SPE Library

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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Conference Proceedings

Effects Of Novel Extensional Mixing Elements On Fiber Length Distribution In Composite Extrusion

Molin Guo, May 2018

A new extensional mixing element (EME) for twin-screw extrusion was applied to compound polypropylene (PP)/glass fibers (GF), polypropylene (PP)/carbon fibers (CF), and polyethylene oxide (PEO)/polyethylene terephthalate fibers (PET-F) composites, and the effects of EME on fiber length distribution have been studied compared to two kinds of shear flow dominated Kneading Blocks (KB) screw configurations. Composites structures were characterized, and good dispersion of the fiber fillers in the systems has been achieved. It was concluded that EME can reduce the breakage of the stiff glass fibers and carbon fibers in the mixing zone compared with the KB, resulting in longer fibers remained after passing through the EME than the KB based on optical fiber length distribution measurements. Although flexible polyethylene terephthalate (PET) fibers are hard to cut by conventional KB, EME can easily break them into small pieces by very high pressure generated.

Role Of Interfacial Crystallization In Designing Polyolefin Blends From Mixed Stream Recycle Feeds

Alex Jordan, May 2018

Polyolefin production requires ~8% of global oil and natural gas production for monomer supply and the energy required for polymerization; often these polyolefins are used in short term applications such as packaging. While researchers work toward long term solutions involving sustainable polymers, the short term focus on how to better recycle polyolefins currently in the production/consumption cycle must be addressed. Given their chemical similarity and similar density, recycled polyolefins are difficult to separate from recycle streams often resulting in mixed stream recycle feeds. Previously we presented the role of residual oligomer after Ziegler-Natta polymerization of polyethylene (PE) and isotactic polypropylene (iPP) in preventing cross interfacial crystallization of immiscible PE-iPP bilayers which resulted in weak interfacial adhesion. We also presented strategies for promoting cross interfacial crystallization via processing (rapid interfacial quenching) and materials selection (thickened interfaces) in PE-iPP bilayers. Here we investigate the role of interfacial adhesive strength between three PE-iPP blends in the absence of applied shear during processing. With poor interfacial adhesion between PE/iPP, brittle failure of each blend was observed, as expected with immiscible polymer pairs. When interfacial adhesion strength exceeded that of the strength of component homopolymer, exciting synergism was observed between PE/iPP blends. Processing in the presence of applied shear flows (injection molding and film extrusion) will also be discussed. This finding highlights the importance of considering interfacial strength when designing mixed polyolefin recycle streams.

Designing And Computational Validation Of Extensional Mixing Elements (Emes) For Improved Dispersive Mixing In Extrusion Operations

Vivek Pandey, May 2018

Extensional Mixing Elements (EMEs) have been developed to impart extension dominated flow in twin screw extruders (TSE) through hyperbolic contraction channels. In this manuscript, EMEs for TSE have been made more aggressive by incorporating double hyperbolic contraction (contraction in horizontal as well as vertical direction) and were also successful in designing novel modular screw design for single screw extruder (SSE) to have dispersive and distributive mixing simultaneously. The design geometry of EMEs have also been optimized for both TSE and SSE using computational simulations.

Examination Of Power Consumption On Melt Spinning: Mono And Bi-Component Fibers

Javier Vera Sorroche, May 2018

The power consumption of a melt spinning extrusion module with mono and bi-component capability was under consideration, especially when analyzing the effects of process settings and downstream equipment on the total power consumption of the extrusion line. Experiments were conducted to quantify in real-time the effects of barrel temperature profiles, godet roll temperatures and godet roll speeds on the total power consumption when the extrusion line was operated to produce both mono and bi-component fibers. Between the effective use of extrusion processing conditions and optimization of the downstream equipment, the results have shown that there is a significant opportunity to save energy for the total power consumption. In bi-component mode, the downstream equipment was found to cause the highest effect on the total energy consumption. In mono-component mode, an optimal combination between metering pump and extruder motor appeared to be crucial for the optimization of the melt spinning system. Specific energy consumption was more favorable when the metering pumps were operated at higher speeds.

Effect Of Scale Up On Thermal Homogeneity And Energy Efficiency In Single Screw Extrusion

Javier Vera Sorroche, May 2018

Extrusion scale up is the procedure of replicating a plastic extrusion process in order to predict the performance of large production size extruders on the basis of geometrically similar small extruders. Extrusion processes are often developed on small extruders, so the effective scale up of these extrusion processes is very desirable as a means of increasing production rates. Although, studies on scale up procedures have been performed for several decades, no further studies have been undertaken to examine the influence of screw geometry on extrusion performance and energy consumption. In this work, in-process monitoring techniques incorporating thermocouple grid sensors and an energy meter have enabled real time examination of the extruder scale up by comparing the thermal and energy characteristics of a 38 mm diameter single screw extruder to that of a similar extruder with 63.5 mm screw diameter. Experiments, employing identical screw geometries, extruder set temperatures and range of screw speeds, were carried out on both machines with LDPE to quantify the effect of extruder scale on the measured throughputs, melt temperature homogeneity, die pressure and energy consumption.

Characterization Of Stress In A Twin-Screw Extruder For Processing And Extrusion Of Extrinsically Self-Healing Thermoplastics

Connor Armstrong, May 2018

Capsule breakup percentage in a co-rotating twin screw extruder is studied for the purpose of producing extrinsically self-healing polymers. A method of real-time characterization of stresses using calibrated stress beads and an optical probe was devised for this research. Three different strengths of stress beads are used to represent poly(urea-formaldehyde) (PUF) encapsulated healing agents. Stress bead breakup percentage was depicted over a selected range of statistically significant operating conditions: screw speed (N) and specific throughput (Q/N). Central composite design grids were created to analyze experimental results and generate a set of predictive equations for stress bead percent breakup. This paper examines the relationship between co-rotating twin screw extrusion operating conditions and breakup of PUF encapsulated extrinsic healing agents. It also marks the first step in understanding extrusion of efficient self-healing polymer composites.

Preliminary Study Of Birefringence Distribution In Blown Film

Jin Wang, May 2018

A birefringence scanner was used in this study to measure the distribution of birefringence in blown films. The objective of this study was to evaluate the birefringence scanner as a new tool for blown film research. Seven films were made on a small-scale research line at various process conditions (i.e., thickness, blow up ratio (BUR), rate and frost line height (FLH)). Clear in-plane birefringence variations were found in all films. More significant birefringence variation was found in the cross machine direction (CD) of the film and less variation in the machine direction (MD). The birefringence variation on the CD direction could be caused by uneven flow and cooling in the die and air ring. There were no clear relationships found among mechanical properties of films, process conditions and average in-plane birefringence in the films studied. This demonstrates that birefringence scan of film is a very useful tool for studying the fundamentals of blown film process.

Energy Gap Method (EGM) Applied To Improve Extrusion Energy Performance: Successful Case Studies

Juan Carlos Ortiz Pimienta, May 2018

A novel and upgraded strategic decision methodology to increase energy efficiency in industrial processes, the Energy Gap Method (EGM), is presented. For this methodology, six different specific energy consumption levels are proposed. Five gaps or differences between specific energy consumptions can be calculated: production, quality, process, technological, and R&D gaps. Three industrial successful case studies enhancing the energy efficiency, two in extrusion blow molding and one in sheet extrusion are presented, obtaining specific energy consumption (SEC) reductions between 14 and 65%.

Investigation Of The Effect Of Stabilizer System, Medium And Temperature On The Fatigue Crack Growth Resistance Of Polypropylene For A Proper Material Selection

Joerg Fischer, May 2018

For a proper selection of materials for solar-thermal applications, the failure behavior of various polypropylene (PP) grades was investigated by fatigue crack growth (FCG) experiments. The four tested material grades differed in their stabilizer system. To determine the effect of environmental media (chlorinated water with a chlorine content of 5 ppm, air and deionized water) and elevated temperatures (95°C and 80°C), cracked round bar specimens were tested on an electro-dynamic testing machine equipped with a special desigend media containment.Tests at all environmental conditions revealed a significant influence of the stabilizer systems on the FCG resistance. While at all conditions the stabilization with a hindered amine light stabilizer resulted in the best FCG behavior, depending on the environmental loading different PP grades showed the worst FCG resistance. In terms of media dependence of the crack growth behavior, for all PP grades, the best and worst FCG behavior were obtained in deionized water and chlorinated water, respectively. Results received from tests under two different temperatures showed that the FCG resistance decreased with increasing temperature in all tested environments and for all PP grades.

Tan Delta - The Dimensionless Property That Tells You Almost Everything You Need To Know About A Polymeric Material

Michael Sepe, May 2018

Dynamic mechanical analysis (DMA) has been a useful technique for characterizing polymeric materials for over fifty years. Often material comparisons focus on elastic modulus since it is a property similar to something we are familiar with from published data sheets. But a less well known property that arises from DMA, tan delta, provides immense insight into a wide range of behaviors in polymers. This paper will review the definition of this property and illustrate some examples of how it can be used to assess the relative performance of polymeric materials for short-term and long-term use.

Fractography: The Science & Art Of Determining How Plastics Break

Farzana Ansari, May 2018

In recent decades, the engineering industry has seen a stronger emphasis on cost- and energy-efficient materials. As a result, polymers have increasingly been adopted in load-bearing applications, replacing traditional “engineering materials” such as metals and ceramics in multiple industries, from aerospace vehicles to medical devices. With this transition comes an increased need for understanding how such load-bearing polymers inevitably fail, especially with respect to cracking and fracture. Fractography – the science and art of “reading” fracture surfaces – is a powerful failure analysis tool for dealing with fractured plastic components. Fracture surface features can tell a story regarding the stress state and environment a polymer experienced during fracture, potentially eliminating hours of exploratory testing to replicate the exact failure mechanism. This tutorial will provide an overview of fracture features commonly observed for various plastics, and how those features can be related to the exact mechanism of failure. The various tools of fractography will be explored, highlighting the importance of both low and high magnification in identifying where a crack initiated and how it may have propagated. Traditional brittle and ductile fracture features will be covered, as well as more nuanced failure mechanisms such as environmental stress cracking (ESC). A deeper dive into the fractography of three commonly used commodity plastics will demonstrate the influence of composition and stress state on fracture features, as well as exhibit the value of recreation testing under controlled loading and environmental conditions.

Any Buldging Or Paneling Issues For Your Packages?

Jay Yuan, May 2018

Bottle Internal Pressure Analysis and Test for Hot Fill (BIPATH) is a container, closure, and process design and optimization program for packages that experience pressure or vacuum during any part of the supply chain. It was originally developed for the hot fill PET bottle design at Stress Engineering Services, Inc. (SES) in 2006. Over the years, BIPATH has evolved and expanded to encompass a wide range of container types and pressure/vacuum-prone filling, processing and distribution systems. The container types include injection/extrusion blow-molded plastic bottles and cans, injection-molded or thermoformed tubs and cups, and aluminum and steel cans. The pressure/vacuum-prone filling, processing and distribution systems include hot fill, retort, high pressure process (HPP), carbonation, nitrogen dosing, steam flushing, altitude and temperature change in distribution, air-shipping, product out-gas or oxygen consumption, oxygen/CO2 ingress or egress and plastic creep deformation over time. BIPATH calculates the package pressure allowable, which is the pressure or vacuum that the package can sustain without any unacceptable deformations or distortions, and the package pressure residual, which is the pressure or vacuum generated inside the package. The ratio of the pressure allowable and pressure residual, known as package pressure safety factor, offers bottle suppliers and brand owners a simplistic way to measure how well (or bad) the package would perform at the early stage of the package and product development process since no physical bottle or finished good samples are required for the BIPATH program. The pressure or vacuum can be better managed and optimized using BIPATH through changes in container and closure design, product content, process conditions (pressure, temperature and duration profiles), and shelf life commitment. The validity and versatility of BIPATH program in managing the pressure or vacuum has been demonstrated in real world packaging and process design and optimization since 2006. The theoretical foundation of the program and a case study are presented in this paper.

Fatigue Resistance And Failure Characterization Of Glass Fiber Reinforced Pa Grades

Patrick R. Bradler, May 2018

The fatigue crack growth and failure behavior of five different short glass fiber reinforced polyamide (PA) grades was investigated on specimen level using compact type (CT) specimens. By using a testing device enabling superimposed mechanical and environmental loading, the effect of environmental conditions (23°C in air and 80°C in water), matrix material (polyamide 66 and polyamide 6T/6I) and glass fiber content (30 w%, 40 w% and 50 w%) on the fatigue crack growth kinetics was determined. Tests at 80°C in water exhibited an inferior fatigue crack growth resistance. Furthermore, for PA grades with a similar glass fiber content, an influence of the matrix material was revealed. PA grades with a higher glass fiber content indicate a better fatigue crack growth and failure behavior.

Raman Spectroscopic Detection Of Microscopic Structural Changes In Polyethylene During Photodegradation

Yusuke Hiejima, May 2018

Raman spectroscopy is applied to elucidate microscopic structural changes in low-density polyethylene under ultraviolet irradiation. The crystallinity estimated with the 1418 cm-1 band shows a stepwise increase at ~600 h accompanied by obvious decrease of the molecular weight, suggesting chemicrystallization. The increase of crystallinity and the thinning of amorphous layer at ~600 h lead to macroscopic shrinkage of the specimen, inducing the formation of surface cracks. It is also suggested that contraction of interchain distance and conformational changes take place gradually during photodegradation.

How To Use Thermoanalytical Methods For Failure Analysis

Tobias Pflock, May 2018

Thermal analysis is one of the most prominent techniques to find out about failures of plastic parts. The talk will comprise the most important methods such as DSC (Differential Scanning Calorimetry), TGA (Thermogravimetry), TMA (Thermomechanical Analysis) and DMA (Dynamic Mechanical Analysis) and relate them to following application questions:• How can I identify polymers better in failure analysis?• How can I find out about the composition of a polymer compound?• What is the reason for part shrinkage after processing and what does that have to do with internal stresses?• How does temperature influence the mechanical performance of my part and what does a glass transition really look like?

Fracture Properties Of Hdpe Exposed To Chlorinated Water

Susan Mantell, May 2018

HDPE is often used in applications that include both structural and environmental loads. In this study, the effect of an oxidative environment on HDPE mechanical performance is evaluated. Thin 75 micron HDPE samples are exposed to 5ppm chlorinated water at 70C for up to 1250 hours. Changes in polymer morphology as a function of exposure time are evaluated and compared with fracture and tensile test data. FTIR data show an increase in the carbonyl group after 250 hours of exposure, while GPC data show a 20-50% loss in molecular weight after 500 hours exposure. The decrease in molecular weight is associated with shortening of the higher molecular weight chains. Essential work of fracture data and strain at break show significant loss in ductility for exposed samples. This set of data demonstrates the correlation between morphology changes and embrittlement in unimodal HDPE.

All Encompassing Extrusion Technology For Producing A Wide Spectrum Of Simultaneously Bioriented Films

Adolfo Edgar, May 2018

Most flexible packaging companies purchase and convert BOPP, BOPET and BOPA films of various types which are predominantly made using the sequential, tenter frame biorientation process. These same converters may have in-house coextrusion capabilities to produce PE based barrier films with PA and EVOH layers. Recent advances in Triple Bubble technology now make it possible to produce all these film types, simultaneously bioriented, with a single coextrusion line. Simultaneous biorientation delivers enhanced film properties over sequential biorientation, allows the use of high barrier EVOH grades that will not biorient sequentially, and facilitates the customization of films for specialty applications.

New Surface Treatment Protocol Discovery For Extrusion Coating

Rory Wolf, May 2018

Extrusion coating and lamination processes are integral for converting many of today’s high performance flexible packaging structures, most notably pouch structures. Extruding a polyolefin as a coating or using it to laminate primary and secondary substrates, such as paper, aluminum foil, OPET, and/or OPP to form a composite packaging structure is well known in the art. Depending upon the end use, such composite structures will also desirably have good adhesion, flexibility, barrier properties and heat resistance. For example, food storage pouches need sufficient adhesion strength to be handled during filling of the pouch, during preparation and storage and subsequent heat seal resistance during immersion in boiling water and subsequent handling. This study examined how the use of atmospheric plasma surface treatment technology compares to the use of corona as pretreatments in promoting seal strength of extrusion-coated flexible packaging structures specifically involving oriented polypropylene (OPP) and OPET. Results indicated a significant improvement in peel strength with the use of atmospheric plasma under specific application conditions.

Thermo-Rheological Modeling And Simulation Of Heat Sealing Process For Multi-Layer Flexible Packaging Applications

Vinod Kumar Konaganti, May 2018

Heat sealing processes are the most widely used sealing technique in form-fill-seal packaging applications. This process involves the optimization of sealing temperature, dwell time and sealing pressure to achieve a hermetic seal between two monolayer/multilayer polymer films. During this process, the heat transfers through the film structure, melts the resin at the interface and allows the polymer molecular chains to diffuse across the interface to develop the required seal strength. In order to develop strong seals at the interface, it is important to understand the interactions between thermal and rheological behavior of each layer in the multilayer structure as well as the dynamics of melting and crystallization at the seal interface.A novel phenomenological model based on thermo-rheological properties of polymers in the sealing regime has been developed to describe the heat sealing behavior of multilayer polymer films as a function of processing/operating conditions and resin architectural characteristics. In this modeling framework, a dynamic model combining heat transfer and deformation during the squeeze flow has been implemented to understand the coupled effects of phase change (melting/crystallization) and polymer rheology on the heat sealing behavior. The present model is capable of predicting the temporal variations of the interfacial temperature and seal behavior by considering the effects of: (a) non-isothermal squeeze flow of polymer films; (b) processing conditions (seal pressure, seal bar temperature, and dwell time); (c) resin molecular characteristics; and (d) phase transitions (melting/crystallization). The predicted seal characteristics are compared with the experimental data to validate simulation results. This model may serve as a robust tool for efficient multilayer film structure development and optimization of various processing/operating conditions.

Heat Transfer Modelling In Multilayer Films Used For Flexible Packaging

Dan Ward, May 2018

Heat transfer through multilayer or coextruded films is an important but often overlooked consideration that affects package converting operations and end-use package integrity. Predicting or modelling heat transfer in coextruded films is difficult because thermodynamic properties of polymers such as specific heat (Cp) and thermal conductivity (k) are not constant with changing temperature. NOVA Chemicals recently developed test methods for estimating Cp and k over a broad range of temperatures which enabled us to develop a predictive heat transfer model for multilayer films containing up to 9 polymer layers. The model provides useful guidance on polymer selection, coex layer ratios and layer placement when specific temperature or thermal performance targets are required.Two case studies will be presented that demonstrate how heat transfer modelling can be used to optimize multilayer structure design for improved performance. The first study demonstrates how interior polymer layers affect sealant cooling rates after the seal jaws are opened. By accelerating sealant cooling rates, the apparent hot tack strength and hot tack temperature window can be increased. The second study demonstrates how multilayer film thickness, the types or polyethylene or Nylon and layer distributions affect heat retention during vacuum thermoforming. When more heat is retained during the forming process, the finished package typically has better gauge uniformity and part definition.