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.
It is well known that melt processing post-consumer (PCR) or post-industrial (PIR) recycled resins can generate foul odors due to contamination and/or thermal degradation. Additional components, such as printing inks and adhesives in plastic packaging, may be viewed as contaminates in the recycled resin and can contribute to this problem. Some of these odors could be from volatile organic compounds, VOC’s, with known safety concerns. With a growing need in the flexible packaging industry to increase circularity through the use of PCR and PIR materials, there comes an increase in risk for health concerns and food safety. Amcor has developed methods using gas chromatography, GC, along with heated headspace sampling, HS, to chemically identify and measure the VOC released from PCR/PIR that have known safety concerns such as acrolein, methyl acrolein, and benzene. These methods help Amcor evaluate the quality of PCR/PIR sources to determine feasibility for certain applications, and aid in the design of next-generation recycle ready packaging films. This will be a discussion on the development of the testing methods along with results of VOC analysis.
Single-use bags have been banned or restricted around the world. Substitute alternatives have been explored, including biodegradable bags, reusable bags and the use of other materials such as paper or cotton. The Life Cycle Assessment (LCA) is the most widely accepted tool for carrying out comparative studies between alternatives. In this study, the literature on LCA of grocery bags was reviewed in search of common conclusions. In general, reusable plastic bags are identified as the alternative with the lowest environmental impact , obtaining on average a 73% reduction in the climate change index compared to the alternative with the highest impact in each analysis. Reuse and recycling have a lower environmental impact than composting, landfilling or incinerating. Open challenges are discussed, including the requirement for the development of a new index to quantify plastic leakage into the environment.
With climate change worsening, people have become more conscious of their environmental impact. Companies are receiving growing pressure to use increasing content of post-consumer recycled (PCR) plastics in their products. However, PCR plastics differ from virgin materials in several mechanical, physical, and rheological properties, posing design and molding challenges for manufacturers. In this work, a polypropylene (PP) compound is produced and characterized using different contents of PCR PP to model its properties as a function of PCR content. A numerical approach is then proposed to determine the maximum content of PCR PP suitable for a given application. Furthermore, a robust design approach is proposed to identify engineering changes for both part and mold design that can make the part performance insensitive to lot-to-lot variations of the PCR properties.
About 4 billion people around the world are suffering from water scarcity, which is expected to increase due to increasing global warming [1, 2]. One of the solutions to address the water scarcity challenge is to tap the 13,000 trillion of water present in the atmospheric air in the form of fog, droplets, or vapor . Simple fog collection systems effectively harvest water without investing energy in highly humid environments , but they are ineffective in arid regions like Arizona, where the humidity is low. Alternatively, adsorbents designed to capture water vapor during colder nights and release it during the hotter day could provide a passive solution to harvest water vapor in the arid regions of the world [5,6]. Recently, porous polymeric hydrogels have been reported for water droplets harvesting from the air. The gels were fabricated with thermoresponsive polymers, such as polypyrrole chloride penetrated PNIPAM, that can switch to hydrophilic and hydrophobic structures at lower critical solution temperature (LCST) and upper critical solution temperature (UCST), respectively [7,8]. By leveraging their switchable wetting properties, the water droplets were captured during the night at higher humidity and lower temperature conditions and collected during the day at lower humidity and higher temperature conditions. However, the influence of LC/UCST on the hydrogel's chemical and morphological structures has not been investigated, as well as harvesting water vapor present in arid regions. In this work, we report the fabrication of thermoresponsive P(NIPAM-co-BzDMA) copolymeric hydrogel to collect water vapor from the air across all humidity conditions. The hydrogels were fabricated by tuning the temperatures and compositions to achieve large surface area-to-volume ratios, ordered porous structures, and excellent switch between the hydrophilic-hydrophobic wetting properties. The gels synthesized at LCST at BzDMA salt concentration of 15% could uptake 20% higher water than their counterparts. Experimental: The P(NIPAM-co-BzDMA) gels were synthesized by thermally initiated polymerization at LCST or UCST to determine the influence of their switchable hydrophilic-hydrophobic structures on the efficacy of crosslinking . Then the PNIPAM was copolymerized with BzDMA salt at three concentrations of 10%, 15%, and 20% by weight. The synthesis was carried out for 4 hours under nitrogen and then freeze-dried for 12 hours in vacuum environments. The resulting porous gels were named based on their salt concentrations as P(NIPAM-co-10%BzDMA), P(NIPAM-co-15%BzDMA), and P(NIPAM-co-20%BzDMA). The surface functional groups of the hydrogels were determined using Fourier Transform Infrared Spectroscopy (FT-IR, Bruker, Germany). The morphological and crosslinking structure of the gels were evaluated using scanning electron microscopy (SEM, Hitachi Instrument, Japan). The thermoresponsive phase change behavior of the materials was verified using a Differential Scanning Calorimetry (DSC) at a heating rate of 2 C/min from 10 to 60C under a nitrogen environment (DSC, TA Instrument, USA). The switchable wetting properties of the gels were examined through water contact angles (WCA) measured at 20 and 40C. The water vapor adsorption-desorption isotherms were measured using an intelligent gravimetric analyzer (IGA, Hiden Isochema Ltd., UK). Results & Discussion: The successful synthesis of PNIPAM at LCST and UCST was confirmed from the FT-IR spectra. It showed two intense peaks at 1677 and 1563 1/cm, corresponding to C=O and N-H or C-N, respectively. The spectra also showed bimodal peaks at 1390 and 1379 1/cm from the isopropyl, peaks at 2987 and 2942 1/cm from methylene, and a broad peak at 3310 1/cm from N-H stretching . Relative to LCST, the functional groups showed more intense peaks for PNIAM @UCST. It could be because the large number of oxygen radicals generated at higher temperatures could increase crosslinking of PNIPAM. The SEM images of the P(NIPAM-co-BzDMA) hydrogels showed interconnected microporous structures caused by freeze-drying . Compared with PNIPAM@UCST, the PNIPAM@LCST had orderly distributed pores. The BET (Brunauer, Emmett, and Teller) surface area of the PNIPAM@UCST and PNIPAM@LCST were 2.91 mˆ2gˆ-1 and 2.67 mˆ2gˆ-1, respectively. At LCST, the slow copolymerization reaction rate and the homogeneous hydrophilic-hydrophilic structures of copolymers created orderly-distributed, uniform pores across the hydrogels. In contrast, at UCST, the fast copolymerization reaction rate and heterogeneous hydrophilic-hydrophobic networks of copolymers produced randomly-distributed, nonuniform pores. The BzDMA could react and maintain a stable morphological structure with both gels. The DSC thermograms confirmed that both PNIPAM and P(NIPAM-co-BzDMA) could change phase at approximately 32 C. Next, the WCAs measurements showed that all gels exhibit superhydrophilicity at 20C and hydrophobicity at 40 C, as intended. The adsorption-desorption isotherms of hydrogels showed an S shape curve suggesting water vapor can be harvested without losses. However, below LCST, due to superhydrophilicity of PNIPAM and P(NIPAM-co-BzDMA), the water molecules have a higher affinity to bind with the adsorbent, swell and cause a larger hysteresis loop and higher water uptake capacity. The water uptake capacity was found to be 20% highest for P(NIPAM-co-BzDMA) at 15% salt concentration than its counterparts. Conclusions: Our results suggest the influence of synthesis temperature-dependent chemical structures on the overall water vapor uptake capacities and collections was negligible. However, the gels synthesized below LCST and 15% salt concentrations slowed the copolymerization reaction rate, created uniform morphology, and delivered a higher water uptake capacity. Based on these process parameters and compositions, scalable hydrogel-based adsorbents can be designed for large-scale water vapor harvesting across all climate conditions, especially in highly-needed arid regions. References: 1. G. Meran, M. Siehlow, C. von Hirschhausen, The Economics of Water: Rules and Institutions. Springer Nature (2021). 2. M. M. Mekonnen, et al. Sci. Adv 2 (2), e1500323 (2016). 3. H. Kim, et al. Science 356 (6336), 430-434 (2017). 4. J. Ju, et al. Nat. Comm. 3 (1), 1-6 (2012). 5. N. Hanikel, et al. Nat Nanotechnol 15 (5), 348-355 (2020). 6. P.A. Kallenberger, et al. Comm. Chemistry 1(28), 1-6 (2018). 7. F. Zhao, et al. Adv. Mater. 31 (10), 1806446 (2019). 8. K. Matsumoto, et al. Nat. Comm. 9 (1) 1-7 (2018). 9. H. Yang, et al. Adv. Mater. 2013, 25 (8), 1150-1154. 10. Y. Dong, et al. Appl. Surf. Sci. 307, 7-12 (2014). 11. Z. Shen, et al. Soft Matter 8 (27), 7250-7257 (2012). 12. W. Xu, et al. ACS Cent Sci 6 (8), 1348-1354 (2020).
Orange peels have high cellulose content and they are available in good quantities. The present study aimed to a produce bioplastic composite based on orange peels. Orange peels were ground using a semi-automatic grinder before the pre-treatment step. The peels were immersed in a 15% sodium hydroxide NaOH solution for 4 hours at 60°C to remove the lignin, hemicelluloses, and other pectic substances. Then, they were neutralized with 1% acetic acid before being washed with distilled water and dried overnight at 60°C in a convective oven. Different natural additives, including starch, glycerol, agar-agar, and D- sorbitol, were added to the orange peels to develop the bioplastic material for optimized mechanical and plasticizing properties. To enhance the mechanical properties of the orange peel bioplastic, calcium carbonate was used in different weight percentages.The ultimate tensile strength of the orange peels bioplastic samples increased from 0.9 MP to 2.4 MPa with the addition of 8 wt% calcium carbonate. On the other hand, the fracture point decreased from 20% to almost 13% strain by the addition of calcium carbonate, the bioplastic become more brittle as the weight percentage of calcium carbonate increased. The bending tests showed that the maximum deflection achieved before fracture is equal to 12 mm and that the specimen can withstand forces up to 6.2 N. This indicates that the achieved biomaterial has a remarkable bending strength and can withstand up to 6.2 N before fracture, proving that it has a strong bending behavior. The deflection decreased by about 20% when 8 wt% of calcium carbonate existed in the matrix and the bending withstand force reduced to about 5.0 N. It is expected that applying a coating layer to the orange peels bioplastic end products makes them more attractive and expands their commercial applications.
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.
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