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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A Fracture Mechancis Approach to Service Life Prediction of Hdpe Fusion Joints in Nuclear Applications
Limiting failure mode for long term performance of High Density Polyethylene (HDPE) pressure piping is slow crack growth (SCG), which is governed by the sustained stress levels (pressure and axial loads), and increases exponentially with elevated temperatures. Preliminary findings indicated the much lower resistance to SCG exhibited by HDPE butt-fusion pipe joints when compared to the parent pipe material. The integrity of HDPE pipe joints and the critical flaw size evaluation has now become a focus for the nuclear industry, regulators, and the plastic pipe industry. The ASME Boiler and Pressure Vessel Code Committee Sections III, IX, and XI address the use of HDPE piping in nuclear safety related applications. This current study is a summary of the findings till date on the crack driving force (Stress Intensity Factor), material fracture resistance (SCG tests on butt-fusion pipe joint materials), and service life prediction models for critical flaw size determination.
Pitfalls of MFI Targeting in the Specification of Golf Ball Thermoplastic Polyurethane Cover Layers
Injection moldable thermoplastic polyurethanes (TPUs) have been used in golf ball cover layers since the 1980s and can provide an attractive combination of formulation flexibility, performance, ease of processing, and overall lower cost when compared to cast thermoset polyurethane and polyurethane-urea systems. In developing raw material specifications for TPU and in their polymerization at the material supplier, melt flow index (MFI) is often used as a means to target certain processing and property requirements. However, using MFI as the only metric for quantifying a given TPU formulation can lead to problems as it does not capture polymerization and thermal history dependent structural variations inherent to these materials. In this study, final golf ball performance attributes, mechanical properties, thermal properties, dynamic mechanical properties, and dynamic rheological properties of two batches of TPU with identical composition and MFI were compared and contrasted. The results will be used to illustrate why TPU copolymer segmental structure and both temperature and time dependent morphology are important in the processing characteristics and properties of these versatile materials.
Isothermal Crystallization Behavior of Poly(Lactic Acid)/Cellulose Nanofiber Composites with Presence of CO2
The isothermal melt crystallization behavior of poly(lactic acid) (PLA)/cellulose nanofiber (CNF) at atmospheric pressure and two CO2 pressures was investigated using regular and high-pressure differential scanning calorimeters (DSC). The DSC analysis and polarized optical microscope (POM) result indicated that CNFs acted as crystal nucleating agents and accelerated the crystallization kinetics by providing more nuclei and decreasing the crystallization half-time. It was found that the crystallization kinetics of PLA materials was changed depending on the crystallization temperature, CNF content, and CO2 pressure. During isothermal process, the crystallization kinetic constant, k, increased with temperature up to a critical isothermal temperature before decreased; increasing CO2 pressure accelerated the crystallization kinetics of PLA at temperatures below 110 øC, but depressed at higher temperatures. The highest crystallinity was achieved at 15 bar.
Combinatorial Effects of Kneading Elements on Mixing in Twin-Screw Compounding
Modularity in the design of screw configurations is one of the most advantageous characteristics in twin-screw extrusion. In the compounding of polymers and solid additives, various mixing section geometries are used to distribute and disperse the minor phase within the polymer matrix. Thus, quantitative determination of the mixing efficiency of a particular screw configuration can greatly improve final product quality. Kneading blocks are the standard screw elements used to perform the mixing operation. This paper will discuss the mixing performance of various kneading blocks with regards to paddle size, mixing section length, and positioning. Mixing will be characterized through a design of experiment approach and the evaluation of the residence stress distribution for a range of operating conditions.
Injection Molding of Nano-Features ? A Study on Filling and Birefringence
The ability of the polymer melt to enter into the micro- or nano-structures is a crucial factor for successful molding operations and their final usability. When molding a rectangular plate with nano-features on top of it, it was observed that the nano-features are filled completely, away from the fan gate and only partially filled near the gate. A fundamental understanding based hypothesis driven approach helps to understand and solve the non-uniform filling behavior and leverage existing commercial modeling tools effectively. Based on the hypothesis, recommendations were made for further experimental studies, which showed a significant improvement in the filling of the nano-features completely throughout the part. Further studies focused on reducing the non-uniform birefringence by optimizing the gate design, using Moldflow? and Abaqus?.
Effect of Thin Walling and Foaming on TPO Part Performance
Two prominent strategies for decreasing injection molded part weight are thin walling of solid parts and foaming parts via supercritical fluids or chemical blowing agents. These strategies not only affect part weight but also mechanical performance. Advanced Composites has evaluated the effect of both of these strategies on part performance in a laboratory plaque study. Part density and weight were measured along with tensile, flexural, and notched impact properties. In the case of wall thickness reduction, the decrease in stiffness was more substantial than the reduction in weight on a percentage basis. Injection foaming resulted in a greater percentage of impact reduction than weight reduction but demonstrated advantages in flexural stiffness. These findings have ramifications for both part design and material selection.
Properties of Crosslinked Polyurethane-Clay Nanocomposites
Polyurethanes (PU) are versatile materials displaying desirable properties that can be modified through the addition of fillers. The introduction of organoclay into the matrix can change the mechanical and overall properties of the polymer. In this paper, the effect of clay concentration on the behavior of crosslinked polyurethane was investigated. The prepared systems were evaluated through analytical techniques in which their rheological and dynamic mechanical properties were studied. Results demonstrated that the introduction of clay improved the storage modulus by more than 30%. Furthermore, clay decreased the molecular weight and viscosity of nanocomposite solution by 40% and 90%, respectively for up to 10 wt% clay, which significantly improves processability.
Phase Morphology and Electrical Conductivity of Polypropylene/Polylactic Acid Blends Filled with Multi-Walled Carbon Nanotubphase
The selective localization of multiwalled carbon nanotubes (MWCNTs) was studied in a ternary system containing polypropylene (PP), polylactic acid (PLA), and MWCNTs. With a proper composition, the selective localization of MWCNTs in PP/PLA blends with more viscous PLA phase decreased the electrical percolation threshold of the blend to 0.15 vol. %, which was 4 times lower than that of the PP/MWCNT composites. Despite the predictions suggested by the thermodynamic measurements, the transmission electron microscopy (TEM) micrographs revealed the localization of carbon nanotubes in the PP phase instead of the PLA. Moreover, decreasing the viscosity ratio of PP/PLA did not cause the MWCNTs? to migrate to the PLA phase. The electrical conductivity measurements showed that the blend system with less viscous PLA phase had a lower conductivity due to its coarser morphology. The selective localization of MWCNTs in these blend systems was explained in terms of the relative molecular mobility of the phase during processing.
Thermal Analysis of Soy Flour Elastomer Composites
Biobased plastics are becoming viable alternatives to petroleum-based plastics because they decrease dependence on petroleum derivatives and tend to be more environmentally friendly. Raw materials such as soy flour are widely available, low cost, lightweight, and can have high strength. In this study, soy flour was utilized as a filler in thermoplastic elastomer composites. Because weak interfacial adhesion between the soy flour and the elastomer and low water resistance pose challenges, a surface pretreatment, acetylation, was investigated for composites with soy flour concentrations of 10 wt%, 15 wt% and 20 wt%. Previous studies of the mechanical properties of these composites at 10 wt% determined that acetylation resulted in ultimate strength comparable to that of the pure elastomer. In this study, the chemical pathways of the reaction were verified and the thermo-mechanical properties characterized. Interfacial adhesion was characterized through scanning electron microscopy (SEM); the study determined that the acetylation reaction increased interfacial adhesion as indicated by smaller particle sizes and less agglomeration. Thermal properties were determined though thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Acetylation reduced the intake of water by the soy flour, thus increasing the thermal stability of the composites. Increased thermal stability was indicated by a rise in decomposition temperature.
Effect of Catalyst on Compatibilization of Poly(lactic acid) / Polyamide Blends
The effects of catalysts p-toluenesulfonic acid (TsOH) on trans-reactions in poly (lactic acid) (PLA)/polyamide (PA11) blends were investigated in this study. The extent of reaction was tracked using solubility, modulated differential scanning calorimetry (MDSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). The organic acid catalyst appeared to induce trans-reaction but also reduced overall molecular weight in PLA/PA11 blends. The interchange reactions appeared to compatibilize the blends as evidenced by calorimetry and microscopy.
Anisotropic Thermal Conduction in Polymeric Materials
The strong coupling of mechanical and thermal effects in polymer processing flows has a significant impact on both the processability and final properties of the material. Simple molecular arguments suggest that Fourier?s law must be generalized to allow for anisotropic thermal conductivity in polymers subjected to deformation. In addition, theoretical results suggest a linear relationship between the thermal conductivity and stress tensors, or a stress-thermal rule. In our laboratory we have developed a novel optical method based on Forced Rayleigh Scattering (FRS) to obtain quantitative measurements of components of the thermal diffusivity tensor in polymers subjected to deformations. We have found the stress-thermal rule to be valid for several polymer systems in both shear and elongational deformations. More recently, we have developed a novel technique based on Infrared Thermography (IRT) that complements FRS and allows for the study of a wider range of polymeric materials.
Failure Analysis of Copolyester Clamps
Cracking and subsequent failure of a clamp feature on a broken copolymer component occurred through brittle fracture as a result of environmental stress cracking. Environmental stress cracking (ESC) is a phenomenon whereby a particular plastic resin is affected by a specific chemical agent while under stress. ESC occurs commonly in polymeric components but the fractographic features of copolyester are similar in both ESC and creep. The analytical techniques employed in this article provide a guideline by which to properly determine the root cause of failure for copolyester components and describes characteristics typically observed in copolyester ESC failures.
Experimental Results of Melt Modulation Packing Parameters Control on Cold-Runner Injection Molding Final Product Quality
This paper details the experimental results performed on a clear polymer, STYRON? 685D (GPPS), to investigate the impact of varying the packing processing parameters on its final quality. Packing processing parameters, including packing pressure and packing time, have significant impact on the internal molecular orientations, mechanical properties and optical performance of injection molded polymeric products. Experimental results have been obtained from three melt modulation control methods to control the packing pressure, packing time and control valve angle during each cold-runner injection molding cycle.
Experimental Analysis of Fibers Orientation and Mechanical Properties in Injection Molding of Thermoplastic Reinforced Materials by Rapid Heat Cycle Molding
Injection molding of reinforced thermoplastic materials is increasingly used in order to obtain high specific mechanical properties and good surface finishing. In this work a rapid heat cycle molding (RHCM) technology was employed to study the influence of injection molding parameters on fibers orientation and mechanical properties of thermoplastic fiber reinforced injection molded parts. X-ray computed tomography (CT) was employed to allow a direct observation of the fibers orientation. The injection molding parameters investigated were mold temperature, injection speed and part thickness. The experiments show that the mechanical properties are maximized by high part thickness, low mold temperature and injection velocity. However, the variation of the investigated injection molding conditions had a negligible effect of fibers orientation.
Mechanistic Model Simulation of a Compression Molding Process: Fiber Orientation and Fiber-Matrix Separation
A mechanistic model was implemented in order to simulate the fiber motion in the SMC process (Sheet Molding Compound). In this model, each fiber is represented by a chain of segments interconnected by articulations. A balance of forces and torques is considered for each of these segments in order to determine the velocity and position of each of them during the simulation. This balance of forces and torques includes hydrodynamic effects (drag forces and torques), fiber-fiber contact forces and bending moments.
Regarding the fiber orientation, the results of the mechanistic model were compared with experimental results in the literature. It was found that the model is in good agreement with the experiments, but it slightly over predicted the orientation. The fiber matrix separation phenomenon was observed and it was concluded that it increases with the fiber content and with the fiber-fiber friction coefficient.
The Effect of Localized Heating on Polyethylene Tubing
Polyethylene (PE) tubing is used in a wide variety of industrial and residential applications, including as a means of transporting water for use with appliances and other equipment. Temperature limits are applied to PE tubing to prevent premature failure due to loss of mechanical properties from heat and oxidation effects, especially in pressure-carrying systems. Product lifetime will be shortened by oxidation and subsequent embrittlement, which allows crack initiation, propagation and ultimately a fluid path through the tubing wall. In this case study, we present an example of the effects of localized external heating on hot water carrying PE tubing.
On the Use of Self-Assembling Block Copolymers to Toughen an Aromatic Amine-Cured Epoxy
Block copolymers have received considerable attention in epoxy toughening due to the wide variety of nanostructures that can be produced. In this study, a series of self-assembling diblock and triblock copolymers were added to aromatic amine-cured epoxies. In most cases, spherical micelles formed and diameters as small as 20 nm were imaged. Increases in toughness were observed in all cases and the toughening mechanism involved the formation of a crack-tip plastic zone. It is important to note that the size of these plastic zones are relatively small when compared to those generated by more traditional toughening agents.
Rheological Behavoir and Structual Development of Thermoplastic Polyurethane Annealed at High Temperature
The changes in phase transition behavior and structure were investigated through varying hard-to-soft segment ratios of a model thermoplastic polyurethane (TPU) system. Dynamic rheological measurements showed a high temperature phase transition related directly to the hard segment content. Extensional viscosity also detected a relationship between the hard segment content and the material?s strain-hardening behavior. Annealing the samples near the phase transition temperature caused an increase in moduli as well as an inversion in extensional behavior. Understanding the material property changes associated with changes in composition and annealing could provide a route to further tailor these versatile materials.
Applications for Recycled Pots, Tubs and Trays
With pots, tubs and trays being a recent addition to recyclables collections, end markets and values are yet to develop in the same way as plastic bottles. The value of pots, tubs and trays depends primarily on the level of contamination and polyolefin content (polypropylene (PP) and polyethylene (PE) plastics). An assessment was undertaken to review markets conditions affecting the recycling of polyethylene terephthalate (PET) pots, tubs and trays (PTTs). This considered the supply of clear PET, potential available markets, and alternative technologies to provide a comparative assessment of market values (e.g. EFW, landfill, export markets). The actual cost of disposal of PTTs is somewhere between œ44.9m and œ55.5m. The business case for collecting pots, tubs and trays develops further when actual values are gained per tonne, and with new sorting facilities for pots, tubs and trays being commissioned, once end markets have developed the financial benefits to local authorities in the UK will increase. This work focuses on finding markets for recycled PTTs with a number of trials at major manufactures across Europe.
Functionalization of Soy Fatty Acid Alkyl Esters as Bioplasticizers
The combination of various functional groups such as epoxy, acetoxy, methoxy, thiirane, aziridine on the acyl chain of soy fatty acid alkyl esters have been synthesized and evaluated as plasticizers in poly vinyl chloride (PVC) applications. Numerous synthetic procedures such as epoxidation, methoxylation, acetylation, thiiration, and aziridination were used for synthesizing multifunctional soy fatty acid alkyl esters. Epoxidized soybean oil fatty acid alkyl ester served as the key intermediate to incorporate most of the functional groups on the fatty acid backbone. The physical and analytical properties of bioplasticizers such as acid and saponification values are acceptable for plasticizer applications. The high viscosity and darker color of aziridine and thiirane derivatives limit their usefulness, whereas the physical properties of the other derivatives were acceptable. The plasticizer evaluation of methoxy, acetoxy soy fatty acid esters (methyl and n-butyl) demonstrated good compatibility with PVC, high efficiency (Shore Hardness) and gelling properties and were comparable to commercial plasticizer, diisononylphthalate (DINP).
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