Thermal Field-Flow Fractionation and Gas Chromatography−Mass Spectrometry in Determination of Decomposition Products of Expandable Polystyrene after Reactions in Pressurized Hot Water and Supercritical Water

Abstract

Nonbiodegradable polymers are an environmental concern, and various techniques have been developed to recycle and reuse them. Pressurized hot water, or supercritical water, is an interesting alternative as a reaction medium for depolymerization, since water is a readily available "green" solvent and its physicochemical properties can be widely adjusted in the vicinity of the critical point. In the present study, various reaction conditions (reaction time, temperature, and use of additives and catalysts, i.e., H 2 O 2 , Pd, NaOH, and HCl) were applied to obtain as high styrene monomer yields as possible in the decomposition of industrial expandable polystyrene (EPS) in a pressurized, high-temperature aqueous medium. Other main reaction products were of interest as well. Reactions were carried out in laboratory-constructed reactors made of Hastelloy. The highest styrene recoveries, ca. 57 wt % of the initial EPS load as measured by gas chromatography-mass spectrometry (GC-MS), were obtained after NaOH addition in 20 min reaction time at 400 °C. Without additives, the highest yields were only ca. 13% of the initial load. Other main reaction products were acetophenone, benzaldehyde, benzene, ethylbenzene, phenol, and toluene. Thermal field-flow fractionation (ThFFF) was used after the degradation of EPS to check for possible high molar mass products. When the temperature was raised to 400 °C and higher, EPS residues were not detected in fractograms. Low molar mass EPS residues (M < 100.000) could not be detected because their signals were overlapped by the enlarged void peak signals due to monomer components. As a whole, the analytical techniques (GC-MS and ThFFF) employed in the characterization of EPS degradation in a pressurized, high-temperature medium complemented each other well and showed good performance.

Completely Recyclable Monomers and Polycarbonate: Approach to Sustainable Polymers

“…In the polymeric field, it remains of great interest to depolymerize used or waste polymers to convert into the corresponding starting monomers suitable for repolymerization reactions that reform recycled materials no different from the virgin polymer. Usually, depolymerization is performed under harsh conditions such as high temperatures, or/and high‐pressures, and therefore giving the low selectivity for the desired products . In 2007, Kamimura and Yamamoto reported the efficient depolymerization of polyamides in an ionic liquid at 300 °C to give the corresponding monomeric lactam in good yields (35–86 %) .…”

Production of Chemicals in Supercritical Water

“…Fang treated polystyrene in SCW, and found that it is dissolved above 769.3 K, and then homogeneous reaction takes place above 843.5 K to produce styrenelike product [53]. Kronholm also treated polystyrene, and obtained styrene recovery of 57 wt% with NaOH addition in 20 min at 673 K [54]. Without NaOH, the highest yield was only 13 wt%.…”

Chemical Synthesis of CO2-Based Polymers with Enhanced Thermal Stability and Unexpected Recyclability from Biosourced Monomers

“…The vast majority of synthetic polymers frequently used in modern life are derived from petrochemicals; therefore, the environmental concerns associated with both the raw materials used to make them and their end-of-life options have pushed increasing efforts toward the development of sustainable polymers based on naturally occurring or biomass-derived renewable feedstocks. − Especially, it is highly desirable to design sustainable polymers with a unique recyclability that can be completely depolymerized to the respective monomers via thermal, , mechanical, or chemical methods, − the recovered building blocks of which can be reused to produce polymers with a virgin quality. The development of completely recyclable polymers has become an emerging frontier in polymer chemistry; however, the efficient synthesis of monomers or/and polymers with the desirable physical properties and mechanical strengths required for practical uses from renewable feedstocks under environmentally friendly conditions still represents a challenge. − Usually, harsh conditions such as high temperatures or/and high pressures are necessary for the depolymerization to give the original monomers. , An elegant breakthrough in this area stemmed from the laboratory of the Chen research group, where the efficient ring-opening polymerization of γ-butyrolactone, a biomass-derived and previously considered “nonpolymerizable” monomer, selectively affords poly­(γ-butyrolactone) with linear and cyclic topologies; more importantly, both of the structures could be recycled back into the monomer in quantitative yield by pyrolysis at >200 °C or in the presence of a catalyst under room temperature. − In comparison with the diverse synthetic polymers used currently, the complete recovery of the precursor building blocks via chemical recycling still remains limited. , …”

“…12−14 Usually, harsh conditions such as high temperatures or/and high pressures are necessary for the depolymerization to give the original monomers. 15,16 An elegant breakthrough in this area stemmed from the laboratory of the Chen research group, where the efficient ring-opening polymerization of γ-butyrolactone, a biomass-derived and previously considered "nonpolymerizable" monomer, selectively affords poly(γ-butyrolactone) with linear and cyclic topologies; more importantly, both of the structures could be recycled back into the monomer in quantitative yield by pyrolysis at >200 °C or in the presence of a catalyst under room temperature. 17 −19 In comparison with the diverse synthetic polymers used currently, the complete recovery of the precursor building blocks via chemical recycling still remains limited.…”