Bio-Based Trivalent Phytate:A Novel Strategy for Enhancing Fire Performance of Rigid Polyurethane Foam Composites

Biomass phytic acid has potential flame retardant value as the main form of phosphorus in plant seeds.In this study,phytate-based flame retardants aluminum phytate(PA-Al)and iron phytate(PA-Fe)were synthesized and characterized.Subsequently,they were introduced into rigid polyurethane foam(RPUF)as flame retardants by one-step water-blown method.The results indicated that RPUF/PA-Fe30 exhibited the highest char residue of 22.1 wt%,significantly higher than 12.4 wt%of RPUF.Cone calorimetry analysis showed that the total heat release(THR)of RPUF/PA-Al30 decreased by 17.0%and total smoke release(TSR)decreased by 22.0%compared with pure RPUF,which were the lowest,demonstrating a low fire risk and good smoke suppression.Thermogravimetric analysis-Fourier transform infrared spectrometer(TG-FTIR)implied the release intensity of flammable gases(hydrocarbons,esters)and toxic gases(isocyanate,CO,aromatic compounds,HCN)of composites was significantly reduced after the addition of PA-Fe.The analysis of char residue indicated that the RPUF composites formed a dense char layer with a high degree of graphitization after the addition of PA-Al/PA-Fe,endowing RPUF composites with excellent mass&heat transmission inhibition effect and fire resistance in the combustion process.

Thermal Decomposition and Kinetics of Rigid Polyurethane Foams Derived from Sugarcane Bagasse

Rigid polyurethane foams were fabricated with five kinds of liquefied sugarcane bagasse polyols （LBP）. The foams derived from sugarcane bagasse were investigated by thermogravimetric analysis （TGA）, and the thermal degradation data were analyzed using the Coast-Redfern method and Ozawa method to obtain the reaction order and activation energy. The results indicate that the sugarcane bagasse-foams exhibit an excellent heat-resistant property, whereas their pyrolysis procedures are quite complicated. The reaction as first order only takes place from 250 to 400 ℃, and the pyrolysis activation energies vary from 20 to 140 kJ/mol during the whole pyrolysis process.

Preparation of Boron-coated Expandable Graphite and Its Application in Flame Retardant Rigid Polyurethane Foam

A novel boron-coated expandable graphite（BEG） material was prepared by first wrapping polyvinyl alco- hoI（PVA） onto expandable graphite（EG） and then condensing with boric acid. The obtained BEG was characterized by scanning electron microscopy（SEM）, Fourier transform infrared（FT1R） spectroscopy, X-ray photoelectron spec- troscopy（XPS）, and tbermogravimetric analysis（TGA）. The fire performance and mechanical properties of the rigid polyurethane foam（RPUF） filled with BEG were investigated by limiting oxygen index（LOl）, horizontal and vertical burning, cone calorimetry（CONE）, and electronic tensile tests. BEG shows an improved compactness of the char layers upon thermal expansion, which is effective for the flame retardancy of RPUF. With a loading of 10%, RPUF/BEG exhibited a higher LOI, 〉10% reduction in heat release rate and carbon monoxide release, as well as a decrease in smoke release during the beginning of combustion compared to RPUF/EG. Moreover, the compressive strength and modulus of RPUF/BEG were increased. The improved flame retardancy of BEG on RPUF can be attributed to the suppression of the ＂popcorn effect＂ of EG by PVA-boric acid, and the improved mechanical property can be attributed to the presence of PVA.

Recent advances in fire-retardant rigid polyurethane foam

Driven by global environmental concerns,many efforts have been made to develop halogen-free flame retardants for rigid polyurethane foam(RPUF).These environmentally benign flame retardants are mainly divided into(i)reactive,(ii)additive,and(iii)coating types.The last decade has witnessed great progress of these three strategies,which enhance the fire safety of RPUF and maintain even improve the thermal insulation properties.This comprehensive review focuses on the up-to-date design of the reactive,additive,and coating flame retardants,and their effects on flame retardancy and thermal conductivity of RPUF.Moreover,the practical applications of the as-prepared flame-retardant RPUFs are highlighted.Finally,key challenges associated with these three kinds of flame retardants are discussed and future research opportunities are also proposed.

EFFECT OF SURFACE MODIFICATION OF MONTMORILLONITE ON THE PROPERTIES OF RIGID POLYURETHANE FOAM COMPOSITES

This study investigated the influence of various organically modified montmorillonites （organoclays） on the structure and properties of rigid polyurethane foam （RPUF） nanocomposites. The organoclays were modified with cetyltrimethyl ammonium bromide （CTAB）, methyl tallow bis（2-hydroxyethyl） quaternary ammonium chloride （MT2ETOH） and tris（hydroxymethyl）aminomethane （THMA） and denoted as CMMT, Cloisite 30B and OMMT, respectively. MT2ETOH and THMA contain hydroxyl groups, while THMA does not have long aliphatic tail in its molecule. X-ray diffraction and transmission electron microscopy show that OMMT and Cloisite 30B can be partially exfoliated in the RPUF nanocomposites because their intercalating agents MT2ETOH and THMA can react with isocyanate. However, CMMT modified with nonreactive CTAB is mainly intercalated in the RPUF matrices. At a relatively low filler content, the RPUF/CMMT composite foam has a higher specific compressive strength （the ratio of compressive strength against the apparent density of the foams）, while at relatively high filler contents, RPUF/Cloisite 30B and RPUF/OMMT composites have higher specific compressive strengths, higher modulus and more uniform pore size than the RPUF/CMMT composite.

Processing and properties of rigid polyurethane foams based on bio-oils from microwave-assisted pyrolysis of corn stover

A new kind of rigid polyurethane(PU)foam was synthesized from the oil phase of bio-oils from microwave-assisted pyrolysis of corn stover.The recipes for the PU foams consisted of polyol-rich bio-oils,water as blowing agent,polyethylene glycol(PEG)as both polyol donor and plasticizer,diphenylmethane-4,4’-diisocyanate(polymeric MDI)as cross-linking agent,silicon-based surfactant,and tin-based catalyst.The mechanical properties of rigid foams were measured with universal testing machine(Instron4206).The effects of individual ingredients on the physical and mechanical properties of the foams were studied.It was found that water content,bio-oil content,and isocyanate dosage were important variables in making PU foams in terms of mechanical strength,density,and cellular structure Under optimal conditions,the compression strength of the prepared PU foams reached 1130 kPa with a density of 152.9 g/L.The results show that bio-oils are potential renewable polyol sources for making rigid PU foams.

Synergistic Optimization of Toughness and EMI Shielding Properties in Rigid Polyurethane Composites by Designing Ring Structures on the Surface of Carbon Fibers

How to achieve both toughness and enhanced electromagnetic interference shielding effectiveness(EMI SE)of carbon fibers(CFs)reinforced rigid polyurethane(RPU)composites is a significative challenge at present.In this work,a ring-shaped zinc coating was deposited on the short CFs by electrodeposition technique.It is expected to improve the interfacial properties between the fibers and the resin matrix as well as enhance the EMI shielding properties of the composites by changing the surface morphology and roughness of the fibers.Results showed that the surface free energy of the ring-shaped zinc modified carbon fibers(RS-CFs)increased from 49.0 mJ/m^(2) to 53.2 mJ/m^(2),indicating that the surface roughness and wettability of the CFs were effectively improved.In comparison with the pristine short carbon fibers/rigid polyurethane(CFs/RPU)composites,tensile strength and tensile toughness of RS-CFs modified composites were increased by 27.1% and 121.4%,respectively.In addition,the bending and impact strengths of RS-CFs reinforced RPU composites were also improved.Notably,the electrical conductivity of RS-CFs/RPU composites reached 1.2×10^(-5) S/m,which was much higher than that of CFs/RPU composites at 1.4×10^(-10) S/m.Moreover,the EMI SE of the modified composites reached 22 dB,which was 152.9% higher than that of CFs/RPU composites.The enhanced electrical conductivity and EMI shielding properties of the composites could be attributed to the synergistic effect of the porous structure in the RPU matrix and the CFs modified by the metal coating.

Effect of dosage of expandable graphite,dimethyl methylphosphonate,triethanolamine,and isocyanate on fluidity,mechanical,and flame retardant properties of polyurethane materials in coal reinforcement

In this study,orthogonal experiments were conducted to investigate the influence of expandable graphite(EG),dimethyl methylphosphonate(DMMP),triethanolamine(TEA),and isocyanate content on the compressive and bonding strengths,oxygen index,and fluidity of rigid polyurethane foam(RPUF).The results revealed that EG significantly increased the oxygen index of RPUF,enlarged the diameter of foam cells,and decreased the cell-closed content in foam;thus,leading to a pressure drop in RPUF.However,excessive EG was capable of reducing the fluidity of polyurethane slurry.TEA exhibited significant influence on the compressive strength of RPUF,which dropped initially,and then increased.DMMP had a remarkable effect on the flame retardant property and compressive strength of RPUF.Compressive strength of RPUF initially displayed an increase followed by a decrease with increasing dosage of DMMP,and achieved the maximum value at DMMP dosage of 4%.DMMP could effectively reduce the diameter of RPUF cells leading to an increase in the percentage of close area in foam.DMMP displayed the flame-retardation effects mainly in the gas phase leading to a significant enhancement in the oxygen index of RPUF.Moreover,the compressive strength and bonding strength of RPUF decrease significantly with the increase of isocyanate content due to the increased blowing efficiency by the CO_2.The oxygen index and flowing length of foam increased with the increase in isocyanate dosage.

Viscoelastic and Thermal Properties of Polyurethane Foams Obtained from Renewable and Recyclable Components

This article deals with the study of the viscoelastic and thermal properties of polyurethane (PU) rigid foamsfrom biobased and recycled components. Rapeseed oil (RO) and recycled poly(ethylene terephthalate)(PET) were used to synthesize PU polyols. Addition of adipic acid (ADA) to polyol resulted in improvedthermal and viscoelastic properties of foam materials. ADA content was varied from 1 to 6 wt%. Results ofthe dynamic mechanical spectra indicate an increase of the storage modulus E′ and the loss modulus E″ inthe whole temperature range for specimens with higher loading of ADA. In addition, damping factor shiftedto higher temperatures, but damping intensity remained almost unaffected by the compositions. Scanningelectron microscopy of the foams’ cross sections testified that the average cells’ size of 110 mm was unaffectedby the ADA content in polyol.

3D finite element analysis of composite noise barrier con- structed of polyurethane products

This paper presents a numerical investigation on the structural performance of an innovative noise barrier consisting of poly-block, rigid polyurethane foam （RPF） and polyurea. The mechanical characteristics of RPF as well as the flexural resistance of the proposed wall system （poly-wall） were established and presented in another study. The experimental results are used in the current study to develop, calibrate and verify 3D finite element （FE） models of the wall system. The components of the poly-wall including steel rebars, poly-blocks and RPF cores were simulated and then verified using the results of experiments conducted on the wall components. The results of numerical analysis exhibited a satisfactory agreement with the experimental outcomes for the entire wall system. The verified numerical models were then used to conduct a parametric study on the performance of poly-wall models under uniform wind load and gravity load. The findings of the current study confirmed that the structural performance of poly-wall is satisfactory for noise barrier application. Simulation techniques for improvement of the numerical analysis of multi-martial 3D FE models were discussed.

Sub-Atmospheric Pressure Coupled with Width Effect on Downward Flame Spread over Energy Conservation Material Polyurethane Foam

Rigid polyurethane(PUR)foam,a sustainable thermosetting building facade porous polymer material,has been widely applied in the construction industry for energy conservation.Additional knowledge of the fire safety performance of PUR foam at different altitudes and sample widths is required.Comparative lab-scale experiments were conducted in the Lhasa plateau(66.5 kPa)and the Hefei plain(99.8 kPa)in China.Flame propagation characteristics(average flame spread rate and flame height)were measured at different widths and atmospheric pressures of the test locations.Experimental results show that the dependence of dimensionless flame heights on sample width shows negative power law relationships with index of−w/5.4 to−w/5.8.Both flame height and flame spread rate were lower under low ambient pressure conditions as H f P0.26~0.33 and Vf P0.057~0.568.Flame spread rate decreased with increasing sample width in the convection regime before a critical width of 4 cm–8 cm,after which the flame spread rate increased in the radiation regime.Results of this study contribute to the science of combustion,fire safety and energy conservation,and provide a basis for fire safety protocols for historical heritage buildings in the Lhasa plateau.