Modification And Foaming Properties Of Phenolic Resin

Phenolic foam exhibits excellent heat insulation, flame retardant, acid corrosionresistance performances, but itself exists low intensity, poor toughness problems etc. Inorder to improve the toughness, phenolic resin being synthesized, urethane prepolymer andattapulgite were used to modify phenolic foam respectively. The influences of polyurethane,attapulgite on mechanical properties, thermal conductivity, oxygen index and cell structureof foam were investigated.Foamable phenolic resin was prepared with trioxymethylene and phenol under thealkaline conditions. The effects of reaction temperature and time, formaldehyde/phenolmolar ratios and catalyst content on resin viscosity were discussed. The results showed thatthe resin viscosity increased gradually with increased of reaction temperature and time,however, it showed increased first and declined with the molar ratio rose, catalyst amountsimproved. When reaction temperature was85℃, reaction time was3.5h, molar ratio offormaldehyde to phenol was1.6:1, mole percentage ratio of NaOH to phenol was7.5%, theresin was synthesized that viscosity arrived4.0Pa·s, be favorable to foam.Isocyanate-terminated polyurethane, in which the soft segment doing well to improve thetoughness of phenolic foam, was used to blend with foamable phenolic resin. The resultsshowed that adding9.0wt%polyurethane, compressive strength and bending strength ofphenolic foam reached0.18MPa,0.10MPa respectively. Adding12.0wt%polyurethane,both reduced to0.16MPa,0.09MPa respectively. Oxygen index fell slightly, reduced from34.0of unmodified to31.0; variation of thermal conductivity was not obvious, decreasedfrom0.039W/m·K to0.035W/m·K. The more foaming agent amount, the expansion ratiowas higher, apparent density and compressive strength was smaller. However, the morecuring agent content, the curing speed was faster, apparent density and compressivestrength was larger. Under the conditions of amount of Tween80was7.0wt%, amount ofn-pentane was13.0wt%, p-toluene sulfonic acid/phosphoric (4:1) was18.0wt%, phenolicfoam was prepared whose apparent density in54.5kg/m3, compressive strength arrived0.18MPa.Attapulgite was used as reinforcer. Etherification cross-linking reaction interactions whichexisted between silanols on the surface of attapulgite and hydroxy-methyl in the resin, enhanced degreeof cross link, in favor of reinforcing phenolic foam. The results showed that adding20.0wt% attapulgite, compressive strength of foam increased from0.09MPa to0.19MPa. However,compressive strength reduced to0.19MPa when attapulgite content was30.0wt%. As theinorganic modifier, attapulgite also improved flame resistance of foam, oxygen index rosefrom33.0to39.0, but has little effect on thermal conductivity of foam, increased from0.032W/m·K to0.034W/m·K. The more foaming agent amount, the expansion ratio washigher, apparent density and compressive strength was smaller. However, the more curingagent content, the curing speed was faster, apparent density and compressive strength waslarger. Under the conditions of amount of Tween80was7.0wt%, amount of n-pentane was10.0wt%, amount of p-toluene sulfonic acid/phosphoric acid/water (2:2:1) was15.0wt%,phenolic foam was prepared whose apparent density, compressive strength was56.9kg/m3,0.19MPa respectively.