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.
Effects of moisture exposure on scratch performance of polymethylmathacrylate (PMMA) and polypropylene (PP) were investigated. Three different grades of PMMA and PP with varying levels of polarity and molecular weight were chosen and their scratch resistance compared in both dry and moist conditions. Linear increasing load scratch tests were performed according to ASTM D7027/ISO 19252 standards. Results indicate a drop in scratch resistance with initial exposure to moisture in all three PMMA systems. In the two highly polar PMMA systems, the scratch resistance recovers to that of the dry condition after exposure to moisture while PP scratch resistance remains unchanged. It is proposed that the moisture absorbed initially acts as a plasticizer causing weakening of the surface for PMMA. In the case of more polar systems this moisture absorption continues until saturation where water molecules cluster and impart a degree of lubrication and consequently improve scratch resistance.
A novel method of improving the ductility of injection molded plastic parts has been developed. By applying either gas-laden pellet technology or microcellular injection molding to polymer blends or composites of proper material formulations, the ductility and toughness of the molded foam parts can be significantly improved compared to those of solid parts. The key is to achieve a microcellular structure with a sub-micro scale immiscible secondary phase. Upon tensile loading, cavitation of the secondary phase facilitates the interconnection of microcellular voids to form channels such that the stretched component becomes a bundle of fibrils. This change in structure turns the fracture mechanism from crack propagation across the matrix into shear yielding of a bundle of fibrils in the loading direction. Compared with other toughening methods, this method achieved a more significant improvement in ductility and toughness with reduced material consumption and lighter part weights.
High solvating plasticizers have recently been of interest in industry in regards to PVC melt compounding. Dibenzoate plasticizers comprise a family of high solvating plasticizers that have been known for the beneficial effects they impart to vinyl. In the pursuit of improving dry blend characteristics and conserving manufacturing energy usage, a study was conducted to determine the effects of dibenzoate plasticizers both alone and in blends with general purpose plasticizers. The dry blends were analyzed using a torque rheometer under both isothermal and constant heat ramp conditions. Experiments with plasticizers on a PVC resin have shown dibenzoates to improve processing time over the use of general purpose plasticizers alone, and plasticizer blend experiments have given insight into the utility of incremental benzoate usage. Further experimentation indicated that pressure application to dry blends gives further insight into the level of plasticizer incorporation.
In order to reduce the energy consumption in processing and improve the productivity, Direct Fiber Feeding Injection Molding (DFFIM) technology is developed and established. In this study, the carbon fiber (CF) from four different companies and polycarbonate (PC) resins were used to mold the CF/PC dumbbell specimens. Nano Indentation technique with cycle load test method was adopted to evaluate the interfacial property of CF/PC composites and Kelly-Tyson Model was used to calculate the interfacial shear strength based on tensile test and the fiber length distribution. Scanning electron microscope (SEM) observation on the interface after tensile test was applied to relate the change in mechanical properties with the interfacial fracture mechanisms. It is found that Nano Indentation test with cycle load method is an effective method to estimate the interfacial property and the results reveal good agreement to Kelly-Tyson model. Due to the different interfacial property, these four kinds composite have significant different mechanical properties.
A major design consideration and benchmark for a high quality injection molding hot runner system is color change performance. The focus of this project was to evaluate the effect of temperature uniformity and surface finish on color change performance and frozen layer formation. Trials were conducted using two hot-sprues, with different surface finishes and configurable heating elements, representative of typical configurations. The thermal profile of each sprue was mapped at steady state conditions prior to processing. Sprue pulls were then performed to study the efficiency of each color change and results. It was determined that temperature uniformity greatly altered a system’s color change performance. Cool regions in the sprue formed frozen layers of the original material that would re-melt over subsequent cycles negatively impacting the color change performance. The effect of surface finish on color change performance was less definitive and dependent upon frozen layer formation.
This research work presents the first developed multilayer co-extrusion system for high viscosity elastomer materials. Three unvulcanized rubber materials were chosen; two butyl rubbers and a polyisoprene. The elastomers were characterized under oscillatory shear conditions and placed into either a rheologically ‘matched’ or a ‘mismatched’ category. Multilayer co-extrusion was achieved at a total of 8 layers then 32 layers; with two different extrusion rates. Results show good layering performance for both systems; however, interestingly, the rheologically mismatched systems showed a better layer quality as well as a more stable variation coefficient with an increasing amount of layers.
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%.
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).
A novel additive manufacturing approach was investigated for fabrication of steel tooling with microstructured surfaces. Varying processing parameters (printing pressure and speed) as well as material viscosity provided better control of microfeature height and width. Viscosity significantly affected feature uniformity, with higher viscosity materials producing narrow lines and more uniform feature heights. This tooling was unchanged after 5000 injection molding cycles, and so, has great potential as microstructured tooling for microfluidic devices.
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.
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.
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.
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.
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 (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 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.
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.
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.
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.
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.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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