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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.
Yasamin Kazemi, Sai Wang, Amir Ameli, Kejing Yu, Chul B. Park, May 2015
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.
Kendra Allen, David Grewell, Eric Cochran, May 2015
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.
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.
David C. Venerus, David Nieto Simavilla, Jay D. Schieber, May 2015
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.
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.
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.
Luca Crema, Giovanni Lucchetta, Filippo Zanini, Simone Carmignato, May 2015
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.
Camilo Perez, Daniel Ramirez, Tim A. Osswald, May 2015
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.
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.
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.
Jesse L. Gadley, Joao Maia, Ricardo Andrade, May 2015
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.
Jonathan Mitchell, Edward Kosior, Paul East, May 2015
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.
Dharma R. Kodali, Lucas Stolp, Subbarao Kandula, Benjamin Woldt, Michael Grass, May 2015
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).
Olivia Keane, Johannes M”ller, Humza Jafferji, John W. Song, Emmanuelle Reynaud, Daniel F. Schmidt, May 2015
Decades after their initial discovery, polymer nanocomposites find use in a wide range of commercial applications. BCC Research indicates that the global nanocomposite market is worth ~$1.4 billion, with clay nanocomposites accounting for ~60%, and will grow to ~$4.2 billion by 2019. Novel nanocomposites are therefore both scientifically interesting and industrially relevant. Jafferji, Schmidt and Reynaud have previously described the mechanical properties of copolyester / clay nanocomposites based on Eastman?s Tritan TX1000 copolyester in combination with commercial nanoclay. These materials represent the first melt-blended polymer nanocomposites based on a commercial high-Tg amorphous thermoplastic that give increases in modulus, strength, and elongation at break with no loss in impact properties or clarity. In addition, IR imaging during tensile testing enabled us to identify a change change in the deformation mechanism of these materials (as measured by their ability to convert work to heat) with increasing nanoclay content.
Here, we report on analogous nanocomposites of Eastman?s Tritan TX2000 copolyester. Our previous results were unexpected for amorphous nanocomposites ? but x-ray diffraction (XRD) identified local ordering in the TX1000 systems which was enhanced through clay addition. In contrast, TX2000 is entirely amorphous and possesses a higher glass transition temperature. Otherwise, these systems are highly comparable. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) both confirm the lack of crystallinity in the TX2000 based materials. XRD further indicates that TX2000 is at least as clay-compatible as TX1000. While thermal stability is reduced on clay addition and hardness measurements are inconclusive, clarity is retained with little or no change in color. These results, in combination with ongoing mechanical characterization, will provide a better appreciation for structure-properties relations in this class of copol
Short term stress relaxation tests were performed to observe mechanical effects of ageing and annealing on injection molded High Density Polyethylene (HDPE). The investigation revealed no definite relationship between ageing time and relaxed stress. Two different annealing parameters were used to investigate the effect of annealing on injection molded samples. Samples annealed for longer time showed more consistency and higher relaxation modulus than the samples annealed for shorter time and the control samples. The effect of ageing on annealed samples was also studied in this work.
When developing complex compounded polymer blends, utilizing experimental design methods can aid in understanding the main effects of each component as well as higher order interactions between components. Even more intricate models allow the analysis of process variables and the complex interactions with the blend properties. This paper will review the fundamentals of mixture-process variable (MPV) experimental designs, ordinary least squares linear regression, and response surface methods as they apply to formulation of engineered polymer compounds. Response surfaces are generated for a multicomponent polyamide blend used in automotive interior applications including the effect of a single process variable where mechanical and appearance properties are all modeled and evaluated for optimal levels using desirability functions.
Edward Kosior, Jon Mitchell, Kelvin Davies, Martin Kay, Rafi Ahmad, Edwin Billiet, Jack Silver, May 2015
Polypropylene (PP) from packaging is a significant polymer in the mixed plastics waste stream and closed loop recycling of it back into packaging would enable considerable carbon savings to be realised and generate significant revenues. Recent estimates suggest that 143,000 tonnes of the total PP packaging is used for food-grade application. One of the remaining barriers to closing the loop on the recycling of PP food packaging waste back to food grade applications is the absence of an automated method for sorting PP packaging waste to separate a stream consisting of at least 99% PP packaging that has been previously used for food from other non-food PP packaging. Machine readable inks (including fluorescent pigments) have shown great potential for the identification and separation of plastic packaging. Unlike existing NIR sorting practices, these technologies are not polymer specific and could be applied to targeted streams like food grade PP packaging and others, using commercial labelling and decoration methods and sorted using MRF infrastructure with only minor modification. This report describes the work of an identification technique which is based on fluorescent pigments that can be applied to labels and packaging as a machine readable ink (MRI) to enable the automatic separation of target materials such as the sorting of food grade PP packaging for closed loop recycling. Based on the audit of commercial of PP waste indicating that 55% detectability of existing packages together with potential yields of 98% from the sorting trials, it can be estimated that of the 143,000 tonne of PP food packaging, 77,077 tonnes could be recovered each year in the UK. This would increase dramatically if label design and application was modified to better accommodate identification and sorting requirements.
Nicolas Sunderland, Terry Davis, Dave Rocco, Jim Lorenzo, May 2015
The LED lighting market continues to grow rapidly as consumers recognize the benefits of this technology over incandescent and fluorescent fixtures. However, the relatively high price of LED bulbs has forced manufacturers to explore ways to reduce costs. Since the electronic component costs are usually fixed, other components such as the simple heat sink offer an opportunity to reduce costs and improve performance through unique assembly processes. Developers at Bayer MaterialScience have created several polycarbonate grades aimed at LED applications, each with a potential to reduce cost, through the elimination of secondary operations and improved design freedom. This list includes thermally conductive polycarbonate. Thermal management of electronics has traditionally been handled using highly conductive metal alloys. The unique properties of thermally conductive polycarbonate and the lower processing temperatures compared with die casting provide an integrated assembly opportunity that can reduce cost and eliminate thermal interface, potting materials and assembly steps. Two polymer technologies, thermally conductive polycarbonate and polyurethane have been combined to allow in-mold electronic component assembly and encapsulation reducing the number of components while creating a finished part in a mold without additional manual assembly. Compared to traditional manufacturing, this process reduces labor cost, increases supplier competition and improves thermal contact by elimination of relatively low conductivity thermal interface materials (TIM).
Polymer composites filled with hexagonal boron nitride (hBN) are of great interests to researchers nowadays because they are considered to be potential candidates used for heat conduction and electrical encapsulation. In this paper, two grades of hBNs (AC6041 and PTX 60) of different sizes and structures were used as hybrid fillers in order to enhance the formation of thermally conductive networks. The effective thermal conductivity (keff) of the composites was tailored by varying the hybrid filler compositions. The keff reached a maximal value when the volume fraction of hBNAC6041 in the hBNs varied from 50% to 67% at a filler loading of 18.7 vol. %. In addition, an empirical model was proposed to explain the competing effect of using hybrid fillers on the PMC?s keff.
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