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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Ultrasonic Joining of Through-the-Thickness Reinforced Ti-4Al-6V and Polyetherimide Hybrid Joints
Ultrasonic joining is an alternative direct-assembly joining technology to produce through-the-thickness reinforced hybrid joints between surface-structured metals and unreinforced or fiber-reinforced thermoplastics. As a result, joint damage tolerance can be improved. This paper presents a preliminary evaluation on the influence of joining energy on the joint formation, microstructure and mechanical performance of Ti-6Al-4V-Polyetherimide hybrid joints. Process-related microstructural changes and mechanical performance of optimized were assessed. The ultimate lap shear force of hybrid joints was six times higher (1860 ± 260 N) than the non-reinforced reference joints (292 ± 7 N). A considerable increase of ten times in displacement at break for ultrasonic joints was also achieved in comparison to reference joints. This is an indication that joint damage tolerance was increased due to an efficient load transfer by pin interlocking between the metal and polymer parts. Initial joint failure was by bearing – a non-catastrophic failure type – while shearing of the metallic pins was responsible for the final parts’ separation during lap shear testing.
An Overview on the Materials and Mechanical Behavior Used in Fused Deposition Modeling
Additive manufacturing offers significant opportunities for the production of final parts and products. Fused deposition modeling is a polymer additive manufacturing process widely used to build unreinforced and fiber-reinforced thermoplastic parts using the principle of extrusion. This work aims to review the state-of- the-art of fused deposition modeling by discussing the main advantages and limitations of the process. The building and processing parameters and their influence on mechanical behavior are addressed. A lack of understanding of these relevant parameters was identified. This literature review has shown that a deeper understanding of processing and material properties is needed to enable fused deposition modeling to become a standard manufacturing process in core industries.
Multilayer Polyethylene Films Having Grease Resistant Properties
Inter-material substitution and disruptive innovation continue to change the packaging world. The development of multilayer coextrusion lines have facilitated the transition from rigid containers to flexible packaging. A new family of barrier high density polyethylenes was discovered to have grease resistant properties. Unfortunately, only a few elementary methods exist for determining a package’s resistance to grease permeation. In addition, most grease permeation methods only provide a qualitative measure of grease penetration. As interest grows for incorporating recyclable plastic film structures into packaging for high fat content products, a simple technique is required for determining a film’s grease barrier properties and for ranking of different flexible film structures. Hence, a semi-quantitative method to measure grease/oil permeation through multi-layer films has been developed, and the results of several multilayer film structures are presented to delineate the efficacy of different film resins in improving the grease barrier properties of polyethylene multilayer films. The present study shows that it is now possible to develop cost effective and recyclable polyethylene film packaging structures with good grease barrier performance by utilizing certain single site catalyzed PE resin architectures.
Anisotropic Thermo-Viscous-Elastic Residual Stress Model for Warp Simulation of Injection Molded Parts
The residual stresses in injection molding process are developed due to the restriction of thermal contraction during the cooling, coupled with the frozen layer growth with the varying pressure history. The stress relaxation behavior of plastic materials also complicates the stress field. A thermo-viscoelastic model is a natural choice for predicting the residual stress in the injection molding process, but it is computationally very expensive and requires materials’ relaxation spectrum data which are not readily available in most of material databases. This study used a simplified anisotropic thermo-viscous-elastic model to calculate the residual stress development in three-dimensional simulation of injection molding process. The validation cases showed that the proposed model is able to predict the final shrinkage, warpage and molded-in residual stresses reasonably well.
Modification of LLDPE by UV-Irradiation
Linear low density polyethylene (LLDPE) is used widely in applications like lamination and agricultural films, as well as a modifier for low density polyethylene (LDPE) and high density polyethylene (HDPE). The melt strength of LLDPE is modified in this study by introducing long chain branching (LCB) and/or crosslinking to its backbone through UV initiated radical reactions. Benzophenone (BP) is added as a photo-initiator to form free radicals and a UV lamp is used to irradiate solid sheets of the molded LLDPE resin, at different time intervals and intensity, according to a design of experiments (DOE). This paper aims to study the effect of photo-initiation on material properties, using linear-viscoelastic (LVE) rheological measurements, and differential scanning calorimetry (DSC).
Elucidating the Cause of Surface Roughness in Melt Compounded PVC Plasticized by High-Solvators
High-solvating plasticizers, like dibenzoates, have shown marked success in their ability to plasticize PVC. This unique interaction has proven beneficial for formulators as dibenzoates are fast-fusing at lower temperatures, decreasing time and energy costs during processing. However, when plasticizers are used in processing conditions involving high shear, a characteristic surface roughness or, “nerviness” can be observed on a two roll mill . Using FTIR, gelation studies, tensile data and gloss measurements, this investigation aims to determine the cause of this morphology. The results indicate that secondary crystallite formation is likely the cause of the nerviness observed in flexible PVC. As well, nerviness was manifested formulations plasticized with DINP, and 1,2-cyclohexanedicarboxylic acid diisononylphthalate (DIDC), suggesting nerviness is an inherent phenomenon with PVC fusion that shifts to lower processing temperatures with high-solvating plasticizers.
Microencapsulation of Pamitic Acid with Polylactic Acid Shell for Thermal Energy Storage
Microencapsulation of vegetable-derived palmitic acid (PA) in bio-based polymer shell of polylactic acid (PLA) by solvent evaporation and oil-in-water emulsification was investigated. This study deals with the preparation and characterization of PLA-PA microcapsules. Chemical structures, morphology of microcapsules, and thermal properties were determined by Fourier transform inferred spectroscopy, scanning electron microscopy, and differential scanning calorimetry, respectively. In short, this work has demonstrated the possibility to fabricate 100% bio-based phase change material microcapsules for thermal energy storage applications.
Micro Components with Locally Different Properties Realized by Segmented Tempered Injection Molding
Influencing mold temperature during injection molding via dynamic tempering affects the melt’s cooling conditions and, therefore, can lead to a change in component properties. The current research presents an innovative dynamically tempered mold technology with different temperature zones within the cavity, which enables the production of micro components with locally different component properties. Results with iPP show that due to influencing internal component properties such as morphology and degree of crystallization, significant differences in mechanical component properties can be achieved.
Effect of Flow Lines on the Metallization of Laser-Structured Polymer Parts
Molded interconnect devices (MID) offer great potential for circuit board applications, especially regarding three-dimensional shaping and functional integration. Applying circuits to polymer substrates can be performed by means of laser patterning methods. In these, the matrix polymer is filled with a special metal additive, enabling laser activation and subsequent metallization. Important effects emerge during processing of the matrix polymer. In this work, the influence of the gate geometry and the resulting flow behavior during injection molding on the quality of the metallization is investigated.
Online Melt Viscosity Measurement during Injection Molding for New Control Strategies
Part quality and its reproducibility are crucial factors for the productivity of injection molding processes. While machine parameters can be reproduced with a high accuracy, disturbing influences may cause different processes regarding the melt state in the cavity and consequently production rejects. Fluctuations in the melt viscosity influence the pressure distribution within the cavity and have a strong impact on part quality. Therefore, viscosity fluctuations can cause differences in warpage or even under- or overpacked cavities. Fluctuations can occur due to differences in the residual moisture of the plastics material, the use of regrind material, batch variations or interruptions in the production process. To compensate the effects of different raw material viscosities onto the process, a determination of the current viscosity is required. Within this paper different concepts of viscosity measurement for polymer melts are reviewed with regards to applicability in an online control system for injection molding. The concepts range from machine based parameters to concepts using in-mold sensors. A new mold concept using pressure sensors within the hot runner manifold is presented. The feasibility is analyzed in numerical injection molding simulations. Finally, the simulation results are validated using practical injection molding trials.
Novel Interface-Modified Bionanocomposites with Improved Processability and Electricity
Novel interface-modified bionanocomposites with improved processability and AC conductivity was developed and examined in the experiments. The results indicated that the interface-modified bionanocomposites exhibited an approximately 2-fold decrease in complex viscosity and mechanically reinforced properties as compared to neat polylactic acid (PLA) and those without interfacial compatiblizer. Interface improvement from maleated PLA was observed on the fractured surface and also confirmed through the increased Young’s modulus and the improved thermal and electrical properties. The micromechanical models were applied to predict the mechanical properties of the bionanocomposites in the matrix. At 5~7 wt% GNPs loadings the electrical conduction path was achieved inside the PLA matrix through the formation of the effective three-dimensional conductive networks in these bionanocomposites. It was interestingly noted that above the percolation threshold the increasing graphene loadings resulted in lower but higher AC conductivity. The mechanisms in unusual decrease in AC conductivity above percolation threshold were discussed and elucidated.
Durability Evaluation to Residual Chlorine on Plastic Pipes
Recently, the polymer electrolyte fuel cells (PEFC) cogeneration systems with plastic pipes for hot water supply has been commercialized in Japan. The pipes for hot water supply are installed with bending from the polymer electrolyte fuel cell to inside a house without using fittings. However, it is expensive and hard to replace these plastic pipes. These pipes which installed with bending were not evaluated in the residual chlorine solutions for long term. Accordingly, it is important to evaluate the durability and to predict the lifetime of these bent pipes. This study intended to evaluate the bent pipes in the residual chlorine solutions early. The residual chlorine solution immersion test for the bent polybutylene (PB) pipes and the bent double-layer crosslinked polyethylene pipes (PEX2) was conducted at 80°C, 90°C and 98°C. In the residual chlorine solution immersion test, the concentration of the residual choline solution is 5 ppm and 10 ppm for 80°C, 5 ppm for 90°C and 5 ppm for 98°C. As a result, it took much time to get the results back from this immersion test beyond expectation. It was found that the bent polybutylene (PB) pipes had the cracks over for 36,000 hours at 5 ppm in 90°C, over for 40,000 hours at 10 ppm in 80°C and over for 44,000 hours at 5 ppm in 80°C. On the other hand, the bent double-layer crosslinked polyethylene pipes (PEX2) in the residual chlorine solution immersion test did not have the crack at all over for 47,000 hours.
Heat Sealing in Semicrystalline Polymer Films
This work investigates the non-standard microstructural aspects that might play a critical role in the heat sealing process of semi-crystalline polymer films. Two different ethylene-propylene copolymers having widely different Seal Initiation Temperatures (?SIT=18°C) but similar melting points (?Tm=2°C) were chosen for this study. The contribution of both the amorphous phase and the crystalline phase to heat sealing was investigated utilizing Dynamic Mechanical Analysis and Thermal Fractionation DSC respectively. Initial results indicate that the melting distribution of the thermally fractionated material plays a critical role in determining SIT. Other potentially contributing factors like isothermal crystallization kinetics, the kinetics of entanglement in the melt state are currently being investigated.
Preparation and Characterization of Thermoplastic Polyurethane (TPU) Foams with a Large Variety of Cell Sizes
In this study, thermoplastic polyurethane (TPU) foams were fabricated by batch foaming using supercritical carbon dioxide (ScCO2) at different foaming temperatures and saturation pressures. Experimental results revealed that lower saturation pressures would increase the sensitivity of cell sizes to varying foaming temperatures due to the different crystallization behaviours of TPU at different saturation pressures. As a result, lower saturation pressure seemed to provide more flexibility for researchers to develop multifunctional TPU composite foams by taking advantage of foaming-assisted alignment of fillers along their cell walls.
Thermally Insulated Bimodal Polystyrene/Multi-Walled Carbon Nanotube Nanocomposite Foams
We developed a bimodal polystyrene (PS)/multi-walled carbon nanotube (MWCNT) nanocomposite foam with a thermal conductivity of 30 mW/m-K without using any insulation gas. The MWCNTs were critical to the heat transfer because they decreased radiation significantly through the foams. A theoretical model has been proposed to analyze the thermal conductivity in nanocomposite foams. The proposed model verified the superior heat-blocking characteristics of the bimodal cellular morphology and the MWCNTs as follows: (1) The primary large cells acted to decrease the solid conduction; (2) The secondary small cells induced the Knudsen effect on gas conduction; and (3) The MWCNTs intensively blocked the IR transmission.
A Novel PPESK Fibrous Membrane Separator Based on Electrospinning Technique for Lithium-Ion Battery
In order to improve the low porosity, poor thermal stability and insufficient electrolyte wettability of commercial polyolefin separator, the novel PPESK fibrous membrane separator has been fabricated via electrospinning for the use of lithium-ion batteries. By the use of high-speed collection drum, the tensile strength of the electrospinning oriented PPESK fiber membranes increase significantly and reaches 18.9 MPa. Hot oven testing shows that oriented PPESK fiber membranes are thermally size stable at a high temperature of 220 ?. The oriented PPESK fiber membrane exhibits high level of porosity (83%) and excellent electrolyte uptake (720%). Moreover, the ionic conductivity increases to 1.85 mS cm-1 compared with the 0.41mS cm-1 of commercial Celgard 2400 separator. In addition, the lithium-ion battery assembled with electrospinning oriented PPESK fiber membrane shows high capacity retention, stable cycle performance and excellent rate capability. Therefore, the electrospinning oriented PPESK fiber membrane is likely to be a promising candidate of high-power lithium-ion battery owing to its comprehensive outstanding characteristics.
Filler Content and Properties of Highly Filled Filaments for Fused Filament Fabrication of Magnets
Fused filament fabrication (FFF) is a very popular additive manufacturing technique for the production of geometrically complex polymeric parts. FFF can also be used for the production of sintered magnetic parts, as part of the shaping, debinding and sintering (SDS) process. In order for sintering to be possible, it is recommended to prepare feedstock materials with 50 vol% or more filler content. However, when the filler content increases the properties required for FFF change. In this paper the mechanical properties of filaments, the viscosity of the molten feedstock, and surface properties of the solidified feedstock were investigated as a function of strontium ferrite powder content (53 to 60 vol%). In addition printing trials were performed. It was observed that mechanical properties significantly decrease, the viscosity increases and the surface tension showed no changes as a function of powder loading. All materials were in principle printable, but the printing temperature had to be adjusted to print the most highly filled material due to its lower mechanical properties and higher viscosity.
Preparation of PA6/LLDPE Blends by Rotational Molding
Blends of linear low density polyethylene (LLDPE) and polyamide 6 (PA6) were produced by rotational molding. Blends of 10, 20 and 30% vol. of PA6 in LLDPE were previously prepared using two methods: dry blending using a high shear mixer, and melt-compounding using a twin-screw extruder. The objective of the work is to study the morphological and mechanical properties of rotomolded parts of polymer blends. The results indicated that the rotomolded parts of the blends obtained by previous extrusion generated smaller and better dispersed PA6 particles in the LLDPE matrix. The mechanical properties are also found to be influenced by the blend preparation method.
Experimental Study on Fiber Attrition of Long Glass Fiber-Reinforced Thermoplastics under Controlled Conditions in a Couette Flow
Fiber attrition of long glass fiber-reinforced polypropylene in a Couette Flow was studied to obtain a fundamental understanding of the physics in fiber breakage. The developed experimental setup of the Couette rheometer in combination with the developed fiber length measurement technique is able to provide repeatable, accurate and robust data sets to quantify the fiber length reduction during the processing of fiber-filled materials. This article summarizes the first results of an ongoing experimental study on fiber breakage at the Polymer Engineering Center at the University of Wisconsin- Madison. The impact of fiber concentration, initial fiber length, residence time, melt temperature and processing speed was quantified and studied. The proposed procedure aims to isolate the effect of process variables on fiber breakage. Even for the gentlest processing conditions, the results indicate that the residual fiber length after processing is less than 50% of the initial fiber length. For the most severe processing conditions, the results suggest a reduction to less than 10% of the initial fiber length, which highlights the challenges that fiber breakage poses for processing of long glass fiber-reinforced thermoplastics.
Modified Polylactide with Improved Thermal and Rheological Properties for Foaming
Polylactide (PLA) is the most important bioplastic on the market due to its good mechanical properties and the permanent growth of the production capacity. One drawback of commercial polylactide is its too low melt strength and melt extensibility, which is disadvantageous in terms of foaming. To overcome these commercial grades need to be modified. Therefore, several chemical modifiers were used to induce crosslinking, chain extension or grafting by means of reactive extrusion on a twin-screw extruder. The best results were achieved with organic peroxide. With this modifier the melt strength and the crystallization rate were improved and lead to foams with a closed-cell structure and low density. Organic peroxide was found to be more efficient than the commercial multifunctional epoxide modifier.
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