Preparation And Properties Of Silica Aerogels And Their Composites

Silica aerogel as a new type of nano material with large porous surface area has wide application prospects in many aspects,such as heat insulation and catalytic adsorption.However,due to its complex preparation process and poor mechanical properties,silica aerogels severely restrict the application of silica aerogels.The purpose of this project is to simplify the preparation process and extend the application scope of silica aerogels.The experiment mainly consists of three parts:（1）Using fluoride ion as catalyst,the effects of catalyst dosage,ethanol dosage,modifier type and dosage,DCCA type and dosage on the gel time,density,porosity,thermal conductivity and morphology of the material were studied.The results show that when n（TEOS）:n（H₂O）:n（EtOH）:n（F^-）:n（DMF）=1:6:3:0.1:0.25,the modifier is in molar ratio to n-hexane.When it is 1:8 trimethylchlorosilane（TMCS）,the prepared silica aerogel has the best performance.At this time,the gel time of the sample is 487 s,and the density of the sample is 0.1353 g/cm³.The porosity is 93.85%,the thermal conductivity is 0.032 W/（m·K）,the contact angle to water is 143.5°,and the average specific surface area is 663.72 m²/g.The internal pore diameter of the aerogel is 12.52nm calculated according to the BJH method.（2）Powder silica aerogel was added to polycaprolactone diol to disperse,and silica aerogel-TPU composite was prepared by reaction with 4,4-diphenylmethane diisocyanate.The effects of R value and silica aerogel addition on the mechanical properties,hydrolysis resistance and high temperature stability of the composites were investigated.The results show that when the amount of silica aerogel is 2%and the value of R is 1.1,the composite has the best comprehensive performance.At this time,the tensile strength of the composite is 49.19 MPa and the elongation at break is421.3%,thermal conductivity is 0.178 W/（m·K）,T_3%is 291.3℃.From the scanning electron micrograph,the silica aerogel has good dispersibility in the substrate.（3）The polystyrene material was modified by adding silica aerogel in the process of suspension polymerization.The initiator content,oil-water ratio,silica aerogel addition amount and composite polymerization time were studied.The effects of bulk conversion,average particle size,average molecular weight,tensile yield strength,Tg,high temperature stability and the like.The results show that when the amount of initiator is 0.6 g,the ratio of oil to water is 1:8,and the amount of silica aerogel is1.5%,the composite has the best comprehensive performance.At this time,the polymerization time of the composite is 230 min,and the conversion rate is 84%,average particle diameter was 3.2 mm,number average molecular weight was 25190,PDI was 2.156,yield strength was 22.9 MPa,Tg was 95.13℃,and T_3%was377.81℃.