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Tailoring of polyesters for bead foams with enhanced thermal resistivity and investigation of structure-property-relationships during expansion and fusion

Subject Area Polymer Materials
Synthesis and Properties of Functional Materials
Plastics Engineering
Organic Molecular Chemistry - Synthesis and Characterisation
Preparatory and Physical Chemistry of Polymers
Term from 2020 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 436509183
 
Final Report Year 2023

Final Report Abstract

The main objective of the interdisciplinary joint project between the Chair of Polymeric Materials at the University of Bayreuth (LSPW) and the Leibniz Institute of Polymer Research Dresden (IPF) was to gain a scientific understanding of the processes that occur during the foaming and welding of expanded poly(butylene terephthalate) particle foams (E-PBT). These foams are of great importance due to their high temperature resistance and low density. Until the start of the project, the foaming and fusion of PBT particle foams was only possible after addition of a multifunctional chain extender (CE). So far, the influence of CE on the resulting structure was not sufficiently understood scientifically. Therefore, the influence of the chemical structure of PBT on the foamability and properties of the resulting foams was investigated. To reflect the complexity of the structural influences, the chemical structure of PBT was systematically modified by incorporating suitable comonomers (IPF) and recording the resulting changes in properties (melting and crystallization behavior, crystallinity, shear and extensional rheology, batch tests for foamability, etc.) (IPF and UB). The PBT copolyesters with different chain structures (linear with different molar masses, shortshort-chain branched by incorporation of dilinoleic derivatives, highly branched, as well as with incorporated Diels-Alder reactive furan groups) were synthesized at IPF on laboratory and small pilot plant scale, and chemically characterized by NMR spectroscopy and size exclusion chromatography (SEC). The properties of these materials were subsequently characterized at UB, or jointly by UB and IPF. Linear PBTs in the molar mass range from 49 to 98 kDa showed an optimum at 90 kDa in terms of foam density and morphology as well as bead fusion behavior, thus proving that foaming PBT (with certain restriction) is also possible without CE. The incorporation of dilinoleic derivatives into PBT copolyesters yields defined short-chain branches. These short-chain branches lead to strain hardening similar as CE do, thus improving foamability and foam parameters (density, cell density, etc.). The blending of PBT and PBT in the extrusion foam process also leads to an improvement in foamability due to transesterification reactions. Furthermore, the additional use of a Diels-Alder linker of the bismaleimide type improves the weldability (particle fusion) of the PBT/PBF foam particles. The numerous scientific results resulting from the synthesized model systems could only be achieved through the excellent interdisciplinary cooperation of the project partners. All working hypothesis stated in the proposal could be successfully verified. Most of the significant results of the project were jointly published in a total of 7 peer-reviewed scientific publications and several scientific presentations.

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