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 History Effect of PTFE
Failure analysis is often thought of as a technical support service for the sole purpose of fixing underperforming materials, components, systems, or processes which typically result from unforeseen, unexpected, or underestimated conditions or changes. In most cases, identifying the root cause of the issue at hand and providing a mitigation strategy are the primary functions of failure analysis, however more value can be extracted from these efforts. While it is imperative that a root cause and mitigation strategy are identified in the most efficient and effective manner, having the mindset that each effort presents an opportunity for improvement and innovation can drive an even greater impact from these investigations.
One case study will be discussed where during the process of identifying root cause and mitigation strategies of a polytetrafluoroethylene (PTFE) tube failure, additional materials characterization methods and understanding were developed that could have impact on both current and future materials characterization techniques and technology innovations. Specifically thermomechanical analysis techniques were developed to accurately identify the maximum temperature exposure of PTFE tube segments. These techniques were made possible by discovering that PTFE has an inherent thermomechanical memory behavior that effectively records the most prominent temperature excursions while under mechanical stress or applied strain.
Progress in Assessing Fiber Orientation and Flexibility with Increased Fiber Lengths
The mechanical performance of a fiber reinforced injection molded composite is determined by the fiber length and orientation within the part. During processing, significant fiber length attrition can occur which will result in a broad distribution of fiber lengths. In this work, we investigate three fiber length distributions created from the same base formulation in order to gain an understanding of fiber orientation dynamics and shear stress during the startup of simple shear flow. Results show that the rate of fiber orientation and the extent of fiber alignment will decrease with increases in fiber length. Differences in the fiber length appear to be more pronounced in measurements of shear stress in simple shear flow than direct measurements of fiber orientation. A semi-flexible orientation model is used to compare the bending contribution to stress based on measured values of fiber orientation. Trends in predicted bending stress seem to coincide with the experimental values.
A New DSC Thermopile Sensor for combined Heat Flux and Power Compensated Measurements
Claus Linseis, Linseis GmbH, Vielitzer Str. 43, 95100 Selb, Germany
The Differential Scanning Calorimetry (DSC) is the most popular analytical method used in thermal analysis for polymers. The DSC technique is applied to measure the specific heat capacity, phase transitions, curing, kinetics etc.
The performance of a DSC instrument depends on its resolution and sensitivity. However up to now it was not possible to optimize both performance parameters at the same time. There are two basic concepts of DSC instruments- the Power Compensated DSC which has a high resolution and low sensitivity and the Heat Flux DSC with an opposite characteristics.
A new DSC thermopile sensor was designed which can be operated in both modes, heat flux and power compensate. For samples with weak phase transitions or for smallest sample quantities the heat flux mode is used to achieve the highest sensitivity. For applications with several peaks within a narrow temperature range, the sensor can be switched to the power compensated mode with highest resolution.
Non-linear Rheology in Shear and Extensional Flows of Maleated PP-Clay Nanocomposites
The strain dependence of large amplitude dynamic shear moduli and the transient extensional viscosity were investigated for model polymer nanocomposites with organoclays. A linear maleic anhydride grafted polypropylene copolymer was compounded with 5 wt% each of two different organically modified clays that had different onium ion surfactants and different aspect ratios. The non-linear storage modulus for the compound with the higher aspect ratio particles showed a two stage drop with increasing strain which highlights the breakup of two structures at different rates?an entanglement network of particle attached chains with free chains and another entanglement network of free chains alone. The same nanocomposite melt also displayed a greater extent of strain hardening in uniaxial extensional flow. Both effects may be attributed to a stronger polymer mediated entanglement network in this nanocomposite.
Dispersion Effect of Extensional Flow for PP/CNT Nano-Comosite with Blister Disk of Twin Screw Extruder
Extensional flow has been shown to be more efficient solution for improving the dispersion of nano-composites as compared to shear flow. One of the production processes of nano-composites is melt extrusion with co-rotating twin screw extruder (TSE) which is superior in terms of productivity and mixing performance. Our objective is the optimization of Blister Disk geometry which has many holes for improving the dispersion of nano-composites. The holes were drilled through the Blister Disk seal ring segments to create extensional flow in TSE.
However, it was difficult to evaluate the mixing effect of Blister Disk because the flow patterns are complex in TSE, and there is some possibility of no flow through the holes of Blister Disk. To evaluate the dispersion effect of only holes, fundamental evaluation equipment was developed.
Firstly, the stress magnitude was investigated for each elongational flow and shear flow by changing the geometries (e.g., hole numbers, hole diameter and hole width) with 3D numerical simulation. Then, the dispersibility variation of polypropylene (PP) and Carbon Nano Tube (CNT) nano-composite was investigated by using various geometries of Blister Disk with fundamental evaluation equipment.
Transversal Molecular Orientation of Isotactic Polypropylene at Conventional Processing
Structure and properties of an extruded sheet and an injection-molded plate composed of isotactic polypropylene (PP) containing a small amount of N,N?-dicyclohexyl-2,6-naphthalenedicarboxamide as a ?-form nucleating agent have been studied. The nucleating agents exist as needle-shape crystals in the molten state of PP. They orient to the flow direction at processing. Moreover, PP chains crystallize on the surface, in which chain-axis of PP molecules orient perpendicular to the long axis of the nucleating agent. Consequently, PP chains orient perpendicular to the flow direction in the extruded sheet, because the needle crystals orient to the flow direction by the hydrodynamic force. Furthermore, in the case of injection-molded products, the direction of molecular orientation in the skin layer is parallel to the flow direction owing to the flow-induced crystallization. In contrast, PP chains orient perpendicular to the flow direction in the core layer because of the crystallization from the nucleating agents. The anomalous molecular orientation is responsible for the reduced anisotropy in thermal expansion
Nonlinear Structural Analysis of Short Fiber Filled Injection Molded Parts
Short fiber filled injection molded plastic parts are widely used in industrial applications due to their enhanced stiffness-to-weight and strength-to-weight ratios compared to homogeneous plastics and metals. Injection molding simulation software packages can be used to predict the distribution of fiber orientation throughout a part, in addition to the warped shape of the ejected, room-temperature part. In order to facilitate subsequent nonlinear (progressive failure) structural simulation of the short fiber filled part, Autodesk has developed new software to seamlessly link the results of injection molding simulation with nonlinear structural response simulation that features a multiscale progressive failure model for short fiber filled plastics. This paper describes the theoretical foundations and capabilities of the new software.
Preparation and Tube Shortening Effects of Multi-walled Carbon Nanotubes on Electrical and Mechanical properties of Polycarbonate/MWCNT Composites
The effect of nanotube preparation method (freeze drying (FD) vs. oven drying (OD) during synthesis) and length of three multi-walled carbon nanotubes (MWCNTs) on the dispersion and further on the percolation and mechanical behavior of polycarbonate (PC)/MWCNTs composites was investigated. Nanocomposites were melt mixed in a twin-screw micro-compounder at concentration of 0.1-3.0 wt% MWCNTs. Tensile strength was independent of MWCNT concentration while the Young?s modulus slightly increases and strain at break appreciable decreases when compare with pure PC. Scanning electron microscopy (SEM) and light microscopy (LM) micrographs revealed that at sub-micron scale shorter MWCNTs were found to be better dispersed than longer tubes, while at the macro scale the dispersion of long and short MWCNTs was comparable. Also, MWCNTs prepared by oven drying methods were found to be better dispersed at the sub-micron scale. Nanotubes with longer lengths (or aspect ratio (AR)) exhibited higher percolation thresholds (pcS) irrespective of differences in dispersion.
Chemorheological Behaviors of a Reactive Epoxy-Amine System during Isothermal Curing
For a typical reactive epoxy-amine system, the initial (Tg0) and ultimate glass transition temperatures (Tgì) prior to curing and after full cure were measured, respectively, by nonisothermal differential scanning calorimetry (DSC). The chemo-rheological behaviors during isothermal curing of the system were investigated at various temperatures below, near and above the ultimate Tgì by means of dynamic rheometry. According to the characteristics of the time-evolving viscoelastic material functions of the curing system, physical transformations, such as gelation and vitrification, occurring during isothermal curing are identified and analyzed. The dependences of such transformations are then presented in terms of a cure temperature-time-transformation (TTT) diagram, which is of critical importance to providing a practical guidance for the relevant process development in manufacturing a medical device.
A Framework for Viscosity Model Research in Injection Molding Simulation, Including Pressure and Fiber Orientation Dependence
A framework for the use of user-defined viscosity routines inside a commercial injection molding simulation package is presented. This functionality will allow external academic researchers to directly modify the injection molding simulation and study the utility of any newly proposed models on complex parts and processes. This functionality is illustrated by the use of two example cases. In the first example, alternative models for pressure dependence of viscosity are coded via this framework and the resulting pressure predictions are compared against molding data. The second example examines the role of fiber orientation in modifying viscosity and therefore influencing the filling pattern and the fiber orientation distribution itself. Comparison is again made with a reported molding case.
Effects of Gas Counter Pressure and Dynamic Mold Temperature Control on the Mechanical/Foaming/Surface Roughness Properties of Microcellular Injection Molded PP Parts
This study investigated the effects of the gas counter- pressure technique (GCP) and dynamic mold temperature control (DMTC) on the mechanical/foaming/surface roughness properties of microcellular injection molded Polypropylene (PP) parts. In the gas counter-pressure technique nitrogen fills up the cavity during the injection molding process. This can delay the foaming process and affect the microcellular injection molding process. The results showed that the tensile strength decreases with the counter pressure and increases as holding time is increased, while the flow length decreases as the holding time increases. The cell size decreases as the holding time increases. The surface roughness is improved by the foaming PP with high DMTC.
Systematic Determination of Parameter Influences on Wall Thickness Distribution for the New Special Injection Molding Process Direct GITBlow
The special injection molding process GITBlow, developed by Polymer Engineering Paderborn (KTP), combines the established processes gas-assisted injection molding and blow molding. With GITBlow large, thinwalled hollow space geometries can be created. The preform is produced via gas-assisted injection molding and is then further inflated via a second gas injection. In this study the influence of the varied parameters on the temperature distribution in the preform wall are analyzed. Subsequently a guideline is developed for the approximate optimization of material specific operating points, especially concerning the required parameter settings for the first gas injection.
Effects of Cycloalkylcarboxylic acid Derivatives as Coadsorbents on the Photovoltaic Performance of Dye-Sensitized Solar Cells
Effects of cycloalkylcarboxylic acid derivatives as coadsorbents on the photovoltaic performance of D908 dye sensitized nanocrystalline TiO2 solar cells were investigated. Cyclopentylacetic acid (CPAA) coadsorption was revealed to improve both the photocurrent and the photovoltage of the solar cells.
The improved photocurrent was probably due to suppression of self-quenching of the excited electrons in the dyes by coadsorption of CPAA on the TiO2 and increased the electron-injection yields from the dye to the TiO2.The improved photovoltage was probably due to suppression of recombination between the injected electrons and I3- ions on the TiO2 surface.
ATR-FTIR spectroscopy indicated that CPAA coadsorption increased the content of bound dye on the TiO2 surface. This result suggests that CPAA coadsorption improved the photocurrent of the solar cells.
New Hydrogenated Styrenic Block Copolymers for Compounding Solutions
Two new hydrogenated styrenic block copolymers of the poly(styrene-b-ethylene/butylene-b-styrene) or SEBS type, MD6958 and MD6959, were designed with high molecular weight, enhanced rubber segment midblock and relatively higher polystyrene content. MD6958 has the same molecular weight as G1633, the highest molecular weight grade produced by Kraton Polymers. The enhanced rubber segment midblock means that both polymers contain higher butylene content in the midblock than other traditional SEBSs such as G1651 and G1633. Polystyrene content is 35% for MD6958 and 40% for MD6959, respectively. This paper reports the characteristics of these polymers and properties of their compounds with oil and polyolefin. The high melt flow, decent high temperature performance and low hardness of their compounds open up new formulating opportunities to solve challenges faced by applications requiring both good processibility and excellent high temperature performance.
Compatibilized Polyetherimide and Polyarylene Sulfide Blends
Polyetherimide and Polyarylene sulfide resins are high performance thermoplastics; both are characterized by excellent combination of properties but are also deficient on few. Their blends are expected to overcome the shortcomings of the individual resins. Unfortunately, they form incompatible blends with phase separation and delamination with little or no phase interaction between the two phases which will result in reduced properties. In this report, compatibilized blends of amorphous polyetherimide, thermoplastic polyimide (TPI) and polyetherimide-siloxane copolymer resins with semi-crystalline polyarylene sulfide resins are described which offers excellent mechanical properties, thermal resistance and chemical resistance, suitable for many high temperature applications.
Synthesis and Characterization of Biopolyesters from Refined Crude Glycerol and Succinic Acid
The synthesis of biopolyesters based on refined crude glycerol and succinic acid was studied aiming to determine the influence of the molar ratio of reactants (glycerol to succinic acid) in the extent of reaction and main physic chemical properties of the products. Industrial crude glycerol refined up to 96 wt% glycerol content was employed as monomer for the synthesis along with succinic acid and the reaction was stopped before reaching the gel point in order to obtain non cross-linked products. These polyesters were characterized by gas chromatography, FTIR and thermal gravimetric analysis. It was shown that the molar ratio of reactants employed determines the amount of unreacted monomers present in the final product.
Synthesis of Lignin Based Carbon Particles and Their Performance as Fillers in Bionanocomposites
Bioethanol lignin based carbonaceous powder was prepared using carbonization and ball milling optimization to provide a material that may be used as a substitute to carbon black. The resulting carbon powder showed greater surface area and thermal conductivity to carbon black with particle sizes around 1 micrometer. The carbonized ball milled lignin was then compared against commercial carbon black as filler in the formation of thermoplastic composites. The lignin based carbon filler was able to perform similarly to carbon black by increasing the thermal conductivity but no enhancement in the electrical conductivity was evident for the biobased filler.
Impacts of Different Mechanisms on Carbon Nanotubes/ Polymer Nanocomposites? Piezoresistivity
Superior electrical conductivity and extremely high aspect ratios of carbon nanotubes (CNTs) have made them effective filler to fabricate electrically conductive polymer nanocomposites (PNCs). Through disruption of the CNT conductive network, variation in the tunneling resistance among CNTs, and piezoresistivity of CNTs, PNCs also exhibit piezoresistivity for strain sensing applications. In this work, an improved three-dimensional CNT network model has been extended to investigate the piezoresistive behaviours of PNCs. Simulation results demonstrated good agreement with various experimental measurements. Subsequently, numerical studies were conducted to elucidate the impact of each mechanism on PNCs? macroscopic piezoresistive responses to external strain.
Process Planning of Mold Components with Feature Recognition and Group Technology
The machining process of plastic injection mold components is complex and continuously changing, and traditional practices rely on the experience and technique of professionals. In order to avoid the impact on business operations and losses, the geometric information of computer-aided design (CAD) systems should be converted into the manufacturing system required for computer-aided process planning (CAPP) and computer-aided manufacturing (CAM) systems through the integration of automatic feature recognition and group technology; thereby eliminating manual planning and shortening the planned lead time to realize CAD/CAPP/CAM integration and application. As part design is feature-based, each processing step can be regarded as a feature. This study applied hybrid recognition technology integrating the graph-based approach, rule-based approach and hint-based approach to analyze and identify injection mold component shape features. Then, it established classification coding for data description according to the injection mold components before searching for the corresponding manufacturing processes in the database using the group technology. The case proved that the CAPP in this study could reduce about 90% of the working time needed. It could accelerate the component planning process and integrate with the mold manufacturing scheduling to realize automated design and manufacturing.
Thermal Analysis of Conventional and Rapid Tooling for Injection Molding
The thermal behavior of inserts manufactured via rapid tooling was compared to conventional machined inserts. Machined T-420 stainless steel, direct metal laser sintered bronze and jetted digital-ABS photopolymer inserts were studied. Full 3D models of the inserts, part, and mold geometry were created and analyzed via computer simulation of the process. The thermal gradients and their effects on the part geometry (shrinkage and warpage) were studied for each set of inserts. The thermal properties of the inserts were found to have a significant impact on the processing variables and the part quality. The results showed that the digital ABS inserts present the greatest variance in part dimensions, as well as the highest temperature gradients.
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