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.
Extrusion thermoforming of very large parts such as those used in the appliance industry can exceed the melt strength limits of a given polymer. This study was undertaken to define new rheological tests capable of defining the molecular design required to avoid excessive sag in the heating step of the thermoforming process and to identify the optimum temperature for forming. Damping factor (tan = G’’/G’), also known as “tan delta”, can be used as a tool to identify fabrication conditions, molding window size, and the effect of added recycle streams. In addition, we compare polymer families that challenge our ability to thermoform large parts. Semi-crystalline materials must be run at or above their melting point temperature (Tm). Tm is well above the glass transition temperature (Tg) and the temperature delta (Tm - Tg) may exceed the width of any rubber plateau region in the melt state. These rheological characteristics are related back to the entanglement density of a given polymer and compared to the width of the rubber plateau.
This manuscript aims at investigating the influence of biocarbon content on the morphology of binary immiscible blends. Herein, polyamide 6 (PA6) and polypropylene (PP) were prepared at blending ratios 20/80 and 80/20. The dispersed droplet size was determined from scanning electron microscopy measurements and compared to the elastic and loss modulus of the systems measured by oscillation rheology. The biocarbon content showed a significant effect on the dispersed droplet size. In case of the PP dispersed phase the use of high biocarbon content is beneficial to decrease the droplet size while systems containing PP in the matrix should use a low amount of biocarbon.
With increasing interest towards biobased and/or biodegradable polymers that generate high performance composites, instead of petroleum based products, creates new opportunities and research challenges. Polylactide (PLA) is supposed to be one of the most promising biodegradable polyesters because of its high mechanical strength, high modulus and good biodegradability. However, the low melt strength of PLA has greatly limited its melt processing such as casting or blowing film, and finally limit its application as packaging. Therefore, firstly the mechanical properties of the PLA were modified by blending with PBS and PBAT; then the melt rheological properties of PLA ternary blends were modified by peroxide in reactive extrusion, and the enhancement effects were evaluated by rheological studies here. Rheological properties revealed that peroxide can greatly enhance the melt strength of PLA ternary blends. A PLA ternary blends/peroxide system can be a good candidate to fabricate biodegradable films with high toughness via stretching shaping process such as casting or blown film.
While barrier, optical, dielectric, and mechanical properties of multilayer polymer films have been studied extensively, there is comparatively little regarding the melt rheology of these multilayer films that would inform secondary processes such as thermoforming and biaxial orientation. Here we expand on our previous work regarding polyethylene/polypropylene (PE/iPP) solid-state adhesion to study the molten interface of 640 layer PE/iPP films. The interfacial tension of a metallocene linear low density polyethylene (mlE) and metallocene iPP (miP) system was measured by blending miP into mlE. The small amplitude oscillatory shear (SAOS) data was fitted with the Palierne model to extract an interfacial tension. Interfacial slip of the multilayer mlE/miP system was observed at shear stresses greater than 10 kPa. While neither mlE or miP homopolymer exhibited strain hardening behavior, the 640 layer mlE/miP system possessed a higher plateau extensional viscosity than anticipated as well as pronounced strain hardening behavior. These results suggest the molten interface has a significant impact in the secondary processing of extruded polyolefin films and may be an avenue to enhance thermoformability of iPP films.
This research work is focused on the melt extrusion of poly (3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) with poly (butylene adipate-co-terephtalate) (PBAT) and nanoclay followed by preparing polymer nanocomposite sheets using compression moulding. The effect of nanoclay on various properties such as water barrier, tensile strength, differential scanning calorimetry (DSC) and rheology was investigated. The results conclude the addition of nanoclay in PHBV/PBAT blend matrix improved the water barrier and tensile strength up to ~12% and ~20% respectively. The differential scanning calorimetry (DSC) analysis shows a slight improvement in melting and crystallization temperatures of PHBV/PBAT blend matrix by adding nanoclay. The melt rheology has confirmed a good dispersion of nanoparticles in PHBV/PBAT blend matrix. Hence, such a polymer bionanocomposites may be one of the potential candidate for packaging applications. The developed biocomposites from biodegradable plastics show promise in sustainable packaging applications.
A new rheology measurement for the gum rubber and rubber compounds has been conducted using screw rheometer. This device uses a new viscometric flow analysis of single screw extruders to measure shear viscosity, which is based upon 'the closed dischage' extrusion characteristic equation. The screw rheometer, which is characterized by self-plasticating, self-deaeration, mixing during measuring and fast measuring time, shows the average polymer properties of the sample because the measurement volume is large enough. This study especially shows that shear viscosity and stress relaxation experiments of gum rubber and compounds can be performed by using this device. The measured viscosity is a function of shear rate, thus it can be used for the analysis of processing, machine design and quality control of the rubber manufacturing. Also, a rubber relaxation time experiment was devised as a method to confirm the relaxation time in the processing range and is named 'Engineering Relaxation Experiment'.
Tiger stripes of polypropylene copolymers are studied by modeling the mold filling process as a non-isothermal two-phase flow using a level-set method. It has been shown that the Level Set method is capable of modeling the evolution of the flow field at and behind the melt front. An area of large velocity contrast between the skin layer of high shear rates and the center core of low shear rates has been observed behind the melt front under relevant injection molding conditions. The large velocity contrast appears to be a direct origin of the flow instability. The instability in terms of alternative occurrence and disappearance of the oscillatory strain rate is proposed to be a possible root cause of the tiger stripes. The comparison of the materials of different rheology suggests that shear thinning may be a useful property to mitigate the risk with the tiger stripes.
Selective laser sintering (SLS) produces three dimensional shapes by repeatedly sintering and resurfacing a powder bed in a layer-by-layer fashion. Our short-term goal is to better understand the processing changes of a polyamide-11 powder laser sintered printing process when silica nanoparticles are added. Ultimately, we want to evaluate whether such nanocomposites results in superior z-axis strength and an overall increase in fracture resistance. Although polyamide-12 (PA-12) is more commonly used in SLS printed parts, polyamide-11 (PA-11) has the advantage of being a bio-based polymer. Like PA-12, PA-11 is a semicrystalline polymer but has a higher melting point (201 ⁰C powder / 191 ⁰C part). Rheology and solution viscometry tests confirm a molecular weight increase during printing, through a post-polymerization process. SLS printed PA-11 tensile specimens exhibit a 1.8 GPa modulus, an ultimate tensile strength of 55 MPa, and a strain to break of 66 %. Although it is not stiffer nor stronger than PA-12, PA-11 is significantly more ductile. The goal of the present study is to determine the effect of colloidal silica nanoparticle content (0 – 4 wt%) on processing behavior and mechanical properties.
The primary objective of this work was to evaluate the processing and mechanical, rheological and thermal properties of a 2 and 10 weight percent loading of MCC in amorphous polyamide (APA). Modified, unmodified MCC and commercial MCC (FI-1 fibers) were investigated. Melt-blended composites of the various MCCs and amorphous polyamide were prepared by single and twin-screw extrusion, then injection molded into test specimens. Rheological properties of 2 and 10% MCC filled composites were studied using a rotational parallel plate rheometer. The mechanical behavior of all three filled polymer composites were examined by studying storage and loss modulus with frequency. Also, the influence of moisture content in neat and cellulose reinforced composites were also investigated. These results indicate the need for extensive moisture control for amorphous nylon and microcrystalline cellulose.
A series of designed hydrogenated styrenic block copolymers have been synthesized for better understanding their molecular structural correlation with rheological and mechanical properties. The block copolymers are widely used in extrusion and injection molding; however, they are often compounded with other materials such as polyolefin and oil to avoid the processing issues caused by the nature of phase separation. Combining other materials would, in the meantime, reduce the elastic property and affect the application that require elastic recovery property. As the demand of elastic film and fiber is growing, this study offers an insight of the molecular design for processability and end-use applications. The structural parameters include molecular weight, styrene content, and vinyl content. The rheological property was performed within linear viscoelastic limit, and the mechanical property was measured under nonlinear deformation. These two sets of properties show different structural dependences demonstrated in this study.
Due to global competition, manufacturing firms must target innovation in production processes and technologies that allow the mass manufacturing of customized products through highly efficient processes. Motivated by the concept of the hybrid production system, an innovative platform technology, known as Polymer Injection Forming (PIF), was recently developed. In the PIF process, the best-in-class manufacturing technologies in polymers and metals, viz., injection-molding and sheet metal forming, are integrated to manufacture sheet metal-polymer hybrids in a single operation. In this process, the polymer melt serves as a forming medium and deforms the inserted sheet metal during the filling phase of the injection molding process. So far, most studies have focused on the influence of the injection molding process parameters on blank deformation and specification of the final deformed sheet metal part. While doing so, these studies have either totally neglected the polymer part or have only considered its rheological characterization as a forming medium. In this work, for the first time, the melt flow development of the PIF process is investigated, and a schematic flow field is presented. Subsequently, this investigation is extended to the online process parameters which are acquired with a set of in-mold instrumentations. Finally, morphology and crystallinity of cross-section of the samples produced by this process is investigated and compared with the sample produced via conventional injection molding condition.
It is known from literature [1, 2] that the rheological properties of polymer melts are influenced by the degree of long chain branching (LCB). Therefore, it is very important to understand the influence of LCB on the solid-state properties to help improve material design for unique applications. The objective of the present study is to demonstrate the use of extensional rheology as a tool to understand FR performance pertaining to dripping. Further, we also demonstrate the synergistic role of LCB in polycarbonate resins for improving FR performance.
Additive manufacturing (AM) has revolutionized the way in which products are designed and manufactured, where parts are built from the ground up, layer upon layer. For polymer based additive manufacturing, we have improved upon that by applying an innovative strategy that allows for functionally gradient multi material printing with single extrusion head. The innovation incorporates a rotating nozzle that introduces a controllable shear rate of the polymer melt, altering the melt rheology. 3-D printing a couple of materials that have different melting temperatures into a single part is challenging, since the temperature of the nozzle has to be tuned constantly to match the melt temperature of the material being extruded to achieve a desired performance. Otherwise, over extrusion or under extrusion will occur due to the different viscosities of the materials. In this study, a 3-D printer with single extrusion head that can print different materials into one part without changing the temperature of the melt is proposed. The proposed technique also allows extrusion based 3D printing to precisely optimize products performance by mixing different materials. Keywords: Additive manufacturing, 3D printing, Multi material printing, PLA.
The target of this research was to fabricate and optimize a new 3D printable biobased material that can be used for biomedical applications that require biodegradability, biocompatibility and good mechanical properties. This research was successful in preparing a biobased filament made of 70% Poly (lactic acid) (PLA) and 30% Poly (butylene succinate) (PBS) and 3D printing this filament using Fused Filament Fabrication (FFF) technique. The rheological properties were investigated prior to 3D printing and the 3D printed specimens’ mechanical properties were compared to control specimen processed with injection molding method. The V-notched Izod impact testing of the 3D specimens showed about 30% higher impact toughness in comparison to the injection molded specimens.
Fill time has long been regarded as the primary parameter to monitor and control during first stage filling of the injection molding process. Fill time is the result of a given first stage mold volume (shot volume) that is to be filled at a given volumetric flow rate. The most common industry method for evaluating the recommended fill time on the molding floor is known as the Rheology Curve or Relative Viscosity vs. Relative Shear Rate Curve (RV Curve). The RV Curve is one of the main principles taught worldwide in scientific molding courses in the injection molding industry. A company’s processing policies and procedures often reference the RV Curve as the method of choice for establishing an ideal volumetric flow rate and resulting fill time. Other methods may include the utilization of mold filling simulation software, personal experience based on similar parts and molds, or comprehensive Design of Experiments (DOE). This study focuses on the RV Curve and calls the method into question from a mathematical standpoint based on the formulas used to derive the RV curve. The study also discusses an alternative method as a potential replacement to the RV Curve.
A commodity polybutene-1 (PB-1) resin has been chemically modified through reactive processing. Samples produced by using various amounts of peroxide have been analyzed in terms of their molecular and rheological properties. Molecular weight distributions (MWD) as determined by gel permeation chromatography (GPC) indicate that polydispersity (PDI) remains constant but weight-average molecular weight (Mw) decreases with increasing peroxide amount. Linear viscoelastic measurements indicate that the modified samples are thermo-rheologically simple, zero-shear viscosity decreases with increasing peroxide concentration and flow activation energy remains constant.
Read the March 2019 issue of the SPE Applied Rheology Division newsletter.
This paper deals with the behavior of thermoplastic melt, which is excited by oscillations via piezoelectric actuators. The experimental setup is designed to transmit vibrations directly into the melt. The result of this procedure is a reduced viscosity for two different thermoplastic resins of up to 23 %. Amplitude and melt temperature have little to no effect on viscosity reduction during oscillation.
We have investigated the flame retardant (anti-dripping properties) of a polycarbonate resin by using a dynamic mechanical analysis. A UV curable polycarbonate resin showed a strong rubbery plateau as a function of UV dosage and the amount of UV active end group. The average storage modulus is defined in the rubbery plateau region from 160 to 190°C with average storage modulus of 9 MPa being a threshold value to achieve optimum flame rating.
Die build-up negatively impacted the capacity of a compounding line for the production of a polyolefin-based wire and cable formulation. This paper discusses a root cause analysis performed on the die build-up defect, the identified solution, and the resulting economic impact.
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