High performance flame retardant rigid polyurethane foam with high thermal insulation

Medientyp: E-Book

Titel: High performance flame retardant rigid polyurethane foam with high thermal insulation

Beteiligte: Acuña Domínguez, Pablo Alberto [VerfasserIn]

Erschienen: [Erscheinungsort nicht ermittelbar]: [Verlag nicht ermittelbar], 2021

Sprache: Englisch

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Entstehung:

Hochschulschrift: Dissertation, 2021

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Beschreibung: The fire hazard of polymeric materials causes fatal losses to people´s life, property and on top of that, commonly it derives to social problems due to these damages. The integral fire-hazard assessment was involved in thermal conductivity, ignition behavior, heat release, smoke production and toxic effluents. Polyurethane (PU), is one of the most used materials in our daily life´s, being integral part of freezers, cars, buildings, footwear, food packaging …etc. Indeed, PU is a very versatile material, being found on different applications, such as elastomers, adhesives, thermoplastics and on top of that, rigid (RPUF) and flexible (FPUF) foams. However, as most of the polymeric materials, it is very flammable with high risk of fire spreading. For that reason, fire/flame retardants (FRs) are commonly used as useful solutions to avoid the risk of a fire. In this PhD thesis, the thermal and fire behavior of different fire-retardant systems of RPUFs has been systematically investigated. The thermal conductivity has been of special importance particularly in terms of nanofillers-based polymers, as the commercial use of RPUFs is mainly as insulators. This thesis aimed also at the study of the mechanical properties of fire-retardant RPUF as it can be commonly used as mechanical reinforcement as well as the cellular structure, due to the direct influence in both thermal conductivity and mechanical performance. The nanostructures used as FR additives on this thesis include carbon-based materials such as expandable graphite (EG) and graphene oxide (GO) as well as novel synthesized phosphorous-nitrogen-based FRs (P-N FRs). Besides, the use of green natural resources to obtain RPUFs, partly suppressing the use of petroleum-based materials, has been encouraged on this thesis. The studies based on these solutions to obtain higher thermal and fire stability as well as good mechanical performance were explored separately with the FR mechanism investigation. In detail, the strategies based on novel concepts were adopted to obtain high flame retardancy (Chapter 4), synergistic effect to achieve higher compressive strength (Chapter 5) and the use of new natural resources combined with high thermal insulation (Chapter 6). Obtaining multifunctional properties into one sole system was demonstrated in Chapter 7. 1) In terms of flame retardancy, the use of EG as FR additive offered a feasible solution. The use of three different EGs (EG1, EG2 and EG3) with different particle size and rate of expansion was primarily investigated in a commercial foam. The big size of EG affects the structure of the foam by reducing its cell size, increasing the density and so, the thermal conductivity. The internal cellular structure of the PU gets dramatically affected by EG, thus the compressive performance of the foam was diminished due to slippage between the damaged cellular structure and the EG. Above all, EG acted as an excellent additive FR which reduces the heat released (peak (PHRR) and total heat (THR)), total smoke production (TSP) and mass loss in a commercial RPUF (cone calorimeter test (CCT), 50 kW/m2). The different particle size (EG1/EG2 and EG3) and rate of expansion (EG1 and EG2/EG3) were highlighted inside this research. It was discovered that to have an outstanding FR effect, it is necessary to use high particle size and high rate of expansion, with the aim of maximizing the performance of EG as FR. The particle size maximizes the blocking effect of EG and the rate of expansion favors lower smoke production; i.e. mass transfer. For this reason, PHRR, THR, TSP and mass loss were incredibly improved by EG with a high particle size and high rate of expansion (EG3). A loading up to 8 wt. % was enough to achieve V-0 rating in the vertical burning test (UL94). Indeed, PHRR was incredibly reduced up to a 51 %, THR was reduced up to a 47 %, TSP was reduced up to an impressive 82 % and mass loss were reduced by a 39 % less compared to the commercial reference PU. On the other hand, it was seen that the high particle size of EG3, affects negatively on the cellular structure, leading to a dramatic decrease of the compressive strength compared to the neat RPUF or a lower particle size EG-filled foam (EG1/EG2). 2) In terms of improved flame retardancy by a synergistic effect and higher compressive strength, solving the problem with EG, a system combining P-N FRs and EG was designed. It was reported in the literature that phosphorous species can impart good flame retardancy on RPUF by acting as synergistic agents for other FRs. Phenylphosphonic-aniline salt (FR1) was synthetized and used as a synergistic with EG at 8 wt. % loading into a commercial RPUF. A ratio of 12/1 (EG/FR1) was demonstrated to obtain the highest results with respect to flame retardancy and compressive strength. The optimal sample RPU3 increased the limited oxygen index (LOI) value from 19.2 % to 29.8 % and reached V-0 rating on the UL94 test. The PHRR was reduced up to 45 %, THR decreased to a 24 % and the TSP 58 %. It is highlighted that the optimal sample obtained better FR results than the sample with only EG at 8 wt. % loading, confirming a synergistic improved effect between FR1 and EG. A combined synergistic FR mechanism by the barrier effect of EG in condense phase and radical capture mechanism of FR1 in gas phase was proposed after a deep study. Finally, aiming to solve the commonly known low performance of EG-based RPUFs in the compression strength, it was discovered that the compressive strength of the new foams increased a 9 % compared with the reference commercial foam. There is a good interfacial adhesion between FR1 and PU matrix besides an increasing density of the foam provoked by the stiff phenyl groups in the FR1 structure and the proposed reaction of isocyanate (-NCO) groups at the PU end chains and FR1 to produce urea groups. However, an increase in thermal conductivity was observed as the FR1 content increased. The thermogravimetric analysis (TGA) indeed indicated that EG and FR1 accelerated the degradation of the foam but increased the char residue. 3) In terms of thermal insulation and the use of natural resources to obtain a RPUF, A system based on a modification of castor oil; a natural oil with secondary hydroxyl (-OH) groups, and the use of novel nanomaterials, such as GO was proposed. First, castor oil was modified to increase the number of primary -OH groups, as they react faster with -NCO groups to produce a more crosslinked structure. Secondly, the double bonds of the remainder castor oil unsaturated fatty acid structure were used as an essential part and they were epoxidized. Finally, with the aim of getting a polyol with intrinsic flame retardancy, a commonly known phosphonic acid was used as modifier to be introduced into the epoxidized oil structure via ring opening reaction. With these modifications, a polyol with intrinsic flame retardancy, higher viscosity and increased OH number was synthetized (CPPA). This polyol was used as a substitute for the commercial polyol from the previous reference foam and produced a novel biobased FR RPUF (BIO2). This novel idea was able to reduce the thermal conductivity by a 14 % to only 33.8 mW/mK with respect to the commercial foam as well as maintained the density at levels closer to the ones used as the commercial insulators. Also, the LOI increased up to a 24 %. Following this incredible result, EG and GO were used as additives due to its previously studied flame retardancy and thermal insulation effect, respectively. BIO2/EG/GO; with 6 wt.% of additives, including 0.5 wt. % of GO, was able to obtain reduced thermal conductivity (34.2 mW/mK) as well as a V-0 rating in the UL94 test. The covalent bonds between GO and the PU matrix increased the crosslinking density of the foam and the gas barrier effect of GO; towards the lower cell size achieved, improved the insulation capacity of the foam. Moreover, the LOI was increased to 27.2 %. The reason behind is the combination of a condensed phase barrier insulation effect against heat and mass transfer from EG and GO towards an intumescent FR effect of CPPA. The use of EG as previously stated, reduced the compressive strength whereas on the other hand, GO was able to maintain the compressive strength closer to the initial value of BIO2. 4) In terms of the multifunctional properties, the combination of thermal insulation, flame retardancy and high compressive strength into one unique system was proposed and demonstrated. GO was modified by a novel and green method with a P-N FR (FP1) to achieve higher flame retardancy and higher compressive strength and it was used in comparison to BIO2/EG/GO. PGO; the modification of GO with FP1, as an additive was able to improve the characteristics of GO by an incredible manner. The thermal insulation was maintained at similar levels with only a slight increase because of the density increment. The LOI was as a high as 27.6 % and reduced t...

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