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.
In this paper, we investigated the rheological properties of high density polyethylene (HDPE) based composites filled with different amounts of graphene nanoplatelets. The composites samples were prepared in the form of films by the method of melt mixing. A parallel-plate rheometer was used to measure the rheology properties, including the complex viscosity, storage modulus and viscous modulus. The LVE range of all the samples was determined firstly, and then we studied the rheological properties of pure HDPE and graphene/HDPE composites. The effect of graphene content on the rheological properties of the graphene/HDPE composites at 150 °C was especially investigated. The results showed that the complex viscosity of the graphene/HDPE composites was decreased and then increased with increasing the content of graphene from 0.25 to 1.0wt%. However, increased graphene content did not exhibit distinct effect on storage modulus and viscous modulus of graphene/HDPE composites.
During the plasticization of polymers with fillers and reinforcing materials within the special process of inline injection molding compounding (IIMC), agglomerations of the additives cannot be excluded. The agglomerations lead to uncertain process management, which is why this study evaluates a process for rapid determination of agglomerates and degree of agglomeration for further development of the IIMC. In addition to the degree of agglomeration, the tensile strength was also investigated in order to detect a correlation between the determined parameters.
Silicone Rubber and especially High-Consistency Silicone Rubber (=HCR), are typically processed in the extrusion process. Due to the high requirements in terms of the material properties and the geometric dimensions, a fundamental knowledge of the whole process including experiences in tool design are essential. In this study, HCR with different Shore-hardnesses are extruded on a vertical silicone extrusion line with various breaker plates with different length to diameter ratios (=L/D-ratio) in order to analyze the influence on the whole extrusion process. It has been shown that soft materials, regardless of die geometry, achieve higher throughputs compared to harder compounds. Increasing counter pressure, e.g. due to longer die lengths, reduces the volume flow rate per revolution and reduces the throughput. Tools with a small L/D ratio achieve the highest throughput. With regard to die design, it can be seen that dies with a smaller L/D ratio have clear advantages: due to their short length, they represent a smaller pressure consumer. As a result, the dwell time in the extruder is shorter and the risk of scorch is reduced. The absolute value of the swelling behavior is larger, but can be predicted with high accuracy. Shorter tools also show less flow instabilities.
Drop Dart testing is one of a number of standard characterization techniques employed as a means to characterize film toughness. In this test, a dart with varying weights are dropped from a prescribed height on a film and the weight at which 50% of the tests penetrate the films is reported. It was found that friction between the dart head and the film can adversely affect the results in this test. Application of talc to the surface of the film prior to the test, thus reducing friction between the dart head and the film, improved results significantly in metallocene catalyzed linear low density polyethylene films. The addition of slip and antiblock often resulted in significant improvement as well. These results call into question the utility of the test as it is presently implemented to measure true, intrinsic film toughness. On the other hand, if anomalous frictional effects were to be eliminated through the routine application of talc to the film surface, then the validity of the test can be restored.
Polymers in engineering applications generally display a tradeoff between stiffness and toughness. In the case of polypropylene (PP), glass fibers are often added to increase stiffness, but at the cost of toughness. Conversely, when rubber is added to PP either in reactor or post reactor, toughness is increased, but at the cost of stiffness. However, when polyester fibers are added to polypropylene, this tradeoff can be obviated. Polypropylene-polyester fiber composites display a combination of stiffness and toughness not accessible to PP homopolymer, impact copolymers or other compounded products. The primary toughness mechanism is pullout of the polyester (PET) fibers.
A new evaluation method for inline viscosity measurements in injection molding is presented, which allows characterizing the pressure dependence of a plastic melt within one cycle. A viscosity measurement die in combination with a flow spiral mold was used. A fit of the increasing pressure curves allows selecting various counter pressures that can be used to calculate the pressure coefficients. This method exemplarily is demonstrated for Polypropylene (PP). The resulting pressure coefficients show a good accordance to literature values, but are slightly lower in comparison to the data calculated with other methods.
Since cellulose acetate (CA) shows no adhesive properties in the two-component injection molding process with bio based thermoplastic polyurethane (TPU), blends of CA and polybutylene succinate (PBS) were produced to decrease the interfacial tension between the materials. While the interfacial tension was calculated from the results of a drop shape analysis, the adhesion strength was measured in peel tests according to the guideline VDI 2019. The comparison of the results gave information about whether the drop shape analysis is a valid method to analyze the adhesive characteristics of material combinations for two-component injection molding. Moreover, tensile tests were performed, to characterize the mechanical properties of the CA/PBS blends. It could be shown, that decreasing the interfacial tension between the two components by blending the CA with the PBS increased the adhesion strength. Adding 30 % PBS caused a cohesive failure of the soft component in peeling tests, showing a bonding strength of at least 147 N.
In a previous communication, we discussed results from a thermal investigation in which we studied strategies to accelerate physical aging of polymeric glasses . 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.
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