A Research On The Silane Surface Modified PP Fibers Toughening SiO₂ Aerogel Composites

SiO2 aerogel,a porous material with extremely light texture,is made up of crosslinked nanoscale SiO2 particles.Because of the mesoporous aperture inside,it has a variety of special characteristics which are very different from the regular materials.Its thermal conductivity,which is very impressive among all of its characteristics,is even lower than that of the static air.So it was widely known as an excellent heat insulating material.However,the poor mechanical properties have been a difficulty for its storage and transportation.There is a necessarity to enhance it so as to satisfy the requirement of a heat insulating material.In this paper,ethylsilicate(TEOS)was used as a precursor source of silica,with hydrochloric acid being the acid catalyst and ammonia being the alkali catalyst respectively.Two kinds of modified polypropylene(PP)melt-blown fiber was used as the reinforceing phase for the SiO2 aerogel.The so-called 'two-step' methord was carried out to prepare the aerogel fiber composite materials.PP melt-blown fiber is a kind of organic fiber,which has a low density and a good tensile and toughness.While it generally not reacts with acid or alkali,the PP fiber won't be damaged in the aerogel preparation process.So it can be used as a perfect kind of reinforcing material for aerogel.In this paper,two different kinds of modified PP fiber were used as reinforcing phase,with silane coupling agent,the(3-aminopropyl)triethoxysilane(APTES),as the compatilizer between SiO2 aerogel and modified PP fiber.PP-g-AA-APTES fiber and PP-g-GMA-APTES fiber were prepared using the PP-g-AA fiber during an amidation process and PP-g-GMA fiber during a ring cleavage process with APTES respectively.Then these two kinds of fibers were used seprerately to reinforce the SiO2 aerogel.And the PP-g-AA-APTES/SiO2 aerogel composite and the PP-g-GMA-APTES/SiO2 aerogel composite material were successfully prepared.The various influence factors for the performance of the composite materials in the process were also studied.The major achievements were showed below.(1)The best preparating conditions for PP-g-AA-APTES/SiO2 aerogel composites and PP-g-GMA-APTES/SiO2 aerogel composites were that the dosage ratio of EtOH and TEOS is 7:1,with alkali catalytic procedure's pH being 8.5,the ageing time being 24 h,and TMCS being the surface modifing agent.(2)The study of the basic properties of two kinds of modified PP fiber/SiO2 aerogel composite material.Comparing with pure PP fiber/SiO2 composite,there would be a rise in the density of the SiO2 aerogel composite at 5%to 10%,with porosity reduced.However the density was still much smaller compared with glass fiber SiO2 aerogel composite(about 25%off).During this study,the minimum density of PP-g-AA-APTES fiber/SiO2 aerogel composite was 0.277 g/cm3 with a porosity of 57.26%.And the minimum density of PP-g-GMA-APTES fiber/SiO2 composite aerogel was 0.273 g/cm3 with a porosity of 57.88%.The water contact Angle of both types were above 135 °,which represent good hydrophobic performance.(3)The study of the micro performance for two kinds of modified fiber was also carried.Comparing with pure PP fiber/SiO2 aerogel composite,there was a 6%decrease in the two kinds of modified fiber/SiO2 aerogel composites' specific surface aera.But comparing with the glass fiber/SiO2 aerogel composite,the specific surface aera of two kinds of modified fiber/SiO2 aerogel composite was about 40%to 50%higher.During this study the highest specific surface area of PP-g-AA-APTES fiber/SiO2 aerogel composite was 701.0201 O2/g.And highest specific surface area of the PP-g-GMA-APTES fiber/SiO2 aerogel composite was 719.2781 m2/g.(4)The study of two kinds of modified fiber micro performance was also carried.Comparing with pure PP fiber/SiO2 aerogel composite,there would be a 5-10%rise in the thermal conductivity.But it was still much lower than that of the glass fiber/SiO2 aerogel composite(40-50%lower).The minimum thermal conductivity of PP-g-AA-APTES fiber/SiO2 aerogel composite aerogel was 0.028 W/(m· K)and 0.026 W/(m·K)for PP-g-GMA-APTES.(5)The mechanical properties of two kinds of modified fiber/SiO2 aerogel composites were studied.The tensile strength of two modified fiber/SiO2 aerogel composite were 2-6%higher than that of the pure PP fiber/SiO2 composite.But the tensile properties of them were 25%and 40%lower than that of glass fiber respectively.During this study the maximum tensile strength of PP-g-GMA-APTES fiber/SiO2 aerogel composite was 2.05 MPa,and the maximum tensile strength of PP-g-AA-APTES fiber/SiO2 aerogel composite was 2.13 MPa.And the folding resistance,however,was 75-140%and 110-160%higher than that of pure PP/SiO2 aerogel composite.Comparing with the glass fiber/SiO2 aerogel composite,the folding resistance was 150-210%and 220-230%higher.As was also explored,the effect of silane coupling agent on the improvement for the mechanical properties of the two kinds of the modified fiber/SiO2 aerogel composite was also studied.The compatibility and the binding force of the modified PP fiber/SiO2 aerogel composite was also studied and explained with data.