Preparation And Structure-property Relationship Of Light And Flame-retardant Phenolic Foams

In recent years, the fires of urban high-rise buildings frequently occur in China, which notonly imperil people’s lives and properties, but also produce a large number of harmful smokeand pollute the environment. One of the main ignition sources of city building fires is organicthermal insulation materials, which are widely used in the exterior wall of modern building.Thereby, flame retardant construction materials have been receiving increasing attention. As akind of flame retardant foam featured with non-moltening, difficuity in producing flow drops,less toxic smoke generation during the combustion process, flame retardation, low toxicity andheat resistance, phenolic foam would be used as an ideal thermal insulation material and getmore extensive applications in the construction field.Traditional high solid resol phenolic resins （HSRPRs）（70～85%）, which are prepared bydehydration of phenolic resins （about50%） that are synthesized by reaction between phenoland formaldehyde solution （37wt%）, would usually generate a large amount of industrialwastewater. Meanwhile, phenolic foams （PFs） have some disadantages, such as fragility, highproduction cost, etc. Hence, it is necessary to study and develop an efficent way to solve theexisting problems in phenolic resins and foams, as well as to prevent the contamination ofwaste water during the process of resins production. To this end, we aim to develop highperformance PFs.In this thesis, an advanced and undehydrated technology was used to synthesize HSRPRswith the solid content of70～85%. The effects of formaldehyde/phenol （F/P） molar ratio andcatalysts on the properties of HSRPRs were inverstigated in the process of HSRPRspreparation. The process of PFs was also studied. Particularly, we analyzed the effects of acidcuring agent on the properties of PFs in detail, and created the mathematical model of apparentdensity-mechanical properties of PFs. The wood fibers modified by different surface treatmentmethods were used to enhance PFs. Halogen-free synergistic flame retardant systems wereused to prepare the flame retardant composite PFs. The acid pretreatment method was applied to modify inorganic materials and to prepare inorganic material composite PFs. The mainresults and discoveries are described as follows:1. preparation and characteration of HSRPRsA series of HSRPRs were synthesized with different molar ratios of formaldehyde tophenol （1.6,1.8,2.0,2.2and2.4） using sodium hydroxide as catalyst. HSRPRs with bestproperties were obtained when the F/P molar ratio was2.0. These HSRPRs have the viscosityof2567mPa·s, solid content of79.25%, gel time of725s, free formaldehyde content of0.86%,free phenol content of3.01%and hydroxymethyl concentration of36.56%. And the thermalstability was also the best. The residue （600℃） of HSRPRs decreased when the F/P molarratios increased. The low F/P molar ratios of HSRPRs had higher Ea values than that of highmolar ratios, indicating that less heat was needed to cure HSRPRs at high molar ratios thanthose at low molar ratios. The reaction orders of five different F/P molar ratios werenon-integer, and the result indicated that the curing reaction was quite complicated. The resulthad a guiding significance on choosing the right F/P molar ratios during the manufacturing ofHSRPRs.2. The effects of catalysts on the properties of HSRPRs and PFsBarium hydroxide （Ba（OH）₂）, triethylamine （（C₂H₅）₃N） and sodium hydroxide （NaOH）were chose as catalysts in the synthesis of HSRPRs and the preparartion of PFs at70℃. Theeffects of different catalysts on the properties of HSRPRs and PFs were investigated. Theresults showed that the catalytic efficiency of three kinds of catalysts was listed as follows:NaOH＞（C2H5）3N＞Ba（OH）2. The optimal properties of phenolic resins and foams wereachieved when the phenolic resins were prepared with NaOH as catalyst. And the viscosity,solid content, free phenol, free formaldehyde, gel time and the amount of residual carbon of theresin （NaOH as catalyst） were8625mPa·s,79.88%,3.36%,0.5%,397s and59.31%（900℃）respectively. The compression strength, bending strength, mass loss rate, limited oxygen index（LOI）, initial decomposition temperature and the amount of residual carbon of PFs （NaOH ascatalyst） were0.24MPa,0.39MPa,11.1%,44.5%,107℃and60.15%（900℃） respectively. And PFs was characterized to have smaller cells with a diameter of100²00μm, and relativelyuniform cell distribution.3. Research on the preparation process and model of density-mechanical properties of PFsSurfactant （polysorbate-80）, blowing agent （petroleum ether）, and curing agent （mixedacid） were selected to prepare PFs at70℃. The influences of amount of surfactant, blowingagent and curing agent on the properties of PFs were investigated. The results showed that thesuitable amount of surfactant and blowing agent were10%and5%respectively, and theproperties of foams was the best using hydrochloric acid/phosphoric acid/p-toluene sulfonicacid/water as curing agent, and the suitable amount of curing agent was15%. Themathematical model of density-mechanical properties was established by the foam model ofGibson-Ashby’s mechanical properties and density. The results showed that there was a goodexponential relationship between mechanical properties and density. The exponential valueswere in the range of1.2352².1672. The exponential values of compression properties were inthe range of1.2521¹.4848, and the exponential values of bending properties were in the rangeof1.2352².1672.4. Study on foaming model of phenolic foamPolyoxyethylene-80（surfactant）, petroleum ether （blowing agent） and mixed acids （curingagent） were selected to prepare PFs at different foaming temperatures. The effects of foamingtemperature, amount of surfactant, foaming agent, curing agent on the foaming speed andaverage cell diameter of PFs were investigated. Foaming speeds and average cell diameter ofPFs were obtained by experiments tests. The mathematical models of foaming speed andaverage cell diameter were obtained by nonlinear fitting of these experiment data. The modelof foaming speed, which reflected a relationship between foaming temperature, amount ofsurfactant, foaming agent, curing agent and the growth speed of foam volume, was set up. Andthe model of average cell diameter, which reflected a relationship between foamingtemperature, amount of surfactant, foaming agent, curing agent and average cell diameter offoam, was established. These models could provide basic theories for the guidance to the research on the application of PFs. In the meantime, It is meaningful for this basic theory toguide the preparation of PFs and optimize preparation technology.5. Preparation and characteration of PFs with Eco-friendly Halogen-free Flame RetarantThe retardant additives, including eco-friendly halogen-free flame retardants （APP）, charforming agent （PER）, and synergist （ZnO, MoO₃, CuCl₂, and SnCl₂）, were added in HSRPRsto fabricate the flame retardant composite phenolic foams （FRCPFs）. The effects of theseretardant additives on the performance and properties of FRCPFs were investigated. It wasfound that LOIs of FRCPFs significantly increased and reached to around73%. HRR, AHRE,THR, EHC, O₂C, TOC, and emission of toxic gases （COP and COY） remarkably decreased,while for SEA and TSR, they significantly increased. The flame-retardant system agreed withthe gasphase flame-retarding mechanism. The results showed that FRCPFs had excellentfire-retarding performance, although it has a minor negative effect in respect of reduction in thesmoke release. APP/PER/ZnO was concluded as a better flame-retardant system for PFs.6. Modification of the wood fiber surface and the research on the preparation andcharacteration of wood fiber composite PFsThe wood fibers pretreated by alkali, coupling coupling agents and alkali-couplingcoupling agents were used to prepare fiber composite PFs. The effects of wood fibers onproperties of PFs were studied. The results showed that the mechnical properties of treatedfiber composite PFs increased to different levels, compared with untreated fiber composite PFs.Especially the properties of treated fiber composite PFs were better while using silane couplingagent （A-171）-sodium hydroxide composite treatment and silane coupling agent （KH-792）treatment method. The results indicated after pretreatment, the interfacial compatibilitybetween fiber surface and resins significantly improved. But limiting oxygen indexs of treatedfiber composite PFs decreased to different levels, compared with untreated fiber composite PFs.This indicated that there was no positive effect of fiber modification on the flame retardant ofwood fiber composited PFs.7. Preparation and initial investigation of inorganic materials composite PFs Pulverized fuel ash and bentonite were modified to phosphate by15wt%phosphoric acidand used to prepare inorganic material composite PFs. The effects of acidification method ofinorganic materials and amount of inorganic materials on the properties of PFs wereinvestigated. The results showed that the mechnical properties of acidification-treated inorganicmaterials composite PFs increased to different levels, compared with untreated inorganicmaterial composite PFs. The cells of PFs were smaller and cell distribution was relativelyuniform. Particularly, the properties of acidification-treated pulverized fuel ash composite PFswere better. The results showed that the suitable inorganic material for composite PFs waspulverized fuel ash treated by acidification method. But limited oxygen indexs of inorganicmaterial composite PFs decreased to different levels, compared with phenolic foam.