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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Equipment and Material Considerations for Microcellular Foaming
Microcellular foaming processes are now proven technologies and integral part of the “mainstream” in polymer conversion operations. The present paper is a joint effort between two companies (Dow and Mucell) to address key aspects necessary to achieve a more efficient use of materials and resources via physical foaming. The paper reviews in detail all aspects that influence performance, paying special attention to the synergies that arise between hardware and material selection. A comparison of performance between chemical and physical blowing is analyzed, highlighting the advantages of microcellular foaming.
High Temperature Aesthetic Grade Liquid Crystal Polymers for Consumer Applications: Not Just For Connectors Anymore
For many years the use of high flowing engineered resins, such as Liquid Crystal Polymer (LCP), have been used for very detailed and intricate parts in the electronics and connector industries where function and performance far outweigh any need for coloristic attributes. Today we find the uses of such resins extending out to more visible consumer products that need the performance and functionality of the LCP with the additional demand of excellent aesthetics. This paper looks to show where the coloring of LCP and the producing of aesthetically pleasing parts has brought LCP’s from behind the scenes to center stage for the consumer products industry.
Simulating the directionality of liquid crystalline polymers
In this paper a practical method of modeling directionality of crystals in liquid crystalline polymers (LCPs) is studied. The main components of this method represent the effects of shear on crystals, the effects of crystals on each other and the effects of movement of crystals with the flow. The implementation of this simulation is done by coding a user defined function (UDF) in ANSYS® FLUENT®. The results of the simulation are shown in two and three dimensions. The presented results show promising closeness to the physical phenomenon associated with the directionality of LCPs. The proposed method can be used as an estimation of the directionality of crystallines during the processing.
Crystallographic Analysis of Electrospun Poly(?-caprolactone) Nanofibers by 2-D Wide-angle X-ray Diffraction (2D WXRD)
The crystalline morphology of electrospun PCL nanofibers was studied. Random and aligned nanofibers were obtained by a conventional plate collector and a two-parallel-conductive-plate collector, respectively. Scanning electron microscopy (SEM) and 2D wide-angle X-ray diffraction (2D WXRD) were employed to characterize the nanofibers. The degree of crystallinity of aligned nanofibers was higher than that of randomly aligned nanofibers. The crystallites in the nanofibers were highly oriented along the nanofiber axis, as were the molecular chains. The estimated crystallite size in the nanofibers suggested that a single nanofiber was composed of dozens of nanofibrils and a nanofibril was further composed of crystallites along the nanofiber axis with an amorphous region of extended PCL molecular chains between neighboring crystallites.
Mechanical Properties of Interconnected Porous Elastomers Fabricated by a Microsphere-Templating Casting Process
The mechanical properties of interconnected porous polysiloxane elastomers under tension and compression were studied in this work. The porous elastomer was found to be highly deformable and had non-affined tensile deformation. The increase of pre-set strains and strain rates in cyclic tension and compression resulted in an increase of stresses at pre-set strains and hysteresis. The permanent sets after unloading process non-linearly decreased as the strain rates were lowered in cyclic compression while the strain rates seemed to have very limited influence over permanent sets in cyclic tensile testing.
Crystallization of Polypropylene: The Effect of Shear and Temperature
The final mechanical properties of a plastic product which is made of semi-crystalline polymers depend significantly on the molecular properties and the applied processing conditions. Particularly, the formation of flow induced structures via polymer crystallization plays a major role in defining the final attributes of the product. In this paper, the effects of shearing and temperature on the flow induced crystallization of several polypropylenes are examined using rheometry. Generally, strain and strain rate found to enhance crystallization in simple shear at temperatures between the melting and crystallization points. The effects of molecular weight and its distribution are also examined and observed to have a strong influence on flow induced crystallization structures.
Microcellular Foaming of Poly(lactide acid)/Nanosized Calcium Carbonate Composites
This article focused on the study of the effect of nanosized CaCO3 on foam morphology of PLA using CO2 as the foaming agent. The thermal properties were investigated through the TG and DSC methods. The presentation of CaCO3 acted as nucleation site to facilitate the crystallization of PLA that resulted the greatly increase of PLA crystallization up to 69.14%. The SEM results showed that the addition of CaCO3 significantly improved the foam morphology, cell size decreased and cell density increased greatly. When the content of CaCO3 is 30wt%, they are similar to the content of 20wt%. Because of the incompatibility of CaCO3 and PLA, the addition of CaCO3 decreased the mechanical properties of PLA.
Foaming Morphology of Microcellular Injection Molded Parts - Simulation and Experimental Characterization
We present the morphological study of microcellular injection molded product using amorphous and semi-crystalline polymers with nitrogen. The cellular structure and cell distribution probed by scanning electron microscope (SEM) were compared with three-dimensional simulation of cell size and density distribution. The morphological comparisons between SEM photos and simulations were analyzed for three different locations along the flow direction. Good agreement between simulation and real molded part prove the capability of commercial CAE software in 3D prediction of microcellular foaming process; furthermore, expensive morphological study from SEM can be economically assisted by simulation tool for industrial application.
Preparation an dMicrocellular Foaming Investigation of Poly (Lactic Acid)/Talc Composites
This study investigated the influence of talc content on the mechanical/thermal properties and crystallization behavior of PLA/talc composites. Talc was compounded with poly (lactic acid) (PLA) via a triple screw extruder, and the foaming properties of the blends were investigated by using a homemade foaming device. Carbon dioxide was used as the blowing agent. The impact strength were significantly increased (by 10%-31%) at the expense of a certain degree of reduction of tensile strength. Owing to the nucleation effect of talc, the 5% talc blends received the maximum crystallinity (43.8%). Furthermore, when the talc content was 10%, the foaming sample obtained the maximum cell density and the minimum cell size.
A Nanoscaled Three Dimensional Structure Created By Using Electrospun Poly(?-Caprolactone) (PCL) Nanofibers and Induced PCL Crystallization
A nanoscale, three-dimensional structure consisting of poly(?-caprolactone) (PCL) nanofibers covered by periodically spaced PCL crystal lamellae was successfully created using a self-induced crystallization method. The shish-kebab structure was obtained by inducing PCL crystallization on electrospun PCL nanofibers immersed in a PCL solution followed by solvent evaporation. The resulting structure highly resembled the nanotopography of natural collagen nanofibrils in the extracellular matrix (ECM) of natural tissues and thus could be a good in vitro model for tissue engineering scaffolds.
Use of a Stack Mould to Increase the Productivity and the Quality in the Injection Molding
The main objective of this research was to study the effect of the injection process conditions over the quality and final properties of plastic parts made in stack moulds. For that, there were used CAD/CAE tools. As a result, it was obtained that when the melt and mold temperatures are increased, the volumetric shrinkage of the molded parts is also increased, and this coincides with the obtained results in hot runners’ moulds. By other hand, when the holding/packing pressure is increased, it is observed a decrease in the parts volumetric shrinkage, as well as in cold and hot runners’ moulds. When the melt temperature increased and the injection velocity decreased, the residual stress in the plastic parts are reduced.
Injection Molding of Rigid Vinyls
Rigid Polyvinyl Chloride and Chlorinated Polyvinylchloride are highly viscous materials that are susceptible to thermal degradation. This combination makes them very challenging to process consistently and often require temperature conditions that are quite a bit different than what someone who has processed other thermoplastics is used to. Also, these materials require some special modifications to the molding machine to facilitate processing. By understanding how the polymer is responding to the process conditions imposed on it, a stable, repeatable process can be established that will produce consistent, high quality parts
Processing effects on permanent electrically conductive HDPE- Conductive Carbon Black composites
Conductive carbon black is still today the most used solution to give permanent electrical conductivity to plastic materials. Electrical conductivity of the final material is known to be affected by processing history and especially final transformation processes as they can induce changes in the filler properties or distribution. In a recent work we highlighted the large difference in the percolation curves of the electrical resistivity of compression and injection molded samples of conductive and extraconductive carbon black loaded HDPE. Such difference can be addressed to different effects such as surface induced segregation, carbon black structure reduction or different crystallization of the polymeric matrix. In this work we investigate by simple but specific tests the relative importance of these factors evaluating their contribution to the modification of the final electrical properties of the material.
Thermo-Mechanical Property Prediction for Long Fiber-Filled Thermoplastics Composites
Following on from the long fiber orientation and long fiber breakage model implementations in the past, long fiber enhanced polymer composite property calculation models have been implemented for long fiber-filled injection moldings. These long fiber composite properties are useful in terms of residual stress calculation, warpage prediction and subsequent structural analysis. Major differences between long fiber and short fiber composite property enhancements include the non-uniform fiber length distribution across injection molded parts and possible de-bonding between fiber and matrix. This paper addresses these differences by presenting a recently implemented micro-mechanical models specific to long fiber composites, which makes use of calculated long fiber orientation and fiber length distributions. A case study on fiber orientation distribution (FOD), fiber length distribution (FLD) and subsequent long fiber composite property distributions are given for injection molding simulation.
PVDF/ Carbon Nanotubes/Nanoclay Nanocomposites For Piezolectric Applications
Poly(vinylidene) fluoride (PVDF) nanocomposite samples were prepared by incorporation of carbon nanotubes (CNT) and nanoclay into PVDF using a twin screw extruder. Carbon nanotube was added to improve electrical conductivity and nanoclay was included to enhance ? crystal formation for piezoelectric property. X-ray diffraction (XRD) results showed that partial melt intercalation of PVDF in clay was achieved. The XRD results also revealed that CNT and nanocaly addition increased ? phase crystal amount in PVDF. FTIR spectroscopy measurements confirmed the XRD results and showed that the effect of nanoclay on ? phase crystal formation of PVDF was more prominent than CNT. It was found that shear rate applied during crystallization would improve ? phase crystal formation but only for the neat PVDF. Conductivity results showed that addition of CNT improved conductivity as a percolation of 2 wt. % was observed. It was found that clay incorporation into CNT nanocomposite could improve conductivity more.
Simulation of Cooling Using a New Model for the Determination of the Thermal Diffusivity in Injection Molding by Means of the Radial Function Method (RFM)
A numerical simulation using a meshless method is developed to describe the cooling of injection molded slits of different thicknesses with an improved thermal diffusivity model that considers the effect of cooling rates and processing conditions. For the filling phase, the fountain flow effect is taken in account. Numerical results are analyzed by examining the effects of the traditional and improved thermal diffusivity model. The predicted effect agrees well with previous measured data. For the case studied in this paper, the use of the traditional model results in a temperature underestimation.
Observation of Higher Order Structure at Heat Seal Parts on Uniaxial Drawn PP Film
Heat seal technology is an essential technique for intermediate packaging material for various industries. There are different kinds of sealing technologies, which would be selected for suitable heat sealed properties of the film. Heat sealing technique is conventional technology for heat sealed film by control temperature, pressure and dwell time. The conditions of heat sealed are important for controlled peel strength and heat sealed properties of the film. Furthermore, film strength depends on the drawn ratio and molecular orientation of film. However, the heat sealing ability of higher molecular orientation films are poor due to loss the heat sealing energy for relaxation of oriented molecules in polymer films. Therefore, it is very important to investigate the relationship between heat sealing conditions, molecular orientation, and higher order structure in polymer films on properties of heat sealed film. In this study, cast polypropylene (CPP) film was heat sealed by using heat sealing technique. The heat sealed condition was set at heat sealed time of 0.1 second with pressure of 0.2 MPa at various heat sealed temperature of 145 to 150 °C. The difference of higher order structure of these films was discussed on the basis of results of micro-Raman spectroscopy, FT-IR spectroscopy, DSC and peel test. From the result, it was found that higher order structure of PP films at heat sealed parts depends on heat sealing time, temperature, and drawn ratio of PP films.
Effect of Talc Filler on Recycled PET Blends Injection Moldings
Recycled PET (RPET) is known to exhibit brittle behavior in the presence of notches. Therefore, we tried to improve the toughness and other properties of RPET by incorporating E-GMA, talc filler and engineering plastics as an impact modifier and talc to increase the rigidity and heat distortion temperature of RPET. As a result, these blends with E-GMA exhibited significantly higher stiffness and strength especially with increasing E-GMA content. In addition, these blends with talc filler indicated the high heat distortion temperature due to increase the crystalinity of RPET blends. Therefore, it was found that talc played an important role in enhancing the heat resistance of RPET. Some injection molding parts, i.e. tray, chopstick, and so on, were produced from these compound materials.
Influence of Cooling Condition on Recycled PET Pellets
In this study we have developed “dry-less pellets”, which absorbs less moisture and do not require additional drying prior to molding. The developing technique namely “Hot Air cooling System” involves coolinging the strands slowly with hot air on a metal conveyor. This study was carried out to clarify a relationship between moisture absorption fraction and crystalline structure of dry-less recycled poly(ethylene terephthalate) (RPET) pellets. Two diffent cooling systems of extrusion processes were performed including water cooling method and hot air cooling syatem. The effect of hot air cooling temperature on properties of RPET pellets was investigated. Karl Fischer moisture titration, differential scanning calorimetry (DSC) and density measurement were used to characterize the pellets to determine the structures of the dry-less pellets. From the results, we have succeeded for preparing the “dry-less pellets” by controlling the hot air cooling temperature condition in the extrusion process. The crystallization process of RPET pellets is an important characteristic for the “dry-less RPET pellets”.
The Effect of High-Recycle-Content on CSD PET Bottle's Thermal Stability
It is not uncommon to see a 25-30% post-consumer recycled (PCR) content in a carbonated soft drink (CSD) PET bottle on the market. With the growing availability of PCR resin, food and beverage brand owners are pushing for higher recycling content in their packaging. Recent studies have been published showing that high-recycling-content in PET packaging will adversely affect the performance of pressurized bottles when compared to virgin material or low-recycling-content counterparts. However, little has been done to quantify the degradation of the specific material properties that govern pressurized bottle performance. This paper focuses on quantifying changes in the short- and long-term material properties that govern a bottle’s ability to retain its original shape when subjected to sustained carbonation pressurization. This performance attribute is typically characterized as ‘thermal stability,’ which is the ability of the package to retain its shape and molded-in feature definition over time, after pressurization. Two commercially available packages, one molded of 100% recycled PET and another molded of typical PET (30% recycled PET content), are used to extract the test samples. The study indicates that the effect of the high-recycle-content on the CSD PET bottle cannot be over-looked. The results of the tensile tests show that the 100% recycled PET is stiffer and tougher in the axial direction (up to 26%), but softer and weaker in the hoop direction (up to 14%), compared with its typical PET counterpart. Based on the creep test results, the 100% recycled PET also creeps 50% faster. This will have a noticeable effect on the bottle’s thermal stability, which is only 1-2% (height and diameter growth or contraction under carbonation pressure) for most commercial packages on the market. The effect will become more pronounced for non-cylindrical designs or designs with non-cylindrical features. Failure to adequately retain the bottle’s shape (thermal stability) will a
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