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.
Utilizing lignin-containing cellulose nanocrystals (HLCNCs) as reinforcing agents to poly(lactic acid) (PLA) for nanocomposites was studied for the first time. The PLA/HLCNCs nanocomposites were prepared by extrusion and injection molding. The freeze-dried HLCNCs showed micron scale agglomerates. As indicated by the water contact angle measurements, the HLCNCs were more hydrophobic than dealkaline lignin and traditional, lignin-free CNCs derived from high cellulose content wood pulp. Thermogravimetric analysis (TGA) showed that the HLCNCs started to degrade at about 300°C. The thermal stability of nanocomposites was slightly lower than neat PLA. The Young’s modulus of nanocomposites containing 1%, 2% and 5% CNCs was improved by 21.0%, 18.4% and 17.7%, respectively, while the strain at break was improved by 73.2%, 63.4%, and 54.9% compared to neat PLA. The nanocomposites (PLA/2%HLCNC) exhibited increased microductility and plastic deformation over neat PLA during tensile test. No statistically significant changes in the tensile strength were found with HLCNC addition. The results provide some practical and fundamental insight of PLA/HLCNCs nanocomposites to be used for flexible packaging films. Future work to improve the dispersion of HLCNCs in the PLA matrix as well as in the CNC drying approach is suggested.
With glass being heavy, expensive, and fairly brittle there is a market for flame-retardant acrylic (PMMA). Acrylic has optimal transparency, mechanical properties, and cost of production; therefore, adding flame retardant capabilities would be valuable for glass replacement applications. Blends of monomer and polymer PMMA, a unique nanostructured chemical Polyhedral Oligomeric Silesquioxane (POSS), and 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-Oxide (DOPO) were prepared to obtain transparent flame retardant acrylic. The results show that the synergistic additives had significant effect on the flame retardancy of the acrylic, with minor effect on optical and mechanical properties.
Highly filled polymer compounds can present processing challenges, including high screw shaft torque, energy consumption, die pressure and melt temperature rise. Previous theoretical development and experimental evaluations of highly filled polymer melts showed that the rheology can be described with a percolation model [1-4]. This paper re-evaluates a batch mixer characterization method used to measure the effects of filler concentration on melt processing. The experimental results are compared with capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide. The theoretical treatment of the rheology as a particulate percolating system with power-law behavior is used to analyze rheometer and batch mixer data. The effects of resin molecular weight, filler type and size on rheology and melt processing are described.
In order to maintain desired properties of insulating products, while also complying with ever-increasing regulatory pressure on blowing agents, emphasis of academic and private sector foams research has shifted to minimizing the radiative and solid conduction components of heat transfer in rigid closed-cell foams. Although methods and equipment for measuring total thermal conductivity of low density, insulating rigid polymeric foams are well established , and there are theoretical models [4 - 6] for estimating individual contribution of each heat transfer mode, experimental methods for direct measurement of the latter are lacking. In this paper, we offer a method for measurement of individual heat transfer modes (conductivity through solid, conductivity through gas, and radiative transfer) in rigid, low density polymeric foams by employing measurements in ambient atmosphere and in vacuum, as well as specific specimen preparation.
Heat stability of polyolefin materials is of great interest as the need for long lifetimes is expected for certain applications. Accelerated tests are often used where materials are tested under elevated temperatures, in which unrealistic degradation may occur. This paper aims to demonstrate the importance of choosing adequate temperatures for accelerated ageing test. Also, a nondestructive surface chemistry tracking method is employed to provide insight into degradation as a fast and convenient alternative to mechanical testing. A comparison is made between the two tracking metric results under different temperatures, which revealed the importance of selecting an adequate ageing temperature for comparing materials with different melting temperatures. Above the polymer melting temperature the decrease in crystallinity allows more oxygen to diffuse into the polymer and may cause unrealistic failure, resulting in invalid comparisons under high testing temperatures.
The scratch performance of a series of cast polyurethane elastomers (CPU) upon exposure to water is investigated. Four different kinds of CPU were chosen and their scratch performances were compared in dry and water-saturated conditions. The CPU model systems were synthesized containing the same isocyanate and chain extender, 4,4'-methylene diphenyl diisocyanate (MDI) and 1,4-butane diol (BDO), to form the same type of hard segment, with four different soft segments (polyols): polytetramethylene ether glycol (PT), polycaprolactone (PC), ethylene oxide and propylene oxide based polyether polyol (PET) and adipic anhydride based polyester polyol (PES). Scratch tests were carried out according to the ASTM D7027/ISO 19252 standard. Results indicate the changes in scratch performance are closely correlated with the variations in coefficient of friction, tensile true stressstrain behavior as well as dynamic mechanical behavior of all the CPU model systems upon water exposure. Fundamental structure-property relationships of CPU affected by water content are discussed.
Thermoplastic elastomers (TPE) including thermoplastic polyolefins (TPO) and thermoplastic vulcanizates (TPV) are promising elastomeric materials for automotive applications such as headlight surrounds, bumper covers, door gaskets, etc. TPEs offer a combination of great thermoplastic processability and outstanding rubbery properties, however, the process of recycling scrap and post-consumer products and reprocessing them into useful products have always been challenging. In addition, tire rubbers have been one of the most problematic sources to recycle, due to their large volume and durability. Innovative and effective methods are critical to reuse the recycled tire rubbers in value-added products other than their traditional use for fuel values. In this study, micron-size rubber powders (MRPs) were fabricated from recycled truck tires in large volume, and used as fillers for the twin screw extruder (TSE) compounding of recycled TPOs. TPO was chosen as the base resin for compounding because of its excellent reprocessability, good compatibility with the micron-size tire rubbers, and reasonable low cost. A compatibilizer was studied to enhance the uniform incorporation of micro-size rubber powders into the base resins and improve the overall performance of the compounds in a cost-effective way. The chemical structure of the recycled TPOs was confirmed by FTIR, and the thermal stability and compositional analysis of the recycled tire rubbers were characterized by TGA. The physical and mechanical properties (hardness, MFI, tensile, Izod impact, etc) were extensively tested to study the overall performance of the compounds. The surface details of injection molded parts are studied and improved for automotive and commodity applications.
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.
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.
In this paper, we describe a methodology for determining elastic stretch properties of polymer fluids from purely shear data. The theory is founded on the basis of decoupled rubber elasticity and relaxation, to uncover the rubber elasticity portion of contribution to viscoelasticity. This would not only produce a means for linking shear with extension, but potentially would also provide a new paradigm for studying the relation between structure and deformation for dissipative materials. A case study is presented to emphasize the potential applicability of the methodology when only partial data is available.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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