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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In-Situ Characterization of Thermoplastic Polyurethane Reaction Kinetics Using Rheo-FTIR
Understanding polymerization kinetics during reactive extrusion maintains the potential to improve processing efficiency. This study focused on understanding the kinetics and mechanical development of aromatic thermoplastic polyurethanes (TPU). The results indicate that rheology coupled with spectroscopy techniques provides a means to capture chemical and physical property development. Information on the development of materials during controlled reactions may then be applied to scenarios in extrusion of reactive systems. This study noted a significant change in both reaction rate and storage modulus as the hard segment content of the system increased from 26.4% to 55.6%.
Trends in Failure of Synthetic Polymers and Human Biopolymers
Some trends in failure are due to errors of design or bad judgment (plastics) or unwise life conditions (human biopolymers). An encouraging trend for human biopolymers is synthetic polymers designed as replacements for damaged biopolymers (electrical polymers for nerves, and targeted drug delivery). Environmental, recycling and health effects on failure are a strong recent trend in polymer failure. Examples are bisphenol A (BPA) and phthalate plasticizers, both limited by bans for health reasons. PVC is also attacked for health reasons. Even if a plastic is very worthy, inexpensive and was accepted for years, it may be considered for banning (PE thin bags).
Hydrogels for Arterial Modelling and Tissue Scaffolding
Models of human blood vessels have many potential applications as aids in continuing research on new medical devices. The work detailed herein describes the development of a hydrogel material to mimic the mechanical and biological response of a range of human arteries. The developed hydrogels were characterized via swelling studies, differential calorimetry and spectroscopic techniques, while viscoelastic property measurement was investigated primarily using rheological testing methods. A range HEMA/NVP hydrogel materials were successfully developed with properties comparable to a range of arteries, namely, the thoracic and abdominal aorta with storage moduli (G’) varying from 43kPa to 64kPa depending on the formulation. This paper also describes the construction of a mathematical model for the viscoelastic properties of these materials, representing the time-dependent behaviour of the simulated areterial material when subjected to loading and unloading phenomena.
Development of Expanded PLA Bead Foams: A Promising Substitute of Expanded PS and PP Products
In this study, for the first time, we developed microcellular PLA bead foams with double crystal melting peak structure followed by steam-chest molding of the foamed beads. The generated high melting temperature crystals during the saturation significantly affected the expansion ratio and cell density of the PLA bead foams by enhancing the PLA’s melt strength and promoting heterogeneous cell nucleation around the crystals. The tensile mechanical properties of the molded EPLA bead foams showed that EPLA bead foams with double melting peak structure can be a promising substitute not only for EPS products but also for expanded polypropylene (EPP) products.
Processing Research and Development of ‘Green’ Polymer Clay Nanocomposites Containing Polyhydroxybutyrate, Vinyl Acetates, and Modified Montmorillonite Clay
The purpose of this research was to determine the feasibility of direct melt-blending (intercalation) montmorillonite nanoclay to polyhydroxybutyrate along with vinyl acetate, at different weight percentages, to enhance plasticization using typical plastic processing equipment and typical processing methodology. Single screw and twin screw extrusion, Banbury mixer compounding, and compression molding were used to intercalate montmorillonite, and for sample preparation purposes, to test tensile and flexural strength of the resultant polymer clay nanocomposites (PCN) developed. Dynamic mechanical analysis of tensile strength and flexural strength was compared as a result of this processing. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and melt flow analysis (MFI) were used to determine the thermal and flow properties of the PCN materials produced during the research.
Light Weight Multifunctional Composites with Enhanced Mechanical Properties
In this study, polypropylene (PP) composites reinforced with short glass fibers (GF) and expanded graphite nanoplatelets (xGnP) were produced by melt compounding and injection molding. Quasi-static tensile tests and morphological observations were carried out in order to investigate how the morphology and the mechanical properties of the composites were affected by the combined effect of two fillers of rather different size scales (i.e. micro- and nano- scale). The results indicate that it is possible to introduce the nano-materials at the GF-PP interphase and significantly improve the tensile modulus of the composites, leading to lighter and stronger composites, as part of the higher density GF can be replaced with a small amount of the nano-materials. In addition to decreasing the weight of the composite, the processability is significantly improved as the increase in polymer viscosity reduces with decreasing the GF content. In conclusion, the results lead to hybrid composites that combine the advantages of nano-materials and micro-size reinforcements.
Gas Plasma for Molecular Re-Engineering of Microfluidic Devices
Technology advances in the microfluidics industry are rapidly expanding global usage of low cost Point-of-Care and companion diagnostics. Although commodity polymers meet the cost profile, they often do not meet all key performance criteria; most notably stable surface wetting of biological fluids or reagents. Gas plasma technologies are increasingly employed to meet the demands of material selection through the molecular re-engineering of surfaces. Plasma modification using low temperature gas enables stable wetting with long shelf-life, chemical functionalization without wet chemistries, and thin film coating for promoting adhesion, barrier, or anti-fouling properties. The work herein provides an overview of plasma surface technologies and their role in the emerging diagnostic arena.
Thermotropic Liquid Crystalline Polymers and Their Fiber Reinforced Composites for Hydrogen Storage Applications
Thermotropic liquid crystalline polymers (TLCPs) are attractive candidates for manufacturing hydrogen fuel storage vessels because of the combination of their outstanding mechanical, barrier, and thermal properties. In this paper, basic mechanical properties of both unfilled and fiber reinforced TLCPs are reported. Significant enhancement in stiffness is observed by incorporating glass fiber and carbon fiber into TLCP matrices. Solidification behavior of TLCPs was studied by rheological experiments in an effort to establish processing conditions. Results reported in this paper build a solid foundation for understanding TLCPs' behavior and help establish parameters for processing these materials via extrusion blow molding.
The Influence of Atmospheric Pressure Plasma Surface-Modified Polymers PVDF, ECTFE, and Peek on Primary Mesenchymal Stem Cell Response
The body’s response to an implanted material depends upon many factors, including biological interactions at the interface of the implant and its surroundings. Selectively modifying the surface of biomaterials is a practical approach to induce a site-specific desirable biological response. The fluoropolymers, polyvinylidenedifluoride (PVDF), ethylene-chlorotrifluoroethylene (ECTFE), and engineering resin, polyetheretherketone (PEEK), are known for their chemical resistance, thermal stability, and low surface energy, a great combination for low biological activity and, thus long-term stability, but very little integration with surrounding tissue. Atmospheric pressure plasma (APP) a clinically-safe plasma method, was applied to the substrates to functionalize the plastic surfaces for a more polar and hydrophilic environment. Freshly isolated mesenchymal stem cells (MSCs) were cultured on the surfaces in order to expand on the limited knowledge of topographical effects on differentiation of stem cells. To assess the cellular activity on each surface, modified and unmodified, biological assays were performed to understand cellular morphology, cytoskeletal structure, viability, and differentiation. Surface energy calculations via contact angle measurements showed a significant increase after plasmatreatment on each material. Crystal violet assay indicated an increase in cell viability from APP compared to unmodified surfaces. Visualization of nuclei and - tubulin via immunofluorescence indicated greater cellular activity from APP treatment. Scanning electron microscopy (SEM) imaging showed spherically-shaped MSCs had greater activity and attachment on the APP treated surfaces.
Fabrication and Improved Performance Evaluation of Poly-(3-Hydroxybutyrate-co-3-Hydroxyvalerate) with High Molecular Weight Natural Rubber for Novel Composites
PHBV (Poly (3-hydroxybutyrate-co-3-hydroxyvalerate)) is a bio-derived semi-crystalline polymer of interest to the packaging industry looking for alternatives to the petroleum based materials currently used. The brittle nature of PHBV material requires blending with other polymers such as Poly (?-caprolactone) (PCL), Poly (L-lactic acid) (PLA), and natural rubber. Natural rubbers (NR), cis-1,4-polyisoprene, are classified as elastomers due to their high elasticity and yield strength. Therefore, the objective of this study was to characterize the thermal and mechanical properties of PHBV blended with natural rubber in two different concentrations.
The Open Hole Compression Test for Evaluation of the Effects of Fiber Waviness in Fiber Reinforced Composites
In this study, we investigate the open-hole compression (OHC) test for evaluating the effects of fiber waviness in continuous fiber reinforced composites. The OHC specimens are fabricated from carbon fiber / epoxy into unidirectional laminate containing intentional waviness defects. The effect of the waviness morphology is also investigated by evaluating the effects of the resin pocket at the root of the waviness profile. Temporal evaluations of the load-deformation response, microscopy and acoustic emissions are used to understand the failure modes from the waviness specimens. The waviness specimens show different failure modes and can be structurally correlated to either kink zone formation and fiber fracture or interlaminar damage. The results also show the influence of the notch and the resin pocket on the interlaminar strain responsible for initiation of damage in the composite specimens.
Improvement of Melt Strength and Crystallization Rate of Polylactic Acid and its Blends with Medium-Chain-Length Polyhydroxyalkanoate through Reactive Modification
Poly(lactic acid) (PLA) was reactively modified by using a multifunctional co-agent (triallyl trimesate) in the presence of dicumyl peroxide. The viscosity, elasticity and melt strength of PLA increased substantially following reactive compounding. Furthermore, the rate of crystallization of co-agent in modified PLA was significantly higher than that of the pristine PLA and a distinct crystallization peak appeared. Reactively modified blends of PLA with an elastomeric polyhydroxyoctanoate exhibited similar features, and significant improvements in blend morphology.
Catastrophic Failure of Fiber-Reinforced Thermoplastic Lawnmower Wheels
Three instances of riding lawnmower, fiber-reinforced thermoplastic wheel failures resulting in serious injuries have been examined. The wheels fractured violently due to the presence of fatigue cracks. The failure mechanism is fatigue initiation and growth during normal service followed by brittle overload fracture upon handling (e.g., tire inflation). One of the wheel failures is described in detail herein. Several design and manufacturing issues may have contributed to the failure: (1) cracks initiate and grow by fatigue at weak points in the design; (2) glass fiber orientation is nonrandom and predominantly in a direction that is ineffective in preventing fatigue crack propagation; (3) voids in the plastic weaken the part by reducing the effective cross sectional area; and (4) the polypropylene resin was apparently contaminated with polyamide. Crack path analysis was a very valuable tool used to understand the fractures.
Thermal, Mechanical, Rheological and Dielectric Properties of Clay-Containing SEBS Nanocomposites: Effect of Morphology
In this paper, intercalated vs. exfoliated structures of clay-containing nanocomposites of polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene are studied. The morphology of the nanocomposites, characterized earlier by microscopy and Small Angle X-Ray Scattering, is confirmed through the study of the thermal, mechanical, rheological and dielectric behavior. In particular, the improvement of the thermal stability of the polymer matrix was induced by the intercalated structure while the viscoelastic behavior and the mechanical and dielectric relaxation phenomena were more sensitive to the exfoliated structure.
Effect of Solvent Volatility on Diameter Selection of Nanofibers Produced by Gas Jet Fiber Process
Gas Jet Fiber (GJF) process involves aerodynamic forces to draw a jet of polymer solution from a nozzle and to convert it into polymer nanofibers. The jet of polymer solution undergoes rapid stretching and turns into solid nanofibers as the solvent evaporates. The nanofibers are collected as non-woven mat. An important parameter defining the nanofiber properties is fiber diameter. This work investigates selection of diameter of nanofibers from homogenous solutions of two immiscible polymers in two mutually miscible solvents. Several morphological forms such as interpenetrating network, bilobal, and core-shell are obtained by selecting two solvents with different vapor pressure and solubility parameters. This paper addresses the roles of polymer solution viscosity and solvent volatility in defining polymer fiber diameter varying between 1 µm and 100 nm.
Increased Strength and Thermal Conductivity in MWCNT/Epoxy Composites by Ultrasonication Aided Internal Mixing
To explode epoxy processing methods and overcome limitations of shear mixing and ultrasonication, internal mixer containing laminated kneading block structured rotors are designed and then the unites assemble configuration is optimized by evaluating mixing parameters of epoxy mixing field with the help of POLYFLOW software. Moreover, tip ultrasonication horn is integrated into the sealed barrel positioning at confluence areas between couple rotors to apply ultrasonication field simultaneously during mixing. Kinds of multi-wall carbon nanotubes are mixed with epoxy to prepare reinforced composite. Series characterizations are performed, including SEM, TGA/DSC, tensile test and thermal conductivity measurements to verify the equipment’s mixing capability. At 1.5wt% loading rate, significant mechanical improvements (above 27%) and thermal conductivity increase (above 22%) are observed, indicating excellent nanotubes dispersion and distribution in epoxy matrix.
Bio-Based Elastomers from Cationic/Free Radical Polymerization of Soybean Oil
Recently bio-based polymers procured from different natural resources have attracted greater attention as the viable eco-friendly alternatives to traditional petroleum-based products. Among various bio-based materials, vegetable oils represent one of the most abundant, low cost renewable material having the potential to be an ideal alternative to chemical feedstock/ traditional synthetic polymeric materials. Different derivatives of vegetable oils can be used as preliminary resources for the synthesis of a variety of materials (e.g. polyols, glycol, lubricants and plasticizers for polymers) owing to the high reactivity of their oxirane rings. So in this project, we have synthesized different soybean oil based elastomer using cationic/ free radical polymerization. Some preliminary study on the dynamic mechanical behavior of the synthesized elastomer has also been carried out.
Study of Mechanical Properties of Soy Flour Additives in Elastomer Composites
Bio-based polymers and biofiller polymers are becoming viable alternatives to petroleum-based plastics and offer increase bio-content at the end of service life compared to conventional plastics and rubbers. Advantages of soy flour include being lightweight, low cost, high strength and stiffness but interfacial adhesion poses to be an issue. In this project, soy flour as an additive to synthetic rubber matrix based composites were studied. Surface modification such as acetylation and grafting with PMMA were compared to untreated soy flour composites. In general, untreated as soy concentration increased, the mechanical properties of the composites decreased. In contrast, pretreated soy flour (acetylated soy flour and grafted soy flour) at 10wt% performed comparable to that of the neat rubber and resulted in an increase in tensile stress.
Effect of Feature Spacing when Injection Molding Parts with Microstructured Surfaces
The effects of microfeature spacing on the replication of thermoplastic elastomer features was investigated using micropillars with two diameters (10 and 20 ?m) and three spacing ratios (0.5:1, 1:1, and 2:1). The tooling and part features were characterized for feature depth and height as well as feature definition using scanning electron microscopy and optical profilometry. Feature spacing significantly affected the replication of micropillars using a thermoplastic elastomer. This replication was competition between cooling and pressurization of the melt. Wider spacing between smaller features allowed cooling in the tooling lands to dominate the feature filling. Higher pressures did not always produce better feature replication, suggesting that cooling effects in the tooling “holes” restricted filling. High pressures also produced surface porosity in the molded pillars.
Comparison of Microstructured Surfaces Using Injection Molding and Nanoimprint Lithography
For the first time, thicker (2.4-mm) polycarbonate and polymethylmethacrylate sheets were employed in thermal nanoimprint lithography. The replication of microfeatures using this process was influenced primarily by imprinting temperature and not by imprinting pressure and time. Imprinting of thicker sheets generally showed the same replication trends as injection molding – i.e., channel depth increased with lower viscosity materials, definition of the channel bottom improved with increased solidification time, and land formation required complete replication of the channels. The higher temperatures in injection molding increase thermal and shear-induced stresses, thus increasing shrinkage and decreasing feature definition.
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