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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The post-consumer single-use polyethylene-based plastic bags supplied by the supermarket grocery stores, are converted into new materials with improved mechanical properties using a thermo-mechanical recycling process. The low-density polyethylene (LDPE) sourced from waste plastic bags, is injected into a high shear internal mixer and compounded with the additives such as acrylonitrilebutadiene copolymer or nitrile rubber (up to 10 wt%) and also treated with an organic peroxide curing agent. The resultant materials exhibit high ductility and elasticity, with a maximum tensile strength of 20.3 MPa, stiffness of 1262 MPa, elongation of approximately 500%, and impact strength of 62 kJ/m2 depending on materials compositions. These mechanical properties are profoundly higher than those of neat recycled LDPE. It is observed that the post-consumer plastics contain a significantly high amount of calcium mineral of approximately 30 wt% (13 vol %), which plays a key role in improving mechanical properties during high shear blending with additives such as nitrile rubber. The melt-rheological characteristics such as complex viscosity and storage modulus of the materials are analyzed to evaluate the thermal recyclability and thermoplastic nature of the materials.
Presently, polymers such as high density polyethylene(HDPE) are utilized for an extensive array of applications because of their low weight, economical production, and exceptional physical and chemical properties. Thermal analysis and rheological measurements are the ideal techniques for characterizing the material properties of polymers. This paper employs thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and capillary rheometry to collate the contrasting nature of two HDPE resins. These resins will be referred to as HDPE A and HDPE C and are similar to two resins (Sample A and Sample C) included in a previous publication  that focused on blow molding parison sag and swell. TGA was used to investigate the thermal stability of these polymeric materials, as they were ultimately decomposed inside a furnace. DSC was conducted to examine the thermal transition behaviors of the polymers. Capillary rheometry was run to construct shear viscosity and extrudate swell versus shear rate data through single and twin bore configurations under varying temperatures. These measurements were conducted under testing conditions that are representative of industrial processes, such as extrusion blow molding. HDPE C was found to exhibit greater extrudate swell than HDPE A, as measured by capillary rheology measurements, and these data correspond to the earlier published results that Sample C exhibited greater parison diameter, thickness, and weight swell than Sample A as measured with a lab scale extruder.
A particle additive is reported that simultaneously improves ductility and biodegradation behavior of poly(lactic acid) (PLA). Our approach explores the use of encapsulation technology to create degradation-promoting additives while limiting any breakdown of the matrix during melt extrusion and service life. In addition to promoting biodegradation such encapsulated particles are designed to enhance toughness of the matrix. Such dual use particles have the potential to broaden the uses of PLA. In this work, particle properties are examined and the accompanying tensile behavior and compostability of the composite investigated. Particles were dispersed within the PLA matrix by extrusion to 3D printer filament. Elongation at break was improved over neat PLA with limited loss of yield strength. Degradation rate in compost is accelerated and decoupled from environmental conditions by embedding a degradant material into the PLA matrix itself, aided by encapsulation technology that isolates and protects the degradant. The additive has been found to improve mechanical properties while accelerating the biodegradation of parts produced by extrusion-based methods.
This research investigated the effect of the addition of Orotic Acid (OA) on the crystallization kinetics of Polylactic Acid (PLA) in quiescent and non-quiescent conditions. A differential scanning calorimetry (DSC) study was used to investigate and understand the effect of the addition of orotic acid on 2500 HP PLA under quiescent conditions. DSC technique was utilized to capture the crystallinity, melting point, and other thermal parameters of PLA-OA blends. Conventional injection molding (CIM) was used to investigate the influence of adding OA into PLA under non-quiescent conditions. Two concentrations of orotic acid, 0.3 wt% and 0.7wt% were mixed with neat PLA and then investigated. It was observed that the 0.3 wt.% orotic acid provided significant improvement in crystallization kinetics by increasing the crystallinity and reducing the incubation time. Both blends under quiescent conditions showed almost the same crystallinity in which the maximum crystallinity that was observed was around 63% in the blend of the PLA/0.7OA at 85°C. For 2500HP PLA, Orotic acid (OA) showed to be an effective nucleating agent. A small amount (0.3 wt%) was sufficient to achieve 61% of crystallinity in injection molding at 80°C mold temperature.
A method was developed for fabricating recycled composites from post-consumer polyethylene terephthalate (PET) carpets and recycled PET resins. Compression molding of the components under different pressures, temperatures, and compositions was performed. Preliminary molding conditions were arrived at based on analyzing the differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and melt viscosity data for different raw material combinations. Molding factors were screened to define applicable ranges for each parameter. The effects of configuration and composition of components, temperature, molding time, and pressure were considered in the screening process. Mechanical properties of composites were determined by 3-point flexural (according to ASTM D790) and creep tests. The molded materials showed acceptable mechanical strength and modulus values required for structural applications.
Ultrasonic welding (USW) is a surface mating process where absorbed moisture in the surfaces of hydrophilic materials can negatively affect the weld joint quality and strength. USW is a secondary processing operation that is performed post-molding or extruding. Hence, during the storage time between primary processing and USW, the parts are susceptible to moisture absorption. Therefore, it is necessary to characterize the moisture sensitivity to meet the specified weld strength. Moisture sensitivity of Industrial standard test parts (ISTeP) made with PLA, PBS, and PLA/PBS 25/75 blend was characterized for USW in this study. ISTeP parts were moisture conditioned for one week at different relative humidity (RH) levels and then tested for weld strength. It was found that the weld strength decreased with increase in RH for 100% PLA ISTePs but it was not statistically significant. Above 65% RH, weld strength of 100% PBS was significantly decreased. Scanning electron microscopy of weld areas after the pull test revealed an increased amount of trapped porosity in the fractured surfaces of high relative humidity samples. It was also demonstrated that PBS and PLA/PBS composite can be ultrasonic welded.
In this paper, the tensile properties of indoor and outdoor post-consumer recycled (PCR) polycarbonates (PC) have been compared with virgin PC at various aging conditions. 50% recycled PCs showed comparable tensile strength at breakage (~70 MPa) and maximum strain (~190 - 200%) before aging, when compared to virgin PC of same MFR of ~10 g/10 min. Three different high temperature and high humidity aging conditions were investigated: 40oC 90% RH, 60oC 90% RH, and 85oC 85% RH for up to 500 hours. Strength at breakage was found to decrease as the aging stress or aging time (with the same aging condition) was increased. Both the indoor resins were comparable in strength up to 60oC 90% RH. But in 85oC 85% RH both showed significant drop in strength. On the other hand, outdoor PCR resin showed much better performance (only ~12% degradation) in 85oC 85% RH compared to other two indoor resins (25 - 40% degradation). Outdoor UV aging characteristics were also compared between 0%, 50% and 75% PCR and degradation up to 600 hours were found to be within 5%.
Recycling of plastic waste at Forward Operating Bases. (FOBs) is continuing to be a topic of considerable interest to the Department of Defense. A previous paper  by the current authors described the need and opportunity to convert this waste stream to plastic lumber that could be used by the warfighter for various construction applications at forward operating bases (FOBs). The selected technique of flow intrusion molding of recycled PET (rPET) into 1 inch by 1 inch by 36 inch test specimens showed feasibility of this recycling technique and the resulting specimens were very stiff with high modulus but they failed during testing in a brittle fashion with fragmentation. This is not a desirable failure mode and work was conducted to improve the ductility of the plastic lumber specimens using both chain extenders and impact modifiers. This paper describes the investigation of using additives to improve ductility and therefore the utility of rPET to make plastic lumber using flow intrusion molding and the resulting performance characteristics.
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The recyclability of plastic components has become an important objective in the product development process of packaging and technical products. In this study an approach is taken to produce hard-soft combinations with a better recyclability by using an adhesion and, at the same time, recycling layer. This additional layer is placed between the hard and the soft component. The intermediate layer shows good adhesion to both components for the use phase of the product. At end-of-life-stage of the products, the two components can be separated by melting the intermediate layer and shearing of the parts in recycling machines. Polypropylene (PP) as the hard component and thermoplastic polyurethane (TPU) as the soft component are combined with an EBA (Polyethylene-n-butylacrylate) functioning as the intermediate layer by an overmolding injection molding process. The peel strength is investigated for the combination hard component/ intermediate layer, intermediate layer/ soft component and for the combination of all three materials. The combination without the intermediate layer shows no adhesion of the two components. For simulating a separation process the peel tests are carried out at higher temperatures. The results show a lower bond strength at temperatures around 80 °C and the failure location between the TPU part and the EBA-layer. Furthermore, the results show that with the functional intermediate layer two materials can be joined for the use phase and also separated by heating at the end-of-life-stage.
This study was conducted to show the effects of inclusion of highly degraded surface material in recycled ocean plastic HDPE. Two primary materials were studied, one (HDPE-SD) contains high surface degradation while the other (HDPE-MP) had the surface removed for comparison. Each material was mechanically recycled (granulated, compounded, granulated) and then injection molded to create test specimens. Optical microscopy was performed before processing to observe and measure the surface degradation. After molding, FTIR, DSC, rheology, and mechanical characterizations were done to draw conclusions about the impacts of the degraded surface on the recycled properties. Inclusion of the degraded surface was found to increase fracture elongation, zero shear viscosity and lower the melt temperature. These findings were related to the chemical structures observed via FTIR. Additionally, comparisons and insights on the challenges and benefits of recycling ocean plastics are described.
One of the major issues the plastics industry is trying to solve today is the lack of a circular economy. Plastics do not biodegrade fast enough to keep up with the waste being generated, and therefore present ecological and environmental problems. To take discarded plastics and continuously give them new life in a variety of applications is the goal of many plastics industries. However, to reprocess recycled plastics has shown many challenges. iMFLUX’s Auto-Viscosity Adjust (AVA) technology has made doing so easier with their low, constant pressure injection molding process. This technology enables the injection molding process the ability to independently adjust parameters in real time. This research focuses on comparing the dimensional and mechanical integrity of virgin ABS and PCR ABS in the conventional and iMFLUX processes. It was determined that the conventional process had better mechanical integrity with the virgin ABS than iMFLUX, and the iMFLUX process had less deviation overall between dimensions and material transition.
Unlike other thermoplastics, polystyrene can be thermally recycled into its monomer form. During the continuous depolymerization of polystyrene in the twin screw extruder, low-molecular volatile substances are gradually split off at temperatures above 400 °C. Depolymerization in a twin screw extruder offers a number of advantages for the recycling of polystyrene. The heating time in a twin screw extruder is short and high material throughputs can be achieved. The reaction products are removed directly by a vacuum system. To make the depolymerization of polystyrene more efficient and to increase process stability, the vacuum system has been optimized with regard to the vacuum dome geometry. As a result, the reaction products are removed faster and the migration of the low-viscosity melt into the vacuum dome is avoided. In addition, the constructive adaptation of the vacuum dome geometry made it possible to increase the realizable vacuum pressures during depolymerization from 400 mbar to 50 mbar and the maximum condensate yield from approx. 30 % to over 60 %. Depolymerization in a twin-screw extruder thus represents a promising process for recycling polystyrene on an industrial scale.
Thermosets play a key role in the modern plastics industry. Their high density of chemical crosslinks result in excellent mechanical properties for high-performance applications, but also prevent them from being readily reprocessed once formed. We have recently developed degradable, recyclable versions of existing high-performance thermosets by incorporating small quantities of a cleavable co-monomer additive. This approach maintains the performance profiles of the parent materials while seamlessly integrating with existing manufacturing workflows.
Photooxidative processes that lead to chain scission and chain linking in polymers play an important role in polymer degradation. These processes are induced by both ultraviolet and visible light absorption. Antioxidants can enhance the usable life-time of polyethylene, and some fillers can act as a UV screen and also as a chain terminating and peroxide decomposing agent in the polyethylene UV degradation. In this paper a reaction model is developed and described for UV degradation of polyethylene containing a hindered amine as an antioxidant and carbon black as filler. The degradation mechanism follows free radical initiation, propagation, termination, and stabilization steps. Reactions between free radicals and antioxidants with carbon black are considered. Mass balance on each reacting species gives the model equations that are solved using parameters that are either estimated or fitted. The model gives key parameters responsible for the degradation and stabilization.
One of the streams from plastics waste collection is a mixed polyolefin stream, which cannot be separated completely with reasonable effort at the current technological state. The aim of this work was to investigate the influence of the processing route, realized by different plastic processing machines, on the properties of selected polyolefin blends, made from different PP and PE grades as well as compatibilizing additives, to mimic the mixed polyolefins found in post-consumer waste. We found, that the processing route influences the properties in regard to the shear brought into the materials – only dry-blended and injection molded blends yield lower properties than the ones which were prepared by the other processing machines. This is more pronounced when compatibilizers were added. These results show that several processing machines can be used to establish such blends, which is an important finding for mixed polyolefin stream recycling, as there not only a good mixture in the blend needs to be established, but also the processing machine has to be stable and unsusceptible to foreign materials in the stream.
Levels of plastic waste accumulating in the oceans are continuously rising and prompting an increase in concern on their negative environmental impacts. To help close the gap and create a circular life cycle for ocean plastics, this study begins to show the changes in chemical and engineering properties of polyolefins collected from a marine environment. Three ocean plastic polyolefins, high density polyethylene, low density polyethylene, and polypropylene, were mechanically recycled and then injection molded. The ocean plastics‚Äô chemical characteristics were then characterized via FTIR to observed the impacts of environmental degradation. Thermal, rheological, and mechanical properties were all studied and related to the chemical structures and typical accepted values. All ocean plastic olefins were found to have properties similar to their terra-firma counterparts, however degradation was observed and is discussed in terms of the measured properties.
Improving the reusability of plastic parts, increasing the usage of post-consumer resin (PCR), and converting mixed PCR streams into high value resins are three key challenges facing the plastic recycling industry. To address these challenges, CirKular+‚Ñ¢ products were developed by Kraton Polymers to enable plastics upcycling and circular economy solutions. These products enable multi-resin compatibilization and performance enhancement of PCR resins across a wide range of applications. By leveraging the versatile chemistry of styrenic block copolymers, polymeric additives have been developed that benefit plastic recycling in multiple ways, such as improvement in properties of recycled resins and blends of virgin and recycled resins, and compatibilization of mixed PCR resin streams. In addition, these polymeric additives provide the performance enhancement at low loading levels, which in turn leads to an excellent balance of properties and low formulation cost. In this paper, several application-specific test results and case studies will demonstrate the value of these polymeric additives.
In response to government and consumer demand for sustainable solutions to the escalating plastic waste crisis, plastic compounders and manufacturers are seeking to increase the level of post-consumer recycled content in their product formulations. The inherent variability of recycled resin streams presents challenges related to operational efficiency and product performance; thus, there is an increased need for processing aids that can assist manufacturers in their quest to balance operational efficiency with sustainability. GreenMantra¬Æ Technologies has developed and commercialized an innovative advanced chemical recycling technology that converts recycled plastics into specialty polymers and synthetic waxes that can function as processing aids in plastic production. This paper presents two case studies that demonstrate how GreenMantra‚Äôs additives enhance the manufacturing efficiency of plastic extrusion processes and maintain the physical properties of polymer systems containing 25-100% recycled plastics. Certified as containing 100% post-consumer recycled plastics, GreenMantra‚Äôs additives enhance the sustainability of the polymer system while enabling the formulation flexibility for plastic manufacturers to incorporate higher recycled plastic content without sacrificing performance.
This article shows the effect of melt mixing parameters such as temperature and time on the macromolecular chain structure of Recycled Poly(ethylene terephthalate) using a batch mixer. The objective was to develop a pretreatment of PET to reduce molecular weight and crystallinity in preparation for microbial degradation. A depolymerization kinetic model was built to understand the irreversible structural changes caused via melt processing of RPET. Chain scission reaction occurred faster at higher temperatures, as evidenced by molecular weight calculated from intrinsic viscosity measurements.
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