Our previous work focused on depolymerizing polyethylene terephthalate (PET) in twin-screw extrusion, as part of a broader project to continuously separate PET from polyolefins in the melt. This study focused on linear low-density polyethylene (LLDPE) and PET films and the use of ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and bis(2-hydroxyethyl) terephthalate (BHET) to depolymerize the PET in the extruder to levels above 90% Mw. In this work, the focus will shift to achieving separation of the two polymers in the twin-screw extruder, which is made possible due to a 90% reduction in the Mw of the PET, which caused a decrease of its viscosity by several orders of magnitude. Owing to the viscosity difference and pressure buildup in the die, the low-viscosity PET preferentially exited a degassing vent instead of going through the die. This is because the flow of the PET would travel through a non-pressure vent rather than through a high-pressure die. However, owing to the higher viscosity of the LLDPE, the pressure was too high to pass through such a small diameter vent hole. Supercritical CO2 (SCCO2) was used to assist in this extraction, but SCCO2 negatively impacted the overall degree of separation. Through analysis of the separated materials, it was concluded that a high separation of the two materials was achieved. TGA and FTIR confirmed that the material separated from the vent was 100% PET. The material removed from the die was composed of 95% LLDPE and 5% PET.

ABSTRACT One of the most significant challenges to overcome in the plastic industry is the development of sustainable, closed‐loop recycling methods. Within this waste, specifically, there is the challenge of trying to separate and recycle multilayer films. This study investigated twin‐screw extrusion methods to recycle linear low‐density polyethylene (LLDPE) and polyethylene terephthalate (PET) films via glycolysis, using ethylene glycol (EG/MEG), diethylene glycol (DEG), triethylene glycol (TEG), and bis(2‐hydroxyethyl) terephthalate (BHET) through depolymerization reactions and subsequent in‐melt separation. This paper focuses on identifying the best depolymerization catalyst and content, whereas a future paper focuses on the actual in‐melt separation process. The depolymerization method results in low‐molecular‐weight (Mw) PET, which is suitable for extraction from high‐viscosity LLDPE in a twin‐screw extruder (TSE). Once separated, each polymer can be further chemically mechanically upcycled to create a closed loop recycling method. The first factor studied will be the effect of two different depolymerizing reagents, EG (MEG, DEG, TEG) and BHET, to determine which is more efficient. Second, the percentages of reagents incorporated into the reactions were studied. Finally, the depolymerization reaction time was determined. The results revealed that 8% DEG/TEG or 10% BHET was the most effective at depolymerizing PET for extraction from 61,700 to 6500 g/mol.

Aerogels prepared using freeze-drying methods have the potential to be insulation materials or absorbents in the fields of industry, architecture, agriculture, etc., for their low heat conductivity, high specific area, low density, degradability, and low cost. However, their native, poor water resistance caused by the hydrophilicity of their polymer matrix limits their practical application. In this work, a novel, controllable, and efficient templating method was utilized to construct a highly hydrophobic surface for freeze-drying aerogels. The influence of templates on the macroscopic morphology and hydrophobic properties of materials was investigated in detail. This method provided the economical and rapid preparation of a water-resistant aerogel made from polyvinyl alcohol (PVA) and montmorillonite (MMT), putting forward a new direction for the research and development of new, environmentally friendly materials.

Clay-based aerogels have attracted considerable attention in recent decades due to their natural, low-toxicity features and controllable, porous structures. By incorporating various additives and processing under specific conditions, clay-based aerogel composites have tremendous potential in a wide range of applications. In this chapter, first a series of reinforced clay aerogels enhanced by various polymer matrixes, fibers, or other chemicals are briefly introduced and display the enhancing mechanical and other resultant properties. The state of the art of the clay-based aerogel processing and impact factors are discussed to elucidate the strategy to tailor aerogels with specific morphology. The impressive properties and applications, attributed to the incorporation of additives and the design of the structure, are highlighted, and mechanisms behind these features are also concluded. In the end, the current gap and future direction about the development are identified. This chapter is expected to provide sufficient background and experience to assist the development of the advanced, clay-based aerogels in academia and industry.

Improving the mechanical properties and fire resistance at the same time has become a tough challenge in the study of high-performance biomass foamlike materials. To tackle this dilemma, fully biomass-based aerogels based on renewable porcine gelatin (PG) and phytic acid sodium salt (PA) were designed through a green freeze-drying method. Owing to the low flammability and the strong interaction of these two compounds, the resulting aerogels exhibited both high fire resistance and extra-strong strength, offering a novel solution to the aforementioned difficulty. Benefitting from the design of the strong physical cross-linking structure of PG, PA, and clay, the compressive modulus value of the aerogel was as high as 25.1 MPa, nearly 180 times that of the poly(vinyl alcohol) control. These biobased aerogels exhibited extremely low flammability and superior smoke suppression, that is, the limiting oxygen index values of the aerogel were as high as 50.1%, and the total smoke release decreased from 213 to 13.5 m2 in comparison with those of commercial PU foam. All the results indicated that green aerogels with excellent combination properties will be promising in the future.

In an ever-evolving world, new technologies and innovations are constantly discovered that offer improved utility to humanity. However, these new technologies come with safety risks that are not often well understood prior to commercialization. Time and time again, improper analysis has led to adverse effects on humans, a glaring example being halogenated flame retardants. While excellent gas-phase radical inhibitors and possessing an overall impressive flame-retardant capability, they are often carcinogenic and reprotoxic in nature to humans [1], [2]. For this reason and many others (e.g., climate concerns), bio-based flame retardants have gained increasing attention in the last few decades, particularly with respect to the often-highly-flammable polymeric materials. With a wide range of bio-based material solutions being researched to this day, a proper understanding of characterization techniques is necessary to build a "toolbox" for material analysis. In this chapter, we introduce and describe these techniques, giving literature examples and universal testing/analysis standards whenever possible.

Sodium hydroxide was used as a base catalyst to reduce the flammability of poly(vinyl alcohol) (PVA) aerogels. The base-modified aerogels exhibited significantly enhanced compressive moduli, likely resulting in decreased gallery spacing and increased numbers of “struts” in their structures. The onset of decomposition temperature decreased for the PVA aerogels in the presence of the base, which appears to hinder the polymer pyrolysis process, leading instead to the facile formation of dense char. Cone calorimetry testing showed a dramatic decrease in heat release when the base was added. The results indicate that an unexpected base-catalyzed dehydration occurs at fire temperatures, which is the opposite of the chemistry normally observed under typical synthesis conditions.

Clay aerogels are a relatively unexplored form of matter that are only now being investigated for use in the reinforcement of organic polymers. We have recently demonstrated an efficient process for producing these aerogels; we now report our preliminary work describing the preparation and properties of polymer/clay aerogel composites, including temperature-responsive materials.

Abstract Poly(ethylene terephthalate) (PET) and polyamide (PA) are immiscible polymers, which requires the use of compatibilizers to stabilize the morphology and achieve acceptable property levels. Therefore, controlling the degree of dispersion, especially the size of the disperse PA droplets in the PET matrix is of paramount importance. This study aims to improve the mixing, i.e., minimize PA droplet size, in immiscible and compatibilized PET/PA and PET/Nylon-MXD6 (MXD6) blends by resorting to extension-dominated mixing in twin-screw extrusion (TSE). MXD6 is an aromatic polyamide similar in polarity to PET, so it is expected that it will blend more effectively than is the case with aliphatic nylon-6 and PET. Two screw configurations are used, a benchmark shear-dominated screw with kneading blocks (KBs) in an aggressive configuration, and an extension-dominated screw configuration with static mixers with hyperbolic C–D channels, recently developed by our group, in place of the KBs. The results show that the use of extensional mixing elements (EMEs) in place of KBs results in a significant decrease of both average and maximum droplet size for all blends, and up to more than one order of magnitude between the most extreme cases of the KB-processed immiscible blend and EME-processed compatibilized blends.

Poly (ethylene 2,2′-bifuran-5,5′dicarboxylate) (PEBF) is a new biosourced polyester recently reported to have significant enhancement of oxygen barrier properties and glass transition temperature when compared to poly (ethylene terephthalate). We report herein our independent studies on the polymerization and properties of this new polyester. Our findings are contrasted to an earlier report. While the Tg of 106–108 °C was confirmed to be consistent with the early data, we observed crystallization on both cooling and heating cycles in the DSC which were not previously observed, higher tensile elongation to break values, and significantly lower oxygen permeabilities compared to the earlier report. Preliminary uniaxial orientation experiments indicate that this polymer is a good candidate for biaxial orientation processing. We discovered that both the monomer, dimethyl-2,2′-bifuran-5,5′-dicarboxylate (BFE), and the polymer are subject to thermal oxidation which was explored with cyclic voltammetry on the monomer. Experiments with added antioxidant during the polycondensation show marked reduction in the thermal oxidation as observed by color reduction and enhanced stability to melt processing.

Bio-based flame retardants (FRs) were employed to successfully reduce the flammability of acrylonitrile–butadiene–styrene (ABS), achieving results comparable to a commercial brominated ABS product ...

Biological molecules can be obtained from natural sources or from commercial waste streams and can serve as effective feedstocks for a wide range of polymer products. From foams to epoxies and composites to bulk plastics, biomolecules show processability, thermal stability, and mechanical adaptations to fulfill current material requirements. This paper summarizes the known bio-sourced (or bio-derived), environmentally safe, thermo-oxidative, and flame retardant (BEST-FR) additives from animal tissues, plant fibers, food waste, and other natural resources. The flammability, flame retardance, and-where available-effects on polymer matrix's mechanical properties of these materials will be presented. Their method of incorporation into the matrix, and the matrices for which the BEST-FR should be applicable will also be made known if reported. Lastly, a review on terminology and testing methodology is provided with comments on future developments in the field.

Three chain extenders, pyromellitic dianhydride (PMDA), ethylene carbonate (EC), and a polymeric-epoxide, were investigated for improving recycled p(ethylene terephthalate) (r-PET) properties with melt extrusion. The amount of additives and processing temperatures were also varied to check for melt degradation. Small amplitude oscillatory shear experiments were performed to probe rheological changes with different chain extenders. Capillary rheometry with haul-off was also performed to measure extensional viscosity and melt strength. Higher loadings of the chain extenders were found to improve properties of r-PET. These chain extenders definitely increased melt viscosities when incorporated at the higher level of the ranges examined, matching that of virgin PET. EC addition resulted in high shear thinning of the polymer. Epoxy and PMDA added to r-PET produced products with the same extensional viscosity as v-PET. Haul-off experiments demonstrate superior performance by epoxy-modified r-PET compared to v-PET.

ABSTRACTA series of 16‐layer polypropylene/flame retardant (PP/FR) film/foam composite structures were produced by microlayer coextrusion. A highly branched PP was used in the foam layers to increase strain hardening and cell stability, while the PP used in the film layers was a high shear viscosity grade to confine bubble growth. In addition to improved tensile properties, the PP/FR composite film/foams exhibited five times the compression modulus of PP/FR composite foams at each FR loading level. The thermal stabilities of the composites were investigated, exhibiting three step decompositions. The FR particles were effective in decreasing flammability by forming intumescent char. The PP/FR‐film/foam‐20 showed self‐extinguishing behavior in a modified vertical burn test, while the PP/FR‐foam‐20 sample continued to burn. Cone calorimetry demonstrated that PP/FR film/foams had lower heat release than PP/FR foams due to the unique alternating film/foam structure of PP/FR film/foams. Scanning electron microscopy imaging of the residual chars from fire testing that the PP/FR composite film/foams showed a more continuous protective char surface when compared with PP/FR composite foams at each FR concentration. The combined data indicate that the formation of a surface film on top of a foam ensures a robust intumescent fire protective barrier for partly foamed materials and shows a new way toward lightweight materials with improved fire safety performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48552.

Transparent films composed of 65 alternating layers of high density polyethylene and ethylene/vinyl alcohol copolymer were produced and evaluated for their oxygen and water vapor barrier performance. Such high barrier films are of special interest for encapsulation of flexible organic electronic devices; these devices are extraordinarily sensitive to degradation by oxygen and/or water. In the present work, the multilayered films were produced using a layer multiplying process, and in some cases, they were further modified by applying organic and inorganic barrier coatings. An optimized film included coatings of both parylene C and alumina, achieving an oxygen transmission rate of <10(-3) cc/m(2).day and a water vapor transition rate of 4.6 x 10(-4) g/m(2).day; these values are useful in encapsulating organic photovoltaic devices.

Low density composites of sodium montmorillonite and poly(amide-imide) polymers have been created using an ice templating method, which serves as an alternative to the often-difficult foaming of high temperature/high performance polymers. The starting polymer was received in the poly(amic acid) form which can be cured using heat, into a water insoluble amide-imide copolymer. The resulting materials have densities in the 0.05 g/cm3 range and have excellent mechanical properties. Using a tertiary amine as a processing aid provides for lower viscosity and allows more concentrated polymer solutions to be used. The concentration of the amine relative to the acid groups on the polymer backbone has been found to cause significant difference in the mechanical properties of the dried materials. The synthesis and characterization of low density versions of two poly(amide-imide) polymers and their composites with sodium montmorillonite clay are discussed in the present work.