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
Study of the Impact of Induced Condensing Agents on Ethylene Polymerization in Gas Phase Reactors (Paper)
A widely-used approach to control overheating in the gas phase polyethylene systems is the so-called “condensed operating mode” where liquid species are injected together with the monomer feed. These liquid species, usually alkanes, are called "induced condensing agents" (ICA). Upon entering the reactor, the liquefied components vaporize and the latent heat of evaporation helps to cool the system. It has recently been demonstrated that the inert species most typically used for this purpose can strongly influence the solubility of all species in the growing polymer particles. Different thermodynamic models are available that can capture this type of behavior, but all of them rely on a set of adjustable parameters than cannot be predicted a priori. To add to the complications, very limited solubility data is available for multicomponent systems; it is therefore very difficult to obtain realistic model parameters for olefin polymerization systems. We have chosen to work with the Sanchez-Lacombe equation of state, as it is one of the most widely applied thermodynamic models in polymer industry. The interaction parameters used in the Sanchez-Lacombe Equation of State will be identified by fitting equilibrium solubility data which are measured experimentally using a pressure-decay technique in standard laboratory equipment. A simple operating protocol allows us to generate solubility data for a limited cost. Gas phase composition is measured with an upgraded Micro GC, allowing us to estimate individual solubilities in mixes of different process gases. All this thermodynamic data has been incorporated into a single particle model to estimate the concentration and temperature gradient through a growing polymer particle. This model underlines the importance of using an accurate thermodynamic and diffusion model in order to have a good representation of the dynamics of mass and heat transfer in the polymer particle. It also demonstrates the impact of using different type and quantity of ICA on the particle characteristics.
Study of the Impact of Induced Condensing Agents on Ethylene Polymerization in Gas Phase Reactors (Presentation)
A widely-used approach to control overheating in the gas phase polyethylene systems is the so-called “condensed operating mode” where liquid species are injected together with the monomer feed. These liquid species, usually alkanes, are called "induced condensing agents" (ICA). Upon entering the reactor, the liquefied components vaporize and the latent heat of evaporation helps to cool the system. It has recently been demonstrated that the inert species most typically used for this purpose can strongly influence the solubility of all species in the growing polymer particles. Different thermodynamic models are available that can capture this type of behavior, but all of them rely on a set of adjustable parameters than cannot be predicted a priori. To add to the complications, very limited solubility data is available for multicomponent systems; it is therefore very difficult to obtain realistic model parameters for olefin polymerization systems. We have chosen to work with the Sanchez-Lacombe equation of state, as it is one of the most widely applied thermodynamic models in polymer industry. The interaction parameters used in the Sanchez-Lacombe Equation of State will be identified by fitting equilibrium solubility data which are measured experimentally using a pressure-decay technique in standard laboratory equipment. A simple operating protocol allows us to generate solubility data for a limited cost. Gas phase composition is measured with an upgraded Micro GC, allowing us to estimate individual solubilities in mixes of different process gases. All this thermodynamic data has been incorporated into a single particle model to estimate the concentration and temperature gradient through a growing polymer particle. This model underlines the importance of using an accurate thermodynamic and diffusion model in order to have a good representation of the dynamics of mass and heat transfer in the polymer particle. It also demonstrates the impact of using different type and quantity of ICA on the particle characteristics.
Polyolefin Molecular Simulation for Critical Physical Characteristics (Paper)
The physical properties of polyolefins determine the suitability of the polymers for various products and industries. The combination of monomer, comonomers, and chain microstructure can all impact these properties. The physical properties can be predicted and explored using molecular simulation. We have developed efficient molecular modeling methodologies that take advantage of advances in compute hardware to study polymers and to evaluate the physical properties. Among the physical properties critical to polyolefins that can be explored by molecular simulation are glass transition, order transition, and solvent interaction. The glass transition can be determined by a systematic study of the volume versus temperature behavior. In addition to the glass transition of a single structure, the uncertainty within a single simulation and across multiple replicates can be determined. During the slow cooling of polyolefins, ordering can also occur. This ordering is impacted by the branching behavior of the polymers. Finally, the solvent behavior of polyolefins can be explored through simulations of direct interactions. In this talk the simulation methods for these properties will be described and examples in linear and branched polyolefins will be given.
Polyolefin Molecular Simulation for Critical Physical Characteristics (Presentation)
The physical properties of polyolefins determine the suitability of the polymers for various products and industries. The combination of monomer, comonomers, and chain microstructure can all impact these properties. The physical properties can be predicted and explored using molecular simulation. We have developed efficient molecular modeling methodologies that take advantage of advances in compute hardware to study polymers and to evaluate the physical properties. Among the physical properties critical to polyolefins that can be explored by molecular simulation are glass transition, order transition, and solvent interaction. The glass transition can be determined by a systematic study of the volume versus temperature behavior. In addition to the glass transition of a single structure, the uncertainty within a single simulation and across multiple replicates can be determined. During the slow cooling of polyolefins, ordering can also occur. This ordering is impacted by the branching behavior of the polymers. Finally, the solvent behavior of polyolefins can be explored through simulations of direct interactions. In this talk the simulation methods for these properties will be described and examples in linear and branched polyolefins will be given.
Predicting Molecular Weight and Composition Distribution for Gas-Phase Polyethylene Products
A mathematical model was developed to simulate a laboratory-scale gas-phase ethylene/1-hexene copolymerization process using a multi-site metallocene catalyst. The kinetic scheme includes activation, propagation, chain-transfer to hydrogen, β-elimination, deactivation and reinitiation. A three-site model with 33 parameters was developed to predict number-, weight- and Z-average molecular weights, along with polymerization rate and overall hexene incorporation. In addition, the model predicts the molecular-weight and comonomer-incorporation distributions for the polymer accumulated in the reactor at the end of the batch. Statistical methods were used to rank the kinetic parameters from most-to least-estimable, based on the available industrial data. A mean-squared-error criterion was used to determine the appropriate number of parameters to obtain reliable model predictions. Parameters were estimated, using gas flow rate and composition data obtained over the course of each experimental run, along with polymer characterization data at the end of each run. Data sets not used for parameter fitting were used for subsequent model validation.
Overview of the Current Plastic Recycling Landscape
Trends in plastic waste management, recycling and reuse are evolving rapidly – the demand for single use plastics continues to grow and more complex plastic applications are further challenging existing infrastructure. Finding a solution requires action across all steps of the value chain (from product design to consumer education to collection to separation to recycled polymer reuse), as well as across stakeholders (from chemical companies to converters to brand owners to recycling companies to governments to investors and public figures). Chemical recycling, conversion, and decomposition technologies offer further flexibility to recover and reuse a broader set of materials and potentially provide the missing piece in the recycling equation. However, the economics of these technologies is not yet proven.
Chemical Recycling: Upcycling of End-of-Life Plastics
There is no time to lose in figuring out how to solve the plastic challenge and increase both the recycling rates and the recycled content in product. In parallel of this regulatory drive, many large brand owners have committed to reach 100% of recyclable packaging by 2030. Plastic Energy has developed a solution to address low-value mixed plastics that cannot be mechanically recycled. The Thermal Anaerobic Conversion (TAC) produces recycled oils (TACOIL) from end-of-life plastics. The TACOIL is then used as a new feedstock for the (petro)chemical industry to generate recycled plastics by replacing virgin oil with TACOIL. Our TAC process is a low-pressure thermal depolymerization process patented in Europe and the US. To be more specific, the shredded, densified and then molten feedstock is pumped into the oxygen free reactors at a controlled rate and temperature. The multicomponent hydrocarbon vapour produced in the reactor passes through our patented contactor vessel which finally controls the hydrocarbon chain length and quality before entering the condensation system. The TACOIL is then be subjected to various additional purification / polishing steps before being sent to the steam-crackers of the chemical industry. In addition of having two industrial plants running 24/7 more than 330 days per year for the past 3 years, Plastic Energy through its experience has managed to stabilise the output the specifications required by the chemical industry. This has led to the value-chain validation of the circularity of the Plastic2Plastic process by the ISCC+ to produce the Certified Circular Polymers. This chemical recycling process effectively upcycles the plastic through conversion to the original monomers in each process of recycling, making it safe and reusable as a food-grade product. After explaining the technical and industry experience of reach an optimal product and efficient operations, the presentation will stress some real-life Plastic2Plastic applications developed with the value-chain, and will continue on the upscaling and expansion of the capacities of Plastic Energy and the potential of the chemical recycling industry in improving recycling and creating a circular economy.
China’s Plastic Waste Import Ban: Global & Regional Implications
China used to import large volumes of polymer waste from around the world. The sudden 2017 decision by the Chinese government to ban imports of recyclables created a supply chain gap for plastic waste processors in China. He-Ro will outline how this supply chain gap issue has been addressed by the PR China plastic waste processors & how the value chain has adapted. With additional plastic waste bans now in place in other Asian countries, will this ’new system’ created by the plastic waste processors be rolled out across Asia and the rest of the world? Will their learnings form a base for other countries to build their own supply chain infrastructure?
Developments in End-of-Life Technologies for Multilayer and Barrier Flexible Packaging
Flexible packaging is more economical than other formats because of its lower material and energy consumption and manufacturing and transport costs. It also provides reduced waste of packaged products, particularly food, generates much less packaging waste than rigid formats and has favorable LCAs. Consequently, its use, particularly in multilayer barrier films and pouches, has been steadily growing and replacing rigid packaging. Despite this, it is still opposed by environmental groups due to difficulties in end-of-life collection, sorting and processing and concerns about “single-use” packaging and sustainability. Because of its film and multilayer construction, and often food-waste contamination, post-consumer flexible packaging is not readily mechanically recyclable and is presently generally landfilled, so that environmental groups have pressured food and other companies to stop using it. To combat this, and to eradicate landfilling, the food, packaging and recycling industries are supporting a wide range of initiatives including: a). improved mechanical recycling systems to handle film packaging and the development and introduction of supporting collection, identification and sorting technologies and infrastructure; b). new package designs and materials facilitating mechanical recyclability by reducing polymer types and number of layers, mono-material and all-polyethylene pouches, compatibilizer incorporation, and using barrier adhesives and coatings and recyclable and biodegradable barrier materials; c). economic film layer separation and recovery methods; d). chemical recycling processes to produce monomers or valuable feedstocks; e). waste-to-energy recovery systems such as anaerobic gasification and plasma pyrolysis; and f). pyrolytic waste-to-fuel and waste-to-chemicals recovery operations. These developments are surveyed to demonstrate the wide range and intensity of current activities.
Recycled Material Standard (RMS)
The Recycled Material Standard (RMS) is in early development stages and is ultimately meant to serve as a voluntary, market-based tool to be implemented by value chain participants and audited independently by credible third-party certification bodies. The purpose of the standard is to address some of the challenges that brands, their suppliers, and the recycling industry are facing in trying to incorporate higher amounts of recycled content into packaging or finished products. The RMS is being developed by GreenBlue for common packaging materials including paper, plastic, glass and metal, but could be employed for the same materials in markets other than packaging (e.g. the use of recycled plastic in composite lumber). The RMS will use two independent tracking system options which will be defined in separate parts of the standard: 1. The chain of custody (CoC) system will specify material management requirements within an organization in order to demonstrate that recycled content materials and products purchased, labelled and sold as RMS certified originate from recovered materials (derived from post-consumer and post-industrial sources). The chain of custody system will allow for claims to be made using either an average percentage method or credit-based claims. 2. The attributes of recycled content (ARCs) will be a certificate-based trading scheme tracked through a registration body to provide an investment mechanism for new processing capacity. Organizations purchasing ARCs will help support the development of new, additional capacity for processing recycled materials. Purchasing ARCs will also allow companies to communicate the environmental benefits associated with these materials in place of virgin raw materials.
Agilyx's Role in Commercial Recovery of Chemical Value in Post-Use Plastics
Global plastic recycling rates are stagnant at roughly 10%. At the same time, plastic production exceeds 300 million tons a year and is projected to continue growing. Polyolefins account for nearly half of the world's plastics. Agilyx was established with the primary goal of dramatically increasing the world's recycling of plastics and polymers. This single focus led to innovations in polymer depolymerization technology that Agilyx deploys on a commercial scale. As Agilyx treats post-use plastics as a hydrocarbon reserve and a valuable resource, new business models emerge that support the circular plastics industry. Its 15+ years of experience working with its technology has resulted in a profound understanding of post-use polymers as well as their supply chains and variability. The company advances circular solutions for polyolefins and polystyrene using its proprietary pyrolysis technology in conjunction with vertical feedstock management. Ongoing research and development programs bolster Agilyx’s leading position in the market through continuous innovation and improvement to overall process performance, financial profiles, and the development of new product slates. Agilyx creates chemical and circular recycling pathways for end-of-use plastics through innovations, know-how, and processes that are environmentally and economically sustainable.
Technology for Ultra-pure Recycled PP
Consumers increasingly expect and demand sustainable products without performance and price trade-offs, and companies, like P&G, have established long-term sustainability goals that include the use of large percentages recycled resins in their products and packaging. To satisfy consumers’ expectations and achieve companies’ goals, P&G has developed a novel purification technology that converts contaminated recycled resins into virgin-like resins. The proprietary technology is based on the use of a hydrocarbon solvent at elevated temperature and pressure, and a novel combination of standard chemical engineering unit operations, such as liquid – liquid extraction, sedimentation, size exclusion and adsorbent filtrations, and devolatilization. These processes purify the recycled resins via removal of odor, volatile organic chemicals, and other organic and particulate contaminants and additives. Initial focus of the technology is on polypropylene (PP); however, purifications of other polymers are currently under development. The PP purification technology was patented by P&G and licensed to Innventure, which launched PureCycle Technologies (PCT) in September 2015 to commercialize the technology. The 70-ton capacity pilot plant started operation in July 2019, and commercialization is slated to start in 2021/22 with a ~50 kta capacity plant.
Surface Characterization of Polyolefins Modified by Surface Initiated Radical Polymerization
Direct surface modification of polymer films by surface-initiated polymerizations has been carried out. The introduction of initiating sites on the polymer materials and successive polymerization produce surface-tethered polymer chains on the polymer surface. The surface-selective modification controls the surface properties such as wetting, lubrication, and adhesion without sacrificing the bulk performances. Among various procedures for the initiating group introduction and subsequent polymerization proposed so far, this study focuses polymer brush grafting to polymer films through surface-initiated radical polymerizations. Researches on grafting polymer chains to five different types of solid polymers, poly(methyl methacrylate)-based copolymer, Br-containing polyolefins, poly(butylene terephthalate) (PBT), poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-co-TrFE)], and poly(ether-ether ketone) (PEEK) are summarized. The surface-initiated polymerization produces thick stable polymer brush layer on polymer films with various morphologies. The polymer surfaces are homogeneously covered with polymer brushes without serious defects to change the surface properties without sacrificing the bulk performances and the morphology.
Stochastic Estimation of the Lifetime of Polyethylene Pipe with Arbitrarily Located Defects (Paper)
Polyethylene is one of most popular materials for various piping applications. There are three failure modes for polyethylene pipes, i.e. ductile fracture with large plastic deformation (mode I), quasi-brittle fracture with slow crack growth (mode II) and mechano-chemical fracture with localized degradation (mode III), and mode II failure mode is frequently observed from field fracture samples. So, according to standard tests from ISO and ASTM, the resistance to slow crack growth of pipe-grade polyethylene resins should be evaluated. However, it is commonly observed that there is quite large scatter of test results, and many factors such as defect locations, defect sizes, loading conditions, specimen geometry etc. should be considered to analyze test results. So, stochastic approaches are required to estimate the lifetime of polyethylene pipe under mode II failure. In this study, slow crack growth behaviors of polyethylene pipe are simulated for defects with arbitrarily located defects, and the simulation results are analyzed by a continuous probability function. In many cases, it is observed that slow crack growth with mode II failure is in discontinuous manner, so the crack layer theory with new Green’s functions is applied to simulate the slow crack growth behavior from the arbitrarily located defect.
Stochastic Estimation of the Lifetime of Polyethylene Pipe with Arbitrarily Located Defects (Presentation)
Polyethylene is one of most popular materials for various piping applications. There are three failure modes for polyethylene pipes, i.e. ductile fracture with large plastic deformation (mode I), quasi-brittle fracture with slow crack growth (mode II) and mechano-chemical fracture with localized degradation (mode III), and mode II failure mode is frequently observed from field fracture samples. So, according to standard tests from ISO and ASTM, the resistance to slow crack growth of pipe-grade polyethylene resins should be evaluated. However, it is commonly observed that there is quite large scatter of test results, and many factors such as defect locations, defect sizes, loading conditions, specimen geometry etc. should be considered to analyze test results. So, stochastic approaches are required to estimate the lifetime of polyethylene pipe under mode II failure. In this study, slow crack growth behaviors of polyethylene pipe are simulated for defects with arbitrarily located defects, and the simulation results are analyzed by a continuous probability function. In many cases, it is observed that slow crack growth with mode II failure is in discontinuous manner, so the crack layer theory with new Green’s functions is applied to simulate the slow crack growth behavior from the arbitrarily located defect.
Leverage Materials Science to Frozen Food Packaging (Paper)
Polyethylene (PE) is widely used in packaging applications today due to its low cost, good processability, and superior toughness. Coextruded blown films are commonly used in PE-based frozen food packaging, with linear low density polyethylene (LLDPE) making up more than 80% of the structure. In recent years, there has been a strong desire to down-gauge the film while maintaining the incumbent packaging abuse performance. Therefore, a LLDPE resin with better abuse performance at cold temperature (< 0 °C) is needed to satisfy the market need. Much research has been done to establish the relationship between the molecular architecture of PE and the dart impact resistance (related to the toughness) at room temperature, but the knowledge at cold temperature is still very limited. Based on our study, high dart impact resistance of LLDPE film at room temperature does not guarantee high dart impact at cold temperatures. Therefore, more knowledge is needed about the cold temperature toughness of LLDPE. In this paper, we provide a fundamental understanding of the influence the basic molecular architecture (e.g. melt index, molecular weight distribution, glass transition temperature) of LLDPE resin has on the dart impact resistance at cold temperature. Dart impact resistance is measured on LLDPE blown films using an Instrumented Dart Impact instrument in a temperature controlled chamber. The results provide guidance for film converters to select LLDPE products to meet the abuse performance needs of PE-based frozen food packaging.
Leverage Materials Science to Frozen Food Packaging (Presentation)
Polyethylene (PE) is widely used in packaging applications today due to its low cost, good processability, and superior toughness. Coextruded blown films are commonly used in PE-based frozen food packaging, with linear low density polyethylene (LLDPE) making up more than 80% of the structure. In recent years, there has been a strong desire to down-gauge the film while maintaining the incumbent packaging abuse performance. Therefore, a LLDPE resin with better abuse performance at cold temperature (< 0 °C) is needed to satisfy the market need. Much research has been done to establish the relationship between the molecular architecture of PE and the dart impact resistance (related to the toughness) at room temperature, but the knowledge at cold temperature is still very limited. Based on our study, high dart impact resistance of LLDPE film at room temperature does not guarantee high dart impact at cold temperatures. Therefore, more knowledge is needed about the cold temperature toughness of LLDPE. In this paper, we provide a fundamental understanding of the influence the basic molecular architecture (e.g. melt index, molecular weight distribution, glass transition temperature) of LLDPE resin has on the dart impact resistance at cold temperature. Dart impact resistance is measured on LLDPE blown films using an Instrumented Dart Impact instrument in a temperature controlled chamber. The results provide guidance for film converters to select LLDPE products to meet the abuse performance needs of PE-based frozen food packaging.
Scratch Behavior of Polymer Coatings
Polymer coatings have been widely used to improve the tribological performance of various products in electronics, optics, and automotive applications. To further enhance the tribological performance, multilayer polymeric coating and/or single layer composite coating can be applied on polymer substrate. In this study, three-dimensional finite element method (FEM) modeling has been carried out to explain the scratch-induced deformation and damage mechanisms observed in polymer/composite coatings applied on polymer substrate. The stress and strain field analysis using FEM explains the mechanics behind the observed scratch behavior of coating systems. The results show that coating layer thickness and mechanical properties significantly affect the scratch resistance of coating systems. Furthermore, anisotropic behavior of composite coating can significantly influence the scratch behavior. The study provides useful insights toward designing surface damage resistant coating systems.
On Characterization of Dart Impact Resistance of Thin Plastic Films
We investigate the role of film/dart friction on the results of dart impact test used to characterize toughness of plastic films against impact (biaxial loading) at a high speed (~3 m/s). Utilizing an instrumented dart impact (IDI) capability, impact tests were conducted for plastic films exhibiting a wide range of dart impact values under standard test conditions. A Steel dart and a Polytetrafluoroethylene (PTFE)-coated dart were used with the former representing a high-friction interaction and the latter a low-friction one at the film/dart interface. Our results indicate that differentiation between films on the basis of their impact toughness may change dramatically depending on friction. Load-displacement curves obtained from the IDI tests, a simplistic analysis of forces, failed samples, finite element simulations, and high-speed tensile tests help us rationalize our findings about the effect of friction on impact toughness of films.
New Styrenic Block-copolymer Impact Modifiers for TPO Compounds
Polypropylene (PP) is commonly used in various interior and exterior parts of an automobile for several reasons, such as low cost and ability to tailor properties using additives. These compounded PP formulations are also referred to as thermoplastic polyolefin or TPO. A key additive used in these TPO compounds is an impact modifier to improve the impact resistance of the part. In this presentation, we discuss development of new styrenic block-copolymers (SBCs) as an impact modifier for TPO compounds. Typically, a combination of polyolefinic elastomer (POE) and SBCs are used as impact modifiers for TPO, which provides an appropriate balance of cost and impact performance. In these formulations, the role of the SBC is to compatibilize the POE with PP and achieve a desirable morphology (mainly desirable elastomer domain size and distribution), which results in acceptable impact performance. In this presentation, we report development of a series of polymers to further increase the compatibility of SBC with POE and PP and consequently improve the impact resistance. A few of these new polymers led to a significant increase in impact strength compared to existing formulation without significantly affecting other physical properties, such as stiffness and melt flow. We also performed morphological investigations to confirm the hypothesis of improved compatibilization leading to better impact resistance. These new impact modifiers can enable the use of TPO compounds in newer applications demanding higher performance, such as thin-walled and low-density parts.
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