Superior Properties through Feedstock Development for Vat Photopolymerization Additive Manufacturing of High-Performance Biobased Feedstocks

Vat photopolymerization additive manufacturing (Vat AM) technologies have found niche industrial use being able to produce personalized parts in moderate quantity. However, Vat AM lacks in its ability to produce parts of satisfactory thermal and mechanical properties for structural applications. The purpose of this investigation was to develop high-performance resins with glass transition temperatures (Tg) above 200 °C for Vat AM, evaluate the properties of the produced thermosets and establish a structure–property relationship of the thermosets produced. Herein, we have developed SLA-type resins that feature bio-derived monomer hesperetin trimethacrylate (HTM) synthesized from the flavonone hesperetin. Diluents 4-acryloyl morpholine, styrene, 4-methyl styrene and 4-tert butylstyrene (tbutylsty) were photocured with HTM as the monomer and all produced thermosets with Tg values above 200 °C. Investigations of suitable crosslinkers urethane dimethacrylate, the vinyl ester CN 151 and Ebecryl 4859 (Eb4859) showed that each crosslinker displayed different benefits when formulated with HTM as the monomer and tbutylSty as the diluent (HTM:crosslinker:tbutylSty with mass ratio 2:1:2). The crosslinker CN 151 produced the thermoset of greatest onset of thermal decomposition temperature (T0) of 352 °C. Eb4859 produced the thermoset of highest tensile strength, 19 ± 7 MPa, amongst the set of varied crosslinkers. The formulation featuring UDM (HTM:UDM:tbutysty) offered ease of processing and was seemingly the easiest to print. Investigations of reactive diluent showed that styrene produced the thermoset of the highest extent of cure and the overall highest tensile strength, 25 ± 5 MPa, while tbutylSty produced the thermoset with the greatest Tan-δ Tg, 231 °C. HTM was synthesized, formulated with diluents, crosslinkers and initiators. The HTM resins were then 3D printed to produce thermosets of Tg values greater than 200 °C. The polymer properties were evaluated and a structure–reactivity relationship was discussed.

Chemical Recycling of WEEE Plastics—Production of High Purity Monocyclic Aromatic Chemicals

More than 200 kg real waste electrical and electronic equipment (WEEE) shredder residues from a German dismantling plant were treated at 650 °C in a demonstration scale thermochemical conversion plant. The focus within this work was the generation, purification, and analysis of pyrolysis oil. Subsequent filtration and fractional distillation were combined to yield basic chemicals in high purity. By means of fractional distillation, pure monocyclic aromatic fractions containing benzene, toluene, ethylbenzene, and xylene (BTEX aromatics) as well as styrene and α-methyl styrene were isolated for chemical recycling. Mass balances were determined, and gas chromatography–mass spectrometry (GC-MS) as well as energy dispersive X-ray fluorescence (EDXRF) measurements provided data on the purity and halogen content of each fraction. This work shows that thermochemical conversion and the subsequent refining by fractional distillation is capable of recycling WEEE shredder residues, producing pure BTEX and other monocyclic aromatic fractions. A significant decrease of halogen content (up to 99%) was achieved with the applied methods.

Polystyrene Biodegradation by Tenebrio molitor Larvae: Identification of Generated Substances Using a GC-MS Untargeted Screening Method

A GC-MS method has been applied to screen and evaluate the generation of chemical compounds during the biodegradation of polystyrene (PS) with Tenebrio molitor larvae. Several resulting compounds have been identified, including trimers 2,4,6-triphenyl-1-hexene and 1,3,5-triphenylcyclohexane, the volatiles acetophenone and cumyl alcohol, and 2,4-di-tert butylphenol, a non-intentionally added substance (NIAS) present in the plastic material. The PS monomers styrene and α-methyl styrene were also identified in the extracts. Bioactive molecules present in the biomass of the studied insects were identified, such as the free fatty acids myristic, palmitic, and oleic acid. Undecanoic acid was also found, but in lower mass fractions. Finally, biochemically formatted amides resulting from their respective fatty acids were identified, namely tetradecanamide, hexadecanamide and oleamide. The formation of all these substances seems to suggest enzymatic and biochemical activity occurring during the biodegradation of PS, and their amounts varied throughout the experience. The overall degradation rate of PS resulted in a 13% rate, which highlights the potential of biorecycling using these insects.

N-Arylbenzo[b]phenothiazines as Reducing Photoredox Catalysts for Nucleophilic Additions of Alcohols to Styrenes: Shift towards Visible Light

N-Phenylphenothiazines are an important class of photoredox catalysts because they are synthetically well accessible, they allow the tuning of the optoelectronic properties by different substituents, and they have strong reduction properties for activation of alkenes. One of the major disadvantages of N-phenylphenothiazines, however, is the excitation at 365 nm in the UV-A light range. We synthesized three differently dialkylamino-substituted N-phenylbenzo[b]phenothiazines as alternative photoredox catalysts and applied them for the nucleo­philic addition of alkohols to α-methyl styrene. The additional benzene ring shift the absorbance bathochromically and allows performing the photocatalyses by excitation at 385 nm and 405 nm. This type of photoredox catalysis tolerates other functional groups, as representatively shown for alcohols as substrates with C–C and C–N triple bonds.