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In a previous communication, we discussed results from a thermal investigation in which we studied strategies to accelerate physical aging of polymeric glasses [1]. Specifically, we performed thermal annealing and pressure conditioning on four distinct epoxy-based thermosetting resins and evaluated the physical aging behavior using Differential Scanning Calorimetry. Additionally, we evaluated, from a thermal perspective, the influence of molecular properties and network architecture on the tendency of these glasses to age. We showed that, from a thermal perspective, pressure conditioning imparts an aging which is distinct from that produced via thermal annealing and that cross-link density appears to have a stronger influence than backbone stiffness in affecting the tendency (rate) of aging. Based on the intriguing results from this previous work, in this communication, we extend the comparative investigation between pressure conditioning and thermal annealing by examining the glasses using both linear and non-linear mechanical metrics. In doing so, we aim to uncover in greater detail how pressure influences the nature of polymer glasses and facilitates accelerating their physical aging behavior.
Coiled filament mats (CFM) are manufactured within an extrusion process and special downstream peripherals. A large number of endless polymer strands are joined to form a spatial mat structure. The individual, randomly arranged melt strands are connected at the contact points, thus enables the structure to be held together. Possible fields of application can be found wherever foam mats are currently used. CFM products offer a number of advantages, such as good air circulation, suitability for allergy sufferers and good cleaning possibilities. In order to achieve defined and reproducible product properties as a foam mat substitute, it is necessary to determine the physical properties using a suitable test setup. This paper will provide a comprehensive overview of the state of the art in the production of CFMs, tests of mattresses and foam structures and current research. Subsequently, the first experimental investigations are presented which for the first time associate the influencing parameters in mat manufacturing with mat criteria.
Smart materials are designed materials that have properties that can undergo controlled change by external stimuli and these materials are increasingly being used as sensors and actuators for robotics and artificial intelligence systems. In this study, polymeric bilayers acted as smart materials that could bend, curl, and twist after applying and releasing a mechanical strain. The polymeric bilayers were created using polyolefin thermoplastic elastomers (TPEs). Ethylene octene copolymer TPEs (POEs) with different degrees of crystallization were compression molded separately then adhered to one another through compression molding. The samples were then cut into strips of varying length to width (L/W) ratios and uniaxially strained. After release of the strain the strips either bent, curled, twisted, or showed a combination of 2 responses depending on the elastic recovery ratio of the 2 layers and the applied strain. This study showed that easily processable TPEs can be used as actuators for mechanical strain applications and the deformations can be reversed through heat application at low temperature for a very short period of time.
A weight reduction of 10 % can enhance the fuel efficiency of a combustion engine vehicle by 6 to 8 % and the travel range of a battery electric vehicle by as much as 10%. Automotive composites can offer massive weight savings over steel. Besides this these materials also offer other advantages such as improved noise, vibration and harshness or NVH performances, corrosion resistance and resistance against denting. Composite materials can help in part integration leading to lower tooling cost and high speed to market due to lesser tooling lead time. The automotive parts produced using mass producing processes such as sheet molding compound (SMC) technology can offer composite parts (with sp. gravity 1.8 to 1.9) that are 20 to 25 % lighter than steel parts. Efforts are underway to develop composite materials which can offer weight savings of up to 30 to 70 % over steel. Nanocomposite technology has attracted significant interest as a light-weighting technique in recent years. This technique is however limited by the high cost of the nano-particles. In this project we have explored the use of a least expensive nano-material to manufacture and stabilize light-weight sheet molding compounds with specific gravity down to 1.25. Because of their higher surface to volume ratio we can obtain the required performances with lower loading levels of the nano-particles thereby offering the advantage of reduced density. For reaching specific gravity down to 1.45 the SMC technology is combined exclusively with nano-technology. To reduce it further down to 1.25 the nano-SMC technology has been combined with hollow glass microspheres or glass bubble technology. The major challenge was to realize the reinforcing effect of the nano materials by ensuring good compatibility with the resin matrix and high degree of dispersion. Through careful design and execution of experiments, the raw material compositions and their mixing sequence have been optimized for attaining well dispersed compositions of lightweight composite materials with specific gravity in the range of 1.65 to 1.25. The composites so designed and developed have been characterized for their molding, mechanical and painting performances. Overall, the performances have been found to be comparable or in some instances higher than that of the competition. Further the formulations have been fine-tuned for uniform pigmentation based on the orders received from two of the leading OEMs; one requiring lightweight parts of Sp. gravity of 1.45 and the other one requiring lightweight parts with Sp. gravity of 1.28. Although these parts are intended for under the hood applications they require good finish as they would be visible during maintenance and care.
A transitioning layer was introduced between the matrix and the dispersed phase of the otherwise incompatible components. The transitioning phase should have good interactions with both the components, resulting in lower interfacial energy between the phases. Theoretically, it is hypothesized that if the sum of the interfacial tension between the transitioning phase and both the components of the composite is smaller than the interfacial tension between the two components, the encapsulation of the dispersed phase by the transitioning phase is spontaneous, which will lead to better interphase interfacial interactions. Since this compatibilizing technique relies purely on judicial selection of a polymer with suitable surface energy as the transitioning layer, no tedious chemical synthetic processes are required. To illustrate the proposed technique, incompatible Poly(lactic acid)/Thermoplastic Starch (PLA/TPS) blend is compatibilized with Poly(butylene succinate) (PBS) as the transitioning layer in this study. With PBS encapsulating the dispersed TPS phase, PLA/PBS/TPS 60/10/30 wt% demonstrate a better mechanical synergy, with significant improvement in strength, ductility and toughness as compared to PLA/TPS 70/30wt%. This technique can also be applied to design other multicomponent blends or composites.
From a functional point of view, the single-screw extrusion process can be divided into several processing steps, one of which involves melt conveying and pressurization. To generate the pressure needed for pumping, the polymer melt must be conveyed and pressurized by the processing machine. We have recently proposed a heuristic model for predicting the conveying characteristics of power-law fluids in three-dimensional metering channels [1-2]. Here, we present an experimental validation of this novel melt-flow theory. In the first part, experiments were carried out on a well-instrumented single-screw extruder, employing various extruder screws, materials, and processing conditions. In the second part, we implemented our heuristic melt-conveying model in a network-theory-based simulation routine to replicate in silico the conveying behavior of the metering zones experimentally investigated. For a wide range of processing conditions, the predictions for the axial pressure profile along the screw are in excellent agreement with the experimental data.
Mixing is an important elementary step in polymer processing to achieve the required melt quality. In this work three-dimensional simulations were carried out investigating the mixing behavior of polymer melt flow through different pineapple mixers. We compared the mixing of a common pineapple mixer with channels arranged with 𝜃" = 45° and 𝜃' = 135° with two scientifically designed pineapple mixers with both angles 𝜃 less than 90°. The scientifically designed pineapple mixers were originally proposed and have been practiced by Prof. C. Chung. The axial velocity field, pressure consumption and viscous dissipation are evaluated. Further we investigated the distribution of the flow through the different channel directions. Axial distributive mixing is analyzed by means of the residence time distribution and its normalized variance. Cross-channel mixing is investigated by means of the scale-ofsegregation. Our simulations show that the scientifically design pineapple mixers show considerably better mixing than the common pineapple mixer.
This work compares the efficiency of two ground tire rubber (GTR) surface treatments: a coupling agent (maleated polyethylene, MAPE) addition via solution treatment and a devulcanization process using a microwave treatment. The treated and untreated GTR particles were dry-blended with linear low density polyethylene (LLDPE) to produce the compounds via rotational molding. In particular, the effect of MAPE and microwave treatments were investigated to modify the physical (density) and mechanical (tension, flexion and impact) properties of the resulting compounds at room temperature. The results showed that both GTR treatments led to limited increase of tensile strength and impact strength, while the tensile modulus, elongation at break, flexural modulus and density were almost unchanged for a fixed GTR content.
During polymer melts extrusion wide range of unstable phenomena (die drool, slip-stick, wall slip, melt fracture etc.) can occur. These instabilities significantly limit production rate and decrease final product quality. Due to significant viscoelastic nature of polymer melts, secondary flows (vortices) inside the processing tools can also occur. In these vortices, polymer melt slowly rotates which significantly extends residence time at high processing temperature. This can lead to unwanted thermal degradation. Contrary to majority of flow instabilities visually detected on extrudate surface, vortices are always hidden inside processing tools. Thus, the study of them can only be done through visualization cells and special experimental techniques mapping velocity fields (particle tracking or laser-Doppler velocimetry) or stress fields (flow induced birefringence). Despite vortices are stress induced instability, theirs study is commonly performed through velocity fields only, which is however not fundamentally correct.
This work is focused on development of novel method for study of vortices in polymer melt extrusion based on flow induced birefringence. Testing of the proposed method has been done for LDPE Lupolen 1840H polymer melt. Vortex boundary obtained from stress field have been directly compared with velocity one visualized through rotating gel particle tracking. Effect of temperature and shear rate on vortex area have also been studied and successfully correlated with laser-Doppler velocity data available in open literature for the same polymer melt and similar processing conditions.
In this work, 1.5D film casting membrane model proposed by Silagy et al. (Polym Eng Sci 36:2614-2625, 1996) was generalized considering single-mode modified Leonov model as the viscoelastic constitutive equation and energy equation coupled with crystallization kinetics taking temperature as well as stress induced crystallization into account. The model has been successfully validated for the linear isotactic polypropylene by using experimental data collected under extremely high cooling rate processing conditions (86°C/s), which were taken from the open literature. It has been found that utilization of flow induced crystallization significantly improves model predictions, especially for the film temperature and crystallinity. The model was consequently used to understand the role of heat transfer coefficient on the neck-in phenomenon as well as on the film velocity, temperature and crystallinity profiles.
Linear low density polyethylene (LLDPE) cast stretch films were produced to evaluate the effects of line speed, air gap, frost line and film thickness on the morphology of the prepared films. Surface morphology of the films were observed using scanning electron microscopy (SEM). It was found that the most effective parameter on the surface morphology of the films is line speed followed by air gap. In addition, relaxation behavior of LLDPE resins was investigated using rheological measurements. For the films with similar thicknesses but prepared at different line speeds the time scale for the melt to relax was correlated with the crystal phase development in the films, which affected the microstructure and crystalline morphology of the films.
The use of thermoplastic based fiber reinforced materials in demanding structural applications concerning long-term loading in combination with elevated temperatures and media influences requires comprehensive but experimentally practicable materials characterization. While for the long-term estimation of the time dependent deformation behavior a number of extrapolation methods for creep and creep rupture characterization is available, most of these methods are still rather time consuming.
An useful approach for time-efficient creep characterization is the stepped isothermal method (SIM), which primarily was established for fiber and textile materials [1, 2]. The first goal of the present paper was to investigate the applicability of SIM for glass fiber reinforced PA6.6 and PPA materials in the saturated wet state. For this purpose, a specific media cell with an integrated deformation measuring system was built up for creep tests under water immersed test conditions for standard tensile test specimens. Based on the stepwise increased test temperature, the creep deformation was accelerated and subsequently used for the creation of creep modulus master-curve generation in accordance to SIM. Generally, plausible results for the time dependent creep modulus of the materials at 60 °C in wet state were obtained, also in good agreement with the corresponding short-term Young´s modulus values.
Further on, a new methodical approach for the estimation of the long-term creep rupture behavior was developed. The established stress rate accelerated creep rupture test method (SRCR) allows for very time-efficient creep rupture estimation based on a series of stress rate dependent tests at various initial load levels. In the present study, this method was successfully implemented on glass fiber reinforced PPA materials. The time dependent creep rupture strength was obtained over a time range up to more than 5 years, also in good agreement with the results of additionally performed conventional creep rupture tests.
Barrier melting sections are extremely common and useful for single-screw extruders. Some common mistakes in their design and operation, however, can reduce their performance. A common mistake when attempting to decrease the discharge temperature for a single-screw extrusion process is to decrease all barrel temperature zones. This method, however, can cause the specific rate of the extruder to decrease for screws that use barrier melting sections. This paper will describe the problem, provide laboratory extrusions that demonstrate the problem, and then provide a case study.
Accelerated aging is used throughout the Medical Device sector and other sectors to evaluate materials and devices in an accelerated fashion. Accelerated aging has several typical modes, depending on the type of materials and functional mechanisms involved. One mode is related to stress relaxation and creep, which impacts the function of parts under sustained strain or stress as well as influencing time to develop cracks. This paper explores viscoelastic behavior of moderate melt flow medical grade polycarbonate as related to accelerated aging. The relationships between stress relaxation, creep, and complex modulus (as a function of time and temperature) are discussed. An example demonstrating the correlations between stress relaxation, creep, and Dynamic Mechanical Analysis (DMA) master curve data for a medical-grade polycarbonate is provided. Additionally, Q10 factors as intended for accelerated aging are estimated for stress relaxation of medical-grade polycarbonate using DMA master curve results.
Accelerated aging is used throughout the Medical Device sector and other sectors to evaluate materials and devices in an accelerated fashion. Accelerated aging has several typical modes, depending on the type of materials and functional mechanisms involved. One mode is related to stress relaxation and creep, which impacts the function of parts under sustained strain or stress as well as influencing time to develop cracks. This paper explores viscoelastic behavior of moderate melt flow medical grade polycarbonate as related to accelerated aging. The relationships between stress relaxation, creep, and complex modulus (as a function of time and temperature) are discussed. An example demonstrating the correlations between stress relaxation, creep, and Dynamic Mechanical Analysis (DMA) master curve data for a medical-grade polycarbonate is provided. Additionally, Q10 factors as intended for accelerated aging are estimated for stress relaxation of medical-grade polycarbonate using DMA master curve results.
Accelerated aging is used throughout the Medical Device sector and other sectors to evaluate materials and devices in an accelerated fashion. Accelerated aging has several typical modes, depending on the type of materials and functional mechanisms involved. One mode is related to stress relaxation and creep, which impacts the function of parts under sustained strain or stress as well as influencing time to develop cracks. This paper explores viscoelastic behavior of moderate melt flow medical grade polycarbonate as related to accelerated aging. The relationships between stress relaxation, creep, and complex modulus (as a function of time and temperature) are discussed. An example demonstrating the correlations between stress relaxation, creep, and Dynamic Mechanical Analysis (DMA) master curve data for a medical-grade polycarbonate is provided. Additionally, Q10 factors as intended for accelerated aging are estimated for stress relaxation of medical-grade polycarbonate using DMA master curve results.
In this work, the 3-D porous hydroxyapatite (HA)-modified polyurethane (PU) scaffold successfully fabricated by using simple ultrasonic assisted method. The hydrophilcity, water absorption and mechanical properties of HA-modified PU scaffold were significant higher than those of PU scaffolds. Compared with PU scaffold, the addition of HA nanoparticles could effectively improve the attachment and growth of human umbilical vein endothelial cells (HUVECs) cultured on the HA-modified PU scaffold. These results suggest that HA-modified PU scaffold possesses a great potential to be used as tissue engineering scaffold and the ultrasonic assisted technique could be a simple, effective and universal method to decorate the tissue engineering scaffold.
This paper presents a study about the effects of material properties on the modeling of the microcellular injection molding process. In particular, the effects of gas solubility and diffusivity data on the simulation results were examined. Often, actual measured data are not available for these properties. The effectiveness of using a generic equation to estimate these values has been evaluated by comparing the simulation results from this to a simulation that uses the actual measured data. The study indicates that by properly using these estimated material properties data, meaningful simulation results can be obtained.
Computer simulation to model the manufacturing as well as the performance of plastic part requires a good understanding of the material properties at the representative conditions. The same material behaves differently during different processes, e.g. extrusion is a shear dominated process, while thermoforming is elongation dominated. Additionally, viscoelastic effects may be relevant to capture since they control the amount of die swell depending on the geometry and process conditions. Additionally, plastics are also non-linear materials and exhibit non-linear stress-strain behavior that can possibly be rate dependent as well. This paper is a review highlighting the different processes that have been modeled before and the different material models that are required for a successful simulation will be discussed. The following case studies will be used to highlight the material models; catheter extrusion, tray thermoforming, and catheter kinking.
In this study, agricultural proteins were compounded into synthetic isoprene rubber (IR) and sulfur-cured. A constant filler loading of 8 parts per hundred rubber (phr) was used to evaluate the reinforcing capabilities of two full proteins, i.e., corn zein (Zein) and gliadin from wheat (Gd), a hydrolyzed protein, i.e., trypsin hydrolyzed gliadin (THGd), and a neat amino acid, i.e., arginine (Arg). Cure meter testing, tensile testing, and swelling experiments were performed to assess the curing kinetics, Young’s moduli (E), hysteresis, and crosslink densities of the vulcanizates. The filled vulcanizates exhibited comparable or higher E and [X] than an unfilled IR Control, but slower curing kinetics. The hysteresis, or unrecoverable mechanical energy, decreased with increasing elongation in the filled vulcanizates, which was opposite the behavior of the IR Control.
This paper presents the design and development of a chassis mounted pick-up truck front bumper for the 2018 Ranger Raptor which meets pedestrian safety performance.
Truck bumpers are traditionally made of steel to meet customer expectations of a durable vehicle capable of suitable crash protection performance, firmness of feel and rugged styling.
Pedestrian safety performance is increasingly becoming a regulation for the sale of vehicles in selected markets around the world.A traditionally mounted steel bumper does not have suitable energy absorption to meet this regulatory requirement.
The bumper developed by Ford of Australia uses sandwich plastic bumper fascia with a steel support structure to meet the conflicting requirements of a soft front for pedestrian protection and a solid substructure to meet low speed crash requirements including static and dynamic stiffness for durability.
In this work, neat polypropylene (PP) foam boards was produced under different saturation pressure and foaming temperature by using supercritical CO2 as a blowing agent in an industrial-scale batch foaming system. In addition, the effort was made to prepare for flame-retardant PP foam samples by introducing a basic magnesium sulfate whisker (MSW). The preliminary results showed that with addition of MSW, PP composite samples have increased Limiting Oxygen Index (LOI) and increased tensile property. As the increase of amount of MSW, the average cell sizes of PP foams have little change but the cell densities were decreased thus the volume expansion ratios were decreased as result. To obtain low-density flame-retardant PP foam products, systemic study on the foaming condition on cell morphology need be conducted.
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