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.
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.
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.
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.
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 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.
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?
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.
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.
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.
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 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.
It is well known that gas permeability of packaging is a key element for improving food shelf life . In order to achieve desired gas barrier for specific gas species as well as maintain other physical properties and being cost efficient, multilayer structures are widely used in packaging industry to meet different requirements. It is a trend that the industry is transforming from monolayer structure and 3-layer structure to 5-layer structure, 9-layer structure and even 11-layer structure . Multilayer structures not only provide flexibility for manufacturers to apply various functionalities, but also potentially reduces the cost of complex packaging systems. However, multilayer co-extrusion process itself is sometimes a challenge for many producers. In this study, an alternative technique, which produces materials with layer-like morphology is reported. These materials are innovatively formulated and engineered so that multilayer-like morphology arises after they are simply extruded through a single extruder. These materials can be used as monolayer films or co-extruded with other polymers. Good gas barrier (both OTR and WVTR) properties are discovered for these materials. Nevertheless, these materials depending on the specific grade can be used for cast film, blown film and biaxially-orientation film.
Accurate understanding of changeover time (i.e., the time it takes to change formulations) in a blown film line can minimize waste and maximize production. Previous work examined changeover time in extruders, and residence time distribution for blown film [Wang et. al., ANTEC Tech. Papers, 2015, Wang et. al., ANTEC Tech. Papers, 2017]. This work uses transmission UV-Vis spectroscopy with a copper phthalocyanine tracer to examine the factors affecting changeover time for a blown film line. Our results show that throughput is the strongest factor influencing changeover time, and material rheology is a weaker but potentially important factor.
Much of transparent, flexible high-barrier packaging film is based on biaxially oriented polypropylene (BOPP). The biaxial orientation process improves the barrier to both oxygen and water vapor; yet this must be combined with other layers or an organic coating to satisfy the product requirements. This paper reports on further improvements of 40% in barrier to both oxygen and water vapor in BOPP-NC over BOPP after incorporating a masterbatch additive based on nanoclay into the polypropylene. The biaxial orientation was carried out on extruded sheets of 300 micron thickness with a Karo IV apparatus. The maximum area stretch ratio achieved during biaxial stretching of the resulting compound was equal to that obtained with the base polypropylene. TEM showed that the dispersion of nanoclay was maintained after the biaxial stretching while XRD studies revealed that the crystalline lamellar width in the BOPP-NC was larger than in BOPP.
A novel polyethylene product was developed for making biaxially oriented polyethylene (BOPE) films via a commercial scale tenter frame line. As compared to the conventional polyethylene grade with a similar density and a similar melt index, the novel polyethylene could be stretched to 5x in the machine direction and 9x in the transverse direction in a wide temperature window. The BOPE film exhibited higher modulus, higher dart and puncture impact strength, easier tear, and better optical properties than the incumbent blown film used in lamination film applications. A laminated film with a BOPE layer was also evaluated and compared to the incumbent film that had a biaxially oriented polyamide layer. The BOPE laminated film showed equivalent performance at a lower film cost.
A method to measure oxygen permeance in a sealed flexible packaging, based on ASTM F2714 – 08 (standard test for oxygen headspace analysis of packages using fluorescent decay) is proposed. This method allows to consider the effect on the barrier properties of the sealing integrity, the packaging geometry and the defects due to handle or quality issues (pinholes, wrinkles, among others). This kind of measurements are relevant for the adequate design of packaging, a better estimation of the shelf life and the evaluation of quality problems. Traditionally, the oxygen permeance and oxygen transmission rate (OTR) in packaging films are measured using the standard coulometric method (ASTM D3985). In this method, the samples are taken from the roll or cut from a complete package. In this case, oxygen permeance is measured under ideal conditions, without considering the real packaging application scenario. Oxygen permeance measurements on four different barrier-level packages were carried out with the proposed method and with the standard coulometric method. Results are compared and the advantages and disadvantages of the proposed method are described.
Recently, many automation technologies and equipment are applied for new injection molding systems to execute automation for Industry 4.0. However, there are also a huge numbers of the existed injection machines or systems which are not ready for automation yet. Indeed, before automatic manufacturing, how to retain good quality is one of the crucial factors in injection molding. In this study, we have focused on how to discover the under-performance problem of some existed injection machine to face the automation challenge using CAE technology. In the real testing case, we have demonstrated that CAE simulation prediction can be regarded as the ideal target for manufacturing. Furthermore, it is also estimated the difference between simulation prediction and real experimental result quantitatively. However, after careful comparison on the amount of the driving force to generate deviation from the target, the real experimental result presents almost the same trend and the same amount as numerical prediction did. Moreover, we also tried to compensate the under-performance of the real experiment using a series of packing pressure settings suggested by numerical simulation. Results showed that quality can be improved significantly.
Plastic injection molding has become an important technique in traditional industry in recent years. In the process of injection molding, many manufacturers rely on the experiences of skilled workers, rather than utilizing an efficient method to eliminate processing defects, resulting in difficulties in quality control and increased total cost. To solve the problem of defect removal effectiveness, computer-aided engineering (CAE) is often employed, which can eliminate molding defects, through simulation analysis, before manufacturing. However, some unpredictable problems remain during the actual molding, which require the assistance of field technicians.The outcomes of injection molding, which involve injection pressure, cooling time, and warping deformation, have an intricate connection with control factors, which cannot be classified by regular linear programming. Back Propagation Neural Network (BPNN) has excellent predictive ability in solving non-linear problems. It can accurately predict the results after executing a series of training data. This study combined the orthogonal Taguchi Method and BPNN to construct a computing system for predicting the analysis result of CAE, and analyze the influence of multi-layer structure on prediction accuracy. The results showed that using the Taguchi Method to optimize the parameters of BPNN can increase the accuracy of prediction. Using the optimized network parameters can reduce the prediction error of the maximum injection pressure and maximum cooling time to less than 1%. However, there is still an error of 7.26% for the prediction on warping deformation, which demands further investingation of training data.
Thin polymeric microfluidic chip design (chip thickness 0.6mm or less) is desired for lab-on-chip device due to rapid heat transfer across thickness direction. This feature results in better bonding property and temperature control during diagnostic analysis. It also offers good optical properties for the observation of fluidic mixing, filtering and reaction in the multi-layer and multi-functional chip design. However, polymer melt filling for thin chip poses great challenges as the frozen layer along melt flow path is built up rapidly for conventional injection moulding process. Some moulding defects may associate with thin chip design such as short shot, warpage, thickness variation and birefringence etc. In this paper, a series of Moldflow simulation studies were conducted to virtually investigate the effects of thin chip melt filling characteristics for both conventional injection moulding (CIM) and injection compression moulding (ICM) processes. The simulation results show that injection compression process is an enabling moulding technique for a polycarbonate (PC) based 0.6mm polymeric micro reactor chip design. Compared to CIM process, there is more than 30% improvement on chip micro feature replication accuracy and chip deflection.
This is an invited paper for the Join IMD-PD3 Session.For a plastic part or assembly to perform as expected, proper consideration must be given to material selection, part design, tooling, and processing. In many instances, design errors are misclassified as tooling, processing or material issues. It is also not uncommon to attribute design related failures to customer abuse! As an example, a sharp transition in the wall thickness can cause:- Flow marksMisclassified as poor gate design or location, inadequate cooling, too little or too much holding pressure, high injection speed causing chain breakdown or pigment degradation, contamination, etc.- Poor chemical resistance and cracks Misclassified as the chemical resistance of the material- Failure in dropMisclassified as processing issues causing high molded stresses, material weakness, customer abuse, etc.- WarpageMisclassified as uneven packing pressures, poor cooling, etc.Numerous actual parts will be shown to illustrate the foregoing.
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