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Synergy in flame-retarded epoxy resin - Identification of chemical interactions by solid-state NMR
(2017)
The potential synergists aluminium diethylphosphinate (AlPi), boehmite (AlO(OH)) and melamine polyphosphate (MPP) were compared in flame-retardant epoxy resin (EP)/melamine poly(magnesium phosphate) (S600). The pyrolysis, the fire behaviour as well as the chemical interactions in the gas and condensed phases were investigated by various methods. Flammability was investigated by cone calorimeter and oxygen index (OI). The thermal and thermo-oxidative decomposition were studied by thermogravimetric analysis coupled with FTIR spectrometer. The special focus was on the Investigation of structural changes in the condensed phase via solid-state NMR of 27Al and 31P nuclei. By the comparison of epoxy resin with only one additive or with S600 in combination with AlPi, AlO(OH) or MPP, it was possible to calculate the synergy index. The best performance in terms of fire behaviour was observed for EP/S600/MPP with a PHRR (Peak heat release rate) of 208 kW m-2 due to slight synergy. In the case of THE (total heat evolved), clear synergy occurred for EP/S600/AlPi and EP/S600/AlO(OH). By solid-state NMR, different phosphates and aluminates were identified, indicating the chemical interactions between S600 and AlPi, AlO(OH) or MPP. The systematic multi-methodical approach yielded insight into the synergistic effects in the flame-retarded epoxy resin.
Distinct approaches are used to reduce the fire risks of polymers, a key issue for many industrial applications. Among the variety of approaches, the use of synergy in halogen-free multicomponent systems is one of the most auspicious. To optimize the composition of such flame-retardant systems it is essential to understand the mechanisms and the corresponding chemistry in the condensed phase. In this work different methods are used, including cone calorimeter, thermogravimetry (TG), and TG-FTIR, with the main focus on the solid-state NMR analysis of the solid residues. The structural changes in the condensed phase of two thermoplastic elastomer systems based on copolymer styrene-ethylene-butadiene-styrene (TPE-S) were investigated: TPE-S/aluminium diethylphosphinate (AlPi)/magnesium hydroxide (MH) and TPE-S/AlPi/zinc borate (ZB)/poly(phenylene oxide) (PPO). Strong flame inhibition is synergistically combined with protective layer formation. 13C-, 27Al-, 11B- and 31P MAS NMR (magic angle spinning nuclear magnetic resonance) experiments using direct excitation with a single pulse and 1H31P cross-polarization (CP) were carried out as well as double resonance techniques. Magnesium phosphates were formed during the pyrolysis of TPE-S/AlPi/MH, while for the system TPE-S/AlPi/ZB/PPO zinc phosphates and borophosphates were observed. Thus, the chemistry behind the chemical interaction was characterized unambiguously for the investigated systems.
A systematic comparison of chemical interactions and fire behaviour is presented for the thermoplas-tic elastomer (block copolymer styrene-ethylene-butadiene-styrene) (TPE-S)/diethyl- and methylvinylsiloxane (Si)/poly(phenylene oxide) (PPO), flame-retarded with aluminium diethylphosphinate (AlPi)and with ammonium polyphosphate (APP), respectively. TPE-S/APP/Si/PPO performed better in the conecalorimeter test (reduction in peak heat release rate from 2042 to 475 kW m−2), but TPE-S/AlPi/Si/PPO inthe flammability tests (oxygen index (OI) and UL 94). This difference was caused by the different modes ofaction of APP (more in the condensed phase) and AlPi (mainly in the gas phase). Thermogravimetry cou-pled with Fourier transform infrared spectroscopy (TG-FTIR) was used to analyse the mass loss and theevolved gas products, while a Linkam hot-stage cell to investigate the decomposition in the condensedphase. Moreover, a detailed analysis of the fire residues was done using solid-state NMR.13C MAS NMRshowed that both flame-retarded compositions form graphite-like amorphous carbonaceous char, orig-inating from PPO.31P MAS NMR and29Si MAS NMR delivered important information about interactionbetween phosphorus and the siloxane. For TPE-S/AlPi/Si/PPO aluminium phosphate and silicon dioxideoccurred, while also silicophosphate was produced in TPE-S/APP/Si/PPO. The direct comparison of two ofthe most prominent halogen-free flame retardants containing phosphorus delivered meaningful insightsinto the modes of action and molecular mechanisms controlling flame retardancy.
Solid-state NMR Identifying the Chemistry in Multicomponent Flame-retarded Polyolefin Systems
(2017)
Understanding of the interaction in multicomponent flame-retarded polymeric system is crucial to obtain the best performance at the possible lowest load of additives. In this work, polyolefine based systems are investigated by solid state NMR and cone calorimetry. As a polymer matrix thermoplastic elastomer based on styrene (TPE-S) was chosen. Different combination of additives was investigated in order to identify the chemistry occurring during the pyrolysis. As additives aluminium diethylphosphinate (AlPi), ammonium polyphosphate, zinc borate (ZB), poly(phenylene oxide) (PPO), magnesium hydroxide (MH) and dimethyl- methylvinyl siloxane (Si) were used. Fire residues remained after the cone calorimeter test were analyzed by solid state NMR (31P, 27Al, 13C, 11B, 29Si). The formation of different phosphates and aluminates was identified, indicating the chemical interaction between the additives. Detailed investigation delivered meaningful insights into the chemistry controlling flame retardancy.
As polypeptoids become increasingly popular, they present a more soluble and processable alternative to natural and synthetic polypeptides; the breadth of their potential functionality slowly comes into focus. This report analyzes the ability of an alkyne-functionalized polypeptoid, poly(N-propargyl glycine), to crosslink upon heating. The crosslinking process is analyzed by thermal analysis (differential scanning calorimetry and thermogravimetric analysis), Fourier-transform infrared, electron paramagnetic resonance, and solid-state NMR spectroscopy. While a precise mechanism cannot be confidently assigned, it is clear that the reaction proceeds by a radical mechanism that exclusively involves the alkyne functionality, which, upon crosslinking, yields alkene and aromatic products.
Synergistic multicomponent systems containing melamine poly(metal phosphate)s have been recently proposed as flame retardants. This work focuses on the decomposition pathways, molecular mechanisms and morphology of the fire residues of epoxy resin (EP) flame retarded with melamine poly(zinc phosphate) (MPZnP) to explain the modes of action and synergistic effects with selected synergists (melamine polyphosphate (MPP) and AlO(OH), respectively). The total load of flame retardants was always 20 wt.%. The decomposition pathways were investigated in detail via thermogravimetric Analysis coupled with Fourier transform infrared spectroscopy. The fire residues were investigated via elemental analysis und solid-state nuclear magnetic resonance spectroscopy. The morphology of intumescent fire residues was investigated via micro-computed tomography and scanning electron microscopy.
EP + (MPZnP + MPP) formed a highly voluminous residue that showed structural features of both EP + MPZnP and EP + MPP, resulting in a highly effective protection layer. EP + (MPZnP + AlO(OH)) preserved the entire quantity of phosphorus content during combustion due to the Formation of Zn₂P₂O₇ and AlPO₄.
Unilateral and solid-state nuclear magnetic resonance
(NMR) analyses were performed on a parchment
fragment of the Dead Sea Scroll (DSS). The analyzed
sample belongs to the collection of non-inscribed and
nontreated fragments of known archaeological provenance
from the John Rylands University Library in Manchester.
Therefore, it can be considered as original DSS material
free from any contamination related to the post-discovery
period. Considering the paramount significance of the DSS,
noninvasive approaches and portable in situ nondestructive
methods are of fundamental importance for the determination
of composition, structure, and chemicalphysical
properties of the materials under study. NMR studies
reveal low amounts of water content associated with
very short proton relaxation times, T1, indicating a high
level of deterioration of collagen molecules within scroll
fragments. In addition, 13C cross-polarization magicangle-
spinning (CPMAS) NMR spectroscopy shows characteristic
peaks of lipids whose presence we attribute to
the production technology that did not involve liming.
Extraction with chloroform led to the reduction of both
lipid and protein signals in the 13C CPMAS spectrum
indicating probable involvement of lipids in parchment
degradation processes. NMR absorption and relaxation
measurements provide nondestructive, discriminative, and
sensitive tools for studying the deterioration effects on the
organization and properties of water and collagen within
ancient manuscripts.
Solid state NMR spectroscopy was applied to determine the overall degree of substitution (DS) and the degrees of substitution at C-6 (DSC-6) and C-2/3 (DSC-2/3). Four commercial methyl cellulose samples were used, having a DS between 0.51 and 1.96 as determined by wet-chemical analysis. The strategy and optimization of the NMR data acquisition as well as the data evaluation procedures are explained in detail. Optimization of the approach mainly comprised (a) maximizing the signal by choice of NMR probe, MAS spinning frequency and B0 field, (b) minimizing the measurement time by a Torchia-type experiment and (c) suppressing probe background by rotor-synchronized echo detection. Data evaluation used simply the integration of three different spectral ranges in the 13C NMR spectrum. The results of the experiments were in good agreement with the wet-chemical data. The NMR approach takes about the same analysis time as the conventional hydrolysis/chromatography analysis. However, it is a generally applicable and simple alternative without need for an extended sample preparation which is most useful if wet-chemical/chromatographic analyses are undesired or unavailable. Further studies have to concentrate on the validation of the analytical method and application to a larger sample array.
Three methyl celluloses with completely uniform substitution pattern, 2-O-methyl cellulose (1), 3-O-methyl cellulose (2) and 6-O-methyl cellulose (3), were prepared according to the cationic ring opening polymerization approaches starting from substituted 1,2,4-orthopivalate derivatives of D-glucose. These samples allowed for the first time to sort out the methyl substitution effects on solid-state NMR chemical shifts and relaxation. Dipolar dephasing experiments allowed the detection and assignment (1H, 13C) of the methyl groups. In 1 and 2, these resonances overlapped with those of C-6, whereas in 3, the methyl signal experienced a low-field shift into the region of C-2,3,5. 13C T1 experiments were used to verify different relaxation behavior of the carbon sites, particularly the short relaxation time of at the carbon substitution site next to the methyl groups. This effect was used to unambiguously identify the 13C chemical shifts of the carbons carrying the methoxyl substituent, although they overlap with all resonances in the C-2,3,5 region. The data obtained for the standard samples with uniform substitution will now be used as the basis for determining methylation patterns and substitution degree in commercial methyl celluloses.