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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Various topics related to sustainability in plastics, including bio-related, environmental issues, green, recycling, renewal, re-use and sustainability.
Microcellular Foaming Behavior of Biodegradable Poly (3- Hydroxybutyrate-CO-3-Hydroxyvalerate)/Polylactic Acid Composites
In this paper, Biodegradable poly (3-hydroxybutyrate-co- 3-hydroxyvalerate) (PHBV)/polylactic acid (PLA) biocomposites were prepared using the Hakker rheometer. We investigated the effect of various PLA content on the PHBV’s thermal properties and on its foaming behavior. The differential scanning calorimetry (DSC) results showed that the presence of PLA facilitate the cold crystallization of PHBV matrix. Along with the addition of PLA, the melt temperature of composites are lower than pure PHBV. SEM results of foamed samples presented that the addition of PLA led to the various foaming morphologies, and cell morphologies was changed from close cell to open cell as increasing the content of PLA in the PHBV matrix. The changed foaming morphology was attributed to the phase morphology and composites melt strength changed, and the resultant mechanism was also proposed.
Microencapsulation of Pamitic Acid with Polylactic Acid Shell for Thermal Energy Storage
Microencapsulation of vegetable-derived palmitic acid (PA) in bio-based polymer shell of polylactic acid (PLA) by solvent evaporation and oil-in-water emulsification was investigated. This study deals with the preparation and characterization of PLA-PA microcapsules. Chemical structures, morphology of microcapsules, and thermal properties were determined by Fourier transform inferred spectroscopy, scanning electron microscopy, and differential scanning calorimetry, respectively. In short, this work has demonstrated the possibility to fabricate 100% bio-based phase change material microcapsules for thermal energy storage applications.
Micro-Graphite Enhanced Extrusion Foaming of PET Resin
Extrusion foaming of neat and recycled polyethylene terephthalate (PET) resins are difficult due to their high melting temperature and low melt strength. Chemical crosslinking modification of the PET resins is the most widely used method to solve this problem. However, the modified resins are expensive and difficult to be re-used. In this work, micro-graphite or nanoclay particulates were added to PET to adjust its melt viscosity and strength and to serve as a nucleation agent to facilitate cell growth during extrusion. Micro-graphite is an excellent infrared attenuation agent (IAA) that may provide enhanced thermal insulation to PET foams. Using our small lab extruder, the foamed micro-graphite/PET composite extrudates could reach a low density of 0.21 g/cm3, close to that achieved by chemical crosslinking modified PET resins, using injected hydrofluorocarbon (HFC) as a blowing agent in extrusion. Properties of the PET foam including density, cell size, and crystallinity depend on particulate type and processing conditions.
Micropelletization of Virgin and Recycled Thermoplastic Materials
Traditional polymer powder and micropellet based processes, such as powder bed fusion and rotational molding, have been in increased demand in modern processing industries. These processes require polymer powders and micropellets with a small particle size, narrow size distribution and defined geometry for a variety of polymer resins. Therefore, micropelletization technologies, where particles in the size range of 50 to 1000 µm are generated, have been attracting growing attention over the past decade. A new technique, developed at the Polymer Engineering Center, yields micropellets with a controlled morphology and narrow particle size distribution. In this process, a polymer melt is extruded through a capillary and is subsequently stretched with a hot air stream until flow instabilities cause it to break up into particles. Small changes in process conditions result in different size distributions and particle shapes, such as lentil-like pellets, fibers and thread segments. This work shows how material properties and processing parameters influence the produced micropellets. Besides the processing of virgin thermoplastic material, recycled high density polyethylene flakes are used as feedstock for the micropelletization process in order to show the capability of this process to contribute to current polymer recycling efforts.
Modified Polylactide with Improved Thermal and Rheological Properties for Foaming
Polylactide (PLA) is the most important bioplastic on the market due to its good mechanical properties and the permanent growth of the production capacity. One drawback of commercial polylactide is its too low melt strength and melt extensibility, which is disadvantageous in terms of foaming. To overcome these commercial grades need to be modified. Therefore, several chemical modifiers were used to induce crosslinking, chain extension or grafting by means of reactive extrusion on a twin-screw extruder. The best results were achieved with organic peroxide. With this modifier the melt strength and the crystallization rate were improved and lead to foams with a closed-cell structure and low density. Organic peroxide was found to be more efficient than the commercial multifunctional epoxide modifier.
Multilayer EVOH/HDPE Packaging in Processing and Performance of Recycled HDPE
Kuraray, EVAL Europe N.V. (EE) produces Ethylene Vinyl Alcohol copolymers (EVAL™), which are used in multilayer structures in a combination with a wide range of materials such as High Density Polyethylene (HDPE) to produce multilayer bottles to provide superior barrier properties to gases, flavours or bring functional barriers against external contaminants such as mineral oils (MOSH,MOAH). Bottles are typically made by Co-Extrusion blow moulding (Co-EBM) technology and are used for beverage packaging such as dairy products and specialty milk and other packaging applications for sauces or dressings or for the packaging of medical products for which the Water Barrier of HDPE is of added value. The objective of the study was to investigate if multilayer EVOH/HDPE rigid packaging material, which is a percentage of the post-consumer recycling stream, can be effectively sorted with the HDPE stream and decontaminated back to food grade approved for use as Post-Consumer Recycled (PCR)-HDPE into food packaging applications. Multilayer rigid food packaging found in the post-consumer recycling stream has been represented in the design of materials guides and recycling guides as ‘may be suitable’ for recycling. The present work investigates the recyclability of EVOH barrier packaging due to the growing trends of multilayer rigid food packaging and more importantly, as recovery systems strive towards a better circular economy. The steps taken to produce food grade rHDPE with analysis included; Audits of the HDPE fraction at Viridor MRF, testing on automated NIR sorting equipment at Tomra (Titech), compounding in a low pressure, elevated temperature, food-grade decontamination process and overall migration testing conducted by Smithers-Pira. The evaluation showed that post-consumer HDPE (rHDPE) material containing at least 0.25% EVOH (equivalent to 5% multilayer EVOH/HDPE packaging) can be “super cleaned” to food grade quality without any significant impact on the process performance or physical properties compared to rHDPE only. The results showed that at the levels of multilayer EVOH packaging typically found in the recycled HDPE stream, the rHDPE can be processed and utilized in a full range of applications, without impact on migration characteristics or physical properties compared to rHDPE alone.
PHA and PLA Biodegradable Plastics with Rice Straw Filler to Create Biobased Structural Insulating Panels (BSIPs)
Biobased composites were produced with PHA and PLA biodegradble plastics with rice straw and walnut shells as fillers. Rice straw laminate bio-composite boards were produced with PHA and PLA biodegradable plastic pellets with rice straw in a Leitritz twin screw extruder. Rice straw and walnut shells were added to PHA/PLA plastic to form a rice straw composite with 40% filler and 60% plastic. The pellets were compression molded to form the skins of the BSIP. PLA foam was used to produce the biobased foam core. The PHA, PLA, rice straw, and walnut shell mixtures were injection molded and different concentrations of rice straw and walnut shell filler. Tensile testing results show that PHA/PLA blend had 16% lower modulus and 33% less load than PLA by itself. Walnut shells and rice straw reduced the tensile strength and elongation of the plastic composite but increased the tensile modulus. Walnut shells and rice straw also decreased the impact strength of the plastic biocomposite. The biocomposite panels can be combined with a PLA foam core to form the biobased structural insulating panels.
Plastic Packaging Recycling Using Intelligent Separation Technologies for Materials (PRISM)
A new way of rapidly sorting packaging into high purity streams (> 99%) has been developed based on intelligent labels with invisible markers that can be detected and sorted using existing high-speed optical sorting systems used in MRFs with minor modifications. The principles have been proven using a range of commercially available UV responsive fluorescent markers with high emission yields. A full-scale commercial optical sorting trial was conducted at the MRF facilities of Tomra in Germany. Sorting of used plastic packaging for closed loop recycling back into food packaging requires positive identification and sorting of the recycled materials to a higher standard. The operators of commercial food grade recycling processes are required to demonstrate the recycled materials meet relevant European Food Safety Authority (EFSA) criteria; these require at least 95% (PET) and 99% (HDPE) of the feed material must have been used for food contact in their first life. The initiation of closed loop food grade recycling of PP packaging is awaiting a viable technical solution to differentiate the food grade packaging. From previous sorting trials, it can be estimated that of the 143,000 tons of PP food packaging used annually , 77,077 tons could be recovered each year in the UK. The objective of this project was to further develop the fluorescent marker technology investigated in earlier projects that has the potential to meet EFSA requirements and to extend the scope to different applications, enabling and facilitating the sorting of different polymers to a high degree of purity. The scope of the project included the optimisation of fluorescent compounds, evaluation of their stability in the supply chain and the ability of the compounds to be effectively removed during the cleaning and decontamination process. The project investigated the viability of the technology and its capacity to be implemented in the UK and elsewhere. Unlike existing NIR sorting systems , this technology uses commercial labeling and decoration methods to sort targeted streams potentially including food-contact plastics, bioplastics, chemical packaging, automotive plastics, black plastics and different grades of one plastic. This technique has the potential to create new recycling loops for food grade PP, milk bottle sorting and PET products. The project demonstrated that the use of commercial labels incorporating fluorescent markers can be used to sort plastic bottles and packaging with high yields and purity.
Processing of In-Plant Mechanically Recycled PA-12
The increasing public awareness and demand for a more sustainable handling of the earth’s resources has led to the idea/ concept of a circular economy. Within this concept materials will be re-used in a closed loop system rather than being down-cycled or inappropriately managed (disposed via landfill) at the end of their life-cycle. Based on previous research, Polyamide 12 (PA-12) is a promising material candidate in the sports and leisure sector and its ability for being reprocessed via injection molding has been investigated. While other PAs tend to show a decrease in impact properties on mechanical recycling, PA-12 is shown to be able to overcome these problems when reprocessed at a higher melt temperature, yielding samples with improved impact properties compared to the primary material.
Reduction of Energy Consumption in Injection Molding of Polypropylene Parts through the Optimization of Mold Thermal Control
The environmental impact of the injection molding process is mostly due to electricity consumption. This is particularly significant for packaging applications, which are the largest application sector for the plastics industry. In this work, electricity consumption measurements of the process were performed, considering a large packaging plant. In particular, the energy consumption related to mold thermal control were analyzed and minimized through a representative case study. The effects of alternative cooling channels configurations and different process parameters were experimentally investigated, considering also their influence on the quality of the molded parts. The results indicated that the common industrial practice for mold thermal control is highly inefficient. The implementation of electricity consumption measurements allowed the optimization of molds thermal control leading to considerable economic savings.
Relationships between Low Temperature Impact Performance and Structures of Rotationally Molded Crosslinked High Density Polyethylene
The low temperature impact performance of rotationally molded specimen is of great importance for the final products. Crosslinked high density polyethylene (XL-HDPE) is a preferred material for large chemical and fuel tank due to its superior environmental stress crack resistance and high impact strength. In the present research the drop weight impact strength (defined as ARM impact strength) of rotationally molded XL-HDPE was carried out at -40°C and the relationships between impact strength and microstructures were investigated. The results confirmed that the microstructures of XLHDPE molecules in the innermost surface layer dominated the low temperature impact performance of rotationally molded XL-HDPE articles.
Research and Application of Gas Counter Pressure Technique to the Strength of Co-Injection Molding
With people’s daily life full of various plastic products, many molding technologies are developed in order to reduce production cost, increase product strength, improve product appearance, and adhere to environmental protection. Co-injection molding is also known as sandwich molding, producing composite plastic products with a multilayer structure through one injection procedure. Most manufacturers use secondary recycled material or high strength plastics as the core material to reduce material cost and increase product strength or utilizes an appropriate proportion of materials to improve product strength and surface quality. This study employs the GCP(Gas Counter Pressure) technique in the co-injection molding process to increase product strength. As co-injection molding has two flow front behaviors of melt, the skin layer thickness distribution and core penetration length are difficult control, and the fountain flow effect results in an unstable injection of core melt. Therefore, the gas counter pressure technique in co-injection molding can inhibit the flow front behavior. This study discusses the effect of the gas counter pressure technique on core penetration and mechanical strength as well as the effect of penetration length and penetration section of core melt on mechanical strength under different gas counter pressure intensities. The experimental results show that the gas counter pressure mechanism enhances core material penetration stability, changes the penetration length and penetration section of core material, and effectively enhances the end product strength.
Rotational Molding of Polylactic Acid and Agave Fiber Biocomposites
In this work, biocomposites of agave fibers (Agave tequilana Weber var. Azul) and polylactic acid (PLA) were produced by rotational molding. In particular, a simple dry-blending technique was used to disperse the agave fibers in the biodegradable polymer matrix. The effect of fiber content was studied (0, 10, 20, 30, and 40 wt.%) and the samples were characterized in terms of morphology, density and porosity to relate with mechanical properties (tensile, flexion, impact and hardness). The results showed that rotomolded biocomposites were successfully produced, but had high porosity leading to lower properties for fiber contents above 10%. It was possible to observe that low fiber contents produced the best morphology, indicating that there is an optimum fiber content to get well-distributed fibers in the matrix.
The Influence of Blend Composition on the Properties of LDPE-PA6-EVAL-Blends
The aim of this work was to investigate the effects of the composition on the properties of LDPE-PA6-EVAL blends with an emphasis on the influence of the EVAL grade on the system. Furthermore, also the effects of additional compatibilization by maleic anhydride grafted PE on the blend properties should be investigated. We found, that EVAL has some compatibility with PA6, as long as the vinyl alcohol content is high enough, in this case at least 62 mol%. This results, in combination with the high shear intensity applied, in a fine dispersed morphology and reasonable properties. In case of the non-compatible EVAL grade, the addition of MAPE improves the properties like impact strength and elastic modulus, which can also be seen from the morphology of the samples. The addition of a compatibilizer also shows an expectable stabilization effect, which can be seen by comparing the morphology of the extruded melt strands after compounding with the morphology of the injection molded specimen afterwards. In conclusion this shows that with compatibilisation, the blend properties are stable and sufficient for various applications, therefore such blends could be reused for another life cycle.
Using Micronized Recycled Tire Rubbers in Thermoplastic Polyolefins as a Value-Enhanced Solution to Sustainability
Thermoplastic elastomers (TPE) including thermoplastic polyolefins (TPO) and thermoplastic vulcanizates (TPV) are promising elastomeric materials for automotive applications such as headlight surrounds, bumper covers, door gaskets, etc. TPEs offer a combination of great thermoplastic processability and outstanding rubbery properties, however, the process of recycling scrap and post-consumer products and reprocessing them into useful products have always been challenging. In addition, tire rubbers have been one of the most problematic sources to recycle, due to their large volume and durability. Innovative and effective methods are critical to reuse the recycled tire rubbers in value-added products other than their traditional use for fuel values. In this study, micron-size rubber powders (MRPs) were fabricated from recycled truck tires in large volume, and used as fillers for the twin screw extruder (TSE) compounding of recycled TPOs. TPO was chosen as the base resin for compounding because of its excellent reprocessability, good compatibility with the micron-size tire rubbers, and reasonable low cost. A compatibilizer was studied to enhance the uniform incorporation of micro-size rubber powders into the base resins and improve the overall performance of the compounds in a cost-effective way. The chemical structure of the recycled TPOs was confirmed by FTIR, and the thermal stability and compositional analysis of the recycled tire rubbers were characterized by TGA. The physical and mechanical properties (hardness, MFI, tensile, Izod impact, etc) were extensively tested to study the overall performance of the compounds. The surface details of injection molded parts are studied and improved for automotive and commodity applications.
Welding of PLA
This project focuses on the characterization of bioplastics joined with impulse heat sealing and ultrasonic welding. Polylactic acid (PLA), which is typically derived from starch rich crops such as corn, was studied. This material was welded in two forms, rigid samples and film. Ultrasonic welding was used to weld rigid PLA samples and PLA films were joined with impulse welding. A characterization of the mechanical properties of this bio-based plastic was completed with a tensile test to determine which welding parameters were the most influential on the material strength. In reference to ultrasonic welding weld time, weld distance and velocity effected weld strength the most. In reference to impulse welding of films, heating time and temperature were the dominant welding parameters relative to weld strength. In addition the interfacial healing activation energy was calculated to predict interfacial healing for the different types of welding.
Improving the mechanical properties of fatty acid starch esters
The novel use of sago starch and vinyl laurate in densified carbon dioxide increases the reactivity of esterification and produces final products that have higher degrees of substitution.
Developing greener composites from cellulose nanocrystals and biopolyurethane
Environmentally friendly nanocomposite materials from bio-based polyurethane and cellulose nanocrystals show significantly improved mechanical properties with only 1 nanocrystal filler.
Improved filler-matrix interfaces in environmentally friendly polymeric composites
Wood-plastic composites can be optimized with the addition of waste paper fibers, coupling agents, and bioderived polymers.
A novel high-performance biobased polyamide
Poly(pentamethylene oxamide) exhibits excellent mechanical, thermal, and water absorption properties, and is suitable for the fabrication of plastics, as well as parts in the automobile and electronics industries.
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