstrated strong lap shear pull force strength, replacing the carcinogenic Dichloromethane (DCM), DCM/Glacial acetic acid 90/10 or the more aggressive stress-crack inducing 100% Cyclohexanone solvents. The article also describes Hansen solubility parameter as an engineering mechanism in determining miscibility and understanding the bonding performance of acrylic copolymers, and other medical plastics such as medical grade polycarbonate (PC), and Methyl methacrylate Acrylonitrile Butadiene Styrene (MABS) to various tubing materials.

Ageing Effects On Two-Component Injection Molded Thermoplastic Elastomers On Polyamide-12
Anna-Maria Persson, May 2020

The effect of ageing on the adhesion between thermoplastic elastomer materials and glass fiber reinforced polyamide-12 materials was evaluated. Test specimens were made by two-component injection molding, and the melt temperatures and the glass fiber fraction were varied. Adhesion before and after ageing was assessed via peel tests. Ageing (11 weeks at 70 °C with 62% relative humidity) severely reduced the adhesion strength. This could be explained by broken covalent bonds and/or disentanglement in the interphase. The individual materials were not severely affected by the ageing.

Extension of the Rivlin Polynominal for the simulation of the non-linear material behaviour of TPE
Christoph Zimmermann, May 2020

The non-linear material behaviour of thermoplastic elastomers (TPE) show a considerably higher stiffness compared to pure elastomers due to the presence of the thermoplastic phase. The approximation of non-linear material behaviour via generally known hyperelastic material models illustrate some deficits regarding the initial stiffness and the course at higher deformation. In order to ensure a precise dimensioning of TPE parts via the finite element analysis (FEA), current hyperelastic material models have to be extended by user-defined formulations. For this purpose, the existing Rivlin polynomial is extended by an additional material parameter as exponent. This extension leads to a more accurate prediction of the non-linear material behaviour. Even the simple extended Neo-Hooke material model shows a good accuracy regarding the determined material behaviour and the initial stiffness of the used practical part.

Overmolding of Thermoplastic Elastomers Onto Hard Substrate Materials
Ernest Kumeh, May 2020

Historically, soft thermoplastic elastomer (TPE) materials have been applied onto the hard substrate materials via an overmolding process in order to enhance the performance of the molded articles. In this process, it is important that the soft TPE adheres well enough to the substrate materials to maintain the desired performance. Depending on the characteristics of the substrate material, a TPE must be formulated to facilitate the adhesion of a TPE onto the substrate during an overmolding process. KRAIBURG TPE has engineered and marketed TPEs that can bond to a variety of hard substrates including metals. The adhesion characteristics of these TPEs are presented in this paper.

Trends in Bio-renewable Thermoplastics Elastomers
Krishna Venkataswamy, October 2010

Thermoplastic elastomers (TPEs) have been traditionally compounded and manufactured from raw materials based on fossil fuels. Current trends in marketplace abounds sustainability programs. TPEs are no exception to this trend. In a recent editorial, the authors stated “Through research and application, sustainability can evolve from a catchphrase to a societal one”. More than two decades ago the Brundtland Commission (formerly the World Commission on Environment and Development, WCED), deliberated sustainable development issue and gave a definition of sustainability: “Sustainable development meets the needs of the present without compromising the ability of future generations to meet their own needs.

Evaluation of Shape Memory Properties of Polyurethane Nanocomposites with High Hard Segment Content
F. Cao | S. C. Jana, May 2008

Shape memory polyurethane (SMPU) with high hard segment content offers good shape recovery ratio and high recovery stress. This study considered further improvement of shape recovery stress with the introduction of nanoclay. Reactive nanoclay particles were tethered onto polyurethane chains via urethane groups and provided extra crosslink points. This led to increase of modulus and recovery stress, e.g., a recovery stress of 19 MPa with 5 wt% clay compared to 13.5 MPa for unfilled PU. The recovery ratio of SMPU was not influenced by the addition of clay. The influence of stretching rate, stretching ratio, and stretching temperature on shape recovery force was studied.

It Seals, Feels, Flexes, and is Called Thermoplastic Elastomer
Prithu Mukhopadhyay, May 2000

Slowly but surely, new developments in thermoplastic elastomers (TPEs) are providing alternatives to traditional rubbers. They can provide cost-effective, high performance replacements to EPDM, neoprenes and polyurethanes. Parts or items can be designed ergonomically with TPEs. Who can refuse a plastic part that offers good feel, comfort and easy control? TPEs' popularity is understandable since they are processed like thermoplastics, yet perform like rubbers. That's no surprise. TPEs are two-phase blends system: a hard thermoplastic phase combined with a soft rubber phase. As Advanced Elastomer Systems (AES) puts it, "with TPEs like Santoprene, you can flex your imagination". No exaggeration indeed! Whether the soft-grip handle of MACH3 razor or the velvety, tactile feel of colourful Contura staplers - TPEs are taking the centre stage.

Mix & Match: New Developments Offer New Applications
Prithu Mukhopadhyay, November 1998

Injection molding process imparts a complex thermal deformation history to polymer melts. The complexity rises with multiphase blend systems. How about development in areas of new materials? Can we not get new resins that would give faster cycle times, high ultimate strength and elongation values combined with a wide spectrum of shore A and shore D hardness grades?

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