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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Rheological Properties of Polyethylene Blend with Poor Mixing
The effect of mixing condition on flow instability at capillary extrusion was studied using linear low-density polyethylene (LLDPE) blends. Two types of LLDPE with different molecular weights were blended by various mixing devices and conditions. It was found that the onset of flow instability is sensitive to the mixing method even though their linear viscoelastic properties are almost identical. The blend obtained by poor mixing conditions shows shark-skin failure even at a low shear stress, although the blend prepared by intensive mixing provides smooth surface at the same shear stress. This is attributed to the low onset shear stress of shark-skin failure for the blend prepared by poor mixing. Furthermore, a blend by poor mixing is found to show a significantly low value of the maximum draw ratio at hot-stretching. The result suggests the existence of mechanically-weak points, which leads to cohesive failure at strand surface by the abrupt stretching at the die exit, i.e., the shark-skin failure.
A New Gas Diffusivity Measurement Technique for CO2 Infused Polymer System during Gas Desorption
In this study, theoretical CO2 diffusivity coefficients in amorphous polymers were calculated from dielectric constant changes during CO2 desorption. Compared with experimental diffusivity coefficients from a gravimetric method, these values agree well with each other. Three amorphous polymer films made from Polystyrene (PS), Polycarbonate (PC), and Cyclic Olefin Polymer (COP) resins were saturated with supercritical CO2 under high pressure in a pressure chamber. Then, the CO2 infused films were removed from the chamber for gas desorption experiments. Both capacitance and weight changes of the samples were recorded by an Inductance, Capacitance and Resistance (LCR) meter and a scale simultaneously. The dielectric constant changes of the polymer/CO2 systems were calculated from the capacitance change measurements during gas desorption experiments. The trend of dielectric constant changes is found to be similar to that of the CO2 weight percentage changes during gas desorption. A mathematical model was built to predict the CO2 weight percentages at any given time during a desorption process from the measured dielectric constants. The theoretical diffusivity coefficients were obtained from the predicted CO2 weight percentage changes and these theoretical diffusivity coefficients agree well with the experimental data.
Multi-Material Joining for Carbon Fiber Thermoplastic B-Pillar
Multi-material joining methods for carbon fiber reinforced thermoplastic structures are documented in this paper, for a B-Pillar design. The two-part Pillar is comprised of two different thermoplastic materials for the hat (Nylon-based) and spine (Elium-based) sections, respectively. It was also joined to a steel rocker at its base prior to high energy drop tower testing to demonstrate the overall Pillar crash performance. Adhesive bonding, adhesive selection, bonding cycle, and traction law development for modeling are presented along with Pillar assembly procedures. Overall performance of the joining approach was validated by full-scale high energy drop tower testing.
Improving the Flame Retardancy of Polypropylene/Rice Husk Composites Using Graphene Nanoplatelets and Metal Hydroxide Flame Retardants
In this study, rice husk/polypropylene composites filled with graphene nanoplatelets and two kinds of metal hydroxide flame retardants, aluminum hydroxide (ATH) and magnesium hydroxide (MH), were compounded using a Brabender Plasticorder. The flammability and mechanical properties of natural fiber composites of different formulations were evaluated. The horizontal burning test results showed that plain 50 wt% PP/rice husk composites demonstrated a horizontal burning rate of 36.08 mm/min. When flame retardant or nanographite was added to the composite, the burning rate reduced to 20 mm/min. On the other hand, a synergetic effect was observed when graphene nanoplatelets were used in conjunction with aluminum hydroxide (ATH) or magnesium hydroxide (MH). Horizontal burning rates were significantly reduced. Additionally, materials self-extinguished during the testing period under some circumstances. The horizontal burning rate of these samples was as low as 5.66 mm/min. The results of mechanical testing showed that adding graphene nanoplatelets not only improves the flame retardancy, the stiffness of the composites increases as well.
Simulative Evaluation of the Temperature Influence on Different Types of Pre-Distributors in Spiral Mandrel Dies
Thermal inhomogeneities in spiral mandrel dies, which occur especially in the pre-distributor, can lead to an uneven flow distribution despite a rheologically optimized design of the die. Against this background an integrative thermal and rheological flow simulation has been developed at the IKV, in which the whole pre-distributor can be modelled non-isothermally. The simulation takes both the non-linear flow behavior of the melt and the thermal phenomena in the die material into account. In this contribution, the developed simulation model is used to evaluate and compare the temperature influence on the melt distribution in three different types of pre-distributors. These are a 23-pre-distributor of a radial spiral mandrel die, a 24-pre-distributor of an axial spiral mandrel die and a star pre-distributor with vertical redirection. The simulations show that in case of the 23- and 24-pre-distributor, both the external tempering of the die and the dissipative shear heating lead to an uneven temperature distribution in the melt and thus cause an inhomogeneous melt pre-distribution. In case of the star pre-distributor, the die tempering has no significant effect on the flow distribution. However, the dissipation leads to an uneven heat-up of the melt in the area of the redirection, which results in an uneven melt flow at the outlets of the pre-distributor. In the next step, thermal design measures are introduced into the pre-distributors in order to homogenize the flow rate distribution at the outlets of the pre-distributors. By integrating heater cartridges, brass inserts and insulating gaps into the die, a more homogeneous flow rate distribution at the outlet of each pre-distributor can be achieved.
Improved Injection Molding of Ultra-High Molecular Weight Polyethylene Using Supercritical Nitrogen
Ultra-high molecular weight polyethylene (UHMW-PE) was injection molded using a microcellular injection molding (MIM) process to introduce supercritical nitrogen (SC-N2) into the melt to decrease the viscosity of the polymer and improve processability while reducing degradation. Solid and foamed parts were produced. Rheological tests indicated that a viscosity reduction during processing decreased the material’s tendency to degrade during injection molding. Although the SC-N2 processing did not improve the tensile strength of the molded parts, it significantly improved the processability of UHMW-PE via injection molding. Micro-computed tomography (µCT) images illustrated the internal structures of the parts and revealed sink marks in the solid formed SC-N2 processed samples, even when packing pressure was applied.
The 3D Viscoelastic Simulation of Multi-Layer Flow inside Film and Sheet Extrusion Dies
In this study, the multi-layer polymer flow inside film and sheet extrusion dies was researched by the multi-layer experiment and the simulation. From the experimental results, the phenomenon that the distribution of each layer changes severely near the edge was founded. That phenomenon was attributed to the second normal stress difference of viscoelastic fluid such a polymer. Therefore the multi-layer flow simulation was conducted by using a viscoelastic model which can calculate the normal stress effect. It showed that the simulation results of the distribution of each layer were well agreement with the experimental results.
Man-Made Cellulose Fiber Reinforced Polypropylene – Characterization of Fracture Toughness and Crack Path Simulation
This investigation focuses on the fracture toughness of injection molded man-made cellulose fibers reinforced composites with PP as their matrix and 30wt% fiber content. The influence of the fiber orientation and the addition of a coupling agent on the fracture toughness was determined using SEM and a micro computer tomography. It was verified that a reinforcement with man-made cellulose fibers leads to significantly higher values of the critical Jc-integral in comparison to glass fiber reinforcement. A notch direction parallel to the flow direction shows higher values which is a result of less local strains around the crack path, as well as of a higher amount of fiber pull-outs in the fractured surface. The coupling agent MAPP creates stronger fiber-matrix adhesion, which results in a decreasing of the Jc-values due to less fiber pull-outs. The determined values of the critical Jc-integral and the crack deflection due to the materials anisotropy were used to apply a crack deflection criterion. The resulting calculated crack paths achieved a good approximation to the experiments.
Measurement and Modeling of Flow Behaviour for Melt Blown Polymer Melt in Very Wide Deformation Rate Range
In this work, linear PP Borflow HL504 FB, having melt flow rate equal to 450 g/10min, has been characterized by using rotational and capillary rheometry as well as by the instrumented injection molding machine. The measured data, that shows first as well as second Newtonian plateau, were consequently fitted by four conventional models (Cross, Carreau, Generalized Quemada and Carreau-Yasuda models) as well as by two novel viscosity models (modified Quemada and Carreau models) suggested here for the first time. It has been revealed that the modified 5-parametric Quemada model shows the highest flexibility to describe the flow viscosity curve for the investigated polymer melt in comparison with the other utilized models.
Applied Rheology for Characterization of Nanofiber Based Filters
Full 3D polydisperse particle filtration modeling at low pressures has been performed for a polyurethane nanofiber based filter prepared via electrospinning process in order to more deeply understand the filter clogging and the cake formation. In this work, realistic SEM image based 3D filter model, transition/free molecular flow regime, Brownian diffusion, aerodynamic slip, particle-fiber and particle-particle interactions together with a Euclidian distance map based methodology to calculate the pressure drop have been utilized. Model predictions have been compared with relevant experimental data in order to validate the used assumptions, methodologies and numerical scheme. The effect of particle-particle as well as particle-fiber interactions on the nanofiber based filter efficiency, pressure drop and the quality factor during the filter clogging has been investigated in more detail.
On the Role of Extensional Rheology, Elasticity and Deborah Number on Neck-In Phenomenon during Flat Film Production
In this work, viscoelastic, isothermal extrusion film casting modeling utilizing 1D membrane model and modified Leonov model was performed in order to understand the role of planar and uniaxial extensional viscosities, extensional strain hardening, Deborah number and die exit stress state (captured here via the second to first normal stress difference ratio –N2/N1). It has been found that the neck-in can be expressed via simple set of dimensionless analytical equations utilizing all above mentioned variables, and thus providing detail view into complicated relationship between polymer melt rheology, die design, process conditions and unwanted neck-in phenomenon.
Microstructural Analysis of Amorphous and Crystalline PET in Presence of Antiplasticizers
Additives such as low molecular weight diluents (LMWD) can be added at low concentrations to poly (ethylene terephthalate) (PET) to improve barrier properties significantly. Orientation during PET processing, on the other hand, causes strain induced crystallization which can increase the diffusion pathway and lessen the amorphous chain mobility. The objective of this work is to analyze the effect of LMWD additives, such as dimethyl terephthalate (DMT) and dimethyl isophthalate (DMI) and strain induced crystallization on the free volume and microstructure of PET and correlate this with barrier properties. Films made of pure PET and PET/LMWD using single screw extruder were oriented using Long Extensional Tester at a relatively fast rate of 200%/s (4 in/s) to prevent any relaxations in the rubbery stage. TGA and FTIR were used to quantify the concentration of DMT and DMI in the PET matrix. Positron Annihilation Lifetime Spectroscopy (PALS) and WLF equation showed a reduction in the fractional free volume (FFV) after strain induced crystallization and introducing additives to the amorphous PET. Dynamic Mechanical Analysis (DMA) experiment was performed to study the long/short range chain motions. ß relaxation studies showed more restriction in the chain motion in presence of additive or crystallization in PET matrix which affect the diffusion process. Permeation measurements were conducted using different gases (O2 and CO2). Permeation studies demonstrated the lowest permeability for oriented PET with 3 wt.% DMT and the highest for amorphous PET.
Sensitive Mechanochromisms Based on a Polymer Bilayer Structure
We have designed a series of mechanochromic devices inspired by nature with the capabilities of changing transparency and “switching on/off” luminescence in response to mechanical stimuli. The key to accomplish these excellent optical properties is to control strain-induced surface engineering, that is, the longitudinal cracks opening and transverse invaginated folds. All of these devices are comprised of a rigid thin layer atop polydimethylsiloxane (PDMS) based elastomer, which can be facilely and quickly fabricated. For transparency change mechanochromism, the folds and cracks with excellent light trapping and scattering capabilities can endow high opaqueness to the originally highly transparent samples. The evolution of crack opening and fold–ridge mechanisms are captured through finite analysis that incorporates damage and cracks in the rigid thin layer. For luminescent mechanochromism, the strain-tunable cracks on the UV shield layer act as “gates” to mediate the traveling of UV light to “switch on/off” the luminescence of mechanochromism. This device exhibits a remarkably high strain responsive sensitivity, demonstrating an excellent sensing capability for detecting mechanical failure or damage. All the mechanochromisms also show outstanding durability and reversibility.
Influences of Molecular Structure on the Rheological Properties and Foamability of Modified Polypropylene
This work combined the grafting maleic anhydride(MAH) onto polypropylene (PP) and the coupling reaction between diamine and MAH grafted PP (PP-g-MAH) into a single step through a twin screw extruder. Detailed molecular weight analysis, rheological characterization and foaming tests were conducted subsequently. The investigation indicated that the concentration of reagents plays a key role in control of the chain structure. By the combination of SEC and rheological analysis, the optimum amount of MAH and diamine for preparing LCB-PPs is decided. However, the optimum peroxide loading during branching modification is not clear and need further evidence. To solve this problem, a foaming test was carried out to assess the performance of the modified PP with different peroxide loading. The results demonstrate that an intermediate level of modification (peroxide concentration, 0.2-0.4 wt%) is already sufficient for the optimization of foaming process.
Long-Term Performance of Thermoplastic Polyolefin Pipe Material Characterized by Cracked Round Bar Test
The long-term performance is critically important for safety assessment of pressurized pipe materials. In the present work, cyclic cracked round bar (CRB) test was utilized to investigate the slow crack growth behavior in a compounded polyolefin pipe material exhibiting flame retardant and antistatic properties (FRTPO). The applicability of the CRB method to evaluate the long-term performance of compounded polyolefin material was also discussed and validated. We demonstrate, for the first time, that the PP-based FRTPO pipe compound displays, surprisingly, excellent long-term performance comparable to that of commercial PE100 pipe material.
High Gas Barrier Materials with Multilayer Morphology for Packaging Applications
Multilayer films are widely used in packaging industry to fulfil different applications. It is well known that multilayer structure is essential for high gas barrier packaging using EVOH, because moisture has negative effects on EVOH’s barrier properties [1, 2]. In order to effectively use EVOH in barrier applications, usually a moisture barrier layer and a tie layer are required [3, 4]. In this study, specially prepared polymeric compounds based on EVOH and polyolefin with good dispersion, proper compatibility/incompatibility and viscosity match are prepared. These special materials all yield a morphology that is similar to multilayered structure after the resins are extruded into thin film. Different from some previous researches [5, 6, 7], our technique involves with a precompound process, which ensure the multilayer morphology to form after resins are extruded into thin films. With multilayer-like morphology inside, EVOH phase is extended and protected. Therefore, good gas barrier (both OTR and WVTR) properties agreeing with series model calculation are reported for all film samples. These materials with multilayer-like morphology have also shown decent adhesion with different PE reins, so 3- layer instead of 5-layer films are successfully fabricated, which are applicable in barrier packaging applications in terms of barrier and optical properties. It is expected that these special materials with multilayer-like morphology inside can be used as monolayer films or a layer in multilayer structures to enhance the barrier performance as well as process flexibility of EVOH resins.
Enhanced Hydrophobicity of Electrospun Polyvinylidene Fluoride-Co-Hexafluoropropylene Membranes by Introducing Modified Nanosilica
Electrospun nanofiber membranes consisting of Polyvinylidene fluoride-co-hexafluoropropylene blended with nanosilica nanocomposites were successfully prepared using electrospinning technique in this paper. The neat PcH, PcH-nanosilica, and Pch-modified nanosilica nanocomposite membranes were characterized by water contact angle, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), respectively. Results showed that the addition of nanosilica increase the hydrophobicity of the membranes. Blended with 5 wt% modified nanosilica, the water contact angle of membrane could reach up to a maximum value (136°). Membrane morphological analysis presented that the resultant membrane had the thinnest diameter and roughness surface, which confirmed the enhancement of hydrophobicity of the membrane.
Foaming Behavior of the Multilayered PS/PA6 Blend and its Anisotropic Mechanical Properties
Polystyrene (PS)/Polyamide 6 (PA6) film with highly-oriented and aligned PA6 ribbons in PS matrix is prepared by the tape extrusion. Using carbon dioxide (CO2) as a blowing agent, the foaming behavior of this multilayered PS/PA6 film was studied at foaming temperature lower than melting temperature of PA6 and higher than transition glass temperature of PA6. The results show that the cell size of the obtained foam is smaller than that of pure PS foam because the solid PA6 ribbon not only acts as heterogeneous agent but also can restrict cell growth. Moreover, the cell is oriented along the direction perpendicular to the ribbons direction, which exhibits anisotropic mechanical properties.
Development of High Thermal Insuation Polypropylene Foams Blown in Injection Molding with Mold Opening
Polypropylene (PP) foams with a low thermal conductivity (less than 40 mW/m·K) and a low density (0.1-0.2 g/cm3) were fabricated by the foam injection molding technology with mold opening while using CO2 as a blowing agent. PTFE fibrils manufactured by in-situ fibrillation using a co-rotating twin screw extruder were used to improve the melt strength and the strain hardening property. The crystallization behavior and the rheological properties were studied, to demonstrate that the dispersed PTFE fibrils effectively enhanced the crystallinity and, thereby, increased the melt strength, and induced a strain hardening behavior. When foamed in injection molding, the fibrillated PTFE containing PP showed much more improved foaming behavior. The thermal conductivity mainly depended on the expansion ratio of foam, although the quality of the cells (i.e., the size and uniformity) also influenced those properties.
Blends of Poly(Propylene Carbonate)/Hydrogenated Nitrile Butadiene Rubber: Morphology and Thermal Properties
The morphology and thermal properties of poly(propylene carbonate) (PPC) and hydrogenated nitrile butadiene rubber (HNBR) blends obtained via a meltmixing process were studied. Morphology of the blends with different compositions was observed by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were performed to study miscibility and thermal stability of the blends. SEM image showed that PPC/HNBR blends are phase-separated at the microscopic scale and each phase showed characteristic Tg in DSC. The addition of HNBR is demonstrated as a mean to significantly improved thermal stability of PPC phase under air atmosphere.
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