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- 2019 (2) (entfernen)
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- Englisch (2) (entfernen)
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- Flame retardant (2)
- Dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (1)
- Foams (1)
- Lignin (1)
- Phospha-Michael addition (1)
- Polyesther (1)
- Polyisocyanurate (1)
Organisationseinheit der BAM
A series of new flame retardants (FR) based on dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) incorporating acrylates and benzoquinone were developed previously. In this study, we examine the fire behavior of the new flame retardants in polyisocyanurate (PIR) foams. The foam characteristics, thermal decomposition, and fire behavior are investigated. The fire properties of the foams containing BPPO-based derivatives were found to depend on the chemical structure of the substituents. We also compare our results to state-of-the-art non-halogenated FR such as triphenylphosphate and chemically similar phosphinate, i.e. 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO), based derivatives to discuss the role of the phosphorus oxidation state.
Our approach includes the preparation of blends of preferably liquid-crystalline polyesters with Lignin, but also the synthesis of new polyesters with Lignin-related monomer units.
While most studies employ pulped Lignin directly, we first purified the Kraft Lignin by fractionation, followed by chemical modification of the terminal OH groups. Acetylation results in the reduction of glass transition temperatures (Tg) below 200°C, improved processability in the melt with complete melting of the Lignin sample, and higher thermostability.
These Lignin fractions were melt-mixed in a mini-twin-screw extruder with polyesters. The chemical structure of the polyesters was systematically varied between poly(ethylene terephthalate), (PET); poly(ethylene terephthalate-co-oxybenzoate), (PET/HBA); liquid crystalline polyesters with fully aromatic structure; and polyesters with Lignin-related monomers like ferulic and vanillic acid). The polymer influence on the blending behavior with Lignin was examined. SEM revealed phase-separated blends with partial compatibilization of the phases indicated by the shift of Tg’s. The influence of the polyester and the Lignin on decomposition and combustion was accessed by thermogravimetry (TGA), TGA-FTIR and pyrolysis-combustion flow calorimetry (PCFC) and compared to the decomposition of polyesters. The main focus was to achieve melt-spinnable blends for fibres with improved flame retardancy or as precursors for carbon fibers. Blends of Lignin fractions with the aromatic-aliphatic polyesters (here preferably PET/HBA) were successfully spun into fibers with lab-scale melt-spinning equipment. X-ray measurements revealed orientation of the fibers with Lignin. The E-moduli raised with increasing purity of the Lignin fractions (e.g., by removal of reducing sugars).
The structure of the polymer matrix determines the decomposition and combustion behavior of the blends with Lignin. Incorporation of aliphatic subunits reduces the amount of remaining char formed in TGA and PCFC from about 40-45 wt% for fully aromatic polyesters to 18-25 wt% for semiaromatic polyesters (at almost comparable carbon content in the polymer), while the maximum temperature of combustion decreased from 480-530°C for the former to 410-465°C for the latter. Lignin fractionation and acetylation yields samples with high char content (36 wt%) and extremely low heat release capacity (80-90 kJ/gK) with combustion maximum temperature at 405°C. Lignin/ PET/HBA blends combine the low HRC with intermediate char and offer interesting opportunities for polyester fibers with improved flame retardancy without adding P-containing FRs.
The flame retardancy behavior was explored by limiting oxygen index measurements on injection-molded parts and fibers.