Phenolic foams,modified by nano-metallic oxides,improved in mechanical strengths and friability

Two kinds of nano-metallic oxides (nano-Al₂O₃ and nano-ZrO₂) were introduced separately into phenolic (PF) foams, and a series of PF foams modified with different loadings of the two nano-oxides were prepared. The test results of mechanical properties indicated that the flexural, compressive and impact strengths of the PF foams, modified by nano-Al₂O₃ at 5 phr loading, increased by 33, 46 and 51 % in the above order, and the strengths of the PF foams modified by nano-ZrO₂ at 5 phr loading increased by 31, 30 and 49 % in the same order, compared to the corresponding data of pure PF foam. The pulverization ratio of the modified PF foams decreased gradually with the increase in nano-oxides contents. The pulverization ratio of the PF foam modified by nano-oxides at 5 phr, decreased to 2.3 % for Al₂O₃ and that of ZrO₂ decreased to 2.2 %, which were quite lower than the pure PF foam value of 8 %. The combustion characteristics of the PF foams, modified by the nano-oxides, were evaluated by the limiting oxygen index (LOI), UL-94 and cone calorimetry tests. The LOI values of the foams modified by both nano-Al₂O₃ and nano-ZrO₂ decreased slightly with an increase in the loading of the nano-oxides, still all above 36 %. The UL 94 test results indicated that all foams could pass a V0 rating. The cone calorimeter results showed that the peak heat release rates of the modified foams were lower than 50 kW/m². Moreover, thermal stability of the foams modified by the nano-oxides was investigated.