Monomer Recycling and Repolymerization of Post-Consumer Polyester Textiles

Due to the presence of dyes and additives, textile recycling is challenging, therefore the majority of textile waste is downcycled to low-value products, incinerated or landfilled. In this study, a continuous depolymerization of post-consumer polyester textiles was conducted by alkaline hydrolysis. The degree of depolymerization was assessed and found to be 94 %. After recovering and analyzing the terephthalic acid and ethylene glycol the monomers were successfully polymerized to regain a food grade quality recycled polyethylene terephthalate. The presented recycling approach allows a closed-loop recycling of textiles.     

Thermal degradation in bulk and thin films of 2-, 4-, and 6-arm polystyrene stars with a C60 core

The thermal stability (TS) of hexa-, tetra-, and di-arm polystyrene (PS) stars with a C₆₀ core was studied by thermal gravimetric analysis and mass-spectrometry. The quantitative production of volatile products, their composition and their formation kinetics during heating of (PS_xC₆₀) are reported. A bimodal release of styrene is observed. The first release takes place about 100 °C before the depolymerization temperature of styrene and all the C₆₀ comes out at this lower temperature. That results from a complete breaking of the weak PS-C₆₀ bonds followed by a partial depolymerization of the PS arms initiated by the so formed radicals. The amount of PS ‘surviving’ this first depolymerization step increases with the length of the arms and its TS is close to that of pure PS. The thermal stability of the PS_xC₆₀ stars decreases if the number of arms increases and, from the activation energy of the release of styrene and C₆₀, it was possible to estimate the PS-C₆₀ bond strength for these three adducts.     

溶剂法回收废旧聚苯乙烯泡沫塑料

根据溶解度参数原则筛选溶解废旧聚苯乙(烯PS)泡沫塑料的溶剂。结果表明:醋酸正丁酯和二甲苯以体积比1:2形成的复合溶剂效果较好,在40℃时,废旧PS泡沫塑料的溶解度可达0.82g/ml。采用正庚烷作为溶剂回收过程的沉淀剂能够回收得到90%以上的PS原料。同时,对废旧PS泡沫塑料的热稳定性及其溶解前后的化学结构分别进行了TGA和FTIR表征。结果表明:该回收过程仅仅是溶解消泡,并没有发生解聚反应且,无溶剂残留。最后利,用黏度法测定回收后的PS黏均分子量约为2.815×105。     

Compatibilization and morphology development of immiscible ternary polymer blends

We report a novel and effective strategy that compatibilizes three immiscible polymers, polyolefins, styrene polymers, and engineering plastics, achieved by using a polyolefin-based multi-phase compatibilizer. Compatibilizing effect and morphology development are investigated in a model ternary immiscible polymer blends consisting of polypropylene (PP)/polystyrene(PS)/polyamide(PA6) and a multi-phase compatibilizer (PP-g-(MAH-co-St) as prepared by maleic anhydride (MAH) and styrene (St) dual monomers melt grafting PP. Scanning electron microscopy (SEM) results indicate that, as a multi-phase compatibilizer, PP-g-(MAH-co-St) shows effective compatibilization in the PP/PS/PA6 blends. The particle size of both PS and PA6 is greatly decreased due to the addition of multi-phase compatibilizer, while the interfacial adhesion in immiscible pairs is increased. This good compatibilizing effect is promising for developing a new, technologically attractive method for achieving compatibilization of immiscible multi-component polymer blends as well as for recycling and reusing of such blends. For phase morphology development, the morphology of PP/PS/PA6 (70/15/15) uncompatibilized blend reveals that the blend is constituted from PP matrix in which are dispersed composite droplets of PA6 core encapsulated by PS phase. Whereas, the compatibilized blend shows the three components strongly interact with each other, i.e. multi-phase compatibilizer has good compatibilization between the various immiscible pairs. For the 40/30/30 blend, the morphology changed from a three-phase co-continuous morphology (uncompatibilized) to the dispersed droplets of PA6 and PS in the PP matrix (compatibilized).     

Sulphurous additives for polystyrene: Influencing decomposition behavior in the condensed phase

The thermal decomposition behaviour of polystyrene (PS) containing sulphur and phosphorus additives was investigated, using thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA‐FTIR). It was found that the additives influence the decomposition process of the polymer in the condensed phase, resulting in a decrease in styrene monomer formation and an increase in styrene oligmer derivatives. Via reference measurements with binary mixtures it was found that the presence of sulphur additives influences the radicalic decomposition process of PS. In combination with quantum chemical calculations it was concluded that this is due to the formation of radicals that abstract hydrogen from the polymer matrix at lower temperatures, disfavouring the radicalic decomposition pathway leading to styrene. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41665.     

Ethylbenzene into styrene with carbon dioxide over modified vanadia–alumina catalysts

Dehydrogenation of ethylbenzene to styrene with carbon dioxide has been investigated using various vanadia–alumina catalysts to exhibit high activity and selectivity. Redox behavior of vanadium oxide played a key role in the dehydrogenation. Among several additives, antimony oxide has been found for improving catalyst stability as well as catalytic activity to produce styrene, revealing that the addition of the antimony oxide leads to the easier redox cycle between fully oxidized and reduced vanadium species.     

Blends of SBS triblock copolymer with poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polystyrene mixture

Blends of styrene–butadiene–styrene (SBS) or styrene–ethylene/1‐butene–styrene (SEBS) triblock copolymers with a commercial mixture of polystyrene (PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) were prepared in the melt at different temperatures according to the chemical kind of the copolymer. Although solution‐cast SBS/PPO and SBS/PS blends were already known in the literature, a general and systematic study of the miscibility of the PS/PPO blend with a styrene‐based triblock copolymer in the melt was still missing. The thermal and mechanical behavior of SBS/(PPO/PS) blends was investigated by means of DSC and dynamic thermomechanical analysis (DMTA). The results were then compared to analogous SEBS/(PPO/PS) blends, for which the presence of a saturated olefinic block allowed processing at higher temperatures (220°C instead of 180°C). All the blends were further characterized by SEM and TGA to tentatively relate the observed properties with the blends' morphology and degradation temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2698–2705, 2003     

Depolymerization protocol for linear,branched, and crosslinked end‐of‐life silicones with boron trifluoride diethyl etherate as the depolymerization reagent

An important issue for current society is the accumulation of large amounts of end‐of‐life polymers, which are mainly deposited in landfills, converted by thermal recycling or down cycling to low‐quality materials. In contrast to that, the feedstock recycling of end‐of‐life polymers to produce new high‐quality polymers is only applied to a small portion of waste. In more detail, low‐molecular weight chemicals are generated by this methodology; they can be polymerized in a second step to produce new high‐quality polymers. Notably, with these depolymerization‐polymerization processes, contributions to a more sustainable, resource‐conserving, and environmentally benign society can be made. In this regard, we have set up a capable protocol for the depolymerization of polysiloxanes, which are applied extensively in numerous technological applications. Boron trifluoride diethyl etherate was used as a depolymerization reagent to transform Si? O bonds in linear, branched, and crosslinked silicones to Si? F bonds. As depolymerization products, difluorodimethyl silane for linear polysiloxanes and methyl trifluorosilane for branched polysiloxanes were obtained; these were suitable synthons for new polymers and will allow an overall recycling of polysiloxanes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42814.     

Cellulose Regeneration and Chemical Recycling: Closing the “Cellulose Gap” Using Environmentally Benign Solvents

Strategies to mitigate the expected “cellulose gap” include increased use of wood cellulose, fabric reuse, and recycling. Ionic liquids (ILs) are employed for cellulose physical dissolution and shaping in different forms. This review focuses on the regeneration of dissolved cellulose as nanoparticles, membranes, nonwoven materials, and fibers. The solvents employed in these applications include ILs and alkali solutions without and with additives. Cellulose fibers obtained via the carbonate and carbamate processes are included. Chemical recycling (CR) of polycotton (cellulose plus poly(ethylene terephthalate)) is addressed because depending on the recycling approach employed, this process is akin to regeneration. The strategies investigated in CR include preferential dissolution or depolymerization of one component of the blend, and separation of both components using ILs. It is hoped that this review focuses the attention on the potential applications of regenerated cellulose from its solutions and contributes to the important environmental issue of recycling of used materials.     

Phase modification of SEBS block copolymer by different additives and its effect on morphology,mechanical and dynamic mechanical properties

The objective of this study is to examine the phase modification of styrene–ethylene butylene–styrene (SEBS) block copolymer by different additives and its influence on morphology and mechanical, and dynamic mechanical properties. The additives chosen are the coumarone–indene (CI), phenol–formaldehyde (PF), paraffin hydrocarbon (PAHY) resins, as well as aromatic oil (AO), polystyrene (PS), polypropylene (PP), ethylene vinyl acetate (EVA) (VA 28 and 45%), and ethylene propylene diene monomer (EPDM) rubber. It is interesting to note that of all the additives, PP has the most prominent effect. The mechanical properties of SEBS polymer are enhanced to a large extent by PP. The value of tan δ maximum of SEBS at both the low and the high temperature transitions is decreased. All the resins and PS increase the storage modulus and the tensile modulus of the SEBS polymer. CI resin and AO modify the hard and soft phases of SEBS polymer. AO, EPDM rubber, and EVA lower the mechanical strength of the SEBS polymer. The results are explained on the basis of morphologystudied with the help of scanning electron microscopy. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2015–2025, 1998     

Chemical recycling of polymer composites induced by selective variable frequency microwave heating

The application of variable frequency microwave (VFM) heating to achieve rapid thermal depolymerization of polymer composites is reported for the first time. The thermal and chemical influence of composite additives on polymer decomposition has been studied for a set of chemically recyclable polymers, including polyphthalaldehyde, polypropylene carbonate, two polyhydroxyalkanoates, and nylon 6. Carbon-based additives, specifically nanocarbon particles, were used as effective microwave absorbers to controllably degrade the surrounding polymer matrix into valuable, monomeric compounds. Depolymerization and byproduct confirmation were quantified by gel permeation chromatography and nuclear magnetic resonance spectroscopy. Synergistic effects can be leveraged from pre-treating composite samples to further reduce the total microwave energy required to depolymerize composite samples. This study establishes the use of VFM heating for chemical recycling of polymer composites that can be leveraged toward a plastic circular economy.     

Thermal decomposition of polystyrene in supercritical methanol

The degradation of polystyrene (PS) in supercritical methanol was carried out under reaction temperatures ranging from 340 to 420°C and pressures of 10–30 MPa. The selectivity of liquid products was investigated at various reaction conditions. As the reaction proceeded, the selectivity of styrene monomer, dimer, 1,3-diphenyl propane, and 1,3-diphenyl butane had a declining tendency, whereas that of the rest (i.e., toluene, ethyl benzene, isopropyl benzene, and 3-phenyl propanol, etc.) had an inclining tendency. The sequences of decomposition reaction could be reasoned by analyzing the variation of selectivity of liquid products. The kinetic behavior of PS in supercritical methanol had been investigated. The degradation processes of PS in such supercritical fluids could be formulated by the first-order kinetic law at the initial stage of reaction. The activation energy for the degradation in supercritical methanol was evaluated to be 117.2 kJ/mol and it was also compared with the activation energies for depolymerization in other supercritical fluids and that for thermal pyrolysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Block copolymers of styrene containing oligomeric esters of terephthalic acids

A new generation of block copolymers were synthesized starting with depolymerized PET by glycolysis with some oligomeric diols. α,ω‐Dihydroxy poly(dimethyl siloxane)s, hexylene glycol, poly(ethylene oxide)glycols, and ethylene glycol were used as diols. The dihydroxy‐terminated depolymerization products containing a terephthalyl group and oligomeric diols were used to prepare a diradicalic macroinitiator (MI). These MIs were used to polymerize the styrene monomer. The new block copolymers obtained were characterized by physical and chemical methods and mechanical and thermal analyses. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 648–653, 2000     

Comparison of polystyrene,poly(styrene/acrylonitrile), high-impact polystryrene,and poly(acrylonitrile/butadiene/styrene) with respect to tensile and impact properties

The tensile behaviors of polystyrene (PS), poly(styrene/acrylonitrile) (SAN), high-impact polystyrene (HIPS), and poly(acrylonitrile/butadiene/styrene) (ABS) were examined systematically in the wide range of strain rate, 1.7 × 10^?4–13.1 m/s. When glassy and brittle PS was a criterion, the incorporation of a polar group (SAN) only strengthened the hardness, and the fracture mode was the same as for PS. The introduction of dispersed rubber particles (HIPS) weakened the hardness a little but offered a new deformation mechanism, i.e., microcrazing (whitening), and contributed to the improvement of impact strength. In the heterogeneous system, the enhancement of matrix strength [e.g., preorientation or blending with poly(phenylene oxide) for HIPS] makes possible another deformation mechanism, i.e., shear band formation (cold drawing), which is superior to microcrazing for achieving higher impact strength. ABS, which incorporates concurrently two factors (polar group to matrix phase and dispersed rubber particles), can be regarded as an enhancement of the matrix strength of HIPS. In spite of the remarkable magnitude of its impact strength compared with that of the other three polymers, the deformation mechanism of ABS was limited to microcrazing. This indicated that only the introduction of a polar group (as nitrile group) could not strengthen the matrix as much as preorientation or blending with poly(phenylene oxide).     

Co‐injection molding of immiscible polymers: Skin‐core structure and adhesion studies

In this article, the microstructure and the adhesion developed in co‐injected specimens obtained with polypropylene (PP; core) and polystyrene (PS; skin) were studied as a function of process conditions and additives used. The study shows that the incorporation of low amounts of fillers such as Nanoclays and styrene‐ethylene‐butadiene‐styrene (SEBS) copolymer to the core material, working as compatibilizers, improves the adhesion at lower and higher polymer melt temperatures, respectively. The authors concluded as well that the use of such fillers, also improves the reproducibility of the process. The adhesion was assessed by shear tests using double lap shear specimens. A data acquisition system was attached to the mold to evaluate the pressure inside the cavity. Results of the in‐mold pressure profiles corresponded well when compared with MoldFlow predictions, and demonstrated that the adhesion of both materials is also related to their behavior and shrinkage inside the mold. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers.     

Ionic Liquids in Biomass Processing

The ionic liquids have emerged as new solvents and catalysts for processing biomass to value added chemicals and fuels. This review will present the recent developments in applications of ionic liquids in lignocellulosic biomass pretreatments, depolymerization, biodiesel synthesis, dehydration of carbohydrates to renewable feedstock chemicals as well as further transformations of biomass derived feedstocks such as furfural, 5‐hydroxymethylfurfural and levulinic acid to value added chemicals. In addition, the recycling of ionic liquids used in biomass processing is also discussed in the review.     

In situ thermal reduction of graphene oxide in a styrene–ethylene/butylene–styrene triblock copolymer via melt blending

We report an in situ thermal reduction of graphene oxide (GO) in a styrene–ethylene/butylene–styrene (SEBS) triblock copolymer matrix during a melt‐blending process. A relatively high degree of reduction was achieved by melt‐blending premixed GO/SEBS nanocomposites in a Haake mixer for 25 min at 225 °C. Infrared spectral results revealed the successful thermal reduction of, and the strong adsorption of SEBS on, the graphene sheets. The glass transition temperature of polystyrene (PS) segments in SEBS was enhanced by the incorporation of thermally reduced graphene oxide (TRGO). The resultant TRGO/SEBS nanocomposites were used as a masterbatch to improve the mechanical properties of PS. Both the elongation at break and the flexural strength of PS/SEBS blends were enhanced with the addition of the TRGO. Our demonstration of the in situ thermal reduction of GO via melt blending is a simple, efficient strategy for preparing nanocomposites with well‐dispersed TRGO in the polymer matrix, which could be an important route for large‐scale fabrication of high‐performance graphene/polymer nanocomposites. © 2013 Society of Chemical Industry     

废聚酯的循环利用

废聚酯可通过化学解聚等手段来实现其循环利用。阐述了废聚酯循环利用领域的研究现状。介绍了目前国内外开发的废聚酯循环利用工艺方法，其主要方法有水解法、甲醇解聚法、乙二醇解聚法等。     

Anomalous mechanical behavior upon recycling of poly(phenylene‐ether)‐based thermoplastic elastomer

Recycling of thermoplastic elastomers based on poly (phenylene ether) (PPE) was studied in detail. The quaternary blend comprising of styrene–ethylene–butylene–styrene (SEBS)/ethylene vinyl acetate (EVA)/PPE‐PS (polystyrene) showed improvement in mechanical properties upon recycling, which was correlated with the formation of crosslinked network in the system. Presence of crosslinked network was confirmed by the gel content analysis. The blend components involved in the crosslinking were evaluated by gel morphology analysis. Fourier transform infrared spectroscopy revealed the chemical composition of the crosslinked gel. Crosslinking mechanism was established based on the reactivity of allylic EVA radical during recycling. Rheological study supported the notion of crosslinking upon recycling that resulted in higher storage modulus (G′) as a manifestation of restrained flow by network formation. On the basis of the earlier data, a reaction mechanism for crosslinking was proposed. Finally, structure–property correlation was developed through morphological, chemical, and rheological analysis to understand the anomalous enhancement in mechanical properties upon recycling. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

微米级单分散聚苯乙烯微球的制备

以苯乙烯(St)为单体、偶氮二异丁腈(AIBN)为引发剂、聚乙烯吡咯烷酮(PVP)为分散稳定剂,在乙醇-水反应介质中,采用分散聚合法制备了微米级单分散聚苯乙烯(PS)微球。分别用电镜扫描和激光粒度仪表征了PS微球表面形貌、粒径及粒度分布,探讨了影响PS微球粒径及粒度分布的诸多因素。结果表明,AIBN用量(以单体质量计,下同)大于5.0%或PVP用量(以单体质量计,下同)小于2%时,PS粒子间有聚并现象;当St浓度为10%、AIBN用量为2.5%、PVP用量为5.5%、醇水质量比为90∶10、聚合温度为70℃时,制备的PS微球粒径为1.612μm、粒度分散系数为0.357,微球单分散性及球形度最佳。