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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Aging Behavior of Polyamide 12 during Selective Laser Melting Process ? Influence on Mechanical Properties
Selective laser melting is a well-established manufacturing technique in prototype construction. In recent years a tendency to rapid manufacturing applications and the production of ready to use components with this technology can be observed. If components made by laser melting are desired to be applied in technical series products, their achievable properties play a major role. The high process temperatures in combination with long build times during laser melting process lead to chemical and physical aging mechanisms on the polymeric feed material. The unmolten partcake material, which acts as a supporting structure, can be removed after each building process and reused for further processes. To achieve part properties which endure the necessary mechanical loads, refreshing of partcake powder with 30 up to 50 % by weight virgin material is necessary. However, constant refreshing strategies will lead to varying component properties due to an undefined aging state of the basic partcake material. Therefore, a fundamental understanding of the correlation between the feed material aging state and resulting mechanical properties is alienable.
This paper deals with the analysis of the relationship between the aging state of the feed material focused on rheological behavior, mechanical part properties and deformation behavior. Therefore, polyamide 12 powder is used for at least five processing cycles without refreshing. Before and after each build process, bulk and material characteristics like bulk density, hausner ratio, viscosity number, melt volume rate and average molecular weight were determined. Tensile tests were conducted in order to study the mechanical material and deformation behavior. Finally, mechanical behavior as a function of feed material can be evaluated. On this basis, powder life cycles in dependency of mechanical properties can be derived.
Influence of Cellulosic Filler Content and Morphology on the Drying and Processing of Polylactide Acid (PLA) Composites
This study examines the influence of different amounts of filler content and particle size on residual moisture in Polylactide Acid (PLA) compounds after drying. Also the influence of a hydrolysis stabilizer is verified. The measurement parameters for this study are the melt viscosity rate and differential scanning calorimetry. The results show a distinct influence of filler content and particle size on the residual moisture of the PLA compounds. An increase of both parameters leads to rising residual moistures. With increasing residual moistures, melt viscosity increased also. Due to the usage of an empirically determined formula, melt viscosity measurements of PLA compounds with varying moistures and filler content can be compared. The usage of the hydrolysis stabilizer caused a significant reduction of the melt viscosity of a PLA compound, while retaining the same residual moisture.
Engineering Resin Based on Post-consumer Recycled Polyamide 66 from Carpets
This study provides foundation for the development of a post-consumer recycle resin with low purity Post Consumer Recycle Polyamide 66 (PCR-PA66) and no delamination. These resin were developed using a novel concept of maximizing usage of low purity PCR-PA66 while maintaining part functionality. Main impurities in the PCR-PA66, which are calcium carbonate, latex, polypropylene, colorants and additives need to be taken into consideration to come up with a robust product. From these contaminants polypropylene (PP) present in the carpet backing and carried over in the PCR-PA66 stream causes serious potential for delamination and will be discussed in depth. A fixed amount of glass reinforcement provides part functionality, and total aim reinforcement was targeted to 36%. Delamination test was developed and this study aimed to uncover how to predict, measure and avoid potential of delamination while maximizing usage of low purity PCR-PA66. This paper describes the properties of optimized resins and boundary regions.
Effects of Gamma Sterilization on Low Density Polyethylene Film
Low-Density Polyethylene (LDPE) films were exposed to gamma irradiation at exposure levels of 40 kGy and 80 kGy. Virgin pellets, 0 kGy, 40 kGy, and 80 kGy films were then tested for melting behavior, crystallization behavior, secondary thermal transitions, complex tensile modulus, and molecular weight. Modulated Differential Scanning Calorimetry (mDSC) and standard DSC were used to characterize the thermal performance and Dynamic Mechanical Analysis (DMA) was used to characterize the complex modulus. GPC was used to characterize the molecular weight.
In this case, small changes in the thermal and modulus mechanical properties were found at 40 and 80 kGy irradiation levels. However, at the same time large increases to the molecular weight were observed. The antioxidant concentration was found to be relatively stable at these gamma irradiation levels. Although additional stress-strain behavior is needed for full validation, overall the LDPE film studied here offers excellent resistance to gamma sterilization. But even for this LDPE, gamma irradiation does have a significant effect on the structure in terms of defect incorporation, chain scission, and crosslinking. This study supports the understanding that it is critical to verify performance as a function of irradiation dose for new formulations, grades, or polymer chemistries of medical-grade polymers.
Linear and NonLinear Rheology of Poly(Butylene succinate)/Fumed Silica Nanocomposites
In this work, the role of shear deformation on the microstructure of nanocomposites formed by compounding poly(butylene succinate) (PBS) with neat and surface functionalized fumed silica is explored by melt state rheology. The rheology results uncover a unique structural evolution from shear start-up in nanocomposites, including formation of a physical network under steady shear. The linear viscoelastic responses show that the shear-induced network can result in increased elasticity and a second shear thinning regime at low frequency. The materials compounded with hydrophobic organically modified silica display shear-induced reinforcement at lower particle loadings than those with hydrophilic fumed silica. These results indicate that reinforcement in nanocomposites can be controlled by filler surface functionality and shearing effects. This method enables improved mechanical properties with low filler loadings.
Effects of Shear and Extensional Flows on the Electrical Properties of Polycarbonate/Carbon Nanotube Composites during Injection Molding
Electrically conductive composites made from polycarbonate (PC) and two different types of carbon nanotube (CNT) were compounded and subsequently molded in order to glean effects of the injection molding process on the electrical properties of the materials. A typical multiwalled CNT and a highly branched, crosslinked CNT were investigated to determine the effect of initial nanotube morphology. All composites were molded through three geometries: shear dominated, mixture of shear and extension, and extension dominated. It was determined that the initial nanotube morphology was the largest contributing factor to the final electrical properties of the composites.
Toughness Study of Center Cracked Polypropylene Films with Temperature Effect
The manufacturing of a cast film with high orientation has little forgiveness for imperfections embedded within the polymer web. Imperfections such as gels, dirt and other contaminants can lead to web breakage and hence downtime which affects productivity. In this study, the effect of defect size on the failure of a web is studied using a model system that simulates the defect by a slit crack. The toughness of the film can be assessed as a function of defect size. In this study, polypropylene (PP) cast films were used for this investigation and the toughness is determined using an MTS Sintech Tensile tester.
Our test results showed that un-notched PP homopolymer films exhibit fully ductile behavior at both temperatures, 23øC and 40øC. However, increasing the center crack length resulted in decreased in toughness and at above 3 mm in crack length, the PP cast film failure mechanism changed from fully ductile to brittle like failure.
Development of Crosslinked Polyethylene by Using a Tin-Free Silane Cocktail
A linear low density polyethylene was crosslinked using a vinyl cyclic alkoxy silane, initiator, and non-tin catalyst. At first, silane cocktails were developed by mixing vinyl cyclic alkoxy silane, initiator, anti-oxidant, and various non-tin catalysts. Next, using such silane cocktails, a series of crosslinked polyethylenes (XLPEs) were produced. The mechanical properties and extent of crosslinking of resulting XLPEs were compared to those of a XLPE produced by using dibutyl tin dilaurate as a catalyst. The result indicated that cyclic silane cocktails containing non-tin catalyst can effectively crosslink the polyethylene.
Rheological Characterization on Thermal Stability and Flow Instability of Ethylene-Tetrafluoroethylene Copolymer
Viscoelastic properties of ethylene-tetrafluoroethylene copolymer (ETFE) in the molten state are evaluated in detail considering the thermal stability during the measurement at high temperature with/without oxygen. It is found that random chain scission reaction occurs without crosslinking even under a nitrogen atmosphere at 300 §C. The steady-state shear compliance Je0, which is affected by the molecular weight distribution strongly, is unchanged during the chain scission, suggesting that the chain scission occurs with keeping the molecular weight distribution. According to the classical theory on the random scission reaction, this result demonstrates that the polydispersity (Mw/Mn) of the virgin ETFE sample, prior to the exposure to thermal history, is closed to 2. On the other hand, ETFE shows crosslinking reaction under air condition even in the cone-and-plate rheometer. The degree of crosslinking is estimated by the plateau modulus G?plateau in the low frequency region.
In addition, flow instability at the capillary extrusion is evaluated. ETFE shows several types of melt fracture over a critical shear stress, e.g., shark-skin, slip-stick and wavy melt fracture. It is interesting to note that quasi-stable flow region is observed between slip-stick and wavy melt fracture regions. It suggests that ETFE can be processed at a high out-put rate condition by the steady slip.
Bioplastics for Solar Thermal Applications: Potential of Bio-Poly(Ethylene) and Poly(Trimethylene Terephthalate) for Swimming Pool Solar Collectors
Within this study bioplastics ? bio-poly(ethylene) and poly(trimethylene terephthalate) ? i.e. polymers based on renewable resources, are comprehensively evaluated and tested as to their principle applicability as absorber mate?rial in swimming pool solar collectors. Investigations showed that the considered bioplastics possess a high potential for application in solar thermal devices in general. However, further optimization, especially of long-term performance and maximum operating temper?ature by tailoring molecular and super-molecular structure as well as by addition of additives and fillers is required.
A New Method for the Calculation of the Spherulite Growth in Solidifying Semi-Crystalline Polymer Melts
This paper presents a new algorithm named Continuous Cellular Growth" (CCG) method for the calculation of the crystal growth process of spherulites in solidifying semi-crystalline polymer melts. The concept is developed in one dimension then transferred to three dimensions and finally implemented as an executable algorithm in the in-house code Sph„roSim. The CCG method is compared to an inaccurate but fast Monte-Carlo based and an accurate but slow integration based growth algorithm which uses a Raytracing method. It turns out that the results of the CCG method are very close to those of the integration method with differences of only a few percent. Howeverthe computation time was reduced by two orders of magnitude compared to the Raytracing method and thus is only slightly above the computation time of the Monte Carlo algorithm."
A Novel Method to Make Highly Crystalline PET Articles by Powder Compaction
Highly crystalline parts of PET are difficult to produce by conventional injection moulding methods, as PET crystallises slowly from the melt. Here, a method adapted from powder metallurgy is employed to fabricate highly crystalline PET articles. It involves using highly crystalline PET powder and compacting it at 5-30øC below the bulk melting temperature of the PET (that is, at 230 to 255øC). This allows consolidation of the powder to form a part with the high crystallinity levels similar to the original powder. The highly crystalline articles of PET made by powder compaction had a Vicat softening point > 200øC, high modulus, high hardness, and high creep resistance.
Development of a Relaxation Model for Annealing of Plastic Films and Sheets
Controlling shrinkage levels during converting is one of the most important critical customer requirements for many applications of plastic films and sheets. Shrinkage levels of 40-60% are common for cast films and calendared sheets. Shrinkage reduction can be accomplished by a subsequent annealing process after the extrusion casting/calendaring process. In this paper, we established a relaxation model for predicting the shrinkage level of plastic films/sheets upon the completion of the annealing process. Specifically, this model correlated shrinkage level of plastic films/sheets after annealing with the relaxation time of a polymer obtained by dynamic rheological measurement as well as the annealing conditions such as temperature profile and residence time. This relaxation model is very useful for determining the design parameters of an annealing process as well as for optimizing the annealing conditions such as annealing temperature and line speed.
Effects of Compounding Set-Up on Electrical Conductivity Properties of Carbon Black Filled Compounds
Conductive carbon black is commonly used to permanently modify the electrical properties of plastic compounds from insulating to conductive. Some applications require a high degree of dispersion; for example, thin sheets for electronic packaging, cable semicons or electrically conductive pipes do not tolerate undispersed carbon black. In this article we investigate three compounding routes via twin screw extruder showing how incorrect setups can dramatically decrease the quality of the final compounds. We also show that poor carbon black feeding or very high melt viscosity of concentrated compounds (like masterbatch) can have detrimental effects on the electrical properties. Finally, we show that the degree of dispersion is strongly dependent not only on the melt viscosity but also on the carbon black selected.
Direct Adhesion of Plastic and Stainless Steel Using Conductive Heating in the Injection Molding Process
The injection molding process enables the production of plastic/metal hybrid components in large scales. State of the art is the use of adhesion promoters to achieve a joining of the incompatible materials. This material bonding technology allows a wide, homogeneous force transmission into the hybrid component. Therefore the metal components are coated upstream.
It is possible to waive adhesion promoters and achieve a direct bond between plastic and metal. In this case the metal insert has to be heated up to a temperature in the range of the melt temperature of the polymer. This paper describes an innovative heating concept for metallic inserts wherein the metal insert acts as a direct heating resistor.
New Materials for Fluid Injection Technique ? Improved Properties with Reactive Polyurethanes
Even though the solidification behavior of reactive polyurethane (PU) differs from that of thermoplastics, this material can be used for the projectile injection technique. The technology combines the excellent properties of PU with the economic benefits of injection molding and enables the production of complex elastomeric fluid-conducting hoses with adjustable flexibility and high impact strength. Additionally, the integration of a continuous fiber reinforcement leads to improved bursting strength in comparison to short fiber-reinforced thermoplastics.
The Effect of Crosslinks on the Mechanical Properties of Elastomers: Experimental Characterization and Modeling
The conditions of the forming process influence the crosslinking distribution in rubber parts and therefore the resulting mechanical properties significantly. In order to ensure a precise dimensioning of rubber parts, a method has been developed that considers the process-related crosslinking distribution in structural simulations. The dependency of the mechanical properties on the local crosslinking degree is taken into account by coupling a process simulation with a program for structural finite element analysis (FEA). For this purpose, an interface is implemented, which correlates the crosslinking parameters of the process simulation with mechanical characteristics and passes these data to a subsequent structural analysis simulator. The developed method is based on physical and mechanical tests of partially and fully crosslinked elastomers.
LLDPE-EVOH High Barrier Blend Films Fabricated by Multiplication Extrusion
Blends of linear low-density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) with different weight fractions are prepared by a twin-screw extruder at A. Schulman Inc., Akron. These compounded blends are then melt-extruded to fabricate thin films at CWRU, Cleveland. We discover that with 50-50 weight fraction, co-continuous morphology exists. Different numbers of multipliers are therefore utilized to tailor the morphology of the extruded blend films with 50-50 weight fraction. As the number of multipliers increases, the blend film morphology transforms from an elongated and layer-like structure to homogeneous mixture feature. This is because during the multiplication process, the multipliers behave similar to static mixers that physically break the elongated and layer-like structure into tiny domains. As the morphology evolves, the physical properties of the extruded blend films change dramatically accordingly. Both the gas permeability and the light transmission rate of these films increase as the number of multipliers increases. More interestingly, the tensile mechanical behaviors become isotropic at different deformation directions. Atomic force microscopy (AFM) is utilized to investigate the morphology of the blend films. Oxygen transport rate (OTR) and water vapor transport rate (WVTR) of these blend films are measured by MOCON units. The transmission rate and mechanical properties are studied by UV-vis and a mechanical tensile stretcher (MTS), respectively.
Degradation of Microcellular PLGA-PEG Copolymer for Use in a Drug Delivery System for the Urinary Bladder
For the treatment of diseases of the bladder a drug delivery system (DDS) has been developed which can be applied intravesically. The DDS is composed of multiple carriers that consist of non-absorbable, drug-carrying microspheres which are embedded in a foamed absorbable matrix. After degradation of the absorbable matrix, the non-absorbable microspheres are eliminated through the urethra.
The foamed absorbable matrix is fabricated out of a poly(D,L-lactide-co-glycolide)-co-polyethylen glycol diblock copolymers due to its short degradation time. These polymers are temperature sensitive and therefore manufactured by the CESP process (Controlled Expansion of Saturated Polymers). The foam structure, which influences the degradation, is controlled by the process parameters.
Within this paper the influence of the process parameters on the degradation of the implants is investigated.
Failure Analysis of a Fractured Polyamide 6 Shock Absorber Housing
A polyamide 6 shock absorber housing on a jogging stroller fractured completely during service. A range of techniques were utilized in the failure analysis, including DSC, TGA, FTIR, ICP-OES, SEM-EDS, and mechanical testing. Lithium grease, calcium, and chlorine were detected on and near the fracture surface. Fracture morphology observed by SEM suggests chemical interaction played a role in initiating the fracture. The combination of mechanical stress and the presence of known environmental stress cracking (ESC) agents in CaCl2 and LiCl is suspected to have led to time-dependent crazing, cracking, and eventual fracture of the housing.
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